cholesterol is a ubiquitous molecule that 
 plays a vital role in 
 maintaining the overall integrity of eukaryotic cells by giving rise 
 to the requisite structure , fluidity , and organization of the membrane .
it is synthesized endogenously through an extensive 
 multistep biosynthetic pathway , with the 
 first sterol in the pathway being lanosterol .
interestingly , of all 
 the sterol intermediates between lanosterol and cholesterol , none 
 possess cholesterol s ability to order and condense lipid membranes ; however , the details regarding cholesterol s structural interactions 
 within the membrane are poorly understood .
one of the more intriguing aspects of this 
 planar tetracyclic molecule 
 pertains to its two structurally distinct faces : its -face 
 contains two protruding methyl groups that are conspicuously absent 
 on its -face ( figure 1a ) .
there has 
 been much speculation that this facial asymmetry may be essential 
 for cholesterol s unique membrane condensing abilities as well 
 as being essential to the way in which it interacts with and stabilizes 
 neighboring lipids and transmembrane proteins . to test this theory , 

models have been used to simulate the properties and interactions 
 of a demethylated form of cholesterol ( 18,19-di - nor - cholesterol , which 
 lacks the -face methyl groups ) . however , direct experimental evidence has not been obtained , as 
 the molecule has never been previously synthesized . herein , we describe 
 the first synthesis of a  smoothened 
18,19-di - nor - cholesterol , 
 which we have completed as part of a collaborative effort , in hopes of providing a way to experimentally 
 measure its effects on lipid membranes and other important transmembrane 
 interactions .
( a ) structures of cholesterol and 18,19-di - nor - cholesterol ; 
 the 
 -face methyl groups of cholesterol ( shown in red ) are absent 
 in 18,19-di - nor - cholesterol .
blue numbers are methyl groups absent in 18,19-di - nor - cholesterol ; 
 red letters label each ring .
wedged bonds are referred to as having 
 a -configuration , and dashed bonds , an -configuration .
utilizing a nine - step sequence 
 developed in our laboratory , commercially 
 available 19-nor - testosterone was first transformed into perhydrochrysenone 
 derivative a ( scheme 1 ) . in this 
 transformation ,
the unwanted c18 methyl group was removed while still 
 preserving the trans - c , d ring fusion .
additionally , 
 the cis - a , b ring fusion of compound a allows for the later introduction of the  double 
 bond .
the -stereochemistry of the hydroxyl group at c3 in compound a is not important , as the 3-hydroxy group will be 
 established during the  double bond introduction 
 ( see figure 1b for numbering ) .
as depicted in our retrosynthesis ( scheme 1 ) , starting from a , we can essentially fragment 
 our 
 synthesis into three main parts : d - ring contraction , side - chain installation , 
 and introduction of the  double bond .
installation 
 of the double bond was chosen as the final step in our synthesis of 
 18,19-di - nor - cholesterol because of its high reactivity toward a variety 
 of reaction conditions and because it could be obtained from 18,19-di - nor - epicoprostanol 
 ( c ) via enone formation and double bond deconjugation .
it was then envisaged that synthon c could be obtained through the addition of an isohexyl side chain 
 to a steroid precursor containing a ch2coor group at c17 . 

synthon b fits this description and could be accessed 
 from a by an oxidative d - ring - opening ( to yield a 1,4-diester ) , 
 a dieckmann condensation to reclose the ring , the removal of the 16-ketone group , and a one - carbon homologation 
 reaction at c17 to give synthon b. the success 
 of this entire approach , however , is contingent upon 
 whether ring closure via the dieckmann condensation ( preceding the 
 c17 homologation reaction ) would yield the desired 17-carbomethoxy 
 group as the major isomeric product ( scheme 2 , compound 4 ) .
although four isomers are possible , extrapolating 
 results from previous studies on the synthesis of a - nor - steroids and examining the steric interactions at play in our di - nor system 
 led us to expect that this transformation would , in fact , yield our 
 desired product ( see supporting information scheme 
 s1 ) .
this was therefore seen as our most critical , and yet 
 most elegant , synthetic step , as this reaction would simultaneously 
 contract the d - ring and selectively install a c17 functional 
 group while preserving the trans - c , d ring fusion . to begin , we first protected perhydrochrysenone derivative a as the acetate ( 2 ) before carrying out a chromium(vi)-mediated , 
 oxidative d - ring - opening and esterification to give 1,4-diester ( 3 ) .
the key step in our synthetic approach was next . employing 
 dieckmann condensation conditions , compound 3
was heated at 40 c for 45 min in basic meoh to yield 
 a single -ketoester product .
a crystal structure confirmed 
 the stereochemistry to be that of the expected 17-methyl ester 
 ( 4 ) ( see the supporting information ) . after removing the 16-keto group via formation of thioketal 5 followed by raney nickel dethioketalization to yield compound 6
having little success with the arndt eistert 
 homologation reaction , we chose to proceed via the introduction 
 of a carbonitrile group .
we first protected compound 6 as a methoxymethyl ether ( 7 ) and then reduced the ester 
 moiety using lialh4 to afford primary alcohol 8 .
a carbonitrile 
 was then introduced via a two - part procedure , wherein a methanesulfonyl 
 ester was formed and then stirred at 65 c for 16 h with nacn 
 in dmf to give carbonitrile 9 , which was subsequently 
 hydrolyzed to carboxylic acid 10 ( scheme 2 ) . for steroids 
 with a c18 methyl group , the introduction 
 of a side - chain via an -substitution at c20
is known to favor 
 the desired ( r)-diastereomer ; however , this selectivity is attributed to steric interferences 
 caused by the c18 methyl group , which 
 is absent in our 18,19-di - nor series . after confirming that alkylations 
 at c20 are not stereoselective for 18-nor - steroids , we used evans 
 chiral auxiliary [ ( r)-4-benzyl-2-oxazolidinone ] to 
 ensure ( r)-stereochemistry at c21 .
however , 
 in a variety of subsequent alkylation attempts , we were unable to introduce the entire isohexyl group in 
 satisfactory yield , presumably because of the added bulk of the chiral 
 auxiliary .
therefore , we instead installed the side chain in two pieces , 
 first utilizing the highly reactive allyl iodide , to obtain compound 12 as the desired ( r)-diastereomer in 86% 
 yield .
next , we needed to remove the chiral auxiliary in order 
 to generate the c21 methyl group ( currently positioned as the carbonyl 
 carbon ) .
although one - step reduction procedures failed to remove the 
 chiral auxiliary , it was found to be 
 easily removed by first hydrolyzing the benzyloxazolidinone and then 
 reducing the resultant carboxylic acid with lialh4 to give primary alcohol 13 . at this point , with all critical stereocenters intact , 
 a crystal structure was obtained ( see the supporting 
 information ) .
finally , deoxygenation was completed via a simple 
 two - part protocol by first forming the methylsulfonate ester and then 
 displacing this group using lialh4 to reveal the c21 methyl group and 
 give compound 14 .
transformation of the allyl group 
 into the isohexyl side chain 
 was the last step in completing the construction of synthon c. although the side chain was not introduced in one piece 
 via our initial plan , transformation of the allyl group into an isohexyl 
 chain was straightforward and higher yielding overall than the initial 
 isohexyl introduction attempts .
accordingly , the terminal olefin was 
 oxidatively cleaved using o3/me2s to give the 
 crude aldehyde intermediate , which was immediately treated with isobutyl(triphenyl)phosphonium 
 bromide under wittig conditions to give the isohexenyl side chain 
 of compound 15 in 85% yield as a single double bond isomer 
 whose stereochemistry we did not determine . a subsequent hydrogenation 
 proceeded near quantitatively , affording 18,19-di - nor - epicoprostanol 
 ( 16 ) and completing the synthesis of synthon c ( scheme 3 ) .
lastly , we needed to introduce the  double bond , which is well - known in literature , through formation 
 of a -3-ketone followed by deconjugation . therefore , we first synthesized the 3-keto - precursor ( 17 ) , which was easily obtained by first removing the methoxymethyl 
 protecting group of compound 16 with anhydrous hcl and 
 then oxidizing the resulting crude alcohol using jones reagent 
 to give ketone 17 . however , subsequent attempts to introduce 
 the -3-ketone proved to be difficult in the absence 
 of the c19 methyl group . after having little success with a 
 variety of steroid protocols , we ultimately 
 adapted a general procedure for the formation of ,-unsaturated 
 ketones , wherein bromination of a silyl enol ether first yields an 
 -bromoketone that undergoes a dehydrobromination . after optimizing 
 conditions ,
compound 17 was treated with trimethylsilyl 
 triflate ( tmsotf ) and et3n to form the tms - enol ether in 
 situ . upon cooling the reaction to 78 c and adding nahco3 and n - bromosuccinimide ( nbs ) , the intermediate 
 bromoketone ( obtained as a mixture of bromides ;
see supporting information scheme s2 ) was heated in the presence 
 of li2co3 and libr in dmf at 120 c for 
 16 h to generate the desired -3-ketone ( 18 ) in a moderate 32% yield , with an unwanted -3-ketone 
 byproduct obtained in 55% yield ( reflecting the ratio of the bromide 
 intermediates ) .
although the desired -3-ketone 
 was the minor 
 product , of the reaction protocols attempted this protocol gave the 
 highest product yield and the least amount of byproducts .
it was also far more economical than the other 
 attempted procedures , in that we were consistently able to recover 
 and reuse starting material 17 via hydrogenation of the 
 unwanted -3-ketone .
thus , after hydrogenation , 
 using 10% pd / c , starting material 17 could be recovered 
 in 54% yield . by running this reaction sequence three consecutive 
 times
, we were able to obtain our desired 18,19-di - nor - cholest-4-ene-3-one 
 ( 18 ) in a respectable 60% yield , with 16% of our total 
 starting material ( 17 ) recovered .
deconjugation 
 was the final step in our synthesis , which proved 
 to be relatively straightforward using typical literature protocols .
compound 18 was dissolved in ac2o and tmsi to form the dienol acetate , which was then reduced 
 with nabh4 in etoh .
this simultaneously deconjugated the 
 enone and set our final stereocenter ( 3-oh ) , affording our target 18,19-di - nor - cholesterol ( 1 ) in 60% yield ( 3.6% overall from perhydrochrysenone a ) ( scheme 4 ) .
the synthesis of the smoothened 18,19-di - nor - cholesterol was achieved 
 starting from commercially available 19-nor - testosterone .
the novel 
 use of the dieckmann condensation was key to accessing our target 
 molecule , allowing us to contract the d - ring to a 5-membered 
 ring and to simultaneously introduce a modifiable functional group and set the stereochemistry 
 at c17 while maintaining the trans - c , d ring fusion . 

furthermore , the completion of this molecule can now allow for the 
 direct comparison of cholesterol and demethylated 18,19-di - nor - cholesterol 
 in a variety of biological and biophysical studies , some of which 
 are currently underway .
chromatography was performed 
 using flash chromatography grade silica gel ( 3263 m ; 
 scientific adsorbents ) .
nmr spectra were recorded in cdcl3 at 400 mhz ( h ) , 100 mhz ( c ) , or 400 mhz ( 2d cosy ) .
chemical shifts 
 (  ) are reported downfield from internal me4si (  : 
 0.00 ) .
high resolution fab - ms determinations were made with a matrix m - nitrobenzyl alcohol , using nai as necessary , utilizing 
 a double - focusing analyzer composed of a magnetic sector followed 
 by a electrostatic sector .
all other chemicals were used as purchased without further 
 purification unless noted . to a stirred solution of a(13 ) ( 5.28 g , 19.1 mmol ) at 0 c under 
 n2 in anhydrous pyridine ( 20 ml ) was added acetic anhydride 
 ( 3.6 ml , 38 mmol ) dropwise followed by a catalytic amount of 4-dimethylaminopyridine 
 ( 116 mg , 0.95 mmol ) .
the reaction mixture was allowed to warm to 25 
 c and was stirred for 16 h. the pyridine was then evaporated 
 in vacuo , and the crude residue was then redissolved in dcm ( 100 ml ) 
 and washed with 1 m hcl ( 3  25 ml ) followed by h2o ( 2  25 ml ) .
the residue was 
 purified by column chromatography on silica gel ( etoac / hexanes , gradient 
 elution ) to yield compound 2 as colorless crystals in 
 96% yield ( 5.83 g , 18.3 mmol ) .
compound 2 : mp 169171 
 c ( etoac / hexanes ) ; [ ]d 6.7 
 ( c = 0.22 , chcl3 ) ; ir : 2931 , 2905 , 2858 , 
 1724 , 1243 , 1032 cm ; h nmr ( cdcl3 )  4.75 ( m , 1h , choac ) , 2.252.43 
 ( m , 4h ) , 2.04 ( s , 3h , oac ) , 2.121.10 ( m , 20h ) , 0.750.92 
 ( m , 2h ) ; c nmr ( cdcl3 )  212.1 , 170.8 , 
 74.4 , 48.8 , 47.3 , 46.3 , 43.4 , 41.5 , 40.3 , 37.4 , 35.2 , 34.2 , 32.3 , 
 31.4 , 30.5 , 29.5 , 26.0 , 25.7 , 25.3 , 21.7 ; hr - fab ms [ m + na ] calcd for c20h30o3na : 341.2093 , found 341.2099 .
compound 3 was 
 prepared according to a literature procedure . a stock solution of cro3/h2o / acoh
( 5.0 g/7.10 
 ml/8.35 ml ; w / v / v ) was first prepared .
then , in a two - necked flask 
 fitted with a dropping funnel and a reflux condenser , compound 2 ( 3.05 g , 9.58 mmol ) was dissolved into a solution of acoh / h2o / meoh 600:20:1 ( 30 ml ) at 60 c . the stock cro3/h2o / acoh solution ( 13.5 ml )
was then added via dropping 
 funnel to compound 2 , taking care not to heat the reaction 
 mixture above 65 c ( 1 drop/5 s ) .
the reaction flask 
 was allowed to stir for 2 h at 60 c , at which time starting 
 material disappearance was observed by tlc . at this point ,
heated 
 h2o was added ( 30 ml , 60 c ) , the stirring was stopped , 
 and the reaction was gradually cooled to room temperature .
the reaction 
 was allowed to stand for 16 h , during which time the desired compound 
 precipitated .
cold h2o ( 10 ml ) was then added , and the 
 precipitate was then filtered off and washed several times with cold 
 h2o and dried in vacuo .
after 3 h of drying , the compound 
 was redissolved in meoh ( 100 ml ) and cooled to 0 c under n2 .
acetyl chloride ( 10 ml ) was slowly added dropwise to the 
 flask , and after 10 min , the reaction was brought to rt .
after 16 
 h , the reaction was cooled to 0 c and neutralized with saturated 
 aqueous nahco3 .
the reaction was diluted with h2o ( 100 ml ) and extracted with dcm ( 4  50 ml ) .
the organic layers 
 were combined , dried over na2so4 , and concentrated 
 in vacuo .
the residue was purified by column chromatography on silica 
 gel ( etoac / hexanes , gradient elution ) to yield compound 3 as a white amorphous solid in 44% yield ( 1.49 g , 4.21 mmol ) .
compound 3 : mp 5254 c ( amorphous solid , etoac / hexanes ) ; 
 [ ]d + 13.4 ( c = 0.19 , 
 chcl3 ) ; ir : 3401 , 2928 , 2863 , 1737 , 1436 , 1270 , 1161 cm ; h nmr ( cdcl3 )  3.64 
 ( br s , 7h , choh , 2  ome ) , 2.550.72 
 ( m , 24h ) ; c nmr ( cdcl3 )  173.6 ( 2 ) , 
 71.6 , 51.5 , 51.5 , 47.0 , 43.7 , 40.1 , 39.3 , 38.7 , 37.3 , 36.1 , 35.1 , 
 35.0 , 32.4 , 31.5 , 29.7 , 28.9 , 25.5 , 25.5 ; hr - fab ms [ m + na ] calcd for c20h32o5na : 375.2147 , found 375.2150 .
similar to the literature , in a flame - dried flask under n2 , 
 na(s ) ( 0.60 g , 26 mmol ) was dissolved portionwise into anhydrous meoh 
 ( 15 ml ) .
the excess meoh was then evaporated off , leaving only a small 
 amount ( 2.5 ml ) to prevent the generated naome from precipitating . 

anhydrous thf ( 50 ml ) was added to the flask followed by the dropwise 
 addition of a solution of compound 3 ( 2.63 g , 7.46 mmol ) 
 in anhydrous thf ( 100 ml ) .
the reaction was refluxed at 100 c 
 for 45 min and then promptly cooled to 0 c and neutralized with 
 1 m hcl .
the reaction mixture was then diluted with h2o ( 150 ml ) and extracted with etoac ( 4  50 ml ) .
the organic extracts 
 were then combined , dried over na2so4 , and concentrated 
 in vacuo .
the residue was purified by column chromatography on silica 
 gel ( etoac / hexanes , gradient elution ) to give compound 4 as colorless crystals in 70% yield ( 1.65 g , 5.22 mmol ) .
compound 4 : mp 163164 c ( etoac / hexanes ) ; [ ]d 86.8 ( c = 0.19 , chcl3 ) ; ir : 3399 , 2924 , 2861 , 1756 , 1727 , 1440 , 1271 , 1051 cm ; h nmr ( cdcl3 )  3.76 
 ( s , 3h , co2me ) , 3.66 ( br s , 1h , h-3 ) , 2.91 ( d , 1h , j = 12.8 hz ) , 2.51 ( dd , 1h , j = 18.0 hz , j = 6.8 hz ) , 1.182.11 
 ( m , 19h ) , 0.921.11 ( m , 2h ) ; c nmr ( cdcl3 )  210.4 , 169.7 , 71.8 , 62.3 , 52.6 , 48.0 , 47.0 , 46.3 , 43.3 , 
 40.1 , 37.6 , 36.4 , 35.5 , 31.3 , 30.2 , 29.9 , 29.3 , 26.8 , 25.9 ; hr - fab 
 ms [ m + h ] calcd for c19h29o4 : 321.2066 , found 321.2064 . following a literature 
 procedure , compound 4 ( 1.58 
 g , 4.93 mmol ) was dissolved into acoh ( 12 ml ) and ethanedithiol ( 1.04 
 ml , 12.3 mmol ) . to prevent the reaction mixture from solidifying , 
 the flask was cooled in an ice bath no longer than 2 min before adding 
 bf3hoac ( 3.43 ml , 24.7 mmol ) dropwise .
the reaction 
 was then allowed to stir at 0 c for 10 min and then for another 
 30 min at rt .
the flask was then cooled to 0 c and neutralized 
 with saturated aqueous nahco3 .
the reaction mixture was 
 then diluted with h2o ( 25 ml ) and extracted with dcm ( 4 
  25 ml ) .
the organic extracts were then combined , dried over 
 na2so4 , and concentrated in vacuo .
the residue 
 was purified by column chromatography on silica gel ( etoac / hexanes , 
 gradient elution ) to give compound 5 as colorless crystals 
 in 95% yield ( 1.86 g , 4.68 mmol ) .
compound 5 : mp 103105 
 c ( etoac / hexanes ) ; [ ]d 65.0 
 ( c = 0.14 , chcl3 ) ; ir : 3368 , 2923 , 2861 , 
 1735 , 1438 , 1210 , 1156 , 1056 , 1033 , 731 cm ; h nmr ( cdcl3 )  3.74 ( s 3h , ome ) , 3.64 ( br 
 s 1h , h-3 ) , 3.403.45 ( m , 1h ) , 3.303.34 ( m , 1h ) , 3.133.22 
 ( m , 2h ) , 2.86 ( d , 1h , j = 11.3 hz ) , 2.51 
 ( dd , 1h , j = 13.3 hz ,
j = 5.5 hz ) , 1.181.97 ( m , 18h ) , 1.021.13 
 ( m , 1h ) , 0.850.97 ( m , 2h ) ; c nmr ( cdcl3 )  172.4 , 71.9 , 69.7 , 65.9 , 52.5 , 51.7 , 49.7 , 48.3 , 47.6 , 
 41.1 , 40.2 , 40.1 , 37.3 , 36.5 , 35.6 , 31.4 , 30.1 , 30.0 , 29.6 , 26.6 , 
 26.1 ; hr - fab ms [ m + na ] calcd for c21h32o3s2na : 419.1691 , found 
 419.1698 .
grace and 
 co. raney4200 , slurry in h2o , active catalyst ) was successively 
 washed and decanted with deionized h2o ( 3 ) and etoh 
 (  ) . once rinsed thoroughly ,
the catalyst was kept in a solution 
 of etoh to keep it from drying .
compound 5 ( 1.87 
 g , 4.71 mmol ) was dissolved in etoh ( 30 ml ) .
a slurry of activated 
 raney nickel ( 17 g ) in etoh ( 30 ml ) was added portionwise , and the 
 reaction was refluxed at 80 c for 1.5 h. the reaction was then 
 cooled to rt , and the crude reaction mixture was filtered through 
 a short column of silica gel ( eluting several times with etoac / etoh 
 1:1 ) to remove the raney nickel and concentrated in vacuo .
the residue 
 was purified by column chromatography on silica gel ( etoac / hexanes , 
 gradient elution ) to give compound 6 as colorless crystals 
 in 95% yield ( 1.37 g , 4.47 mmol ) .
compound 6 : mp 123125 
 c ( etoac / hexanes ) ; [ ]d + 43.0 
 ( c = 0.10 , chcl3 ) ; ir : 3350 , 2924 , 2864 , 
 1735 , 1596 , 1440 , 1208 , 1156 , 1050 cm ; h nmr ( cdcl3 )  3.65 ( s 3h , ome ) , 3.64 ( br s 1h , 
 h-3 ) , 2.25 ( m , 1h ) , 0.951.99 ( m , 22h ) , 0.720.90 ( m , 
 2h ) ; c nmr ( cdcl3 )  177.1 , 71.8 , 52.0 , 
 51.6 , 50.2 , 49.2 , 48.5 , 40.1 , 37.5 , 36.4 , 35.7 , 31.5 , 30.3 , 29.9 , 
 29.8 , 28.6 , 27.4 , 26.6 , 26.2 ; hr - fab ms [ m + h ] calcd 
 for c19h31o3 : 307.2278 , 
 found 307.2273 .
compound 6 ( 1.34 g , 4.37 mmol ) was dissolved in anhydrous dcm ( 200 ml ) and 
 cooled to 0 c under n2 .
n , n - diisopropylethylamine ( 3.05 ml , 17.5 mmol ) was added followed 
 by the dropwise addition of chloromethyl methyl ether ( 0.66 ml , 8.8 
 mmol ) .
the reaction was allowed to warm to rt and left to stir for 
 16 h. upon completion , the reaction was washed with h2o 
 ( 50 ml ) , brine ( 50 ml ) , and h2o ( 50 ml ) , dried over na2so4 , and concentrated in vacuo .
the residue was 
 purified by column chromatography on silica gel ( etoac / hexanes , gradient 
 elution ) to give compound 7 as colorless crystals in 
 98% yield ( 1.50 g , 4.28 mmol ) . compound 7 : mp 6669 
 c ( cold hexanes ) ; [ ]d + 43.8 ( c = 0.18 , chcl3 ) ; ir : 2929 , 2867 , 1733 , 1440 , 
 1144 , 1107 , 1041 cm ; h nmr ( cdcl3 )  4.68 ( s 2h , och2och3 ) , 3.67 ( s 3h , co2me ) , 3.54 ( m , 1h , h-3 ) , 3.37 
 ( s 3h , och2och3 ) , 2.25 ( m , 
 1h ) , 0.971.99 ( m , 22h ) , 0.770.90 ( m , 2h ) ; c nmr ( cdcl3 )  177.1 , 94.7 , 77.0 , 55.3 , 52.0 , 51.7 , 
 50.3 , 49.3 , 48.5 , 40.4 , 37.5 , 35.8 , 33.7 , 31.7 , 30.4 , 29.8 , 28.7 , 
 27.5 , 27.1 , 26.6 , 26.3 ; hr - fab ms [ m + h ] calcd for c21h35o4 : 351.2535 , found 
 351.2536 .
compound 7 ( 2.89 g , 8.25 mmol ) 
 was dissolved in anhydrous thf ( 300 ml ) and then cooled to 0 c 
 under n2 .
over 30 min , lialh4 ( 1 m in thf ; 8.25 
 ml , 16.5 mmol ) was added dropwise to the reaction mixture , and upon 
 completion of lialh4 addition , the reaction was found to 
 be complete .
the reaction was quenched by the careful addition of 
 h2o ( 0.63 ml ) followed by 15% aqueous naoh ( 0.63 ml ) , and 
 the reaction was allowed to stir for 30 min at rt .
another aliquot 
 of h2o ( 1.90 ml ) was added , and within 5 min a white precipitate 
 formed .
the precipitate was filtered off , and the filtrate was dried 
 over na2so4 and concentrated in vacuo .
the residue 
 was purified by column chromatography on silica gel ( etoac / hexanes , 
 gradient elution ) to give compound 8 as colorless crystals 
 in 91% yield ( 2.42 g , 7.50 mmol ) .
compound 8 : mp 7678 
 c ( etoac / hexanes ) ; [ ]d + 41.4 
 ( c = 0.14 , chcl3 ) ; ir : 3401 , 2928 , 2865 , 
 1441 , 1144 , 1107 , 1041 cm ; h nmr ( cdcl3 )  4.69 ( s 2h , och2och3 ) , 3.623.73 ( m 1h ) , 3.453.57 ( m , 2h , h-3 ) , 
 3.37 ( s 3h , och2och3 ) , 0.721.99 
 ( m , 25h ) ; c nmr ( cdcl3 )  94.7 , 77.0 , 
 66.8 , 55.3 , 52.3 , 48.8 , 48.7 , 47.1 , 40.5 , 37.8 , 35.9 , 33.7 , 31.7 , 
 30.8 , 30.1 , 28.3 , 27.1 , 27.1 , 26.6 , 26.3 ; hr - fab ms [ m + na ] calcd for c20h34o3na : 345.2406 , found 345.2404 . to a solution of compound 8
( 0.90 g , 2.8 mmol ) in anhydrous dcm ( 30 ml ) at 0 c under n2 was added et3n ( 1.17 ml , 8.37 mmol ) .
mscl ( 0.43 
 ml , 5.6 mmol ) was dissolved in anhydrous dcm ( 0.6 ml ) and added dropwise 
 to the reaction flask .
after 30 min at 0 c , the reaction was 
 quenched with ice and subsequently washed with cold saturated aqueous 
 nahco3 ( 10 ml ) , cold brine ( 10 ml ) , and cold h2o ( 10 ml ) , dried over na2so4 , and concentrated 
 in vacuo at rt .
the reaction flask was allowed to dry for 2 to 3 h 
 under vacuum , and the residue was dissolved in anhydrous dmf ( 60 ml ) , 
 and the flask was fitted with a reflux condenser .
nacn ( 0.68 g , 14 
 mmol ) was crushed into a powder and added to the reaction flask , and 
 the mixture was stirred at 65 c for 16 h. the reaction was then 
 cooled to 25 c , and ice was added to the reaction mixture , causing 
 the product to precipitate .
the product was then filtered , washed 
 several times with h2o , and dried in vacuo .
the crude compound 
 was purified by column chromatography on silica gel ( etoac / hexanes , 
 gradient elution ) to give compound 9 as colorless crystals 
 in 85% yield ( 0.79 g , 2.4 mmol ) .
compound 9 : mp 113115 
 c ( etoac / hexanes ) ; [ ]d + 46.1 
 ( c = 0.17 , chcl3 ) ; ir : 2934 , 2909 , 2867 , 
 2851 , 2244 , 1143 , 1106 , 1040 cm ; h 
 nmr ( cdcl3 )  4.67 ( s 2h , och2och3 ) , 3.473.58 ( m 1h , h-3 ) , 3.35 ( s , 3h , 
 och2och3 ) , 2.44 ( dd , 1h , j = 16.8 hz , j = 5.5 hz ) , 2.32 ( dd , 1h , j = 16.3 hz , j = 6.7 hz ) , 1.881.99 ( m , 4h ) , 0.741.86 
 ( m , 21h ) ; c nmr ( cdcl3 )  119.3 , 94.7 , 
 76.9 , 55.3 , 51.7 , 50.8 , 48.5 , 40.6 , 40.3 , 37.6 , 35.8 , 33.6 , 31.6 , 
 29.7 , 29.6 , 29.5 , 27.7 , 27.1 , 26.4 , 26.2 , 21.2 ; hr - fab ms [ m + na ] calcd for c21h33no2na : 354.2409 , found 354.2403 . in a flask fitted with a reflux condenser , 

compound 9 ( 1.98 g , 5.97 mmol ) was dissolved in ethylene 
 glycol ( 150 ml ) at 120 c .
to this was slowly added a solution 
 of 50% aqueous naoh ( 20 ml ) , and the reaction was allowed to stir 
 for 16 h at 120 c .
the reaction was then cooled to 25 c 
 and acidified to a ph 4 with 6 n hcl .
the reaction mixture was then 
 extracted several times with dcm ( 4  50 ml ) .
the organic fractions 
 were then combined , dried over na2so4 , and concentrated 
 in vacuo .
the crude compound was purified through a short column of 
 silica gel ( meoh / dcm , 1% isocratic elution ) to give compound 10 as colorless crystals in 85% yield ( 1.78 g , 5.07 mmol ) . 

compound 10 : mp 164166 c ( dcm / hexanes ) ; 
 [ ]d + 35.7 ( c = 0.12 , 
 chcl3 ) ; ir : 3367 , 2914 , 2866 , 1701 , 1141,1109 , 1047 cm ; h nmr ( cdcl3 )  4.69 
 ( s 2h , och2och3 ) , 3.493.59 
 ( m 1h ,
h-3 ) , 3.37 ( s , 3h , och2och3 ) , 2.52 ( dd , 1h , j = 14.9 hz , j = 4.7 hz ) , 2.14 ( dd , 1h , j = 15.3 hz , j = 9.4 hz ) , 1.452.03 
 ( m , 13h ) , 0.931.36 ( m , 10h ) , 0.710.85 ( m , 3h ) ; c nmr ( cdcl3 )  179.7 , 94.6 , 77.1 , 55.3 , 
 51.7 , 51.6 , 48.8 , 41.0 , 40.5 , 39.1 , 37.7 , 35.9 , 33.7 , 31.7 , 30.0 , 
 30.0 , 29.8 , 27.9 27.1 , 26.5 , 26.3 ; hr - fab ms [ m + na ] calcd 
 for c21h34o4na : 373.2355 , 
 found 373.2349 .
following literature methodology , to a solution of compound 10 ( 0.36 
 g , 1.0 mmol ) dissolved in anhydrous thf ( 15 ml ) under n2 at 0 c was added et3n ( 0.79 ml , 5.7 mmol ) .
the 
 reaction was cooled to 0 c , and pivaloyl chloride ( 0.19 ml , 
 1.5 mmol ) was added dropwise .
the reaction was stirred at 0 c 
 for 2 h. then , licl ( 0.22 g , 5.1 mmol ) and ( r)-4-benzyl-2-oxazolidinone 
 ( 0.27 g , 1.5 mmol ) were added , and the reaction was allowed to slowly 
 warm to 25 c and was then stirred for 16 h. the reaction was 
 then cooled to 0 c , quenched with saturated aqueous nahco3 , and further diluted with h2o ( 30 ml ) .
the organic extracts 
 were combined , dried over na2so4 , and concentrated 
 in vacuo .
the crude compound was purified by column chromatography 
 on silica gel ( etoac / hexanes , gradient elution ) to give compound 11 as colorless crystals in 96% yield ( 0.50 g , 0.99 mmol ) . 

compound 11 : mp 143145 c ( cold etoac ) ; 
 [ ]d + 10.2 ( c = 0.25 , 
 chcl3 ) ; ir : 3392 , 2928 , 2865 , 1783 , 1699 , 1386 , 1212 , 1106 , 
 1039 cm ; h nmr ( cdcl3 ) 
  7.117.29 ( m , 5h ) , 4.62 ( s 2h , och2och3 ) , 4.574.64 ( m , 1h , nch ) , ( overlapping 
 doublets , 2h , och2ch ) , 3.433.51 
 ( m , 1h , h-3 ) , 3.30 ( s , 3h , och2och3 ) , 3.23 ( dd , 1h , j = 13.1 hz , j = 3.3 hz , chhph ) , 3.03 
 ( dd , 1h , j = 16.6 hz ,
j = 4.1 hz , chhc(o)n ) , 2.662.79 
 ( overlapping doublets , 2h , chhc(o)n , chhph ) , 0.652.03 ( m , 25 h ) ; c nmr ( cdcl3 )  173.5 , 153.7 , 135.5 , 129.6 ( 2 ) , 129.1 ( 2 ) , 
 127.5 , 94.7 , 77.0 , 66.3 , 55.4 , 55.4 , 51.6 , 51.5 , 48.8 , 40.6 , 40.5 , 
 40.4 , 38.1 , 37.8 , 35.9 , 33.7 , 31.7 , 30.4 , 30.0 , 29.9 , 28.0 , 27.1 , 
 26.6 , 26.3 ; hr - fab ms [ m + na ] calcd for c31h43no5na : 532.3039 , found 532.3043 . in a flame - dried flask under n2 , compound 11 ( 1.32 g , 2.59 mmol ) was dissolved in anhydrous 
 thf ( 50 ml ) , and the reaction mixture was cooled to 78 c . 

nahmds ( 1 m in thf ; 4.32 ml , 4.53 mmol ) was added dropwise , and the 
 reaction was allowed to stir for 1 h at 78 c .
allyl 
 iodide ( 0.47 ml , 5.2 mmol ) was then added dropwise , and the reaction 
 was stirred at 78 c for another 1 h. after 1 h , the 
 reaction was quenched with saturated aqueous nh4cl , h2o was added ( 50 ml ) , and the reaction was extracted several 
 times with etoac ( 4  50 ml ) .
the organic fractions were then 
 combined , dried over na2so4 , and concentrated 
 in vacuo .
the crude compound was purified by column chromatography 
 on silica gel ( etoac / hexanes , gradient elution ) to give compound 12 as a white foamy solid in 86% yield ( 1.22 g , 2.23 mmol ) , 
 with recovery of unreacted starting material 11 in 7% . 

compound 12 : [ ]d 28.2 
 ( c = 0.13 , chcl3 ) ; ir : 3369 , 2927 , 2865 , 
 1782 , 1697 , 1640 , 1384 , 1208 , 1105 , 1040 cm ; h nmr ( cdcl3 )  7.157.29 ( m , 5h ) , 
 5.705.81 ( m , 1h , ch = ch2 ) , 4.935.03 ( overlapping doublets , 2h , ch = ch2 ) , 4.61 ( s , 2h , och2och3 ) , 4.544.62 ( m , 1h , nch ) , 4.014.06 
 ( overlapping doublets , 2h , och2ch ) , 3.923.96 
 ( m , 1h , chc = o ) , 3.413.49 ( m , 1h , h-3 ) , 3.29 ( s , 3h , 
 och2och3 ) , 3.24 ( dd , 1h , j = 13.2 hz , j = 3.2 hz , chhph ) , 2.56 ( dd , 1h , j = 13.2 hz , j = 2.8 hz , chhph ) , 2.382.48 ( m , 1h , chhch = ch2 ) , 2.242.32 ( m , 1h , chhch = ch2 ) , 1.381.85 ( m , 14h ) , 0.851.21 ( m , 9h ) , 0.600.78 
 ( m , 2h ) ; c nmr ( cdcl3 )  176.1 , 163.4 , 
 135.8 , 135.7 , 129.6 ( 2 ) , 129.1 ( 2 ) , 127.4 , 117.0 , 94.6 , 
 76.9 , 65.9 , 56.0 , 55.3 , 52.0 , 49.6 , 48.7 , 46.4 , 45.2 , 40.3 , 38.2 , 
 37.6 , 35.8 , 34.8 , 33.7 , 31.6 , 30.7 , 30.1 , 27.6 , 27.2 , 27.0 , 26.4 , 
 26.2 ; hr - fab ms [ m + h ] calcd for c34h48no5 : 550.3533 , found 550.3539 . following a reported procedure , a solution of compound 12 ( 1.65 
 g , 3.00 mmol ) was dissolved in thf / h2o 5:1 ( 40 ml ) at 0 
 c followed by dropwise addition of 30% aqueous h2o2 ( 3 ml ) .
this was followed by the portionwise addition 
 of lioh ( 0.25 g , 6.0 mmol ) over 30 min .
the solution was allowed to 
 slowly come to rt . after stirring for 16 h ,
the reaction was acidified 
 to ph 1 with 1 m hcl and was immediately extracted with etoac ( 4  
 20 ml ) .
the organic extracts were combined , dried over na2so4 , and concentrated in vacuo for 3 h. the crude intermediate 
 carboxylic acid was then redissolved in anhydrous thf ( 30 ml ) at 0 
 c under n2 .
lialh4 ( 2 m in thf ; 3.75 ml , 
 7.50 mmol ) was added dropwise , and the reaction was brought to 25 
 c and stirred for 16 h. upon reaction completion , the reaction 
 was cooled to 0 c and quenched carefully with 1 m hcl .
the reaction 
 was then diluted with h2o ( 30 ml ) and extracted with etoac 
 ( 4  20 ml ) .
the organic fractions were then combined , dried 
 over na2so4 , and concentrated in vacuo .
the 
 crude compound was purified by column chromatography on silica gel 
 ( etoac / hexanes , gradient elution ) to give compound 13 as colorless crystals in 91% yield ( 1.02 g , 2.73 mmol ) .
compound 13 : mp 8991 c ( etoac / hexanes ) ; [ ]d + 37.2 ( c = 0.13 , chcl3 ) ; ir : 3401 , 2928 , 2866 , 1639 , 1440 , 1144 , 1107 , 1040 cm ; h nmr ( cdcl3 )  5.755.86
( m , 
 1h , ch = ch2 ) , 4.955.04 ( overlapping 
 doublets , 2h , ch = ch2 ) , 4.66 ( s , 
 2h , och2och3 ) , 3.463.62 
 ( m 3h , h-3 , ch2oh ) , 3.34 ( s , 3h , och2och3 ) , 2.102.19 ( m , 1h , 
 chhch = ch2 ) , 0.902.12 ( m , 
 25h ) , 0.700.85 ( m , 2h ) ; c nmr ( cdcl3 )  138.5 , 115.8 , 94.6 , 77.0 , 65.2 , 55.2 , 52.0 , 48.8 , 48.3 , 
 44.9 , 42.6 , 40.4 , 37.8 , 35.8 , 33.6 , 32.7 , 31.7 , 30.8 , 30.1 , 28.2 , 
 27.1 , 26.5 , 26.2 , 25.7 ; hr - fab ms [ m + na ] calcd for c24h40o3na : 399.2875 , found 
 399.2883 . to a solution of compound 13
( 1.04 g , 2.76 mmol ) in anhydrous dcm ( 80 ml ) at 0 c under 
 n2 was added et3n ( 1.54 ml , 11.0 mmol ) .
mscl 
 ( 0.43 ml , 5.5 mmol ) was dissolved in anhydrous dcm ( 30 ml ) , and this 
 solution was added dropwise to the reaction flask .
after 30 min at 
 0 c , the reaction was quenched with ice and subsequently washed 
 with cold saturated aqueous nahco3 ( 25 ml ) , cold brine 
 ( 25 ml ) , and cold h2o ( 25 ml ) , dried over na2so4 , and condensed in vacuo at rt .
the reaction flask 
 was allowed to dry for 2 to 3 h under vacuum , the residue was then 
 dissolved in anhydrous thf ( 40 ml ) , and the flask was fitted with 
 a reflux condenser .
lialh4 ( 2 m in thf , 13.8 ml , 27.6 mmol ) 
 was added dropwise to the reaction flask , and the mixture was stirred 
 at 50 c for 1 h. the reaction was then cooled to 0 c , 
 quenched carefully with 1 m hcl , subsequently diluted with h2o ( 30 ml ) , and extracted with etoac ( 4  20 ml ) .
the organic 
 fractions were then combined , dried over na2so4 , and concentrated in vacuo .
the crude compound was purified by column 
 chromatography on silica gel ( etoac / hexanes , gradient elution ) to 
 give compound 14 as colorless crystals in 94% yield ( 0.93 
 g , 2.6 mmol ) . compound 14 : mp 5557 c ( cold 
 hexanes ) ; [ ]d + 41.9 ( c = 0.16 , chcl3 ) ; ir : 2933 , 2910 , 2861 , 1437 , 1147 , 1105 , 
 1046 , 913 cm ; h nmr ( cdcl3 )  5.705.85 ( m , 1h ) , 4.954.99 ( overlapping 
 doublets , 2h ) , 4.68 ( s , 2h , och2och3 ) , 3.493.59 ( m , 1h , h-3 ) , 3.37 ( s , 3h , och2och3 ) , 2.112.19 ( m , 1h ) , 0.751.98 
 ( m , 27h ) , 0.87 ( d , 3h , j = 6.7 hz ) ; c nmr ( cdcl3 )  138.7 , 115.3 , 94.7 , 77.1 , 
 55.3 , 52.6 , 49.5 , 48.8 , 48.4 , 40.5 , 38.5 , 37.8 , 35.9 , 35.9 , 33.7 , 
 31.8 , 31.6 , 30.3 , 28.3 , 27.1 , 26.9 , 26.5 , 26.3 , 18.1 ; hr - fab ms [ m 
 + na ] calcd for c24h40o2na : 383.2926 , found 383.2925 . combining two reported procedures , ozone gas was bubbled into a solution of compound 14 ( 0.62 g , 1.7 mmol ) and dissolved in dcm ( 50 ml ) at 78 c 
 until the reaction turned light blue in color ( ca .
, the ozone generator was turned off , and oxygen was allowed 
 to bubble into the flask until the blue ozone color disappeared ( ca . 
 5 min ) .
acetic acid ( 10 ml ) was added to the flask , and subsequently 
 the dcm was evaporated under reduced pressure .
dcm ( 10 ml ) was 
 then added back to the flask containing the acetic acid and crude 
 ozonide intermediate .
c 
 under n2 , and dimethyl sulfide ( 25 ml ) was added dropwise . 
 wanting to avoid possible byproduct formation ,
the reaction was carefully 
 monitored . after stirring at 25 c for 5 h ,
it was then placed in a freezer ( 5 c ) 
 for 16 h to slow reaction progress .
the reaction was then stirred 
 an additional 8 h at rt followed by another 16 h at 5 c , after 
 which the starting alkene was found to be completely converted into 
 an aldehyde intermediate .
the reaction was diluted with dcm ( 50 ml ) , 
 washed with h2o , saturated aqueous nahco3 , and 
 brine , dried over mg2so4 , concentrated , and 
 dried under high vacuum for 2 h. during this time , in a separate flask , 
 isobutyltriphenylphosphonium bromide ( 2.39 g , 3.5 mmol ) was dissolved 
 into anhydrous thf ( 50 ml ) under n2 and cooled to 0 c . 

nahmds ( 1 m in thf ; 3.08 ml , 3.08 mmol ) was added dropwise to the 
 reaction flask , and the mixture was stirred for 30 min at 0 c , 
 becoming bright orange in color .
tris[2-(2-methoxyethoxy)ethyl]amine 
 ( tda-1 ) ( 68 l ) was then added to the bright orange ylide followed 
 by the dropwise addition of the crude aldehyde dissolved in anhydrous 
 thf ( 50 ml ) .
, the remaining ylide was quenched by the addition 
 of a few drops of saturated aqueous nh4cl .
the thf was 
 evaporated under reduced pressure , etoac ( 50 ml ) was added , and the 
 mixture was sequentially washed with h2o , saturated aqueous 
 nahco3 , and brine , dried over na2so4 , and concentrated in vacuo .
the crude compound was purified by column 
 chromatography on silica gel using dcm / hexanes gradient elution to 
 remove excess triphenylphosphine and transitioning to a etoac / hexanes 
 gradient elution to give compound 15 as colorless crystals 
 in 85% yield ( 0.58 g , 1.5 mmol ) .
compound 15 : mp 7476 
 c ( cold hexanes ) ; [ ]d + 44.0 ( c = 0.32 , chcl3 ) ; ir : 2929 , 2866 , 1456 , 1375 , 
 1145 , 1106 , 1046 , 917 cm ; h nmr ( cdcl3 )  5.165.26 ( m , 2h ) , 4.70 ( s , 2h , och2och3 ) , 3.503.59 ( m , 1h , h-3 ) , 3.38 
 ( s , 3h , och2och3 ) , 2.532.62 
 ( m , 1h ) , 1.082.11 ( m , 28h ) , 0.95 ( d , 3h , j = 1.2 hz ) , 0.94 ( d , 3h , j = 1.6 hz ) , 0.87 ( d , 3h , j = 6.8 hz ) ; c nmr ( cdcl3 )  138.06 , 127.0 , 94.7 , 77.1 , 
 55.3 , 52.6 , 49.8 , 48.9 , 48.5 , 40.6 , 37.9 , 36.5 , 35.9 , 33.7 , 31.8 , 
 31.5 , 31.4 , 30.3 , 28.3 , 27.2 , 26.9 , 26.7 , 26.6 , 26.3 , 23.4 , 23.3 , 
 18.4 ; hr - fab ms [ m + na ] calcd for c27h46o2na : 425.3396 , found 425.3389 .
compound 15 ( 0.56 g , 1.4 mmol ) 
 and 10% pd / c ( 200 mg ) were added to a borosilicate sealable glass 
 vessel containing etoac ( 50 ml ) .
the reaction vessel was attached 
 to the parr hydrogenator ( shaker - type ) , and the air was evacuated 
 and replaced with h2 at 60 psi .
the reaction was allowed 
 to shake for 3 h , at which time the h2 was evacuated under 
 vacuum for 30 min .
the vessel was repressurized and removed from the 
 hydrogenator , and the reaction mixture was filtered through celite 
 ( taking care to wash the pd / c several times with etoac ) .
the eluent 
 was concentrated and recrystallized from cold hexanes to give compound 16 as colorless crystals in 99% yield ( 0.56 g , 1.4 mmol ) . 

compound 16 : mp 6465 c ( cold hexanes ) ; 
 [ ]d + 40.2 ( c = 0.17 , 
 chcl3 ) ; ir : 2928 , 2867 , 1456 , 1375 , 1145 , 1107 , 1045 , 916 
 cm ; h nmr ( cdcl3 )  
 4.70 ( s , 2h , och2och3 ) , 3.493.59 
 ( m , 1h , h-3 ) , 3.38 ( s , 3h , och2och3 ) , 0.731.99 ( m , 33h ) , 0.860.87 ( 3 , d , 9h ) ; c nmr ( cdcl3 )  94.7 , 77.1 , 55.3 , 52.6 , 
 50.0 , 48.9 , 48.1 , 40.6 , 39.6 , 37.9 , 36.0 , 35.5 , 33.8 , 33.7 , 31.8 , 
 31.6 , 30.3 , 28.4 , 28.2 , 27.2 , 26.7 , 26.6 , 26.4 , 25.7 , 23.0 , 22.8 , 
 18.4 ; hr - fab ms [ m + na ] calcd for c27h48o2na : 427.3552 , found 427.3556 . to a flask containing compound 16 ( 306 mg , 0.76 mmol ) 
 in meoh ( 15 ml )
after 
 stirring 16 h at rt , the reaction was neutralized with saturated aqueous 
 nahco3 , further diluted with h2o ( 30 ml ) , and 
 extracted with dcm ( 4  15 ml ) .
the organic extracts were combined 
 and evaporated to give the crude alcohol intermediate , which was immediately 
 redissolved in acetone ( 30 ml ) .
jones reagent ( 0.5 ml ; 30% 
 cro330% h2so440% h2o ) was added dropwise until the solution remained a light 
 brown color . at this time , a few drops of isopropyl alcohol were added 
 to quench the remaining jones reagent , and the reaction solution was 
 filtered through a short silica column and eluted several times with 
 etoac to remove chromium byproducts . the eluent was collected and 
 concentrated and then purified by column chromatography on silica 
 gel ( etoac / hexanes , gradient elution ) to give compound 17 as colorless crystals in 97% yield ( 263 mg , 0.73 mmol ) . compound 17 : mp 5962 c ( amorphous solid , etoac / hexanes ) ; 
 [ ]d = + 40.9 ( c = 0.17 , 
 chcl3 ) ; ir : 2951 , 2927 , 2911 , 2861 , 1712 , 1463 cm ; h nmr ( cdcl3 )  2.60 ( t , 1h , j = 14.0 hz ) , 0.862.32 ( m , 32h ) , 
 0.860.88 ( 3 , d , 9h ) ; c nmr ( cdcl3 ) 
  213.2 , 52.4 , 50.0 , 48.4 , 48.0 , 43.1 , 40.2 , 39.6 , 38.5 , 37.8 , 
 36.7 , 35.4 , 33.7 , 31.4 , 30.8 , 30.4 , 28.3 , 28.1 , 28.0 , 26.6 , 25.8 , 
 25.7 , 23.0 , 22.7 , 18.4 ; hr - fab ms [ m + na ] calcd for c25h42ona : 381.3133 , found 381.3132 .
compound 17 ( 225 mg , 0.63 mmol ) was added to a flask containing anhydrous 
 dcm ( 4 ml ) and et3n ( 0.22 ml , 1.6 mmol ) and cooled to 0 
 c under n2 .
trimethylsilyl trifluoromethanesulfonate 
 ( tmsotf ) ( 0.17 ml , 0.94 mmol ) was added dropwise , and the reaction 
 was allowed to stir for 30 min at 0 c .
after formation of the 
 silyl enol ether ( vide tlc ) , the reaction was cooled to 78 

c , and following a general literature procedure , nahco3(s ) ( 77 mg , 1.3 mmol ) and nbs 
 ( 168 mg , 0.94 mmol ) were then added sequentially .
the reaction was 
 allowed to warm to 40 c over a period of 30 min . upon 
 formation of the intermediate bromide ,
the reaction was quenched by 
 the addition of saturated aqueous na2s2o3 ( 1 ml ) , removed from the dry ice bath , and allowed to stir 
 at 25 c for 5 min .
the reaction was further diluted with dcm 
 ( 4 ml ) and washed with h2o ( 2  5 ml ) . the organic 
 phase was then dried over na2so4 , concentrated 
 in vacuo , and dried under vacuum for 30 min . according to standard 
 protocol
, the crude bromide compound 
 was then redissolved in anhydrous dmf ( 7.5 ml ) , libr ( 162 mg , 1.88 
 mmol ) and li2co3 ( 324 mg , 4.39 mmol ) were added , 
 and the reaction was heated to 120 c for 16 h. upon the formation 
 of two new products ( vide tlc ) , the dmf was removed , and the crude 
 mixture was purified by column chromatography on silica gel ( etoac / hexanes , 
 gradient elution ) to yield the undesired -3-ketone 
 in 55% ( 123 mg , 0.34 mmol ) yield and the desired -3-ketone ( 18 ) in 32% ( 71 mg , 0.20 mmol ) yield . the 
 undesired -3-ketone was then hydrogenated using 
 the conditions in the synthesis of compound 16 , regenerating 
 reuseable starting material ( 17 , 122 mg , 0.34 mmol ) . in repeating this sequence of protocols two more times , the desired 
 enone ( 18 ) was obtained as colorless crystals in 60% 
 yield ( 135 mg , 0.38 mmol ) , with starting material ( 17 ) recovered in 16% yield ( 36 mg , 0.10 mmol ) .
compound 18 : mp 6567 c ( cold hexanes ) ; [ ]d + 64.3 ( c = 0.10 , chcl3 ) ; ir : 
 2951 , 2930 , 2862 , 1678 , 1619 , 1466 , 1257 cm ; h nmr ( cdcl3 )  5.81 ( s , 1h ) 2.332.47 
 ( m , 2h ) , 2.182.33 ( m , 3h ) , 1.882.06 ( m , 4h ) , 0.811.78 
 ( m , 21h ) , 0.840.86 ( 3 , d , 9h ) ; c
nmr ( cdcl3 )  200.1 , 167.2 , 124.5 , 52.1 , 49.7 , 49.1 , 47.8 , 47.3 , 
 42.9 , 39.5 , 36.7 , 35.8 , 35.5 , 33.7 , 31.5 , 31.1 , 31.0 , 28.2 , 28.1 , 
 26.7 , 26.6 , 25.6 , 23.0 , 22.7 , 18.3 ; hr - fab ms [ m + h ] calcd 
 for c25h41o : 357.3157 , found 357.3151 .
similar to 
 a reported literature method , to a flask 
 containing ac2o ( 6 ml ) and nai ( 140 mg , 0.93 mmol ) at 0 
 c under n2 was added trimethylsilyl chloride ( 0.11 
 ml , 0.89 mmol ) dropwise .
the reagents were stirred for 30 min at 0 
 c , after which compound 18 ( 57 mg , 0.18 mmol ) was 
 added .
the reaction was allowed to slowly warm to rt , and stirring 
 was continued another 16 h. upon formation of the 18,19-di - nor - cholesta-3,5-dien-3-ol 
 acetate intermediate , the reaction was neutralized with a 1:1 mix 
 of et3n / diethyl ether , water ( 5 ml ) was added , and the 
 reaction was then extracted with hexanes ( 4  2.5 ml ) , dried 
 over na2so4 , and concentrated in vacuo .
the 
 residue was immediately purified by column chromatography ( etoac / hexanes 
 gradient elution ; adding 0.5% et3n to each gradient ) 
 on a silica gel column packed with hexanes / et3n ( 49:1 ) . 

the dienol acetate intermediate was collected , the solvents were removed , 
 and the compound was redissolved in etoh and cooled to 0 c . 

nabh4 ( 60 mg ) was added portionwise over 15 min , the reaction 
 was allowed to come to rt , and stirring was then continued for another 
 1 h. the reaction mixture was then quenched with a few drops of saturated 
 aqueous nh4cl , and the solvents were evaporated .
the crude 
 product was redissolved in dcm ( 20 ml ) and washed with brine ( 2  
 20 ml ) .
purification by column chromatography 
 on silica gel ( etoac / hexanes , gradient elution ) gave 18,19-di - nor - cholesterol 
 ( 1 ) as colorless crystals in 60% yield ( 39 mg , 0.11 mmol ) . 

compound 1 : mp 124126 c ( dcm / hexanes ) ; 
 [ ]d + 23.4 ( c = 0.19 , 
 chcl3 ) ; ir : 3373 , 2926 , 2853 , 1449 , 1375 , 1056 cm ; h nmr ( cdcl3 )  4.60 ( dd , 1h , j = 5.6 hz , h-6 ) , 3.513.58 ( m , 1h , 
 h-3 ) , 2.50 ( m , 1h ) , 0.802.12 ( m , 29h ) , 0.860.88 ( 3 , 
 d , 9h ) ; c nmr ( cdcl3 )  137.3 , 121.8 , 
 71.4 , 53.0 , 49.9 , 47.7 , 45.2 , 45.2 , 43.1 , 43.0 , 39.6 , 35.7 , 35.6 , 
 33.9 , 32.0 , 31.3 , 31.1 , 30.6 , 28.3 , 28.2 , 26.7 , 25.7 , 23.0 , 22.8 , 
 18.4 ; hr - fab ms [ m + na ] calcd for c25h42ona : 381.3133 , found 381.3136 .
 herein , 
 we report the first synthesis of a demethylated form of 
 cholesterol ( 18,19-di - nor - cholesterol ) , in which the c18 and c19 methyl 
 groups of the -face were eliminated . 
 recent molecular simulations 
 modeling 18,19-di - nor - cholesterol have suggested that cholesterol s 
 opposing rough -face and smooth -face play necessary 
 roles in cholesterol s membrane condensing abilities and , additionally , 
 that specific facial preferences are displayed as cholesterol interacts 
 with different neighboring lipids and transmembrane proteins . 
 inspired 
 by these poorly characterized biochemical interactions , an extensive 
 18-step synthesis was completed as part of a collaborative effort , 
 wherein synthesizing a  smoothened  cholesterol analogue 
 would provide a direct way to experimentally measure the significance 
 of the -face methyl groups . 
 starting from known perhydrochrysenone a , the synthesis of 18,19-di - nor - cholesterol was accomplished 
 with an excellent overall yield of 3.5% . 
 the use of the highly stereoselective 
 dieckmann condensation and the employment of evans chiral 
 auxiliary were both key to ensuring the success of this synthesis . 
Introduction
Discussion and Results
Conclusions
Experimental Section