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The font in St Andrew 's Church , South Croydon |
Out of Great Tribulation ; memorial chapel , Norbury Medthodist church , 1948 |
I Am Among You As He That Serveth ; stained glass window design , St. Edmund 's , Pitlake , 1962 |
= Gambia women 's national football team = |
The Gambia women 's national football team represents the Gambia in international football competition . The team , however , has not competed in a match recognised by FIFA , the sport 's international governing body , despite that organised women 's football has been played in the country since 1998 . The Gambia has two youth teams , an under @-@ 17 side that has competed in FIFA U @-@ 17 Women 's World Cup qualifiers , and an under @-@ 19 side that withdrew from regional qualifiers for an under @-@ 19 World Cup . The development of a national team faces challenges similar to those across Africa , although the national football association has four staff members focusing on women 's football . |
= = The team = = |
In 1985 , few countries had women 's national football teams . While the sport gained popularity worldwide in later decades , the Gambia 's national team only played its first game in 2007 . That game was not FIFA @-@ recognised . As of March 2012 , the team was unranked by FIFA , and as of the following month the Gambia had not played in a FIFA @-@ sanctioned match . The team has not participated in major regional and international tournaments , including the Women 's World Cup , the 2010 African Women 's Championship or the 2011 All @-@ Africa Games . |
The country did not have a FIFA @-@ recognised youth national team until 2012 , when the Gambia under @-@ 17 women 's team competed in Confederation of African Football qualifiers for the FIFA U @-@ 17 World Cup , to be held in Azerbaijan in September 2012 . The Gambia had fielded an under @-@ 17 team of 24 players , narrowed from an initial pool of 49 young women . Two girls from the SOS Children ’ s Village Bakoteh were chosen as a members of the team . The Gambia first played Sierra Leone in a pair of qualifying matches for the tournament . Gambia won the first match 3 @-@ 0 in Banjul , the Gambia 's capital . The return match was delayed in for 24 hours and played in Makeni . The Gambia beat Sierra Leone 4 @-@ 3 to qualify for the final round . The Gambia then beat Tunisia 1 @-@ 0 at home and won 2 @-@ 1 in Tunisia . Adama Tamba and Awa Demba scored the Gambia 's goals . Tunisia 's only goal was a Gambian own goal . The win qualified Gambia for the 2012 Azerbaijan World Cup . |
The Gambia also has an under @-@ 19 team that was to play in the African Women 's U @-@ 19 Championship in 2002 . The Gambia 's first match was against Morocco , but the team withdrew from the competition . |
= = Background and development = = |
The development of women 's football in Africa faces several challenges , including limited access to education , poverty amongst women , inequalities and human rights abuses targeting women . Funding is another issue impacting the game in Africa , where most financial assistance comes from FIFA and not national football associations . Another challenge is the retention of football players . Many women footballers leave the continent to seek greater opportunity in Europe or the United States . |
Gambia 's national football association was founded in 1952 , and became affiliated with FIFA in 1968 . Football is the most popular women 's sport in the country , and was first played in an organized system in 1998 . A national competition was launched in 2007 , the same year FIFA started an education course on football for women . Competition was active on both the national and scholastic levels by 2009 . There are four staffers dedicated to women 's football in the Gambia Football Association , and representation of women on the board is required by the association 's charter . |
= Plain maskray = |
The plain maskray or brown stingray ( Neotrygon annotata ) is a species of stingray in the family Dasyatidae . It is found in shallow , soft @-@ bottomed habitats off northern Australia . Reaching 24 cm ( 9 @.@ 4 in ) in width , this species has a diamond @-@ shaped , grayish green pectoral fin disc . Its short , whip @-@ like tail has alternating black and white bands and fin folds above and below . There are short rows of thorns on the back and the base of the tail , but otherwise the skin is smooth . While this species possesses the dark mask @-@ like pattern across its eyes common to its genus , it is not ornately patterned like other maskrays . |
Benthic in nature , the plain maskray feeds mainly on caridean shrimp and polychaete worms , and to a lesser extent on small bony fishes . It is viviparous , with females producing litters of one or two young that are nourished during gestation via histotroph ( " uterine milk " ) . This species lacks economic value but is caught incidentally in bottom trawls , which it is thought to be less able to withstand than other maskrays due to its gracile build . As it also has a limited distribution and low fecundity , the International Union for Conservation of Nature ( IUCN ) has listed it as Near Threatened . |
= = Taxonomy and phylogeny = = |
The first scientific description of the plain maskray was authored by Commonwealth Scientific and Industrial Research Organisation ( CSIRO ) researcher Peter Last in a 1987 issue of Memoirs of the National Museum of Victoria . The specific name annotatus comes from the Latin an ( " not " ) and notatus ( " marked " ) , and refers to the ray 's coloration . The holotype is a male 21 @.@ 2 cm ( 8 @.@ 3 in ) across , caught off Western Australia ; several paratypes were also designated . Last tentatively placed the species in the genus Dasyatis , noting that it belonged to the " maskray " species group that also included the bluespotted stingray ( then Dasyatis kuhlii ) . In 2008 , Last and William White elevated the kuhlii group to the rank of full genus as Neotrygon , on the basis of morphological and molecular phylogenetic evidence . |
In a 2012 phylogenetic analysis based on mitochondrial and nuclear DNA , the plain maskray and the Ningaloo maskray ( N. ningalooensis ) were found to be the most basal members of Neotrygon . The divergence of the N. annotata lineage was estimated to have occurred ~ 54 Ma . Furthermore , the individuals sequenced in the study sorted into two genetically distinct clades , suggesting that N. annotata is a cryptic species complex . The two putative species were estimated to have diverged ~ 4 @.@ 9 Ma ; the precipitating event was likely the splitting of the ancestral population by coastline changes . |
= = Description = = |
The pectoral fin disc of the plain maskray is thin and diamond @-@ shaped with narrowly rounded outer corners , measuring 1 @.@ 1 – 1 @.@ 3 times longer than wide . The leading margins of the disc are gently concave and converge at a broad angle to the pointed tip of the snout . The small eyes are placed close together , and behind them are the spiracles . The nostrils are elongated and have a skirt @-@ shaped flap of skin between them . The small mouth bears prominent furrows at the corners and contains two slender papillae on the floor . Small papillae are also found around the outside of the mouth . There are five pairs of gill slits . The pelvic fins are fairly large and pointed . |
The tail is short , barely exceeding the length of the disc when intact , and has a broad and flattened base leading to usually two stinging spines . After the stings , the tail becomes slender and bears a long ventral fin fold and a much shorter , lower dorsal fin fold . Most of the body lacks dermal denticles ; a midline row of 4 – 13 small , closely spaced thorns is present behind the spiracles , and another row of 0 – 4 thorns before the stings . The dorsal coloration is grayish green , becoming pinkish towards the disc margins ; there is a dark mask @-@ like shape around the eyes and a pair of small dark blotches behind the spiracles . The tail behind the stings has alternating black and white bands of variable width , ending with black at the tip . The underside is plain white and the ventral fin fold is light grayish in color . This species grows to 24 cm ( 9 @.@ 4 in ) across and 45 cm ( 18 in ) long . |
= = Original design = = |
The Type 1 gold dollar depicts a head of Liberty , facing left , with a coronet or tiara on her head bearing her name . Her hair is gathered in a bun ; she is surrounded by 13 stars representing the original states . The reverse features the date and denomination within a wreath , with the name of the nation near the rim . |
Contemporary reviews of the Type 1 design were generally favorable . The New York Weekly Tribune on May 19 , 1849 described the new dollar as " undoubtedly the neatest , tiniest , lightest , coin in this country ... it is too delicate and beautiful to pay out for potatoes , and sauerkraut , and salt pork . Oberon might have paid Puck with it for bringing the blossom which bewitched Titania . " Willis ' Bank Note List stated that " there is no probability of them ever getting into general circulation ; they are altogether too small . " The North Carolina Standard hoped that they would be struck at the Charlotte Mint and circulated locally to eliminate the problem of small @-@ denomination bank notes from out of state . Coin dealer and numismatic author Q. David Bowers notes that the head of Liberty on the Type 1 dollar is a scaled @-@ down version of that on the double eagle , and " a nicely preserved gold dollar is beautiful to behold " . |
= = Modifications = = |
Mint records indicate the first gold dollars were produced on May 7 , 1849 ; Longacre 's diary notes state instead that the first were struck on May 8 . A few coins in proof condition were struck on the first day , along with about 1 @,@ 000 for circulation . There are five major varieties of the 1849 gold dollar from Philadelphia , made as Longacre continued to fine @-@ tune the design . Mintmarked dies were sent by Longacre 's Engraving Department at the Philadelphia Mint to the branch mints at Charlotte , Dahlonega ( in Georgia ) , and New Orleans ; coins struck at the branches resemble some of the types issued from Philadelphia , depending on when the dies were produced . Of the coins struck at the branch mints in 1849 , only pieces struck at Charlotte ( 1849 @-@ C ) exist in multiple varieties ; most are of what is dubbed the " Closed Wreath " variety . Approximately five of the 1849 @-@ C Open Wreath are known ; one , believed the finest surviving specimen , sold at auction for $ 690 @,@ 000 in 2004 , remaining a record for the gold dollar series as of 2013 . One of the changes made during production was the inclusion of Longacre 's initial " L " on the truncation of Liberty 's neck , the first time a U.S. coin intended for full @-@ scale production had borne the initial of its designer . All issues beginning in 1850 bear the Closed Wreath . Beginning in 1854 , the gold dollar was also struck at the new San Francisco Mint . |
The continued flow of gold from California made silver expensive in terms of gold , and U.S. silver coins began to flow out of the country for melting in 1849 , a flow that accelerated over the next several years as the price of the metal continued to rise . By 1853 , a thousand dollars in silver coin contained $ 1 @,@ 042 worth of bullion . As silver coins vanished , the gold dollar became the only federal coin in circulation between the cent and the quarter eagle ( $ 2 @.@ 50 piece ) . As such , it was struck in large numbers and widely circulated . According to Bowers in his book on the denomination , " the years 1850 to 1853 were the high @-@ water mark of the gold dollar , the glory years of the denomination when the little gold coins took the place of half dollars and silver dollars in everyday transactions . " This time came to an end in 1853 when Congress passed an act reducing the weight of most silver coins , allowing new issues of them to circulate . |
As early as 1851 , New York Congressman William Duer alleged that that Patterson had made the gold dollar too small in diameter on purpose to provoke criticism . Patterson retired that year after 16 years in his position , and under his successor , George N. Eckert , annular gold dollar and half dollar patterns were struck . Public Ledger reported that although gold dollars would not be struck in annular form , gold half dollars would be , to help fill the need for change . With the new Pierce administration , Thomas M. Pettit took office as Mint Director on March 31 , 1853 . In April , Treasury Secretary James Guthrie wrote to Pettit that there were complaints that the gold dollar was too small , often lost or mistaken for a small silver coin , and enquiring about reports the Mint had experimented with annular dollars . Pettit replied , stating that none had been preserved , but enclosed a silver piece of equivalent size . He noted that while there would be technical difficulties in the production of the annular dollar , these could be overcome . In a letter dated May 10 , Pettit proposed an oval @-@ shaped holed piece , or an angular @-@ shaped coin , which would lessen the production problems . Pettit died suddenly on May 31 ; Guthrie did not let the issue fall , but queried Pettit 's replacement , James Ross Snowden , concerning the issue on June 7 . As U.S. coins were required to bear some device emblematic of liberty , the secretary hoped that artists could be found who could find some such design for an annular coin . |
The Act of February 21 , 1853 , that had lightened the silver coins also authorized a gold three @-@ dollar piece , which began to be produced in 1854 . To ensure that the three @-@ dollar piece was not mistaken for other gold coins , it had been made thinner and wider than it would normally be , and Longacre put a distinctive design with an Indian princess on it . Longacre adapted both the technique and the design for the gold dollar , which was made thinner , and thus wider . An adaptation of Longacre 's princess for the larger gold coin was placed on the dollar , and a similar agricultural wreath on the reverse . The idea of making the gold dollar larger in this way had been suggested in Congress as early as 1852 , and had been advocated by Pettit , but Guthrie 's desire for an annular coin stalled the matter . In May 1854 , Snowden sent Guthrie a letter stating that the difficulties with an annular coin , especially in getting the coins to eject properly from the press , were more than trivial . |
Nevertheless , the Type 2 gold dollar ( as it came to be known ) proved unsatisfactory as the mints had difficulty in striking the new coin so that all details were brought out . This was due to the high relief of the design — the three Southern branch mints especially had trouble with the piece . Many of the Type 2 pieces quickly became illegible , and were sent back to Philadelphia for melting and recoinage . On most surviving specimens , the " 85 " in the date is not fully detailed . The Type 2 gold dollar was struck only at Philadelphia in 1854 and 1855 , at the three Southern branch mints in the latter year , and at San Francisco in 1856 , after the design was designated for replacement . To correct the problems , Longacre enlarged the head of Liberty , making it a scaled @-@ down version of the three @-@ dollar piece , and moved the lettering on the obverse closer to the rim . This improved the metal flow and design sharpness so much that early numismatic scholars assumed the reverse was also altered , though in fact no change was made and the Type 2 and Type 3 reverses are identical . |
= = = Design of Type 2 and 3 dollars = = = |
The Type 2 and 3 gold dollars depict Liberty as a Native American princess , with a fanciful feathered headdress not resembling any worn by any Indian tribe . This image is an inexact copy of the design Longacre had made for the three @-@ dollar piece , and is one of a number of versions of Liberty Longacre created based on the Venus Accroupie or Crouching Venus , a sculpture then on display in a Philadelphia museum . For the reverse , Longacre adapted the " agricultural wreath " he had created for the reverse of the three @-@ dollar piece , composed of cotton , corn , tobacco , and wheat , blending the produce of North and South . This wreath would appear , later in the 1850s , on the Flying Eagle cent . |
Art historian Cornelius Vermeule deprecated the Indian princess design used by Longacre for the obverses of the Types 2 and 3 gold dollar , and for the three @-@ dollar piece , " the ' princess ' of the gold coins is a banknote engraver 's elegant version of folk art of the 1850s . The plumes or feathers are more like the crest of the Prince of Wales than anything that saw the Western frontiers , save perhaps on a music hall beauty . " |
= = War years = = |
The gold dollar continued to be produced in the late 1850s , though mintages declined from the figures of two million or more each year between 1850 and 1854 . Only about 51 @,@ 000 gold dollars were produced in 1860 , with over two @-@ thirds of that figure at Philadelphia , just under a third at San Francisco , and 1 @,@ 566 at Dahlonega . Roughly a hundred are known of the last , creating one of the great rarities from Dahlonega in the series . |
The other candidate for the rarest from that mint is the 1861 @-@ D , with an estimated mintage of 1 @,@ 000 and perhaps 45 to 60 known . Two pairs of dies were shipped from Philadelphia to Dahlonega on December 10 , 1860 ; they arrived on January 7 , 1861 , two weeks before Georgia voted to secede from the Union , as the American Civil War began . Under orders from Governor Joseph E. Brown , state militia secured the mint , and at some point , small quantities of dollars and half eagles were produced . Records of how many coins were struck and when have not survived . Since dies crack in time , and all the mints were supplied with them from Philadelphia , coining could not last , and in May 1861 , coins and supplies remaining at Dahlonega were turned over to the treasury of the Confederate States of America , which Georgia had by then joined . Gold coins with a face value of $ 6 were put aside for assay . Normally , they would have been sent to Philadelphia to await the following year 's meeting of the United States Assay Commission , when they would be available for testing . Instead , these were sent to the initial Confederate capital of Montgomery , Alabama , though what was done with them there , and their ultimate fate , are unknown . The rarity of the 1861 @-@ D dollar , and the association with the Confederacy , make it especially prized . |
Dahlonega , like the other two branch mints in the South , closed its doors after the 1861 strikings . It and the Charlotte facility never reopened ; the New Orleans Mint again struck coins from 1879 to 1909 , but did not strike gold dollars again . After 1861 , the only issuance of gold dollars outside Philadelphia was at San Francisco , in 1870 . |
The outbreak of the Civil War shook public confidence in the Union , and citizens began hoarding specie , gold and silver coins . In late December 1861 , banks and then the federal Treasury stopped paying out gold at face value . By mid @-@ 1862 , all federal coins , even the base metal cent , had vanished from commerce in much of the country . The exception was the Far West , where for the most part , only gold and silver were acceptable currencies , and paper money traded at a discount . In the rest of the nation , gold and silver coins could be purchased from banks , exchange agents , and from the Treasury for a premium in the new greenbacks the government began to issue to fill the gap in commerce and finance the war . |
= = Final years , abolition , and collecting = = |
Since gold did not circulate in the United States ( except on the West Coast ) in the postwar period , much of the production of coins of that metal in the United States was double eagles for export . Accordingly , although 1 @,@ 361 @,@ 355 gold dollars were struck in 1862 — the last time production would exceed a million — the mintage fell to 6 @,@ 200 in 1863 and remained low for the rest of the coin 's existence , excepting 1873 and 1874 . The Mint felt it improper to suspend coinage of a coin authorized by Congress , and issued proof coins ( generally a few dozen to the tiny numismatic community ) from specially @-@ polished dies , also producing enough circulation strikes so that the proof coins would not be unduly rare . In 1873 and 1874 , old and worn gold dollars held by the government were melted and recoined , generating large mintages of that denomination . This was done in anticipation of the resumption of specie payments , which did not occur until the end of 1878 . Once specie again circulated at face value , the gold dollar found no place in commerce amid large quantities of silver coinage , either released from hoarding or newly struck by the Mint . The government expected that the resumption of specie payments would cause the dollar and other small gold coins to circulate again , but the public , allowed to redeem paper currency , continued to use it as more convenient than coins . |
In the 1870s and 1880s , public interest grew in the low @-@ mintage gold dollar . Collecting coins was becoming more popular , and a number of numismatists put aside some gold dollars and hoped for increases in value . The Mint most likely channeled its production through some favored Philadelphia dealers , though proof coins could be purchased for $ 1 @.@ 25 at the cashier 's window at the Philadelphia facility . Banks charged a premium for circulation strikes . They were popular in the jewelry trade , mounted into various items . The coins were often exported to China or Japan , where such jewelry was made . The dollars were often damaged in the process ; the Mint refused to sell into this trade and did its best to hinder it . Nevertheless , Mint officials concluded that jewelers were successful at getting the majority of each issue . Proof mintages exceeded 1 @,@ 000 by 1884 , and remained above that mark for the remainder of the series , numbers likely inflated by agents of jewelers , willing to pay the Mint 's premium of $ .25 per coin . Another use for the gold dollar was as a holiday gift ; after its abolition the quarter eagle became a popular present . |
James Pollock , in his final report as Mint Director in 1873 , advocated limiting striking of gold dollars to depositors who specifically requested it . " The gold dollar is not a convenient coin , on account of its small size , and it suffers more proportionately from abrasion than larger coins . " His successors called for its abolition , with James P. Kimball , before he left office in 1889 , writing to Congress that except as jewelry , " little practical use has been found for this coin " . Later that year , the new director , Edward O. Leech , issued a report stating that the gold dollar " is too small for circulation , and ... [ is ] used almost exclusively for the purposes of ornament . The last year in which the gold dollar was struck was 1889 . Congress abolished the gold dollar , along with the three @-@ cent nickel and three @-@ dollar piece , by the Act of September 26 , 1890 . |
A total of 19 @,@ 499 @,@ 337 gold dollars were coined , of which 18 @,@ 223 @,@ 438 were struck at Philadelphia , 1 @,@ 004 @,@ 000 at New Orleans , 109 @,@ 138 at Charlotte , 90 @,@ 232 at San Francisco and 72 @,@ 529 at Dahlonega . According to an advertisement in the February 1899 issue of The Numismatist , gold dollars brought $ 1 @.@ 80 each , still in demand as a birthday present and for jewelry . That journal in 1905 carried news of a customer depositing 100 gold dollars into a bank ; the teller , aware of the value , credited the account with $ 1 @.@ 60 per coin . In 1908 , a dealer offered $ 2 each for any quantity . As coin collecting became a widespread pastime in the early 20th century , gold dollars became a popular specialty , a status they retain . The 2014 edition of R.S. Yeoman 's A Guide Book of United States Coins rates the least expensive gold dollar in very fine condition ( VF @-@ 20 ) at $ 300 , a value given for each of the Type 1 Philadelphia issues from 1849 to 1853 . Those seeking one of each type will find the most expensive to be a specimen of the Type 2 , with the 1854 and 1855 estimated at $ 350 in that condition ; the other two types have dates valued at $ 300 in that grade . |
= = Commemorative gold dollars = = |
The gold dollar had a brief resurrection during the period of Early United States commemorative coins . Between 1903 and 1922 nine different issues were produced , with a total mintage of 99 @,@ 799 . These were minted for various public events , did not circulate , and none used Longacre 's design . |
= Johnson – Corey – Chaykovsky reaction = |
The Johnson – Corey – Chaykovsky reaction ( sometimes referred to as the Corey – Chaykovsky reaction or CCR ) is a chemical reaction used in organic chemistry for the synthesis of epoxides , aziridines , and cyclopropanes . It was discovered in 1961 by A. William Johnson and developed significantly by E. J. Corey and Michael Chaykovsky . The reaction involves addition of a sulfur ylide to a ketone , aldehyde , imine , or enone to produce the corresponding 3 @-@ membered ring . The reaction is diastereoselective favoring trans substitution in the product regardless of the initial stereochemistry . The synthesis of epoxides via this method serves as an important retrosynthetic alternative to the traditional epoxidation reactions of olefins . |
The reaction is most often employed for epoxidation via methylene transfer , and to this end has been used in several notable total syntheses ( See Synthesis of epoxides below ) . Additionally detailed below are the history , mechanism , scope , and enantioselective variants of the reaction . Several reviews have been published . |
= = History = = |
The original publication by Johnson concerned the reaction of 9 @-@ dimethylsulfonium fluorenylide with substituted benzaldehyde derivatives . The attempted Wittig @-@ like reaction failed and a benzalfluorene oxide was obtained instead , noting that " Reaction between the sulfur ylid and benzaldehydes did not afford benzalfluorenes as had the phosphorus and arsenic ylids . " |
The subsequent development of ( dimethyloxosulfaniumyl ) methanide , ( CH3 ) 2SOCH2 and ( dimethylsulfaniumyl ) methanide , ( CH3 ) 2SCH2 ( known as Corey – Chaykovsky reagents ) by Corey and Chaykovsky as efficient methylene @-@ transfer reagents established the reaction as a part of the organic canon . |
= = Mechanism = = |
The reaction mechanism for the Johnson – Corey – Chaykovsky reaction consists of nucleophilic addition of the ylide to the carbonyl or imine group . A negative charge is transferred to the heteroatom and because the sulfonium cation is a good leaving group it gets expelled forming the ring . In the related Wittig reaction , the formation of the much stronger phosphorus @-@ oxygen double bond prevents oxirane formation and instead , olefination takes place through a 4 @-@ membered cyclic intermediate . |
The trans diastereoselectivity observed results from the reversibility of the initial addition , allowing equilibration to the favored anti betaine over the syn betaine . Initial addition of the ylide results in a betaine with adjacent charges ; density functional theory calculations have shown that the rate @-@ limiting step is rotation of the central bond into the conformer necessary for backside attack on the sulfonium . |
The degree of reversibility in the initial step ( and therefore the diastereoselectivity ) depends on four factors , with greater reversibility corresponding to higher selectivity : |
Stability of the substrate with higher stability leading to greater reversibility by favoring the starting material over the betaine . |
Stability of the ylide with higher stability similarly leading to greater reversibility . |
Steric hindrance in the betaine with greater hindrance leading to greater reversibility by disfavoring formation of the intermediate and slowing the rate @-@ limiting rotation of the central bond . |
Solvation of charges in the betaine by counterions such as lithium with greater solvation allowing more facile rotation in the betaine intermediate , lowering the amount of reversibility . |
= = Scope = = |
The application of the Johnson – Corey – Chaykovsky reaction in organic synthesis is diverse . The reaction has come to encompass reactions of many types of sulfur ylides with electrophiles well beyond the original publications . It has seen use in a number of high @-@ profile total syntheses , as detailed below , and is generally recognized as a powerful transformative tool in the organic repertoire . |
= = = Types of ylides = = = |
Many types of ylides can be prepared with various functional groups both on the anionic carbon center and on the sulfur . The substitution pattern can influence the ease of preparation for the reagents ( typically from the sulfonium halide , e.g. trimethylsulfonium iodide ) and overall reaction rate in various ways . The general format for the reagent is shown on the right . |
Use of a sulfoxonium allows more facile preparation of the reagent using weaker bases as compared to sulfonium ylides . ( The difference being that a sulfoxonium contains a doubly bonded oxygen whereas the sulfonium does not . ) The former react slower due to their increased stability . In addition , the dialkylsulfoxide by @-@ products of sulfoxonium reagents are greatly preferred to the significantly more toxic , volatile , and odorous dialkylsulfide by @-@ products from sulfonium reagents . |
The vast majority of reagents are monosubstituted at the ylide carbon ( either R1 or R2 as hydrogen ) . Disubstituted reagents are much rarer but have been described : |
If the ylide carbon is substituted with an electron @-@ withdrawing group ( EWG ) , the reagent is referred to as a stabilized ylide . These , similarly to sulfoxonium reagents , react much slower and are typically easier to prepare . These are limited in their usefulness as the reaction can become prohibitively sluggish : examples involving amides are widespread , with many fewer involving esters and virtually no examples involving other EWG 's . For these , the related Darzens reaction is typically more appropriate . |
If the ylide carbon is substituted with an aryl or allyl group , the reagent is referred to as a semi @-@ stabilized ylide . These have been developed extensively , second only to the classical methylene reagents ( R1 = R2 = H ) . The substitution pattern on aryl reagents can heavily influence the selectivity of the reaction as per the criteria above . |
If the ylide carbon is substituted with an alkyl group the reagent is referred to as an unstabilized ylide . The size of the alkyl groups are the major factors in selectivity with these reagents . |
The R @-@ groups on the sulfur , though typically methyls , have been used to synthesize reagents that can perform enantioselective variants of the reaction ( See Variations below ) . The size of the groups can also influence diastereoselectivity in alicyclic substrates . |
= = = Synthesis of epoxides = = = |
Reactions of sulfur ylides with ketones and aldehydes to form epoxides are by far the most common application of the Johnson – Corey – Chaykovsky reaction . Examples involving complex substrates and ' exotic ' ylides have been reported , as shown below . |
The reaction has been used in a number of notable total syntheses including the Danishefsky Taxol total synthesis , which produces the chemotherapeutic drug taxol , and the Kuehne Strychnine total synthesis which produces the pesticide strychnine . |
= = = Synthesis of aziridines = = = |
The synthesis of aziridines from imines is another important application of the Johnson – Corey – Chaykovsky reaction and provides an alternative to amine transfer from oxaziridines . Though less widely applied , the reaction has a similar substrate scope and functional group tolerance to the carbonyl equivalent . The examples shown below are representative ; in the latter , an aziridine forms in situ and is opened via nucleophilic attack to form the corresponding amine . |
= = = Synthesis of cyclopropanes = = = |
For addition of sulfur ylides to enones , higher 1 @,@ 4 @-@ selectivity is typically obtained with sulfoxonium reagents than with sulfonium reagents . Many electron @-@ withdrawing groups have been shown compatible with the reaction including ketones , esters , and amides ( the example below involves a Weinreb amide ) . With further conjugated systems 1 @,@ 6 @-@ addition tends to predominate over 1 @,@ 4 @-@ addition . |
= = = Other reactions = = = |
In addition to the reactions originally reported by Johnson , Corey , and Chaykovsky , sulfur ylides have been used for a number of related homologation reactions that tend to be grouped under the same name . |
With epoxides and aziridines the reaction serves as a ring @-@ expansion to produce the corresponding oxetane or azetidine . The long reaction times required for these reactions prevent them from occurring as significant side reactions when synthesizing epoxides and aziridines . |
Several cycloadditions wherein the ylide serves as a " nucleophilic carbenoid equivalent " have been reported . |
Living polymerizations using trialkylboranes as the catalyst and ( dimethyloxosulfaniumyl ) methanide as the monomer have been reported for the synthesis of various complex polymers . |
= = Enantioselective variations = = |
The development of an enantioselective ( i.e. yielding an enantiomeric excess , which is labelled as " ee " ) variant of the Johnson – Corey – Chaykovsky reaction remains an active area of academic research . The use of chiral sulfides in a stoichiometric fashion has proved more successful than the corresponding catalytic variants , but the substrate scope is still limited in all cases . The catalytic variants have been developed almost exclusively for enantioselective purposes ; typical organosulfide reagents are not prohibitively expensive and the racemic reactions can be carried out with equimolar amounts of ylide without raising costs significantly . Chiral sulfides , on the other hand , are more costly to prepare , spurring the advancement of catalytic enantioselective methods . |
= = = Stoichiometric reagents = = = |
The most successful reagents employed in a stoichiometric fashion are shown below . The first is a bicyclic oxathiane that has been employed in the synthesis of the β @-@ adrenergic compound dichloroisoproterenol ( DCI ) but is limited by the availability of only one enantiomer of the reagent . The synthesis of the axial diastereomer is rationalized via the 1 @,@ 3 @-@ anomeric effect which reduces the nucleophilicity of the equatorial lone pair . The conformation of the ylide is limited by transannular strain and approach of the aldehyde is limited to one face of the ylide by steric interactions with the methyl substituents . |
The other major reagent is a camphor @-@ derived reagent developed by Varinder Aggarwal of the University of Bristol . Both enantiomers are easily synthesized , although the yields are lower than for the oxathiane reagent . The ylide conformation is determined by interaction with the bridgehead hydrogens and approach of the aldehyde is blocked by the camphor moiety . The reaction employs a phosphazene base to promote formation of the ylide . |
= = = Catalytic reagents = = = |
Catalytic reagents have been less successful , with most variations suffering from poor yield , poor enantioselectivity , or both . There are also issues with substrate scope , most having limitations with methylene transfer and aliphatic aldehydes . The trouble stems from the need for a nucleophilic sulfide that efficiently generates the ylide which can also act as a good leaving group to form the epoxide . Since the factors underlying these desiderata are at odds , tuning of the catalyst properties has proven difficult . Shown below are several of the most successful catalysts along with the yields and enantiomeric excess for their use in synthesis of ( E ) -stilbene oxide . |
Aggarwal has developed an alternative method employing the same sulfide as above and a novel alkylation involving a rhodium carbenoid formed in situ . The method too has limited substrate scope , failing for any electrophiles possessing basic substituents due to competitive consumption of the carbenoid . |
= Treaty of Ciudad Juárez = |
The Treaty of Ciudad Juárez was a peace treaty signed between the then President of Mexico , Porfirio Díaz , and the revolutionary Francisco Madero on May 21 , 1911 . The treaty put an end to the fighting between forces supporting Madero and those of Díaz and thus concluded the initial phase of the Mexican Revolution . |
The treaty stipulated that Díaz , as well as his vice president Ramón Corral , were to step down by the end of May , and that he was to be replaced by Francisco León de la Barra as interim president and hold presidential elections . Those who had suffered losses due to the revolution would be the indemnified , and there would be a general amnesty . Díaz resigned on May 25 , and interim president Francisco León de la Barra was the new incumbent . Díaz and his family , his vice president Corral , plus José Yves Limantour and Rosendo Pineda left Mexico for exile . |
Significantly , the treaty did not mention or institute any social reforms that Madero had vaguely promised on previous occasions . It also left the Porfirian state essentially intact . Additionally , Madero supported the unpopular idea that all land disputes were to be settled through the courts , staffed by the old judges , a decision that led to outbreaks of sporadic violence , particularly in rural areas . |
On June 7 , 1911 , Madero entered Mexico City . In October 1911 he was elected president , under the banner of the Partido Constitucional Progresista , along with José María Pino Suárez , his new running mate as vice @-@ president . Madero pushed aside Francisco Vázquez Gómez , the vice presidential candidate for the Anti @-@ Reelectionist Party in 1910 , as being too moderate . |
= = Military developments leading up to the treaty = = |
The rebellion against the government of Porfirio Díaz broke out in late 1910 , after Díaz had his rival Francisco Madero imprisoned and had announced his own victory in a falsified election . Madero 's earlier vague promises of agrarian reforms had attracted many supporters . He himself escaped from prison and fled to Texas , from where he issued his famous Plan of San Luis Potosí . This manifesto called for an armed uprising against the Porfiriato and establishment of free and democratic elections . As a response to Madero 's proclamation , violent clashes began throughout Mexico in November 1910 . |
In the Guerrero district of Chihuahua , Pascual Orozco attacked Federal troops and sent dead soldiers ' clothing back to Díaz with the message , " Ahí te van las hojas , mándame más tamales " ( " Here are the wrappers , send me more tamales . " ) He then began operations which threatened Ciudad Juárez . Additionally , political support for Madero 's rebellion came from Abraham González , who accepted the Plan of San Luis Potosí . |
At roughly the same time , agrarian unrest in the state of Morelos turned into a full blown rebellion under the leadership of the Zapata brothers , Emiliano and Eufemio . |
= = = Orozco and Villa take Ciudad Juárez = = = |
Encouraged by the news of the uprisings , Madero crossed the border back into Mexico in February 1911 . He was joined by Pancho Villa and Orozco and in April the army began approaching Ciudad Juárez . Orozco and Villa led the way with 500 men each , while Madero followed up with 1 @,@ 500 riders . The city was besieged by the end of the month , after Madero 's army encountered some resistance in the Chihuahuan countryside . Madero asked the commander of the city 's garrison to surrender but the latter refused , hoping that the fortifications he had constructed would allow him to defend the city until reinforcements arrived . Concerned also with the possibility that a direct attack on the town would cause artillery shells to cross the border into the United States which could provoke an outside intervention , and faced with a series of peace proposals from Díaz , Madero hesitated in attacking the city . He in fact ordered his commanders to lift the siege . Orozco , however disregarded the order and , joined by Villa , attacked . After two days of fighting the city fell to the insurrectionists . Madero intervened personally to spare the life of the city 's commander , Gen. Navarro , whom both Orozco and Villa wanted executed for his previous killing of rebel POWs . This , coupled with the fact that both leaders were ignored by Madero in his political appointments , outraged and estranged them from him . |
Subsets and Splits