m 299 0 5 m me 286 1 m co 285 5 m cho 257 1 m c 3 h 5 o 209 10 m phco 192 38 134 60 105 100 77 50 exact mass calculated for c 20 h 26 o 3 3 14 1882 found 314 1887 the aldehyde 2 1 36 g 4 3 mmol was dissolved in ch 2 cl 2 15 ml and a 40 aq n bu 4 noh solution 5 6 ml 5 57 g 8 6 mmol was added the resulting mixture was stirred at room temperature for 16 h diluted with methylene chloride 30 ml washed with water dried na 2 so 4 and concentrated under reduced pressure a residue was chromatographed on silica gel with hexane ethyl acetate 95 5 to afford a mixture of aldehyde 2 and its 20 epimer 730 mg 53 yield in ca 1 1 7 ratio by 1 h nmr this mixture of aldehydes 730 mg 2 3 mmol was dissolved in thf 5 ml and nabh 4 175 mg 4 6 mmol was added followed by a dropwise addition of ethanol 5 ml the reaction mixture was stirred at room temperature for 30 min and it was quenched with.