The isomeric trans-(E)-, trans-(Z)-, cis-(E)-, and cis-(Z)-vinyloxiranes 7, 9, 17, and 19 were prepared from 2- (benzyloxy)ethanol by sequential Swern-Wittig or Swern-Horner-Emmons propionate condensation, DIBAH reduction, Sharpless epoxidation, Swern oxidation, Wittig or Horner-Emmons acetate condensation, and a second DIBAH reduction. Addition of lithium dimethylcuprate and lithium methylcyanocuprate to these epoxides in THF-ether at -20 to 0 °C afforded the allylic alcohols 22, 25, ent-23, and ent-22 as the major products. These products are formed by anti addition to the lower energy conformer (s-trans for 7, 17, and 19 and s-cis for 9) of the respective vinyloxirane. The conformational preferences of transition-state-like geometries of the vinyloxiranes, calculated with the aid of Still’s MacroModel program, were in agreement with the observed trends.
ASJC Scopus subject areas
- Organic Chemistry