Stereoselectivity in the anionic oxy-Cope rearrangement of acyclic vinyl sulfides

Abstract Novel anionic oxy-Cope (AOC) rearrangements of substituted 5-alkylthio-1,5-dien-3-ols were studied. Aqueous quench gave new access to compounds with a nucleophilic vinyl sulfide and an electrophilic aldehyde in a 1,5 relationship. 3,4- Anti and 3,4- syn 1 E ,5 Z -5-hexylthio-4-methyl-1-phenylhepta-1,5-dien-3-ols were synthesised separately by stereoselective aldol reaction, thioesterification and alkylidenation of the resulting thioesters to give Z -vinyl sulfides with ⩾90% stereoselectivity. AOC rearrangement of the 3,4- syn substrate gave predominantly 3,4- syn Z -vinyl sulfide while the 3,4- anti substrate gave mostly 3,4- syn E -vinyl sulfide, via chair-like transition states with the oxyanion pseudo-equatorial. Stereochemistry was assigned by NOE taking advantage of the conformational stability of the products.