Syn or anti selective Michael addition of allyl phenyl sulphone and phenyl prenyl sulphone to enoates derived from D-mannitol

Article abstract of DOI:10.1016/S0040-4039(98)01073-9

Prenyl and allyl sulphones (3α,β) were deprotonated with BuLl in THF and the resulting carbanions were allowed to react with enoates prepared from D-(+)-mannitol. A major diastereomer (control at the two newly created stereogenic centers) was obtained from enoates E-lb-e (Ethyl and t-Butyl ester, respectively) in d.e. up to 90%. Syn-stereoselectivities were observed when the reactions were stopped at r.t. while at -78°C anti- stereoselectivities predominated. Enoate E-1a (methyl ester) led to anti- addition regardless the temperature at which the reaction was quenched. However, a syn-stereoselectivity was found when the reaction was run in the presence of HMPA. The stereochemical assignments for both newly generated stereogenic centers were based on the transformation of the adducts into the corresponding β,γ-disubstituted γ-lactones, followed by measurements of ¹H,¹H coupling constants and hoe experiments.