Dichotomous Regiochemistry of Aldehyde and Ketone in the Reaction with Dithio-Substituted Crotyllithium

Article abstract of DOI:10.1021/jo00381a026

The crotyllithium compound 1 generated from (E)-2-(1-propen-1-yl)-1,3-dithiane reacted with an aldehyde to give γ-products in favor of the anti isomer.This regio- and diastereoselective reaction is applicable to syntheses of trans β,γ-disubstituted γ-lactones, including natural products of (+/-)-eldanolide and (+/-)-trans quercus lactone.The γ(1,2)-adducts obtained from the reaction of 1 and enals underwent alkoxy-Cope rearrangements on treatment with KH.The consequence is virtually complete α(1,4)-addition of crotyllithium 1 to α,β-unsaturated aldehydes.Crotyllithium 1 reacted with ketones at either the α- or the γ-site, depending on the nature of respective ketone.The regiochemistry is well interpreted by the hard and soft acids and bases principle, when the steric effect is a minor controlling factor.The effects of HMPA and reaction temperature on the regioselectivity were also evaluated.