Stereoselective synthesis of alcohols, XXII. E/Z‐selectivity on addition of α‐substituted allylboronates to aldehydes

Abstract α‐Heterosubstituted allylboronates 7 are prepared. Addition of 7 to aldehydes results in E/Z‐isomeric homoallyl alcohols 13 and 14. The reasons for the predominant formation of the Z‐isomer 14 are discussed. The Z‐bromo olefins 16 and 20 obtained in this way serve as starting point for chain extension or formation of δ‐lactones 21.