Regiochemical Convergence in the Reaction of Heterosubstituted Allylic Carbanions via Allylic Aluminum and Boron "Ate" Complexes

Article abstract of DOI:10.1021/jo00180a027

The regiochemistry in reactions of heterosubstituted allylic carbanions (1) is highly controlled via allylic aluminum or boron "ate" complexes which direct both carbonyl compounds and reactive halides to the α-position with high regioselectivity.For example, carbonyl compounds react with the oxygen- (3), sulfur- (12), selenium- (20), and silicon- (25) substituted allylic carbanions at the α-position via the ate complexes.Although the reactions of the ate complexes (2) with aldehydes generally produce a mixture of erythro and threo isomers, the aluminum ate comlex of 3b gives the erythro isomer (5) with very high stereoselectivity.This procedure is applied to the stereoselective synthesis of exo-brevicomin (9).With allylic halides, the oxygen- (3a) and sulfur- (12) substituted allylic carbanions again react at the α-position via the ate complexes.However, the coupling mode is entirely different; the α-α' coupling product (10) is obtained from 3a, while the α-γ' coupling product (15) is produced from 12.