Increased Felkin-Anh selectivity using AlMe(3) in the addition of vinyllithiums to alpha-chiral aldehydes: do "ate" complexes play any role?

[reaction: see text] AlMe(3) dramatically increases the diastereoselectivity of addition of vinyllithiums to alpha-chiral aldehydes but decreases that of methyllithium. Our results are explained in terms of an addition of the free vinyllithium on the Me(3)Al-aldehyde complex.