α-Substituent effect on olefination of ester carbonyl groups with ynolates

In the olefination reaction of ester carbonyl with ynolate, an α-hetero (N, O, S)-substituent on the substrates was found to markedly improve the yields of tetrasubstituted olefins, even though it was sterically hindered. The α-substituent effect may be due to several factors including the addition based on the polar Felkin–Anh model and restricted conformation of the initial adducts.