Anomalous threo-diastereoselectivity in allylic silane- or stannane–aldehyde condensation reactions: new interpretation of the antiperiplanar vs. synclinal problem on the transition-state conformations

Abstract
Unusual threo-diastereoselectivity has been observed in the intermolecular reactions of β-substituted crotyl-silane or-stannane with 2-benzyloxypropanal under chelation conditions, which implies preference for the synclinal over the antiperiplanar transition state.