 Kobayashi and Horibe demonstrated this in the synthesis of dihydroxy thioester derivatives, using a tin-based chiral Lewis acid.The transition structures for reactions with both the R and S catalyst enantiomers are shown below.The Baylis-Hillman reaction is a route for C-C bond formation between an alpha, beta-unsaturated carbonyl and an aldehyde, which requires a nucleophilic catalyst, usually a tertiary amine, for a Michael-type addition and elimination.