Boron aldol additions with erythrulose derivatives:: dependence of stereoselectivity on the type of protecting group

Boron aldol additions of 1-O-silylated 3,4-di-O-benzyl- and 3,4-di-O-benzoyl-L-erythrulose and achiral aldehydes using dicyclohexylboron chloride have been investigated. The dibenzyl derivative gave syn/syn stereoisomers with high stereoselectivity, whereas the dibenzoyl derivative gave syn/anti stereoisomers. It is believed that, while the dibenzoyl erythrulose gives rise to the E enolate in the presence of dicyclohexylboron chloride, as usually observed with this reagent, only the Z enolate is formed in the case of the dibenzyl derivative. (C) 1999 Elsevier Science Ltd. All rights reserved.