Diastereoselective aldol reactions of (Z)-N-[bis(methylthio)methylene]-α,β-didehydroglutamates

In the reaction of the enolates of (Z)-N-[bis(methylthio)methylene]-alpha,beta-didehydroglutamates with aldehydes, the retroaldolization process is faster than the aldol reaction, thus inhibiting the obtainment of the desired targets 6. However, in the presence of TMS-Cl as trapping agent, the equilibrium can be deplaced and the aldols 6 are obtained in the form of their TMS-derivatives 8. In the presence of BF3 or TBAF, either the syn or the anti adducts can be selectively obtained with good yields and diastereoselectivities.