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

In the reaction of the enolates of (Z)-N-[bis(methylthio)methylene]-alpha,b eta-didehydroglutamates with aldehydes, the retroaldolization process is fa ster than the aldol reaction, thus inhibiting the obtainment of the desired targets 6. However, in the presence of TMS-Cl as trapping agent, the equil ibrium can be deplaced and the aldols 6 are obtained in the form of their T MS-derivatives 8. In the presence of BF3 or TBAF, either the syn or the ant i adducts can be selectively obtained with good yields and diastereoselecti vities.