HIGHLY ENANTIOSELECTIVE AND DIASTEREOSELECTIVE BORON ALDOL REACTIONS OF ALPHA-HETEROSUBSTITUTED THIOACETATES WITH ALDEHYDES AND SILYL IMINES

Boron enolates derived from alpha-heterosubstituted thioacetates and b earing menthone-derived chiral ligands react with aldehydes to give an ti aldols with excellent diastero- and enantiocontrol. Boron enolates derived from tert-butyl alpha-halothioacetate and bearing menthone-der ived chiral ligands react with imines with excellent diastero- and ena ntiocontrol to give syn alpha-halo-beta-aminothioesters, which can be converted to the corresponding aziridines by simple ring closure durin g LAH reduction. A key precursor of antibiotics (+)-thiamphenicol and (-)-florfenicol was synthesized. (C) 1997 Elsevier Science Ltd.