ASYMMETRIC ALDOL REACTIONS OF TRIFLUOROMETHYL KETONES WITH A CHIRAL NI(II) COMPLEX OF GLYCINE - STEREOCONTROLLING EFFECT OF THE TRIFLUOROMETHYL GROUP

Asymmetric aldol reactions between trifluoromethyl ketones and a Ni(II ) complex of the Schiff base of glycine with (S)-o-[N-(N-benzylprolyl) amino]benzophenone (BPB) have been studied. Sterically demanding aryl and sec-alkyl trifluoromethyl ketones, and highly enolizable benzyl tr ifluoromethyl ketone failed to react with the Ni(II) complex, while n- alkyl and acetylenyl trifluoromethyl ketones reacted readily and gave good yields (56-87%) of the aldol products with high diastereomeric ex cess (90-98%). Decomposition of the resultant complexes gave diastereo and enantiomerically pure (2S,3S)-3-trifluoromethyl-3-substituted ser ines of biomedicinal interest. A mechanistic working model that accoun ts for the observed sense of diastereoselectivity is discussed. Copyri ght (C) 1996 Elsevier Science Ltd