Asymmetric 1,4 addition of Grignard reagents to chiral alpha,beta-unsaturated esters in the presence of Lewis acids

The synthesis of enantiomerically enriched a-amino acids is described, by m eans of the diastereoselective conjugate addition of Grignard reagent to (S )-2-acetamidoacrylic ethoxycarbonyl-phenyl-methyl ester 1 and its N-Boc der ivative 5 in the presence of Lewis acids. The addition of magnesium organoc uprates has also been analysed. The reaction proceeds with good yields and variable diastereoselectivities, depending on the organometallic reagent an d on the Lewis acid utilised, (C) 1999 Elsevier Science Ltd. All rights res erved.