This report describes the synthesis of enantiomerically pure (S)- and (R)-alpha-vinylalanines and (S)- and (R)-alpha-ethynylalanines, four quaternary alpha-amino acids, using a straightforward synthetic route and starting from (S)- and (R)-N-Boc-N,O-isopropylidene-alpha-methylserinals. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.