Asymmetric synthesis of bicyclic alpha-amino acids by a Diels-Alder reaction to a new chiral alpha,beta-didehydroalanine derivative

A new chiral cyclic alpha,beta-didehydroalanine derivative, (6S)-6-isopropy l-3-methylene-5-phenyl-3,6,dihydro-2H-1,4-oxazin-2-one, has been prepared b y in situ aminomethylation-elimination of a chiral glycine-derived precurso r. This oxazin-2-one acts as a reactive dienophile ire highly diastereosele ctive Diels-Alder reactions with cyclopenta- and cyclohexadiene. The major cycloadducts have been isolated and hydrolyzed to afford enantiomerically p ure (-)-endo-2-aminobicyclo[2.2.1]heptane-2- and exo-2-aminobicyclo[2.2.2]o ctane-2-carboxylic acids. (C) 1999 Elsevier Science Ltd. All rights reserve d.