Cyclic α-Amino Acids by Pd-mediated Cycloisomerization and Coupling Reactions

Article abstract of DOI:10.1016/S0040-4020(98)00267-1

Stereoselective syntheses of cyclic α-amino acids are described.The α-carbon of the amino acid is incorporated into a five- or six-membered vicinal dimethylenecycloalkane or conjugated methylenecycloalkene.Palladium-catalysis was used for cycloisomerization of intermediate enynes and intramolecular Heck type cyclizations of bromoindenes.A stereoselective elimination from a homoallylic Pd-intermediate is described.Enantiomerically pure substrates for the cyclization reactions were available by stepwise alkylations of the chiral auxiliary (R)-2,5-dihydro-3,6-dimethoxy-2-isopropylpyrazine with bromo-alkenes and -alkynes.