Stereoselectivity in the construction of rigidified homoserine analogues

Methyl substituted cyclohexyl-1-amino-3-hydroxy-1-carboxylic acid derivativ es have been prepared from 5,5-tethered dienes of (2R)-2,5-dihydro-2-isopro pyl-3,6-dimethoxypyrazine in stereoselective syntheses. Ring closing metath esis reaction of the diene 2 afforded a heterospirenone which was the subst rate for conjugate addition with an alkyl cuprate. Reduction of the adduct followed by hydrolytic cleavage of the heterocyclic ring provided a cyclic a-amino acid derivative. The absolute configuration at the new stereocenter s in the products were established by X-ray crystallography analyses. (C) 2 001 Elsevier Science Ltd. All rights reserved.