DIASTEREOSELECTIVE SIDE-CHAIN ALKYLATION OF (PROLINOLYMETHYL)OXAZOLESAND (PROLINOLYMETHYL)OXADIAZOLES

Diastereoselective alkylation of the alpha-position of (S)-(prolinolyl methyl)oxazoles and -oxadiazoles 1 leading to side-chain modified prod ucts 2 and 3 was achieved by reaction with LDA and alkylating agents o r aldehydes. The products 2 and 3 are precursors of non-natural chiral alpha-amino acids. The influence of substituents, reagents, and react ion conditions on the diastereoselectivity of the alkylation was inves tigated. A model was proposed explaining the stereochemical outcome of the reaction. Corresponding a-acylation of prolinolylmethyl heterocyc les 1 with chloroformates affording chiral alpha-amino eaters 4 were n ot stereoselective.