Sila-substitution of the alpha-amino acid proline: Synthesis of rac- and (R)-4,4-dimethyl-4-sila-proline ethyl ester

In context with studies on silicon-containing alpha-amino acids and peptide s, a strategy for the synthesis of the 4-sila-proline skeleton was develope d. The synthesis of rac- and (R)-4,4dimethyl-4-sila-proline ethyl ester [ra c-2 and (R)-2] is described. Compounds rac-2 and (R)-2 (greater than or equ al to 99% ee) were prepared by two-step syntheses, starting from 3,6-dietho xy-2,5-dihydropyrazine and (R)-3,6-diethoxy-2-isopropyl-2,5-dihydropyrazine respectively.