Stereoselective reactions. IX. Synthetic studies on optically active .BETA.-lactams. I. Chiral synthesis of carbapenam and carbapenem ring systems starting from (S)-aspartic acid.
Stereoselective reactions. IX. Synthetic studies on optically active .BETA.-lactams. I. Chiral synthesis of carbapenam and carbapenem ring systems starting from (S)-aspartic acid.
A new enantioselective synthesis of the keto ester(16) containing β-lactam ring system has been developed using the chiral lactone(1) as a starting material.
On the basis of the principle of hard and soft acids and bases, a highly diastereoselective ''asymmetric soft acid-soft base imine alkylation'' was developed. 4-Acetoxyazetidin-2-one (5) was alkylated with the tin(II) enolates of 3-acyl-(4S)-ethyl(and isopropyl)-1,3-thiazolidine-2-thiones 7a,b and 21a,b. The resultant alkylation products (9a,b and 24a,b) could be converted to 17, the key intermediate for the syntheses of both thienamycin (2) and imipenem (3), and to 35, the key intermediate for the synthesis of 1-beta-methylcarbapenem.