A New Synthetic Approach to 5‐Dethia‐4‐methyl‐5‐oxacephems.

Abstract

A New Synthetic Approach to 5-Dethia-4-methyl-5-oxacephems. -Starting from azetidinone (I), diastereomeric 3-methylene and 3-oxo-cephams (VI)/(VII) and (VIII)/(IX), resp., are prepared via Lewis acid promoted cyclization of acetate (IV) providing diastereomer (VI) with ca. 80% diastereomeric excess. Bromide (II) is prepared in six steps starting from (S)-ethyl lactate. For comparison, the corresponding racemic cephams lacking a methyl group at C-4 or bearing 4,4-dimethyl at C-4 are also synthesized. -(KALUZA*, Z.; KAZIMIERSKI, A.; LEWANDOWSKI, K.; SUWINSKA, K.; SZCZESNA, B.; CHMIELEWSKI, M.; Tetrahedron 59 (2003) 31, 5893-5903; Inst. Org. Chem., Pol. Acad. Sci., PL-01-224 Warsaw, Pol.; Eng.) -Klein 45-205