Efficient and practical synthesis of 1⊝methylcarbapenems

Abstract An efficient and practical method of synthesizing 1β-methylcarbapenem, S-4661, was developed. (4 R )-4-[(1S)-1-Methylallyl]-2-azetidinone 2, prepared from commercially available acetoxy-azetidinone 3 , was converted to the β-keto ester 6 in four steps. The iodonium ylide 5 was prepared from 6 , then cyclized to obtain the bicyclic β-keto ester 4 . Finally, 4 was processed to the target product, S-4661, by conventional procedures.