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Communication | Special issue | Vol 5, No. 1, 1976, pp.419-426
Published online, 1st January, 1970
DOI: 10.3987/S-1976-01-0419
Synthesis of 3-Substituted Cephems from Penicillins via 4-Dithio-2-azetidinone Intermediates

Yoshio Hamashima,* Tadatoshi Kubota, Koji Ishikura, Kyoji Minami, Kazuya Tokura, and Wataru Nagata

*Shionogi Research Laboratories, Shionogi & Co. Ltd., Fukushima-ku, Osaka 553-0002, Japan

Abstract

Cyclization of monocyclic dithioazetidinones 9 to the 3-substituted cephems is accomplished. When substituents at the β position of esters 9 are electron withdrawing such as chloro or sulfonyloxy, the benzothiazol-2-ylthio group migrates to position 3 of the cephem nucleus to give 3-thio derivatives 5 and 6. In contrast, when the substituents at the β position are weakly electron withdrawing, normal cyclization occurs giving 3-acyloxy derivatives 10. Reaction of γ-bromo-β-keto ester 16 with sodium borohydride and successive treatment with triphenylphosphine affords 3-hydroxycephem 11 albeit in poor yield. Base treatment of γ-bromo enamino ester 15 or γ-bromo-β-acetoxy ester 20 gives the corresponding 2,3-bis-substituted cephems 18 or 21.