Nuclear analogs of β-lactam antibiotics. XVII. Stereospecific synthesis of penem and carbapenem precursors

Abstract

ALAIN MARTEL, JEAN-PAUL DARIS, CAROL BACHAND, MARCEL MENARD, TONY DURST, and BERNARD BELLEAU. Can. J . Chem. 61, 1899 (1983). The transformation of methyl 6-a-bromopcnicillanatc (6) to N-mcthoxalyl-(3S)-bro1no-(4R)-chloro-2-azctidinonc (8) is described. Azctidinone 8 was convertcd, in a stereoselective manner, to (3S)-bromo-(4R)-tritylthio-2-azctidinonc (9). Subsequent reduction of the 4-bromo substituent with zinc afforded the chiral (4R)-tritylthio-2-azetidinonc ( lo) , a useful internicdiate for the synthesis of penems. Azetidinonc 8 was also convertcd to the reactive (3S)-bromo-(4R)-cliloro-2-azetidinone (11). Treatment of thc (4R)-chlorodcrivativc 11 with 11-butyl or allylcuprate afforded the (4R)-butyl and (4R)-allylazctidinones 12 and 13 as the predominant diastcreomers. Finally, an improved synthcsis of 11 to 13 using tctraallyltin is also described.

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