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Paper | Regular issue | Vol 36, No. 7, 1993, pp.1529-1539
Published online, 1st January, 1970
DOI: 10.3987/COM-92-6326
Synthesis of Penams from 1H-Azetidinones by Intramolecular Carbenoid Insertion

Pierluigi Bissolino, Marco Alpegiani, Daniela Borghi, Ettore Perrone, and Giovanni Franceschi*

*Farmitalia Carlo Erba R&D, Via C.Imbonati 29, 20146 Milano, Italy


Construction of the penam ring system has been achieved by dirhodium tetraacetate cyclization of 4-thio-1H-azetidinone derivatives bearing an α-diazoester appendage. The sulfur atom of 4-thioethers interferes by reacting with the electrophilic metal carbene, but the corresponding sulfone and sulfoxides undergo the prescribed cyclization exclusively. Nmr studies on obtained bisnorpenams indicate pseudoequatorial puckering for the thiazolidine ring of the S-sulfoxide, while the parent sulfide and the R-sulfoxide exist as pseudoaxial conformers.