An Efficient Route to 4/5/6 Polycyclic β‐Lactams

Abstract

AbstractThe synthesis of 4/5/6 polycyclic β‐lactams by enyne metathesis and Diels−Alder reactions is described. Compared to the synthesis of 4/6/6 and 4/7/6 polycyclic β‐lactams previously reported by our laboratory, formation of the strained 4/5/6 compounds requires alternative reaction conditions. Indeed, the synthesis of the 4/5 bicyclic diene 12 was more difficult than those of the 4/6 (13) and 4/7 (14) dienes. The strain of the 4/5 system could be observed by NMR spectroscopy and molecular modelling. Moreover, the reactivity of 4/5 diene 12 towards Diels−Alder cycloaddition was also different from that of the 4/6 (13) and 4/7 (14) dienes. Cycloadditions with 4/5 diene 12 therefore had to be performed in lithium perchlorate/diethyl ether (LPDE) or in an ionic liquid in order to proceed in good yields with various dienophiles. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)