Expeditious entry to enantiopure mono- and bis(tricyclic) β-lactams by single or double [2+2] cycloaddition of allenynes

A thermal methodology for the expeditious preparation of structurally novel strained tricyclic β-lactams containing a cyclobutene ring has been developed. Besides, the first examples accounting for the intramolecular double [2+2] cycloaddition of bis(allenyne)s have been achieved through thermolysis of C2-symmetric or unsymmetric bis(β-lactam-allenyne)s, which have been prepared by copper-promoted alkyne homo- or cross-coupling reactions. The bis(tricyclic) ring structures bearing a central seven-membered ring arise from the regioselective cyclization of the alkyne with the distal bond of the allene, most likely via a radical intermediate. A variety of diversely functionalized mono- and bis(tricyclic) azetidinones can be prepared in good yield through a totally regioselective thermal [2+2] cycloadditionreaction of β-lactam-tethered allenynols, which may imply the formation of radical intermediates involving the distal allene bonds. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Peer Reviewe