SYNTHESIS OF CARBON-BRIDGED DIBENZAZOCINES AND DIBENZODIAZOCINES - REGIOCHEMICAL CONTROL ELEMENTS IN THE BECKMANN REARRANGEMENT

A synthetic route for the conversion of carbon-bridged dibenzocycloheptanes and dibenzazepines, readily available by intramolecular [3 + 2] cycloaddition methodology, to carbon-bridged dibenzazocines and dibenzodiazocines is presented. The key transformations involve the Beckmann rearrangement of intermediates 5, 12, 14, and 15 to the various possible lactam products. Factors controlling the observed regiochemistry of the rearrangement process, leading to regiochemical control of the Beckmann products, are discussed from a mechanistic viewpoint. A rationale for the observed selectivity in the hydride reduction of the urethane lactams 16, 21, 22, and 24 is also presented. The overall approach affords a facile and generally useful transformation of olefin aldehydes of general structure D to the bicyclics F and/or G via the cycloadducts E.