CASCADE CYCLIZATIONS

The one-step construction of complex polycyclic frameworks from monocyclic precursors, that is, the initiation and controlled termination of entire reaction cascades, is also possible in radical reactions. The selective formation of C-C bonds with radicals has become a useful synthetic method as is shown in the syntheses of 1 (hirsutene) and 2 (the framework of cedrane). In each case, the cyclization was triggered by Bu3SnH/azobis(isobutyronitrile). Hanessian et al. have extended this method with a variation in which dienes and trienes are cyclized with Me3SnH generated in situ, and the C-Sn bond formed is then subjected to oxidative cleavage (3 --> 4). [GRAPHICS]