Annulated heterocycles through a radical-cation cyclization: synthetic and mechanistic studies

The wide range of chemical transformations possible with furans and thiophenes. especially reactions leading to dearoinatization of the nucleus, make them highly versatile synthons for complex molecule construction. As part of a program to exploit this intrinsic reactivity, we have developed a convenient method to prepare annulated versions of these heterocycles. The strategy is based on a two-step annulation involving the initial conjugate addition of a heteroaryl organometallic to an enone with trapping of the enolate as the silyl enolether. Anodic oxidation of this molecule leads to the initial formation of a radical-cation that is trapped in a heteroaryl-terminated cyclization to give the annulated products. (c) 2006 Published by Elsevier Ltd.