Some new Nazarov chemistry

The Nazarov cyclization is a 4 pi-electron conrotatory cyclization of a pentadienyl cation that leads to a five-membered ring, typically a cyclopentenone. Because the mechanism is well defined, it is often possible to make accurate and useful stereochemical predictions regarding the course of the reaction. Because the reaction intermediates are carbocations, it is also possible to devise tandem processes whereby the initial cyclization is followed by one or more C-C bond forming processes. In recent years, a number of advances have been made in the asymmetric version of the Nazarov cyclization, adding to its usefulness in total synthesis. It is the goal of this review to introduce the reader to some of the newer methodological advances roughly spanning the past ten years, and to do so within a mechanistic framework. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).