摘要：

This chapter reviews the ongoing utility of carbenes and carbenoids in heterocyclic synthesis. Three principal carbene-based approaches to the construction of heterocycles can be recognized, which are (1) the carbene cyclization reaction, (2) ring contraction or expansion with carbene intermediacy, and (3) cyclization or cycloaddition of unstable primary products of carbene reactions. The first approach is realizable via a variety of typical carbene reactions. Cyclizations not involving a heteroatom include formation of a new C-C bond as a result of an intramolecular C-H insertion of a carbene or its addition onto multiple carbon-carbon bonds. The second approach involves ring modification. Ring-contraction carbene reactions include the Wolff-like rearrangement, transannular formation of an ylide, or C-H insertion followed by ring fragmentation. The third carbene-based approach to heterocycles consists in cyclization or cycloaddition of unstable intermediates of carbene reactions. Intermolecular carbene addition to the heteroatom of C=Z bond produces an ylide capable of being stabilized via 1,3- or 1,5-cyclization.

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