Nenitzescu carbazole synthesis

Indoles are obtained by specific cyclizations (Fischer synthesis, Reissert synthesis, Batcho-Leimgruber synthesis, Nenitzescu synthesis), as are carbazoles from biphenylene or diphenyl-amines and pyrrolidines (Hofmann-Loffler reaction). 

The most extensively used approach is route A (Scheme 1). Some of the more commonly employed indole syntheses, such as the Fischer, Bischler, Nenitzescu and the Gassman procedures, also fall into this category.Of these, the Fischer indole synthesis (Scheme 2) has been most widely applied. However, the requirement of properly substituted starting materials, which can often be difficult to fulfil, and/or the lack of regio-selectivity in the cyclizative step, limit its utility. An example of the use of the Fischer indole synthesis in the synthesis of a carbazole alkaloid is given in Scheme 3. 

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