Borsche–Drechsel cyclization

Borsche–Drechsel cyclization
Named after	Walter Borsche Edmund Drechsel
Reaction type	Ring forming reaction
Identifiers
RSC ontology ID	RXNO:0000532

The Borsche–Drechsel cyclization is a chemical reaction used to synthesize tetrahydrocarbazoles by the acid-catalyzed cyclization of cyclohexanone arylhydrazones. The reaction is was first described by Edmund Drechsel in 1888 and by Walter Borsche in 1908.

Borsche–Drechsel cyclization is the central step in Borsche–Drechsel carbazole synthesis, where in the first step phenylhydrazine is condensed with cyclohexanone to form the cyclohexanone phenylhydrazone, and in the final step the resulting tetrahydrocarbazole is oxidized to carbazole itself.

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