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 was first described by Edmund Drechsel [de] in 1888[1] and by Walther Borsche [de] in 1908.[2]
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.
Mechanism
[edit]The reaction has been described in the literature[3] as proceeding in a manner similar to the Fischer indole synthesis.
Here, the acid-catalyzed proton transfer first converts the cyclohexanone phenylhydrazone 1 to the intermediate 2. Subsequently, a heat-induced sigmatropic reaction occurs to produce 3, which is protonated and cyclizes into 4. Elimination of ammonia then leads to the final product, the tetrahydrocarbazole 5.
See also
[edit]References
[edit]- ^ E. Drechsel (1888). "Ueber Elektrolyse des Phenols mit Wechselströmen". Journal für praktische Chemie (in German). 38 (1): 65–74. doi:10.1002/PRAC.18880380105. ISSN 0021-8383. Wikidata Q56441554.
- ^ W. Borsche (1908). "Ueber Tetra- und Hexahydrocarbazolverbindungen und eine neue Carbazolsynthese. (Mitbearbeitet von. A. Witte und W. Bothe.)". Justus Liebigs Annalen der Chemie (in German). 359 (1–2): 49–80. doi:10.1002/JLAC.19083590103. ISSN 0075-4617. Wikidata Q29029226.
- ^ Lie, J. J. (2009). Name Reactions. Springer. p. 60. ISBN 978-3-642-01052-1.