Borsche-Drechsel cyclization

The Borsche-Drechsel cyclization is a name reaction in organic chemistry . The reaction was published in 1888 by the German chemist Edmund Drechsel and in 1908 by the German chemist Walther Borsche . The reaction allows the synthesis of nitrogen-containing heterocycles from phenylhydrazones .

Overview reaction

Cyclohexanonphenylhydrazone reacts with an acid (in the example sulfuric acid) in the heat to form tetrahydrocarbazole:

The reaction can be transferred to phenylhydrazones substituted on the aromatic ring and phenylhydrazones of other cyclic ketones.

Reaction mechanism

The reaction mechanism is described in the literature and proceeds like the Fischer indole synthesis :

Acid-catalyzed proton rearrangement turns the cyclohexanone phenylhydrazone ( 1 ) into intermediate 2 . In a subsequent sigmatropic rearrangement caused by heat , a special form of the pericyclic reaction , intermediate stage 3 is created . A cation is formed by protonation with an acid. This then cyclizes through to intermediate stage 4 . Tetrahydrocarbazole ( 5 ) is formed through the formal elimination of ammonia .

application

The Borsche-Drechsel cyclization is a key reaction in the synthesis of carbazoles . To do this, 5 is flavored to 6 with an oxidizing agent :

Individual evidence

↑ Edmund Drechsel: About electrolysis of phenol with alternating currents. In: J. Prakt. Chem. 38 (1), 1888, pp. 65-74, doi: 10.1002 / prac.18880380105 .
↑ Walther Borsche (with the collaboration of A. Witte and W. Bothe): About tetra- and hexahydrocarbazole compounds and a new carbazole synthesis. In: Justus Liebigs Annalen der Chemie 359 (1-2), 1908, pp. 49-80, doi: 10.1002 / jlac.19083590103 .
↑ ^a ^b ^c Z. Wang: Comprehensive organic name reactions and reagents Volume 1 . John Wiley, Hoboken (NJ) 2009, ISBN 978-0-470-28662-3 , pp. 471-473 .
↑ ^a ^b Bradford P. Mundy, Michael G. Ellerd, Frank G. Favaloro, Jr .: Name Reactions and Reagents in Organic Synthesis . John Wiley & Sons, Hoboken (NJ) 2005, ISBN 0-471-22854-0 , pp. 108 .
^ JJ Lie: Name Reactions , Springer, 2009, ISBN 978-3-642-01052-1 , p. 60.

[1] Edmund Drechsel: About electrolysis of phenol with alternating currents. In: J. Prakt. Chem. 38 (1), 1888, pp. 65-74, doi: 10.1002 / prac.18880380105 .

[2] Walther Borsche (with the collaboration of A. Witte and W. Bothe): About tetra- and hexahydrocarbazole compounds and a new carbazole synthesis. In: Justus Liebigs Annalen der Chemie 359 (1-2), 1908, pp. 49-80, doi: 10.1002 / jlac.19083590103 .

[:Wang-3] Z. Wang: Comprehensive organic name reactions and reagents Volume 1 . John Wiley, Hoboken (NJ) 2009, ISBN 978-0-470-28662-3 , pp. 471-473 .

[:Mundy-4] Bradford P. Mundy, Michael G. Ellerd, Frank G. Favaloro, Jr .: Name Reactions and Reagents in Organic Synthesis . John Wiley & Sons, Hoboken (NJ) 2005, ISBN 0-471-22854-0 , pp. 108 .

[5] JJ Lie: Name Reactions , Springer, 2009, ISBN 978-3-642-01052-1 , p. 60.