Thermal ring contraction of dibenz[b,f]azepin-5-yl radicals: New routes to pyrrolo[3,2,1-jk]carbazoles

Lynne A. Crawford, Hamish McNab, Andrew R. Mount, Stuart I. Wharton

Research output: Contribution to journalArticlepeer-review

Abstract

Flash vacuum pyrolysis (FVP) of N-allyl- or N-benzyldibenz[b,f]azepine at temperatures from 750 to 950 degrees C gives pyrrolo[3,2,1-jk]carbazole as the major product. The mechanism of the ring contraction involves dibenzazepin-1-yl radical formation, followed by transannular attack and formation of a 2-(indol-1-yl)phenyl radical which cyclizes. The mechanism is supported by independent generation of 2-(indol-1-yl)phenyl radicals by two different methods, and the use of 1-(2-nitrophenyl)indole as a radical generator gives an optimized synthetic route to pyrrolo[3,2,1-jk] carbazole (54% overall yield in two steps from indole). The first substituted pyrrolo[3,2,1-jk]carbazoles have been synthesized by FVP methods and also by reactions of the parent compound with electrophiles, leading to a range of 4-substituted pyrrolocarbazoles.

Original languageEnglish
Pages (from-to)6642-6646
Number of pages5
JournalThe Journal of Organic Chemistry (JOC)
Volume73
Issue number17
DOIs
Publication statusPublished - 5 Sept 2008

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