title: Thermal ring contraction of dibenz[b,f]azepin-5-yl radicals: new routes to pyrrolo[3,2,1-jk]carbazoles.
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.
authors.affiliation: School of Chemistry, The University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, UK.
authors.forename: Lynne A
authors.initials: LA
authors.lastname: Crawford
authors.forename: Hamish
authors.initials: H
authors.lastname: McNab
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Mount
authors.forename: Stuart I
authors.initials: SI
authors.lastname: Wharton