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TitleA flexible approach to pyrido[4,3-b]carbazoles. The syntheses of 8,10-dimethoxy-5-methyl-, 5,11-dimethoxy-7,10-dimethyl- and 9-fluoro-5,11-dimethylpyrido[4,3-b]carbazoles by variations of the 'type D' route
Author(s)Hall, R. J.
Dharmasena, P.
Marchant, J.
Campos, Ana M. F. Oliveira
Queiroz, Maria João R. P.
Raposo, M. Manuela M.
Shannon, P. V. R.
Palladium acetate oxydation
Diphenylamine precursors
Pomeranz–Fritsch cyclisation
Acid-catalysed condensation
Issue date1993
PublisherRoyal Society of Chemistry
JournalJournal of the Chemical Society, Perkin Transactions 1
CitationHall, R.J.; Dharmasena, P.; Marchant, J.; Oliveira-Campos, A. M. F.; Queiroz, M. J. R. P.; Raposo, M. M. M.; Shannon, P. V. R. A flexible approach to pyrido[4,3-b]carbazoles. The syntheses of 5-methyl-8,10-dimethoxy; 5,11-dimethoxy-7,10-dimethyl and 9-fluoro-5,11-dimethylpyrido[4,3-b]carbazoles by variations of the type D route. J. Chem. Soc. Perkin 1 1993, 1879-1889
Abstract(s)Syntheses of three different pyridocarbazoles are described. Palladium acetate oxidation of 4-cyano-N-(3,5-dimethoxyphenyl)-2-methylaniline 19 and reduction of the resultant 3-cyano-4,6-dimethoxy-1-methylcarbazole 23 with diisobutylaluminium hydride gave the corresponding formylcarbazole 22. Modified Pomeranz–Fritsch cyclisation then gave, as the major product, 8,10-dimethoxy-5-methylpyrido[4,3-b]carbazole 32. Acid-catalysed condensation of 4,7-dimethoxyindole with hexane-2,5-dione gave 5,8-dimethoxy-1,4-dimethylcarbazole 37 which underwent an atypical regiospecific formylation to give 3-formyl-1,4-dimethoxy-5,8-dimethylcarbazole 39. This was converted by standard methods into 5,11-dimethoxy-7,10-dimethylpyrido[4,3-b]carbazole 7. The cyclisation reactions of the formylcarbazoles 26 and 43 were studied by 1H NMR spectroscopy which enabled the isolation of intermediate N-tosyl-1,2-dihydropyridocarbazoles. An unambiguous synthesis of 9-fluoroellipticine 8 is described from 5-fluoroindole for the first time.
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