The Synthesis of Carbazoles from 3-Vinylindoles with Tetracyanoethylene and Dimethyl Acetylenedicarboxylate

Wayland E Noland, William C. Kuryla, Ronald F. Lange

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The tricyanovinylation of indole has been extended to substituted indoles, including 1-methylindole, 2-methylindole and 1,2-dimethylindole, giving the corresponding 3-tricyanovinylindoles (Ib-Id) in good yields. Several derivatives of the latter are described. Tricyanovinylation of skatole occurred in the 1-position, giving 3-methyl-1-tricyanovinylindole (Ie) in 77% yield. 3-Tricyanovinylindole (Ia) and l-methyl-3-tricyanovinylindole (Ib), acting as dienes, undergo Diels-Alder reactions with dimethyl acetylenedicarboxylate, resulting in the loss of hydrogen cyanide and forming the corresponding dimethyl 3,4-dicyanocarbazole-l,2-dicarboxylates (X). Saponification of the latter, followed by esterification of the resulting tetraacids with diazomethane, yielded the corresponding tetramethyl carbazole-l,2,3,4-tetracarboxylates (XI). The one derived from indole (XIa) was prepared independently, along with three minor products CXVIII-XX), by the reaction of indole with dimethyl acetylenedicarboxylate in 1:2 molar ratio. The latter reaction probably involves an intermediate 3-vinylindole (XII) which acts as a diene in a Diels-Alder reaction with a second molecule of dimethyl acetylenedicarboxylate. These reactions appear to represent the_ first examples of the 3-vinylindole synthesis of carbazoles. Decarboxylation of the carbazole tetraacids by pyrolysis with soda-lime gave carbazole in both cases, N-demethylation having occurred in the N-methyl case. Since N-methylcarbazole does not demethylate under the same conditions, it is suggested that the N-demethylation occurs by intramolecular nucleophilic displacement (in a 6-membered ring transition state) of the methyl group by the neighboring 1-carboxylate anion.

Original languageEnglish (US)
Pages (from-to)6010-6017
Number of pages8
JournalJournal of the American Chemical Society
Issue number22
StatePublished - 1959


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