Tetracyanoethylene with indole

In contrast to the reactivity of the nitroethylenes, acrylonitrile generally reacts with indoles to form the l-(2-cyanoethyl) derivatives (B-70MI30500,79MI30501), whereas Michael addition at the 3-position requires the catalytic effect of copper(II) salts. The addition-elimination reaction of pyrroles and indoles with l,l-dicyano-2-ethoxyethylene proceeds in low yield (<30%) to give the dicyanovinyl derivatives, which can be converted by standard procedures into the formyl compounds (81H(16)1499). Tetracyanoethylene forms charge transfer complexes with indoles, which collapse to the Michael adduct anions and subsequently eliminate a cyanide ion with the formation of the tricyanovinylindole (B-70MI30500). 

Benzo[Z)]furans and indoles do not take part in Diels-Alder reactions but 2-vinyl-benzo[Z)]furan and 2- and 3-vinylindoles give adducts involving the exocyclic double bond. In contrast, the benzo[c]-fused heterocycles function as highly reactive dienes in [4 + 2] cycloaddition reactions. Thus benzo[c]furan, isoindole (benzo[c]pyrrole) and benzo[c]thiophene all yield Diels-Alder adducts (137) with maleic anhydride. Adducts of this type are used to characterize these unstable molecules and in a similar way benzo[c]selenophene, which polymerizes on attempted isolation, was characterized by formation of an adduct with tetracyanoethylene (76JA867). 

Tetracyanoethylene yields a colored it-complex with aromatic compounds in the case of aromatic amines, phenols and indoles these then react to yield the corresponding tricyanovinyl derivatives [3, 4]. 

Tricyanovinylindole (57) and its 1-methyl derivative, obtainable from the parent indoles and tetracyanoethylene, combine with dimethyl acetylenedicarboxylate to give the corresponding carbazoles. That derived from indole (58) has been hydrolyzed and esterified yielding (55). 

The reaction of 1,2,4-triazino[5,6-/>]indole-3-thione (93a X= SH) with tetracyanoethylene affords, as one of three products, the thiazolotriazinoindole (94). The 3-hydrazino compound (93b X= NHNH,) gives the triazolotriazinoindole (95) and triazepinotriazinoindole (96) [94T9997],... 

The purple charge-transfer complex of indole with tetracyanoethylene decomposes in neutral or basic media to the 3-substituted indole (164), whereas under acidic conditions the 2-(tricyanovinyl)-isoraer is formed. The cyclo-adducts of l-benzyl-3-vinylindole to tetracyanoethylene and maleic anhydride are the cyclobutane (165) and the tetrahydrocarbazole (166), respectivelyThe reaction of 9-methyl-l,2,3,4-tetrahydrocarbazole (167) with dimethyl acetylenedicarboxylate in aqueous acetic acid yields a mixture of the bridged compounds (168) and (169). The photo-adduct (170) of methyl acrylate to 1-benzoylindole rearranges to the benzazepine (171) in hot xylene... 

As with chloranil, one should be aware of the possibility of a displacement reaction with TCNQ or TCNE (tetracyanoethylene). Indole has been observed to react with TCNE in solution at ordinary temperatures. A reaction with JV-alkylanilines is also observed. Amines have been observed to displace a cyano group from TCNE and TCNQ. Formation of these... 

The chiral holmium(III)-complex-catalysed Diels-Alder cycloaddition of siloxyvinylindoles (70) with e-deficient olefins (71) formed exo-substituted hydro-carbazoles (72) in up to 99% yield and 94% ee. Alkylation of these cycloadducts gave tricyclic compounds (73) with four continuous chiral centres (Scheme 20). The thermal 4-i-2-cycloaddition reaction of 7-substituted 4-styrylcoumarins with A-phenylmaleimide and tetracyanoethylene in nitrobenzene yielded 3,4-annulated coumarins. The thermal Diels-Alder cycloaddition of ( )-l,3-dihydro-3-phenacylidene-2//-indol-2-ones (74) with l,2-dihydro-2-oxospiro[3//-indole-3,2 -[2H,9a//-pyrido[2,l-fe][l,3]oxazines]] (75) produced complex dispirooxindoline fused [l,3]oxazines (76) with high regio- and stereo-selectivity (Scheme 21). " ... 

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