Indolium salts

The use of branched ketones enables preparation of 3/7-indolium salts as illustrated by the synthesis of product 48 (Scheme 29) <2000JHC1571 >. The hydrazine components can also be generated from anilines in a one-pot variant of this route <2004JHC103>. 

Indole can be nitrated with benzoyl nitrate at low temperatures to give 3-nitroindole. More vigorous conditions can be used for the nitration of 2-methylindole because of its resistance to acid-catalyzed polymerization. In nitric acid alone it is converted into the 3-nitro derivative, but in a mixture of concentrated nitric and sulfuric acids 2-methyl-5-nitroindole (47) is formed. In sulfuric acid, 2-methylindole is completely protonated. Thus it is probable that it is the conjugate acid which is undergoing nitration. 3,3-Dialkyl-3H-indolium salts similarly nitrate at the 5-position. The para directing ability of the immonium group in a benzenoid context is illustrated by the para nitration of the conjugate acid of benzylideneaniline (48). 

For azapentatriafulvalenium salts of type 35 the charge distribution was made evident by a comparison of the NMR spectra of these heteroful-valenes and of 3-benzhydrylidene-3H-indolium salts and their common indole precursors (68TL5541).The results suggested that the best description involves extensive delocalization of charge throughout the cyclopropene and indole rings. 

The heterocyclization of peri-aminonaphthoyl compounds allows the preparation of three main types of benzo[crf]indole series, namely, bases 113, benzo[crf]indolium salts 114, and benzo[crf)indole-2-ones 115. Because closure to the nitrogen heterocycle is so facile, peri-amino-substituted naphthaldehydes and naphthyl ketones, even under conditions of their formation, are converted into benzo[crf]indoles 113. Those unsubstituted in position 2, as well as 2-alkyl-substituted benzo[cd]indoles 113 (R = H, Aik), have not been isolated because of their easy oxidation by air. 

The method just described allows high yields of the various N-protonated, N-alkylated, and N-acylated benzo[cd]indolium salts, both... 

The course of reaction and the character of the final products are determined by electronic effects of substituents at the aryl ring (Ar) of N-protonated azomethine 130. The most interesting is the reaction leading to 2-styrylbenzo[crf]indolium salts 132 the formation of which can be represented as the result of a rearrangement of intermediate 134. The latter is afforded by C-acylation of azomethine perchlorate 130. 

Substituted 10//-pyrido[l,2-a]indolium salts, synthesis 91MI24. 

A. A. Schachkus and Yu. A. Degutis, Reaction of 2,3,3-trimethyl-3//-indolium salts with crotonaldehyde, Chem. Heterocycl. Cpds., 1990, 881-883. 

Z. Liu, Y. Gong, W. Li, and L. Jiang, The relationship between spectral properties and structures of substituted 1077-pyrido[l,2-a]indolium salts, ChineseSci. Bull., 37, 1704-1708 (1992). 

NMR spectrum also shows that tryptamine and several jof its N- and C-methyl derivatives are protonated at the 3-position of the indole nucleus in strongly acidic media, to give the corresponding 3//-indolium salts (19)."... 

Addition to vinylogous iminium salts has also been explored. Moriya et al have examined the addition of nucleophiles to 3-(l-pyrrolidinylmethylene)-3//-indolium salt (61) in the synthesis of 3-(l-dialkylamino)aikyl-l//-indoles (62 equation 10). 

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