SYNTHESIS OF INDOLES FROM PYRIDINIUM COMPOUNDS 10.* INFLUENCE OF SOLVENTS ON PROCESS OF INDOLIZATION OF 3-INTROPYRIDINIUM CATIONS BY THE ACTION OF THE N-METHYLIMINE OF METHYL ETHYL KETONE M. A. Yurovskaya, A. V. Karchava, and Yu. G. Bundel' A study has been made of the influence of solvents on the process ofindolization of the methiodide ofsym-3- nitrocollidine by the action of the N-methylimine of methyl ethyl ketone. An inversely proportional relationship has been found between the content of the 3, 7-unsubstituted indole in the indole fractions and the donor strength of the solvent. We had reported previously that the indolization of 1-alkyl-3-nitropyridinium salts by the action of N-alkylimines of asymmetric ketones leads to the formation of a mixture of three compounds of the indole series lla-c; these indoles are not formed in commensurate quantities, and the content of the 3,7-unsubstituted indole lie is quite often no greater than 0.1%, depending on the structure of the cation of the original salt [ 1, 2]. In a previous communication [1] we analyzed the influence of the structure of 3-nitropyridinium cations on the course of the process of indolization by the action of the methylimine of methyl ethyl ketone. This conversion may also be influenced by another factor of no small importance, namely the reaction conditions, in particular the nature of the solvent. In order to evaluate this influence, we selected as a model the sym-3-nitrocollidine salt (I), since it had been established that for this cation, the formation of all three indoles IIa-c takes place in appreciable quantities. Me I Me Me ~'VIe NMe NO2 II MeCH2CMe Me" "N" "Me I Me I Me Me Me Me Me Me I I Me Me b c *For Communication 9, see [1]. M. V. Lomonosov Moscow State Univeristy, Moscow 119899. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, 1187-1190, September 1992. Original article submitted June 29, 1992. 1000 0009-3122/92/2809-1000512.50 9 Plenum Publishing Corporation