R. Fusco, F. Sannicolo
Feb 1, 1978
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Journal
Chemistry of Heterocyclic Compounds
Abstract
A review of the literature data on the Fischer synthesis of indoles from 2,6-disubstituted arylhydrazones is given. As a result of their own experimental studies of the indolization of hydrazones from 8-R-N-amino-1,2,3,4-tetrahydroquinolines the authors established that no less than five different transformations of the cyclohexadienoneimine intermediate, including 1,2 and 1,4 shifts and splitting out of the substituent, may follow attack on the 8 position of the tetrahydroquinoline ring. Attack in the 10 position of the tetrahydroquinoline ring leads to another cyclohexadienoneimine, which undergoes indolization with the loss of apropylamine chain via a different mechanism. It was proved by experiments with labeled compounds that 1,3 migration of the methyl group (R=CH3) is the result of a double 1,2 shift, while the 1,4 shift is a direct reaction.