ACID-CATALYZED CONVERSIONS OF N-(4-NITROBENZYLIDENE)-2-CYCLOPROPYL- AND N-(4-NITROBENZYLIDENE)-2-ALKENYLANILINES. A NEW METHOD FOR THE SYNTHESIS OF DIHYDROQUINOLINES AND QUINOLINES

Abstract

The acid-catalyzed conversions of N-(4-nitrobenzylidene)-2-cyclopropyl- and N-(4-nitrobenzylidene)-2-alkenylanilines have been studied. It has been established that the protonated azomethine unit of N‑(4‑nitrobenzylidene)-2-cyclopropylanilines is not capable of initiating intramolecular heterocyclization with participation of the three-membered ring. Conversion of N-(4-nitrobenzylidene)-2-(1-methylcyclopropyl)aniline to derivatives of quinoline is possible under the influence of concentrated H₂SO₄. Under the same conditions 2-methylcyclopropyl- and cyclopropyl-substituted Schiff's bases form only the corresponding alkenylazomethines (isomerization of the three-membered ring). Under the influence of more moderate acids (trifluoroacetic, polyphosphoric) N-(4-nitrobenzylidene)-2-propenyl- and N-(4-nitrobenzylidene)-2-buten-2-yl)anilines are converted to the corresponding dihydroquinolines and quinolines in high yields. N-(4-Nitrobenzylidene)-2-(2,2-dimethylvinyl)aniline does not form derivatives of quinoline under the influence of the same acids in the given conditions.

Authors: E. V. Trofimova, A. N. Fedotov, S. S. Mochalov, Yu. S. Shabarov, and N. S. Zefirov.

English Translation in Chemistry of Heterocyclic Compounds, 2000, 36 (10), pp 1198-1205

http://link.springer.com/article/10.1023/A%3A1002824917758