Reactions of enamino keto esters of 1,2,3,4-tetrahydroisoquinoline series with nucleophiles

Abstract

Keywords:3,3-dimethyl-1-(5-thioxo-1,5-dihydro-1,2,4-triazol-3-ylmethylidenecarbonyl)-1,2,3,4-tetrahydroisoquinoline, methyl ester of 3-(3,3-dimethyl-1,2,3,4-tetrahydroisoquinolin-1-idene)pyruvic acid, nitrile of 2-cyano-4-dicyanomethylidene-5-(3,3-dimethyl-1,2,3,4-tetrahydroisoquinolin-1-idene)-3-oxopentanoic acid, semicarbazide, thiosemicarbazide, annelation of the pyrrole ring, heterocyclization, ester condensation with malonodinitrile.Enamino keto ester derivatives of 1,2,3,4-tetrahydroquinoline have been obtained previously [1][2][3]. The properties of the keto ester group of these compounds have been studied little up to the present time. The aim of the present work was to investigate the reactions of enamino keto esters of the 3,3-dialkyl-1,2,3,4-tetrahydroisoquinoline series with nucleophiles.The initial enamino keto esters 2a,b were synthesized by the known procedure using dioxopyrrolines 1a,b as starting materials [1,2]. It is known that the reaction of compounds 2a,b with aliphatic amines proceeds on boiling in alcohol with the formation of the corresponding enamino amides [2,3]. Investigation of the reactions of esters 2a,b with aromatic amines showed that on boiling in alcohol or glacial acetic acid no aminolysis was observed. However on boiling compound 1a with thiosemicarbazide in glacial acetic acid a heterocyclization occurred with the formation of ketone 3, having a triazole system in its structure. Boiling compounds 2a,b in glacial acid with semicarbazide hydrochloride leads to annelation of the pyrrole ring with the formation of compounds 4a,b. An intramolecular aminolysis of the ester group therefore occurs in these cases. The observed reaction at the ketone group may be explained by the fact that in acidic medium on going