N-Substituted cyanacetohydrazides in the synthesis of 3,3-dialkyl-1,2,3,4-tetrahydroisoquinolines by Ritter reaction

Cyanacetohydrazide, protected at the nitrogen atom of hydrazide group, underwent cyclocondensation by Ritter reaction with 3,3-dialkylbenzylcarbinols, forming 3,3-dialkyl-1,2,3,4-tetrahydroisoquinolines. The reagents used for the protection of hydrazide group were benzaldehyde, benzoyl chloride, phenyl isocyanate, and phenyl isothiocyanate. As a result, N-substituted derivatives of 2-(3,3-dialkyl-3,4-dihydroisoquinolin-1(2Н)-ylidene)acetohydrazide were obtained – N-phenylmethylidene ethanehydrazide, acetylbenzohydrazide, and N-phenylhydrazinecarboxamide. Cyanacetohydrazide that was acylated with phenyl isothiocyanate gave a heterocyclization product – 1,3,4-thiadiazole under these conditions.