Efficient Synthesis and Some Transformations of 1-Hydrazinyl-5,6,7,8-tetrahydroisoquinolines Involving Rearrangement of the Pyridine Ring

—A procedure was developed for the synthesis of 1-hydrazinyl-3-arylamino-5,6,7,8-tetrahydroisoquinoline- 4-carbonitriles via recyclization of the pyridine ring in 3-amino-2-aryl-1-sulfanylidene-1,2,5,6,7,8- hexahydroisoquinoline-4-carbonitriles by the action of hydrazine hydrate. The recyclization products were converted to new heterocyclic systems, 7,8,9,10-tetrahydro[1,2,4]triazolo[3,4- a ]isoquinolines and 1-(3,5-dimethyl- 1 H -pyrazol-1-yl)-5,6,7,8-tetrahydroisoquinolines, by reactions with triethyl orthoformate and acetylacetone, respectively. Treatment of 1-hydrazinyl-3-arylamino-5,6,7,8-tetrahydroisoquinoline-4-carbonitriles with sodium azide in acetic acid gave 1-azido-3-arylamino-5,6,7,8-tetrahydroisoquinoline-4-carbonitriles, and azide–tetrazole isomerism of the latter was studied. The state of the azide–tetrazole equilibrium was found to depend on the solvent polarity and substituent nature in the arylamino group. The structure of 5-(2-methoxyanilino)- 7,8,9,10-tetrahydro[1,2,4]triazolo[3,4- a ]isoquinoline-6-carbonitrile was confirmed by X-ray analysis, and intermolecular hydrogen bonds were detected in its crystal structure. The synthesized compounds were evaluated for antimicrobial activity.