A new fused tetrazole ring system: Tetrazolo [1,5-b] isoquinoline

Tetrazolo[1,5-α]isoquinoline ( 5b ), the linear benzologue of tetrazolopyridine, has been prepared. In contrast to the angular isomers ( 1b and 2 ) the linear system exists in solution predominantly in the tautomeric azido-form ( 5a ) and even in the crystalline state contains a certain amount of 3-azidoisoquinoline ( 5a ). The tautomeric equilibrium in solution was studied by nmr spectroscopy.