Novel Synthesis of Pyrano[2,3-d]Thiazole, Thiazolo[3,2-a]Pyridine, and Pyrazolo [3′,4′:4,5] Thiazolo[3,2-a]Pyridine Derivatives

Abstract

Cyclocondensation of 2-cyanomethyl-4-thiazolidinone (1) with tetracyanoethylene (2) furnished pyrano[2,3-d]thiazole derivative (4) . Benzo[e]pyrano[2,3-d]thiazole derivative (6) was obtained by cyclization of compound (1) with salicylaldehyde. In a similar manner, condensation of compound (1) with 2-hydroxy-1-naphthaldehyde in refluxing ethanol yielded naphtho[e]pyrano[2,3-d]thiazole derivative (7) . Interaction of compound (9) with benzylidenemalononitriles (10) (1 : 1 molar ratio) at reflux temperature in ethanol in the presence of piperidine afforded thiazolo[3,2-a]pyridines (12a-c) . Treatment of compound (12a) with hydrazines furnished pyrazolo[3′,4′:4,5] thiazolo[3,2-a]pyridines (14a,b) . The reaction of compound (1) with benzyli-denecyanoacetate (16) yielded 5-hydroxythiazolo[3,2-a]pyridine derivative (21) . Cyclization of bis(thiazolinone) (23) with benzylidenemalononitriles (10) produced bis(thiazolopyridine) derivatives (25a,b) .