HETEROCYCLIC SYNTHESIS WITH NITRILES - SYNTHESIS OF SOME NEW MERCAPTO-SUBSTITUTED HETEROCYCLES FROM ALKYLIDENEMALONONITRILE

Alpha-(Thiocyanatomethyl)benzylidenemalononitrile undergoes azo coupling with diazotized aromatic amines (ArNH2) to afford azo derivatives. The azo derivatives (Ar=Ph, 4-MeC6H4, 4-ClC6H4, 4-MeOC6H4) were readily cyclized on reflux in aqueous NaOH to 3(2H)-pyridazinimine derivatives. These latter compounds were transformed into the corresponding pyrrole derivatives on reflux in glacial acetic acid with Zn dust presumably via reductive cleavage of the N-N bond followed by recyclization with loss of ammonia. Under similar conditions the azo derivative (Ar=2-NCC6H4) Was cyclized into 6H-pyridazino[3,2-a]quinazolin-6-imine derivative which was easily transformed into the 6H-pyridazino[3,2-a]quinazolin-6-one on reflux in ethanolic HCI. This last compound was also obtained from the azo derivatives (Ar=2-HOOCC6H4 and 2-MeOOCC6H4) by reflux in aq NaOH. The starting benzylidenemalononitrile reacts also with arylmethyleneamalononitrile or ethyl arylmethylenecyanoacetate (aryl=Ph, furyl, or thienyl) to afford substituted benzonitrile derivatives.