Preparation of Some New Benzylidenemalononitriles by an SNAr Reaction: Application to Naphtho[1,2-b]pyran Synthesis

T h e reaction o f 4-fluoro-3-nitrobenzylidene malononitrile ( 3 ) with piperidine and 1-naphthol yields the addition-elimination product ( 9 ) rather than the expected naphtho [l,2-blpyran (7).This reaction is extended to produce other 3,4-disubstituted benzylidenemalononitriles (1 0)-(1 3).These compounds are then reacted with 1-naphthol and 4methylmorpholine producing the naphtho[l ,2-blpyrans (1 4)-The reaction o f 1-naphthol with benzylidenemalononitriles and piperidine is knownl.2t o produce 2-amino-4-aryl-4H-naphtho[l,2-b]pyran 3-carbonitriles.This interesting reaction presumably proceeds via a carbon-centred Michael type attack of the naphthol onto the unsaturated nitrile, followed by cyclisation of the naphthol oxygen onto the nitrile and imine-enamine isomerisation.Our interest in the biological activity' of this series prompted us to investigate this reaction with the intention of preparing some close analogues of naphthopyran (5).We were particularly interested in compounds possessing a substituent adjacent t o the n i t r o group.The,.first starting material examined was 4-chloro-3-6