SYNTHESIS AND INTRAMOLECULAR [4-CYCLOADDITION REACTIONS OF 4-PYRIDAZINECARBONITRILES WITH ALKYNE SIDE-CHAINS(2])

The preparation of a series of new 3-(alkynyl-X)-substituted 4-pyridaz inecarbonitriles 2-5 (X = O, NH) is described. The compounds are shown to undergo thermally induced intramolecular Diels-Alder reactions wit h inverse electron demand, affording the fused benzonitilles 6-8. Inco rporation of a 1,2-phenylene unit into the side chain, as in the case of compounds 10 and 13, results in a more favorable conformation of th e dienophilic substructure and thus to a pronounced acceleration of th e [4+2] cycloaddition reaction.