Nitriles in heterocyclic synthesis. A novel synthesis of spiropyran-4-ylindolidene derivatives

The structure of the products of reaction of 2-oxo-3-dicyanomethylidene-2,3-dihydroindole (1a) and 2-oxo-3-cyanoethoxycarbonylmethylidene-2,3-dihydroindole (1b) with the pyrazolin-5-one derivatives 2a,b could be established via 13C nmr and high resolution 1H nmr to be the spiropyranylindolone derivatives 5a-d.