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 .