Preparation of N-methacryloxyethyl derivatives of spiropyrans of the indoline series

Abstract

Reaction of 2,3,3-trimethylindolenine with ethylene iodohydrin gave 1-hydroxyethyl-2,3,3-trimethylindoleninium iodide, which gives 3a,4,4-trimethyloxazolidino[3,2-a]indoline on treatment with sodium carbonate solution. Condensation of the latter with 5-nitro- and 3-methoxy-5-nitrosalicylaldehydes gives, respectively, N-hydroxyethyl derivatives of 6′-nitro- and 6′-nitro-8′-methoxyspiro(indoline-2,2′-benzopyrans) (V, VI), while condensation with 3-nitrosalicylaldehyde gives 4,4-dimethyl-3a-(2-hydroxy-3-nitrostyryl)oxazolidino[3,2-a]indoline (VII). Acylation of nitrospiran V and oxazolidinoindoline VII with methacrylyl chloride in pyridine proceeds at the free hydroxyl groups, while a mixture of derivatives of 1-(β-methacryloxyethyl)spiropyran and 3a-(2-methacryloxy-3-nitrostyryl)oxazolidinoindoline is formed under the same conditions from nitromethoxyspiropyran VI. Acylation of V in acetone in the presence of sodium bicarbonate gives 4,4-dimethyl-3a-(2-methacryloxy-5-nitrostyryl)oxazolindo-[3,2-a]indoline. The mechanism of the isomeric transformations of the various forms that contain spiropyran and oxazolidino-indoline rings was studied by means of electronic spectra. The photochromic properties of the spiropyrans were investigated.