Synthesis of 3′-acyl-substituted indoline spiropyrans

The reaction of 1,3,3-trimethyl-ω-formyl-2-methyleneindoline with substituted salicylaldehydes in most organic solvents is accompanied by decarbonylation and gives known spiropyrans that do not contain a formyl group; however, 3′-formyl-substituted spiropyrans can be obtained in low yields in dimethyl sulfoxide. The reaction of 1,3,3-trimethyl-ω-acetyl-2-methyleneindoline with 3-bromo-5-nitrosalicylaldehyde gave a 3′-acetyl-substituted compound in the open merocyanine form with a branched chromophore chain. 3′-Acyl-substituted indoline spiropyrans can be obtained by acylation of the appropriate compounds that do not contain substituents in the 3′ position. Indoline spiropyrans with 3′-acyl substitutents do not have photochromic properties.