Condensation of formyl-substituted indoline spiropyrans with 3 H -indolium salts: specific features

A condensation reaction between formyl-containing spiropyrans and iodides of 1,2,3,3-tetramethyl-3 H -indolium derivatives was studied. The reaction results in a mixture of products with a strong predominance of one of them irrespective of the structure of the starting compounds. The structures of the compounds formed during the reaction were determined based on the NMR, IR, and mass spectroscopy data. The dependence of the yield of the major reaction product on the structure of the starting compounds was studied. The prerequisites for the observed reaction pathway were established and the reaction mechanism was proposed using the results of quantum-chemical calculations based on analysis of the molecular electrostatic potential and the dual descriptor of reactivity.