Stereoselective formation of dicondensed spiropyran product obtained from the reaction of excess Fischer base with salicylaldehydes: first full characterization by X-ray crystal structure analysis of a DC·acetone crystal

The structure and stereochemistry of the dicondensed spiropyran product (, X=COOH) obtained from reaction of excess Fischer base with substituted salicylaldehydes has been fully assigned as with (8R, 10R) configuration on the basis of single crystal X-ray diffraction analysis. The stereoselective formation of DC molecules indicates that the most plausible mechanism for DC formation involves dehydration of the cyclic carbinol intermediate with the aid of intramolecular H-bonding via transition structure TS1‡.