Chiral Symmetry Breaking of Spiropyrans and Spirooxazines by Dynamic Enantioselective Crystallization

Dynamic enantioselective crystallization enabled the chiral symmetry breaking of two spiropyrans and one spirooxazine. The three spiro compounds afforded racemic conglomerate crystals, and easily racemized in alcoholic solution without irradiation. Optically pure enantiomorphic crystals were obtained by vapor‐diffusion crystallization or attrition‐enhanced deracemization (Viedma ripening). Their absolute configurations were determined by single‐crystal X‐ray analysis and each enantiomorphic crystal was correlated with its solid‐state circular dichroism (CD) spectrum. Spiro‐pure enantiomers: Chiral symmetry breaking of two spiropyrans and one spirooxazine was performed by dynamic enantioselective crystallization. The three spiro compounds afforded racemic conglomerate crystals, and easily racemized in methanol without irradiation. Vapor‐diffusion crystallization or attrition‐enhanced deracemization (Viedma ripening) gave optically pure enantiomorphic crystals.