Chiral isothiourea-catalyzed kinetic resolution of 4-hydroxy[2.2]paracyclophane

Organocatalytic desymmetrization provides access to planar chiral [2.2]paracyclophanes

Planar chiral [2.2]paracyclophanes consist of two functionalized benzene rings connected by two ethylene bridges. These organic compounds have a wide range of applications in asymmetric synthesis, as both ligands and catalysts, and in materials science, as polymers, energy materials and dyes. However, these molecules can only be accessed by enantiomer separation via (a) time-consuming chiral separations and (b) kinetic resolution approaches, often with a limited substrate scope, yielding both enantiomers. Here, we report a simple, efficient, metal-free protocol for organocatalytic desymmetrization of prochiral diformyl[2.2]paracyclophanes. Our detailed experimental mechanistic study highlights differences in the origin of enantiocontrol of pseudo-para and pseudo-gem diformyl derivatives in NHC catalyzed desymmetrizations based on whether a key Breslow intermediate is irreversibly or reversibly formed in this process. This gram-scale reaction enables a wide range of follow-up derivatizations of carbonyl groups, producing various enantiomerically pure planar chiral [2.2]paracyclophane derivatives, thereby underscoring the potential of this method.

The hamburger-shape photocatalyst: thioxanthone-based chiral [2.2]paracyclophane for enantioselective visible-light photocatalysis of 3-methylquinoxalin-2(1H)-one and styrenes

A new thioxanthone-based photocatalyst with a [2.2]paracyclophane skeleton and planar chirality has been developed. The catalyst has been successfully applied in the visible light-mediated enantioselective aza Paternò-Büchi reactions of quinoxalinone and styrenes to produce azetidines. The structures of the catalyst derivatives were unequivocally determined by their single crystal X-ray crystallography analysis.