Enantioselective electrosynthesis of inherently chiral calix[4]arenes via a cobalt-catalyzed aryl C–H acyloxylation

Abstract

Inherently chiral calixarenes are known to exhibit versatile functions due to their delicate three-dimensional macrocyclic frameworks. However, the catalytic asymmetric synthesis of these compounds remains largely unexplored and poses a significant challenge. Herein, we report an unprecedented enantioselective electrochemical synthesis of inherently chiral calix[4]arenes. Our approach is based on a 3d metal cobalt-catalyzed asymmetric C–H acyloxylation of the prochiral macrocyclic frameworks. The easily accessible and modifiable chiral salicyloxazoline (Salox) was used as the ligand to efficiently regulate the enantioselectivity. This protocol proceeded smoothly under electrochemically mild conditions and was compatible with a wide range of carboxylic acids, including aryl carboxylic acids and tertiary, secondary, primary aliphatic carboxylic acids, yielding a variety of acyloxylated calix[4]arenes with good yields (up to 94% yield) and excellent enantioselectivities (95–99% ee). The synthetic practicability of this method was demonstrated by the scale-up reaction and the divergent derivatizations of the inherently chiral macrocyclic products.