A rhodium catalyst hogs the spotlight

Photochemistry Photochemistry offers an efficient route to constructing four-membered carbon rings, but the product geometry is hard to control precisely. Even though catalysts can selectively orient the reacting partners, it is hard to outpace the unselective background reaction stimulated by catalyst-free light absorption. Huang et al. devised a chiral rhodium catalyst that enhanced the intrinsic blue light absorption of imidazole-substituted enones by more than 100-fold, thereby accelerating their [2+2] reaction with dienes and styrene derivatives. The acceleration was sufficient to achieve 92 to 99% enantiomeric excess in a wide variety of cyclobutane products, several of which bore contiguous quaternary stereocenters. J. Am. Chem. Soc. 10.1021/jacs.7b04363 (2017).