Illuminating a path uphill to open rings

Organic Chemistry When a chemical compound absorbs light directly, it gets a burst of energy that can propel an otherwise unfavorable reaction forward. In principle, light-absorbing catalysts can likewise channel energy to substrates to push reactions uphill thermodynamically. Nonetheless, the recent surge in photoredox catalysis has largely focused on accelerating favorable transformations. Ota et al. demonstrate that a catalyst system composed of an iridium photoredox chromophore, a phosphate base, and a thiol for hydrogen-atom transfer can isomerize cyclic alcohols to higher-energy linear aldehydes. The high-yielding protocol is compatible with a wide variety of complex substrates. J. Am. Chem. Soc. 141 , 1457 (2019).