Bioinspired intramolecular spirocyclopropanation of quinones as an interrupted photoredox process

Abstract

Intramolecular photoreactions of quinones can be interrupted by proton transfer using small molecules, such as trimethylamine N-oxide. This interruption de-excites the reactive spirocyclopropyl intermediates, the structures of which were for the first time confirmed by isolating them in their neutral form. The mild conditions of this process allow the conversion of a broad spectrum of quinones possessing linear and branched substituents to spirocyclopropanes in a catalytic, diastereoselective, and atom-conserving manner. Density functional theory (DFT) calculations were performed to investigate the possible reaction pathways and the origin of stereoselectivity. The established spirocyclopropanation route might be used to perform unconventional transformations of the side chains of quinones and to provide clues for the co-occurrence of certain natural quinones, hydroquinones, and spirocyclopropanes.