Efforts toward Synthetic Photosynthesis: Visible Light-Driven CO<sub>2</sub> Valorization
Timothy D. Schoch, Jimmie D. Weaver
Abstract
Current methods of urethane preparation from amines invariably involve high-energy and often toxic or cumbersome molecules to make the process exergonic. CO 2 aminoalkylation using olefins and amines represents an attractive albeit endergonic alternative. We report a moisture-tolerant method that uses visible light energy to drive this endergonic process (+25 kcal/mol at STP) using sensitized arylcyclohexenes. They convert much of the photon’s energy to strain upon olefin isomerization. This strain energy greatly enhances alkene basicity, allowing for sequential protonation by and interception of ammonium carbamates. Following optimization steps and amine scope evaluation, an example product arylcyclohexyl urethane underwent transcarbamoylation with some demonstrative alcohols to form more general urethanes with concomitant regeneration of the arylcyclohexene. This represents a closure of the energetic cycle, producing H 2 O as the stoichiometric byproduct.