Aliphatic Aldehydes as CO Surrogates via Photocatalyzed Hydrogen Atom Transfer

The introduction of a carbonyl group enables smooth access to a wide plethora of bulk chemicals such as ketones, amides and esters[1]. The use of carbon monoxide (CO) is ideal for large-scale carbonylation in industry, where infrastructure allows its safe and efficient handling[2]. However, most academic laboratories lack the expertise and equipment required to safely manage even small amounts of this lethal gas, thus inhibiting methodological development. A controlled release of carbon monoxide on a lab scale is possible thanks to CO surrogates[3], which however often implies harsh conditions (strong acids or bases, expensive transition-metal catalysts, prohibitively high temperatures). Herein, we propose aliphatic aldehydes as a new class of CO photosurrogates. Photocatalyzed decarbonylative Hydrogen Atom Transfer (HAT) [4] is leveraged to cleave the formyl C(sp2)−H bond of these chemicals to generate an acyl radical [5]. The latter species rapidly undergoes decarbonylation to provide carbon monoxide. We demonstrate how this simple but effective concept can be exploited to smoothly carry out benchmark aminocarbonylation, carbonylative Suzuki, cyclocarbonylation, and photochemical alkoxycarbonylation reactions. Our approach shows several advantages over the state of the art: i) it is atom-economical, ii) it does not involve the use of expensive or toxic reagents and iii) it can be controlled literally with the flip of a switch.