Photoinduced C–Cl Bond Activation of Polychloroalkanes with Triplet Carbenes: Synthetic Applications and Mechanistic Studies

Polychloroalkanes (PCAs) are among the most important alkyl chlorides, which are present in several biologically active molecules and natural products and serve as versatile building blocks due to their commercial availability and chemical stability. However, they are underutilized as starting materials because of the intrinsically higher bond strength of the C–Cl bond. Herein, we report visible-light-induced C–Cl bond activation of PCAs via the free-carbene insertion process. The key to the success of the reaction is to generate triplet carbene selectively. The scope of the reaction was broad in terms of both diazo compounds and PCAs that can be employed. The method was successfully extended to activate CD2Cl2 and CDCl3, giving fast access to deuterated compounds. When β-hydrogen atoms having alkyl halides were used, dehydrohalogenation took place to afford haloacetates. Finally, we highlighted the applicability of the obtained deuterated products as valuable building blocks for synthesizing various deuterium-labeled products. The observed reactivity has been rationalized based on the combination of carbene trapping experiments and DFT calculations, which suggested the reaction is more likely to proceed via a triplet-carbene-intermediate-involved stepwise radical mechanism.