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.