Photoredox Cleavage of a C_sp3–C_sp3 Bond in Aromatic Hydrocarbons

Abstract

Functionalizing molecules through the selective cleavage of carbon–carbon bonds is an attractive approach in synthetic chemistry. Despite recent advances in both transition-metal catalysis and radical chemistry, the selective cleavage of inert Csp3–Csp3 bonds in hydrocarbon feedstocks remains challenging. Examples reported in the literature typically involve substrates containing redox functional groups or highly strained molecules. In this article, we present a straightforward protocol for the cleavage and functionalization of Csp3–Csp3 bonds in alkylbenzenes using photoredox catalysis. Our method employs two distinct bond scission pathways. For substrates with tertiary benzylic substituents, a carbocation-coupled electron transfer mechanism is prevalent. For substrates with primary or secondary benzylic substituents, a triple single-electron oxidation cascade is applicable. Our strategy offers a practical means of cleaving inert Csp3–Csp3 bonds in molecules without any heteroatoms, resulting in primary, secondary, tertiary, and benzylic radical species.

Selective monodeuteration enabled by bisphosphonium catalyzed ring opening processes

“…In the deuteration of aromatic hydrocarbons, the relatively weakened benzylic C-H bonds can facilitate H/D exchange but have posed severe challenges for the selective monodeuteration. 2 We envisioned that the well-established b-bond cleavage of aromatic radical cations could render a facile approach to achieve benzylic monodeuteration, via selective ring openings of cyclic hydroaromatics and the intermediacy of a benzylic radical intermediate 35,[50][51][52][53][54][55] . Through the use of e cient HAT catalysts, inexpensive and operationally handy deuteration agents such as CH 3 OD can be employed to enforce the desired deuterium atom transfer.…”

Photocatalytic, α-Aminoalkyl Radical-Mediated, Methylene-Extrusive Ring-Closing Transformation of o-Alkynyl and o-Cyano Acrylamides

“…Seminal work by the Leonori and Parasram groups has led to the development of photocatalytic oxidative cleavage of olefins. The Chen and Huang groups have reported the photocatalytic cleavage of benzylic C sp 3 –C sp 3 bonds for subsequent functionalization . The Feng group has developed a photocatalytic strategy for the cleavage of cyclopropanes followed by the formation of C sp 3 –heteroatom bonds, providing new functional group interconversions of small rings.…”

An I2–DMSO catalytic manifold enabled aromatization for C-ring editing of podophyllotoxone

“…Indeed, the sterically inhibited 2-substituted α-tetralone skeleton has been reported to be unreactive in some palladium-catalyzed aromatization, 10 c and the electron-donating E-ring residue and its electrophilic benzyl site are also risky for single-electron oxidation. 12,14 On the basis of our research spotlight on lignan synthesis 15 as well as our long-standing interest in the I 2 –DMSO reaction system, 16 we speculated that it might be possible to take advantage of the special structural characteristics of podophyllotoxone to develop an I 2 –DMSO catalytic manifold that would fulfil our synthetic requirements. The working hypothesis is outlined in Scheme 1b.…”