Reductive Cyclization of Unactivated Alkyl Chlorides with Tethered Alkenes under Visible‐Light Photoredox Catalysis

Abstract

The chemical inertness of abundant and commercially available alkylc hlorides precludes their widespread use as reactants in chemical transformations.P resented in this work is am etallaphotoredoxm ethodology to achieve the catalytic intramolecular reductive cyclization of unactivated alkylc hlorides with tethered alkenes.T he cleavage of strong C(sp 3 )ÀCl bonds is mediated by ah ighly nucleophilic lowvalent cobalt or nickel intermediate generated by visible-light photoredox reduction employing acopper photosensitizer.The high basicity and multidentate nature of the ligands are key to obtaining efficient metal catalysts for the functionalization of unactivated alkylc hlorides. Figure 5. Hypothetical catalytic cycle for the visible-light reductive cyclization of unactivateda lkyl chlorides with tethered alkenes. HAT = hydrogen atom abstraction, HC = homolytic cleavage.

The Merger of Photoredox and Cobalt Catalysis

“…Casitas, Lloret-Fillol, and colleagues applied virtually the same combination of cobalt and photoredox catalysis for the reduction of unactivated alkyl chlorides (Figure 7C) [110]. This transformation clearly demonstrates the advantage of metallaphotoredox chemistry because unactivated alkyl chlorides are known to be inert toward conventional photoredox catalysis.…”

An Exceedingly Low-Coordinate Platinum(0)-Germylene for E–H Bond Activation and Catalytic Hydrodehalogenation

“…We were further encouraged by studies from the Lloret group, where more challenging C(sp 3 )-Cl bonds in alkyl chlorides were cleaved within a catalytic cycle for reductive cyclizations using, once more, a cooperative bimetallic system (Co/Ni) with the key feature of a nucleophilic low-valent metal. 39 Before discussing our own findings, it is worth noting that most catalytic dehalogenation studies have focused on aryl halides, while alkyl halides with stronger C(sp 3 )-X bonds remain less investigated, and in many cases catalysts that efficiently dehalogenate aromatic substrates fail to convert aliphatic versions. 40 Moreover, homogeneous catalysts that hydrodehalogenate alkyl halides have mostly covered bromide substrates, 41,42 showing little success with chloride counterparts.…”

Harnessing the Unique Reactivity of an Exceedingly Low-Coordinate Platinum(0)-Germylene System for E–H (E = H, N, O) Bond Activation and Catalytic Hydrodehalogenation Reactions

“…License: CC BY-NC-ND 4.0 further encouraged by studies from the Lloret group, where more challenging C(sp 3 )-Cl bonds in alkyl chlorides were cleaved within a catalytic cycle for reductive cyclizations using, once more, a cooperative bimetallic system (Co/Ni) with the key feature of a nucleophilic low-valent metal. 23 Before discussing our own findings, it is worth noting that most catalytic dehalogenation studies have focused on aryl halides, while alkyl halides with stronger C(sp 3 )-X bonds remain less investigated, and in many cases catalysts that efficiently dehalogenate aromatic substrates fail to convert aliphatic versions. 24 Moreover, homogeneous catalysts that hydrodehalogenate alkyl halides have mostly covered bromide substrates, 25 showing little success with chloride counterparts.…”