Photoredox/Cobalt Dual Catalysis for Visible-Light-Mediated Alkene–Alkyne Coupling

Abstract

Dual photoredox transition-metal catalysis has recently emerged as a powerful tool for making synthetically challenging carbon–carbon bonds under milder reaction conditions. Herein, we report on the visible-light-mediated controlled generation of low-valent cobalt catalyst without the need for a metallic reductant. It enabled C–C bond formation via ene-yne coupling at room temperature. The generality of this dual catalysis is demonstrated via the creation of sizable molecular diversity with the accommodation of several functional groups.

Hydroxyl Assisted, Photoredox/Cobalt Co‐catalyzed Semi‐Hydrogenation and Tandem Cyclization of o‐Alkynylphenols for Access to 2,3‐Dihydrobenzofurans

“…On the other hand, Co−H mediated hydrocarbonation of alkenes represents another important reaction pattern in photoredox/cobalt dual catalysis (Scheme 1Aa). In this respect, Rovis, [5] Maji, [6] König, [7] Collins [8] and other groups [9] have made excellent contributions. However, after extensive literatures survey, it is surprising to discover that the photochemically generated low‐valent cobalt complexes were rarely utilized in synthetic chemistry (Scheme 1Ab) [10] .…”

Visible‐Light‐Driven Intermolecular Reductive Ene–Yne Coupling by Iridium/Cobalt Dual Catalysis for C(sp3)−C(sp2) Bond Formation

“…Considering the lack of methodologies to achieve C(sp 3 )−C(sp 2 ) bonds with both high atom economy and broad functional‐group tolerance, we envisioned that a photopromoted reaction pathway may provide opportunities to achieve new structural diversity in an environmentally compatible fashion. Herein, we report our findings on an unprecedented visible‐light‐driven intermolecular reductive ene–yne coupling via cobalt/iridium dual catalysis (Scheme b) …”

“…Herein, we report our findings on an unprecedented visiblelight-driven intermolecular reductive ene-yne coupling via cobalt/iridium dual catalysis (Scheme 1b). [10,11] To evaluate the feasibility of this hypothesis, easily accessible 2-octyne (1a)a nd ethyl acrylate (2a)w ere selected as model substrates (Table 1). At the outset of our investigations, we used the following reactionc onditions:C oBr 2 (10 mol %), dppp (10 mol %), [12] Ir(dF(CF 3 )ppy) 2 (dtb-bpy)PF 6 (0.5 mol %) as photocatalyst(PC), N-ethyldiisopropylamine (DIPEA;3 .0 equiv) as sacrificialo rganic reductant and CsOPiv( 0.5 equiv) as ab ase in MeCN under irradiation with a4 .8 WB lue LED strip (entry 1).…”

The Merger of Photoredox and Cobalt Catalysis

“…Cobalt-catalyzed hydrofunctionalization was successfully applied to C-C-bond-forming reactions by Maji and coworkers, who reported reductive hydroalkenylation of electron-deficient alkenes (Figure 4C) [88]. In their mechanistic hypothesis, cobalt hydride, which was obtained by protonation of Co I , inserts into an electron-deficient alkene.…”