Hydrogen-Evolution Allylic C(sp³)–H Alkylation with Protic C(sp³)–H Bonds via Triplet Synergistic Brønsted Base/Cobalt/Photoredox Catalysis

Abstract

Transition-metal-catalyzed allylic C­(sp3)–H alkylation with carbon-center nucleophiles is a straightforward approach to C­(sp3)–C­(sp3) bond formation, which has found widespread application in organic synthesis. However, stoichiometric oxidants are typically required to realize the transformation. Herein, by the triplet synergistic merger of Brønsted base/cobalt/photoredox catalysis, a mild protocol for the hydrogen-evolution allylic C­(sp3)–H alkylation with protic C­(sp3)–H feedstocks was developed in an oxidant-free manner. This operationally simple method enables direct allylic C­(sp3)–H alkylation of a wide range of branched α-olefins with diverse protic C­(sp3)–H feedstocks. The synthetic robustness of this strategy was further demonstrated by the late-stage functionalization of complex molecules and the synthesis of the natural product dihydropallescensin D.

Photoredox streamlines electrocatalysis: photoelectrosynthesis of polycyclic pyrimidin-4-ones through carbocyclization of unactivated alkenes with malonates

“…S12†) 22 has a higher oxidation potential than the base-activated diethyl malonate 2a ( E p/2 = 0.83 V vs. SCE, Fig. S10 and S11†), 32,49 thus it is unlikely that 1a undergoes a preferential oxidation followed by the nucleophilic addition of 2a to the resulting alkene radical cation. 50…”

“…S12 †) 22 has a higher oxidation potential than the base-activated diethyl malonate 2a (E p/2 = 0.83 V vs. SCE, Fig. S10 and S11 †), 32,49 thus it is unlikely that 1a undergoes a preferential oxidation followed by the nucleophilic addition of 2a to the resulting alkene radical cation. 50 The excited-state reduction potential of Ir( ppy) 3 is only 0.31 V vs. SCE (see the ESI †), 51 thus precluding a proton-coupled electron transfer (PCET) from diethyl malonate 2a to excited a Reaction conditions: alkene substrate (0.3 mmol), 2a (0.9 mmol), K 2 CO 3 (0.03 mmol), Ir(ppy) 3 (0.009 mmol), Bu 4 NPF 6 (0.45 mmol), acetone/TFE (11 : 1, v/v, 6.0 mL), 6 W blue LEDs (λ max = 455 nm), CC anode (15 × 15 mm), platinum plate cathode (15 × 15 mm), undivided cell, 1.5 mA, Ar, room temperature, 12 h. b 24 h. c 0.15 mmol of K 2 CO 3 were used.…”

Synthetic Applications of Photochemically Generated Radicals from Protic C(sp3)−H Bonds

“…Just prior to their publication on the three-component carboarylation of alkenes with C(sp 3 )À H acid feedstocks, the Deng group also detailed the oxidative allylation of the same feedstock chemicals using a triple catalytic system (Scheme 32A). [69] The oxidative allylation operates under the synergistic catalysis of Ru(bpy) 3 Cl 2 • 6H 2 O, Co(dmH) 2 PyCl (165), and cesium carbonate. The multicatalytic platform operates on carbon C(sp 3 )À H acids in the presence of 1,1-disubstituted alkenes under blue light LED irradiation in acetonitrile.…”

Formal allylic C(sp3)–H alkylation of α-alkylstyrenes by rearrangement of intermediate alkenyl sulfonium salts

“…4 Recently, Deng and co-workers reported an unprecedented catalytic system for the direct allylic C(sp 3 )–H alkylation of a wide range of branched α-alkenes with diverse protic C(sp 3 )–H feedstocks (Scheme 1a, bottom). 5 Additionally, the sulfur-mediated allylic C–H alkylation of tri- and disubstituted olefins via allylic sulfonium intermediates is also an efficient protocol (Scheme 1b). 6 However, all the above-mentioned approaches offer limited access to allylated carbon quaternary centers.…”