Nickela‐electrocatalyzed C−H Alkoxylation with Secondary Alcohols: Oxidation‐Induced Reductive Elimination at Nickel(III)

Abstract

Nickela‐electrooxidative C−H alkoxylations with challenging secondary alcohols were accomplished in a fully dehydrogenative fashion, thereby avoiding stoichiometric chemical oxidants, with H2 as the only stoichiometric byproduct. The nickela‐electrocatalyzed oxygenation proved viable with various (hetero)arenes, including naturally occurring secondary alcohols, without racemization. Detailed mechanistic investigation, including DFT calculations and cyclovoltammetric studies of a well‐defined C−H activated nickel(III) intermediate, suggest an oxidation‐induced reductive elimination at nickel(III).

Evolution of High‐Valent Nickela‐Electrocatalyzed C−H Activation: From Cross(‐Electrophile)‐Couplings to Electrooxidative C−H Transformations

“…Av ariety of (hetero)arenes 22 f-22 p were employed to probe the versatility of nickela-electrooxidative CÀHt ransformations, uncovering ab road scope of valuable electrophilic functional groups were fully accepted, such as halide,e ster, thioether,n itrile, and even the strongly coordinating pyridine 22 f-22 l (Scheme 13). [60] In contrast with previous transitionmetal-catalyzed chemical or electro-oxidativeC ÀHa lkoxylations of arenes utilizing primary alcohols and some simple secondary alcohols as reagent solvent, [59] the nickela-electrooxidative CÀHo xygenation of arenes provided the desired products in high yields even with sterically encumbered secondary alcohols. [60] Notably,n aturallyo ccurring alcohols, such as menthol, cholesterol and b-estradiol (23 p-23 r), could be also successfully transformed, maintaining the integrity of the stereogenic centers.A dditionally,t he gram-scale electrocatalytic oxidation was achieved without compromising the catalysts' efficacy on scale (24 j).…”

“…In 2020, the Ackermanng roup achieved the nickela-electrooxidative CÀHa lkoxylation of both electron-poor and electrorich arenes 22 with secondary alcohols 23 using Ni(DME)Cl 2 as the catalyst and bulky NaO 2 CAd as the additive in an userfriendly undivided cell set-up (Scheme 12). [60] Under the optimized reaction conditions, the substitution pattern on the quinoline moiety hadastrong impact on the efficacy of the nickela-electrochemical oxidation. Computational studies at the PEB0/Def2TZVP level of theory illustrated that the increasede lectron-density at the quinolinyl nitrogen and the decreasede lectron-density at the free amide nitrogen were found to be criticalfor the electrochemical CÀOf ormation.…”

Nickelaelektro‐katalysierte C‐H‐Alkoxylierung mit sekundären Alkoholen: oxidationsinduzierte reduktive Eliminierung an Nickel(III)

“…Um den elementaren Schritt der C-O-Bildung zu untersuchen, wurde der definierte Nickel(III)-Komplex Ni III -I unabhängig synthetisiert und vollständig charakterisiert, unter anderem durch Einkristall-Rçntenbeugung (Sche-ma 6a,d). [26,28] Der Ni III -I-Komplex wurde in einem katalytischen und einem stçchiometrischen Ansatz verwendet, in dem die Reaktion in An-und Abwesenheit von Strom durchgeführt wurde (Schema 6b,c). CV-Studien mit Ni III -I zeigten eine Oxidation bei einem Potential von 0.50 Vgegen Fc 0/+ (rot;S chema 6e), was auf die Bildung eines formalen Nickel(IV)-Komplexes schließen lässt.…”

“…[b] 3.0 mA, 32 h. [28] Schema 4. a) An/Aus-Experiment. b) Auftragung des elektrischen Stroms gegen das chemische Oxidationsmittel.…”

Electroreductive Cobalt‐Catalyzed Carboxylation: Cross‐Electrophile Electrocoupling with Atmospheric CO2

“…Similarly, Mei and Martin independently realized a nickel-catalyzed carboxylation of allylic alcohols using super-stoichiometric amounts of manganese or zinc powder as the reducing agent. [11] Electrocatalysis with 3d metal catalysts [12] has emerged as a powerful tool for sustainable molecular syntheses. [13] Recent advances for electrocarboxylation [14] include elegant palladium-catalyzed reductive transformations of allyl esters to useful carboxylic acids as reported by Mei (Scheme 1 a).…”