Photocatalytic α‐Oxyamination of Stable Enolates, Silyl Enol Ethers, and 2‐Oxoalkane Phosphonic Esters

Abstract

Fast α-oxyamination of stable enolates, silyl enol ethers, and in situ deprotonated dialkyl 2-oxoalkane phosphonates and diphenyl-2-oxoalkyl phosphine oxides was performed in the presence of [Ru(bpy) 3 ] 2+ (bpy = 2,2Ј-bipyridyl) as a photocatalyst, 2,2,6,6-tetramethylpiperidine nitroxide (TEMPO), and visible light. The key step was the light-induced one-electron

Photocatalytic Dehydrogenative Cross‐Coupling of Alkenes with Alcohols or Azoles without External Oxidant

“…We were pleased to find that radical alkenylation could also be achieved utilizing Acr + -Mes ClO 4 À as the catalyst and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as the terminal oxidant, which is also used as an oxidant in several photocatalytic reactions. [15] As shown in Scheme 2C,p rimary alcohols (especially long chain aliphatic alcohols), secondary alcohols,o rt ertiary alcohols could all be transformed into the desired products in high yields using aphotocatalyst/TEMPO system.…”

Photoredox Catalysis of Aromatic β‐Ketoesters for in Situ Production of Transient and Persistent Radicals for Organic Transformation

“…After irradiation of aromatic β‐ketoester 1 a , 5,5‐dimethyl‐1‐pyrroline‐ N ‐oxide (DMPO), and fac ‐Ir(ppy) 3 in N , N ‐dimethylformamide (DMF) for 60 seconds, characteristic signals for ketyl radical 2 or α‐carbonyl radical 3 were detected by electron spin resonance (ESR; Scheme A). The radical inhibitors 2,2,6,6‐tetramethylpiperidin‐1‐oxyl (TEMPO) and 2,6‐di‐ tert ‐butyl‐4‐methylphenol (BHT) greatly suppressed the reaction, with alkoxyamine 4 formed in only about 10 % yield (Scheme B) . Importantly, the persistent ketyl radical A and transient α‐carbonyl radical B generated through visible‐light irradiation of aromatic β‐ketoester 1 a can couple with 1,1‐diphenylethylene 5 to afford bridged diethyl heptanedioate 6 based on the persistent radical effect (PRE) principle (Scheme C).…”

“…[12] The higher electron affinity and lower LUMO energy of aromatic b-ketoesters compared to alphatic b-ketoester 1y [13] mean that the keto form rather than the enol form acts as an electron acceptor (Table S4 supported by the results of the DFT calculation in the Supporting Information; Scheme 1). Although the photocatalyst *fac-Ir(ppy) 3 (E 1/2 ox + Ir(ppy) 3 /*Ir(ppy) 3 = À1.73 V vs. SCE) [2a] is not able to carry out single-electron transfer (SET) to aromatic b-ketoester 1 a (E red < À1.90 V vs. SCE, E ox >+ 1.90 V vs. SCE in CH 3 CN, Figures S4 and S6), the anion 1 a À (E 1/2 ox 1 aC/1 a À =+ 0.66 V vs. SCE in DMF, Figure S5) [14] resulting from partially deprotonated 1 a would be oxidized by + fac-Ir(ppy) 3 species (E 1/2 red + Ir(ppy) 3 /Ir(ppy) 3 =+ 0.77 V vs. SCE) to regenerate fac-Ir-(ppy) 3 and simultaneously produce transient a-carbonyl radical B. [13] The striking feature of aromatic b-ketoesters is that the enol form enables elimination of a proton to form the anion, and at the same time, the eliminated proton can activate the keto form to significantly decrease the reduction potential of 1 a.…”

“…The radical inhibitors 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) and 2,6-di-tert-butyl-4-methylphenol (BHT) greatly suppressed the reaction, with alkoxyamine 4 formed in only about 10 % yield (Scheme 2 B). [14,15] Importantly, the persistent ketyl radical A [7,11] and transient a-carbonyl radical B [16] generated through visible-light irradiation of aromatic bketoester 1 a can couple with 1,1-diphenylethylene 5 to afford bridged diethyl heptanedioate 6 based on the persistent radical effect (PRE) principle [17] (Scheme 2 C).…”

Photocatalytic Dehydrogenative Cross‐Coupling of Alkenes with Alcohols or Azoles without External Oxidant

“…[14] In this oxidant-free system, acobalt catalyst serves solely as an oxidant of the photocatalyst, thereby reviving the catalytic cycle.Avariety of oxidants were examined to probe the role of the cobalt catalyst. [15] As shown in Scheme 2C,p rimary alcohols (especially long chain aliphatic alcohols), secondary alcohols,o rt ertiary alcohols could all be transformed into the desired products in high yields using aphotocatalyst/TEMPO system. [15] As shown in Scheme 2C,p rimary alcohols (especially long chain aliphatic alcohols), secondary alcohols,o rt ertiary alcohols could all be transformed into the desired products in high yields using aphotocatalyst/TEMPO system.…”