Photoredox Catalysis in Organophosphorus Chemistry

Abstract

The vernal blooming of green chemistry has contributed to the development of visible light catalysis. Active radical species are generatedf rom catalytic amounts of photosensitizers,such as transition-metal complexes and organic dyes, upon visible light irradiation. Stoichiometrica mounts of oxidants, reductants, and radical initiators are avoidedi n most cases. Thus, reactions proceed under milder conditions with ab roader functional group tolerance than found by other methods. Photoredoxc atalysis has been used to form CÀCa nd CÀX( X= O, N, and S) bonds but is comparably underdeveloped in organophosphorus chemistry.H erein, we summarize advances in photoredox catalysis that involve organophosphorus chemistry.T he synthesis of organophosphorusc ompounds by photoredox catalysis, transition-metal complex/photoredoxd ual catalytic systems, andp hotoredox catalysis with phosphorus organocatalysts are discussed. The shortcomings and possible future trendso ft his chemistry are also presented.Scheme1.Various photocatalysts for the cross-couplingr eactionso ftetrahydroisoquinoline with dialkylphophonates and diaryl phosphine oxides[ ppy = 2phenylpyridine, bpy = 2,2'-bipyridine, DMF = N,N-dimethylformamide, AIBN = azobis(isobutyronitrile), PVA = poly(vinyl alcohol), BTF = benzotrifluoride].Scheme3.Thiophosphite-mediated RATC process to form five-membered ring and C sp 3 ÀPb ond.Scheme2.The mechanism for the photocatalyzed cross-coupling reaction [PC = Ir complex, Au complex, eosin Y, or rose bengal)].Scheme9.Direct CÀHp hosphorylationoft hiazoles in cross-coupling hydrogen evolution reaction and the proposed mechanism.Scheme11. Hetero-cross-dehydrogenative-coupling reaction of benzothiazoles and H-phosphonates.Scheme10. Hetero-cross-dehydrogenative-coupling reaction of dialkylphosphiteswith N-protected indole and the tentative reaction mechanism.

Selective P−C(sp3) Bond Cleavage and Radical Alkynylation of α‐Phosphorus Alcohols by Photoredox Catalysis

“…Phosphonoalkynes are important structural motifs for heterocycle synthesis and are typically prepared from nucleophilic or electrophilic alkynylation reactions . We next ascertained if the phosphorus radical from the P−C(sp 3 ) bond cleavage reaction could engage in hitherto unknown radical alkynylations ,. With α‐diarylphosphinoyl alcohol 6 (E p =1.39 V vs. SCE in MeCN) as the model substrate, the widely‐used bromoalkyne and alkynylsulfone acceptors were ineffective (entries 1–2 in Table ).…”

“…Phosphorus radicals are versatile reactive intermediates for organophosphorus syntheses, in which the phosphorus–hydrogen, phosphorus–heteroatom and phosphorus–carbonyl compounds are used as P‐radical precursors – . α ‐Phosphorus alcohols are important structural motifs in organic synthesis, which can be prepared easily by the Pudovik reaction and represent an attractive phosphorus radical precursor .…”

“…α‐Phosphonic diamide alcohols 25 a and 26 a gave 25 and 26 in 70 and 91 % yields, respectively. Alkynyl phosphonic diamides were not previously synthesized and the phosphonic diamide radicals are inaccessible through other methods …”

Visible‐Light‐Catalyzed Phosphonation‐Annulation: an Efficient Strategy to Synthesize β‐Phosphonopyrrolidines and β‐Phosphonolactones

“…[14] Visible light as a sustainable energy has played an important role in chemistry since the pioneering researches reported by MacMillan, Yoon, and Stephenson. [15] The accomplishment on synthesis of organophosphorus compounds via photo-redox catalysis has been documented since 2011, [16] and examples for the synthesis of phosphorylated pyrrolidines and lactones are still very rare to date. [13i,17] In the past several years, our group has been working on exploring concise and efficient methodologies of phosphine radicals and made significant progress.…”

“…J. Chem. sary for phosphonation-annulation (Table 1, entries [15][16]. Next, we tested the influence of reaction atmosphere (Table 1, entry 17).…”