Acyl Radicals from Acylsilanes: Photoredox-Catalyzed Synthesis of Unsymmetrical Ketones

Twelve naphthochromenone photocatalysts (PCs) were synthesized on gram scale. They absorb across the UV/Vis range and feature an extremely wide redox window (up to 3.22 eV) that is accessible using simple visible light irradiation sources (CFL or LED). Their excited‐state redox potentials, PC*/PC.− (up to 1.65 V) and PC.+/PC* (up to −1.77 V vs. SCE), are such that these novel PCs can engage in both oxidative and reductive quenching mechanisms with strong thermodynamic requirements. The potential of these bimodal PCs was benchmarked in synthetically relevant photocatalytic processes with extreme thermodynamic requirements. Their ability to efficiently catalyze mechanistically opposite oxidative/reductive photoreactions is a unique feature of these organic photocatalysts, thus representing a decisive advance towards generality, sustainability, and cost efficiency in photocatalysis.

show abstract

“…[c] Result as in Ref. [28] (reaction time 8h). gave promising results,w ith yields of 47 %, 51 %, and 45 %, respectively (entries 8-10).…”

Section: Synthetic Applications and Comparison Of The Photocatalytic mentioning

confidence: 99%

Naphthochromenones: Organic Bimodal Photocatalysts Engaging in Both Oxidative and Reductive Quenching Processes

et al. 2019

View full text Add to dashboard Cite

show abstract

“…Several reviews give a detailed and excellent overview of the versatile reactivity of acylsilanes . Furthermore, recent applications include photoredox‐catalyzed generation of acyl radicals and subsequent addition to electron‐deficient olefins, photoinduced acylsilane‐aldehyde coupling, enantioselective 1,2‐rearrangement to secondary alcohols, and stereoselective synthesis of allyl ethers from α,β‐unsaturated acylsilanes …”

Section: Introductionmentioning

confidence: 99%

“…[1] Several reviews give a detailed and excellent overview of the versatile reactivity of acylsilanes. [1][2][3][4][5][6][7] Furthermore, recent applications include photoredox-catalyzed generation of acyl radicals and subsequent addition to electron-deficient olefins, [8] photoinduced acylsilanealdehyde coupling, [9] enantioselective 1,2-rearrangement to secondary alcohols, [10] and stereoselective synthesis of allyl ethers from α, -unsaturated acylsilanes. [11] Commonly, acylsilanes are synthesized either by umpolung of an aldehyde by using the Corey-Seebach methodology, subsequent nucleophilic substitution of a silyl halide and deprotection, or by nucleophilic attack of a silyl anion to a carbonyl compound.…”

Section: Introductionmentioning

confidence: 99%

Preparation of Functionalized Acylsilanes by Diol Cleavage of Cyclic 1,2‐Dihydroxysilanes

2019

View full text Add to dashboard Cite

We report a study on diol cleavage of cyclic 1,2‐dihydroxysilanes for the preparation of functionalized acylsilanes. Sodium periodate turned out to be an efficient reagent for this transformation, resulting in good to excellent yields. The method is characterized by mild reaction conditions, and sometimes simple aqueous workup of the reaction mixture was sufficient to obtain the acylsilanes in high purity. An acyclic 1,2‐dihydroxysilane was readily cleaved as well.

show abstract

“…To confirm the energy transfer between at riplet excited state of 8 ( 3 8*) and ag round state of 1c,q uenching experiments were conducted by measuring luminescence spectra of 8 with variousc oncentrations of alkanoylsilane 1c.A ss hown in Scheme 5a,t he emission intensity decreased with increasing concentration of alkanoylsilane 1c.T hese data indicate that the triplet excited state of 8 ( 3 8*) was quenched by 1c through triplet energy transfer. [17] Ap lausible mechanism for this reactioni sd escribed in Scheme5b. The Ir complex 8 is photoexcited under visiblelight irradiation conditions and the resulting singlet excited state of 8 ( 1 8*) is smoothly converted to its triplet excited state ( 3 8*) by intersystem crossing.…”

mentioning

confidence: 99%

Efficient Generation and Synthetic Applications of Alkyl‐Substituted Siloxycarbenes: Suppression of Norrish‐Type Fragmentations of Alkanoylsilanes by Triplet Energy Transfer

Ishida

Yamazaki

Hagiwara

et al. 2020

Chemistry A European J

View full text Add to dashboard Cite

Acylsilanes have been knownt ou ndergo isomerizationt os iloxycarbenesu nder photoirradiation and the thus generated carbenes can be utilized for various synthetic reactions. But this carbene formation is not necessarily efficient with some alkanoylsilanes because Norrishtype fragmentations compete, which limit the synthetic utility of alkanoylsilanes as carbene precursors. In this study,g eneration of siloxycarbenes from alkanoylsilanes by visible-light-inducedenergyt ransfer was examined by using an Ir complex, [Ir{dF(CF 3 )ppy} 2 (dtbpy)]PF 6 ,a nd was successfully applied to the CÀCc oupling reactions with boronic esters or aldehydes. This methodology efficiently suppressed undesired Norrish-type reactions and broadened synthetic utility of alkanoylsilanes.Photocatalytic organic transformations have attracted significant attention in currents ynthetic chemistry.P hotoredox process involving ar adicali ntermediate is gaining importance in this field. [1] Another interesting aspect of photocatalytic reactions is triplet energy transfer processes which enableg eneration of triplet-excited states of organic substrates through energy transfer from photoexcited catalysts. [1b,c,e, 2] From as ynthetic point of view,t riplete nergy transfer is considered to have some benefits [3] as compared to direct photoexcitation of organic substrates:i )highly energetic singlet-excited states of substrates, whichs ometimes induce undesired reactions, can be avoided, and ii)ite nables excitationo fs ubstrates with longer wavelength light than the inherent absorption band of substrates.It has been known that triplet-excited states of acylsilanes 1 undergo a1 ,2-silyl migration to generatet ransienta nd nucleo-philic siloxycarbene intermediates 2 (Scheme 1a). [4] Since Brook and co-workers originally discoveredt his photoisomerization through reaction of siloxycarbene intermediates 2 with polar compounds such as alcohols over fifty years ago, [5] various synthetic reactions utilizingp hotochemically generated siloxycarbenes 2 have been developed by several groups [6] including us. [7] However, in contrast to the reactions of aroylsilanes (1, R 1 = aryl), the use of alkanoylsilanes (1,R 1 = alkyl) has been quite limited. [8] We have already reported intermolecularc oupling reactions of photochemically generated siloxycarbenes 2 with boronic esterso raldehydes under neutral or Lewis acidic conditions (Scheme 1b). [7] Duringt he course of these studies, we noticed that serious undesired photochemical processes competed with siloxycarbene formation in the reactions with somea lkanoylsilanes.F or example, UV irradiation( 365 nm) of am ixture of 4-phenylbutanoylsilane 1a [9] and boronic ester 5 gave styrene along with the desired coupling product 3a in low yield (Scheme 2). The formation of styrene clearly indicated that Norrish type II fragmentation [10,11] competed with the desired photochemical isomerization to siloxycarbene 2 from excited stateso falkanoylsilane 1a.Scheme1.a) Photochemical generation of siloxycarbenes. b) Photoi...

show abstract

Acyl Radicals from Acylsilanes: Photoredox-Catalyzed Synthesis of Unsymmetrical Ketones

Cited by 112 publications

References 83 publications

Naphthochromenones: Organic Bimodal Photocatalysts Engaging in Both Oxidative and Reductive Quenching Processes

Naphthochromenones: Organic Bimodal Photocatalysts Engaging in Both Oxidative and Reductive Quenching Processes

Preparation of Functionalized Acylsilanes by Diol Cleavage of Cyclic 1,2‐Dihydroxysilanes

Efficient Generation and Synthetic Applications of Alkyl‐Substituted Siloxycarbenes: Suppression of Norrish‐Type Fragmentations of Alkanoylsilanes by Triplet Energy Transfer

Contact Info

Product

Resources

About