Visible light-driven conjunctive olefination

Photocatalytic Alkene-Migrative Chain Elongation of 2-Phosphinostyrenes with Aldehydes

The photocatalytic alkene-migrative chain elongation reaction of 2-phosphinostyrenes with aldehydes under mild conditions in response to blue light was demonstrated. A broad range of aldehydes, both aliphatic and aromatic, participated in this reaction to afford alkene-phosphine oxides in a Z-selective manner. Mechanistic experiments suggested the formation of benzophospholene-based ylide intermediates via photocatalytic cyclization of phosphinostyrenes followed by solvent-mediated proton transfer under base-free reaction conditions.

Stereodivergent atom transfer radical addition of α-functionalized alkyl iodides to alkynes: a strategy for selective synthesis of both E- and Z-iodoalkenes

The geometrical control of atom transfer radical addition (ATRA) reactions to alkynes poses significant challenges. Herein, we present a uniform solution by developing a stereodivergent synthetic method for both isomers of the resulting alkene products, starting from the same materials. The synthesis of the thermodynamically more stable isomer utilizes the strategy of uphill catalysis while the accumulation of the less stable isomer is facilitated by a manganese-catalyzed iodo-abstraction/radical rebound process, taking advantage of its reversibility. Various substituted alkyl iodides can be used to provide easy access to both isomers of iodoalkene products with valuable functional groups such as CF3, CF2H, CN, ester, or amide at the allylic position.

Three-component modular synthesis of chiral 1,3-dioxoles via a Rh-catalyzed carbenic olefination cascade

The advance of organic synthesis and the discovery of novel chemical transformations are often propelled by the rational programming of various bond-forming mechanisms and sequences that involve delicate reactive intermediates. In this study, we present an innovative Rh(ii)-catalyzed asymmetric three-component cascade reaction involving IIII/PV-hybrid ylides, aldehydes, and carboxylic acids for the synthesis of 1,3-dioxoles with moderate to good yields and high enantioselectivity. This method utilizes IIII/PV-hybrid ylides as carbene precursors to form α-PV-Rh-carbenes, which initiate the formation of carbonyl ylides, followed by stereoselective cyclization with carboxylate anions and an intramolecular Wittig olefination cascade, ultimately resulting in the modular assembly of chiral 1,3-dioxoles. By employing this strategy, we successfully coupled various aldehydes and carboxylic acids to give chiral non-benzofused 1,3-dioxole scaffolds, highlighting the potential for late-stage functionalization of biologically relevant molecules, versatile synthetic manipulation, and the production of poly-1,3-dioxole macromolecules.

Bifunctional iron-catalyzed alkyne Z-selective hydroalkylation and tandem Z-E inversion via radical molding and flipping

The challenging synthesis of thermodynamic-unfavored cis-olefins through catalytic cross-coupling reactions requires the synergistic interaction of substrate-activating units and configuration-regulating catalysts. Successfully hitting these two birds with one stone, we herein develop a convenient photoredox access to Z-alkenes from alkynes and light alkanes with a bifunctional iron-catalyzed system possessing both C(sp3)-H activation and configuration-controlling abilities. The protocol exhibits 100% atom utilization, mild conditions, a broad substrate scope, and compatibility with multitudinous functional groups. The detailed reaction mechanism and the origin of geometry regulation are well investigated by experimental and computational studies. Progressively, a catalytic amount of diaryl disulfides is introduced for consecutive photoinduced Z-E isomerization via reversible radical addition and flipping. Big steric hindrance substituents assembled on the disulfide emerge necessity for suppressing double-bond migration. This tandem strategy paves a promising way for stereoselective alkene construction and will bring significant inspiration for the development of transition metal photocatalysis.

Photoswitched Stereodivergent Synthesis of Allylic Sulfones

The present Letter demonstrates a photoswitched stereodivergent synthesis of allylic sulfones from sodium sulfinates, triphenylvinylphosphonium chloride, and (hetero)aromatic aldehydes in a single step. Mechanistically, cis-allylic sulfones, generated from the unstabilized ylide intermediates and aldehydes in situ, could be finally converted to trans-allylic sulfones via photochemical isomerization in the presence of a catalytic amount of bis(2-thienyl) ketone.

Carbonyl cross-metathesis via deoxygenative gem-di-metal catalysis

Carbonyls and alkenes are versatile functional groups, whose reactivities are cornerstones of organic synthesis. The selective combination of two carbonyls to form an alkene-a carbonyl cross-metathesis-would be a valuable tool for their exchange. Yet, this important synthetic challenge remains unsolved. Although alkene/alkene and alkene/carbonyl cross-metathesis reactions are known, there is a lack of analogous methods for deoxygenative cross-coupling of two carbonyl compounds. Here we report a pair of strategies for the cross-metathesis of unbiased carbonyls, allowing an aldehyde to be chemo- and stereoselectively combined with another aldehyde or ketone. These mild, catalytic methods are promoted by earth-abundant metal salts and enable rapid access to an unprecedentedly broad range of either Z- or E-alkenes by two distinct mechanisms-entailing transiently generated (1) carbenes and ylides (via Fe catalysis) or (2) doubly nucleophilic gem-di-metallics (via Cr catalysis).

Dual Transition Metal Electrocatalysis: Direct Decarboxylative Alkenylation of Aliphatic Carboxylic Acids

Direct decarboxylative alkenylation of widely available aliphatic carboxylic acids with vinyl halides for the synthesis of alkenes with all substitution patterns has been accomplished by means of Ce/Ni dual transition metal electrocatalysis. The reactions employ alkyl acids as the limiting reagents and exhibit a broad scope with respect to both coupling partners. Notably, simple primary alkyl carboxylic acids could be readily engaged as carbon-centered radical precursors in the reaction. This new alkenylation protocol has been successfully demonstrated in direct modification of naturally occurring complex acids and is amenable to the enantioselective decarboxylative alkenylation of arylacetic acid. Mechanistic studies, including a series of controlled experiments and cyclic voltammetry data, allow us to probe the key intermediates and the pathway of the reaction.

Programmable synthesis of difluorinated hydrocarbons from alkenes through a photocatalytic linchpin strategy

The introduction of difluoromethylene moieties into organic molecules has garnered significant attention due to their profound influence on the physicochemical and biological properties of compounds. Nonetheless, the existing approaches for accessing difluoroalkanes from readily available feedstock chemicals remain limited. In this study, we present an efficient and modular protocol for the synthesis of difluorinated compounds from alkenes, employing the readily accessible reagent, ClCF2SO2Na, as a versatile "difluoromethylene" linchpin. By means of an organophotoredox-catalysed hydrochlorodifluoromethylation of alkenes, followed by a ligated boryl radical-facilitated halogen atom transfer (XAT) process, we have successfully obtained various difluorinated compounds, including gem-difluoroalkanes, gem-difluoroalkenes, difluoromethyl alkanes, and difluoromethyl alkenes, with satisfactory yields. The practical utility of this linchpin strategy has been demonstrated through the successful preparation of CF2-linked derivatives of complex drugs and natural products. This method opens up new avenues for the synthesis of structurally diverse difluorinated hydrocarbons and highlights the utility of ligated boryl radicals in organofluorine chemistry.

Photocatalytic 1,2-Phosphorus-Migrative [3 + 2] Cycloaddition of Tri(t-butyl)phosphine with Terminal Alkynes

Tri(t-butyl)phosphine and terminal alkynes undergo 1,2-phosphorus-migrative [3 + 2] cycloaddition in the presence of a proton source under photocatalytic conditions. The reaction exhibits broad functional group tolerance and affords substituted cyclic phosphonium salts, which are amenable to further derivatization by Wittig olefination. Theoretical studies suggest that the phosphorus 1,2-migration of a β-phosphonioalkyl radical proceeds through a phosphine radical cation-alkene complex as a pseudointermediate, and the two fragments in the intermediate are bound to each other through multiple noncovalent interactions.

A Modular Olefination of Aldehydes with Thiols as Coupling Partners

Olefins range amongst the most important motifs in organic chemistry. Hence, the development of novel olefin syntheses has remained a constant field of research in synthetic chemistry to date. Herein, we report the development of a modular olefination that converts aldehydes into olefins with thiols as reaction partners. The simple, transition metal-free protocol proceeds via an unsymmetrical bissulfone intermediate which is converted into the respective alkene in a Ramberg-Bäcklund-type process. Differently substituted olefins can be synthesized from readily available starting materials in typically good yields and stereoselectivities using basic laboratory chemicals exclusively. Complementary reaction conditions differing in the choice of solvent favor the E/Z-products respectively under kinetic control rendering this protocol an interesting economical addition to the family of olefin syntheses.

Polarity Transduction Enables the Formal Electronically Mismatched Radical Addition to Alkenes

The formation of carbon-carbon bonds via the intermolecular addition of alkyl radicals to alkenes is a cornerstone of organic chemistry and plays a central role in synthesis. However, unless specific electrophilic radicals are involved, polarity matching requirements restrict the alkene component to be electron deficient. This limits the scope of a fundamentally important carbon-carbon bond forming process that could otherwise be more universally applied. Herein, we introduce a polarity transduction strategy that formally overcomes this electronic limitation. Vinyl sulfonium ions are demonstrated to react with carbon-centered radicals, giving adducts that undergo in situ or sequential nucleophilic displacement to provide products that would be inaccessible via traditional methods. The broad generality of this strategy is demonstrated through the derivatization of unmodified complex bioactive molecules.

Enantio- and Z-selective synthesis of functionalized alkenes bearing tertiary allylic stereogenic center

Olefins are ubiquitous in biologically active molecules and frequently used as building blocks in chemical transformations. However, although many strategies exist for the synthesis of stereodefined E-olefines, their thermodynamically less stable Z counterparts are substantially more demanding, while access to those bearing an allylic stereocenter with an adjacent reactive functionality remains unsolved altogether. Even the classic Wittig reaction, arguably the most versatile and widely used approach to construct Z-alkenes, falls short for the synthesis of these particularly challenging yet highly useful structural motives. Here, we report a general methodology for Z-selective synthesis of functionalized chiral alkenes that establishes readily available alkene-derived phosphines as an alternative to alkylating reagents in Wittig olefination, thus offering previously unidentified retrosynthetic disconnections for the formation of functionalized disubstituted alkenes. We demonstrate the potential of this method by structural diversification of several bioactive molecules.

Modular allylation of C(sp3)-H bonds by combining decatungstate photocatalysis and HWE olefination in flow

The late-stage introduction of allyl groups provides an opportunity to synthetic organic chemists for subsequent diversification, furnishing a rapid access to new chemical space. Here, we report the development of a modular synthetic sequence for the allylation of strong aliphatic C(sp3)-H bonds. Our sequence features the merger of two distinct steps to accomplish this goal, including a photocatalytic Hydrogen Atom Transfer and an ensuing Horner-Wadsworth-Emmons (HWE) reaction. This practical protocol enables the modular and scalable allylation of valuable building blocks and has been applied to structurally complex molecules.

Merging Carbonyl Addition with Photocatalysis

The carbonyl group stands as a fundamental scaffold and plays a ubiquitous role in synthetically important chemical reactions in both academic and industrial contexts. Venerable transformations, including the aldol reaction, Grignard reaction, Wittig reaction, and Nozaki-Hiyama-Kishi reaction, constitute a vast and empowering synthetic arsenal. Notwithstanding, two-electron mechanisms inherently confine the breadth of accessible reactivity and topological patterns.Fostered by the rapid development of photoredox catalysis, combing well-entrenched carbonyl addition and radicals can harness several unique and increasingly sustainable transformations. In particular, unusual carbon-carbon and carbon-heteroatom disconnections, which are out of reach of two-electron carbonyl chemistry, can be conceived. To meet this end, a novel strategy toward the utilization of simple carbonyl compounds as intermolecular radical acceptors was developed. The reaction is enabled by visible-light photoredox-initiated hole catalysis. In situ Brønsted acid activation of the carbonyl moiety prevents β-scission from occurring. Furthermore, this regioselective alkyl radical addition reaction obviates the use of metals, ligands, or additives, thus offering a high degree of atom economy under mild conditions. On the basis of the same concept and the work of Schindler and co-workers, carbonyl-olefin cross-metathesis, induced by visible light, has also been achieved, leveraging a radical Prins-elimination sequence.Recently, dual chromium and photoredox catalysis has been developed by us and Kanai, offering a complementary approach to the revered Nozaki-Hiyama-Kishi reaction. Leveraging the intertwined synergy between light and metal, several radical-to-polar crossover transformations toward eminent molecular motifs have been developed. Reactions such as the redox-neutral allylation of aldehydes and radical carbonyl alkylation can harvest the power of light and enable the use of catalytic chromium metal. Overall, exquisite levels of diastereoselectivity can be enforced via highly compact transition states. Other examples, such as the dialkylation of 1,3-dienes and radical carbonyl propargylation portray the versatile combination of radicals and carbonyl addition in multicomponent coupling endeavors. Highly valuable motifs, which commonly occur in complex drug and natural product architectures, can now be accessed in a single operational step. Going beyond carbonyl addition, seminal contributions from Fagnoni and MacMillan preconized photocatalytic HAT-based acyl radical formation as a key aldehyde valorization strategy. Our group articulated this concept, leveraging carboxy radicals as hydrogen atom abstractors in high regio- and chemoselective carbonyl alkynylation and aldehyde trifluoromethylthiolation.This Account, in addition to the narrative of our group and others' contributions at the interface between carbonyl addition and radical-based photochemistry, aims to provide core guiding foundations toward novel disruptive synthetic developments. We envisage that extending radical-to-polar crossovers beyond Nozaki-Hiyama-Kishi manifolds, taming less-activated carbonyls, leveraging multicomponent processes, and merging single electron steps with energy-transfer events will propel eminent breakthroughs in the near future.

Photoinduced Hydrophosphination of Terminal Alkynes with Tri(o-tolyl)phosphine: Synthesis of Alkenylphosphonium Salts

Herein reported is a photoinduced hydrophosphination reaction of terminal alkynes with tri(o-tolyl)phosphine to form alkenylphosphonium salts. The reaction is more sustainable than conventional methods since it dispenses with the need for elaborated starting materials and precious transition metals. The o-methyl groups of tri(o-tolyl)phosphine play two important roles: (1) to guide the phosphorus radical to add onto the terminal sp carbon and (2) to donate a hydrogen atom onto the developing sp² carbon radical intramolecularly.

The Conceptual Development of a Conjunctive Olefination

We recently discovered a functional group tolerant and transition metal-free conjunctive olefination reaction with applications in late-stage functionalization chemistry. In this Synpacts contribution, we analyze the conceptual background that has stimulated the discovery of this reactivity and reflect on the key aspects of its development.