Photogeneration of ß-Borylsilyl Radical via Decarboxylation of N-Hydroxyphthalimide Esters.

Gem-borylsilylalkanes are versatile intermediates in organic synthesis, and the traditional synthesis methods have mainly focused on metal reagents, the insertion reactions of diazo compounds, and hydrosilylation/hydroborylation reactions of unsaturated bonds. Herein, a novel, efficient gem-borylsilylalkanes synthesis via a radical approach is reported. This method introduced a ß-gem-borylsilyl NHPI ester as the precursor of the ß-borylsilyl radical that, coupling with radical acceptors under photo conditions, and the corresponding gem-borylsilylalkanes bearing unsaturated bonds, facilitate subsequent transformations.

Interception of Alkynyl Tetracoordinate Borons with Sulfur Electrophiles beyond the Zweifel Pathway.

Zweifel reaction is a powerful strategy to construct olefins from alkenyl tetracoordinate borons in organoboron chemistry, however, it usually only involves one functional group migration and then undergoes an elimination process affording alkenes or alkynes exclusively. Herein, we disclose several intriguing interception of alkynyl tetracoordinate borons with sulfur electrophiles. Wherein, the substituted benzothiophenes are accessed by consecutive 1,2-migrations and intramolecular electrophilic substitution, meanwhile, the challenging and elusive five/four-membered boracycles are easily assembled, and an approach to alkenyl sulfides with good stereoselectivity was developed as well. Moreover, by adding readily available deuterium sources, the tetrasubstituted deuterated alkenyl sulfides with high deuteration rates are constructed. These protocols not only improve atom economy by prohibiting the elimination of Zweifel intermediate, but also enriches the reaction modes of alkynyl tetracoordinate borons achieving versatile value-added sulfur-containing molecules. Mechanistic investigations illustrate that dichlorosulfoxide (SOCl2) and dialkylaminosulfur trifluoride-type reagents (DAST-type) as surfur sources could promote dual 1,2-aryl migration of alkynyl tetracoordinate borons, which are distinct from traditional Zweifel reaction, and the regulation of steric hindrance could also make four-membered boracycles and alkenyl sulfides feasible. And these transformations feature novel reaction modes and unusual reaction mechanisms with valuable products in high efficiency.

Rh(III)-Catalyzed Regioselective Alkyne Insertion in the Context of C-H Activation and Lactonization Reactions: Synthesis of Fused 1,2-Oxaphospholenes.

Herein, we report an expedient synthesis of fused phosphorus-containing heterocycles via Rh-catalyzed cascade C-H activation, alkyne insertion, and lactonization reactions. The substrate scope and the group tolerance are good, as various substituted benzoic acids, N-methoxybenzamides, and 2-phenylindoles could go through the reactions smoothly to afford the corresponding products in moderate to high yields. Additionally, excellent regioselectivities are shown in the alkyne insertion with the assistance of an electron-withdrawing phosphonate group.

Photo-induced decarboxylative C-S bond formation to access sterically hindered unsymmetric S-alkyl thiosulfonates and SS-alkyl thiosulfonates.

Due to the high reactivity and versatility of benzenesulfonothioates, significant advancements have been made in constructing C-S bonds. However, there are certain limitations in the synthesis of S-thiosulfonates and SS-thiosulfonates, especially when dealing with substantial steric hindrance, which poses a significant challenge. Herein, we present an innovative approach for assembling unsymmetric S-thiosulfonates and unsymmetric SS-thiosulfonates through the integration of dual copper/photoredox catalysis. Moreover, we also realized the one-pot strategy by directly using carboxylic acids as raw materials by in-situ activation of them to access S-thiosulfonates and SS-thiosulfonates without further purification and presynthesis of NHPI esters. The envisaged synthesis and utilization of these reagents are poised to pioneer an innovative pathway for fabricating a versatile spectrum of mono-, di-, and polysulfide compounds. Furthermore, they introduce a class of potent sulfenylating reagents, empowering the synthesis of intricate unsymmetrical disulfides that were previously challenging to access.

Difluorocarbene-induced [1,2]- and [2,3]-Stevens rearrangement of tertiary amines.

The [1,2]- and [2,3]-Stevens rearrangements are one of the most fascinating chemical bond reorganization strategies in organic chemistry, and they have been demonstrated in a wide range of applications, representing a fundamental reaction tactic for the synthesis of nitrogen compounds in chemical community. However, their applicabilities are limited by the scarcity of efficient, general, and straightforward methods for generating ammonium ylides. Herein, we report a general difluorocarbene-induced tertiary amine-involved [1,2]- and [2,3]-Stevens rearrangements stemmed from in situ generated difluoromethyl ammonium ylides, which allows for the rearrangements of versatile tertiary amines bearing either allyl, benzyl, or propargyl groups, resulting in the corresponding products in one reaction under the same reaction conditions with a general way. Broad substrate scope, simple operation, mild reaction conditions and late-stage modification of natural products highlight the advantages of this strategy, meanwhile, this general rearrangement reaction is believed to bring opportunities for the transformations of nitrogen ylides and the assembly of valuable tertiary amines and amino acids. This will further enrich the reaction repertoire of difluorocarbene species, facilitate the development of reactions involving difluoromethyl ammonium salts, and provide an avenue for the development of this type of rearrangement reactions.

Chemo-, regio- and stereoselective access to polysubstituted 1,3-dienes via Nickel-catalyzed four-component reactions.

1,2-Difunctionalization of alkynes offers a straightforward approach to access polysubstituted alkenes. However, simultaneous multi-component cascade transformations including difunctionalization of two alkynes with both syn- and anti-selectivity in one catalyst system is undeveloped and proves to be a significant challenge. Herein, we report a Nickel-catalyzed four-component reaction to access polysubstituted 1,3-dienes using two terminal alkynes, aryl boroxines, and perfluoroalkyl iodides, wherein the reaction forms three new C-C bonds in a single vessel and serve as a modular strategy to access polysubstituted 1,3-dienes with excellent chemoselectivity, good regioselectivity and exclusive stereoselectivity. Control experiments reveal the plausible reaction mechanism and DFT calculations explain the cause for the formation of this unusual four-component reaction. Furthermore, we successfully incorporate two biologically active units into 1,2,3,4-tetrasubstituted 1,3-dienes, which greatly increases the diversity of molecular scaffolds and brings more potential values to medicinal chemistry, the synthetic utility of our protocol is further demonstrated by the late-stage transformations.

Enantioselective copper-catalyzed B-H bond insertion reaction of α-diazo phosphonates to access chiral α-boryl phosphonates.

Chiral phosphorus-containing compounds find applications across various fields, including asymmetric catalysis, medicinal chemistry, and materials science. Despite the abundance of reported highly enantioselective methods for synthesizing various chiral phosphorus compounds, the enantioselective synthesis of α-boryl phosphorus compounds still remains an unknown territory. Here, we report a method for the construction of chiral α-boryl phosphates by asymmetric B-H insertion reaction using α-diazo phosphates as carbene precursors, cheap and readily available copper salt as the catalyst and chiral oxazoline as the ligand. This method can directly afford a series of stable α-boryl phosphates with a yield up to 97% and an enantioselectivity up to 98% ee. The operating procedure of this method is straightforward, offering a broad substrate applicability, remarkable tolerance towards various functional groups, and gentle reaction conditions.

Highly Stereoselective Synthesis of Multisubstituted Olefins from Alkynyl Tetracoordinate Borons and Iodonium Ylides via a Cyclic Intermediate.

We developed an intriguing and practical strategy for highly stereoselective assembly of multisubstituted olefins from alkynyl tetracoordinate boron species via a cyclic intermediate with 1,2-phenyl migration. We also developed a general method for the construction of deuterated trisubstituted alkenes from a cheap deuteration source, D2O, and the corresponding deuterated trisubstituted alkenes were obtained with excellent deuteration rates. This transformation features a novel reaction mechanism, exclusive stereoselectivity, and deuterated trisubstituted alkenes with excellent deuteration ratios.

Difluorocarbene Enables Access to 2,2-Difluorohydrobenzofurans and 2-Fluorobenzofurans from ortho-Vinylphenols.

2-Fluorobenzofurans are the backbone structures of many drug molecules and have many potential therapeutic bioactivities. Despite the potential applications in medicinal chemistry, practical and efficient synthetic methods for the construction of 2-fluorobenzofuran are very limited. Herein, we report an efficient and general method for the construction of 2-fluorobenzofurans. Contrary to the previous functionalizations of the existing backbone of benzofuran, our strategy directly constructs benzofuran scaffolds alongside the incorporation of fluorine atom on C2 position in a formal [4 + 1] cyclization from readily accessible ortho-vinylphenols and difluorocarbene. In our strategy, ClCF2H decomposes into difluorocarbene in the presence of base, which is further captured by the oxygen anion from the hydroxy group in ortho-hydroxychalcones; subsequent intramolecular Michael addition to the α, ß-unsaturated system leads to 2,2-difluorohydrobenzofurans, and further fluorine elimination renders 2-fluorobenzofurans by forming one C-O bond and one C-C double bond. Of note, various complex 2,2-difluorohydrobenzofurans and 2-fluorobenzofurans could be readily accessed through our protocol via the late-stage elaborations.

Copper-catalysed asymmetric hydroboration of alkenes with 1,2-benzazaborines to access chiral naphthalene isosteres.

Bioisosteric replacement has emerged as a clear strategy for drug-structure optimization. Naphthalene is the core element of many chiral pharmaceuticals and drug candidates. However, as a promising isostere of naphthalene, the chiral version of 1,2-benzazaborine has rarely been explored due to the lack of efficient synthetic methods. Here we describe a copper-catalysed enantioselective hydroboration of alkenes with 1,2-benzazaborines. The method provides a general platform for the atom-economic and efficient construction of diverse chiral 1,2-benzazaborine compounds (more than 60 examples) that bear a 2-carbon-stereogenic centre or allene skeleton in high yields and excellent enantioselectivities. Three 1,2-benzazaborine analogues of bioactive chiral naphthalene-containing molecules have been prepared, and a series of transformations around chiral 1,2-benzazaborines have also been developed. Notably, the hydroboration process of this study reveals that the identity of 1,2-benzazaborine plays an essential role in the rate-determining step and catalyst resting state.

Unlocking Diverse π-Bond Enrichment Frameworks by the Synthesis and Conversion of Boronated Phenyldiethynylethylenes.

The π-bond enrichment frameworks not only serve as a crucial building block in organic synthesis but also assume a pivotal role in the fields of materials science, biomedicine, photochemistry, and other related disciplines owing to their distinctive structural characteristics. The incorporation of various substituents into the C═C double bonds of tetrasubstituted alkenes is currently a highly significant research area. However, the synthesis of tetrasubstituted alkenes with diverse substituents on double bonds poses a significant challenge in achieving stereoselectivity. Here, we reported an efficient and convergent route of Cu-catalyzed borylalkynylation of both symmetrical and unsymmetrical 1,3-diynes, B2pin2, and acetylene bromide to the construction of boronated phenyldiethynylethylene (BPDEE) derivatives with excellent chemo-, stereo-, and regioselectivities. BPDEE derivatives could transform into novel tetrasubstituted organic π-conjugated gem-diphenyldiethynylethylene (DPDEE), vinylphenyldiethynylethylene (VPDEE), and phenyltriethynylethylene (PTEE) derivatives by a stepwise process, which provides a flexible platform for the synthesis of complex π-bond enrichment frameworks that were difficult to synthesize by previous methods. The initial optical characterization revealed that the synthesized molecules exhibited aggregation-induced emission (AIE) properties, which further establishes the groundwork for future applications and enriches and advances the field of functional π-conjugated frameworks research.

1,1-Oxycarbonation of Terminal Alkynes via Sequential Borylation, 1,2-Migration, and Oxidation with Oxone.

Alkynes are readily available and multifunctional synthetic intermediates, but their 1,1-oxofunctionalization remains challenging. Herein, we report a 1,1-oxycarbonation of terminal alkynes to construct ketones through sequential borylation, 1,2-carbon migration, and oxidation with Oxone as the proton source and oxidant. The synthetic potential of this transformation is showcased by the broad functional groups, scale-up synthesis, and diverse product transformations.

"Homoleptic" Tetracoordinate Boron Compounds.

"Homoleptic" tetracoordinate boron compounds, in which the central boron atom links to four identical atoms, are a special and important family of boron compounds. During the past decades, they have been extensively employed in inorganic, organic, macromolecular, and materials chemistry. Many of them exhibit a diverse range of outstanding properties, and therefore, the synthesis and application of those compounds have emerged as a hot research topic in modern boron chemistry. This review summarizes and discusses the "homoleptic" tetracoordinate boron compounds, which are organized according to the kinds of atoms coordinated to the central boron.

Recent progress in the catalytic enantioselective reactions of 1,1-diborylalkanes.

Organoboron compounds are environmentally benign, have low toxicity and are versatile reagents that are extensively employed in organic synthesis, especially in the realm of asymmetric synthesis. The last several decades have witnessed a tremendous outburst of asymmetric reactions based on various organoboron compounds. Among them, 1,1-diborylalkanes, which contain two boryl groups at the same sp3-carbon atom, are regarded as some of the most versatile and powerful reagents for their unique structure and unusual reaction mode in organic synthesis. Moreover, owing to the stabilizing effect of the empty p-orbital of the neighboring boron atoms and the inherent good steric-hindrance, 1,1-diborylalkanes often exhibit extraordinary reactivity and stereoselectivity compared to other kinds of organoboron compounds in asymmetric synthesis. Herein, the present highlight summarizes and discusses the recent progress achieved in the catalytic enantioselective reactions of 1,1-diborylalkanes during the past decade.

N-Heterocycle-Editing to Access Fused-BN-Heterocycles via Ring-Opening/C-H Borylation/Reductive C-B Bond Formation.

Skeletal editing of N-heterocycles has recently received considerable attention, and the introduction of boron atom into heterocycles often results in positive property changes. However, direct enlargement of N-heterocycles through boron atom insertion is rarely reported in the literature. Here, we report a N-heterocyclic editing reaction through the combination boron atom insertion and C-H borylation, accessing the fused-BN-heterocycles. The synthetic potential of this chemistry was demonstrated by substrate scope and late-stage diversification of products.

Palladium-Catalyzed Difluorocarbene Transfer Enabled Divergent Synthesis of γ-Butenolides and Ynones from Iodobenzene and Terminal Alkynes.

Herein, we report a ligand-controlled palladium-catalyzed method that enables the synthesis of ynones and γ-butenolides with excellent regioselectivity from the same set of readily available aryl iodides, aryl acetylenes, and BrCF2CO2K. In this reaction, the [PdII]═CF2 does demonstrate electrophilicity and can generate CO readily when reacting with H2O. It is environmentally friendly and safe compared to traditional methods, and the current protocol enables us to afford ynones and γ-butenolides in high yields with excellent functionality tolerance. Moreover, esters can also be obtained with corresponding phenols and alcohols utilizing this strategy. The success of late-stage functionalization of bioactive compounds further illustrates the synthetic utility of this protocol in material development and drug discovery.

Ni-catalysed assembly of axially chiral alkenes from alkynyl tetracoordinate borons via 1,3-metallate shift.

Asymmetric synthesis based on a metallate shift of tetracoordinate borons is an intriguing and challenging topic. Despite the construction of central chirality from tetracoordinate boron species via a 1,2-metallate shift, catalytic asymmetric synthesis of axially chiral compounds from such boron 'ate' complexes is an ongoing challenge. Axially chiral alkenes have received great attention due to their unique characteristics and intriguing molecular scaffolds. Here we report an enantioselective nickel-catalysed strategy for the construction of axially chiral alkenes via a 1,3-metallate shift of alkynyl tetracoordinate boron species. The chemoselectivity, regioselectivity and atroposelectivity can be regulated and well-controlled from readily accessible starting materials with a cheap transition-metal catalyst. Downstream transformations indicate the powerful conversion ability of such compounds in this protocol, and late-stage elaborations of bioactive compounds can also be achieved. Mechanistic experiments reveal that regioselective syn-addition of an aryl-Ni complex with a carbon-carbon triple bond and subsequent 1,3-phenyl migration are the two key steps for the synthesis of axially chiral alkenes.

Palladium-Catalyzed Atroposelective Kinetic C-H Olefination and Allylation for the Synthesis of C-B Axial Chirality.

The direct C-H functionalization of 1,2-benzazaborines, especially asymmetric version, remains a great challenge. Here we report a palladium-catalyzed enantioselective C-H olefination and allylation reactions of 1,2-benzazaborines. This asymmetric approach is a kinetic resolution (KR), providing various C-B axially chiral 2-aryl-1,2-benzazaborines and 3-substituted 2-aryl-1,2-benzazaborines in generally high yields with excellent enantioselectivities (selectivity (S) factor up to 354). The synthetic potential of this reaction is showcased by late-stage modification of complex molecules, scale-up reaction, and applications.

Decarboxylation of ß-boryl NHPI esters enables radical 1,2-boron shift for the assembly of versatile organoborons.

In recent years, numerous 1,2-R shift (R = aliphatic or aryl) based on tetracoordinate boron species have been well investigated. In the contrary, the corresponding radical migrations, especially 1,2-boryl radical shift for the construction of organoborons is still in its infancy. Given the paucity and significance of such strategies in boron chemistry, it is urgent to develop other efficient and alternative synthetic protocols to enrich these underdeveloped radical 1,2-boron migrations, before their fundamental potential applications could be fully explored at will. Herein, we have demonstrated a visible-light-induced photoredox neutral decarboxylative radical cross-coupling reaction, which undergoes a radical 1,2-boron shift to give a translocated C-radical for further capture of versatile radical acceptors. The mild reaction conditions, good functional-group tolerance, and broad ß-boryl NHPI esters scope as well as versatile radical acceptors make this protocol applicable in modification of bioactive molecules. It can be expected that this methodology will be a very useful tool and an alternative strategy for the construction of primary organoborons via a novel radical 1,2-boron shift mode.

Synthesis of Phosphachromones by Cyclized Coupling of Ethyl Hydrogen (Phenylethynyl)phosphonate with Arynes.

A straightforward and efficient strategy for the synthesis of phosphachromones has been reported via the insertion of arynes into P-O bonds. This operationally simple reaction is compatible with different functional groups, affording various phosphachromones by the simultaneous formation of C-P and C-O bonds in one step with moderate to good yields, and the Fries rearrangement involving phosphorus atoms is a key step in the reaction.