Deaminative Arylation and Alkenyaltion of Aliphatic Tertiary Amines with Aryl and Alkenylboronic Acids via Nitrogen Ylides

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.

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, β-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.

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.

Base-promoted triple cleavage of CCl2Br: a direct one-pot synthesis of unsymmetrical oxalamide derivatives

We present a novel, eco-friendly and one-pot approach for synthesizing unsymmetrical oxalamides with the aid of dichloroacetamide and amine/amides in the presence of CBr4 in a basic medium. The use of water as a potent supplement for the oxygen atom source and the detailed mechanism have been disclosed. Moreover, the protocol involves triple cleavage of CCl2Br and the formation of new C-O/C-N bonds, with the advantage of achieving selective bromination using CBr4 with good to excellent yield under mild conditions. The method also demonstrates promise for industrial use, as proven by its effective implementation in gram-scale synthesis conducted in a batch process, along with its utilization in a continuous-flow system.

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.

Cooperative Triple Catalysis Enables Deaminative α-Indolmethylation of Carbonyl Compounds with Gramines

α-Functionalization of carbonyl compounds is an important reaction in synthetic chemistry. However, the development of novel synthetic strategies to realize this reaction is challenging. This study describes the α-indolmethylation of carbonyl compounds using cooperative copper, amine, and hydrogen-bond catalysis. This reaction provides a novel and efficient strategy for developing indolmethylated carbonyl compounds by deaminative coupling of gramines.

Modular and Selective Access to Functionalized Alkynes and Allenes via the Intermediacy of Propargylic Acetates

We report an efficient one-pot, two-step procedure for the modular synthesis of α-difunctionalized alkynes and trisubstituted allenes by sequential cross-coupling of benzal gem-diacetates with organozinc or -copper reagents in the absence of external transition metals. The intermediacy of propargylic acetates enables the divergent and selective synthesis of these valuable products. This method features its readily accessible substrates, relatively mild conditions, wide scope, and scalability in practical synthesis.

Unconventional Transformations of Difluorocarbene with Amines and Ethers

ConspectusFluorine-containing compounds are extensively involved in various fields originating from intriguing and unique characteristics of fluorine atom; notably, in pharmaceuticals, the involvement of a fluorine atom or a fluorine-containing group is a chief technique for improving the pesticide effect and developing new drugs. Difluorocarbene, one of the most important and powerful fluorine-containing reagents, is widely employed and studied in many areas mainly to assemble gem-difluoromethyl molecules, including but not limited to the abundant reactions between difluorocarbene with nucleophilic substrates, Wittig reaction with ketones or aldehydes, cascade reaction with both a nucleophile and an electrophile, or [2+1] cycloaddition with alkenes or alkynes. However, its unconventional and intriguing protocols beyond as a difluoromethyl synthon have rarely been studied, and thus, it is highly desired given its abundance, inexpensiveness and peculiar properties. In this Account, we mainly discuss our discovery with unconventional transformations of difluorocarbene, instead of as a sole difluoromethyl source (different from other dihalocarbene), actually can serve as an electron acceptor to activate C-X bonds (X = N and O) and thus promote a myriad of fascinating transformations for the assembly of versatile valuable products with various aza-compounds (primary/secondary/tertiary amines as well as NH₃ and NaNH₂ and so on) and aliphatic ethers in the absence of transition metals and expensive ligands. Inspired by the electron-deficient characteristics of difluorocarbene, we first found that the isocyanides could be readily formed in situ when the unoccupied orbital of difluorocarbene meets the lone-pair of primary amines; in basic condition, a cascade defluorination and cyclizations could afford plethora of valuable N-containing heterocycles. Meanwhile, we disclosed that cyano anion could be accessible in situ as well when difluorocarbene and NaNH₂ or NH₃ were mixed up in suitable basic conditions, and thus a series of aryl nitrile compounds were obtained in the presence of Pd catalysis and ArI. Interestingly, when difluorocarbene encountered secondary amines, formamides were rendered under mild reactions. Of note, concomitant functionalizations of C and N moieties via cleavage of the unstrained C(sp³)-N bond in the absence of metal and oxidant are sparce, which indeed significantly add versatility and diversity to products. Gratifyingly, by uitilizing difluorocarbene and cyclic tertiary amines, we achieved difluorocarbene-mediated deconstructive functionalizations for the first time, showing successive C(sp³)-N bond scission of amines and simultaneous functionalization of C and N atoms which would be introduced into the products in the absence of transition metals and oxidants. This method provides a brand-new while very universal synthetic pathway to selectively cleave inert unactivated Csp³-N bonds, in which halodifluoromethyl reagents act as both C1 synthon and halo (Cl, Br, I) sources. Fascinatingly, nitrogen ylides are generated in situ from difluorocarbene and tertiary amines, and an intriguing and universal approach for deaminative arylation or alkenylation of tertiary amines was disclosed for the first time in appropriate basic conditions, which represents an intriguing reaction mode to lead to a formal transition-metal free Suzuki cross coupling. Besides, we also disclosed that difluorocarbene could proceed novel atom recombination to render meaningful 2-fluoroindoles or 3-(2,2-difluoroethyl)-2-fluoroindoles from ortho-vinylanilines, 3-fluorined oxindoles from 2-aminoarylketones, in which difluorocarbene acts as a C1 synthon and F1 source simultaneously. Last but not the least, we recently found that the lone-pair-electron of oxygen could trap difluorocarbene as well to form oxonium ylide, which eventually leads to C-O bond cleavage with the formation of difluoromethyl ethers.

Difluorocarbene-Enabled Synthesis of 3-Alkenyl-2-oxindoles from ortho-Aminophenylacetylenes

Herein, we report a transition-metal-free [4 + 1] cyclization pathway from difluorocarbene and ortho-amino aryl alkynone, rendering an effective and universal strategy for the construction of 3-alkenyl-2-oxindoles. Our strategy starts from cheap and accessible ortho-amino aryl alkynone instead of the direct indole skeleton; moreover, in situ generated difluorocarbene from commercially available halogenated difluoroalkylative reagents enables the cleavage of a C-N bond and formation of new C-N bonds and C-C bonds.