Three-Component Coupling Reactions Involving Arynes, Phosphites, and Aldehydes toward 3-Mono-Substituted Benzoxaphosphole 1-Oxides

A mild, efficient, and transition-metal-free three-component coupling reaction involving arynes, phosphites, and aldehydes was established to afford 3-mono-substituted benzoxaphosphole 1-oxides. A range of 3-mono-substituted benzoxaphosphole 1-oxides was obtained from both aryl- and aliphatic-substituted aldehydes in moderate to good yields. Moreover, the synthetic utility of the reaction was demonstrated by a Gram-scale reaction and the transformation of the products into various P-containing bicycles.

Improvements, Variations and Biomedical Applications of the Michaelis-Arbuzov Reaction

Compounds bearing the phosphorus–carbon (P–C) bond have important pharmacological, biochemical, and toxicological properties. Historically, the most notable reaction for the formation of the P–C bond is the Michaelis–Arbuzov reaction, first described in 1898. The classical Michaelis–Arbuzov reaction entails a reaction between an alkyl halide and a trialkyl phosphite to yield a dialkylalkylphosphonate. Nonetheless, deviations from the classical mechanisms and new modifications have appeared that allowed the expansion of the library of reactants and consequently the chemical space of the yielded products. These involve the use of Lewis acid catalysts, green methods, ultrasound, microwave, photochemically-assisted reactions, aryne-based reactions, etc. Here, a detailed presentation of the Michaelis–Arbuzov reaction and its developments and applications in the synthesis of biomedically important agents is provided. Certain examples of such applications include the development of alkylphosphonofluoridates as serine hydrolase inhibitors and activity-based probes, and the P–C containing antiviral and anticancer agents.

Benzyne-Mediated Esterification Reaction

A benzyne-mediated esterification of carboxylic acids and alcohols under mild conditions has been realized, which is made possible via a selective nucleophilic addition of carboxylic acid to benzyne in the presence of alcohol. After a subsequent transesterification with alcohol, the corresponding esters can be produced efficiently. This benzyne-mediated protocol can be used on the modification of Ibuprofen, cholesterol, estradiol, and synthesis of nandrolone phenylpropionate. In addition, benzyne can also be used to promote lactonization and amidation reaction.

The Aryne-Abramov Reaction as a 1,2-Benzdiyne Platform for the Generation and Solvent-Dependent Trapping of 3-Phosphonyl Benzynes

Synthetic methodology utilizing two aryne intermediates (i.e., a formal benzdiyne) enables the rapid generation of structurally complex molecules with diverse functionality. This report describes the sequential generation of two ortho-benzyne intermediates for the synthesis of 2,3-disubstituted aryl phosphonates. Aryl phosphonates have proven useful in medicinal chemistry and materials science, and the reported methodology provides a two-step route to functionally dense variants by way of 3-phosphonyl benzyne intermediates. The process begins with regioselective trapping of a 3-trifloxybenzyne intermediate by an O-silyl phosphite in an Abramov-like reaction to bond the strained Csp carbons with phosphorus and silicon. Standard aryne-generating conditions follow to convert the resulting 2-silylphenyl triflate into a 3-phosphonyl benzyne, which readily reacts with numerous aryne trapping reactants to form a variety of 2,3-difunctionalized aryl phosphonate products. DFT computational studies shed light on important mechanistic details and revealed that 3-phosphonyl benzynes are highly polarizable. Specifically, the distortion in the internal bond angles at each of the Csp atoms was strongly influenced by both the electronegativity of the phosphonate ester groups as well as the dielectric of the computational solvation model. These effects were verified experimentally as the regioselectivity of benzyl azide trapping increased with more electronegative esters and/or increasingly polar solvents. Conversely, replacing the conventional solvent, acetonitrile, with nonpolar alternatives provided attenuated or even inverted selectivities. Overall, these studies showcase new reactivity of benzyne intermediates and extend the aryne relay methodology to include organophosphonates. Furthermore, this work demonstrates that the regioselectivity of aryne trapping reactions could be tuned by simply changing the solvent.

Nucleophilic transformations of azido-containing carbonyl compounds via protection of the azido group

Nucleophilic transformations of azido-containing carbonyl compounds are discussed. The phosphazide formation from azides and di(tert-butyl)(4-(dimethylamino)phenyl)phosphine (Amphos) enabled transformations of carbonyl groups with nucleophiles such as lithium aluminum hydride and organometallic reagents. The good stability of the phosphazide moiety allowed us to perform consecutive transformations of a diazide through triazole formation and the Grignard reaction.

Recent advances in the synthesis of organophosphorus compounds via Kobayashi's aryne precursor: a review

This review systematically summarizes the progress in aryne chemistry for the synthesis of organophosphorus compounds via aryne insertion into the C–P, P–N, P–P, P–O, PP, PN and PS bonds.

Aryne insertion into the PO bond: one-pot synthesis of quaternary phosphonium triflates

A novel transition-metal free synthetic strategy for the direct synthesis of quaternary phosphonium triflates via insertion of aryne into phosphine oxide.

Diphosphination of Arynes with Diphosphines

A diphosphination of arynes with diphosphines has been developed. The reaction of stable aryne precursors, 2-(trimethylsilyl)aryl triflates, with tetraaryldiphosphines proceeds in the presence of fluorine- or carbonate-based activators to deliver the corresponding diphosphinated products, sterically and electronically tuned 1,2-bis(diphenylphosphino)benzene (dppbz) derivatives, which can find wide application in transition metal catalysis and material science. Additionally, preliminary computational studies on the reaction mechanism are also reported.

Mild synthesis of triarylsulfonium salts with arynes

Reactions between arynes and alkyl sulfides have been extensively studied over the past few decades. These reactions commonly end with a dealkylation process and thus deliver thioethers as final products. In contrast, the transformation described furnishes valuable triarylsulfonium salts, in lieu of thioethers, from arynes and diarylsulfides. The reaction features mild conditions and a broad substrate scope. A suite of functional groups such as ketones, esters, nitriles, aryl ethers and aryl halides is tolerated, which can be issues faced by traditional synthetic methods. The practicality of the reaction and its extension to the synthesis of triphenyl selenonium salt are also exhibited herein.

Staudinger reaction using 2,6-dichlorophenyl azide derivatives for robust aza-ylide formation applicable to bioconjugation in living cells

Efficient formation of water- and air-stable aza-ylides has been achieved by the Staudinger reaction. The reaction proceeds rapidly and has been successfully applied to chemical modification of proteins in living cells.

Recent progress in the synthesis of phosphorus-containing indole derivatives

Phosphorus-containing indole derivatives represent a special class of phosphorus-containing nitrogen heterocycles. This review summarizes the recent progress in the synthesis of such compounds, briefly discusses the reaction mechanisms and challenges, and outlines the synthetic opportunities still open.

Expanding the synthesizable multisubstituted benzo[b]thiophenes via 6,7-thienobenzynes generated from o-silylaryl triflate-type precursors

Various 2,3-disubstituted 6,7-thienobenzynes have been efficiently generated from the corresponding o-silylaryl triflate-type precursors by activation with fluoride ions. The method has expanded the scope of synthesizable multisubstituted benzothiophenes, including those with various heteroatom substituents, and can be applied to the synthesis of EP4 antagonist analogs.

Various multisubstituted benzothiophenes, including those with various heteroatom substituents and EP4 antagonist analogs, have been prepared easily via 6,7-thienobenzynes generated from o-silylaryl triflate-type precursors.

Insertion of Arynes into P-O Bonds: One-Step Simultaneous Construction of C-P and C-O Bonds

The insertion of arynes into P-O bonds for the preparation of o-hydroxy-substituted arylphosphine oxides, -phosphinates, and -phosphonates is described. This novel reaction leads to the simultaneous formation of C-P and C-O bonds in one step with good yields and regioselectivities under mild and transition-metal-free conditions. The easy follow-up transformations of the resulting o-hydroxyl group extend these reactions to the facile construction of other ortho-substituted arylphosphorus compounds.

Preparation of Aryne-Nickel Complexes from ortho-Borylaryl Triflates

A facile method for preparing diverse aryne-nickel complexes from readily synthesized ortho-borylaryl triflates is described. Exploratory synthetic applications, including the synthesis of 1,2-difunctionalized arenes, based on the nucleophilic character of the aryne-nickel complexes are also demonstrated.

Generation of cycloheptynes and cyclooctynes via a sulfoxide-magnesium exchange reaction of readily synthesized 2-sulfinylcycloalkenyl triflates

Cycloheptynes and cyclooctynes were efficiently generated via a sulfoxide-magnesium exchange reaction of readily synthesized 2-sulfinylcycloalkenyl triflates. Cycloadditions between various ynophiles and the cycloalkynes generated by this method proceeded efficiently, providing an easy method to prepare a wide range of heterocycles fused with seven- or eight-membered carbocycles.

Thiazolobenzyne: a versatile intermediate for multisubstituted benzothiazoles

Thiazolobenzynes were efficiently generated from ortho-iodoaryl triflate-type precursors, which enabled facile synthesis of various multisubstituted benzothiazoles.

Direct thioamination of arynes via reaction with sulfilimines and migratory N-arylation

A novel method for preparing a diverse range of o-sulfanylanilines is described. Direct thioamination of arynes with sulfilimines gives o-sulfanylanilines, involving C-N and C-S bond formations and migratory N-arylation.

An Alternative Method for Generating Arynes from ortho-Silylaryl Triflates: Activation by Cesium Carbonate in the Presence of a Crown Ether

An alternative method for generating arynes from ortho-silylaryl triflates using cesium carbonate and 18-crown-6 is reported. The method was efficiently applied to a variety of reactions between several arynes and arynophiles. We also demonstrated that the efficiency of aryne generation is significantly affected by the alkali metal countercation of the carbonate.

Pd-catalyzed three-component coupling of terminal alkynes, arynes, and vinyl cyclopropane dicarboxylate

A palladium-catalyzed three-component coupling involving in situ generated arynes, terminal alkynes, and vinyl cyclopropane dicarboxylate has been developed. The process demonstrates the first example of aryne chemistry combined with the ring opening of vinyl cyclopropanes. This efficient method using readily available starting materials generates two new carbon-carbon bonds in one pot.

A mild and facile synthesis of aryl and alkenyl sulfides via copper-catalyzed deborylthiolation of organoborons with thiosulfonates

A simple, efficient, and odorless deborylthiolation of aryl- and alkenylborons with thiosulfonates has been achieved under mild conditions using a copper catalyst.

Synthesis of ortho-haloaminoarenes by aryne insertion of nitrogen-halide bonds

A rapid and general access to ortho-haloaminoarenes has been developed by aryne insertion into N-chloramine, N-bromoamine, and N-iodoamine bonds via two complementary protocols harnessing fluoride-promoted 1,2-elimination of ortho-trimethylsilyl aryltriflates. Typically, electron-deficient N-chloramines effectively react with aryne intermediates generated at elevated temperature with CsF, while less stable N-haloamines are found more efficient under milder, TBAF-mediated aryne formation at room temperature. Both protocols demonstrate a good level of regioselectivity and functional group tolerance. Efforts to elucidate the mechanism of N-X insertion are also discussed. The practical value of this transformation is highlighted by rapid synthesis of novel analogues of the antipsychotic cariprazine.