Copper-Catalyzed Vicinal Chloro-thiolation of Alkynes with Sulfonyl Chlorides

Reactions of alkynes with C-S bond formation: recent developments

Alkynes are important in organic synthesis. This review mainly focuses on recent advances (2013-2023) on alkynes with C-S bond formation, based on more than 30 types of sulfur reagents. The reactions of alkynes with various sulfur-containing compounds including RSSR (disulfides), RSH (thiols), S8 (elemental sulphur), alkynyl thioethers, RSCN, AgSCF3, K2S, Na2S, dithiane, RSCl, NFSI, RNCS, EtOCS2K, thiocarbamate, RSONH2, thiourea, sulfoxide, RSO2N3, CS2, RSO2NH2, RSO2NHNH2, RSO2Cl, RSO2Oar, RSO2SR', DABCO·(SO2)2, Na2S2O5, K2S2O5, RSO2H, RSO2Na and related compounds are discussed. Diverse mechanisms such as radical, electrophilic/nucleophilic addition, rearrangement, C-C bond cleavage, and CuAAC are discussed. The content is organized by substrates and reactivity patterns. We hope it will help in future research in this area.

Copper-Catalyzed 1,2-Sulfonyletherification of 1,3-Dienes

A selective three-component 1,2-sulfonyl etherification of aryl 1,3-dienes enabled by copper catalysis to afford biologically interesting alkenyl 1,2-sulfone ether derivatives through C-S and C-O bond formation is described. The protocol proceeds with the sulfonyl chloride and alcohols under simple, mild, and base-free conditions, providing a straightforward route to sulfonylated allyl ether compounds with broad functional group tolerance and excellent chemo- and regioselectivity. Mechanistic studies indicate that the selective alkene difunctionalization includes a key copper-mediated single-electron transfer process.

One-pot synthesis of 11-sulfenyl dibenzodiazepines via tandem sulfenylation/cyclization of o-isocyanodiaryl amines and diaryl disulfides

A one-pot sulfenylation/cyclization of o-isocyanodiaryl amines has been described for the preparation of 11-sulfenyl dibenzodiazepines. This AgI-catalyzed reaction covers an unexplored tandem process to give seven-membered N-heterocycles. This transformation shows a broad range of substrate scope, simple operation, and moderate to good yields under aerobic conditions. Diphenyl diselenide can also be produced in an acceptable yield.

Copper-Catalyzed C2- or C3-Thioglycosylation of Indoles with N-(Thioglycosides)succinimides: An Effective Strategy for the Total Synthesis of Isatindigotindolosides

Isatindigotindolosides, indoles containing a 1-S-β-glucopyranosyl unit at position C2, show promising bioactivity. Here, we report a copper-catalyzed C2- or C3-thioglycosylation of indoles with N-(thioglycosides)succinimides to construct indole alkaloid glucosides. This reaction is widely tolerant of functional groups, as various indoles and thioglycosides are suitable. It also provides a reliable method for performing late-stage modifications of natural products, such as gramine and melatonin. Total syntheses of isatindigotindolosides I and II were successfully accomplished using the C2-thioglycosylation reaction as a key step.

Photochemical halogen-bonding assisted generation of vinyl and sulfur-centered radicals: stereoselective catalyst-free C(sp2)-S bond forming reactions

The combination of photochemistry and halogen bonding interactions has risen in the last few years as a powerful synthetic tool for the creation of radical intermediates under mild conditions. In the formation of carbon-centered radicals, this reactivity has been to date restricted to the employment of aryl and alkyl halides as precursors. We now envisioned that the halogen-bonding initiated formation of highly reactive vinyl radicals would be a feasible process for the photochemical cross-coupling between thiols and alkenyl halides under basic conditions. The reaction shows indeed a very broad functional group tolerance, is stereoselective, simple and scalable. In-depth mechanistic studies point at the formation of vinyl and sulfur-centered radicals as the intermediates of the reaction and DFT calculations support the pre-formation of a halogen-bonding complex as the initiator of the photochemical transformation. Synthetic applications were developed to extend the utility of this methodology.

Controlling Selectivity in Shuttle Hetero-difunctionalization Reactions: Electrochemical Transfer Halo-thiolation of Alkynes

Shuttle hetero-difunctionalization reaction, in which two chemically distinct functional groups are transferred between two molecules, has long been an unmet goal due to the daunting challenges in controlling the chemo-, regio-, and stereoselectivity. Herein, we disclose an electrochemistry enabled shuttle reaction (e-shuttle) to selectively transfer one RS^- and one X^- group between β-halosulfides and unsaturated hydrocarbons via a consecutive paired electrolysis mechanism. The preferential anodic oxidation of one anion over the other, which is controlled by their distinct redox potentials, plays a pivotal role in controlling the high chemoselectivity of the process. This easily scalable methodology enables the construction of a myriad of densely functionalized β-halo alkenyl sulfides in unprecedented chemo-, regio-, and stereoselectivity using benign surrogates, e.g., 2-bromoethyl sulfide, avoiding the handling of corrosive and oxidative RS-Br reagents. In a broader context, these results open up new strategies for selective shuttle difunctionalization reactions.

DBU-Promoted Deaminative Thiolation of 1H-Benzo[d]imidazol-2-amines and Benzo[d]oxazol-2-amines

A facile and efficient catalyst-/metal-/oxidant-free DBU-promoted deaminative thiolation reaction of 1H-benzo[d]imidazol-2-amines and benzo[d]oxazol-2-amines has been developed at room temperature conditions in a one-pot protocol. This practical three-component strategy represents a novel and environmentally friendly reaction pathway toward the straightforward synthesis of various 2-thio-1H-benzo[d]imidazoles and 2-thiobenzo[d]oxazoles using carbon disulfide as a sulfur source through C-N bond cleavage and C-S bond formation process. Different types of 1H-benzo[d]imidazol-2-amines, benzo[d]oxazol-2-amines, and organic bromides are suitable substrates. The gram-scale and late-stage modification experiments provide the potential applications based on this methodology in the field of organic and medicinal chemistry.

Stereoselective Synthesis of (Z)-1,2-Bis(arylsulfanyl)ethenes with Calcium Carbide as a Solid Alkyne Source

A concise stereoselective synthesis of (Z)-1,2-bis(arylsulfanyl)ethenes by the reaction of arylsulfonyl chlorides with calcium carbide in the presence of cuprous iodide as a catalyst is described. The salient features of this protocol are its use of an inexpensive and easily handled solid alkyne source as a surrogate for flammable and explosive gaseous acetylene, its commercially available starting materials, its high stereoselectivity, and its simple workup procedures. The stereochemical structure of a selected product was determined by single-crystal X-ray diffraction. This method can be extended to a gram scale.

Sulfonyl Chlorides as Thiol Surrogates for Carbon-Sulfur Bond Formation: One-Pot Synthesis of Thioethers and Thioesters

A method to synthesize thioethers and thioesters directly from readily available sulfonyl chlorides is reported. We demonstrate that a transient intermediate formed during phosphine-mediated deoxygenation of sulfonyl chlorides can be trapped in situ by activated alcohols or carboxylic acids to effect carbon-sulfur bond formation. The method is operationally simple and tolerates a broad range of functional groups. Special attention has been focused on the late-stage diversification of densely functionalized natural products and pharmaceuticals.

Tunable photocatalytic oxysulfonylation and chlorosulfonylation of α-CF3 alkenes with sulfonyl chlorides

Tunable photoredox-catalyzed chlorosulfonylation and oxysulfonylation of α-trifluoromethylstyrenes with sulfonyl chloride were facilely achieved by simply manipulating the photocatalyst and solvent.

Recent advances in Cu-catalyzed transformations of internal alkynes to alkenes and heterocycles

Numerous metal-catalyzed reactions involving internal alkynes and aimed towards synthetically and pharmacologically important alkenes and heterocycles have appeared in the literature. Among these, Cu-catalyzed reactions have a special place, which has prompted the investigation and development of carbon-carbon and carbon-heteroatom bond-forming reactions. These reactions possess wide scope, and during the paths of these reactions, either stable or in situ intermediates are formed via the addition of Cu as a core catalyst or synergistic catalyst. In this review, we aim to report different contributions relating to Cu-catalyzed reactions of internal alkynes for the synthesis of different valuable alkenes and heterocycles which have appeared in the literature in the last decade. We anticipate that this appraisal will deliver basic insights for the further advancement of Cu-catalyzed reactions in organic chemistry.

Radical Cyclization of 1,n-Enynes and 1,n-Dienes for the Synthesis of 2-Pyrrolidone

2-Pyrrolidones have aroused enormous interest as a useful structural moiety in drug discovery; however, not only does their syntheses suffer from low selectivity and yield, but also it requires high catalyst loadings. The radical cyclization of 1,n-enynes and 1,n-dienes has demonstrated to be an attractive method for the synthesis of 2-pyrrolidones due to its mild reaction conditions, fewer steps, higher atom economy, excellent functional group compatibility, and high regioselectivity. Furthermore, radical receptors with unsaturated bonds (i. e. 1,n-enynes and 1,n-dienes) play a crucial role in realizing radical cyclization because of the ability to selectively introduce one or more radical sources. In this review, we discuss representative examples of methods involving the radical cyclization of 1,n-enynes and 1,n-dienes published in the last five years and discuss each prominent reaction design and mechanism, providing favorable tools for the synthesis of valuable 2-pyrrolidone for a variety of applications.

Chlorinative Cyclization of Aryl Alkynoates Using NCS and 9-Mesityl-10-methylacridinium Perchlorate Photocatalyst

In a chlorinative cyclization, Mes-Acr-MeClO₄ acted as a visible-light photocatalyst to obtain 3-chlorocoumarins from aryl alkynoates and N-chlorosuccinimide (NCS). The radical initiated reaction proceeded in a cascading manner via Cl^- addition to alkynoates. Next, 5-exo-trig spirocyclization and subsequent 1,2-ester migration led to the formation of C-C and C-Cl bonds.

Facile Synthesis of Sulfonyl Chlorides/Bromides from Sulfonyl Hydrazides

A simple and rapid method for efficient synthesis of sulfonyl chlorides/bromides from sulfonyl hydrazide with NXS (X = Cl or Br) and late-stage conversion to several other functional groups was described. A variety of nucleophiles could be engaged in this transformation, thus permitting the synthesis of complex sulfonamides and sulfonates. In most cases, these reactions are highly selective, simple, and clean, affording products at excellent yields.

NbCl5-Mg Reagent System in Regio- and Stereoselective Synthesis of (2Z)-Alkenylamines and (3Z)-Alkenylols from Substituted 2-Alkynylamines and 3-Alkynylols

The reduction of N,N-disubstituted 2-alkynylamines and substituted 3-alkynylols using the NbCl5-Mg reagent system affords the corresponding dideuterated (2Z)-alkenylamine and (3Z)-alkenylol derivatives in high yields in a regio- and stereoselective manner through the deuterolysis (or hydrolysis). The reaction of substituted propargylamines and homopropargylic alcohols with the in situ generated low-valent niobium complex (based on the reaction of NbCl5 with magnesium metal) is an efficient tool for the synthesis of allylamines and homoallylic alcohols bearing a 1,2-disubstituted double bond. It was found that the well-known approach for the reduction of alkynes based on the use of the TaCl5-Mg reagent system does not work for 2-alkynylamines and 3-alkynylols. Thus, this article reveals a difference in the behavior of two reagent systems-NbCl5-Mg and TaCl5-Mg, in relation to oxygen- and nitrogen-containing alkynes. A regio- and stereoselective method was developed for the synthesis of nitrogen-containing E-β-chlorovinyl sulfides based on the reaction of 2-alkynylamines with three equivalents of methanesulfonyl chloride in the presence of stoichiometric amounts of niobium(V) chloride and magnesium metal in toluene.

Silver-catalyzed synthesis of β-fluorovinylphosphonates by phosphonofluorination of aromatic alkynes

A silver-catalyzed three-component reaction involving alkynes, Selectfluor®, and diethyl phosphite was employed for the one-pot formation of C(sp2)-F and C(sp2)-P bonds to provide an efficient access to β-fluorovinylphosphonates in a highly regio- and stereoselective manner under mild reaction conditions. This reaction is operationally simple and offers an excellent functional group tolerance as well as a broad substrate scope that includes both terminal and internal alkynes. The reaction proceeded through the oxidative generation of a P-centered radical and subsequent fluorine atom transfer.

Synthesis of unsymmetrical disulfides via PPh3-mediated reductive coupling of thiophenols with sulfonyl chlorides

A facile and rapid synthesis of unsymmetrical aryl disulfides using PPh3-mediated reductive coupling of thiophenols with aryl sulfonyl chlorides was described. Good functional group tolerance and scalability were achieved in this strategy. More importantly, the approach enables the introduction of sulfonyl chlorides into the synthesis of asymmetric organic disulfides under catalyst- and base-free conditions. Using this method, unsymmetrical aromatic disulfides could be prepared from inexpensive and readily available starting materials in moderate to excellent isolated yields, through a nucleophilic substitution pathway.

Regio- and stereoselective halothiolation of alkynes using lithium halides and N-thiosuccinimides

Catalyst-free halothiolation of alkynes by using sulfenylhalide generated in situ by readily available lithium halides and N-thiosuccinimides.

Regioselective Chlorothiolation of Alkenes with Sulfonyl Chlorides

Newly developed sulfonyl chloride-based regioselective chlorothiolation of alkenes has been disclosed; the reaction is compatible with a variety of functional groups and can be scaled up to the gram scale with no loss in yield. The employment of readily available reactants, mild reaction conditions, and high regioselectivity makes this process very practical. Mechanistic studies revealed a possible free radical reaction pathway.

Unusual structure of a biphenyl fragment: the important role of weak interactions

1,5-Bis([1,1'-biphenyl]-4-yl)-5-hydroxy-3-methylheptane-1,6-dione, C₃₂H₃₀O₃, was investigated by X-ray analysis, quantum chemical calculations and AIM (atoms in molecules) analysis. It was shown that four intramolecular C-H...π forces are established between the two biphenyl fragments. C-H...π interactions lead to a bending of the biphenyl part. The energy of the intramolecular interactions was estimated and the exclusive role of the moment of force was established.

Hybrid Reaction Systems for the Synthesis of Alkylated Compounds Based upon Cu-Catalyzed Coupling of Radicals and Organometallic Species

A transition metal catalyzed alkylation with an alkyl halide is one of the most difficult reactions to achieve, because of the difficult oxidative addition of an alkyl-halogen bond to a metal, and the tendency of the resulting alkylmetal intermediate to undergo a β-hydride elimination reaction to give an olefin. In this review, we discuss hybrid reaction systems involving Cu catalyzed combination of radicals and organometallic species, which enable facile alkylation reactions to construct C-C and C-heteroatom bonds. This paper highlights recent progress in arylation, alkenylation, alkynylation, cyclization, addition and introduction of heteroatoms via these hybrid reaction systems.

Iodine-Catalyzed Odorless Synthesis of S-Thiocarbamates with Sulfonyl Chlorides as a Sulfur Source

A general and efficient protocol for the direct preparation of various S-thiocarbamates with readily available and inexpensive sulfonyl chlorides as an odorless sulfur source was developed. The employment of easily available reactants, excellent functional group tolerability, and mild reaction conditions make this process very practical.