Use of Elemental Sulfur or Selenium in a Novel One-Pot Copper-Catalyzed Tandem Cyclization of Functionalized Ynamides Leading to Benzosultams

Silver-Mediated [2 + 2 + 1] Cyclization of ortho-Propioloylbenzonitriles with Elemental Selenium: Synthesis of 4H-indeno[1,2-c][1,2]selenazol-4-ones

An efficient silver-mediated [2 + 2 + 1] cyclization protocol of ortho-propioloylbenzonitriles with elemental selenium for the synthesis of 4H-indeno[1,2-c][1,2]selenazol-4-ones has been developed. One C-Se bond, one N-Se bond, and one C-C bond were rapidly constructed in one step. The reaction might proceed via the formation of a highly reactive selenoketene intermediate, followed by intramolecular cyclization.

Copper-Catalyzed Cascade Multicomponent Reaction of Azides, Alkynes, and Selenium: Synthesis of Ditriazolyl Diselenides

A copper-catalyzed cascade multicomponent reaction for synthesizing ditriazolyl diselenides from azides, terminal alkynes, and elemental selenium has been developed. The present reaction features utilizing readily available and stable reagents, high atom-economy, and mild reaction conditions. A possible mechanism is proposed.

Synthesis of 2,5-disubstituted selenophenes via a copper-catalyzed regioselective [2+2+1] cyclization of terminal alkynes and selenium

Herein, a straightforward method for the synthesis of 2,5-disubstituted selenophenes via [2+2+1] cyclization of easily accessible terminal alkynes and elemental selenium has been developed. This reaction features high atom- and step-economy, excellent regioselectivity, good functional group tolerance and the use of stable and non-toxic selenium as a selenium source. A series of control experiments suggests that the reaction might undergo Glaser coupling reaction of two molecules of alkynes, followed by insertion of H₂Se and subsequent cyclization. Moreover, the newly formed products can be further converted to diverse conjugated selenophene-based derivatives, demonstrating their potential applications in organic synthesis and materials science.

Pd-catalysed intramolecular transformations of indolylbenzenesulfonamides: ortho-sulfonamido-bi(hetero)aryls via C2-arylation and polycyclic sultams via C3 arylation

Indolyl substituted iodo-sulfonamides deliver 2-aryl(sulfonamido)indoles in the presence of Pd(OAc)2/Ph3P/Et3N; the same reactants, using Pd(OAc)2/Ph3P/K2CO3, afford indole-fused sultams.

Double C-S bond formation via multiple Csp3-H bond cleavage: synthesis of 4-hydroxythiazoles from amides and elemental sulfur under metal-free conditions

A novel and efficient approach for the synthesis of 4-hydroxythiazoles from amides and elemental sulfur has been developed. In the presence of P₂O₅, DMSO and HMPA, this metal-free protocol proceeds smoothly and tolerates a spectrum of functional groups. Furthermore, this strategy involves the process of double Csp³-S bond formation through the cleavage of multiple Csp³-H bonds for the first time.

Palladium-catalysed cyclisation of ynamides and propargyl tethered iodosulfonamides with boronic acids leading to benzosultams

An efficient and straightforward Pd-catalysed synthesis of diversely substituted sultams utilising ynamides and boronic acids is disclosed; toluene was found to be the most suitable solvent for this transformation. This strategy has been successfully applied to generate dihydrobenzo[d]isothiazole 1,1-dioxides and dihydro-2H-benzo[e][1,2]thiazine 1,1-dioxides. The advantages of this protocol are good functional group tolerance, broad substrate scope, high-yielding reaction and low catalyst loading to access benzofused sultams with five-/six-membered rings. The synthetic utility has been demonstrated by a gram-scale synthesis. A plausible catalytic cycle involving carbopalladation has been proposed for this transformation.

Metal-catalyzed C-S bond formation using sulfur surrogates

Sulfur-containing compounds are present in a wide range of biologically important natural products, drugs, catalysts, and ligands and they have wide applications in material chemistry. Transition metal-catalyzed C-S bond-forming reactions have successfully overcome the obstacles associated with traditional organosulfur compound syntheses such as stoichiometric use of metal-catalysts, catalyst-poisoning and harsh reaction conditions. One of the key demands in metal-catalyzed C-S bond-forming reactions is the use of an appropriate sulfur source due to its odor and availability. The unpleasant odor of many organic sulfur sources might be one of the reasons for the metal-catalyzed C-S bond-forming reactions being less explored compared to other metal-catalyzed C-heteroatom bond-forming reactions. Hence, employing an appropriate sulfur surrogate in the synthesis of organosulfur compounds in metal-catalyzed reactions is still of prime interest for chemists. This review explores the recent advances in C-S bond formation using transition metal-catalyzed cross-coupling reactions and C-H bond functionalization using diverse and commercially available sulfur surrogates. Based on the different transition metal-catalysts, this review has been divided into three major classes namely (1) palladium-catalyzed C-S bond formation, (2) copper-catalyzed C-S bond formation, and (3) other metal-catalyzed C-S bond formation. This review is further arranged based on the different sulfur surrogates. Also, this review provides an insight into the growing opportunities in the construction of complex organosulfur scaffolds covering natural product synthesis and functional materials.

Contrasting Carboannulation Involving δ-Acetoxy Allenoate as a Four-Carbon Synthon Using DABCO and DMAP: Access to Spiro-carbocyclic and m-Teraryl Scaffolds

Spiro-annulation involving δ-acetoxy allenoate and alkyl benzoisothiazole dioxide (N-sulfonyl ketimine) triggered by DABCO/MeCO₂H combination leads to an essentially single diastereomer via chemo- and regiospecific [4 + 2]-carboannulation and a new hydroxyl group is introduced. In contrast, DMAP-catalyzed benzannulation using the same reactants affords unsymmetrical m-teraryls via Mannich coupling, sequential proton transfers, and C-N bond cleavage. Here, δ-acetoxy allenoate serves as a 4C-synthon and the carboannulation is completely base dependent and mutually exclusive.

Synthetic developments on the preparation of sulfides from thiol-free reagents

This critical review covers the main thiolating reagents with respect to their characteristics and reactivities. In fact, they are complementary to each other and bring different thiolation strategies, avoiding the hazardous thiol derivatives.

Cascade cyclization versus chemoselective reduction: a solvent-controlled product divergence

A convenient controllable cascade cyclization and partial reduction of enones for the divergent construction of two types of valuable compounds including polysubstituted thiophenes and saturated ketones are developed.

Synthesis of Dibenzo[d,f][1,3]Diazepines via Elemental Sulfur-Mediated Cyclocondensation of 2,2'-Biphenyldiamines with 2-Chloroacetic Acid Derivatives

The three-component reaction of 2,2'-biphenyldiamines with 2-chloroacetic acid derivatives and elemental sulfur was developed for the practical synthesis of unknown 2-carboxamide-substituted dibenzo[d,f][1,3]diazepines. This protocol is distinguished by efficiency in water and good tolerance to functional groups and can be adapted to a large-scale synthesis. The chemoselective preparation of a variety of 2-S,N,O-substituted dibenzo[d,f][1,3]diazepines was accomplished using the developed method.

Synthesis of 2-Amino-5-acylthiazoles by a Tertiary Amine-Promoted One-Pot Three-Component Cascade Cyclization Using Elemental Sulfur as a Sulfur Source

A novel one-pot three-component cascade cyclization strategy for the synthesis of 2-amino-5-acylthiazoles using enaminones, cyanamide, and elemental sulfur has been developed. The reported methods have demonstrated good tolerance of various functional groups. Up to 28 2-amino-5-acylthiazole compounds bearing diverse structural differences were successfully synthesized from easily obtained starting materials with moderate to excellent yields. Our method provides an effective way for the access of valuable and potentially bioactive 2-amino-5-acylthiazole derivatives.

Cu(i) catalysed annulation of isothiocyanates/isocyanates with 2-iodo-sulfonamides: synthesis of benzodithiazines, benzothiadiazinones, benzothiazinylidene-anilines and benzothiazolylidene-anilines

An efficient Cu(i)-catalysed cyclisation reaction of 2-iodobenzene sulfonamides with aryl-isothiocyanates and isocyanates that affords functionalised benzodithiazines and benzothiadiazinones, respectively, has been developed. Thus, in the reaction with aryl isothiocyanates (Ar-N[double bond, length as m-dash]C[double bond, length as m-dash]S), the C[double bond, length as m-dash]S moiety participates in the cyclisation leading to a dithiazine. By contrast, in the case of aryl isocyanates (Ar-N[double bond, length as m-dash]C[double bond, length as m-dash]O), the N[double bond, length as m-dash]C part is involved in the cyclisation and a thiadiazinone is obtained. Analogous reactions of isothiocyanates with N-tosyl-2-iodo-anilines and 2-iodo-benzyl sulfonamides afford (benzothiazin-2-ylidene)anilines and (benzothiazol-2-ylidene)anilines, respectively. Probable mechanistic pathways are briefly discussed.

Direct access to bis-S-heterocyclesviacopper-catalyzed three component tandem cyclization using S8as a sulfur source

An elemental sulfur atom donor strategy for constructing a thiophene-fused thiazole bis-S-heterocyclic skeletonviaCu-catalyzed three-component tandem cyclization has been developed.

Ring-opening/annulation reaction of cyclopropyl ethanols: concise access to thiophene aldehydes via C–S bond formation

The synthesis of thiophene aldehydes from easily available cyclopropyl ethanol derivatives and potassium sulfide has been developed.

Oxidative dual C–H thiolation of imidazopyridines with ethers or alkanes using elemental sulphur

Dual C–H thiolation reactions using elemental sulphur remain a challenge.

Metal-free direct thiocarbamation of imidazopyridines with carbamoyl chloride and elemental sulfur

Metal-free direct thiocarbamation of imidazopyridines using elemental sulfur.

Pd/Cu-Catalyzed tandem head-to-tail dimerization/cycloisomerization of terminal ynamides for the synthesis of 5-vinyloxazolones

This is the first Pd/Cu-catalyzed tandem head-to-tail dimerization/cycloisomerization of terminal ynamides for the synthesis of 5-vinyl-oxazolones.

Versatile one-pot synthesis of benzo-fused thiacycles by copper catalysis

A series of 2-substituted benzo[e][1,3]thiazines and 2-substituted benzo[b]thiophenes were synthesized using a versatile, simple and efficient copper-catalysed methodology.