Sulfonyl Radical-Induced Regioselective Cyclization of Enamide-Olefin To Form Sulfonylated 6-7-Membered Cyclic Enamines

Remarkable progress has been made in the radical cascade cyclization of heteroaryl- or aryl-tethered alkenes to construct benzene-fused frameworks via the cracking of aryl C-H bonds. In contrast, the radical cascade cyclization of linear dienes through the cracking of vinyl C-H bonds to construct nonbenzene-fused ring frameworks with endocyclic double bonds has significantly lagged behind, and major advances have largely been restricted to the generation of 5-membered heterocycles, such as pyrrolinones. Herein, we report the silver-mediated regioselective sulfonylation-cyclization of linear dienes with sodium sulfinates to form sulfonylated 6- and 7-membered cyclic enamines.

Recent Advancements in Metal-Catalyst-Free Multicomponent Radical Sulfonylation of Alkynes

Vinyl sulfones are crucial building blocks in synthetic chemistry and core structural units of pharmaceutically active molecules, thus extensive investigations have been conducted on the construction of these skeletons. In contrast to the classical synthetic approaches, the radical sulfonylation of alkynes for producing vinyl sulfones has garnered considerable interest because of its mild conditions and high efficiency. Radical sulfonation of alkynes typically begins with the sulfonyl radical attacking the alkynes, followed by further functionalization. Moreover, the association of metal-catalyst-free systems with multicomponent reactions (MCRs) offers an environmentally friendly pathway for efficiently constructing complex scaffolds from readily available partners. However, there is no comprehensive review summarizing the advancements in metal-catalyst-free multicomponent radical sulfonylation of alkynes. Hence, we provide a categorical overview based on the objects of sulfonylation of alkynes (hydrosulfonylation, carbosulfonylation, aminosulfonylation, oxysulfonylation, sulfosulfonylation, selenosulfonylation, and iodosulfonylation), along with interpretations of the reaction mechanisms.

Catalyst-Free α-trans-Selective Hydroboration and (E)-Selective Deuterated Semihydrogenation of Alkynyl Sulfones

Here, we present a straightforward α-trans-selective hydroboration of alkynyl sulfones with NHC-boranes without the need for a catalyst. This reaction is compatible with a wide range of substrates for efficiently producing structurally diverse α-borylated vinyl sulfones in satisfactory yields. The hydride transfer from NHC-borane 2a to alkynyl triflone 1b is studied by density functional theory (DFT) calculations for trans-hydroboration. Moreover, a regiodivergent deuterated semihydrogenation of alkynyl triflones has also been developed using D2O as the deuterium source. A variety of diversity-oriented D-containing vinyl triflones were prepared in good to excellent yields with excellent deuterium incorporation ratios. Synthetic manipulations of the deuterated products are achieved for the conversion into valuable deuterated molecules, indicating the utility of this protocol.

Regio- and Stereoselective Intermolecular 1,2-Difunctionalization of Terminal Alkynes: An Approach to Access (Z)-β-Amidovinylsulfones

We have developed the first I2/base-catalyzed regio- and stereoselective intermolecular β-amidosulfonylation of terminal alkynes using sodium sulfinates and quinoxalinone derivatives. The present methodology is compatible with a broad spectrum of various heterocyclic amides, terminal alkynes, and sodium sulfinates. It provides rapid access to valuable (Z)-β-amidovinyl sulfones at mild conditions. Moreover, the synthetic application of this methodology was demonstrated by the late-stage functionalization of numerous bioactive molecules.

Recent advances in the application of alkynes in multicomponent reactions

Alkynes have two active positions to carry out chemical reactions: C[triple bond, length as m-dash]C and C-H. These two positions are involved and activated in different reactions using different reagents. In this study, we investigated the reactions of alkynes that are involved in multi-component reactions through the C-C and C-H positions and examined the progress and gaps of each reaction by carefully studying the mechanism of the reactions. Firstly, we investigated and analyzed the reactions involving the C[triple bond, length as m-dash]C position of alkynes, including the reactions between derivatives of alkynes with RN3, sulfur compounds (RSO2R', DMSO, S8, DABCO(SO2)2 and DABSO), barbituric acids, aldehydes and amines, COOH, α-diazoesters or ketones, and isocyanides. Then, we examined and analyzed the important reactions involving the C-H position of alkynes and the progress and gaps in these reactions, including the reaction between alkyne derivatives with amines and aldehydes for the synthesis of propargylamines, the reaction between alkynes with CO2 and the reaction between alkynes with CO.

Regio- and Stereoselective Intermolecular Oxysulfonylation of Alkynes with 1,3-Diketones to Access (Z)-β-Sulfonated Enethers

The first multicomponent regio- and stereoselective difunctionalization of alkynes via concomitant C-O and C-S bond formation using 1,3-diketones and sodium sulfinate has been developed for the synthesis of various sulfonated enethers. The viability of this strategy is unveiled by gram-scale, various synthetic modifications and late-stage functionalization. This transformation does not require any prefunctionalization, metal catalysts, and oxidants. The present operationally simple, efficient, and sustainable approach provides various functionalized olefins in a one-pot protocol with high Z-selectivity.

Electrochemical Decarbonylative Aminosulfonylation of Alkynes with Sulfinates and N-(Formyl)anilides

An unprecedented electrochemical three-component reaction of phenylacetylene, sulfinate, and N-(formyl)anilide was discovered. The transformation occurs in an undivided cell with a graphite anode and cathode in DMF in the presence of tetrabutylammonium iodide as an electrolyte. The addition of silver(I) oxide and catalytic amounts of iodine facilitated the reaction significantly. The transformation was also carried out under photoredox-catalyzed conditions.

Stereodivergent Synthesis of (Z)-/(E)-β-Sulfonylacrylamides via Tandem Difunctionalization of Alkynes with Sulfinates and Isocyanides

Stereoselective difunctionalizations of the terminal and internal alkynes with various sulfinates and isocyanides have been achieved to prepare (Z)-/(E)-β-sulfonylacrylamides. The (Z)-β-sulfonylacrylamides were generated via a one-pot process that involves the reaction of terminal alkynes with sulfinates and isocyanides in the presence of iodine in sequential manner. The (E)-β-sulfonylacrylamides were prepared in a two-step synthesis via palladium(II)-catalyzed addition of isocyanide to (E)-β-iodovinylsulfones synthesized from alkynes.

Visible-Light-Mediated Difunctionalization of Alkynes: Synthesis of β-Substituted Vinylsulfones Using O- and S-Centered Nucleophiles

An inimitable illustration of a green-light-induced, regioselective difunctionalization of terminal alkynes has been disclosed using sodium arylsulfinates and carboxylic acids in the presence of eosin Y as the photocatalyst. The present methodology is further demonstrated by employing NH₄SCN as an S-centered nucleophile instead of carboxylic acid. The mechanistic investigation reveals a radical-induced iodosulfonylation followed by a base-mediated nucleophilic substitution. The mechanism is supported by various studies, viz., radical-trapping experiment, fluorescence quenching, and CV studies. In this protocol, (Z)-β-substituted vinylsulfones are obtained, exclusively covering a broad range of alkynes and nucleophiles, which are often unaddressed. The present strategy can tolerate structurally discrete substrates with steric bulk and different electronic properties, which provides a straightforward and practical pathway for the synthesis of highly functionalized (Z)-β-substituted vinylsulfones. Herein, C-O and C-S bonds are assembled simultaneously with the concomitant introduction of important functional groups, viz., ester, thiocyanate, and sulfone.

Metal-Free Radical Thiocyanatosulfonation of Terminal Alkynes in Aqueous Medium

Here we report a novel and practical approach for preparing (E)-β-(thiocyanato)vinyl sulfones through the 1,2-thiocyanatosulfonation of terminal alkynes with NH₄SCN and sulfonyl hydrazides. Advantages of this reaction include mild conditions, the absence of metal, readily available reagents, a broad substrate scope, good functional group compatibility, and excellent stereoselectivity. The radical species-induced pathway is also demonstrated by mechanistic studies.

Atom-Economical Thiocyanation-Amination of Alkynes with N-Thiocyanato-Dibenzenesulfonimide

A highly regioselective protocol for intermolecular thiocyanation-amination of alkynes by N-thiocyano-dibenzenesulfonimide (NTSI) as the SCN and nitrogen sources has been developed. A C-S bond and C-N bond are simultaneously constructed in only one step. The reaction under simple mild conditions features a broad substrate scope, atom economy, high yields (up to 94%), and excellent functional group tolerance.