Metal- and additive-free β-C(sp2)-H decarboxylative alkylsulfonylation of enamides from phenyliodine(III) dicarboxylates and sulfur dioxide

A green process for the direct C(sp2)-H decarboxylative alkylsulfonylation of enamides under metal- and additive-free conditions is reported. This reaction employs phenyliodine(III) dicarboxylates as the alkyl radical precursors and DABCO·(SO2)2 as the sulfur dioxide surrogate. Diverse (E)-alkylsulfonyl enamides are generated in moderate to good yields with high stereoselectivity under extremely mild conditions via a radical process. A broad substrate scope and excellent functional group tolerance are presented. Moreover, a cascade alkylsulfonylation/cyclization reaction of N-methacryloyl enamides occurs smoothly, giving rise to various alkylsulfonylated pyrrolidones.

Four-Component Radical 1,2-Selenosulfonylation of Allenes

Selenosulfones, as pivotal pharmaceutical molecule frameworks, have become a research hotspot in modern organic synthesis due to their vital need for efficient preparation. Herein, we have developed an iron-catalyzed four-component controllable radical tandem reaction of allenes involving cycloketone oxime esters, 1,4-diazabicyclo[2.2.2]octane bis(sulfur dioxide) adduct (DABSO), and diphenyl diselenides for the synthesis of complex selenosulfones. This is the first case of achieving the 1,2-selenosulfonylation of allenes via a radical process, wherein precise control of radical rates and polarity matching enhance high regioselective conversion. The reaction conditions are ecofriendly and mild with step-efficiency by forming two new C-S bonds and one C-Se bond in one pot. Moreover, the 1,2-selenosulfonylation of allenes can be achieved by replacing cycloketone oxime esters with aryldiazonium tetrafluoroborates in this system.

Copper Catalyst-Promoted Regioselective Multicomponent Cascade Cyclization of 3-Aza-1,5-enynes with Sulfur Dioxide and Cycloketone Oxime Esters to Access Cyanoalkylsulfonylated 1,2-Dihydropyridines

Radical cascade cyclization via the cracking of alkenyl C-H has emerged as an attractive and remarkable tool for the rapid construction of ring frameworks with endocyclic double bonds. We developed a cascade reaction of 3-aza-1,5-enynes with sulfur dioxide and cycloketone oxime esters to access cyanoalkylsulfonylated 1,2-dihydropyridines, which can be easily converted to pyridine derivatives. This protocol involves radical addition to the C≡C bond and 6-endo cyclization and features high regioselectivity and a broad substrate scope.

Photocatalytic selective synthesis of (E)-β-aminovinyl sulfones and (E)-β-amidovinyl sulfones using Ru(bpy)3Cl2 as the catalyst

Selectively producing a variety of valuable compounds using controlled chemical reactions starting from a common material is an appealing yet complex concept. Herein, a photocatalytic approach for the selective synthesis of (E)-β-aminovinyl sulfones and (E)-β-amidovinyl sulfones from allenamides and sodium sulfinates was established. This reaction exhibits the traits of an eco-friendly solvent and adjustable amide cleavage, and can accommodate a diverse range of substrates with exceptional functional group tolerance. Based on control experiments and deuterium labeling experiments, a plausible radical reaction pathway is proposed.

SO42- ions as a nucleophilic reagent: straightforward electrochemical access to organosulfates

An electrooxidation direct difunctionalization of alkynes with sulfonyl hydrazides has been developed for the construction of sulfonyl alkenyl sulfates in the absence of metal catalysts and a stoichiometric amount of oxidants. Notably, it is the first example to verify that SO42- ions can act as a nucleophilic reagent for the preparation of organosulfates.

Radical approaches to C-S bonds

Organosulfur functionalities are ubiquitous in nature, pharmaceuticals, agrochemicals, materials and flavourants. Historically, these moieties were introduced almost exclusively using ionic chemistry; however, radical-based methods for the installation of sulfur-based functional groups have recently come to the fore. These radical methods have enabled their late-stage introduction into complex molecules, avoiding the need to preserve labile organosulfur moieties through multistep synthetic sequences. Here, we discuss homolytic C-S bond-forming processes, with a particular emphasis on radical substitution approaches to sulfide, disulfide and sulfinyl products, and the use of sulfur dioxide and its surrogates to build sulfonyl products. We also highlight the mechanistic considerations that we hope will guide further development of radical-based strategies compatible with the various organosulfur moieties that feature in modern chemistry.

Photoredox/Nickel Dual-Catalyzed Stereoselective Synthesis of Distal Cyano-Substituted Enamides

Herein, the efficient photoredox/nickel dual-catalyzed cyanoalkylation reaction of enamides is illustrated. A wide scope of enamides and cycloketone oxime esters was well-tolerated, affording the synthetically versatile and geometrically defined β-cyanoalkylated enamide scaffolds. The synthetic practicality of this protocol was revealed by gram-scale reactions, further transformations of enamides, and late-stage modifications of biologically active molecules.

Iron-Catalyzed Sulfonylthiocyanation of α,β-Unsaturated Amides/Esters via the Insertion of Sulfur Dioxide

An iron-catalyzed four-component sulfonylthiocyanation between α,β-unsaturated amides/esters, TMSNCS, aryldiazonium tetrafluoroborates, and sulfur dioxide (from SOgen) is demonstrated. This protocol is characterized by mild reaction conditions, good functional group compatibility, broad substrate scope, and good to excellent yields, providing a feasible method for the preparation of β-thiocyanated sulfone compounds. The preliminary mechanism investigation shows that a radical pathway may be involved in the process.

DABSO – A Reagent to Revolutionize Organosulfur Chemistry

The introduction of easy-to-handle SO2 surrogates has transformed the field of sulfur chemistry, enabling methodologies utilizing SO2 to be carried out without specialized apparatus, and paving the way for the development of new procedures. This review highlights some of the varied and significant developments associated with one of the most prominent SO2 surrogates: DABSO.

1 Introduction

2 DABSO

3 Reactions with Nucleophilic Reagents

4 Metal-Catalyzed Reactions

4.1 Palladium-Catalyzed Reactions

4.2 Other Transition-Metal Catalysis

5 Radical Reactions

5.1 Aryldiazonium Salts

5.2 Other Aryl Radical Precursors

5.3 Alkyl Radical Precursors

6 Conclusion

Divergent cyanoalkylation/cyanoalkylsulfonylation of enamides under organophotoredox catalytic conditions

An organophotoredox catalyzed divergent cyanoalkylation/cyanoalkylsulfonylation of enamides is described.

Ni and Fe Catalyzed Cascade Radical Reactions of Oxime Esters with Diselenides

A radical cyclization and ring-opening of oxime esters with diselenides was developed. Both Ni(0) and Fe(II) catalysts could be employed for the selenylation of olefin-containing and cyclic oxime ester derivatives....

Exploring the regioselectivity of the cyanoalkylation of 3-aza-1,5-dienes: photoinduced synthesis of 3-cyanoalkyl-4-pyrrolin-2-ones

Regioselective cyanoalkylalkenylation of 3-aza-1,5-dienes with oxime esters induced by visible light.

Metal-free regioselective cascade sulfonylation-cyclization of 3-aza-1,5-enynes with sulfur dioxide and aryldiazonium tetrafluoroborates to construct 1,2-dihydropyridines

Radical cascade cyclization of tethered alkynes has emerged as an efficient tool to construct small but complex cyclic compounds. However, it currently relies on aryl or heteroaryl-tethered alkynes to give...

Visible-light-facilitated P-center radical addition to C[double bond, length as m-dash]X (X = C, N) bonds results in cyclizations

Visible-light-facilitated phosphorus radical reactions have been developed as a powerful and sustainable tool for the synthesis of various organophosphorus compounds. In general, these reactions require stoichiometric amounts of oxidants, and reductants, bases, and radical initiators, leading to uneconomical and complicated processes. Progress has been made over the past few years toward using reactions that proceed under eco-benign and mild reaction conditions. Furthermore, these reactions have broad functional group tolerance, with some facile and economical pathways. Herein, we summarize the discoveries and achievements pertaining to C-P bond formation through a visible light photocatalysis procedure with high atom economy, made by our group and other research groups. It was established that greener and more environmentally friendly approaches do not require an additional oxidant or base. Moreover, we have designed and synthesized a new type of P-radical precursor, which can take part in reactions without the requirement for any additional bases, oxidants, and additives. This breakthrough, pertaining to novel visible-light-induced transformations, will be discussed and a plausible mechanism is proposed, based on corresponding experiments and the literature.