Cyclization of N-Arylacrylamides via Radical Arylsulfenylation of Carbon–Carbon Double Bonds with Sulfonyl Hydrazides

PPh3/I2 Promoted Synthesis of Unsymmetrical Disulfides from Sodium Sulfites and 2-Mercaptobenzo Heterocyclics

A simple and efficient method for the synthesis of unsymmetrical disulfides is reported. Using sodium sulfites and 2-mercaptobenzo heterocyclic compounds as starting materials, the unsymmetrical sulfur-sulfur bonds could be quickly constructed in the PPh3/I2 reaction system under transition-metal-free conditions. This protocol has the advantages of mild reaction conditions, easily available starting materials, and wide substrate scope, showing potential synthetic value for the synthesis of a diversity of biologically or pharmaceutically active compounds.

TBHP-mediated photochemical coupling/cyclization of N-arylacrylamides with thiols

The effective photoredox-mediated oxidative thiolation and cyclization of N-arylacrylamides with thiols leads to biologically interesting 3-thionated oxindoles through C-S and C-C bond formation. This process represents a straightforward reaction that starts from non-prefunctionalized thiolating reagents. Mechanistic studies demonstrated that the TBHP serves as a key radical initiator with visible-light catalysis.

The Application of Sulfonyl Hydrazides in Electrosynthesis: A Review of Recent Studies

Sulfonyl hydrazides are viewed as alternatives to sulfinic acids and their salts or sulfonyl halides, which are broadly used in organic synthesis or work as active pharmaceutical substances. Generally, sulfonyl hydrazides are considered good building blocks and show powerful value in a diverse range of reactions to construct C-S bonds or C-C bonds, and even C-N bonds as sulfur, carbon, or nitrogen sources, respectively. As a profound synthetic tool, the electrosynthesis method was recently used to achieve efficient and green applications of sulfonyl hydrazides. Interestingly, many unique and novel electrochemical syntheses using sulfonyl hydrazides as radical precursors have been developed, including cascade reactions, functionalization of heterocycles, as well as a continuous flow method combining with electrochemical synthesis since 2017. Accordingly, it is necessary to specifically summarize the recent developments of electrosynthesis with only sulfonyl hydrazides as radical precursors to more deeply understand and better design novel electrochemical synthesis reactions. Herein, electrosynthesis research using sulfonyl hydrazides as radical precursors since 2017 is reviewed in detail based on the chemical structures of products and reaction mechanisms.

Cobalt-promoted synthesis of sulfurated oxindoles via radical annulation of N-arylacrylamides with disulfides

An efficient radical annulation of N-arylacrylamides with disulfides is developed for the synthesis of sulfurated oxindoles. The reaction occurs in a facile manner using CoBr₂ as both an initiator and a promoter for the first time and (NH₄)₂S₂O₈ as the oxidant. By controlling the CoBr₂/(NH₄)₂S₂O₈ ratio, a wide range of sulfurated and brominated/sulfurated oxindoles are selectively prepared in good to excellent yields. The present protocol is simple and highly atom economical, and can tolerate a broad range of substrates.

An iodine-mediated new avenue to sulfonylation employing N-hydroxy aryl sulfonamide as a sulfonylating agent

A novel and highly efficient I2/K2CO3 mediated regioselective sulfonylation of thiophenols, aryl acetylenic acid and aromatic alkynes with N-hydroxy sulfonamide has been developed. N-hydroxy sulfonamide has been used for the first time for the synthesis of these sulfones. The scope and versatility of the reaction has been demonstrated by the regio- and stereoselective synthesis of different analogs of sulfones with various structural features.

Recent Advances in Iodine-Promoted C-S/N-S Bonds Formation

Sulfur-containing scaffold, as a ubiquitous structural motif, has been frequently used in natural products, bioactive chemicals and pharmaceuticals, particularly C-S/N-S bonds are indispensable in many biological important compounds and pharmaceuticals. Development of mild and general methods for C-S/N-S bonds formation has great significance in modern research. Iodine and its derivatives have been recognized as inexpensive, environmentally benign and easy-handled catalysts or reagents to promote the construction of C-S/N-S bonds under mild reaction conditions, with good regioselectivities and broad substrate scope. Especially based on this, several new strategies, such as oxidation relay strategy, have been greatly developed and accelerated the advancement of this field. This review focuses on recent advances in iodine and its derivatives promoted hybridized C-S/N-S bonds formation. The features and mechanisms of corresponding reactions are summarized and the results of some cases are compared with those of previous reports. In addition, the future of this domain is discussed.

Thiyl Radicals: Versatile Reactive Intermediates for Cyclization of Unsaturated Substrates

Sulfur centered radicals are widely employed in chemical synthesis, in particular for alkene and alkyne hydrothiolation towards thioether bioconjugates. The steadfast radical chain process that enables efficient hydrothiolation has been explored in the context of cascade reactions to furnish complex molecular architectures. The use of thiyl radicals offers a much cheaper and less toxic alternative to the archetypal organotin-based radical methods. This review outlines the development of thiyl radicals as reactive intermediates for initiating carbocyclization cascades. Key developments in cascade cyclization methodology are presented and applications for natural product synthesis are discussed. The review provides a chronological account of the field, beginning in the early seventies up to very recent examples; a span of almost 50 years.

Fe-Catalyzed decarbonylative cascade reaction of N-aryl cinnamamides with aliphatic aldehydes to construct 3,4-dihydroquinolin-2(1H)-ones

A practical Fe-catalyzed decarbonylative cascade reaction of N-aryl cinnamamides with aliphatic aldehydes to provide C3 alkylated 3,4-dihydroquinolin-2(1H)-ones is developed. Aliphatic aldehydes were oxidatively decarbonylated into 1°, 2° and 3° alkyl radicals conveniently, allowing for the subsequent cascade construction of C(sp3)-C(sp3) and C(sp3)-C(sp2) bonds via radical addition and HAS-type cyclization. The importance of the amide linkage and the selectivity of the 6-endo-trig over 5-exo-trig cyclization pathway were elucidated by experimental results and DFT calculations.

N-Hydroxy sulfonamides as new sulfenylating agents for the functionalization of aromatic compounds

An unprecedented use of N-hydroxy sulfonamides as sulfenylating agents has been established. In the presence of catalytic amounts of iodine and N-hydroxysuccinimide, N-hydroxy sulfonamides participated in sulfenylation with indoles, 7-azaindole, N-methyl pyrrole, and 2-naphthol to afford structurally diverse thioethers in moderate to excellent yields with very high regioselectivity.

TfNHNHBoc as a SCF3 source for the sulfenylation of indoles

An unprecedented use of TfNHNHBoc as an effective SCF₃ source has been established in the copper-catalyzed oxidative sulfenylation of indoles.

Synthesis of N-alkyl-3-sulfonylindoles and N-alkyl-3-sulfanylindoles by cascade annulation of 2-alkynyl-N,N-dialkylanilines

Divergent synthesis of N-alkyl-3-sulfonylindoles and N-alkyl-3-sulfanylindoles from 2-alkynyl-N,N-dialkylanilines and sulfonyl hydrazides has been described.

Aerobic thiyl radical addition/cyclization of N-methacryloyl benzamides for the synthesis of isoquinoline-1,3(2H,4H)-dione derivatives

A highly effective dioxygen-triggered oxidative thiyl radical addition/cyclization of N-methacryloylbenzamides was explored. This method provides convenient access to a variety of useful sulfide-containing 4,4-disubstituted isoquinoline-1,3-diones.

A method for accessing sulfanylfurans from homopropargylic alcohols and sulfonyl hydrazides

A sulfenylation/cyclization reaction has been developed for the synthesis of sulfanylfurans in the presence of iodine.