Visible-light-promoted cascade cyclization of N-arylacrylamides with bromomethyl sulfone: access to sulfonylmethylated phenanthridines

We present a visible-light-promoted radical cascade cyclization reaction via sulfonylmethylation, cyano insertion, and radical cyclization of unactivated alkenes bearing cyano groups. This strategy enables the rapid synthesis of sulfonylmethylated phenanthridines under mild conditions with broad substrate compatibility, operational simplicity, and mild reaction conditions. The developed approach provides a novel pathway for assembling complex polycyclic nitrogen-containing frameworks, addressing a critical synthetic challenge and expanding the toolbox of photochemical transformations in organic synthesis.

One-pot synthesis of tetrasubstituted 2-aminofurans via Au(I)-catalyzed cascade reaction of ynamides with propargylic alcohols

One-pot synthesis of fully substituted 2-aminofurans via a Au(I)-catalyzed cascade reaction of ynamides and propargylic alcohol was realized. Hydroalkoxylation of ynamide with propargylic alcohol, Saucy-Marbet rearrangement, and cyclization of the resultant 3,4-dienamide sequentially proceeds in a one-pot reaction under highly mild conditions to give fully substituted 2-aminofurans.

Synthesis and applications of sodium sulfinates (RSO2Na): a powerful building block for the synthesis of organosulfur compounds

This review highlights the preparation of sodium sulfinates (RSO2Na) and their multifaceted synthetic applications. Substantial progress has been made over the last decade in the utilization of sodium sulfinates emerging as sulfonylating, sulfenylating or sulfinylating reagents, depending on reaction conditions. Sodium sulfinates act as versatile building blocks for preparing many valuable organosulfur compounds through S-S, N-S, and C-S bond-forming reactions. Remarkable advancement has been made in synthesizing thiosulfonates, sulfonamides, sulfides, and sulfones, including vinyl sulfones, allyl sulfones, and β-keto sulfones. The significant achievement of developing sulfonyl radical-triggered ring-closing sulfonylation and multicomponent reactions is also thoroughly discussed. Of note, the most promising site-selective C-H sulfonylation, photoredox catalytic transformations and electrochemical synthesis of sodium sulfinates are also demonstrated. Holistically, this review provides a unique and comprehensive overview of sodium sulfinates, which summarizes 355 core references up to March 2020. The chemistry of sodium sulfinate salts is divided into several sections based on the classes of sulfur-containing compounds with some critical mechanistic insights that are also disclosed.

Visible-light-mediated cascade cyanoalkylsulfonylation/cyclization of alkynoates leading to coumarins via SO2 insertion

A visible-light-mediated cascade cyanoalkylsulfonylation/cyclization of alkynoates with cycloketone oxime compounds for the preparation of 3-cyanoalkylsulfonylcoumarins via SO₂ insertion is reported.

Silver-promoted oxidative sulfonylation and ring-expansion of vinylcyclopropanes with sodium sulfinates leading to dihydronaphthalene derivatives

Silver-promoted sulfonylation and ring-expansion of vinylcyclopropanes with sodium sulfinates is established for the construction of 1-sulfonylmethylated 3,4-dihydronaphthalenes. This sulfonylation process involves a radical pathway, including sulfonyl radical formation, radical addition, ring-opening and cyclization. The 1-sulfonylmethylated 3,4-dihydronaphthalenes can be converted into other useful products.

Pd(II)-Catalyzed Intramolecular Acetoxylative (3 + 2) Annulation of Propargylic Alcohol and Alkene: Polycyclic Oxa-heterocycle Synthesis and Mechanistic Insight

A Pd(II)-catalyzed intramolecular and highly selective acetxoylative (3 + 2) annulation of propargylic alcohol and alkene is reported. Mechanistically, a hydroxy-guided regioselective alkyne acetoxypalladation is followed by 6-exo-trig alkene insertion to form an alkyl-Pd(II) intermediate. After oxidation, the resulting cyclometalated alkoxy-Pd(IV)-alkyl undergoes direct reductive elimination to afford a polycyclic oxa-heterocycle. When an additional coordinating site or ligand accessible by palladium is present, an S_N2-type C-C reductive elimination of alkyl-Pd(IV) instead occurs along with hydroxy acetylation, affording 3-bicyclo[4.1.0]heptan-5-one products.

Inorganic sulfites as the sulfur dioxide surrogates in sulfonylation reactions

Recent advances in the sulfonylation reactions by using inorganic sulfites as the source of sulfonyl group are reported. The approaches employing inorganic sulfites as sulfur dioxide surrogates are attractive and promising for the synthesis of sulfonyl compounds since inorganic sulfites are abundant, easily available and cheap. The transformations using inorganic sulfites as the source of sulfonyl group work efficiently, providing diverse sulfonyl compounds including sulfones and sulfonamides. The sulfonylation reactions can be performed under transition metal catalysis or through radical processes under catalyst- and additive-free conditions. In some cases, a photocatalyst is employed under visible-light irradiation to facilitate the transformation. For the sulfur dioxide surrogate of inorganic sulfites, potassium metabisulfite or sodium metabisulfite has been broadly used in various transformations. However, the reactivities of inorganic sulfites in organic reactions still need to be explored.

Pd(II)-Catalyzed Cyclization-Oxidation of Urea-Tethered Alkylidenecyclopropanes

A Pd(OAc)₂-catalyzed intramolecular oxidative cyclization of urea-tethered alkylidenecyclopropanes with urea as a nitrogen source through a Pd(II)/Pd(IV) catalytic cycle has been presented, giving the corresponding cyclobuta[ b]indoline derivatives in moderate to good yields with a broad substrate scope. The reaction proceeds through a ring expansion of alkylidenecyclopropane along with the nucleophilic attack of nitrogen atom onto the in situ generated palladium carbenoid species as well as an oxidation process.

Benzylic C(sp3)–H bond sulfonylation of 4-methylphenols with the insertion of sulfur dioxide under photocatalysis

Sulfonylation of the benzylic C–H bond is developed through a three-component reaction of aryldiazonium tetrafluoroborates, 4-methylphenols and sodium metabisulfite (Na₂S₂O₅). The inorganic sulfite of sodium metabisulfite is used as the SO₂ surrogate.

Preparation of 2-Amino-5-homoallylfurans via Palladium-Catalyzed Tandem Cycloisomerization/Heck-Type Coupling of Homoallenyl Amides with Allyltrialkylsilanes

The direct access to 2-amino-5-homoallylfurans has been realized by a palladium-catalyzed tandem cycloisomerization/Heck-type coupling between homoallenyl amides and allyltrialkylsilanes, using a novel DDQ/MnO₂ combination as the efficient oxidant. The reaction exclusively affords γ-allylation products in good to excellent yields with broad substrate scope under exceptionally mild reaction conditions. It represents one of the rare examples of the Pd-catalyzed intermolecular Heck-type coupling of allytrialkylsilanes terminated by β-silyl elimination, thus complementing traditional allylation methods because of the excellent γ-selectivity.