TMSCl-Promoted Sulfonylation of Propargylic Alcohols with Sodium Sulfinates for the Construction of (E)-1,3-Disulfonylpropenes and (E)-1-Sulfonylpropenols

A direct and novel transformation of propargylic alcohols with sodium sulfinates for the regio- and stereoselective synthesis of (E)-1,3-disulfonylpropenes and (E)-1-sulfonylpropenols was successfully developed in the presence of TMSCl under mild conditions. The preliminary mechanistic experiments demonstrated that the reaction underwent an unprecedented dual nucleophilic substitution/radical addition process, in which sodium sulfinates were used not only as nucleophiles but also as a sulfonyl radical source.

Construction of Diverse Fused Chromene Frameworks via Isocyanide-Based Three-Component Reaction

A convenient synthetic protocol for diverse fused chromenes was successfully developed by a three-component reaction of alkyl isocyanides, dialkyl but-2-ynedioates, and various cyclic 1,3-dipolarophiles containing o-hydroxyphenyl group. In the absence of any catalyst, the three-component reaction of alkyl isocyanides, dialkyl but-2-ynedioates, and 3-(o-hydroxyarylidene)indolin-2-ones in tetrahydrofuran at 60 °C resulted in unique functionalized spiro[cyclobuta[c]chromene-1,3'-indolines] in good yields and with high diastereoselectivity. However, the similar three-component reaction with 2-(5-halo-2-hydroxyarylidene)indolin-2-ones afforded unexpected chain products in satisfactory yields. In addition, the three-component reaction of alkyl isocyanides, dialkyl but-2-ynedioates, and 2-(o-hydroxyarylidene)-1,3-indanediones in tetrahydrofuran at 60 °C resulted in complex indeno[2',1':5,6]pyrano[3,4-c]chromene derivatives in high yields and with high diastereoselectivity.

TFA-Promoted Cascade Sulfonylation/Rearrangement/Cyclization of 1,5-Diynols and Sodium Sulfinates to Construct Sulfonylated Benzo[b]fluorenes

A novel conversion of 1,5-diynols into sulfonylated benzo[b]fluorenes is reported by a TFA-promoted cascade cyclization with sodium sulfinates under mild conditions. This strategy provides an efficient and practical approach for accessing various sulfonated benzo[b]fluorenes in moderate to excellent yields under metal-free conditions. On the basis of the control experimental results and density functional theory calculations, a possible cascade transformation mechanism consisting of the dehydration of propargylic alcohols, sulfonylation, allenylation, and Schmittel-type cyclization is proposed. It is worth noting that TFA played an important role in this cascade cyclization, which promoted C-SO2R bond cleavage in a propargylic sulfone intermediate to form allenyl sulfones, followed by Schmittel-type cyclization to give the target product.

Copper(II)-catalyzed direct dehydrative alkynylation of 2H-chromene hemiketals with terminal alkynes to 2,2-disubstituted 2-alkynylated 2H-chromenes

The first copper-catalyzed direct dehydrative alkynylation of 2H-chromene hemiketals with terminal alkynes has been uncovered. The use of cheap and readily available CuCl₂ as the catalyst allowed the preparation of various 2,2-disubstituted 2-alkynylated 2H-chromenes in moderate to good yields, which compensates for the limitation of the current methods only suited for the synthesis of 2-monosubsituted 2-alkynylated 2H-chromenes.

Synthesis of 2H-chromenes: recent advances and perspectives

As one type of chromene, 2H-chromenes represent important oxygen heterocycles, which not only widely exist in natural products, pharmaceutical agents and biologically relevant molecules, but have also been used broadly in materials science and organic synthesis. Two major synthetic strategies have been developed towards such compounds. This review mainly focuses on the recent advances in this field, including benzopyran ring formation involving cyclization reactions and the late-stage functionalization of the parent 2H-chromenes.

C-4 benzofuranylation of pyrazolones by a metal-free catalyzed indirect heteroarylation strategy

A metal-free catalyzed indirect heteroarylation of pyrazolones with 2-(3-hydroxy-3,3-diarylprop-1-yn-1-yl) phenols has been developed, and a series of novel 4-benzofuranyl substituted pyrazolone derivatives were obtained in moderate to excellent yields (up to 90%). The process has the salient features of metal-free catalysis, operational simplicity, good substrate compatibility and mild reaction conditions. In particular, the integration of the pyrazolone skeleton and benzofuran scaffold into a single molecule is expected to be of potential interest for medicinal research. In addition, the yield and efficiency are basically maintained in the gram-scale experiment, which makes the practical application of the process more prominent.

Y(OTf)3-catalyzed phosphorylation of 2H-chromene hemiacetals with P(O)-H compounds to 2-phosphorylated 2H-chromenes

A facile synthesis of 2-phosphorylated 2H-chromenes has been accomplished herein via a Y(OTf)₃-catalyzed dehydrative coupling of 2H-chromene hemiacetals with P(O)-H compounds. This protocol features low catalyst loading, mild reaction conditions, broad substrate scope and easy elaboration of the products.

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.

Multicomponent cascade reactions of HKAs: synthesis of highly functionalized 5H-chromeno[4,3-d]pyrimidines

A novel protocol was developed for the construction of functionalized 5H-chromeno[4,3-d]pyrimidines from 3-formylchromones, heterocyclic ketene aminals, and amidine hydrochlorides via a novel cascade reaction involving ring-opening and 1,3-H shift reactions.

TMSBr-Promoted Cascade Cyclization of ortho-Propynol Phenyl Azides for the Synthesis of 4-Bromo Quinolines and Its Applications

Difficult-to-access 4-bromo quinolines are constructed directly from easily prepared ortho-propynol phenyl azides using TMSBr as acid-promoter. The cascade transformation performs smoothly to generate desired products in moderate to excellent yields with good functional groups compatibility. Notably, TMSBr not only acted as an acid-promoter to initiate the reaction, and also as a nucleophile. In addition, 4-bromo quinolines as key intermediates could further undergo the coupling reactions or nucleophilic reactions to provide a variety of functionalized compounds with molecular diversity at C4 position of quinolines.

An Efficient Approach to Phosphorylated Isoindoline Fused with Triazoles via Zn-Catalyzed Cascade Cyclization of 2-Propynol Benzyl Azides and Diarylphosphine Oxides

An efficient approach for the synthesis of phosphorylated isoindoline fused with triazoles via Zn(OTf)₂-catalyzed cascade cyclization of easily prepared ortho-propynol benzyl azides and diarylphosphine oxides is developed. The transformation occurred smoothly in moderate to excellent yields and tolerated various propargylic alcohol substrates.