One-Pot Reaction of Carboxylic Acids, Ynol Ethers, and m-CPBA for Synthesis of α-Carbonyloxy Esters

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.

Pathway to Construct α-Acyloxy Esters by B(C6F5)3-Catalyzed O-H Insertion of Carboxylic Acids with Sulfoxonium Ylides

We report the first example of B(C6F5)3-catalyzed O-H insertion reaction of sulfoxonium ylides and carboxylic acids, achieving efficient construction of diester moieties under metal-free condition. This protocol is characterized by broad substrate tolerance, particularly for various phenylacetic acids, and good compatibility with water/air condition, which is superior to most other methods.

Gold-Catalyzed Regio- and Stereoselective α-Acyloxy-β-Alkynylation of Ynol Ethers

Enol esters and conjugated enynes are valuable structural motifs for synthetic chemistry and material sciences. Herein, the synthesis of tetra-substituted enol ester 2-iodobenzoate derivatives was achieved in good yields at room temperature through a gold-catalyzed acyloxyalkynylation of sensitive ynol ethers with ethynylbenziodoxolones (EBXs), the latter acting as bifunctional reactants. The conversion is highly regioselective with a broad substrate scope. Mechanistically, an Au(III) species is the key intermediate of an Au(I)/Au(III) redox cycle. The reaction is synthetically useful and can easily be scaled up to gram scale.

Ynamides in Radical Reactions: A Route to Original Persubstituted 2-Aminofurans

Mn(OAc)₃/Cu(OAc)₂-mediated reaction between ynamides, derived from oxazolidone or 3-methylindole carboxylate, and cyclic α-dicarbonyl radicals led to the one-pot synthesis of 2-aminofurans. The transformation involves addition of the α-dicarbonyl radical to ynamide, oxidation to ketene-iminium, and polar cyclization steps to provide original persubstituted 2-aminofurans in good to excellent yields. This work represents the first radical route for the synthesis of furans from ynamides.

Regio- and Stereoselective Addition to gem-Difluorinated Ene-Ynamides: Access to Stereodefined Fluorinated Dienes

The first synthesis of gem-difluorinated ene-ynamides is presented via deprotonation of trifluoromethylated N-allenamides and δ extrusion of fluorine. These highly reactive building blocks, owing to their dual functional groups, offer a unique entry to difluorinated dienes and to stereodefined, monofluoro-substituted dienes. Stereoselective addition to the ynamide moiety led to difluorinated dienes. A stereocontrolled domino δ elimination reaction followed by an addition/elimination sequence from trifluoromethylated N-allenamides provided exclusively stereodefined monofluorinated ene-ynamides.

Carboxylic Acid Functionalization Using Sulfoxonium Ylides as a Carbene Source

Functionalization of carboxylic acids using sulfoxonium ylides in the presence of [VO(acac)₂] as a catalyst is reported. The usual carbene source, diazo compounds, failed to produce α-carbonyloxy esters in good yield when compared to sulfoxonium ylides. Various standard spectroscopic and analytical techniques were used to characterize the products formed.

Metal-Free Stereoselective Addition of Propiolic acids to Ynamides: A Concise Synthetic Route to Highly Substituted Ene-Diyne/Dienyne-(E)-N,O-Acetals

A straight forward and sustainable approach for 1,2-addition of propiolic acids to ynamide has led to bench stable sp2 (E)-enol-enamides of enediynes & dienynes. The reaction is chemo, regio, as...