An Atom-Economical Route to Substituted β-Arylethyl Ketones: Phosphomolybdic Acid-Catalyzed Carbohydroxylation of Terminal Alkynes in Organic Carbonate

Cage-Shaped Phosphites Having C3 -Symmetric Chiral Environment: Steric Control of Lewis Basicity and Application as Chiral Ligands in Rhodium-Catalyzed Conjugate Additions

Designing chiral ligands with an axial symmetry higher than C2 -rotational symmetry is one of the most crucial approaches to improving enantioselectivity in asymmetric synthesis. Herein, C3 -symmetric chiral cage-shaped phosphites are reported. Their Lewis basicity and chiral environment are precisely controlled by the tethered group. The cage-shaped phosphites successfully worked as chiral ligands in Rh-catalyzed asymmetric conjugate additions, realizing acceptable yields with excellent enantioselectivity, and were used to synthesize a pharmacologically important molecule.

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.

Copper-Containing Polyoxometalate-Based Metal-Organic Frameworks as Heterogeneous Catalysts for the Synthesis of N-Heterocycles

Three new polyoxometalate-based metal-organic frameworks (POMOFs) [Cu₄(μ₃-OH)₂(tba)₃(H₂O)₅(SiW₁₂O₄₀)_0.5](H₂SiW₁₂O₄₀)_0.5·2.5H₂O (CuSiW), [Cu₃(μ₃-OH)(tba)₃(Htba)(H₂O)₂(HPMo₁₂O₄₀)]·7H₂O (CuPMo), and [Cu₄(μ₃-OH)₂(tba)₃(H₂O)₃(PW₁₂O₄₀)_0.5]₂(PW₁₂O₄₀)·0.5H₂O (CuPW) were constructed using multinuclear copper clusters, 3-(4H-1,2,4-triazol-4-yl)benzoic acid (Htba), and Keggin polyoxometalates (POMs). Different POMs regulate the formation of different multinuclear copper clusters ("boat" tetranuclear clusters in CuSiW, trinuclear clusters in CuPMo, and "chair" tetranuclear clusters in CuPW) and different topological structures of CuSiW, CuPMo, and CuPW (3-connected two-dimensional (2D) network for CuSiW, 4-connected 2D network for CuPMo, and (4,6)-connected three-dimensional network for CuPW). CuSiW, CuPMo, and CuPW as heterogeneous catalysts combine the high stability of MOFs in polar solvents and excellent catalytic activity of POMs and could be used for the synthesis of nitrogen-heterocycle compounds. The condensation cyclization reactions of 2-aminophenols/benzenesulfonyl hydrazines with 1,3-diketones produce benzoazoles and pyrazoles in good to excellent yields under the catalysis of CuPMo. Moreover, the catalyst could be reused at least for 7 runs, and this protocol was suitable for gram-scale reactions.

Heteropolyacid ionic liquid heterogeneously catalyzed synthesis of isochromans via oxa-Pictet-Spengler cyclization in dimethyl carbonate

A recyclable and efficient heterogeneous, green catalyst based on the synthesis of Keggin-type polyoxometalate (H₃PMo₁₂O₄₀) and vitamin B1 analogue 3-ethyl-5-(2-hydroxyethyl)-4-methylthiazol-3-ium (HEMT), i.e., [HEMTH]H₂[PMo₁₂O₄₀] was prepared. Oxa-Pictet–Spengler cyclization of arylethanols and aldehydes were catalyzed to afford various substituted isochromans in moderate conditions with excellent yields using dimethyl carbonate (DMC) as a green solvent. Furthermore, this protocol was applicable in a gram-scale reaction, and the catalyst could be recycled eight times without significant loss of activity.

An efficient heterogeneous and green catalyst [HEMTH]H₂[PMo₁₂O₄₀] was prepared to catalysis the oxa-Pictet–Spengler cyclization of arylethanols and aldehydes to afford isochromans with excellent yields using dimethyl carbonate as a green solvent.

Brønsted Acid-Catalysed Dehydrative Substitution Reactions of Alcohols

The direct, catalytic dehydrative substitution of alcohols is a challenging, yet highly desirable process in the development of more sustainable approaches to organic chemistry. This review outlines recent advances in Brønsted acid-catalysed dehydrative substitution reactions for C-C, C-O, C-N and C-S bond formation. The wide range of processes that are now accessible using simple alcohols as the formal electrophile are highlighted, while current limitations and therefore possible future directions for research are also discussed.

Iron-catalyzed carboarylation of alkynes via activation of π-activated alcohols: rapid synthesis of substituted benzofused six-membered heterocycles

An Fe(OTf)3-catalysed carboarylation of alkynes is reported for the straightforward synthesis of densely substituted 1,2-dihydroquinolines from N-propargyl anilides and π-activated alcohols. The reaction provides a new method for the synthesis of highly substituted benzofused six-membered heterocycles by the formation of two carbon-carbon bonds and one ring in a single step. The power of the methodology was further extended to the synthesis of substituted chromene and thiochromene derivatives in high yields. In addition, substituted quinoline derivatives were also achieved in a single step in the presence of FeCl3 through detosylation/aromatisation. A number of control experiments have been performed and a plausible mechanism has also been proposed to explain the formation of the products.

Self-assembly of Keggin-type U(vi)-containing tungstophosphates with a sandwich structure: an efficient catalyst for the synthesis of sulfonyl pyrazoles

Two Keggin-type U(vi)-containing tungstophosphates with sandwich structure were synthesized and characterized. Compound 1 presents excellent catalytic activity towards the condensation cyclization of sulfonyl hydrazines with 1,3-diketones to synthesize sulfonyl pyrazoles.

Recent advances of Ritter reaction and its synthetic applications

This review provides a comprehensive survey of Ritter reactions from 2014 to 2020.

Copper-catalyzed aerobic oxidative C-C bond cleavage of simple ketones for the synthesis of amides

A Cu-catalyzed oxidative amidation of simple ketones with amines via carbon-carbon (C-C) bond cleavage has been developed. A number of aryl and alkyl ketones could be easily converted to amides using cheap copper salt as the catalyst and O₂ as the oxidant with a wide range of amines, including primary and secondary amines. This method shows a notable advantage of the broad scope for the substrate, thus providing a practical approach to amides. A plausible mechanism is proposed based on the preliminary experiments.

An organocatalytic C–C bond cleavage approach: a metal-free and peroxide-free facile method for the synthesis of amide derivatives

An organocatalyzed C–C bond cleavage approach has been envisioned towards the synthesis of amide derivatives from their corresponding amines and 1,3-dicarbonyls.

Metal-free difunctionalization of alkynes leading to alkenyl dithiocyanates and alkenyl diselenocyanates at room temperature

A simple and practical method for the synthesis of alkenyl dithiocyanates and alkenyl diselenocyanates has been developed via stereoselective difunctionalization of alkynes with NaSCN or KSeCN at room temperature. Through this methodology, a series of alkenyl dithiocyanates and alkenyl diselenocyanates could be efficiently and conveniently obtained in moderate to good yields under mild and metal-free conditions by the simple use of oxone and PhI(OAc)2 as the oxidants.

Ce(iii)-Containing tungstotellurate(vi) with a sandwich structure: an efficient Lewis acid–base catalyst for the condensation cyclization of 1,3-diketones with hydrazines/hydrazides or diamines

A new Ce³⁺ modified Dawson-like polyoxometalate cluster was synthesized, which showed good Lewis acid and Lewis base activities in the condensation reaction.