α,β-Unsaturated N-Acylindoles: An Alternative Class of Michael Acceptors and Their Application in Asymmetric Borylation

Asymmetric 1,4-Addition of Diarylphosphine Oxides to α, β-Unsaturated 2-Acyl Imidazoles

Here we introduce a metal-free, catalytic and enantioselective strategy from α,β-unsaturated 2-acyl imidazoles to the chiral phosphorous 2-acyl imidazoles. Interestingly, this methodology was catalyzed by the classical and commercial oxazaborolidine under mild conditions. This strategy features a wide range of substrates scope with good yields and excellent enantioselectivities. The possible mechanism further suggests the key of this reaction through the cleavage of diarylphosphine oxides using Frustrated Lewis Pairs theory.

Cu-Catalyzed Asymmetric Kinetic Boron Conjugate Addition of γ-Substituted α,β-Unsaturated γ-Lactams

Chiral α,β-unsaturated γ-lactams bearing simple γ- substituents are found in biologically active molecules and natural products, however, their synthesis still remains difficult. Herein, we report an efficient kinetic resolution (KR) of γ-substituted α,β-unsaturated γ-lactams via a Cu-catalyzed asymmetric boron conjugate addition, which also leads to the efficient synthesis of chiral β-hydroxy-γ-lactams with β,γ-stereogenic carbon centers. The KR proceeded smoothly with a wide range of γ-alkyl or aryl substituted substrates including those bearing aromatic heterocycles and different N-protected substrates in up to 347 of s value. Their highly versatile transformations, synthetic utility in biologically active molecules, and inhibitory activities against cisplatin-sensitive ovarian cancer cell A2780 have also been demonstrated. Differing from the well-known mechanism involving Cu-B species in Cu-catalyzed boron conjugate additions, our mechanistic studies using density functional theory (DFT) calculations and experiments indicate that a Lewis acid CuI -catalyzed mechanism is the likely pathway in the catalytic reaction.

Development of Methods to the Synthesis of β-Boryl Acyls, Imines and Nitriles

Organoboron compounds are highly important and versatile synthetic intermediates for the preparation of a wide range of organic molecules. Organoboron compounds have drawn significant attention among organic chemists due to their Lewis acidic property, non-toxicity, and commercial availability. Over the last several decades, there has been a substantial development of new organoboron compounds, useful in organic synthesis. Among all other organoboron compounds, β-boryl carbonyl compounds are the important ones. The β-boryl compounds have appeared as promising intermediates for various synthetic transformations. The 1,4-conjugate addition of diboron reagents to carbon-carbon double bond in the presence of different transition-metal catalysts has been extensively reported by various research groups across the globe. This mini-review outlines the numerous racemic as well as asymmetric β-borylation methods developed to date.

First-Row d-Block Element-Catalyzed Carbon-Boron Bond Formation and Related Processes

Organoboron reagents represent a unique class of compounds because of their utility in modern synthetic organic chemistry, often affording unprecedented reactivity. The transformation of the carbon-boron bond into a carbon-X (X = C, N, and O) bond in a stereocontrolled fashion has become invaluable in medicinal chemistry, agrochemistry, and natural products chemistry as well as materials science. Over the past decade, first-row d-block transition metals have become increasingly widely used as catalysts for the formation of a carbon-boron bond, a transformation traditionally catalyzed by expensive precious metals. This recent focus on alternative transition metals has enabled growth in fundamental methods in organoboron chemistry. This review surveys the current state-of-the-art in the use of first-row d-block element-based catalysts for the formation of carbon-boron bonds.

Enantioselectivity switch in asymmetric Michael addition reactions using phosphonium salts

Efficient access to two enantiomers of one chiral compound is critical for the discovery of drugs. However, it is still a challenging problem owing to the difficulty in obtaining two enantiomers of one chiral catalyst. Here, we report a general method to obtain both enantiomeric products via fine tuning the hydrogen-bonding interactions of phosphonium salts. Amino acid derived phosphonium salts and dipeptide derived phosphonium salts exhibited different properties for controlling the transition state, which could efficiently promote the Michael addition reaction to give opposite configurations of products with high yields and enantioselectivities. Preliminary investigations on the mechanism of the reaction and applications of the products were also performed.

High-Loading Single-Atom Copper Catalyst Supported on Coordinatively Unsaturated Al2 O3 for Selective Synthesis of Homoallylboronates

Single-atom catalysts (SACs) as a bridge between hetero- and homogeneous catalysis have attracted much attention. However, it is still challenging to generate stable single atoms with high metal loadings, and the application of SACs in traditionally homogeneous catalytic reactions is highly desirable. Herein, a Cu SAC with a high Cu loading of 8.7 wt % supported on coordinatively unsaturated Al₂ O₃ was prepared and used in the amine-free synthesis of homoallylboranes. Up to 99 % conversion, 95 % 1,4-selective boration of the enals, and 48-68 % isolated yields of homoallylboranes were achieved, equaling the results of reported homogenous catalysts, and the system was more efficient and stable than nano Cu/γ-Al₂ O₃ . Mechanistic investigation indicated that Cu-Bpin species are the active intermediates of selective boration. The superior catalytic and recycling performance of Cu SAC paves an efficient and green path toward selective synthesis of homoallyborane fine chemicals.

Copper(i)/DM-SEGPHOS-catalyzed enantio- and diastereoselective conjugate boration to α-alkylidene-γ-lactams

A combination of CuCl and DM-SEGPHOS catalyst system has allowed the development of highly enantioselective and diastereoselective conjugate addition of bis(pinacolato)diboron to α-alkylidene-γ-lactams.

β-Borylation of conjugated carbonyl compounds with silylborane or bis(pinacolato)diboron catalyzed by Au nanoparticles

β-Borylation occurs in the Au/TiO₂-catalysed reaction between the silylborane Me₂PhSiBpin and conjugated carbonyl compounds, in contrast to the so far known analogous reaction catalysed by other metals, where β-silylation occurs instead.

Copper-Catalyzed Asymmetric Conjugate Additions of Bis(pinacolato)diboron and Dimethylzinc to Acyl- N-methylimidazole Michael Acceptors: A Highly Stereoselective Unified Strategy for 1,3,5,... n (OH, Me) Motif Synthesis

A unified strategy for the construction of prevalent 1,3,5,... n (OH, Me) motifs based on consecutive copper-catalyzed asymmetric conjugate borylation (ACB) and methylation (ACA) reactions involving α,β-unsaturated 2-acyl- N-methylimidazoles is described. Good yields and high diastereoselectivities have been obtained in ACA and ACB reactions for both matched and mismatched pairs as illustrated in the synthesis of syn/ anti and anti/ anti (Me, OTBS, Me) and (OH, OTBS, Me) motifs.