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

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.

Asymmetric tandem conjugate addition and reaction with carbocations on acylimidazole Michael acceptors

We present here a stereoselective tandem reaction based on the asymmetric conjugate addition of dialkylzinc reagents to unsaturated acylimidazoles followed by trapping of the intermediate zinc enolate with carbocations. The use of a chiral NHC ligand provides chiral zinc enolates in high enantiomeric purities. These enolates are reacted with highly electrophilic onium compounds to afford densely substituted acylimidazoles. DFT calculations helped to understand the reactivity of the zinc enolates derived from acylimidazoles and allowed their comparison with metal enolates obtained by other conjugate addition reactions.

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.

Recent advances in asymmetric borylation by transition metal catalysis

Chiral organoboronates have played a critical role in organic chemistry and in the development of materials science and pharmaceuticals. Much effort has been devoted to exploring synthetic methodologies for the preparation of these compounds during the past few decades. Among the known methods, asymmetric catalysis has emerged as a practical and highly efficient strategy for their straightforward preparation, and recent years have witnessed remarkable advances in this respect. Approaches such as asymmetric borylative addition, asymmetric allylic borylation and stereospecific cross-coupling borylation, have been extensively explored and well established employing transition-metal catalysis with a chiral ligand. This review provides a comprehensive overview of transition metal-catalysed asymmetric borylation processes to construct carbon-boron, carbon-carbon, and other carbon-heteroatom bonds. It summarises a range of recent achievements in this area of research, with considerable attention devoted to the reaction modes and the mechanisms involved.

Synthesis of 1-benzylisoindoline and 1-benzyl-tetrahydroisoquinoline through nucleophilic addition of organozinc reagents to N,O-acetals

A new approach to access 1-benzylisoindoline and 1-benzyl-tetrahydroisoquinoline has been developed through nucleophilic addition of organozinc reagents to N,O-acetals. A number of substituted organozinc reagents were amenable for this transformation, and the desired products were obtained with excellent yields. Moreover, Sc(OTf)3 proved to be an effective catalyst for the formation of 1-benzylisoindoline and 1-benzyl-tetrahydroisoquinoline using such nucleophilic addition.

C-C Bond Cleavage of Unactivated 2-Acylimidazoles

2-Acylimidazoles are widely used as post-transformable carboxylic acid equivalents in chemoselective and enantioselective reactions. Their transformations, however, require pretreatment with highly reactive, toxic methylating reagents to facilitate C-C bond cleavage. Here, we demonstrate that such pretreatment can be avoided and the C-C bond cleaved under neutral conditions without the use of additional reagents or catalysts. The scope of the reaction, including the use of products reported in the literature as substrates, and some mechanistic insights are described.

Catalytic Asymmetric Addition Reactions of Formaldehyde N,N-Dialkylhydrazone to Synthesize Chiral Nitrile Derivatives

A number of nitrile-containing chiral molecules were synthesized via asymmetric nucleophilic addition of formaldehyde N,N-dialkylhydrazone as the nitrile equivalent. Chiral N,N'-dioxide/metal salt complexes enabled the asymmetric addition reactions to both isatin-derived imines and α,β-unsaturated ketones, generating amino nitriles and 4-oxobutanenitrile derivatives in good yields with high enantioselectivities. This protocol was highlighted by avoiding the use of toxic nitrile reagents, wide substrate scope, and versatile transformations of chiral hydrazone adducts into other valuable molecules.

Asymmetric copper-catalyzed conjugate additions of organometallic reagents in the syntheses of natural compounds and pharmaceuticals

Access to enantiopure complex molecular structures is crucial for the development of new drugs as well as agents used in crop-protection. In this regard, numerous asymmetric methods have been established. Copper-catalyzed 1,4-additions of organometallic reagents are robust C-C bond formation strategies applicable in a wide range of circumstances. This review analyses the syntheses of natural products and pharmaceutical agents, which rely on the application of asymmetric Cu-catalyzed conjugate additions of various organometallic reagents. A wide range of available organometallics, e.g. dialkylzinc, trialkylaluminum, Grignard, and organozirconium, can now be used in conjugate additions to address various synthetic challenges present in targeted natural compounds. Furthermore, efficient catalysts allow high levels of stereofidelity over a diverse array of starting Michael acceptors.

Recent advances in Cu-catalyzed C(sp3)-Si and C(sp3)-B bond formation

Numerous reactions generating C-Si and C-B bonds are in focus owing to the importance of incorporating silicon or boron into new or existing drugs, in addition to their use as building blocks in cross-coupling reactions en route to various targets of both natural and unnatural origins. In this review, recent protocols relying on copper-catalyzed sp3 carbon-silicon and carbon-boron bond-forming reactions are discussed.

Copper-catalyzed enantioselective conjugate addition of organometallic reagents to challenging Michael acceptors

The copper-catalyzed enantioselective conjugate addition (ECA) of organometallic nucleophiles to electron-deficient alkenes (Michael acceptors) represents an efficient and attractive methodology for providing a wide range of relevant chiral molecules. In order to increase the attractiveness of this useful catalytic transformation, some Michael acceptors bearing challenging electron-deficient functions (i.e., aldehydes, thioesters, acylimidazoles, N-acyloxazolidinones, N-acylpyrrolidinones, amides, N-acylpyrroles) were recently investigated. Remarkably, only a few chiral copper-based catalytic systems have successfully achieved the conjugate addition of different organometallic reagents to these challenging Michael acceptors, with excellent regio- and enantioselectivity. Furthermore, thanks to their easy derivatization, the resulting chiral conjugated products could be converted into various natural products. The aim of this tutorial review is to summarize recent advances accomplished in this stimulating field.

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.