Deoxygenative Hydroboration of Carboxamides: A Versatile and Selective Synthetic Approach to Amines

Deoxygenative reduction of amides is considered as an attractive method for preparation of synthetically valuable amines. However, the low electrophilicity of the amide carbonyl group, high thermodynamic stability and kinetic...

Access to α,α-Difluoro-γ-amino Acids by Nickel-Catalyzed Reductive Aryldifluoroacetylation of N-Vinylacetamide

A nickel-catalyzed reductive aryldifluoroacetylation of N-vinylacetamide with ethyl chloro(difluoro)acetate and aryl iodides is described. This chelating amide carbonyl group-assisted strategy provides rapid access to a variety of protected α,α-difluoro-γ-amino acids that might have potential applications in peptide chemistry and protein engineering. An advantage of this method is its synthetic simplicity, with no preparation of organometallic reagents.

Recent Progress in Chemistry of β-Lactams

The β-lactams constitute a well-known class of compounds having tremendous biological significance. Besides being a motif of biological interest, they serve as versatile synthons in organic chemistry. In fact, their easy accessibility in the laboratory by several methods combined with inherent reactivity of the β -lactam ring due to ring-strain places it among the most sought for substrate in the arsenal of synthetic organic chemists. Several chemical reagents, heat, and light promote its ring-opening, ring-expansions and rearrangement reactions yielding a wide variety of biologically relevant nitrogen-containing acyclic and heterocyclic compounds. In recent years, the reactivity of differently functionalized β-lactam rings towards diverse kinds of reagents has been investigated. These investigations exploit selective bond cleavage of the β-lactam nucleus via N1-C2, C3- C4, C2-C3 or N1-C4 bond cleavage using simple reagents. The reduction of amide carbonyl group, thionation, and pyrolysis/photolysis have also been explored. These investigations have led to the discovery of many easy synthetic methods for biologically important classes of compounds such as β-amino acids, β-amino esters, amino sugars, amino alcohols, peptides, azetidines, and other heterocyclic compounds. This article discusses the advances made in the studies on the reactivity of β- lactam ring during the last ten years.

Base Metal Catalysts for Deoxygenative Reduction of Amides to Amines

The development of efficient methodologies for production of amines attracts significant attention from synthetic chemists, because amines serve as essential building blocks in the synthesis of many pharmaceuticals, natural products, and agrochemicals. In this regard, deoxygenative reduction of amides to amines by means of transition-metal-catalyzed hydrogenation, hydrosilylation, and hydroboration reactions represents an attractive alternative to conventional wasteful techniques based on stoichiometric reductions of the corresponding amides and imines, and reductive amination of aldehydes with metal hydride reagents. The relatively low electrophilicity of the amide carbonyl group makes this transformation more challenging compared to reduction of other carbonyl compounds, and the majority of the reported catalytic systems employ precious metals such as platinum, rhodium, iridium, and ruthenium. Despite the application of more abundant and environmentally benign base metal (Mn, Fe, Co, and Ni) complexes for deoxygenative reduction of amides have been developed to a lesser extent, such catalytic systems are of great importance. This review is focused on the current achievements in the base-metal-catalyzed deoxygenative hydrogenation, hydrosilylation, and hydroboration of amides to amines. Special attention is paid to the design of base metal catalysts and the mechanisms of such catalytic transformations.

Efficient synthesis of N-butadiene substituted oxindole derivatives

A novel rhodium(iii)-catalyzed amide carbonyl group directed alkenylation reaction between oxindoles and alkenes has been reported, which provides an efficient method for the synthesis of valuable and versatile functionalized N-(2E,4Z)-butadiene substituted oxindole derivatives.

Enzymatically-stable oxetane-based dipeptide hydrogels

A new Fmoc-protected dipeptide incorporating an oxetane ring as a surrogate for the amide carbonyl group is an effective gelator.

Crystal structure ofN-(3-oxobutanoyl)-L-homoserine lactone

The structure and absolute configuration of the title compound, C8H11NO4, which is a known quorum-sensing modulator, have been determined. The molecule exhibits signs of an intramolecular attractive carbonyl–carbonyln→π*interaction between the amide and lactone ester groups, specifically – a short contact of 2.709 (2) Å between the amide oxygen atom and ester carbon atom, approach of the amide oxygen atom to the ester carbonyl group along the Bürgi–Dunitz trajectory, at 99.1 (1)°, and pyramidalization of the ester carbonyl group by 1.1 (1)°. Moreover, a similarn→π*interaction is observed for the amide carbonyl group approached by the ketone oxygen donor. These interactions apparently affect the conformation of the uncomplexed molecule, which adopts a different shape when bound to protein receptors. In the crystal, the molecules form translational chains along theaaxisviaN—H...O hydrogen bonds.

Crystal structure of 1-(piperidin-1-yl)butane-1,3-dione

In the title compound, C9H15NO2, the piperidine ring exhibits a chair conformation. The butanedione subunit exhibits a conformation with the ketone C atom in an eclipsed position with respect to the amide carbonyl group. In the crystal, a two-dimensional layered arrangement is formed by hydrogen bonds of the C—H...O type between the methyl group and the exocyclic methylene unit as donor sites and the amide carbonyl O atom as the acceptor of a bifurcated hydrogen bond. These layers are oriented parallel to theabplane.

Memory of chirality in rebound cyclizations of α-amide radicals

Reduction of (S)-N-(2-bromoallyl)-N-(tert-butyl)-2-methyl-3-phenylpropanamide with tributyltin hydride provides (3S,4S)-3-benzyl-1-(tert-butyl)-3,4-dimethylpyrrolidin-2-one with about 80% retention of chirality at the stereocenter adjacent to the amide carbonyl group. This memory of chirality is suggested to occur by transfer of chirality from a stereocenter to an axis, then from the axis back to a new stereocenter.