Ionic and Covalent Copper(II)-Based Catalysts for Michael Additions. The Mechanism

Copper(II)-Catalyzed Tandem Decarboxylative Michael/Aldol Reactions Leading to the Formation of Functionalized Cyclohexenones

This work describes the development of a new single-pot copper(II)-catalyzed decarboxylative Michael reaction between β-keto acids and enones, followed by in situ aldolization, which results in highly functionalized chiral and achiral cyclohexenones. The achiral version of this Robinson annulation features a hitherto unprecedented Michael reaction of β-keto acids with sterically hindered β,β'-substituted enones and provides access to all carbon quaternary stereocenter-containing cyclohexenones (11 examples, 43-83% yield). In addition, an asymmetric chiral bis(oxazoline) copper(II)-catalyzed single-pot Robinson annulation has been devised for preparing chiral cyclohexenones, including some products that contain vicinal stereocenters (5 examples, 65-85% yield, 84-94% ee). This latter protocol has been successfully applied to the enantioselective formation of the oxygenated 10-nor-steroid core from readily available starting materials.

Copper-catalyzed reactions: Research in the gas phase

Electrospray ionization mass spectrometry (ESI-MS) is becoming an important tool for mechanistic studies in organic and organometallic chemistry. It allows investigation of reaction mixtures including monitoring of reactants, products, and intermediates, studying properties of the intermediates and their reactivity. Studying the reactive species in the gas phase can be advantageously combined with theoretical calculations. This review is focused on ESI-MS studies of copper-catalyzed reactions. Possible effects of the electrospray process on the transfer of the copper complexes to the gas phase are discussed. The plethora of mass spectrometric approaches is demonstrated on copper mediated C-H activations, cross coupling reactions, rearrangements, organocuprate chemistry, and other examples.

Concise Enantioselective Synthesis of Oxygenated Steroids via Sequential Copper(II)-Catalyzed Michael Addition/Intramolecular Aldol Cyclization Reactions

A new scalable enantioselective approach to functionalized oxygenated steroids is described. This strategy is based on chiral bis(oxazoline) copper(II) complex-catalyzed enantioselective and diastereoselective Michael reactions of cyclic ketoesters and enones to install vicinal quaternary and tertiary stereocenters. In addition, the utility of copper(II) salts as highly active catalysts for the Michael reactions of traditionally unreactive β,β'-enones and substituted β,β'-ketoesters that results in unprecedented Michael adducts containing vicinal all-carbon quaternary centers is also demonstrated. The Michael adducts subsequently undergo base-promoted diastereoselective aldol cascade reactions resulting in the natural or unnatural steroid skeletons. The experimental and computational studies suggest that the torsional strain effects arising from the presence of the Δ(5)-unsaturation are key controlling elements for the formation of the natural cardenolide scaffold. The described method enables expedient generation of polycyclic molecules including modified steroidal scaffolds as well as challenging-to-synthesize Hajos-Parrish and Wieland-Miescher ketones.

Regioselective synthesis of novel and diverse naphtho[1,2-b]furan-3-carboxamides and benzofuran-3-carboxamides by cascade formal [3 + 2] cycloaddition

The regioselective synthesis of diverse naphtho[1,2-b]furan-3-amides and benzofuran-3-amides was accomplished by the In(OTf)₃-catalyzed cascade formal [3 + 2] cycloaddition of 1,4-naphthoquinones or benzoquinones with β-ketoamides.

Novel Michael addition products of bis(amino acidato)metal(II) complexes: synthesis, characterization, dye degradation, and oxidation properties

Michael addition reactions of bis(amino acidato)metal(II) complexes (metal = copper, nickel, zinc; amino acid = glycine, dl-alanine, l-alanine) with acrylonitrile have been carried out under various experimental conditions in the absence of a base, resulting in mono- and disubstituted products in high yield, including partially hydrolyzed products. A reaction mechanism for the Michael addition on the nitrogen atom of the coordinated amino acid moiety, replacing the amino hydrogen atom(s), is proposed. All of the products have been characterized by Fourier transform infrared spectroscopy, electron paramagnetic resonance spectra, and elemental and electrochemical analyses. The single-crystal structures of bis( N-cyanoethylglycinato)copper(II) monohydrate ( 1a), diaquabis( N-cyanoethylglycinato)nickel(II), aquabis( N, N-dicyanoethylglycinato)copper(II) ( 2a), and bis[( N-propionamido- N-cyanoethyl)glycinato]copper(II) dihydrate ( 4a) have been confirmed by X-ray diffraction techniques. The products 1a, 2a, 4a, and bis( N-propionamidoglycinato)copper(II) monohydrate ( 3a) have been used as catalysts for the degradation of a phenol red dye and mild oxidation of various organic substrates in the presence of hydrogen peroxide. The monosubstituted complexes have been found to catalyze the reactions to a greater extent than the disubstituted complexes.