Aza-Michael-type addition reaction catalysed by a supported ionic liquid phase incorporating an anionic heteropoly acid

Reinvigorating aza-Michael reactions under ionic liquid catalysis: a greener approach

Cholinium α-amino carboxylates, which debuted in the ionic liquid arena over a decade ago, exhibit superior stability and suitable physical properties relative to other RTILs. Although synthetic pursuits in such media, leveraging their dual role as solvents and catalysts, have been scarce so far, we herein illustrate their catalytic advantage in aza-Michael reactions in terms of low loading, acceleration and improved yields with respect to conventional conditions and other imidazolium-based ILs. These highly structured salts most likely act through multiple and cooperative non-covalent interactions. These mechanistic features have also been investigated through high-level computational analyses as well.

Catalyst-free anti-Markovnikov hydroamination and hydrothiolation of vinyl heteroarenes in aqueous medium: an improved process towards centhaquine

Catalyst-free hydroamination and hydrothiolation of alkenes have been achieved in an aqueous medium. The anti-Markovnikov addition works efficiently in suspended water at room temperature and allows straightforward access to centhaquine, a drug used for the management of hypovolemic shocks in critically ill patients, and its derivatives. Various primary and secondary amines, thiols, and hydrazides were successfully reacted with a number of heteroaryl/aryl-alkenes. The scalability of the process has been demonstrated by synthesizing centhaquine at a 19.65 g scale. A comparative analysis of the present process with previous approaches has been provided on the basis of green chemistry metrics.

ASYMMETRIC SYNTHESIS: A GLANCE AT VARIOUS METHODOLOGIES FOR DIFFERENT FRAMEWORKS

Abstract:

Asymmetric reactions have made a significant advancement over the past few decades and involved the production of enantiomerically pure molecules using enantioselective organocatalysis, chiral auxiliaries/substrates, and reagents via controlling the absolute stereochemistry. The laboratory synthesis from an enantiomerically impure starting material gives a combination of enantiomers which are difficult to separate for chemists in the fields of medicine, chromatography, pharmacology, asymmetric synthesis, studies of structure-function relationships of proteins, life sciences and mechanistic studies. This challenging step of separation can be avoided by the use of asymmetric synthesis. Using pharmacologically relevant scaffolds/pharmacophores, the drug designing can also be achieved using asymmetric synthesis to synthesize receptor specific pharmacologically active chiral molecules. This approach can be used to synthesize asymmetric molecules from wide variety of reactants using specific asymmetric conditions which is also beneficial for environment due to less usage and discharge of chemicals into the environment. So, in this review, we have focused on the inclusive collation of diverse mechanisms in this area, to encourage auxiliary studies of asymmetric reactions to develop selective, efficient, environment-friendly and high yielding advanced processes in asymmetric reactions.

Catalyst-free, aza-Michael polymerization of hydrazides: polymerizability, kinetics, and mechanistic origin of an α-effect

Despite the powerful nature of the aza-Michael reaction for generating C-N linkages and bioactive moieties, the bis-Michael addition of 1° amines remains ineffective for the synthesis of functional, step-growth polymers due to the drastic reduction in reactivity of the resulting 2° amine mono-addition adduct. In this study, a wide range of commercial hydrazides are shown to effectively undergo the bis-Michael reaction with divinyl sulfone (DVS) and 1,6-hexanediol diacrylate (HDA) under catalyst-free, thermal conditions to afford moderate to high molecular weight polymers with M n = 3.8-34.5 kg mol-1. The hydrazide-Michael reactions exhibit two distinctive, conversion-dependent kinetic regimes that are 2nd-order overall, in contrast to the 3rd-order nature of amines previously reported. The mono-addition rate constant was found to be 37-fold greater than that of the bis-addition at 80 °C for the reaction between benzhydrazide and DVS. A significant majority (12 of 15) of the hydrazide derivatives used here show excellent bis-Michael reactivity and achieve >97% conversions after 5 days. This behavior is consistent with calculations that show minimal variance of electron density on the N-nucleophile among the derivatives studied. Reactivity differences between hydrazides and hexylamine are also explored. Overall, the difference in reactivity between hydrazides and amines is attributed to the adjacent nitrogen atom in hydrazides that acts as an efficient hydrogen-bond donor that facilitates intramolecular proton-transfer following the formation of the zwitterion intermediate. This effect not only activates the Michael acceptor but also coordinates with additional Michael acceptors to form an intermolecular reactant complex.

Catalytic Amination of β-(Hetero)arylethyl Ethers by Phosphazene Base t-Bu-P4

We describe the catalytic amination of β-(hetero)arylethyl ethers with amines using the organic superbase t-Bu-P4 to obtain β-(hetero)arylethylamines. The reaction has a broad substrate scope and allows the transformations of electron-deficient and electron-neutral β-(hetero)arylethyl ethers with various amines including pyrrole, N-alkylaniline, diphenylamine, aniline, indole, and indoline derivatives. Mechanistic studies indicate a two-reaction pathway of MeOH elimination from the substrate to form a (hetero)arylalkene followed by the hydroamination of the alkene.

Recent advances in the asymmetric synthesis of pharmacology-relevant nitrogen heterocycles via stereoselective aza-Michael reactions

In this review, recent applications of a stereoselective aza-Michael reaction for asymmetric synthesis of naturally occurring N-containing heterocyclic scaffolds and their usefulness to pharmacology are summarized.

Regioselective 1,4-conjugate aza-Michael addition of dienones with benzotriazole

The regioselective 1,4-conjugate aza-Michael addition of dienones with benzotriazole catalyzed by potassium acetate is described. A series of 3-(benzotriazol-1-yl)-1,5-diarylpent-4-en-1-ones were efficiently synthesized under mild conditions. This protocol has advantages of transition-metal free catalyst, high yield and high regioselectivity.