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Relevant academic research and scientific papers

One-pot dual catalysis for the hydrogenation of heteroarenes and arenes

A simple dinuclear monohydrido bridged ruthenium complex [{(η6-p-cymene)RuCl}2(μ-H-μ-Cl)] acts as an efficient and selective catalyst for the hydrogenation of various heteroarenes and arenes. The nature of the catalytically active species was investigated using a combination of techniques including in situ reaction monitoring, kinetic studies, quantitative poisoning experiments and electron microscopy, evidencing a dual reactivity. The results suggest that the hydrogenation of heteroarenes proceeds via molecular catalysis. In particular, monitoring the reaction progress by NMR spectroscopy indicates that [{(η6-p-cymene)RuCl}2(μ-H-μ-Cl)] is transformed into monomeric ruthenium intermediates, which upon subsequent activation of dihydrogen and hydride transfer accomplish the hydrogenation of heteroarenes under homogeneous conditions. In contrast, carbocyclic aryl motifs are hydrogenated via a heterogeneous pathway, by in situ generated ruthenium nanoparticles. Remarkably, these hydrogenation reactions can be performed using molecular hydrogen under solvent-free conditions or with 1,4-dioxane, and thus give access to a broad range of saturated heterocycles and carbocycles while generating no waste.

Biocatalytic Access to Piperazines from Diamines and Dicarbonyls

Given the widespread importance of piperazines as building blocks for the production of pharmaceuticals, an efficient and selective synthesis is highly desirable. Here we show the direct synthesis of piperazines from 1,2-dicarbonyl and 1,2-diamine substrates using the R-selective imine reductase from Myxococcus stipitatus as biocatalyst. Various N- and C-substituted piperazines with high activity and excellent enantioselectivity were obtained under mild reaction conditions reaching up to 8.1 g per liter.

DECAHYDROQUINOXALINE DERIVATIVES AND ANALOGS THEREOF

A heterocyclic compound represented by the general formula (1) or a salt thereof: wherein m, l, and n respectively represent an integer of 1 or 2; X represents -O- or -CH2-; R1 represents hydrogen, a lower alkyl group, a hydroxy-lower alkyl group, a protecting group, or a tri-lower alkylsilyloxy-lower alkyl group; R2 and R3, which are the same or different, each independently represent hydrogen or a lower alkyl group; or R2 and R3 are bonded to form a cyclo-C3-C8 alkyl group; and R4 represents an aromatic group or a heterocyclic group, wherein the aromatic or heterocyclic group may have one or more arbitrary substituent(s).

HETEROCYCLIC COMPOUNDS FOR TREATING OR PREVENTING DISORDERS CAUSED BY REDUCED NEUROTRANSMISSION OF SEROTONIN, NOREPHNEPHRINE OR DOPAMINE.

A heterocyclic compound represented by the general formula (1) or a salt thereof: wherein m, l, and n respectively represent an integer of 1 or 2; X represents -O- or -CH2-; R1 represents hydrogen, a lower alkyl group, a hydroxy-lower alkyl group, a protecting group, or a tri-lower alkylsilyloxy-lower alkyl group; R2 and R3, which are the same or different, each independently represent hydrogen or a lower alkyl group; or R2 and R3 are bonded to form a cyclo-C3-C8 alkyl group; and R4 represents an aromatic group or a heterocyclic group, wherein the aromatic or heterocyclic group may have one or more arbitrary substituent(s).

Iridium-catalyzed condensation of amines and vicinal diols to substituted piperazines

A straightforward procedure is described for the synthesis of piperazines from amines and 1,2-diols. The heterocyclization is catalyzed by [Cp*IrCl2]2 and sodium hydrogen carbonate and can be achieved with either toluene or water as solvent. The transformation does not require any stoichiometric additives and only produces water as the byproduct. The reaction can be performed between a 1,2-diamine and a 1,2-diol or by a double condensation between a primary alkylamine and a 1,2-diol. At least one substituent is required on the piperazine ring to achieve the cyclization in good yield. The mechanism is believed to involve dehydrogenation of the 1,2-diol to the α-hydroxy aldehyde, which condenses with the amine to form the α-hydroxy imine. The latter rearranges to the corresponding α-amino carbonyl compound, which then reacts with another amine followed by reduction of the resulting imine. Piperazines are prepared by [Cp*IrCl 2]2-catalyzed heterocyclization of 1,2-diols with either 1,2-diamines or primary alkylamines. The reaction is performed in toluene or water and requires no stoichiometric additive. The key step in the mechanism is believed to be the isomerization of an α-hydroxy imine to the corresponding α-amino carbonyl compound. Copyright

A bifunctional PdVMgO solid catalyst for the one-pot selective N-monoalkylation of amines with alcohols

It has been found that a bifunctional metal Pd/base (MgO) catalyst performs the selective monoalkylation of amines with alcohols. The reaction goes through a series of consecutive steps in a cascade mode that involves: 1) the abstraction of hydrogen from the alcohol that produces the metal hydride and the carbonyl compound; 2) condensation of the carbonyl with the amine to give an imine, and 3) hydrogenation of the imine with the surface hydrogen atoms from the metal hydride. Based on isotopic and spectroscopic studies and on the rate of each elementary step, a global reaction mechanism has been proposed. The controlling step of the process is the hydride transfer from the metal to the imine. By changing the crystallite size of the Pd, it is demonstrated that this is a structure-sensitive reaction, whereas the competing processes that lead to subproducts are not. On these bases, a highly selective catalyst has been obtained with Pd crystallite size below 2.5 nm in diameter. The high efficiency of the catalytic system has allowed us to extend the process to the one-pot synthesis of piperazines.

An annulation reaction for the synthesis of morpholines, thiomorpholines, and piperazines from β-heteroatom amino compounds and vinyl sulfonium salts

(Chemical Equation Presented) Heterocycling: Diphenyl vinyl sulfonium salt 1 acts first as an electrophile, then a base, and then again as an electrophile in this operationally simple, high yielding, one-pot synthesis of pharmacologically important morpholines, thiomorpholines, and piperazines. Compound 1 is an excellent synthon for the 1,2-ethane dication.

Iridium catalysed synthesis of piperazines from diols

A green and atom-economical method has been developed for the synthesis of piperazines by cyclocondensation of diols and amines in aqueous media in the presence of a catalytic amount of [Cp*IrCl2]2. The Royal Society of Chemistry.

Aralkyl diazabicycloalkane derivatives for CNS disorders

Certain aralkyl diazabicyloalkyl compounds are described for treatment of CNS disorders such as cerebral ischemia, psychoses and convulsions. Compounds of particular interest are of the formula: STR1 wherein: each of R 1, R 4, R 5, R 6 and R 7 is independ