Tandem aza-Michael additions under high pressure: a shortcut to the azanorbornyl skeleton

The hyperbaric aza-Michael addition of mono- and diamines on α,β-unsaturated β,β-disubstituted mono- and diesters has been studied. While in the case of monoester, this reaction provides a β-aminoester presenting a quaternary center, a direct and efficient access to diester or lactams featuring an azanorbornyl skeleton was obtained when starting from a diester, following an unprecedented double aza-Michael addition.     

Solvent-free double aza-Michael under ultrasound irradiation: diastereoselective sequential one-pot synthesis of pyrrolidine Lobelia alkaloids analogues

Novel 2,5-meso-pyrrolidines have been straightforwardly synthesized from readily available symmetrical double Michael acceptors. The key step rested on an aza-Michael addition of primary alkylamines to bis-enones. Competitive Rauhut-Currier and aza-Michael reactions have been highlighted in protic solvent. Ultrasound activation associated with solvent-free conditions led to the expected pyrrolidines in quantitative yields and excellent stereoselectivities. The optimized conditions have been extended to the sonochemical synthesis of pyrrolidine Lobelia alkaloids analogues in short sequences.     

Solvent-free,catalyst-free aza-Michael addition of cyclohexylamine to diethyl maleate: Reaction mechanism and kinetics

The aza-Michael reaction is the addition of an amine to an electron deficient C=C double bond. This reaction is also used in the synthesis of precursors of polymeric networks. In this study, we paid attention to the kinetics and mechanism of the aza-Michael addition of cyclohexylamine (CHXA) to diethyl maleate (DEM) performed as a solvent-free, catalyst-free reaction and to concurrent reactions. In situ Raman spectroscopy, NMR spectroscopy and gas chromatography/mass spectrometry have shown the occurrence of three simultaneous reactions: (i) the aza-Michael addition of CHXA to DEM leading to diethyl 2-(cyclohexylamino)succinate, (ii) isomerization of DEM to diethyl fumarate (DEF), and (iii) the aza-Michael addition of CHXA to DEF formed by the reaction (ii). All of these reactions proceed with third order kinetics, first order in DEM or DEF and second order in CHXA. We propose a kinetic model that allows kinetic constants to be estimated. Furthermore, a numerical solution of the set of differential equations confirms the expected kinetic equations of reactions (i) and (ii) and gives values of rate constants comparable to the estimated ones. A DFT mechanistic study illustrates the structure of the reaction intermediates and transition states of all reactions and explains the contribution of the second amine molecule in the reaction mechanism.     

Synthesis of (±)-chamobtusin A by a presumed biomimetic aza-cyclization

A total synthesis of (±)-chamobtusin A has been accomplished on the basis of our presumed biosynthetic pathway: the imine formation of keto aldehyde followed by intramolecular aza-Michael addition.     

Activated alkene dependent one-pot, three-component aza-Morita-Baylis-Hillman reaction of ferrocenealdehyde: synthesis of highly functionalized diverse ferrocene derivatives

Activated alkene dependent one-pot, three-component aza-Morita-Baylis-Hillman (aza-MBH) reaction of ferrocenealdehyde afforded simple aza-MBH adduct of ferrocenealdehyde, unusual piperidine, β-amino acid residue, and γ-ketoester derivatives of ferrocene in good yield. The synthetic protocol with MVK has led to an unexpected ferrocenyl piperidine derivative in an excellent yield via diastereoselective domino aza-Michael/double Aldol pathway. Plausible mechanisms for the formation of unusual products and diastereoselectivity have also been described. The products can be used for the concise synthesis of ferrocenyl nitrogen heterocycles and bioconjugates.     

Conjugated additions of amines and β-amino alcohols to trifluorocrotonic acid derivatives: synthesis of ψ[NHCH(CF3)]-retro-thiorphan

The aza-Michael addition of amines and β-amino-alcohols to trifluorocrotonic acid derivatives is described. The reactions occurred in good to excellent yields, but low stereocontrol. The title reaction has been used as a key step for the synthesis of trifluoroethylamine mimics of retro-thiorphan, which showed low inhibitory activity of NEP (constant inhibition at the molar level).     

Organocatalytic enantioselective formal synthesis of bromopyrrole alkaloids via aza-Michael addition

An unprecedented organocatalytic enantioselective formal synthesis of bromopyrrole alkaloid natural products is reported. An organocatalytic aza-Michael addition using pyrroles as the N-centered nucleophile is utilized as the enantioselective step to construct the nitrogen-substituted stereogenic carbon center in bromopyrrole alkaloids in good yield and excellent enantioselectivity. The aza-Michael product is converted via lactamization using a Staudinger-type reductive cyclization to the key intermediate, which was previously used in the total synthesis of bromopyrrole alkaloid natural products.     

Studies toward the total synthesis of nagelamide K

A stereocontrolled strategy toward the synthesis of nagelamide K has been developed. The dimeric imidazole acrylate, diimidazolidenesuccinate, was constructed as a synthetic precursor by a Ni-catalyzed coupling reaction; the microwave-promoted intramolecular aza-Michael addition afforded the imidazo[1,5-a]pyridine core structure of nagelamide K in high stereoselectivity. A detaurine-dediamino analogue of nagelamide K has been prepared.     

Lithium tetrafluoroborate catalyzed highly efficient inter- and intramolecular aza-Michael addition with aromatic amines

Lithium tetrafluoroborate has been demonstrated for the first time to be an efficient catalyst in intermolecular aza-Michael addition aromatic amines to electron deficient alkenes. Suitability of the same catalyst in intramolecular aza-Michael addition leading 2-aryl-2,3-dihydroquinolin-4(1H) ones has also been described.     

Green Aza-Michael Reaction of Aliphatic Amines to á,(a)-Unsaturated Compounds in Water

The hydroamination of olefins is a long-standing goal for transition metal catalysis. And the metal-catalyzed addition of amines to carbon-carbon double bonds is an unsolved, synthetically important problem. Although recent advances have made using lanthanide and precious metal complexes, there are few excellent catalyst that display broad functional group tolerance and useful rates for an intermolecular aza-Michael addition. As such, the development of efficient synthetic methods leading to a-amino carbonyl compounds and derivatives has attracted much attention in organic synthesis. Although recent advances have made this route more attractive, development of cheaper, simpler, and more efficient metal catalyst is highly desirable. We also have been interested in developing a reaction that uses catalytic quantities of minimally toxic, readily available, economic reagent should greatly contribute to the creation of environmental benign processes.The recent interest in aqueous medium metal-mediated carbon-carbon and carbon-heteroatom and formations led to the contributors for such reactions. Furthermore, development of organic reactions in water will contribute to the progress of green and quasi-nature catalysis chemistry. Surprisingly however, there is few report on conjugate additions of amines to a,a-unsaturated carbonyl compounds in water.Herein, we report a new protocol that employs air stable copper salts as efficient catalyst in the aza-Michael reaction under mild reaction conditions. Advantages of the protocol include high-yielding reactions that can be conducted at ambient temperature; the use of readily available and stable copper salts as the catalyst, and the reaction was successfully performed in environmental benign solvent, water.Finally, we have utilized a variety of aliphatic amines successfully with different á,(a)-unsaturated compounds catalyzed by simple hydrophilic ionic liquid, bmimBF4 in water. Interestingly, all the aliphatic amines gave almost quantitative in yield with á,(a)-ethylenic compounds. The present reactions with its mild reaction conditions open a novel entry to synthesis of a-amino carbonyl compounds by simple procedure.     

Efficient Lewis Acids Catalyzed Aza-Michael Reactions of Enones with Carbamates

The β-amino carbonyl functionality is not only a segment of biologically important natural products but also a versatile intermediate for the synthesis of nitrogen-containing compounds.1 The development of novel synthetic methods leading to β-amino ketone, β-amino acids or their derivatives has attracted much attention in organic synthesis.2 Among the traditional methods for generating β-amino carbonyl compounds, Mannich-type reaction is one of the classical and powerful methods.3 However,…     

A simple efficient sequential one-pot intermolecular aza-Michael addition and intramolecular Buchwald–Hartwig α-arylation of amines: synthesis of functionalized tetrahydroisoquinolines

An efficient one-pot sequential intermolecular aza-Michael addition and Pd-catalyzed intramolecular Buchwald–Hartwig α-arylation of secondary amines have been investigated, for the synthesis of tetrahydroisoquinolines. This method is simple and furnished products in very good yield and also successfully applied for the synthesis of novel aza-spirotricylcic ethers.     

Tandem nucleophilic addition-intramolecular aza-Michael reaction: facile synthesis of chiral fluorinated isoindolines

A highly stereoselective synthesis of fluorinated 1,3-disubstituted isoindolines is described. To this end, a tandem reaction consisting of a diastereoselective addition of fluorinated nucleophiles to Ellman's N-(tert-butanesulfinyl)imines followed by an intramolecular aza-Michael reaction has been developed. This strategy allows for the construction of isoindolines bearing several degrees of fluorination (mono-, di-, or trifluoromethyl as well as heavier fluorinated groups). In the majority of all cases, the products are formed as single isomers.     

Organocatalytic enantioselective aza-Michael reaction of nitrogen heterocycles and alpha,beta-unsaturated aldehydes

The asymmetric organocatalytic aza-Michael reaction of several nitrogen heterocycles and alpha,beta-unsaturated aldehydes has been studied in detail; under the optimised conditions, the conjugate addition products have been obtained in high to excellent enantioselectivities.     

Promiscuous Candida antarctica lipase B-catalyzed synthesis of β-amino esters via aza-Michael addition of amines to acrylates

An efficient protocol for the regioselective aza-Michael addition of amines with acrylates using CaL B as a biocatalyst at 60 °C has been developed. The reaction is applicable to a wide variety of primary and secondary amines with different acrylates to synthesize the corresponding β-amino esters with good yields. An alternative route for the synthesis of higher β-amino esters through the additional transesterification step is also studied and was found effective.     

Synthesis of imidazopyridines from the morita-baylis-hillman acetates of nitroalkenes and convenient access to alpidem and zolpidem

A variety of functionalized imidazo[1,2-a]pyridines have been synthesized through a one-pot, room temperature, and reagent-free reaction between MBH acetates of nitroalkenes and 2-aminopyridines. The reaction involves a cascade inter-intramolecular double aza-Michael addition of 2-aminopyridines to MBH acetates. Our methodology is marked by excellent yield, regioselectivity and, above all, adaptability to synthesize imidazopyridine-based drug molecules such as Alpidem and Zolpidem.     

Promiscuous acylase-catalyzed aza-Michael additions of aromatic N-heterocycles in organic solvent

A novel and efficient enzymatic promiscuous protocol for aza-Michael addition of aromatic N-heterocycles to α,β-unsaturated compounds has been described. The reactions were catalyzed by promiscuous zinc-active-site acylase in organic solvent at 50 °C. The strategy works with a broad range of N-heterocycles to afford the corresponding Michael adduct with good yields in several hours (0.5-6 h). This catalytic promiscuity is the first example of metal-active-site enzyme-catalyzed aza-Michael addition for aromatic N-heterocycles.     

Catalyst-free aza-Michael addition of azole to β,γ-unsaturated-α-keto ester: an efficient access to C–N bond formation

An efficient aza-Michael addition of azoles to β,γ-unsaturated-α-keto esters under room temperature conditions has been developed. In this conjugate addition, no additional catalyst is employed. Azole reacts with β,γ-unsaturated-α-keto ester smoothly to afford new C–N bond adducts in good to excellent yields (up to 96%).     

Assembly of nitrogen-containing heterocycles initiated by the aza-Michael reaction

The aza-Michael reaction is considered as the most popular method for the carbon–nitrogen bond formation and the shortest way to β-aminocarbonyl compounds, including β-amino acids and their derivatives. In many cases, conjugate addition of nitrogen-centered nucleophiles to the activated multiple bond triggers a series of cascade transformations being completed by the formation of heterocycles and analogs of natural compounds. The review summarizes the most important advances in the aza-Michael reaction-initiated synthesis of nitrogen-containing heterocycles from unsaturated ketones and enoates.     

Hf(OTf)4-Catalyzed Three-Component Synthesis of N-Carbamate-Protected β-Amino Ketones

Hafnium(IV) triflate (Hf(OTf)₄) has been identified as a potent catalyst for the direct three-component synthesis of β-carbamate ketones. This new method, featuring a low catalyst loading, fast reaction rate, and solvent-free conditions, provided facile access to a diversity of carbamate-protected Mannich bases. A mechanistic investigation indicated that the three-component reaction proceeds via sequential aldol condensation and aza-Michael addition, but not the Mannich-type pathway.