Concise synthesis of α-trisubstituted amines from ketones using N-methoxyamines

Three-component allylation and cyanation utilizing a ketone and an N-methoxyamine are reported. The high nucleophilicity of the N-methoxyamine and high electrophilicity of the corresponding iminium ion enable the concise synthesis of α-trisubstituted amines in a single step.     

Metal-free base-promoted sulfenylation for the synthesis of α-arylthio-α,β-unsaturated ketones

A new sulfenylation reaction has been established, stereoselectively affording 37 examples of α-arylthio-α,β-unsaturated ketones with generally good yields via a metal-free three-component reaction of α-thiocyanate ketones with diaryliodonium salts and 1,2-dicarbonyls. The reaction enabled multiple bond-forming events including C(sp²)–S formation to provide a high-efficient and practical method toward α-arylthio-α,β-unsaturated ketones. The reasonable mechanism for forming α-arylthio-α,β-unsaturated ketones was proposed.     

Selective and facile synthesis of α,β-unsaturated nitriles and amides with N-hydroxyphthalimide as the nitrogen source

The direct conversion of α,β-unsaturated aldehydes to corresponding nitriles promoted by Pd(OAc)₂ and phthalic acid which was hydrolyzed from N-hydroxyphthalimide (NHPI) has been disclosed. Additionally, it was found that when water was used as the solvent, α,β-unsaturated amides was obtained as the main products in good to excellent yields. It was first reported that NHPI was utilized as the nitrogen source to synthesize α,β-unsaturated nitriles and amides from aldehydes. Control experiment demonstrated that aldehydes undergo a process of oximation and dehydration to form nitriles and amides.     

Direct synthesis of 2,4,5-trisubstituted imidazoles and di/tri-substituted pyrimidines via cycloadditions of α,β-unsaturated ketones/aldehydes and N′-hydroxyl imidamides

An efficient route for the synthesis of 5-acetylimidazoles and di/trisubstituted pyrimidines via iron-catalyzed cross-dehydrogenative coupling (CDC), with excellent tolerance and yields, has been developed. In this report, α,β-unsaturated aldehydes/ketones and N′-hydroxyl imidamides undergo [3+2] and [3+3] cycloadditions in two processes, involving iron-mediated Michael reaction, Robinson Annulation and 1,5-electrocyclization.     

Copper-catalyzed synthesis of α-ketothioamides from ketones

In this paper, the conversion of acetophenone to α-ketothioamide was reported in the presence of CuI as the catalyst and S₈/DMF as the coupling partners. The presence of both KF and NaOH was found to be necessary to achieve the high yield of the product. Propiophenone and butyrophenone also reacted in the presence of phenylboronic acid as an additive. Willgerodt-Kindler products were not observed in these reactions.     

Asymmetric synthesis of anti-α-substituted β-amino ketones from sulfinimines

Previously unknown, enantiopure, β-amino ketones were prepared in modest yield by addition of lithium reagents to N-sulfinyl anti-α-substituted β-amino Weinreb amides. Grignard reagents failed to add to these Weinreb amides in contrast to the syn-α-substituted isomers which did. The anti-α-substituted β-amino Weinreb amides were prepared by addition of LiN(OMe)Me to the corresponding N-sulfinyl anti-α-substituted β-amino esters because α-alkylation of N-sulfinyl β-amino Weinreb amide enolates resulted in poor diastereoselectivities.     

An efficient green MCR protocol for the synthesis of 2,4,5-trisubstituted imidazoles by Selectfluor™ under ultrasound irradiation

A simple, efficient and eco-friendly procedure has been developed using Selectfluor™ (15% mol) as a novel catalyst under ultrasound irradiation and solvent-free conditions for the synthesis of 2,4,5-triaryimidazole by a three-component, one-pot condensation of benzil, aryl aldehydes and ammonium acetate. The present methodology offers several advantages such as excellent yields, shorter reaction times (10–15 min) and environmentally benign milder reaction conditions and easy work-up.     

Conjugate addition of lithium N-tert-butyldimethylsilyloxy-N-(α-methylbenzyl)amide: asymmetric synthesis of β-trisubstituted amino acids

Conjugate addition of the homochiral ammonia equivalent lithium N-tert-butyldimethylsilyloxy-N-(α-methylbenzyl)amide to a range of α,β-unsaturated esters gives the corresponding β-amino esters in moderate to good levels of diastereoselectivity. O-Desilylation and cyclisation furnishes homochiral isoxazolidin-5-ones in >99:1 dr after purification. Sequential alkylation of these templates proceeds to give the corresponding 3,4-anti-disubstituted and 3,4,4-trisubstituted derivatives as single diastereoisomers after purification. The first alkylation occurs with high levels of diastereoselectivity on the face of the enolate anti to the C(3)-substituent, whereas the facial selectivity of the second alkylation is governed by a chiral relay effect, which depends upon the relative steric bulk of both the C(3)- and C(4)-substituents. Subsequent hydrogenolysis promotes cleavage of both the N-α-methylbenzyl group and the N-O bond within the isoxazolidin-5-one ring in one pot to give the corresponding β^2,2,3-trisubstituted amino acids directly.     

Transition-metal-free synthesis of multisubstituted N-arylindoles via reaction of arynes and α-amino ketones

A simple transition-metal-free protocol for the synthesis of indoles has been developed using aryne cycloaddition. The in situ-generated arynes couple with α-amino ketones through a one-step N-arylation–nucleophilic addition process under mild conditions and efficiently produce multisubstituted N-arylindoles.     

An access to α, β-unsaturated ketones via dual cooperative catalysis

A dual cooperative organocatalytic approach for the synthesis of α, β-unsaturated ketones is described. This one pot transformation is realized via a domino Knoevenagel-Michael-retro Michael reaction sequence. Various aliphatic ketones reacted smoothly with aromatic as well as aliphatic aldehydes in presence catalytic amount of Meldrum’s acid and bifunctional amine. The highlights of this protocol are the easy availability of catalysts, high selectivity, and functional group tolerance. The reaction proved to highly E-selective with no side products emanating from self-condensation, unlike the base-mediated reactions.     

Enantioselective α-chlorination of β-keto esters and amides catalyzed by chiral imidodiphosphoric acids

Chiral imidodiphosphoric acids were employed as catalysts for the enantioselective α-chlorination of β-keto esters and amides using NCS as the chlorine source, providing a series of optically active products with good to high enantioselectivities (74–95% ee) and excellent yields (92–99%). This represents the first report of the Brønsted acid catalyzed enantioselective α-chlorination of cyclic β-keto derivatives.     

Raman characterization of α- and β-LiFe5O8 prepared through a solid-state reaction pathway

Lithium ferrite, a mixed-inverse spinel of type A_xB_y[A_1−xB_1−y]O₄ was produced through solid state synthesis by calcining a Li₂CO₃/Fe₂O₃ mixture at 900 °C. The presence of both the ordered α-phase and disordered β-phase of LiFe₅O₈ was confirmed by XRD analysis, while formation of the latter was achieved by air quenching from high temperature. Laser Raman analysis was performed on both the α-LiFe₅O₈ and β-LiFe₅O₈ powders in order to achieve a reference set of Raman shifts for the spinel. The strongest, characteristic Raman peaks were determined to be 493, 382, 358, 300, and 263 cm⁻¹ for both phases while smaller peaks at 202 and 236 cm⁻¹ present in the α-phase were diminishing in intensity when the β-phase was present, thus providing unique identifiers for the presence of the disordered ferrite structure. SEM images taken of the synthesized LiFe₅O₈ powders showed particle sizes of less than 300 nm and an even particle size distribution.     

Facile synthesis of α, β-unsaturated esters through a one-pot copper-catalyzed aerobic oxidation-Wittig reaction

An efficient one-pot synthesis of α, β-unsaturated esters through the aerobic oxidation – Wittig tandem reaction of alcohols and phosphorous ylide is developed. This new method operates under mild reaction conditions, and uses CuI/TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) as co-catalyst and air (O₂) as the oxidant. It tolerates a wide range of functionalized benzylic alcohol and aliphatic alcohols.     

Effects of surfactants on morphology in synthesis of α-Mn2O3 nanostructures

Cubic and chain-like structure of α-Mn₂O₃ with a high surface area was prepared by air oxidation of manganese chloride through sol process by adding hexamine and mercaptosuccinic acid as wetting agent, respectively. The as-synthesized products were characterized with X-ray powder diffraction (XRD), Energy Dispersive X-ray spectroscopy (EDX), transmission electron microscope (TEM), and selected area electron diffraction (SAED). The possible formation mechanism of α-Mn₂O₃ cubic and chain-like nanostructures has been proposed and discussed.     

Synthesis of novel α-CF3-trifluoroalanine derivatives containing N-(diethoxyphosphoryl)difluoroacetyl group

An efficient synthesis of biologically interesting α-CF₃-trifluoroalanine derivatives bearing N-(diethoxyphosphoryl)difluoroacetyl moiety in good yields has been elaborated. The key substrate, α-TFM-imino ester, prepared from methyl trifluoropyruvate and (diethoxyphosphoryl)difluoroacetamide, followed by dehydration, was subjected to regiospecific reactions with various nucleophiles, including organometallic, π-donor compounds and sodium borohydride. These novel products may find a viable application in the modification of peptides or serve as potential drug candidates.     

Stereoselective synthesis of α,α-difluoro-β,γ-alkenyl ketones by free-radical reaction of iododifluoromethyl ketones with alkynes

A method for stereoselective synthesis of α,α-difluoro-γ-iodo-β,γ-alkenyl ketones via radical difluoroacetylation of iododifluoromethyl ketones with terminal and internal alkynes was reported. This methodology provides a straightforward access to 3,3-disubstitued allylic difluorides.     

An efficient synthesis of fully substituted pyrazolo[3,4-b]pyridin-5-amines from α-azidochalcones

A facile, mild and efficient procedure for the synthesis of fully substituted pyrazolo[3,4-b]pyridin-5-amines is reported. A mixture of an α-azidochalcone, a 5-aminopyrazole and t-BuOK was stirred in DMF at ambient temperature for 5?min to afford the corresponding pyrazolo[3,4-b]pyridin-5-amines in good to excellent yields.     

Phase transition induced by lithium insertion in αI- and αII-VOPO4

Lithium insertion in α_I-VOPO₄ and α_II-VOPO₄, either by chemical or electrochemical route, leads to the same new compound: α_I-LiVOPO₄ (space group P4/nmm). The structure, resolved by neutron and synchrotron diffraction, is made up of planes of corner-connected PO₄ and VO₅ polyhedra, whereas lithium atoms are located between the layers. The reversal of the short vanadyl bond that corresponds to the insertion-induced α_II-α_I transition finds an explanation in terms of lattice energy. It favors the migration of lithium ions in the (0 0 1) interlayer planes, a key parameter for the electrochemical performance as electrode material in Li-ion batteries.     

Asymmetric synthesis of (+)-preussin from N-sulfinyl δ-amino β-ketoesters

The efficient asymmetric synthesis of the antifungal pyrrolidine alkaloid (+)-preussin (2) was accomplished via the stereoselective reduction of a 5-substituted 3-oxo proline. The oxo proline was prepared from an N-sulfinyl δ-amino β-ketoester, a sulfinimine derived polyfunctionalized chiral building block.     

Selective C-N bond oxidation: demethylation of N-methyl group in N-arylmethyl-N-methyl-α-amino esters utilizing N-iodosuccinimide (NIS)

Demethylation of N-methyl group in N-methyl-N-arylmethyl-α-amino esters was accomplished by the oxidation of the amino group using the N-iodosuccinimide (NIS)/acetonitrile system followed by treatment with O-methylhydroxylamine hydrochloride. This combination of reagents could provide a complementary method to catalytic hydrogenolysis, which certainly cleaves N-arylmethyl groups, in organic synthesis.