Hypervalent iodine (III)-mediated oxidation of aryl sulfonylhydrazones: A facile synthesis of N-aroyl-N′-acyl arylsulfonylhydrazides

We have developed a novel and efficient method for the oxidation of aryl sulfonylhydrazones to N-aroyl-N′-acyl arylsulfonylhydrazides, using hypervalent iodine (III) reagent in good yields at room temperature.     

An efficient synthesis of 2-isoxazolines from α-haloketone oximes and dimethyl sulfonium salts

2-Isoxazolines were synthesized efficiently from a formal [4+1] cycloaddition of nitrosoalkenes and sulfur ylides, which were generated in situ from α-haloketone oximes and dimethyl sulfonium salts. This approach provides a new method to synthesize a range of 2-isoxazolines in high yields and high regioselectivity.     

Molecular iodine: a highly efficient catalyst in the synthesis of quinolines via Friedländer annulation

A mild and efficient route for the synthesis of quinolines and polycyclic quinolines via Friedl?nder annulation, utilizing molecular iodine (1 mol%) as a new catalyst, is described.     

α-Nitro carbonyl compounds in the synthesis of 2,3-dihydrofurans

A new method for the synthesis of 2,3-dihydrofurans from readily available starting enones and α-nitro carbonyl compounds has been developed. This protocol can provide a novel and effective methodology for the preparation of 2,3-dihydrofurans in a stereoselective fashion. With 1,4-dien-3-ones, 2,3-dihydrofurans and cyclohexenecarboxylates were produced and high chemoselectivity was observed in different solvents.     

Molecular complex of iodine with 2,3′-bipyridyl

Thermodynamic data for the formation of a 1:1 charge-transfer (CT) complex of iodine with 2,3′-bipyridyl (2,3′-Bpy) in carbon tetrachloride solution have been obtained from measurements of the blue-shifted iodine band; ΔH⁰ = −28.62±4.78kJ mol⁻¹ and ΔS⁰ = −54.7±1.6 Jmol⁻¹K⁻¹.Infrared spectra of the iodine complex of 2,3′-Bpy in solids, together with those of iodine—bromide and iodine—chloride complexes, have been measured. Comparing the spectra of three halogen complexes with that of 2,3′-Bpy, it is suggested that the nitrogen atom at the 3-position is involved in 1:1 complex formation. Far i.r. spectra of the iodine complex in cyclohexane solution and those of the three halogen complexes in solids have also been obtained. Assignments for the modified IX (X = I, Br and Cl) stretching and the intermolecular NI stretching vibrations have been proposed. The force constants were calculated under the assumption of a linear triatomic model, DIX, where D denotes the donor molecule. The results were compared with those for the pyridine (Py).IX complexes.     

An efficient one-pot synthesis of β-enamino ketones from endo glucal via hypervalent iodine

β-Enamino ketones were successfully synthesized by reaction of endo glycals with primary or secondary amines in the presence of hypervalent iodine reagent in one pot. After the oxidation and protonation taking place on hypervalent iodine agent in acidic condition, endo glucals were effectively converted into the uncyclic β-alkoxyvinyl ketones. Further substitution of β-alkoxyvinyl ketones with primary or secondary amines provided the corresponding β-enamino ketone derivatives in 57-67% yields.     

Regioselective protection of xylose for efficient synthesis of arabino-α-1,3-xylosides

We reported here an efficient regioselective protection strategy for xylose with two-step successive protections on 4- and 2-OH. This method enables the expeditious preparation of various xylose building blocks (3a–c, 5, 6). The rapid selective 2,4-protection especially facilitates the synthesis of 3-substituted xyloside structures. By this approach, typical arabino-α-1,3-xyloside disaccharide and trisaccharide, as fragment structure units from arabinoxylans, have been successfully synthesized.     

Silica triflate as an efficient reagent for the solvent-free synthesis of coumarins

Silica triflate,as a new silica-based reagent,can be used for the efficient synthesis of 4-substituted coumarins via a Pechmann reaction under solvent-free reaction conditions.All reactions were performed at 80℃in good to high yields.     

An efficient synthesis of N-hydroxy-α-amino acid derivatives of high optical purity

Conversion of α-hydroxy esters via triflates into compounds 3 proceeds in chemical yields ranging from 78 to 89% and with optical purities ranging from 76 to 100%.     

Application of ortho-chloro-β-aroylthioamides in synthesis(II): an efficient one-pot, three-component synthesis of tricyclic thiochromeno[2,3-b]pyridine derivatives

Tricyclic thiochromeno[2,3-b]pyridine derivatives have been successfully synthesized in an unusual one-pot multicomponent cascade reaction from ortho-halo-β-aroylthioamides, Meldrum's acid, and aromatic aldehydes. The reaction presumably proceeds via Knoevenagel condensation-Michael addition-cyclocondensation-decarboxylation-rearrangement-intramolecular S_NAr reaction sequence. High bond forming efficiency of this reaction makes it attractive for the synthesis of thiochromeno[2,3-b]pyridine derivatives in a single step operation.     

IBX in an ionic liquid: eco-friendly oxidation of 17α-methylandrostan-3β,17β-diol, an intermediate in the synthesis of anabolic oxandrolone

An easily available hypervalent iodine(V) reagent, 2-iodoxybenzoic acid (IBX) immobilized in the ionic liquid [bmim][Br] was found to be an efficient and eco-friendly protocol for the oxidation of 17α-methylandrostan-3β,17β-diol (1). At ambient temperature oxidation of 1 with IBX gave mestanolone (2) in good yield and with an increased stoichiometric amount of IBX, oxidation adjacent to the carbonyl functionality (α,β-unsaturation) occurred to give dehydrogenated 17β-hydroxy-17α-methyl-Δ¹-androsten-3-one (3) as the major product in a one-pot reaction. The product is easily obtained by extraction with diethyl ether and evaporation of the solvent.     

T3P®-promoted Kabachnik–Fields reaction: an efficient synthesis of α-aminophosphonates

A simple and efficient synthesis of α-aminophosphonates has been developed via the one-pot three-component reactions of aldehydes, amines, and trialkyl phosphites. The reactions occurred rapidly at room temperature in the presence of 1 equiv of propylphosphonic anhydride (T3P®) as the condensing agent, and the α-aminophosphonate products were obtained in high yields.     

Methyl 3-phenylsulphonyl orthopropionate: an efficient reagent for the synthesis of γ-lactones and butenolides

Treatment of methyl 3-phenylsulphonyl orthopropionate with n-BuLi gives the corresponding carbanion which reacts with aldehydes or ketones to yield β-phenylsulphonyl γ-lactones. Base-catalysed elimination of sulphinic acid yields α,β or β,γ-butenolides.     

Efficient Synthesis of Some New 2,3-Dimethylquinoxaline-1-oxides Using Bis(acetoxy)phenyl-λ 3-iodane as an Oxidant

A series of 2-(arylimino)-3-(hydroxyimino)butanes 3a–g, easily accessed by the condensation of variously substituted anilines 1a–g with biacetyl monoxime 2, were efficiently cyclized to afford 2,3-dimethylquinoxaline-1-oxides 4a–g using bis(acetoxy)phenyl-λ ³-iodane as an oxidant. This methodology utilizes a commercially available and environmental benign oxidant to achieve the title compounds in excellent yields under mild conditions.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]     

Oxidation of 1,4-disubstituted-1,2,3-triazoles with H2O2–CF3CO2H: efficient synthesis of 1,2,3-triazole 3-oxides

A collection of 1,2,3-triazole-3-oxides was obtained from oxidation of the corresponding 1,4-disubstituted-1,2,3-triazoles mediated by a H₂O₂–CF₃CO₂H system through a simple protocol in good yields showing high efficiency.     

An expedient and short synthesis of chiral α-hydrazinoesters: synthesis and conformational analysis of 1:1 [α/α-Nα-hydrazino]mers

Different α-hydrazinoesters with high optical purity have been obtained in large scale via an S_N2 protocol. A coupling reaction with a natural amino acid leads to the corresponding dimers, which have been oligomerized in order to obtain the 1:1 [α/α-N^α-hydrazino]mer series. Conformational studies show that these mixed oligomers are self-organized in solution via a succession of γ-turn and hydrazinoturn whatever the absolute configuration of the chiral carbons.     

Reactivity of a propiolate dimer with nucleophiles and an efficient synthesis of dimethyl α-aminoadipate

An enyne dimer (1) of methyl propiolate was reacted with amines to form dimethyl (E,E)-2-amino-2,4-hexadiene dioates with remarkable chemospecificity, regiospecificity, and stereospecificity. This enyne was also reduced by Ph₃P stereospecifically to form dimethyl (E,E)-muconic ester. Hydrogenation of the conjugated amino-diene led to an efficient production of dimethyl α-aminoadipate. A lactam of dimethyl α-aminoadipate was obtained in high yield by simply varying the hydrogenation conditions.     

Stereoselective synthesis of 2,3-diamino-2,3-dideoxy-β-D-mannopyranosyl uronates

With the aim to find an efficient synthetic procedure for the construction of 2,3-diamino-2,3-dideoxy-β-D-mannuronic acids, we evaluated three mannosyl donors: (S)-phenyl 4,6-di-O-acetyl-2,3-diazido mannopyranoside, (S)-phenyl 2,3-diazido-4,6-O-benzylidene mannopyranoside, and (S)-phenyl 2,3-diazido mannopyranosyl methyl uronate. The first two mannosylating agents are rather unselective or slightly α-selective in their condensation with three different acceptors. The mannuronic acid donor on the other hand reliably provides the desired β-mannosidic linkage. A mechanistic rationale is put forward to account for the different behavior of the three donor types. Suitably protected 2,3-diazido mannuronic acids were employed to construct the all-cis-linked tetrasaccharide repeating unit of the capsular polysaccharide of Bacillus stearothermophilus , featuring two 2,3-diacetamido-2,3-dideoxy-β-D-mannuronic acids.     

Enantioselective synthesis of herbertane sesquiterpenes: synthesis of (−)-α-formylherbertenol

The synthesis of 4-hydroxy-3-[(1S)-1,2,2-trimethylcyclopentyl]benzaldehyde [(−)-α-formylherbertenol 1], a herbertane-type sesquiterpene isolated from the leafy liverwort Herberta adunca, from β-cyclogeraniol is described. The synthesis is based on the previously described preparation of an enantiopure 1,2,2-trimethylcyclopentane synthon from which the characteristic aromatic moiety of 1 is elaborated, using a Robinson annulation and a palladium-catalysed methoxycarbonylation of an aryl triflate as key synthetic steps. The synthesis of the natural sesquiterpene (−)-α-herbertenol, also a natural sequiterpene, using the same methodology is also described.