Formation of α-enaminoketones from α-azidoketones: An elimination of molecular nitrogen from α-azidoketones

α-Enaminoketones are readily accessible through reaction of α-bromoketones with sodium azide followed by an elimination of molecular nitrogen. The reaction is base catalyzed and proceeds under relatively mild conditions. An anionic mechanism is proposed.     

Stereochemistry of α-aminoacetophenone oximes : Study of solvent effects

The aminolysis of Z-α-halogenoacetophenone oximes results in different mixtures of E- and Z-α-aminoacetophenone oximes depending on the solvent used. Assignment of configuration can be achieved by ¹³C NMR spectroscopy even if only one isomer is available using a strong solvent dependence of the methylene chemical shift in the case of the Z-isomers. This effect is due to the presence of different conformations in the solvents chloroform and dimethyl sulfoxide. Together with a study by vapor pressure osmometry the results provide an unambiguous proof of intramolecular hydrogen bonding of Z-α-aminoacetophenone oximes in chloroform.     

Diastereoselective α-Alkylation of β-Amino Esters: Preparation of Novel α-Substituted β-Amino Esters from α-Amino Acids

b-Amino acids and their derivatives have attracted considerable attention in recent years due to their occurrence in biologically active natural products, such as dolastatins 11, cyclohexylnorstatine 22 and taxol 33. bAmino acids also find application in the synthesis of blactams4, piperidines5, indolizidines6. Moreover, the peptides consisting of bamino acids, the so called bpeptides, have been extensively studied recently7. Consequently, considerable efforts have been directed to the synt…     

Synthesis of α-substituted iminodiacetate ligands: α-hexadienyl derivatives for the selection of lipoxygenase mimics

Derivatives of iminodiacetic acid (IDA) are important as ligands for metal ions, having numerous applications in separations, sensing, catalysis and medicine. This report describes the preparation of two types of IDA derivatives (1, 2) that could be covalently attached to a polymer or protein surface via a variable length spacer chain. The parent compounds 1 (R′=H) were easily prepared via N-alkylation of dimethyl iminodiacetate with esters of 6-bromo-hexanoic acid and subsequent selective ester hydrolysis. Metal complexes of IDA derivatives having an α-dienyl side chain are required for the selection of histidine-rich proteins with potential lipoxygenase activity. The α-hexadienyl side chain of IDA derivative 2 was selectively introduced in the reaction of (2,4-hexadienyl acetate)Fe(CO)₃ with a glycine-derived TMS-enol ester. Subsequent demetallation, followed by N-carboxymethylation, N-deacylation, N-alkylation with a trichloroethyl 6-halohexanoate, and TCE-ester cleavage provided the desired α-hexadienyl IDA derivative 2. Amide formation with IDA acid 1b demonstrates the feasibility of conjugating the IDA ligands to polymers and proteins while Ni(II)-complexation with the derived IDA triacid 1e shows the complexing ability of the tethered IDA ligand.     

Synthesis of New α-Heterocyclic α-Aminophosphonates

α-heterocyclic α-aminophosphonates were obtained in good yields by N-of several nitrogen heterocycles with α-azido-α-aminophosphonate 1. ¹ Elachqar, A., El Hallaoui, A., Roumestant, M. L. and Viallefont, Ph. 1994. Synthetic Comm, 24: 1279 [CSA][Taylor & Francis Online], [Web of Science ®] , [Google Scholar]     

New general synthesis of α-alkoxyketones via α'-alkylation, α-alkylation and α,α'-dialkylation of α-alkoxyketimines

α-Methoxy- and α-ethoxyketones, as important intermediates in organic synthesis and flavor compounds in food chemistry, were synthesized by deprotonation of N-(1-alkoxy-2-propylidene)isopropylamine, prepared by condensation of the corresponding α-alkoxyacetone with isopropylamine, and subsequent reaction of the corresponding 1-azaallylic anions with alkyl halides to afford α'-alkylated, α-alkylated and α,α'-dialkylated ketimines. Hydrolysis of the imino function led to the desired substituted α-alkoxyketones. The ratio of α-, α'-, and α,α'-(di)alkylated compounds depended on the amount of base used and on the nature of the alkylating reagent.     

Synthesis of Methyl α-d-Allopyranoside and Methyl α-d-Ribo-hexopyranoside: A Convenient Chemoenzymatic Approach

Abstract

An efficient chemoenzymatic synthesis of methyl α-d-allopyranoside and methyl 3-deoxy-α-d-ribo-hexopyranoside starting from methyl 4,6-O-benzylidene-α-d-glucopyranoside is described.     

2,3]-Sigmatropic rearrangement of ynamides: preparation of α-amino allenephosphonates

α-Amino allenephosphonates were easily prepared in two steps from protected amines, propargyl alcohols, and chlorophosphites. First, ynamides were synthesized from unprotected 1-bromopropargyl alcohols using a copper(II) catalyzed coupling reaction. In the second step, the previously prepared ynamides were transformed directly to allenes through a [2,3]-sigmatropic rearrangement of propargyl phosphites. This efficient method led to the formation of a series of α-amino allenephosphonates with diverse substituents on the amine, the phosphonate, and the allene moieties.     

Photochemistry of α-phenoxyacetophenone: an interesting case of intramolecular triplet deactivation

α-Phenoxyacetophenone undergoes efficient intramolecular triplet deactivation involving quenching by the β-phenyl ring. The process is about an order of magnitude faster than in the case of the all-carbon analogue β-phenylpropiophenone. The difference in the rates of intramolecular quenching is attributed to a reduction of the hydrogen eclipsing interactions in the case of the heteroatom-containing backbone. α-Phenoxyacetophenone photodecomposes with a quantum yield of about 0.004 to yield C₆H₅COCH₂ and C₆H₅O^.; in spite of its low quantum yield the process is quite rapid, occurring with an estimated rate constant of 3 × 10⁷ s⁻¹.     

Convenient synthesis of α-diarylmethylphosphonates by HOTf catalyzed Friedel-Crafts arylation of α-aryl α-hydroxyphosphonates

We report a convenient catalytic Friedel-Crafts arylation of α-aryl α-hydroxyphosphonates with various (hetero)aromatic compounds. HOTf (trifluoromethanesulfonic acid) is identified to be the best Brønsted acid catalyst, and the desired α-diarylmethylphosphonates were obtained in up to 41–95% yield.     

Synthesis of α-Telluroketones

α-Telluroketones were prepared by reacting 4-methoxyphenyltellurium trichloride either with ketones or silyl enol ethers of ketones. The products upon pirolysis furnish α-chloro ketones.     

Ni-catalyzed α-arylation of secondary α-bromo-α-fluoro-β-lactam: cross-coupling of a secondary fluorine-containing electrophile

A highly diastereoselective cross-coupling reaction of an α-bromo-α-fluoro-β-lactam with a wide range of aryl Grignard reagents was catalyzed by Ni/bis(oxazoline) in yields of up to 98%. The product was obtained diastereoselectively as an anti-isomer. This is the first successful α-arylation of an α-fluoro-β-lactam to produce diverse α-aryl-α-fluoro-β-lactams.     

Application of ACC method to synchronous luminiscence: determination of α-tocopherol and α-tocopheryl acetate in beverages

A new method based on the Q parameter, that permits the determination of the C_{compound A} /C_{compound B} ratio without preparing calibration graphs of the two compounds, is proposed. This method has been applied to signals obtained by synchronous luminiscence. Simultaneous determination of α-tocopherol and α-tocopheryl acetate in beverages using synchronous fluorescence has been carried out. To isolate the compounds from samples, liquid extraction with n-hexane as the organic phase was employed. The presence of interferences was tested using the apparent content curves (ACC) method and the C_{α-tocopherol}/¶C_{α-tocopheryl acetate} ratio was calculated using the Q parameter. The reproducibility and detection limit for the determination of α-tocopherol and α-tocopheryl acetate were 6.6% and 0.016 mg/L and 1.8% and 0.017 mg/L, respectively.     

TBD-catalyzed α-sulfenylation of cyclic ketones: desymmetrization of 4-substituted cyclohexanones

A low loading of triazabicyclo[4.4.0]dec-5-ene (TBD) catalyzes the α-sulfenylation reaction of ketones employing tetramethylthiuram disulfide (TMTDS) as electrophilic reagent. This methodology is mild, effective and straightforward, rendering the desired products in high yield. Prochiral 4-substituted cyclohexanones can be desymmetrized with remarkable diastereoselectivity following this protocol. The dithiocarbamoyl function was shown to be easily removed upon reduction, affording thiols (1-mercaptan-2-ols).     

Stereoselective hydrofluorination of ynamides: a straightforward synthesis of novel α-fluoroenamides

α-Fluoroenamides, potent rigid fluorinated bioisosters of ureas, have been synthesized by a highly regio- and stereo-selective hydrofluorination of ynamides in anhydrous HF. This reaction provides the first general entry to α-fluoroenamides and can easily be applied to a wide range of substrates.     

Chiron based synthesis of isocoumarins: reactivity of α-substituted carboxylic acids

The asymmetric synthesis of a novel (S)-isocoumarin has been attempted in a single step by the coupling of homophthalic acid with (S)-N-protected amino acids and α-chloroacids at high temperature by exploiting a chiral pool methodology. The coupling of homophthalic acid with N-protected (S)-amino acids gave exclusion of the carboxyl/alkyl group. However, coupling of homophthalic acid with α-chloroacids afforded asymmetric isocoumarins in high yield.     

Addition of some α-halogeno ethers to α-thiooxides of alkenes

Summary Products of the addition of allyl chloromethyl ether, -chloroethyl methyl ether, -acetoxyethyl chloromethyl ether, cyclohexyl chloromethyl ether, and -chloroethyl ethyl ether to the thiooxides of ethylene and propylene have been prepared.