Novel ring enlargement of cyclobutane derivatives by oxidative radical decarboxylation

Cycloadducts obtained via [2+2] photocycloaddition between an unsaturated oxoacid and cycloalkene are readily opened by irradiation at 366nm, in the presence of catalytic amounts of acridine in toluene and under an oxygen atmosphere, leading after treatment with dimethylsulfide to the formation of polycyclic diketones or ketolactones.     

N-arylation of carbamate-protected glycine derivatives via palladium catalysis

A synthesis of N-aryl and N-heteroaryl amino acid derivatives using palladium catalysis is described. Several carbamate-protected glycine derivatives react with aryl and heteroaryl halides using a palladium/Xantphos catalyst system to access the desired synthons.     

Synthesis of 3-aminoaspartic acid derivatives from glycine precursors

3-Aminoaspartic acid derivatives 3 have been synthesized via stereoselective alkylation of α-acetyloxyglycine Schiff base 2 with the enolate of glycine anion equivalent 1 as a carbon nucleophile in the presence of Pd(OAc)₂ and BINAP at room temperature. High chemical yields and moderate stereoselectivities were observed. The enantiomeric excess of the dl diastereomer can be increased to 95% after a single recrystallization from isopropanol and hexanes.     

Azabicyclic amino acids by stereoselective dearomatizing cyclization of the enolates of N-nicotinoyl glycine derivatives

[Structure: see text] On activation by pyridine N-acylation, enolates of N-nicotinoyl and N-isonicotinoyl glycine and alanine derivatives cyclize to yield 6,5-azabicyclic or 6,4-azaspirocyclic lactams. With an N-alpha-methyl-p-methoxybenzyl group the cyclization is diastereoselective; hydrogenation and deprotection yields azabicyclic amino acids in 94:6 er.     

Enzymatic polymerization of aniline and phenol derivatives catalyzed by horseradish peroxidase in dioxane

Phenylenediamines, 4‐aminophenol and 1,4‐hydroquinone were polymerized via the catalysis of horseradish peroxidase in dioxane at ambient conditions by using hydrogen peroxide as the oxidant. Polymers formed in good yields are black powders soluble in dimethylformamide and dimethylsulfoxide. Several factors influencing the polymer yield were examined using 2‐phenylenediamine as substrate. It was found that pH value gave almost no influence in the range between 6.0 and 7.0, while the polymer yield increased as the concentration of the substrate in dioxane increased. The influence of the oxidant amount was still more obvious; larger excess of the oxidant being necessary in getting higher polymer yield. Using the optimized polymerization conditions, the yield of poly(2‐phenylenediamine) was achieved up to 77.8%. Weight average molecular weight of the polymers are higher than 1 × 10⁴ as determined by gel permeation chromatography. The structure of the polymers was characterized by using nuclear magnetic resonance and infrared techniques. Copyright © 2000 John Wiley & Sons, Ltd.     

Direct Non-oxidative Methane Conversion by Non-thermal Plasma: Modeling Study

The direct non-oxidative conversion of methane to higher hydrocarbons in dielectric barrier discharges has been investigated theoretically at atmospheric pressure. Preliminary modeling of the results is presented, based on a well-stirred reactor model to determine the spatially and time-averaged species composition through the solution of balance equations for species, mass, gas and electron energy. The results show good quantitative agreement between model predications and experimental measurements by considering the glow and after-glow regions. Moreover, the model has predicted that there exists a transition where the main product of ethane will transform to acetylene by increasing the specific energy. The dominant reaction paths and the possibility of selective to C₂ hydrocarbons have been discussed. A list of gas-phase reactions has been compiled for modeling methane conversion in non-thermal plasma and can be employed in more sophisticated two- or three-dimensional plasma simulations.     

Direct Non-oxidative Methane Conversion by Non-thermal Plasma: Experimental Study

The direct non-oxidative conversion of methane to higher hydrocarbons in non-thermal plasma, namely dielectric barrier discharge and corona discharge, has been investigated experimentally at atmospheric pressure. In dielectric barrier discharge, the methane is mainly converted to ethane and propane with small amounts of unsaturated and higher hydrocarbons. While in corona discharge, methane was activated mainly to acetylene with small amount of other higher hydrocarbons. Decreasing the gas flow or increasing power input will improve the methane conversion and product yields. It is found that the methane conversion and main product yield against the input specific energy were special functions in both dielectric barrier discharge and corona discharge, independent of the reactor size, and whether fixing flow rate or power input and changing the power input or flow rate. The corona discharge is a promising alternative method for methane conversion to produce acetylene and hydrogen at low temperature.     

Structural basis for a Kolbe-type decarboxylation catalyzed by a glycyl radical enzyme

4-Hydroxyphenylacetate decarboxylase is a [4Fe-4S] cluster containing glycyl radical enzyme proposed to use a glycyl/thiyl radical dyad to catalyze the last step of tyrosine fermentation in clostridia. The decarboxylation product p-cresol (4-methylphenol) is a virulence factor of the human pathogen Clostridium difficile . Here we describe the crystal structures at 1.75 and 1.81 ? resolution of substrate-free and substrate-bound 4-hydroxyphenylacetate decarboxylase from the related Clostridium scatologenes . The structures show a (βγ)(4) tetramer of heterodimers composed of a catalytic β-subunit harboring the putative glycyl/thiyl dyad and a distinct small γ-subunit with two [4Fe-4S] clusters at 40 ? distance from the active site. The γ-subunit comprises two domains displaying pseudo-2-fold symmetry that are structurally related to the [4Fe-4S] cluster-binding scaffold of high-potential iron-sulfur proteins. The N-terminal domain coordinates one cluster with one histidine and three cysteines, and the C-terminal domain coordinates the second cluster with four cysteines. Whereas the C-terminal cluster is buried in the βγ heterodimer interface, the N-terminal cluster is not part of the interface. The previously postulated decarboxylation mechanism required the substrate's hydroxyl group in the vicinity of the active cysteine residue. In contrast to expectation, the substrate-bound state shows a direct interaction between the substrate's carboxyl group and the active site Cys503, while His536 and Glu637 at the opposite side of the active site pocket anchor the hydroxyl group. This state captures a possible catalytically competent complex and suggests a Kolbe-type decarboxylation for p-cresol formation.     

Versatile,stereocontrolled, asymmetric synthesis of E-vinyl glycine derivatives

The preparation of optically active, E-vinyl glycine derivatives is described. The bromoglycinate 4, couples with trialkyltin acetylides in the presence of ZnCl₂ to furnish the anti-alkynes 5. Dissolving metal reduction directly furnishes the N-t-BOC-protected E-vinyl glycine derivatives 6.     

Short and stereoselective synthesis of C-glycosylated glycine derivatives from glycals by radical addition and reduction

Only three steps are required for the convenient synthesis of 2-C-branched glyco-amino acids from glycals with good yields and stereoselectivities.     

Unusually high phosphodiesterolytic activity of La(III) hydroxide complexes stabilized by glycine derivatives

Glycine and N,N-dimethylglycine stabilize La(III) hydroxide complexes of the type La2L2(OH)4 which possess phosphodiesterolytic activity close to that observed with most active tetravalent cations like Ce(IV).     

Tandem intramolecular oxa-Michael addition/decarboxylation reaction catalyzed by bifunctional cinchona alkaloids: facile synthesis of chiral flavanone derivatives

Bifunctional cinchona alkaloids were used to catalyze a tandem intramolecular oxa-Michael addition/decarboxylation reaction of alkylidene β-ketoesters 1, providing a series of flavanone derivatives with up to 97% yield and 93% ee.     

Development of a catalytic aromatic decarboxylation reaction

A palladium-catalyzed aromatic decarboxylation reaction has been developed. With electron-rich aromatic acids, the reaction proceeds efficiently under fairly mild conditions in good yields. The method was useful with complex functionalized substrates containing hindered carboxylic acids.     

An improved approach for the synthesis of alpha,alpha-dialkyl glycine derivatives by the Ugi-Passerini reaction

A general and simple strategy for routine peptide synthesis with alpha,alpha-dialkyl glycines taking advantage of the four-component Ugi-Passerini reaction is presented. The isonitrile required for the reaction can be relatively simple and its selection based on cost, as the group it generates is easily removed under acidic conditions: in addition, this removal is not visibly affected by the bulkiness of the alpha-alkyl groups. Being a good leaving group from the N-terminal amino group of the amino acid, 4-methoxybenzyl was the choice for the amine component of the reaction. The method is illustrated with the synthesis of a series of acyl derivatives of several alpha,alpha-dialkyl glycines. The preparation of the latter compounds is also reported.     

Iron-catalyzed synthesis of glycine derivatives via carbon-nitrogen bond cleavage using diazoacetate

Treatment of tertiary amines with diazoacetate in the presence of a catalytic amount of an iron salt, FeCl(3), in ethanol gave glycine derivatives. In this reaction, a carbon-nitrogen single bond of the amine was cleaved.