Synthesis and properties of the copper(Ⅱ) complexes with stable radical

Four novel copper(Ⅱ) complexes have been synthesized,namely Cu(hfac)2NITPhNO2 (1),Cu(hfac)2NITPhCH3 (2),Cu(pfpr)2NITPhNO2,(3) and Cu(Pfpr)2NITPhCH3 (4),where hfac= hexafluoro-acetylacetonate,pfpr=pentafluoropropionate,NITR.=2-R-4,4,5,5-tetraniethyl-4,5-dihydro-1H-imidazolyl-1-oxyl-3-oxide.(R=4-nitrophenyl,4-methylphenyl).These complexes were rharicter-ized by elemental analyses,IR,electronic spectra and molar conductance.The temperature-dependent magnetic susceptibility of complexes 1 and 3 have been studied in the 4 300 K range,giving I he exchange integral J=10.56 cm-1 for complex 1 and J =-30.9 cm-1 for complex 3.     

Enantioselective electrophilic bond construction to the α-carbon of α-aminoacids

In this report, we describe three possibilities for aminoacid synthesis using an enantioselective electrophilic process. Thus, enantioselective carboxylation, alkylation and protonation of Schiff bases yield optically active aminoacids with e.e. up to 76%.     

Electrochemical oxidative methoxylation of 4H-imidazole 1,3-dioxides to give α-methoxy substituted nitroxyl radicals

Electrochemical methoxylation of substituted 4H-imidazole 1,3-dioxides has been carried out for the first time. Nitroxyl radicals of the 2- and 3-imidazoline series with methoxy groups at the -carbon atom of the radical site were synthesized. The yields and ratios of the electrochemical methoxylation products are close to those observed in the chemical methoxylation carried out with PbO₂ and MnO₂ as oxidants.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp.469–471, March, 1994.     

Claisen rearrangement of allylic α-isocyano-esters—regioselective allylation of α-isocyanoesters at the α-carbon

A regioselective allylation of α-isocyanoesters at the α-carbon was achieved by the Claisen rearrangement of allylic α-isocyanoesters via the corresponding silyl ketene acetals in situ generated.     

Synthesis and utility of the natural type of porphyrin selectively labeled with carbon-13 at α-meso site

A concise synthesis of the 2,4-dimethyldeuteroporphyrin regiospecifically labeled with ¹³C at the α-meso site was developed. The starting material of ethyl 3,4,5-trimethylpyrrole-2-carboxylate was first converted to a ¹³C-labeled 5,5′-dimethyldipyrromethene with ¹³C formic acid, and the resulting dipyrromethene was coupled with 5,5′-dibromodipyrromethene to afford the ¹³C-labeled porphyrin in 26% yield. The paramagnetic ¹³C NMR measurements of myoglobin with the inversion-recovery method allowed us to detect selectively the α-meso-carbon signal of the iron complex. The heme is symmetric about the α,γ-meso carbon axis to prevent the orientational disorder in protein pocket. These results indicate that the ¹³C-enriched 2,4-dimethyldeuteroporphyrin is a new promising tool to elucidate the structure-function relationship of many hemoproteins.     

Reconstruction of the 3D coordinates of α-carbon atoms of proteins from a pair of stereographic figures

Summary In an attempt to promptly use the experimentally determined structures of proteins in modeling studies, we have developed the program ReconstC to generate the 3D coordinates of -carbon atoms from a pair of stereographic figures. Calculations of the 3D coordinates were performed by estimating the stereo parameters systematically. Geometrical features of C traces were used to evaluate the integrity of the calculated structure. The program was applied to four kinds of protein structures to examine the performance. It was found that the root-mean-square deviation of atomic positions between constructed and reference crystal structures ranged from 0.36 to 0.78 Å. The range represents a reasonable accuracy and its automatic feature suggests that our approach would be expedient for providing initial structures for protein modeling studies.     

Synthesis of lactate derivatives via reductive radical addition to α-oxyacrylates

Lactate derivatives are important synthetic precursors to a variety of pharmaceutical products. Previously reported methods to prepare lactates require multiple steps or have limited scopes. Herein, we report a Ni-catalyzed reductive addition of a variety of alkyl iodides to α-oxyacrylates to afford substituted lactates. Exploring the scope of radical acceptors reveals that electron-deficient alkenes, ranging from cyclohexenone to para-caboxystyrene, undergo efficient coupling with alkyl iodides. This method represents an alternative strategy access lactate derivatives.     

A neighbouring group effect leading to enhanced nucleophilic substitution of amines at the hindered α-carbon atom of an α-hydroxyphosphonate

Diethyl α-hydroxy-benzylphosphonate undergoes nucleophilic substitution with primary amines of sufficient reactivity at around 100 °C to afford the corresponding α-aminophosphonates. The substitution can be enhanced by microwave irradiation. The reaction takes place with surprising ease due to the neighbouring group effect of the PO moiety as was justified by DFT calculations carried out to evaluate the mechanism of the substitution under discussion.     

Ruthenium-catalyzed regioselective deuteration of alcohols at the β-carbon position with deuterium oxide

A convenient method for regioselective H/D exchange between D(2)O and alcohols at the β-carbon position using the catalytic system [(p-cymene)RuCl(2)]/ethanolamine/KOH is described. This method is applicable for deuteration of both primary and secondary alcohols. The H/D exchange reactions proceed through an oxidation/modification/reduction reaction sequence. Alcohols are first temporarily oxidized to carbonyl compounds by the hydrogen transfer catalyst. The carbonyl compounds then undergo deuteration at the carbon adjacent to the carbonyl group by keto-enol tautomerization in the presence of D(2)O and a catalytic amount of base. The deuterated carbonyl compounds are then reduced to produce deuterated alcohols. In support of the reaction mechanism, a well-defined bimetallic ruthenium complex was isolated from the reaction of [{(p-cymene)RuCl(2)}(2)] with ethanolamine. The activity of this complex is similar to that of [{(p-cymene)RuCl(2)}(2)]/ethanolamine.     

The Application of the Trichloroacetimidate Method to the Synthesis of α-D-Gluco- and α-D-Galactopyranosides

Abstract

The trichloroacetimidate method has been applied to the construction of α-d-galacto- and α-d-glucopyranosides. The readily available β-trichloroacetimidates of 2,3,4,6-tetra-O-benzyl-d-galacto- and glucopyranose (1-β and 3-β, respectively) have been employed in glycosidations with several monosaccharides (either A, B, C or D) under varying experimental conditions. With the galactose derivative 1-β as a donor and each of the monosaccharides A-D as acceptors, the corresponding disaccharides 1A-1D, were obtained in high yield and with good α-stereoselectivity when employing diethyl ether as solvent and either trimethylsilyl- or tert-butyldimethylsilyl trifluoro-methane sulphonate as catalyst. Glycosidations with the glucose derivative 3-β, as donor, and with the monosaccharide acceptors A, B or D, gave the corresponding disaccharides 3A, 3B and 3D, in high yield but with somewhat lower α-diastereoselectivity than observed with the galactose derivative 1-β. The stereochemical outcome of the reactions is rationalised in terms of possible reaction mechanisms.     

Synthesis of phosphorus-containing polyoxamacrocycles with one to two reactive thiophosphoryl chloride groups

Novel phosphorus-containing polyoxamacrocycles with one to two reactive thiophosphoryl chloride groups 5,6,7,8 were synthesized from bishydroxyl compounds 1,2,3,4 and thiophosphoryl chloride respectively.Their structures were confirmed by ~1H NMR,~(13)C NMR,~(31)p NMR and elemental analysis.     

Synthesis of α-alkoxyalkyltributyllead compounds via the reaction of tributylplumbyllithium with α-chloroethers,and the conjugate addition of tributylplumbyllithium to enones

α-Alkoxyalkyltributylleads 1 were prepared from the reaction of tributylplumbyllithium with α-chloroethers 2. This procedure is more convenient than the conventional method which involves transmetallation from the corresponding α-alkoxyalkyltrialkyltin. Tributylplumbyllithium was also used for the synthesis of β-oxo-organolead 4.     

Effect of flavonols on radiation-induced reactions with the participation of α-hydroxyl-containing organic radicals

The effects of flavonols and structurally related model compounds on the formation of the final radiolysis products of ethanol and aqueous ethylene glycol and 2-methoxyethanol solutions were studied. It was found that the test compounds actively interact with the -hydroxyl-containing radicals of parent substances by several mechanisms to change the direction of radiolytic processes. The applicability of flavonols to the inhibition of radiation-induced free-radical fragmentation of organic compounds was demonstrated for the first time. Mechanisms were proposed to explain the observed effects.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 3, 2005, pp. 171–175.Original Russian Text Copyright © 2005 by Grintsevich, Shadyro.     

Theoretical investigation of the atmospheric chemistry of methyl difluoroacetate: reaction with Cl atoms and fate of alkoxy radical at 298 K

A theoretical study on the mechanism of the reactions of methyl difluoroacetate (MDFA) CF₂HC(O)OCH₃ with Cl atoms is presented. Two conformers relatively close in energy have been identified for MDFA. Geometry optimization and frequency calculations have been performed at the MPWB1K/6-31+G(d,p) level of theory, and energetic information is further refined by calculating the energy of the species using G2(MP2) theory. Transition states (TSs) are searched on the potential energy surface involved during the reaction channels, and each of the TSs is characterized by the presence of only one imaginary frequency. The existence of TSs on the corresponding potential energy surface is ascertained by performing intrinsic reaction coordinate calculation. Our calculations reveal that hydrogen abstraction from the –CH₃ group is thermodynamically and kinetically more facile than that from the –CF₂H group. Theoretically calculated rate constants at 298 K using the canonical transition state theory are found to be in good agreement with the experimentally measured ones. The atmospheric lifetime of CF₂HC(O)OCH₃ was estimated to be 16 years. The atmospheric fate and the main degradation process of alkoxy radical CF₂HC(O)OCH₂O are also discussed for the first time. Our calculation indicates that the fluorine atoms substitution has deactivating effect for the α-ester rearrangement.     

Synthesis of 1,3-Diols: Its Application to the Synthesis of α-Lipoic Acid

1,3-diols have been prepared from monosubstituted olefins, and the utility of this method in the synthesis of α-lipoic acid has been described.     

Synthesis of the substituted spiro segment of halichlorine--use of radical cyclization and stereospecific cuprate addition to an α,β-unsaturated lactam

Radical cyclization (26a,b → 27a,b+28) and cuprate addition (28 → 31) were used as key steps to construct the spiro core 4 of halichlorine.     

One-Pot, Three-Component Coupling Approach to the Synthesis of α-Iminocarboxamides

A one-pot, three-component coupling was accomplished via the nucleophilic addition of an alkylsamarium(III) species to isocyanides and the subsequent addition of the resultant imidoyl samarium(III) species to isocyanates under mild conditions for the formation of α-iminocarboxamides. The developed sequential C-C bond-forming procedure enabled the rapid synthesis of the α-iminocarboxamides in good to excellent yields from readily available starting materials.