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.     

Syntheses of carbocyclic analogues of α-D-glucosamine, α-D-mannose, α-D-mannuronic acid, β-L-idosamine, and β-L-gulose

A versatile synthesis of orthogonally protected derivatives of carba-α-D-glucosamine, carba-α-D-mannose, carba-α-D-mannuronic acid, carba-β-L-idosamine, and carba-β-L-gulose from methyl α-D-mannoside is described. Our synthetic strategy utilizes the palladium-promoted Ferrier carbocyclization and persistent butane-2,3-diacetal protection to produce a key chiral cyclohexanone intermediate, from which all five carbasugar derivatives can readily be obtained.     

Reaction of 2-aminopyridines with α, β-unsaturated acids

The reaction of 2-amino- and 2-amino-5-halopyridines with acrylic, methacrylic, and crotonic acids forms N-(2-pyridyl)- and N-(5-halo-2-pyridyl)--alanines and the betaines 2-amino-1-(2-carboxylatoethyl)pyridinium or 3,4-dihydropyrido[1,2-a]pyrimidin-2-ones, or their homologs.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 80–85, January, 1992.     

Study of thermal behavior of α-PbO2, using TG and DSC

Using two techniques of thermogravimetry and differential scanning calorimetry under O₂ gas atmosphere from 25 to 600°C, the thermal behavior of laboratory-produced compound lead(IV) oxide α-PbO₂ was investigated. The identity of products at different stages were confirmed by XRD technique. Both techniques produced similar results supporting the same decomposition stages for the compound. Three distinct energy changes were observed, namely, two endothermic and one exothermic in DSC. The amount of ΔH for each peak is also reported.     

Structure of N,N-disubstituted α,β-unsaturated α-amino aldehydes

Study of the IR and¹H and¹³C NMR spectra of N,N-disubstituted ,-unsaturated -amino aldehydes showed that in the nature of the electron density distribution these compounds occupy an intermediate position between -unsubstituted amino olefins and ,-unsubstituted aldehydes, being significantly closer to the latter.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2031–2034, September, 1991.     

Vaporization enthalpies and vapor pressures of the major components of opopanax oil, α-santalene,cis α-bisabolene,cis α-bergamotene

Structural Chemistry - The vapor pressures and vaporization enthalpies of the major components of opopanax oil, a medicinal that has been in use since biblical times, are evaluated by correlation...     

First-principles study of structural,elastic, electronic and optical properties of rutile GeO2 and α-quartz GeO2

Structural parameters, elastic, electronic, bonding and optical properties of rutile GeO₂ and α-quartz GeO₂ have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density functional theory (DFT). The ground-state properties obtained by minimizing the total energy are in favorable agreement with the previous work. Two phases of GeO₂ are found to be elastically stable and we have derived the bulk, shear and Young’s modulus, Poisson coefficient for rutile GeO₂ and α-quartz GeO₂. We estimated the Debye temperature of rutile GeO₂ and α-quartz GeO₂ from the acoustic velocity. Electronic and chemical bonding properties have been studied from the calculation of band structure, density of states and charge densities. Furthermore, in order to clarify the mechanism of optical transitions for rutile GeO₂ and α-quartz GeO₂, the complex dielectric function, refractive index, extinction coefficient, optical reflectivity, absorption coefficient, energy-loss spectrum and the complex conductivity function are calculated, which show the significant optical anisotropy in the components of polarization directions (100) and (001) for rutile GeO₂ and α-quartz GeO₂.     

Stereoselective synthesis of α-aryl-2-benzofuranmethanamines and α-aryl-1H-indole-2-methanamines through palladium-mediated annulation of chiral α-arylpropargylamines

The title compounds, valuable chiral synthons for the synthesis of biologically active compounds, have been prepared in good yield and with high stereoselectivity through palladium-catalyzed heteroannulation of 2-iodophenol or 2-iodo-N-mesylaniline with enantiomerically pure or enriched α-arylpropargylamines.     

Investigation of the reaction of α-thioamides, α-esters and α-nitriles with N-halosuccinimides

Investigation of the reaction of α-thioamides, α-esters and α-nitriles with NBS and NCS is described. The scope of this stereoselective oxidative transformation to the β-haloacrylamides, β-acrylates and β-acrylonitriles has been determined. A mechanistic rationale to explain the observed differences in reactivity between the amide, ester and nitrile series is proposed.     

Preparation of α,α-difluoroalkanesulfonic acids

Chlorodifluoromethanesulfonic acid (1) was prepared using a new procedure starting from perchloromercaptan, which is readily obtained from chlorination of CS₂. Modified Swarts reaction transformed N,N-diethyl trichloromethanesulfenamide into N,N-diethyl chlorodifluoromethanesulfenamide, and the latter species was further oxidized and hydrolyzed into chlorodifluoromethanesulfonic acid. The preparations of other two new α,α-difluoroalkanesulfonic acids, phenyl difluoromethanesulfonic acid (2) and 2-phenyl-1,1,2,2,-tetrafluoroethanesulfonic acid (3), are also disclosed. The acids 2 and 3 are stable in the forms of sodium (lithium) salts or in aqueous solutions; however, the pure forms of 2 and 3 can readily undergo defluorinations. 1-3 and their salts have potential applications as superacid catalysts and lithium battery electrolytes.     

Synthesis of BR2 complexes of α-pyrrolyl dipyrrins

A series of BR₂ complexes of α-pyrrolyl dipyrrin were synthesized from BF₂ complex of α-pyrrolyl dipyrrin (3-pyrrolyl BODIPY) by treating it with various alkyl- and aryl magnesium halides under mild Grignard reaction conditions. The BR₂ complexes were functionalized at α-position of the appended pyrrole ring with formyl, chloro and bromo functional groups and these functionalized BR₂ complexes were used further to prepare various novel derivatives of BR₂ complexes. The BR₂ complexes were characterized by HR mass, NMR, absorption, fluorescence, and electrochemical techniques. Two of the BR₂ complexes were structurally characterized by X-ray crystallography. Our studies revealed that the substitution of fluorine atoms at the boron center of 3-pyrrolyl BODIPYs with different alkyl/aryl groups significantly alters their structural, spectral and electrochemical properties. The DFT studies also support the alteration of the electronic properties of the BR₂ complexes.     

Some peculiarities of hydrosilylation of α,ω-divinyloligosilanes

The stability of Si-Si bonds in linear and cyclic permethyloligosilanes and in ,-divinyloligosilanes under conditions of hydrosilylation in the presence of the Speier's catalyst was studied. Polycarbosilanes containing silylene fragments in their backbone chains were prepared by the reaction of 1,4-bis(dimethylsilyl)benzene with ,-divinyloligosilanes. It was found that the structure of these polymers is disturbed due to the side reaction involving the cleavage of the Si-Si bond in vinyloligosilanes under the action of H₂PtCl₆.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2547–2549, October, 1996.     

Stereoselective synthesis of α,α′-diamino-dicarboxylic acids. Part 2

Enantiomerically pure α,α′-diamino-dicarboxylic acids (R,R)-4, (S,S)-5 and (S,S)-7 have been synthesized starting from the glycine-derived chiral synthon (S,S)-1.     

Iridium-catalyzed [2 + 2 + 2] cycloaddition of α,ω-diynes with nitriles

[Ir(cod)Cl](2)/DPPF or BINAP efficiently catalyzed the cycloaddition of α,ω-diynes with nitriles to give pyridines. The reaction can accommodate a very wide range of nitriles. Both aliphatic and aromatic nitriles smoothly reacted with α,ω-diynes to give pyridines. Ten equivalents of unactivated aliphatic nitrile were enough to give the product in high yield. Aliphatic nitriles bearing an acetal or amino moiety could be used for the reaction. The highly regioselective cycloaddition of unsymmetrical diyne bearing two different internal alkyne moieties was achieved. The observed regioselectivity could be reasonably explained by considering the different reactivities of the α-position in iridacyclopentadiene. Regioselective cycloaddition was successfully applied to the synthesis of terpyridine and quinquepyridine. This chemistry was extended to a new and efficient synthesis of oligoheteroarenes. Five aromatic or heteroaromatic rings were connected in a single operation. [Ir(cod)Cl](2)/chiral diphosphine catalyst can be applied to enantioselective synthesis. Kinetic resolution of the racemic secondary benzyl nitrile catalyzed by [Ir(cod)Cl](2)/SEGPHOS gave a central carbon chiral pyridine in 80% ee. The mechanism was analyzed on the basis of the B3LYP level of density functional calculations.     

Synthesis of α, ω perfluoropolyether iodides

Perfluoropolyether (PFPE) diacyl halides of formula XCOCF₂O[(CF₂O)_n(CF₂CF₂O)_m]_pCF₂COX, with X = Cl, F and molecular weight (MW) 400-4000 g mol⁻¹ are smoothly converted in high yields to the corresponding α, ω diiodides in the absence of solvent, employing KI or LiI at 210 °C with extrusion of CO. During the reactions, β-elimination of COF₂ from the terminal difluoromethylene oxide units (CF₂O, C₁ unit) occurs to some extent until a tetrafluoroethylene oxide unit (OCF₂CF₂, C₂ unit) is encountered yielding a OCF₂CF₂I terminus. This considerably alters the MW distribution of the final diiodide especially for low MW PFPEs. Operating in supercritical conditions of CO (scCO) or both scCO and CO₂ (scCO₂) on low (<600 g mol⁻¹) MW diacyl halides, lowers β-elimination from 95 to 52 mol% if KI is used or from 43 to 30 mol% if LiI is used. With higher MW (>600 g mol⁻¹) β-elimination is lowered from 15 to <1 mol% in scCO conditions employing KI.