Β-carbon Atom Research Articles

Organoboron compounds: CDXCV. A regioselective reaction of hydride abstraction in the series of 3-alkyl-3-borabicyclo[4.3.1]decane ate-complexes

The ate-complexes of 3,8-dimethyl-, 3,4,8-trimethyl- and 3,4,4,8-tetramethyl-3-borabicyclo[4.3.1]decane react with acetyl chloride to produce the corresponding 2-(3-methylene-5-methylcyclohex-1-yl)alkyl(dimethyl)boranes. The reaction involves the abstraction of a hydride ion from the bridgehead β-carbon atom. The organoboron compounds thus obtained were oxidized with alkaline hydrogen peroxide to the methylene-3-(2-hydroxyalkyl)-5-methylcyclohexanes.

Structural effect on the electrochemical properties of polythiophene and derivatives

Grafted polythiophenes behave like modified electrodes, and even at large thicknesses, the whole film is electroactive. Due to the fibrillar structure of these polymers, the dopants do not modify the electrochemical characteristics, and the solvent has only a slight influence. When bulky groups are substituted on the β-carbon atoms in the thiophene unit, steric factors increase rapidly and render the oxidation and the reduction more and more difficult, owing to the loss of conjugation in the polymeric chains.

Protonation of allenylidene- and vinylidene-manganese complexes. Crystal and molecular structure of [Cp(CO) 2MnCCHCPh 2] + BF 4t

The cyclopentadienylmanganese carbonyl complexes with terminal allenylidene ligands, Cp(CO) 2MnCCCR 2 (R = Bu t, Ph), are protonated by HX acids (X = Cl, BF 4, CF 3COO) yielding cationic vinylcarbyne complexes of the type [Cp(CO) 2MnCCHCR 2] +X −. One of these, with R = Ph, X = BF 4, was characterized by X-ray crystallography. The MnC bond of 1.665 Å in it is the shortest one known to date. The binuclear μ-vinylidene complexes, [Cp(CO) 2,Mn] 2CCHR′ (R′ = Ph, COOMe) are also protonated at the β-carbon atom of the vinylidene ligand.

A chain growth scheme for the higher alcohols synthesis

A chain growth scheme for the synthesis of alcohols from carbon monoxide and hydrogen is proposed. The scheme describes the alcohol product distribution, assuming one or two carbon addition at the α- or β-carbon atom of the growing alcohol. Estimates of the distribution parameters were obtained from selectivities measured for a range of operating conditions on a Cu ZnO catalyst promoted with 0.5% K 2CO 3. The α-addition is a slow step with a large activation energy (140 kJ/mol) while β-addition is faster and has a smaller activation energy (66 kJ/mol). Large methanol selectivities result from the slow initial α-addition, and large 2-methyl-1-propanol selectivities from α-addition being the only growth step of the 2-methyl-1-propanol intermediate. The rate of chain growth is approximately proportional to the CO partial pressure and the rate of chain termination proportional to the H 2 partial pressure. Addition of alcohols to the synthesis gas resulted in significant increases in the yields of some of the alcohols, consistent with the chain growth scheme.

Anodic dimerization of enamines, 2-cyano-2-phenylvinylamines.

The effects of substituents (R1, R2, and R3) on the electrochemical oxidation of the title enamines, R1-C6H4-C (CN)=CH-NR2R3 (1) were investigated in acetonitrile at a glassy carbon electrode together with the oxidation of a related amine, Ph-CH (CN)-CH2-NMe2 (5). Cyclic voltammetry of 1 showed two or more anodic peaks depending upon the substituents. On controlled potential electrolysis at the potential of the first anodic wave, 1 with R1=H, R2=alkyl, and R3=alkyl or H gave diphenylmethane derivatives in which two molecules of the starting enamine are coupled between the β-carbon atom and the phenyl ring para to the enamino group. Essentially the same results were obtained for 1 with R1=m-Me or m-Cl and R2=R3=Me. A mechanism involving the dimerization of radical cations from 1 is proposed. Electrolysis of 1 with R1=p-Cl or p-Me and R2=R3=Me, on the other hand, gave diphenylethane derivatives via coupling between the β-carbon atoms. No stable product was obtained from 1 with a phenyl group on the nitrogen atom. Results on electrolyses of the amine 5 and 1 with R1=H and R2=R3=Me at the voltammetric peak potential of 5 argue against the possibility that an enamine is formed as an intermediate in the electrochemical dealkylation of aliphatic amines.

Studies on the thermal decomposition of phthalate esters: VIII. Synthesis of bis(2-phenylhexyl) phthalate and thermal decomposition

In order to establish how phthalate esters are provided with heat stability, bis(2-phenylhexyl) phthalate (BPHP) containing side-chains with a phenyl group on each β-carbon atom was synthesized and its heat stability was compared with that of other phthalate esters. It was confirmed that BPHP is very resistant to heat.

Methine chain substituted styryl cyanine dyes—part I

Twenty-seven styryl dyes having 1-naphthyl and 2-naphthyl substituents at the β-carbon atom (β- to the heterocyclic moiety) of the methine chain have been prepared by condensing p-diethylaminophenyl 2-naphthyl ketone, p-dimethylaminophenyl 1-naphthyl ketone and p-dimethylaminophenyl 2-naphthyl ketone with quaternised salts of variously substituted quinaldines and lepidine. The dyes obtained show hypsochromic shifts in absorption maxima compared with their analogues having no substituent in the methine chain wherever comparable data have been available in the literature. The photosensitisation properties of the dyes have also been studied.

Reactions involving additions to the double bond in 4,5-epoxy-2-hexenoic acid esters

4,5-Epoxy-2-hexenoic acid esters add alcohols (in the presence of the alkoxide) and diazomethane to the double bond with retention of the oxirane ring; alkoxylation products and Δ2-pyrazolines are formed. The alkoxide anion and diazomethane add to the positively polarized β-carbon atom of the conjugated ether. The structures of the synthesized compounds were proved by their IR, UV, and PMR spectra.

Esophageal Carcinogenesis in F344 Rats by Nitrosomethylethylamines Substituted in the Ethyl Group<xref ref-type="fn" rid="fn2">2</xref><xref ref-type="fn" rid="fn3">3</xref>

The carcinogenic activity in male F344 rats of five nitrosomethylalkylamines related to nitrosomethylethylamine has been examined. All rats were tested by administration of controlled doses of the compounds in the drinking water. Nitrosomethylbenzylamine was the most potent carcinogen of the five, causing death of most animals with tumors of the upper gastrointestinal tract (mainly the esophagus) within 6 months after a total dose of 0.2 mmol. The remaining compounds, all of which can be considered true derivatives of nitrosomethylethylamine, were less potent than nitrosomethylbenzylamine but also induced a high incidence of tumors of the esophagus. Nitrosomethyl-2-phenylethylamine and nitrosomethylneopentylamine were of comparable potency, while nitrosomethyltrifluoroethylamine was considerably less potent, as measured by the time to death with esophageal tumors. Deuterium-labeled nitrosomethylethylamine, in which deuterium replaces hydrogen on the beta-carbon atom of nitrosomethylethylamine, induced a high incidence of esophageal tumors as well as liver tumors after administration of identical doses. Reactions on the beta-carbon atom of nitrosomethylethylamine might be important as well as oxidation at the alpha-carbon atoms in determining carcinogenic effects.

The hydrogen bromide catalysed decomposition of 3-methylbutan-2-ol

In the presence of hydrogen bromide at 372-446�C 3-methylbutan-2-ol decomposes into methylbutenes and water with rate K2=1013.02exp(-150000/8.314T) ml mol-1s-1 The effects of substitution at the β-carbon atom (C3) are summarized and compared with those at the α-carbon atom (C2). A polar transition state involving mainly the α-carbon atom site is proposed.

Configuration assignments of the amino acid residues and the presence of N-methyldehydroalanine in toxins from the blue-green alga, Microcystis aeruginosa

—The configuration assignment of the α-carbon atom of amino acid residues in four toxin variants from Microcystis aeruginosa have been made by stereospecific enzymic transformations. The relative conformation assignment of the β-carbon atom of β-CH 3-aspartic acid could be made by comparison of the electrophoretic mobility with literature values reported for the authentic compound. The presence of an N-methyldehydroalanine residue, which, due to elimination of methylamine under hydrolytic conditions, previously escaped detection by conventional means, has been confirmed by identification of N-methylalanine in the hydrolysate after reduction of toxin with sodium borohydride.

Synthesis, properties and crystal structure of a dicyclopentadienyl tantalum cyclooctatetraene complex Cp 2TaC 3H 7 · η 2-C 8H 8

Reactions of endo hydride olefin complexes Cp 2M(H)L (M = Ta, Nb; L = C 3H 6, C 4H 8) with C 8H 8 give the tantalocene and niobocene alkyls Cp 2MR · C 8H 8. In solution these complexes partly dissociate giving free cyclooctatetraene and only endo hydride olefin complexes. Temperature-dependent 1H NMR measurements indicate that the C 8H 8 ligand is fluxional on the NMR time scale. The crystal structure of Cp 2TaC 3H 7 · C 8H 8 shows dihapto coordination of the cyclooctatetraene ligand and further reveals the coplanarity of the tantalum atom, the α- and β-carbon atoms of the propyl group and the two coordinated carbon atoms of the C 8H 8 group. In addition there is an unusual planar conformation of the carbon skeleton of the C 8H 8 group.

Electrophilic aromatic substitution. Part 25. The nitration in aqueous sulphuric acid of some cinnamic acids and other styrene derivatives

The rates of nitration of ethyl cinnamate, cinnamic acid, β-nitrostyrene, and trimethyl(styryl)ammonium ion in sulphuric acid of a range of concentrations have been determined. The nitrovinyl and the trimethyl(vinyl)-ammonium groups deactivate the aromatic nucleus by factors of ca. 330 and 60, respectively. The yields of products from ethyl cinnamate and β-nitrostyrene, nitrated over a range of sulphuric acid concentrations, are reported. With ethyl cinnamate the o : p-ratio falls with increasing acidity. The acidity dependences of the rates of reaction of ethyl 4-nitrocinnamate, 4-nitrocinnamic acid, ethyl 3-nitrocinnamate, and 3-nitrocinnamic acid with nitric acid in sulphuric acid show the primary reaction in each case to be attack by the nitronium ion (at the β-carbon atom). The reactions are completed by addition, giving nitroalcohols. A similar but much slower reaction occurs with β,4-dinitrostyrene. In every case the nitroalcohol decomposes in concentrated sulphuric acid to give the nitrobenzaldehyde. With absolute nitric acid, ethyl 4-nitrocinnamate gives the side-chain nitro-nitrate by formal syn-addition. Addition of nitromethane to the reaction solution leads to addition in both stereochemical modes. The nitro-nitrate gives the nitro-alcohol in sulphuric acid, but in aqueous media gives ethyl α-nitro-β-(4-nitrophenyl)acrylates. These apparent side-chain nitrations are thus addition–elimination reactions, as suggested by van der Lee. Similar processes have been detected in the cases of 4-nitrocinnamic acid and β,4-dinitrostyrene.

Fixation and deoxygenation of carbon dioxide to form furans using organophosphorus intermediates

The passage of carbon dioxide through a solution of dimethyl acetylenedicarboxylate during the addition of two equivalents of a trialkyl phosphite leads to the formation of an ylide (3) which reacts with 4-nitrobenzaldehyde to give a furan (5) in which the heterocyclic oxygen and one of the β-carbon atoms in the furan ring are derived from the carbon dioxide.

Synthesis and acetylation of metallocene analogues of chalcones. The double bond acetylation of α,β-unsaturated ketones

Metallocene analogues of chalcones with a metallocene (ferrocene, ruthenocene, cymantrene) bound to the β-carbon atom of the multiple bond, or to the carbonyl group were prepared. The double bond of ferrocene and ruthenocene analogues of chalcones was acetylated when the metallocene was bound to the β-carbon atom of the double bond. No similar double bond acetylation was observed with cymantrene or N-methylpyrrole analogues of chalcones.

Hydride transfer reactions in the series of 1-boraadamantane “ate”-complexes

Lithium 1-alkyl-1-boraadamantanates, obtained from lithium alkyls and the tetrahydrofuran complex of 1-boraadamantane, afford 7-methylene-3-alkyl-3-borabicyclo[3.3.1]nonanes when treated with acetyl chloride. With the use of selectively deuterated lithium [7-D]-1,3,5-trimethyl-1-boraadamantanate, it is shown that the reaction involves the elimination of deuteride ion from the β-carbon atom.

A mechanistic study of the acid- and base-catalysed cleavages of β-trimethylstannylstyrenes

The cleavages of cis- and trans-PhCHCHSnMe 3 in 1/10 AcOD-MeOD have been shown to give cis- and trans-PhCHCHD, respectively. The rates of cleavage of some XC 6H 4CHCHSnMe 3 compounds in 1/10 AcOH-MeOH at 50°C have been measured; there is no significant difference between the rates for cis- and trans-PhCHCHSnMe 3, and the relative rates of cleavage as X is varied are (X  H), 1.0; p-OMe, 7.0; p-Me, 2.3; m-Cl, 0.34; m-Br, 0.36. There is an excellent correlation with σ + constants, with a ρ value of 1.1. The results are interpreted in terms of rate-determining proton transfer to the β-carbon atoms, and it is suggested that acid cleavages of vinylHgX bonds involve analogous mechanisms. PhSnMe 3 is cleaved 20 times as slowly as PhCHCHSnMe 3 in the 1/10 AcOH/MeOH. The rates of cleavage of XC 6H 4CHCHSnMe 3 compounds by a mixture of MeOH (3 vol.) and 2 M aqueous NaOH (2 vol.) have been measured; trans-PhCHCHSnMe 3 is cleaved about 1.3 times as rapidly as its cis-isomer, and about 12 times as rapidly as a mixture of cis- and trans-PhCHCHSnEt 3. The relative rates for the various XC 6H 4CHCHSnMe 3 compounds (mainly trans-isomers) are (X ) H, 1.0; p-OMe, 0.99; p-Me, 0.92; m-Cl, 1.67; m-Br, 1.65. Cleavage of trans-PhCHCHSnMe 3 by NaOD/D 2O/MeOD gives exclusively trans-PhCHCHD. For cleavages in methanolic NaOMe the values of the rate isotope effects, (the ratio k meOH/ k MeOD) are 2.3–2.6, and those of the product isotope effects, PIE (the product ratio RH/RD on cleavage of RSnMe 3 by NaOMe in 1 : 1 MeOH/MeOD) are 4.5–5.0. The results are interpreted in terms of proton transfer from the solvent to the leaving carbon atom in the rate determining step as the SnC bond breaks as a result of the attack of the base anion at tin in a prior or synchronous process. PhCHCHSnMe 3 is cleaved by the aqueous alcoholic base about 5 times as rapidly as PhSnMe 3. Cleavage of trans-PhCHCHSnMe 3 by PHCOCl in presence of AlCl 3 in CH 2Cl 2 gives trans-PhCHCHCOPh, and cleavage of a 90/10 mixture of trans- and cis-PhCHCHSnMe 3 by bromine in CCl 4 gives a corresponding mixture of trans- and cis-PhCHCHBr.

Acid-catalyzed transformations of 5-thio- d-galactose derivatives

Alkyl furanoside and pyranoside derivatives of 5-thio- d-galactose undergo a variety of transformations during methanolysis and other acid-catalyzed solvolysis reactions. Among several novel products obtained are 1,5-anhydro-6- O-methyl-5- thio-α- d-galactofuranose, methyl 6-chloro-6-deoxy-5-thio-α- d-galactopyranoside, 1,6- anhydro-5- O-methyl-6-thio-β- l-altrofuranose, and 2-formyl-5-(methoxymethyl)thiophene. Facile, neighboring-group participation by the sulfur atom in reactions at a β-carbon atom is regarded as the origin of these transformations, which strikingly distinguish the thioaldose from its oxygen analog.

Oxidation of enamine-esters with lead tetra-acetate. Part 1. Products from some N-alkylaminofumarates

N-Methyl- and N-ethyl-aminofumarates are oxidised by lead tetra-acetate to mixtures of heterocyclic polyesters: pyrroles (4), pyridines (6), and pyrrolo[3,2-b]pyrroles (7). Some other N-alkylaminofumarates afford acyclic oxidative dimers, in which enamine molecules are linked through their β-carbon atoms. Dimers of one structure type (13) can be cyclised independently to (4) and (6).

β-Silylcarbonyl compounds as masked enones

β-Trimethylsilylketones and lactones can be brominated (3)→(4) and desilylbrominated (4)→(5) specifically to place a double bond between the carbonyl group and the β-carbon atom to which the silicon had originally been bound. The silyl group therefore is a base- and acid-stable group masking the α,β-unsaturation of enones. Several α-methylene-ketones and -lactones have been prepared in this way. With ketones, the bromination step seems always to introduce bromine mainly or exclusively at the α-position on that side of the ketone on which the β-silyl group is placed, regardless of whether it is the more or the less substituted α-position.