Β-carbon Atom Research Articles

Reactions of co-ordinated ligands. Part 52. Formation and reactivity of molybdenum vinylidene anions; crystal structures of [Mol(η4-CH2CHCHCHCH2But){P(OMe)3}(η-C5H5)] and [Mo(η3-CButCHCHCMe2CO){P(OMe)3}2(η-C5H5)

Reaction of LiBun with the carbyne complexes [Mo(CCH2R){P(OMe)3}2(η-C5H5)](R = Ph or But) affords the red lithium species Li[Mo(CCHR){P(OMe)3}2(η-C5H5)] characterised in solution by 13C and 31P NMR spectroscopy as vinylidene complexes with the negative charge localised on the metal centre. The reactions of the potentially ambident nucleophiles with a wide range of organic electrophilic reagents have been studied. Quenching with Mel, EtBr, SiMe3Cl, EtOCH2Cl, MeSSMe, [graphic omitted], ButCOCl and CH2CHCH2Cl results in attack on the β-carbon atom of the vinylidene with formation of a range of β-substituted carbyne complexes isolated as crystalline materials. In the case of the benzyl-substituted systems there was also evidence for the formation of β,β′-disubstituted carbynes. In contrast, quenching with allyl iodide leads to an unusual reaction and formation of 1,3-diene complexes, this being confirmed by a single-crystal X-ray diffraction study on [Mol(η4-CH2CHCHCHCH2But){P(OMe)3}-(η-C5H5)]. This is explained in terms of a competing allylation reaction at the molybdenum centre. Ultraviolet irradiation of [Mo{CCH(COBut)But}{P(OMe)3}2(η-C5H5)] affords the η3-allyl complex [Mo{η3-[graphic omitted]O}{P(OMe)3}2(η-C5H5)] in a reaction involving an unusual C–H activation.

Vinyl ether hydrolysis. XXIV. 1-Methoxycyclooctene and the question of reversibility of the carbon protonation step

An argument is presented which suggests that hydrolysis of the vinyl ether group of 1-methoxycyclooctene may occur by reversible proton transfer from a catalyzing acid to the β-carbon atom of the substrate, instead of by the conventional reaction mechanism in which this proton transfer is rate determining and not reversible. Hydrolysis of this substrate is then examined by measuring rates of reaction in dilute aqueous solutions of strong mineral acids (perchloric and hydrochloric) as well as in buffer solutions of seven carboxylic acids, biphosphate ion, and 1,1,1,3,3,3-hexafluoro-2-propanol. General acid catalysis is observed and a Brønsted relation with the exponent α = 0.73 is constructed. That, plus the isotope effects kH/kD = 2.9 and 6.0 for catalysis by hydronium ion and acetic acid respectively, as well as the lack of deuterium incorporation into the substrate when the reaction is carried out in D2O with D2PO4−/DPO42− buffer at pD = 8, show that carbon protonation of the substrate is not reversible and that the conventional reaction mechanism is operative. Key words: 1-methoxycyclooctene, vinyl ether hydrolysis, rate-determining proton transfer, Brønsted relation, solvent isotope effect.

Interaction of Tertiary Phosphines with Acetylenic Compouxds. Alkyl Migration Accompanied by C-P Bond Cleavage and Fragmentation During the Interaction of Trialkyphosphines with Phenylacetylene in the Presence of Proton Donors

Abstract We have recently describedphosphobetaines with negative charge on β-carbon atom of vinyl group or on δ-carbon atom of l 1,3-butadienyl group prepared by interaction of trial-kylphosphines with acetylenic and vinylacetylenic compounds, respectively. In the course of developing these investigations an extra route of phosphobetaine formation has been found representing the deprotonation of corresponding phosphonium salts. It has been found that the reaction of trialkylphospliines with phenylacetylene in the presence of proton donors leads to the formation of an intermediate compound containing pentacovalent phosphorus linked with negatively charged oxygen atom. The intermediate undergoes a migration of alkyl group followed either by protonation of β-carbon atom or by unusual cleavage of P-C bond as a result of the electrons back transition:

Vinylphosphite-Vinylphosphonate Rearrangement in Acyclic and Cyclic Systems

Abstract Acyclic vinylphosphites (1) with π-acceptors at the β-carbon atom of vinyloxylic system and some cyclic vinylphosphites, 4-methylen-1,3,2-dioxaphosphorines (2) with electron withdrawing groups at C5 in the heterocycle, and 4-methylen-1,3,2-oxazaphosphorines (3), may undergo earlier unknown vinylphosphite-vinylphosphonate rearrangement. This rearrangement seems formally like a migration of the phosphorus-containing fragment to a-carbon of vinyloxylic system and results in the formation of acyclic vinylphos-phonates (4) in the case of (I), 2-oxo-3-methylen-1,2-oxa-phospholenes (5) and 2-oxo-5-methylen-1,2-azaphospholenes (6) in the cases (2) and (3) respectively. Isomerization is favoured by electrondonating groups at the phosphorus (111) atom. It is likely that the rearrangement of (1) and (2) proceeds through the stage of formation of cyclic oxeten-cation and disubstituted phosphite-anion as intermediates, which then combine to vinylphosphonates.

X-Ray Crystal Structure Analysis of Ca2Pb(CH3CH2CO2)6in the Paraelectric and the Ferroelectric Phases

Absolute crystal structures of Ca 2 Pb(CH 3 CH 2 CO 2 ) 6 (DLP) were determined by X-ray diffraction from monodomain crystals at 70°C above T c and at 45°C and -80°C below T c . The space groups of dextrorotatory crystal are P4 3 2 1 2 and P4 3 above and below T c , respectively. Above T c , β-carbon atoms in three of the independent four propionate ions and α-carbon atom of one propionate ion are in the disordered state having two equilibrium positions with equal occupancy. At 45°C, these carbon atoms are in the partially disordered states. At -80°C, only one β-carbon remains in the partially disordered state, whereas all of the other α- and β-carbons are in the ordered state. The spontaneous polarization is well explained by displacements of Pb, Ca and O atoms along the c -axis.

13C and 19F NMR Spectra of substituted ethyl α-fluorocinnamates. Application of the DSP-NLR equation

13C and 19F NMR spectra of 12 p-substituted and 9 m-substituted ethyl α-fluorocinnamates, along with that of the parent compound, have been recorded and analyzed by DSP and DSP-NLR equations. ϵ values found for the correlation of chemical shifts of both the β-carbon atom of the styrene skeleton and the F atom show near additivity of the effect of individual substituents on C4 shifts in p-disubstituted benzenes. Despite this, correlations using the DSP-NLR equation are not greatly improved over those of the DSP equation, either for sites showing excellent or poor correlations. Also, the magnitude of the ϵ values appropriate for different sites on the side chain show no significant relationship to the percentage of the sensitivity at the site attributed to resonance interaction. Consequently, the utility of the DSP-NLR method seems limited. Substituent effects at F are normal, in contrast to the expectation based on charge alternation that they would be inverse. CNDO/2 charge densities calculated for representative methyl α-fluorocinnamates reveal that π densities at both F and the β-carbon atom of the styrene skeleton accord with normal substituent effects.

Comparative mechanisms of vitamin B 6-catalyzed β-decarboxylation and β-dephosphonylation in model systems

Reaction pathways and mechanisms of vitamin B 6-catalyzed β-decarboxylation and β-dephosphonylation of aminocarboxylix and aminophosphonic acids in model systems are compared. It was found that both reactions require prior transamination of an aldimine intermediate to a ketimine. For ketimines having carboxylate or phosphonate groups substituted on the β-carbon atoms of the keto acid residue, there is a hydrogen ion or metal ion-activated covalent bond pathway which involves a shift of electron pairs toward the coordinated ketimine nitrogen, leading t0 β-γ, C-C or C-P bond fission and release of carbon dioxide or metaphosphate, respectively. Comparison of these reactions indicates that β-decarboxylation is 10 6 faster than the corresponding dephosphonylation reactions. Since only a few studies of vitamin B 6-catalyzed dephosphonylation have been carried out, suggestions are made for further studies with substrates designed to elucidate the reaction mechanisms involved.

ORGANOPHOSPHORUS CHEMISTRY 10. THE BEHAVIOUR OF β-AROYLACRYLIC ACIDS TOWARD NUCLEOPHILIC PHOSPHORUS COMPOUNDS

Abstract The reaction of alkyl phosphites and thiolphosphoric acids with β-aroylacrylic acids 1a,b has been investigated. Dialkyl phosphites (DAP) attacked 1 at the β-carbon atom with respect to the aroyl-carbonyl function, to give phosphonate 1:1 adducts assigned structure 2A. Thiolphosphoric acids (7) attacked 1 at the same centre to give adducts 8. On the other hand, trialkyl phosphites (TAP) converted 1 into the respective esters 5, almost exclusively. Structures of the new products were assigned according to consistent analytical and spectroscopic measurements.

Heterocyclization of acryloyloxiranes to 3-hydroxy-4-piperidinones and 2-(?-hydroxyalkyl)-3-pyrrolidinones in the reaction with methylamine

3-Hydroxy-4-piperidinones and 2-(α-hydroxyalkyl)-3-pyrrolidinones were obtained by the reaction of acryloyloxiranes with methylamine. It is shown that the regiospecificity of the heterocyclization of the products of addition of methylamine to the double bond of the acryloyloxirane is determined by the substituents attached to the α- and Β-carbon atoms of the epoxide ring.

13C-NMR spectra of organomagnesium compounds, alkylmagnesium derivatives

1. The incremental values of the effect of a magnesium group on the13C NMR chemical shifts in dialkylmagnesium and alkylmagnesium halide derivatives have been measured: δα=(−5.1 ±1.2), δΒ=(7.6 ± 0.2), δγ=(7.0 ± 0.7), δαiso=(−2.0 ± 0.2) ppm. 2. The value of the direct carbon-proton SSCC has been shown to be lower than the corresponding value observed in saturated hydrocarbons, by 20 Hz in the case of the α-carbon atom, and by 3 Hz in the case of the Β-carbon atom.

13C nuclear magnetic resonance studies of azide-containing C18 fatty ester derivatives

The 13C n.m.r. spectra of mono-, di-, and tri-azido C18 fatty esters, and seven other C18 derivatives containing an azido and another functional group (acetate, bromo, ethylene, epoxy, hydroxy, methoxy, or tosyl) are reported. The azido group exerts a deshielding effect on the α- and β-carbon atoms. The carbon atom at the γ-position is shielded. The 13C chemical non-equivalence caused by diastereoisomers in some of the derivatives studied is reflected in the different shifts for these asymmetric carbon nuclei.

An enzyme that catalyses the synthesis of lanthionine in the silkworm, Bombyx mori

1. 1. An enzyme that catalyses the synthesis of lanthionine from cysteine was purified 20-fold from the larval fat body of the silkworm, Bombyx mori. 2. 2. The pH optimum is 9.0 and pyridoxal phosphate is a necessary cofactor. 3. 3. From the present results, it seemed plausible that the enzyme catalyses the reaction of substitution at the β-carbon atom of cysteine or serine, resulting in formation of cystathionine or lanthionine in the presence of homocysteine or cysteine as a cosubstrate in the second reaction stage in B. mori.

Vibrational spectroscopic study of the structure of Ti(III) organometallic compounds

A full interpretation was carried out for the vibrational spectra of TiR3, where R= -CH2C6H5, -CH2C(CH3)2C6H5, and-CH2Si(CH3)3. The absorption bands for the Ti-C bonds were delineated. A dimeric structure was established for the compounds studied with a Ti-Ti bond, whose band lies at 230–280 cm−1. There is an interaction of the titanium atom with the β-carbon atom of the ligand for the Ti(III) benzyl and neophyl derivatives.

Preparation of Methyl 2-Arylpropanoates by the Reaction of 2-Hydroxypropiophenone Dimethyl Acetals with Sulfuryl Chloride in the Presence of an Amide or a Weak Base

Abstract Treatment of 2-hydroxypropiophenone dimethyl acetals [p-RC6H4C(OMe)2CH(OH)Me] (1; R=H, i-Bu, OMe, Ph, Br) with sulfuryl chloride in the presence of an amide or a weak base affords methyl 2-arylpropanoates (2) in good to excellent yields via 1,2-aryl migration of 1. The hydrolysis of 2 leads to the corresponding acids, some of which are pharmaceutically important compounds having nonsteroidal anti-inflammatory and analgesic activities. The aryl migration proceeds stereospecifically with complete inversion of configuration at the β-carbon atom.

Supersonic molecular jet spectroscopy of ethylbenzene, the ethyltoluenes, and the diethylbenzenes

Time-of-flight mass spectra are presented for the S1←S0 origin region of jet-cooled 1,2-, 1,3-, and 1,4-diethylbenzene, and 2-, 3-, and 4-ethyltoluene. The spectra for the diethylbenzenes exhibit two origins which are assigned to syn and anti conformations of the ethyl groups relative to the aromatic ring. The existence of two origins in the 1,3-diethylbenzene spectrum, and only one in the 3-ethyltoluene spectrum, strongly implies that the stable orientation of the ethyl groups is with the β-carbon atom of the ethyl group projecting perpendicular to the plane of the aromatic ring. The size and shape of the potential barrier to rotation of the ring methyl group is obtained by treating the methyl group as a one-dimensional rigid rotor and fitting the calculated energy levels to observed features in the spectra. The results (for the para isomer B=5.20 cm−1, V6=31.00 cm−1; for the meta isomer, B=5.40 cm−1, V3=78.00 cm−1; and for the ortho isomer, B=5.50 cm−1, V3=89.00 cm−1) indicate that the methyl group experiences an increased barrier to rotation in the order para<meta<ortho isomer.

Reduction of enamines of the 3,3-dialkyl-3,4-dihydroisoquinoline series

Lithium aluminum hydride reduced enamines of the 3,3-dialkyl-3,4-dihydroisoquinoline series to the corresponding tetrahydroisoquinolines. In the presence of a hydrogen atom at the Β-carbon atom of the enamino ester the action of lithium aluminum hydride and alkylmagnesium bromide leads to the products from the condensation of two molecules of the initial compound.

Homolytic reactions of ligated boranes. Part 7. An electron spin resonance study of the t-butyl isocyanide–boryl radical

Photochemically generated alkoxyl or cyclopropyl, but not n-propyl, radicals abstract hydrogen from t-butyl isocyanide–borane (TBIB) to give the corresponding isocyanide–boryl radical ButNC→BH2(1), which has been studied in solution using e.s.r. spectroscopy. The structure and electronic configuration of (1) is discussed in relation to the isoelectronic propargylic radical ButCC–ĊH2. On the basis of qualitative considerations and molecular orbita calculations it is concluded that (1) is probably bent at nitrogen, unlike propargylic radicals which have a linear C–CC–Ċ skeleton, and that the spin population on the β-carbon atom in (1) is much larger than that in ButCC–ĊH2. In contrast with saturated ligated boryl radicals, (1) does not abstract halogen from alkyl bromides, as judged by e.s.r. spectroscopy, and this low reactivity is probably a consequence of unpaired electron delocalisation in the isocyanide–boryl. The t-butyl radical is formed in lower yield along with (1) when dialkyl peroxides are photolysed in the presence of TBIB. β-Scission of (1) is not the source of But˙ and other possible origins are discussed. γ-Radiolysis of polycrystalline TBIB affords But˙ at 77 K, presumably by dissociative electron capture. One-electron reduction of TBIB in a methanol glass at 77 K or by Me2ĊOH in solution also yields But˙.

SmI 2-Induced highly regioselective reduction of α,β-epoxy esters and γ,δ-epoxy-α,β-unsaturated esters. An efficient route to optically active β-hydroxy and δ-hydroxy esters

α,β-Epoxy esters were rapidly reduced at room temperature to yield β-hydroxy esters with retention of the configurations at the β-carbon atoms by using SmI 2-THF-HMPA system in the presence of N,N-dimethylaminoethanol (DMAE). The conditions were successfully applied to the synthesis of vinylogous δ-hydroxy esters.

Thermal Condensation in Solid State of N-Hydroxyalkyl-2-imidazolidinone

Abstract N-(1-Hydroxyalkyl)-2-imidazolidinones (1) were prepared by a reaction of 2-imidazolidinone with form-, acet-, propion-, and butyraldehyde. In all of these reactions, 1 were unstable and moisture-sensitive substances. The pyrolysis reaction of 1 was found to be a thermal decomposition via a condensation reaction stage after a molten state. The condensation stage obeyed 1/2- and the first-order kinetics. The kinetic data regarding the condensation reaction were evaluated by analyses of the dependences of the area of isothermal DSC curves upon the reaction time. It may be concluded that the difference provided by the reaction order and the activation parameters were caused by the number of the hydrogen atoms on the β-carbon atom adjacent to the carbon attacked the hydroxyl group of side chain in 1. In the decomposition by electron impact of 1 and dimer of 1, the cleavage of the five-membered ring which corresponded to the molecular-ion peak for 2-imidazolidinone (m⁄z 86) was considered to take place after a successive cleavage of the side chain. On the basis of both kinetic studies and ESR or Mass spectral observations, the dimerization mechanism is fully discussed.

THE MASS SPECTRA OF SOME (E)- AND (Z)-α-(PHENYL)-β-(2-THIENYL) ACRYLAMIDES

Abstract Mass spectra of some (E)- and (Z)-α-(4-X-phenyl)-β-(2-thienyl) acrylamides at 70 eV are reported. The stereoisomeric compounds do not show significant differences. The mass spectra show a four centre reaction scheme with NH2 migration to the β-carbon atom and subsequent fission of Cα[sbnd]Cβ bond.