Umpolung Reactivity of Aldehydes toward Carbon Dioxide

Carbon dioxide is an intrinsically stable molecule. Therefore, its activation requires extra energy input in the form of reactive reagents and/or activated catalysts and, often, harsh reaction conditions. Reported here is a direct carboxylation reaction of aromatic aldehydes with carbon dioxide to afford α‐keto acids as added‐value products. In situ generation of a reactive cyanohydrin was the key to the successful carboxylation reaction under operationally mild reaction conditions (25–40 °C, 1 atm CO₂). The resulting α‐keto acids served as a platform for α‐amino acid synthesis by reductive amination reactions, illustrating the chemical synthesis of essential bioactive molecules from carbon dioxide.     

Reactivity of Benzamide toward Sulfonylation

Russian Journal of Organic Chemistry - The ranges of variation of the rate constant (0.031– 0.153 L·mol–1·s–1), energy of activation (21– 55 kJ/mol), and entropy...     

Reactions of Polysaccharide Aldehydes with Aromatic Hydroxy Compounds

Reaction of dextran polyaldehyde with phenol or its derivatives was suggested as a way to modify polysaccharides with aromatic hydroxy compounds.     

Synthesis and Reactivity of Aldehydes of the Adamantane Series

1-Adamantanecarbonitriles are very active in the Stephen reaction, which allows synthesis of the corresponding aldehydes in high yields. Electron-acceptor substituents in the 3 position of the adamantine nucleus exert almost no effect on the yield of aldehydes. Separation of the nitrile group and the adamantane nucleus by one methylene group results in a complete loss of reactivity. A quantitative study of the reactivity of the synthesized aldehydes in the oximation reaction was performed.     

Reactivity of Phosphaalkenes toward Carbene Complexes

Reaction of phosphaalkenes RP=C(NMe 2 ) 2 (R = t -Bu, Me 3 Si), featuring an inverse distribution of electron density about the P--C double bond, with Fischer carbene complexes [(CO) 5 M=C(OEt)Ar] (Ar=Ph, 2-MeC 6 H 4 , 2-MeOC 6 H 4 , M = Cr, W) afforded a mixture of complexes [(CO) 5 M{P(R)=C(NMe 2 ) 2 }] and [(CO) 5 M{P(R)=C(OEt)Ar}]. The treatment of phosphaalkene HP=C(NMe 2 ) 2 with compound [(CO) 5 W=C(OEt)(2-MeOC 6 H 4 )] gives rise to the formation of an ( E / Z )-mixture of [(CO) 5 W{P(CH(NMe 2 ) 2 )=C(OEt)(2-MeOC 6 H 4 )}].     

Reactivity of Arylhydrazones toward Molecular Oxygen

The kinetics and mechanism of reaction of arylhydrazones with molecular oxygen were studied by gas volumetry. The reaction rate was studied in relation to the structure of arylhydrazone and kind of the solvent. The inhibiting power of the compounds toward initiated oxidation of ethylbenzene was evaluated, and the most effective compounds were found, judging from the ratio of the rate constants of the reactions with molecular oxygen and with peroxy radicals arising in the course of ethylbenzene oxidation.     

Reactivity of digallane toward nitrogen-containing compounds

The reactions of [LGa–GaL] (L = dpp-bian = 1,2-bis[(2,6-di-isopropylphenyl)imino]acenaphthene) with ammonia and pyrrolidine in toluene lead to the formation of adducts [L(NH₃)Ga–Ga(NH₃)L], [L(HNC₄H₈)Ga–GaL] and [L(HNC₄H₈)Ga–Ga(HNC₄H₈)L], respectively. In contrast, the reaction between crystalline digallane and an excess of pyrrolidine leads to the formation of compound [LGa(NC₄H₈)(HNC₄H₈)]. The complex [LGa(C₅H₅N)(μ-O)Ga(C₅H₅N)L] was obtain from reaction of digallane with N₂O in the presence of pyridine.     

Reactivity of ketene dithiolates toward alkyl bromides

The reactivity of barbituric/thiobarbituric ketene dithiolates with bromoacetic ester and phenacyl bromide is studied. J. Heterocyclic Chem., (2011).     

Reactivity of diacyloxyiodobenzenes toward trivalent phosphorus nucleophiles

The reaction of diacyloxyiodobenzenes and tetravalent phosphorus nucleophiles was investigated. It was established that both H‐phosphonates and secondary phosphine oxides react with diacetoxyiodobenzene in alcohols in the presence of sodium alcoholates yielding trialkyl phosphates and alkyl phosphinates respectively. For this transformation reactive intermediate 6 is proposed. In contrast to this, the treatment of diacetoxyiodobenzene with 3 equiv of sodium diisopropyl phosphite in THF produces diisopropyl 1‐(diisopropoxyphosphinyl)ethylphosphonate with excellent yield. It was found that diacyloxyiodobenzene/PR₃ system may serve as an acylating agent; the acylation process can proceed via carboxylic acid anhydride or acylphosphonium salt 17 depending on the protocol used. New very efficient method for synthesis of 2,4,6‐trimethylbenzoic anhydride was developed. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:352–359, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10161     

Reactivity of Mitsunobu reagent toward carbonyl compounds

[reaction: see text] The nitrogen-based nucleophile generated from azodicarboxylate and triphenylphosphine displayed an excellent reactivity toward carbonyl compounds to generate a variety of different final products depending on the substituent pattern on the carbonyl carbon. From the structures of these adducts, a straightforward mechanistic interpretation for the formation of different products is provided.     

Reactivity of aromatic compounds toward diphenylcarbonyl oxide

The reactivity of organic compounds (PhH, PhMe, PhF, PhCl, PhOH, PhOEt, PhCHO, Ph₂CO, PhCN, Ph₂S, Ph₂SO, Ph₂SO₂, andp-Me₂C₆H₄) toward diphenylcarbonyl oxide Ph₂COO was characterized by thek ₃₃/k ₃₁ ratio, wherek ₃₃ andk ₃₁ are the rate constants for the reactions of Ph₂COO with the arene and diphenyldiazomethane Ph₂CN₂, respectively. The values ofk ₃₃/k ₃₁ vary from 2.6·10⁻³ (PhCN) to 0.65 (Ph₂S) (70°C, MeCN). The reaction is preceded by formation of a complex with charge transfer from a substrate to Ph₂COO. In the reactions with aromatic substances (except for Ph₂SO, PhCHO, and Ph₂CO), carbonyl oxide behaves as an electrophile. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2197–2201, November, 1998.     

Reactivity of trimethylcyanosilane toward the surface of silica

The reaction of the surface of silica with (CH₃)₃SiCN vapor was studied by IR spectroscopy. It was established that the chemisorption of trimethylcyanosilane belongs to the processes of electrophilic substitution of a proton in free silanol groups. The activation energy, calculated from the kinetic curves, amounts to 22±1 kJ/mole of grafted trimethylsilyl groups.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 1, pp. 117–120, January–February, 1987.     

Microscopic Reactivity of Phenylferrate Ions toward Organyl Halides

Despite its practical importance, organoiron chemistry remains poorly understood due to its mechanistic complexity. Here, we focus on the oxidative addition of organyl halides to phenylferrate anions in the gas phase. By mass-selecting individual phenylferrate anions, we can determine the effect of the oxidation state, the ligation, and the nuclearity of the iron complex on its reactions with a series of organyl halides RX. We find that Ph₂Fe(I)⁻ and other low-valent ferrates are more reactive than Ph₃Fe(II)⁻; Ph₄Fe(III)⁻ is inert. The coordination of a PPh₃ ligand or the presence of a second iron center lower the reactivity. Besides direct cross-coupling reactions resulting in the formation of RPh, we also observe the abstraction of halogen atoms. This reaction channel shows the readiness of organoiron species to undergo radical-type processes. Complementary DFT calculations afford further insight and rationalize the high reactivity of the Ph₂Fe(I)⁻ complex by the exothermicity of the oxidative addition and the low barriers associated with this reaction step. At the same time, they point to the importance of changes of the spin state in the reactions of Ph₃Fe(II)⁻.     

Reactivity of Carboxamides toward Benzoyl Chloride in Acetonitrile

Catalytic action of carboxamides at benzoyl chloride hydrolysis in acetonitrile at 25°C occurs by nucleophilic mechanism. Its first stage consists in reversible interaction between amides and substrate. The rate constants of the direct reaction were determined which characterized the oxygen-nucleophilic reactivity of amides toward benzoyl chloride. The assumption was confirmed that bimolecular addition of benzoyl chloride to the carbonyl oxygen of amides occurred in cyclic transition states.     

原位生成的烯丙基磷叶立德与醛的化学反应性研究

介绍了我们小组最近有关原位生成的烯丙基磷叶立德与醛的化学反应性研究结果.在化学计量叔膦作用下,烯丙基碳酸酯或联烯酸酯经原位生成的烯丙基磷叶立德活性中间体,与醛发生高度立体选择性的三组分Wittig烯化反应和vinylogous Wittig烯化反应,该类反应为合成多取代1,3-二烯衍生物提供了简单、高效的新方法;在催化量叔膦作用下,γ-甲基联烯酸酯经烯丙基磷叶立德关键中间体与醛发生多个膦催化的环化反应,为五元、六元含氧杂环化合物的合成提供了原子经济性的方法.通过氘代实验和核磁跟踪等方法,对上述反应机理进行了初步探索.     

Reactivity of alkyl and polychloroalkyl radicals toward 1-hexene

The kinetics of CCl₃ radical addition to 1-hexene in CCl₃Br and CCl₄ media has been studied. The rate constant of CCl₃ addition to the double bond is shown to be independent of the solvent. The ratios between the rate constants of transfer and allyl chain termination for the alkyl and polychloroalkyl radicals have been estimated by competition methods. Activation parameters for the calculated rate constants are given.

---

CCl₃- 1- CCCl₃Br CCl₄. , . . .

     

Reactivity of electrophilic terminal phosphinidene complexes toward phosphorus ylides

Stabilised phosphorus ylides react with transient terminal phosphinidene complexes [RP---W(CO)₅] (R=Ph, Me) to give products resulting from a formal insertion of P into a C---H bond via an initial nucleophilic attack of the ylidic carbon.     

Reactivity of Cyclohexanol CH Bonds toward the tert-Butylperoxy Radical

The effect of the hydroxy group on the partial rate constants of the reactions of the tert-butylperoxy radical with CH bonds in cyclohexanol at 333 K was studied by the Howard–Ingold method. The overall reaction rate constant increased with decreasing alcohol concentration in chlorobenzene because of complex effects of hydrogen bonds at the steps of chain growth and termination. The hydroxy group activates the -CH bond and deactivates the - and -CH bonds. The reactivity of -CH bonds is close to the reactivity of CH bonds in cyclohexane.     

Reactivity of the CHBr2+ dication toward molecular hydrogen

Structural aspects as well as the stability and reactivity of the CHBr(2+) dication are studied both experimentally and theoretically. Translational energy distributions of the CHBr(+) products from charge transfer between CHBr(2+) and Kr indicate that the dication exists in two isomeric forms, H-C-Br(2+) and C-Br-H(2+). In the reaction of CHBr(2+) with H(2), the dominant channel corresponds to proton transfer leading to CBr(+) + H(3)(+). Other reaction channels involve the formation of the intermediates CH(3)Br(2+) and CH(2)BrH(2+), respectively. Both of the latter dications can either lose a proton to form CH(2)Br(+) or undergo a spin-isomerization followed by cleavage of the C-Br bond. The proposed mechanisms are supported by DFT calculations and deuterium labeling experiments.     

Reactivity of aquacobalamin and reduced cobalamin toward S-nitrosoglutathione and S-nitroso-N-acetylpenicillamine

The reactions of aquacobalamin (Cbl(III)H2O, vitamin B12a) and reduced cobalamin (Cbl(II), vitamin B12r) with the nitrosothiols S-nitrosoglutathione (GSNO) and S-nitroso-N-acetylpenicillamine (SNAP) were studied in aqueous solution at pH 7.4. UV-vis and NMR spectroscopic studies and semiquantitative kinetic investigations indicated complex reactivity patterns for the studied reactions. The detailed reaction routes depend on the oxidation state of the cobalt center in cobalamin, as well as on the structure of the nitrosothiol. Reactions of aquacobalamin with GSNO and SNAP involve initial formation of Cbl(III)-RSNO adducts followed by nitrosothiol decomposition via heterolytic S-NO bond cleavage. Formation of Cbl(III)(NO-) as the main cobalamin product indicates that the latter step leads to efficient transfer of the NO- group to the Co(III) center with concomitant oxidation of the nitrosothiol. Considerably faster reactions with Cbl(II) proceed through initial Cbl(II)-RSNO intermediates, which undergo subsequent electron-transfer processes leading to oxidation of the cobalt center and reduction of the nitrosothiol. In the case of GSNO, the overall reaction is fast (k approximately 1.2 x 10(6) M(-1) s(-1)) and leads to formation of glutathionylcobalamin (Cbl(III)SG) and nitrosylcobalamin (Cbl(III)(NO-)) as the final cobalamin products. A mechanism involving the reversible equilibrium Cbl(II) + RSNO <==> Cbl(III)SR + NO is suggested for the reaction on the basis of the obtained kinetic and mechanistic information. The corresponding reaction with SNAP is considerably slower and occurs in two distinct reaction steps, which result in the formation of Cbl(III)(NO-) as the ultimate cobalamin product. The significantly different kinetic and mechanistic features observed for the reaction of GSNO and SNAP illustrate the important influence of the nitrosothiol structure on its reactivity toward metal centers of biomolecules. The potential biological implications of the results are briefly discussed.