Kinetics of the reaction between dimethyldioxirane and 2-methylbutane

The kinetics of the reaction between dimethyldioxirane and 2-methylbutane in acetone solutions were studied spectrophotometrically at 25 °C. The radical-chain induced decomposition of dioxirane proceeding with the participation of the carbon-centered radicals follows the first-order kinetic law. The reaction is inhibited by dioxygen. In the presence of O₂, the dimethyldioxirane consumption is due to the homolysis of the O−O bond (at a rate constant of 6.3·10⁻⁴ s⁻¹) followed by attack of the C−H bond of 2-methylbutane by the biradical formed. The rate constant of the reaction between the alkyl radical and dimethyldioxirane was estimated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1785–1788, October, 1997.     

X-ray Crystal Structures of Some Arene Oxides

Using a recently disclosed modification to the dimethyldioxirane method we have synthesized four arene monooxides and one trioxide in good to excellent yield. The X-ray crystal structures have been determined for all of these compounds. In the case of the chrysene trioxide the X-ray determination reveals that the structure is bent out of the plane.     

Kinetics and mechanism of the reaction of dimethyldioxirane with cumene

The reaction of dimethyldioxirane with cumene (22–52°C) follows a chain-radical mechanism. The kinetic regularities of this reaction were studied by the chemiluminescence and kinetic UV spectrophotometry methods by monitoring the consumption of dioxirane. The process is inhibited by oxygen. In the absence of O₂, the process is accelerated due to the decomposition of dimethyldioxirane induced by alkyl radicals. In this case, the reaction occurs according to a complicated kinetic law including the first and second orders with respect to dioxirane. Based on the kinetics and reaction products, the scheme of the process was proposed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 694–702, April, 1997.     

Cyclohexanones derived from dihydrocarvone as precursor of chiral dioxiranes for epoxidation of olefins

New ketones having an axial α-fluorine atom and substituents other than fluorine at C8, derived from commercially available (+)-dihydrocarvone, have been prepared and used for epoxidations of trans stilbene, trans methyl p-methoxy cinnamate, trans cinnamyl alcohol and derivatives. It was found that replacement of the H at C8 by a substituent containing an oxygen atom increases the enantioselectivities in all cases. It was also shown that protic substituents (hydroxyl groups) provide a decrease in enantioselectivity in the case of cinnamates probably because of H-bonding dioxirane-substrate. It is noted that the absolute configurations of the various epoxides obtained hold with the usual model involving a spiro-approach on the dioxirane conformation C1 having the α-fluorine axial. Moreover, sub-stoichiometric amounts (0.3 equiv) of ketone can be used in all cases as these ketones do not undergo Baeyer-Villiger oxidation and are recovered.     

烯烃以糖衍生的手性酮为催化剂的有机催化不对称环氧化

由糖衍生的手性酮是非官能化烯烃的有机催化不对称环氧化的一类重要催化剂,它与过氧硫酸氢钾（KHSO5）可原位产生对顺式烯烃、反式烯烃、三取代烯烃和末端烯烃均有效的氧化剂--手性二氧杂环丙烷.本文对由糖衍生的手性酮的合成方法、不对称诱导反应的机理、手性酮糖的分子结构以及反应条件对其催化活性和不对称诱导作用的影响进行了评述.     

Synthesis of oxiranes based on 1,1,2,3,3-pentafluoro-1,5-hexadiene

Interaction of 1,1,2,3,3-pentafluoro-1,5-hexadiene with Br₂ in a MeCOOH medium results in the product of selective bromination of the hydrocarbon double bond,i.e., 5,6-dibromo-1,1,2,3,3-pentafluoro-1-hexene. Epoxidation of the latter with H₂O₂ in an alkaline medium followed by debromination afforded 5,6-epoxy-4,4,5,6,6-pentafluoro-1-hexene for the first time.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1530–1533, August, 1995.     

Products, kinetic regularities, and mechanism of thermal decomposition of ethyl(methyl)dioxirane

The products and kinetic regularities of thermal decomposition of ethyl(methyl)dioxirane (EMD) were studied. The consumption of EMD occurs via four parallel pathways: two isomerizations to ethyl acetate and methyl propionate, solvent oxidation via insertion of the oxygen atom into the C-H bond of a solvent molecule (butanone), and hydrogen atom abstraction from the solvent by dioxirane with radical escape from the cage. The contribution of the latter route to the oxidation of butan-2-one at 35 °C is 43%. Alkyl radicals initiate EMD decomposition in an inert atmosphere. The activation parameters of EMD isomerization to esters and the reaction of EMD with butanone were determined. The isomerization of EMD was studied by the DFT method. The geometric parameters were optimized at the UB3LYP level using the 6-31G** and/or 6-311+G** basis sets. The calculated energies were corrected taking into account zero-point vibrations. The theoretical results are in good agreement with experimental data. The mechanism of EMD thermolysis is considered. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1716–1723, October, 2006.     

Asymmetric oxidation of silyl enol ethers using chiral dioxiranes derived from α-fluoro cyclohexanones

Asymmetric oxidation of silyl enolethers derived from tetralone, 2-methyl-tetralone, propiophenone and deoxybenzoin using chiral dioxiranes generated in situ from oxone and new chiral α-fluorinated cyclohexanones or fructose-derived ketone have been studied. It was observed that tetrasubstituted silyl enolethers are poor substrates, that substitution at C8 of the fluoro-ketones has a significant effect on the enantioselectivities obtained and that the fructose-derived-ketone provides higher enantioselectivities. The absolute configuration of the major hydroxy ketones obtained can be rationalized using a spiro model proposed for epoxidation of olefins.     

Two-way enantioselective control in the epoxidation of alkenes with the keto bile acid-Oxone® system

A number of 3-keto bile acid derivatives has been prepared and evaluated in the asymmetric epoxidation of unfunctionalized olefins with Oxone. The control of the enantioselectivity with the production of both enantiomers is strictly regulated by the bile acid inductor, as a function of substitution at carbons C(7) or C(12). Up to 98% ee has been achieved. The stereochemical outcome of the reaction may be rationalized in terms of spiro transition state model.