Oxidative cleavage of p-methoxybenzyl ethers with methyl(trifluoromethyl)dioxirane

[reaction: see text] The ability of methyl(trifluoromethyl)dioxirane to cleave p-methoxylbenzyl ethers oxidatively in the presence of various additional functional groups has been investigated. These reactions, performed in aqueous acetonitrile, transform a reasonably robust aryl substituent into a dienyl aldehydo ester. The originally generated E,Z-isomer undergoes slow conversion to the more stable E,E-form at 20 degrees C.     

Oxidation of peptides by methyl(trifluoromethyl)dioxirane: the protecting group matters

Representative Boc-protected and acetyl-protected peptide methyl esters bearing alkyl side chains undergo effective oxidation using methyl(trifluoromethyl)dioxirane (1b) under mild conditions. We observe a protecting group dependency in the chemoselectivity displayed by the dioxirane 1b. N-Hydroxylation occurs in the case of the Boc-protected peptides, and side chain hydroxylation takes place in the case of acetyl-protected peptides. Both are attractive transformations since they yield derivatized peptides that serve as valuable synthons.     

Reactions at interfaces: oxygenation of n-butyl ligands anchored on silica surfaces with methyl(trifluoromethyl)dioxirane

The oxygenation of n-butyl and n-butoxy chains bonded to silica with methyl(trifluoromethyl)dioxirane (1) revealed the ability of the silica matrix to release electron density toward the reacting C(2)-H σ-bond through the Si-C(1) and Si-O(1) σ-bonds connecting the alkyl chain to the surface (silicon β-effect). The silica surface impedes neither the alkyl chain adopting the conformation required for the silicon β-effect nor dioxirane 1 approaching the reactive C(2) methylene group. Reaction regioselectivity is insensitive to changes in the solvation of the reacting system, the location of organic ligands on the silica surface, and the H-bonding character of the silica surface. Reaction rates are faster for those organic ligands either within the silica pores or bonded to hydrophilic silica surfaces, which evidence the enhanced molecular dynamics of confined dioxirane 1 and the impact of surface phenomena on the reaction kinetics. The oxygenation of n-butyl and n-butoxy chains carrying trimethylsilyl, trimethoxysilyl, and tert-butyl groups with dioxirane 1 under homogeneous conditions confirms the electronic effects of the silyl substituents and the consequences of steric hindrance on the reaction rate and regioselectivity. Orthosilicic acid esters react preferentially at the methylene group adjacent to the oxygen atom in clear contrast with the reactivity of the carboxylic or sulfonic acid alkyl esters, which efficiently protect this position toward oxidation with 1.     

(1-Naphthyl)(trifluoromethyl) O-carboxy anhydride as a chiral derivatizing agent: eclipsed conformation enforced by hydrogen bonding

The preparation of the (1-naphthyl)(trifluoromethyl) O-carboxy-anhydride 1 and its use as a chiral derivatizing agent with several alpha-chiral primary amines are reported. The very large Delta delta(RS) values observed in (1)H NMR have been correlated with a marked preference of the corresponding alpha-hydroxy-amides for the eclipsed conformation. In comparison, the related O-methylated amides are shown to adopt staggered conformations, which substantiates the critical role of intramolecular hydrogen bonding in maximizing the anisotropic effect.     

Mechanism of singlet oxygen generation during catalytic decomposition of methyl(trifluoromethyl)dioxirane by chloride ions

The mechanism of the chloride ion-induced catalytic decomposition of methyl(trifluoromethyl)dioxirane in trifluoroacetone was studied at the MP4//MP2/6-31+G(d) level of theory. The solvated chloride ion interacts with dioxirane to form an ion-dipole pair, which is transformed into the key intermediate ClO—C(Me)(CF₃)—O⁻ acting as a chain carrier in the catalytic decomposition of dioxirane. The generation of singlet oxygen occurs during the transformations of this intermediate on the singlet potential energy surface.     

Oxygenation of alkane C-H bonds with methyl(trifluoromethyl)dioxirane: effect of the substituents and the solvent on the reaction rate

[Chemical reaction: See text] The mechanism of the oxygenation of alkane C-H bonds with methyl(trifluoromethyl)dioxirane (1a) is studied through the effect of the substituent and solvent on the rate of oxygenation of 2-substituted adamantanes (2). The results suggest a remarkable electron deficiency at the reacting carbon atom in the transition state leading to the regular oxygenation products. The linearity of the Hammett plot reveals that the reaction mechanism does not change within a range of 0.15-0.67 units of sigma(I). A change in the solvent does not affect the distribution of the products, indicating a through-bond transmission of the substituent effect as the origin of the deactivation of the substrate.     

Oxidation of methyl trimethylsilyl ketene acetals to alpha-hydroxyesters with urea hydrogen peroxide catalyzed by methyltrioxorhenium

In the presence of catalytic amounts of MTO, methyltrioxorhenium, methyl trimethylsilyl ketene acetals are oxidized with urea hydrogen peroxide to afford alpha-hydroxy and alpha-siloxy esters. On treatment with potassium fluoride, the alpha-hydroxy esters are obtained in high yields.     

Epoxidation of alkenes with hydrogen peroxide catalyzed by iron(III) porphyrins in ionic liquids

An efficient procedure is described for catalyst recycling and easy product isolation in alkene epoxidation with hydrogen peroxide catalyzed by water-soluble iron(III) porphyrins in environmentally benign and ambient temperature ionic liquids.     

Epoxidation reactions with urea–hydrogen peroxide catalyzed by methyltrioxorhenium(VII) on niobia

Soybean oils (oleic, linoleic, and linolenic acids and their methyl esters) are epoxidized readily with urea–hydrogen peroxide (UHP) when methyltrioxorhenium(VII) supported on niobia is used as the catalyst in chloroform. Simple alkenes are epoxidized by the same method. The epoxide and not a diol is produced.     

Chemistry of trifluoromethyl compounds : I. NMR evidence for bis(trifluoromethyl)zinc and methyl(trifluoromethyl)zinc

Bis(trifluoromethyl)zinc and methyl(trifluoromethyl)zinc have been identified by ¹⁹F and ^1H NMR methods. The compounds were formed in the following reactions: (1) dimethylzinc and bis(trifluoromethyl)mercury and (2) dimethylzinc and bis(trifluoromethyl)cadmium.     

Surprising stereoselectivity in the Payne epoxidation of terpinen-4-ol with acetonitrile/hydrogen peroxide

A surprisingly high level of cis-stereoselectivity in the Payne epoxidation has been identified with the homoallylic alcohol, terpinen-4-ol. Very high efficiencies for hydrogen peroxide are realized under mild conditions. The necessity for peroxyimidic acid stabilization by solvent is replaced by coordination to the directing hydroxyl function, resulting in dramatically improved space yields at up to the one kilogram scale.     

Epoxidation of alkenes and oxidation of alcohols with hydrogen peroxide catalyzed by a manganese(V) nitrido complex

The manganese(V) nitrido complex (PPh(4))(2)[Mn(N)(CN)(4)] is an active catalyst for alkene epoxidation and alcohol oxidation using H(2)O(2) as an oxidant. The catalytic oxidation is greatly enhanced by the addition of just one equivalent of acetic acid. The oxidation of ethene by this system has been studied computationally by the DFT method.     

The reaction of (Sp)-2-(diphenylphosphino)ferrocenecarboxylic acid with carbodiimide reagents: Characterisation of the acid anhydride and urea products

Interaction of (S_p)-2-(diphenylphosphino)ferrocenecarboxylic acid [(S_p)-1] with N,N′-dicyclohexylcarbodiimide (DCC) and N-ethyl-N′-[3-(dimethylamino)propyl]carbodiimide (EDC) have been investigated in order to study the reacting system itself and to characterise side-products typically arising during the diimide-promoted condensation of acid (S_p)-1 with nucleophiles. The reaction between (S_p)-1 and DCC was found to give preferentially the respective urea derivative in the absence of a base, and (S_p)-2-(diphenylphosphino)ferrocenecarboxylic anhydride [(S_p,S_p)-3] when the same reaction was performed in the presence of 4-(dimethylamino)pyridine (DMAP). With EDC, the preference for a reaction pathway was less pronounced: whereas the reaction without the base afforded exclusively the corresponding urea, that in the presence of DMAP yielded a mixture of the urea and anhydride (S_p,S_p)-3.     

Oxidation of methyl phenyl sulfide with hydrogen peroxide catalyzed by Ti(IV)-substituted heteropolytungstate

Alkylammonium salts of Ti(IV)-substituted heteropolytungstate, PW₁₁TiO ₁₀ ⁵⁻ , catalyze the oxidation of methyl phenyl sulfide with hydrogen peroxide. The yield of the corresponding sulfoxide and sulfone is practically quantitative. A³¹P NMR study confirms the formation and reactivity of the PW₁₁O₃₉TiO ₂ ⁵⁻ peroxo complex in organic media.     

Oxidation of triarylphosphines and aryl methyl sulfides with hydrogen peroxide catalyzed by dioxovanadium(V) ion

Although neither vanadium(V) ions nor hydrogen peroxide efficiently oxidize the title substrates, they do so in combination, with vanadium(V) as the catalyst in acidic aqueous acetonitrile. The kinetic data show that, of the two peroxovanadium species present, OV(O2)+ and OV(O2)2-, only the latter reacts at a detectable rate. This unanticipated result can be attributed to the weaker O-O and V-O bonds in the diperoxo complex. The rate constants for both series of substrates follow the Hammett correlation, with rhoP = -1.35 and rhoS = -0.83. To analyze properly the kinetic data for the Ar3P compounds, account must be taken of the protonation to Ar3PH+ in acidic solution. In retrospect, our earlier study [Abu-Omar, M. M.; Espenson, J. H. J. Am. Chem. Soc. 1995, 117, 272-280] of phosphine oxidation catalyzed by MeReO3 failed to do so, and the reaction constant must be corrected from the originally reported value to -1.56.     

Enantioselective reduction of trifluoromethyl ketones with chiral organomagnesium amides (COMAs)

Chiral organomagnesium amides (COMAs), readily prepared from dialkylmagnesiums and chiral secondary amines, can reduce trifluoromethyl ketones to form secondary alcohols with excellent enantioselectivities (up to 98:2 er) and chemical yields (typically >95% conversion, >85% isolated yields). These MPV-type reductions use an achiral hydride source, and the chiral amine is readily recovered. [reaction: see text]     

Ground and electronically excited states of methyl hydroperoxide: comparison with hydrogen peroxide

Equilibrium geometries of the ground states of hydrogen peroxide (H(2)O(2)) and methyl hydroperoxide (CH(3)OOH) have been obtained using quadratic configuration interaction methods with correlation-consistent basis sets. These results are compared with experiments and prior calculations. The dipole moments of the ground states of these two molecules have been calculated. The results illustrate the sensitivity of this quantity to molecular geometry. Several excited states of H(2)O(2) and CH(3)OOH were calculated using the equation-of-motion coupled-cluster singles-and-doubles method. Aside from vertical excitation energies, excited state energies along the O-O, O-H, and C-O dissociation pathways were calculated. The results are expected to be of assistance in resolving discrepancies in the experimental interpretation of the UV absorption spectrum and photodissociation of CH(3)OOH.     

Isotactic-b-syndiotactic stereoblock poly(methyl methacrylate) by chiral metallocene/Lewis acid hybrid catalysts

Stereoblock polymerization with chiral ansa-metallocene/strong Lewis acid hybrid catalysts capable of switching stereospecificity of the methyl methacrylate polymerization produces the highly stereoregular isotactic-b-syndiotactic stereoblock poly(methyl methacrylate).