Showing papers on "Epoxide published in 1993"
TL;DR: The stereochemical preference of the cytosolic epoxide hydrolase, together with the known chiral composition of the endogenous arachidonate epoxide pools, suggests a functional role for this enzyme in the metabolism of these important compounds.
220 citations
TL;DR: In this paper, the reactions of hydrogen peroxide or tert-butyl hydroperoxide with cyclooctene and norbornene, catalyzed by iron(III) tetrakis(pentafluorophenyl)porphyrin chloride and other electronegatively-substituted porphyrins, produced 60-100% epoxide yields.
Abstract: The reactions of hydrogen peroxide or tert-butyl hydroperoxide with cyclooctene and norbornene, catalyzed by iron(III) tetrakis(pentafluorophenyl)porphyrin chloride and other electronegatively-substituted porphyrins, produced 60-100% epoxide yields. The epoxynorbornane yield has the same ratio of exo/endo isomers as is obtained using pentafluoroiodosylbenzene, an oxidant which produces the iron(IV) radical cation (oxene) intermediate. These results demonstrate heterolytic cleavage of these peroxides in the catalyzed reaction
171 citations
118 citations
114 citations
TL;DR: In this paper, the effect of remote polar functionality on the regiochemistry of the ring opening of aliphatic epoxides was studied and the synthesis and nucleophilic additions of suitable 2,3-epoxy-1-alkanol derivatives (epoxides trans-1a-d and cis-2) were carried out.
Abstract: In order to study the effect of a remote polar functionality on the regiochemistry of the ring opening of aliphatic epoxides, the synthesis and some nucleophilic additions (methanolysis, azidolysis, and aminolysis) of suitable 2,3-epoxy-1-alkanol derivatives (epoxides trans-1a-d and cis-2) were carried out. The C-3 selectivity commonly observed when nonchelating ring opening conditions are used is lower than when the epoxides are allowed to react in the presence of metal ions (Li + , Mg 2+ , Zn 2+ ) due to the probable intervention of bidentate-chelated intermediates in the latter case, and in some instances an almost complete C-3 regionselection is obtained
85 citations
TL;DR: Mechanistic precedents support a homolytic hydroperoxide cleavage as the initial step in the synthesis of these epoxyalcohols, which are products of the allene oxide synthase.
81 citations
TL;DR: Soybean peroxygenase catalyzes hydroperoxide reduction exclusively by a heterolytic mechanism leading to a ferryl-oxo complex analogous to peroxidase compound I.
74 citations
TL;DR: In this article, aldehyde and a copper salt catalyst such as Cu(OH)2 have been used for the epoxidation of alkenes at room temperature with molecular oxygen (1 atm).
Abstract: Oxidation of alkanes to the corresponding alcohols and ketones and epoxidation of alkenes can be performed efficiently at room temperature with molecular oxygen (1 atm) in the presence of an aldehyde and a copper salt catalyst such as Cu(OH)2.
70 citations
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61 citations
TL;DR: In this article, different alkenes are epoxidized with high selectivity in the presence of manganese(III) tetraphenylporphyrin-imidazole-sodium periodate-tetrabutylammonium bromide system in CH2Cl2-H2O media, with high yields (80-100%) at room temperature.
Abstract: Different alkenes are epoxidized with high selectivity in the presence of manganese(III) tetraphenylporphyrin–imidazole–sodium periodate–tetrabutylammonium bromide system in CH2Cl2–H2O media, with high yields (80–100%) at room temperature.
TL;DR: Examination of the catalytic activities of the possible Tyr-->Phe mutants, the His-64-->Val mutant, and a protein combining all the tyrosine and histidine mutations indicates that tyrosines may participate in, but are not essential for, protein-mediated epoxidation.
TL;DR: In this paper, the epoxide functionalities of macroporous poly(glycidyl methacrylate-co-ethylene dimethACrylate) beads are hydrolyzed to diol groups in the presence of an acid catalyst.
Abstract: The size-restricted access of molecules to cavities of different sizes has been used in the demonstration of size-selective modification of a porous material. The epoxide functionalities of macroporous poly(glycidyl methacrylate-co-ethylene dimethacrylate) beads are hydrolyzed to diol groups in the presence of an acid catalyst. While sulfuric acid catalyzes hydrolysis of all epoxide groups, bulkier catalysts such as poly(styrenesulfonic acid) only cause hydrolysis to occur within pores large enough to accommodate them. As a result, porous materials containing two types of functionalities segregated respectively in pores larger and smaller than the catalyst are obtained. Similar size-specific functionalization has been achieved with macroporous beads containing benzylidene or tetrahydropyranyl ether groups
TL;DR: In this article, catalytic amounts of AgClO 4 were added to a mixture of organozirconocenes and epoxides, resulting in the rapid formation of chain-extended secondary alcohols.
Abstract: Addition of catalytic amounts of AgClO 4 to a mixture of organozirconocenes and epoxides results in the rapid formation of chain-extended secondary alcohols
TL;DR: In this article, a Hammett correlation of log κ for the acid-catalyzed reactions vs σ + gives a slope p + of -4.2 and only diol products are formed.
Abstract: Rate and product studies of the hydronium ion-catalyzed, hydroxide ion-catalyzed, and spontaneous reactions of styrene oxide and its p-CH 3 O-, p-CH 3 -, p-Cl-, and p-O 2 N-derivatives in water solutions have been carried out. A Hammett correlation of log κ for the acid-catalyzed reactions vs σ + gives a slope p + of -4.2 and only diol products are formed. An intermediate in the hydronium ion-catalyzed hydrolysis of p-methoxystyrene oxide is trapped, subsequent to its rate-limiting formation, by azide ion
TL;DR: Polyvinyl pyridine-supported ceric(IV) complex can be easily prepared and it can catalyse nucleophilic ring opening of epoxides in alcohols under mild conditions with high regio- and stereoselectivity as mentioned in this paper.
TL;DR: In this article, the 3-glycidyloxypropyltrimethoxysilane-silica bonding reaction was investigated and the carbon and bonded epoxide content after the bonding reaction and
TL;DR: In this paper, it was shown that P(Ph) 3 -CH 2 PhR (R= NO 2, Cl, H, CH 3, OCH 3 ) is a latent thermal initiator capable of initiating ring opening polymerization of glycidyl phenyl ether.
Abstract: Phosphonium salts + P(Ph) 3 -CH 2 PhR (R= NO 2 , Cl, H, CH 3 , OCH 3 ) are shown to be latent thermal initiators capable of initiating ring opening polymerization of glycidyl phenyl ether. The benzyl proton is the actual initiation species
TL;DR: In this article, high-resolution electron energy loss spectroscopy (HREELS) was used to investigate the reactions of ethylene oxide and propylene oxide on the clean Rh(111) surface.
TL;DR: The cDNA containing the complete coding region for rat microsomal epoxide hydrolase was cloned into the expression/secretion vector pIN-III-OmpA3 and expressed in Escherichia coli strain TG1, finding a broad pH optimum of 6.5 to 8.5 and the presence of three ionizable groups with pKa values of 5.7 +/- 0.4.
TL;DR: In this paper, a new and efficient enantioselective synthesis of Boc-α-amino acids has been developed, starting from an enantiomerically enriched epoxy alcohol, which involves a regioselectively nucleophilic epoxide opening by diphenylmethylamine (benzhydrilamine), hydrogenolysis/protection of the amino group, and oxidation of the diol moiety.
TL;DR: Triphenylsilanethiol, a white crystalline solid, can be used in the opening of epoxides to form s-hydroxymercaptans or s-dihydroxysulfides.
TL;DR: An enzyme-catalyzed asymmetric hydrolysis of epoxides was achieved using an immobilized crude enzyme preparation derived from Rhodococcus sp.
Abstract: An enzyme-catalyzed asymmetric hydrolysis of epoxides was achieved using an immobilized crude enzyme preparation derived from Rhodococcus sp. (NOVO SP 409). The mechanism of the reaction was shown to occur in a transspecific hydrolytic opening via an S N 2-type of reaction. Depending on the substitutional pattern of the substrate, optically active epoxides and 1,2-diols with varying optical purities were obtained (in one case e.e. 72%).
TL;DR: Several new and novel applications of Zinc borohydride, a non-conventional hydride reducing agent, have been demonstrated for efficient chemo-and regioselective reductions of various important functionalities as mentioned in this paper.
Abstract: Several new and novel applications of Zinc borohydride, a non-conventional hydride reducing agent, have been demonstrated for efficient chemo- and regioselective reductions of various important functionalities. These include : (a) chemoselective reduction of aldehydes over ketones; (b) chemoselective reduction of saturated ketones and conjugated aldehydes over conjugated enones; (c) chemoselective reduction of aliphatic ester over aromatic one; (d) chemoselective reduction of carboxylic acids; (e) chemoselective reduction of 2-nitrocycloalkanones to 2-nitrocycloalkanols; (f) highly selective reduction of monosubstituted conjugated nitroalkenes to the corresponding nitroalkanes and disubstituted ones to the corresponding oximes; (g) regio- and stereoselective reductive cleavage of unsymmetrical alkyl-substituted epoxide to the less-substituted alcohol; (h) regioselective 1,2-reduction of conjugated ketones and aldehydes; and (i) regioselective hydration of alkenes to the less-substituted alcohols.
TL;DR: In this article, the results leading to the synthesis of ISP-1 containing an unusal α, α-disubstituted amino acid and whose immunosuppressive activity only has recently been discovered.
TL;DR: In this article, the photopolymerization of silicon-containing epoxide compounds has been studied using analytical techniques including real-time infrared spectroscopy and differential scanning photocalorimetry.
Abstract: Silicon-containing epoxide compounds bearing Si H groups can be readily prepared in high yields by the regioselective rhodium-catalyzed monohydrosilation of α,ω-dihydrogen functional siloxanes and silanes with vinyl epoxides. The remaining Si H groups in these compounds can be further selectively hydrosilated with unsaturated epoxides to give a series of unique ambifunctional monomers containing two different epoxide groups in the same molecule. The photopolymerization of these monomers has been studied using analytical techniques including real time infrared spectroscopy and differential scanning photocalorimetry. On photopolymerization, the new monomers yield interesting networks. © 1993 John Wiley & Sons, Inc.
TL;DR: The reaction of dimethyldioxirane with several alkynes gives products which are conveniently rationalized by postulating the intermediacy of oxirenes and oxocarbenes.
Abstract: The reaction of dimethyldioxirane with several alkynes gives products which are conveniently rationalized by postulating the intermediacy of oxirenes and oxocarbenes. The latter serve as precursors to H atom or methyl group migration products, as well as to cyclopropane insertion products in some cases. Alkenes, derived from some of these carbene reactions, are partially converted to epoxides
TL;DR: In this article, a study on the stereoselective preparation of a series of 3-methyl-4,5-epoxy alcohols as an entry to polypropionates was undertaken.
Abstract: A study on the stereoselective preparation of a series of 3-methyl-4,5-epoxy alcohols as an entry to polypropionates was undertaken. Initially, the opening of cis and trans TIPS-protected 2,3-epoxy butanols by propynyldiethylalane showed an excellent regioselectivity favoring the monoprotected 1,2-diol products. The resulting propargylic alcohols were stereoselectively reduced to the cis and trans 1-[(triisopropylsilyl)oxy]-3-methyl-4-hexen-2-ols. Iodocarbonatation of these four isomeric homoallylic alcohols was carried out and the stereochemistry of the intermediate iodo carbonates established. Interestingly, a complete anti selectivity (>20:1 anti:syn) was observed when both the syn 3-methyl and cis double-bond geometry were present (3b, 10, and 20). The anti relative configuration for all of the iodo carbonates was established by NMR, and that of 5b was confirmed by X-ray crystallography. This study demonstrated that the relative stereochemistry of the hydroxyl and C(3) methyl groups in combination with the cis or trans geometry of the alkene exerts a significant effect on the stereochemical outcome of the iodocarbonatation reaction. Methanolysis of the iodo carbonates produced the desired 3-methyl-4,5-epoxy alcohols. The application of this chemistry to the reiterative synthesis of polypropionates was carried out with epoxy alcohol 4a (anti isomer), producing a new homologated epoxy alcohol, 22, with six contiguous stereocenters in a highly stereoselective manner
TL;DR: In this article, cyclic α, β-epoxyketones are converted to bi- or tricyclic β-hydroxyketones in the presence of n-Bu3Sn· radical.