Oxirane isomerizations reaction mechanism

Organometallic compounds asymmetric catalysis, 11, 255 chiral auxiliaries, 266 enantioselectivity, 255 see also specific compounds Organozinc chemistry, 260 amino alcohols, 261, 355 chirality amplification, 273 efficiency origins, 273 ligand acceleration, 260 molecular structures, 276 reaction mechanism, 269 transition state models, 264 turnover-limiting step, 271 Orthohydroxylation, naphthol, 230 Osmium, olefin dihydroxylation, 150 Oxametallacycle intermediates, 150, 152 Oxazaborolidines, 134 Oxazoline, 356 Oxidation amines, 155 olefins, 137, 150 reduction, 5 sulfides, 155 Oxidative addition, 5 amine isomerization, 111 hydrogen molecule, 16 Oxidative dimerization, chiral phenols, 287 Oximes, borane reduction, 135 Oxindole alkylation, 338 Oxiranes, enantioselective synthesis, 137, 289, 326, 333, 349, 361 Oxonium polymerization, 332 Oxo process, 162 Oxovanadium complexes, 220 Oxygenation, C—H bonds, 149... 

Kinetic examinations have been made in order to shed light on the reaction mechanism. For oxiranes with asymmetrical structures isomerization takes place in both directions (Eq. 142). ... 

In connection with the oxirane ring opening, the isomerization of oxirane 6 to ketone 9 in an MeCN—LiClO —(Pt) and a CH Clj—Et NClO —(Pt) system has been reported and was explained on the basis of an electron-transfer chain mechanism via 7 and 8 However, 6 is actually converted to 9 under the preelectrolysis conditions so that the transformation may be explained in terms of an EGA catalyzed reaction... 

Cyclododecanone has been synthesized from epoxycyclododecane on a Pd catalyst.Comprehensive work has been carried out on the hydrogenolysis and isomerization of methyloxirane on various metals. The results have been compared with those for oxacycloalkanes with larger rings.The transformations of 1,1-dimethyloxirane and 1-methylepoxycyclopentene have been followed on Pd, Pt, Rh, Cu, and Ni catalysts. The mechanisms of the catalytic reactions have been dealt with in detail. It has been demonstrated that the isomerization of the oxiranes on metals is the primary process, occurring in parallel with hydrogenolysis. The pathway of the reaction depends on the nature of the metal. Deuteration has been utilized to establish the role of hydrogen. 

Cyclohexene oxide and its 3-hydroxy derivatives have been opened regio- and stereospecifically with phosphodiesters. The mechanism of the reaction of oxiranes with sodium dialkyl phosphite and diphenylphosphines has been studied. Cyclopropanecarboxylic acid derivatives have been obtained from substituted oxiranes with triethylphosphonoacetate anion.The mechanism of formation of isomeric alkoxyalkylacetates from oxiranes with alkyl halides and mercuric acetate has been discussed. ... 

Darzens condensation of an aromatic aldehyde with a-bromo-y-valero-lactone has been used in the preparation of ketides. The acid-catalysed decarboxylation of a-phenylglycidic acids is reported to give abnormal products a non-concerted mechanism involving oxiran ring-opening is invoked. a-Halogenoglycidic esters can be obtained by reaction of tris(di-methylamino)phosphine with trichloroacetic acid derivatives in the presence of carbonyl compounds (Scheme 18) cyclohexanone affords the isomeric halogenated pyruvic acid derivative (51) in quantitative yield. ... 

Arnold first discovered that PET reactions of cis- and rrans-2,3-diphenyloxiranes (1 and 2) with electron-accepting sensitizers such as DCN, 1,4-dicyanobenzene, dimethyl terephthalate, and methyl 4-cyanoben-zoate produce the isomeric tetrahydrofuran derivatives 7 and 8 (Scheme 2). The proposed mechanism involves the CC bond cleavage of the oxirane radical cations to give ylide radical cations 3 and 4, followed by back electron transfer (BET) to generate carbonyl ylides 5 and 6. The resulting carbonyl ylides are trapped with dipolarophiles, such as acrylonitrile, maleonitrile, and fumaronitrile, to produce the observed products. In the absence of dipolarophiles, C)S-/ir s-isomerization (1/2 = 0.19-0.28) was observed, which is consistent with the formation of carbonyl ylides 5 and 6, as well as their radical cations 3 and 4. This method was successfully apphed to the synthesis of various tetrahydrofurans (Scheme 3) and dihydrofurans (Scheme 4). ... 

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