Oxiranes formation

Bonse G, Urban T, Reichert D, et al. 1975. Chemical reactivity, metabolic oxirane formation, and biological reactivity of chlorinated ethylenes in the isolated perfused rat liver preparation. Biochem Pharmacol 24 1829-1834. 

Greim H, Bonse G, Radwan Z, et al. 1975. Mutagenicity in vitro and potential carcinogenicity of chlorinated ethylenes as a function of metabolic oxirane formation. Biochem Pharmacol 24 2013-2017. 

Uehleke H, Poplawski-Tabarelli S, Bonse G, et al. 1977. Spectral evidence for 2,2,3-trichloro-oxirane formation during microsomal trichloroethylene oxidation. Arch Toxicol 37 95-105. 

Prolonged exposure to alkaline conditions should be avoided to prevent oxirane formation at this step. 

Benter, Th., M. Liesner, R. N. Schindler, H. Skov, J. Hjorth, and G. Restelli, REMPI-MS and FTIR Study of N02 and Oxirane Formation in the Reactions of Unsaturated Hydrocarbons with NO, Radicals, . /. Phys. Chem., 98, 10492-10496 (1994). 

A very promising new method for converting oxiranes, as well as ketones, into oxetanes has recently been reported. This method uses the carbanion of dimethyl(N-tosyl)sulfoximine and gave good yields in the several cases reported. When this reagent is employed with ketones, oxirane formation is presumably an intermediate stage, but the oxirane is not isolated. The method thus provides an excellent synthesis of spiro-oxetanes from ketones, as the example with camphor in equation (85) shows (79JA6135). 

Wistuba, D., Nowotny, H.P., Trager, O. Schurig, V. (1989) Cytochrome P-450 catalyzed asymmetric epoxidation of simple prochiral and chiral aliphatic alkenes. Species dependence and effect of enzyme induction on enantioselective oxirane formation. Chirality, 1, 127-136... 

Bartsch, H., Malaveille, C., Barbin, A. Planche, G. (1979) Mutagenic and alkylating metabolites of halo-ethylenes, chlorobutadienes and dichlorobutenes produced by rodent or human liver tissues. Evidence for oxirane formation by P450-linked microsomal monooxygenases. Arch. Toxicol., 41, 249-277... 

A one-pot procedure combines the generation of trimethylsulfonium hydrogensulfate (Me3S HS04 ) from dimethyl sulfide, sulfuric acid and methanol, and its use in situ for oxirane formation with carbonyl compounds [451] (Table 4.5). 

Dieihoxyphosphonyl-difluoro-methyl)-2.3-dimethyl- ElOb,. 586 (Oxiran-Formation) 2-(Dicthoxyphosphoryl-di fluoro-methyl)-2.3-dimcthyl- F.lOb,. 586 [F,HC-PO(OR), + H,C — CO-CHfcl-CHj]... 

D Oxidation with Peroxidic Compounds. Oxacyclopropane (Oxirane) Formation... 

Durst and Sharma [86] have reported the stereospecific synthesis of 3-spiro-epoxyazetidin-2-ones 55 (Scheme 14). The oxidation of the diastereoisomers of compound 52 with PCC provided a single acetyl compound 3-acetyl-3-benzyloxy-azetidin-2-one 53. Nonchelation controlled L-Selectride reduction of 53 gave the isomerically pure 3-hydroxyethylazetidin-2-one as the sole reduced product, which was further converted to tosylate 54 using NaH/tosylimidazole. The debenzylation-oxirane formation sequence was conveniently performed as a single pot operation with ammonium formate, 5% Pd/C in refluxing methanol as the hydrogen transfer reagent combination. 

An illustrative example of oxirane formation by the action of alkali on a / -halohydrin is to be found in the reaction sequence involved in the Darzens glycidic ester synthesis (Section 5.7.6, p. 598). Three target molecules, namely 2-phenylaziridine (4), methyl (S)-thiiranecarboxylate (5) and cyclooctene sulphide (6), are selected here to exemplify this intramolecular cyclisation reaction type. 

An interesting synthesis of JH1 170 starting from furan was published by Cavill et al.145). The use of a glycol precursor (193) prior to the oxirane formation guarantees the generation of a uniform 10,11-epoxide, in contrast to the usual m-chloroper-benzoic acid oxidation145) (Scheme 34). 

Since this reaction proceeds according to the SN2 mechanism, inversion takes place at the carbon atom involved (Fig. 2-19). The ring size of epoxides can vary from three- to six-membered rings. The three-membered derivatives belong to the most important subclass of internal ethers and are termed oxirans. A prerequisite for oxiran formation is obviously coplanarity and trans position of the reacting groups (Fig. 2-20). 

The reaction of alkenes with peroxycarboxylic acids to produce epoxides was discovered by Prilezhaev over 80 years ago.14 It is still the most widely used method for epoxidation, and considerable work has been carried out to elucidate the mechanism. The commonly accepted explanation for oxirane formation involves a cyclic polar process where the proton is transferred intramolecularly to the carbonyl oxygen, with simultaneous attack by the alkene rc-bond. This concerted process was suggested by Bartlett,15 and because of the unique planar transition structure it is referred to as the butterfly mechanism (Figure 3.2). 

Different competitive processes are dependent on the diazo compound, on the unsaturated system, and on the solvent. With 1,1,1-trifluorobutan-2-one and diazomethane, the corresponding oxirane is formed almost exclusively. While methyl trifluoropyruvatc reacts with diazomethane to provide a mixture of the oxiranes, reaction of the pyruvate with ethyl diazoacetate provides a stable [3-1-2] cycloadduct.Chiral fluoroalkyl-substituted /i-oxo sulfoxide (e.g., 1) readily react with diazomethane to provide the corresponding chiral epoxides. Use of methanol as solvent favors oxirane formation over the competitive enol ether formation. 

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