2.3- Dimethyloxirane

Many other reagents for converting alkenes to epoxides,including H2O2 and Oxone , VO(0-isopropyl)3 in liquid C02, ° polymer-supported cobalt (II) acetate and 02, ° and dimethyl dioxirane.This reagent is rather versatile, and converts methylene oxiranes to spiro-epoxides. ° ° One problem with dimethyloxirane is C—H insertion reactions rather than epoxidation. Magnesium monoperoxyphthalate is commercially available, and has been shown to be a good substitute for m-chloroperoxybenzoic acid in a number of reactions. 

A similar convergence study has been reported for the B-spline calculation for trans-2,3 dimethyloxirane molecule, et al. [53] The authors in fact comment that the parameter is no more demanding on basis set size than the p parameter, but their data ([53] Fig. 1) show that when the asymptotic is increased from 10 to 15 there is a significantly greater improvement in the former angular parameter. A value of. (max = 15 was chosen for all subsequent B-spfine calculations for oxiranes, and the same limit tends to be applied in the other reported B-spline calculations of chiral molecule PECD [60, 61]. 

Fig. 12.11. Transition structures and /. values for epoxidation of ethene and substituted derivatives by dimethyloxirane. Reproduced from. /. Am. Chem. Soc., 119, 10147 (1997), by permission of the American Chemical Society. 

The metals are also different in the transformation of the cis- and trans-2,3-dimethyloxiranes. The cis-2,3-dimethyloxirane is transformed at a much higher rate than the trans isomer on Pt and Pd catalysts, whereas on Ni the two isomers are converted at almost the same rate.7... 

If a molecule contains carbon atoms that can stabilize the positive charge (e g., a tertiary carbon) the cleavage may also exhibit SN1 character on Pd and Pt catalysts. In accordance with this, hydrogenolysis of 1,1-dimethyloxirane occurred at the more hindered C—O bond over Pt (Scheme 4.6).3... 

The insertion is also promoted by methyl substitution. In the case of 1,1-dimethyloxiranes, the sterically hindered bond is broken on a Pt catalyst too (Scheme 4.63). 

Figure 11.2 Acid-catalyzed hydrolysis of ds-2,3-dimethyloxirane yields (21 ,3J/ )-2,3-butanediol by path (a) and (2 S, 3 S)-2,3-butanediol by path (b).

The best results were achieved by employing N-(3-dimethylaminopropyl)-N -ethylcar-bodiimide hydrochloride (EDC) as coupling agent. After Fmoc deprotection with piperidine in N,N-dimethylformamide, additional diversity could be introduced by acylation of the liberated amine position. Finally, the acyl cyano phosphoranes could be efficiently cleaved by ozonolysis at -78 °C or by utilizing freshly distilled 3,3-dimethyloxirane at room temperature [65]. The released compounds constituted highly activated electrophiles, which could be further converted in situ with appropriate nucleophiles. 

Thermolysis of the syn and anti /J-acetoxy stannanes, obtained by addition of Bu3SnLi to tram- or cis- 1,2-dimethyloxirane and subsequent acetylation, led to (Z)- or (E)-2-butene, respectively, by a stereospecific anti process (equation 34).73. It is postulated that a hyperconjugative interaction of the C—Sn bond facilitates departure of the acetate group in these acyclic systems. The trimethylstannyl and triphenylstannyl analogues likewise undergo anti elimination. 

Furthermore, intercepting the furylpalladium(II) species 130 with an electrophile would result in a carbodepalladation in place of protodepalladation. Therefore, a tandem intramolecular alkoxylation of p.y-acetylenic ketone 127 was realized to afford trisubstituted furan 131 when allyl chloride was added to the original recipe [103]. 2,2-Dimethyloxirane was used as a proton scavenger, ensuring exclusive formation of 3-allylated 2,5-disubstituted furan 131 without contamination by protonated furans. 

Lewis acid SnCLj-assisted reaction between the l,3-thiazole-5-thione 434 and /ra r-2,3-dimethyloxirane led to the m 4,5-dimethyl-l,3-oxathiolane 435 The same Lewis acid enabled a second addition of /ra/ -2,3-dimcthyloxirane onto the C—N bond of the 1,3-thiazole ting of 434, leading to the formation of the tetrahydro-2//-thiazolo[2,3- ]-oxazole adduct 436 (Equation 200) <2000HCA3163>. Condensation of 2,4-dinitroimidazole, 8-bromotheophylline, and 8-bromoadenine with substituted methyloxiranes involved sequential A -alkylation-r/wo-substitution and furnished a series of 2,3-dihydro-imidazo[2,l- ]oxazole derivatives 437, 438, and 439 (Equations 201-203) <2000CCC1126, 2000EJ03489, 2005TL3561, 2004JHC51>. 

Figure 4. Symmetry breaking of the ethanol torsion potential (top, two gauche and one trans conformation) by interaction with a chiral acceptor molecule (dimethyl oxirane, bottom), in this case RR trans 2,3 dimethyloxirane [128]. Note that trans ethanol is less stable in the complex and that the two gauche (g) forms differ in energy.

N. Borho and Y. Xu, Molecular recognition in 1 1 hydrogen bonded complexes of oxirane and trans 2,3 dimethyloxirane with ethanol A rotational spectroscopic and ab initio study. Phys. Chem. Chem. Phys. 9, 4514 4520 (2007). 

We also note that some 2,2-disubstituted oxiranes have toxicological significance, as exemplified by 2,2-dimethyloxirane (2-methyl-l, 2-epoxypropane, 10.43, R = Me). This compound is the toxic metabolite of 2-methyl-prop-1-ene (isobutene), a gaseous alkene widely used as a monomer in the industrial production of adhesives, plastics, and other polymers. Interestingly, detoxification of this epoxide catalyzed by liver epoxide hydrolase was high in the human, intermediate in the rat, and low in the mouse [125], These activities were inversely correlated with the epoxide levels measured in vitro in liver tissue of these species. 

CASRN 558-30-5 molecular formula C4H8O FW 72.11 Chemical/Physical. The second-order hydrolysis rate constant of 2,2-dimethyloxirane in 7.08 mM perchloric acid and 35.3 °C is 11.0/M-sec (Kirkovsky et al, 1998). 

Epoxidation of monoterpenic olefins and A -octalins with dimethyloxirane gives the corresponding epoxides in excellent yields. Some A -octalins are oxidized in a much more stereoselective manner than with m-CPBA . ... 

Figure 21. A1) True racemic composition for enantiomer separation196 of frons-2,3-dimethyloxirane by complexation gas chromatography on nickel(II) bis[3-heptafluorobutanoyl-(D )-camphorale] at 80CC. Integration with a Spectra-Physics SP4100 instrument (peak areas are equal).

With chiral racemic oxiranes one enantiomer reacts faster than the other the degree of kinetic resolution is very high for L-valine/alanine-based dialkoxydihydropyrazines. For example, in the reaction of one equivalent of (2.S )-2,5-dihydro-2-isopropyl-3,6-dimethoxy-5-methyl-pyrazine (1, R1 = CH3) with two equivalents of fW-(//,/ )-2,3-dimethyloxirane (R2,R4 = CH3 R = H) virtually only the (2//,3/ )-oxirane enantiomer reacts with the lithiated dihydropyrazine to give exclusively the (l /, 2/, 2 / )-configuratcd adduct i.e., (2/ ,5S)-2,5-dihydro-5-isopropyl-3,6-dimethoxy-2-[(l/ ,2/ )-2-(2-methoxyethoxymethoxy)-l-methylpropyl]-2-methylpyrazine, entry 7. Likewise, kinetic resolution (intramolecular) occurs upon reaction with rac-7-oxabicy-clo[4.1.0]heptane (entry 8). 

D. L. Trimm Dr. Mayo has suggested that the formation of epoxides via alkenes may well be important and that, in particular, most of the 2,3-dimethyloxiran formed during the oxidation of n-butane is probably... 

Perfluoro(2,2-dimethyloxirane) (1), which cannot rearrange to a ketone, gives the acyl fluoride 2 in the presence of antimony(V) fluoride.31... 

Symmetrically 2,3-disubstituted perfluorooxiranes, such as perfluoro(2,3-dimethyloxirane) and perfluoro(2,3-diethyloxirane), have been converted into the expected ketones (perfluorobutan-2-one and perfluorohexan-3-onc, respectively) in high yields with antimony(V) fluoride, although temperatures over 150 C are required.43... 

The presence of a chlorine on the oxirane ring accelerates the rearrangement and results in regioselective formation of the a-choro ketone. Thus. perfluoro(2-chloro-2-ethyloxirane) (6)46 and pcrfluoro(2-chloro-2,3-dimethyloxirane) (8)45 rearrange to ketones 7 and 9, respectively, at room temperature and within 1 hour. 

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