2.3- Dimethyl-2-butene, epoxidation

Mn(TPP)Cl Ascorbate Cyclohexenol Styrene Styrene oxide Cyclohexene, Epoxide CIS and trans stilbenes, Epoxides CIS- and trans-2-hexenes, Epoxides 2,3-Dimethyl-2-butene, Epoxides [83]... 

Due to the abundance of epoxides, they are ideal precursors for the preparation of P-amino alcohols. In one case, ring-opening of 2-methyl-oxirane (18) with methylamine resulted in l-methylamino-propan-2-ol (19), which was transformed to 1,2-dimethyl-aziridine (20) in 30-35% yield using the Wenker protocol. Interestingly, l-amino-3-buten-2-ol sulfate ester (23) was prepared from l-amino-3-buten-2-ol (22, a product of ammonia ring-opening of vinyl epoxide 21) and chlorosulfonic acid. Treatment of sulfate ester 23 with NaOH then led to aziridine 24. ... 

The cyclohexyloxy(dimethyl)silyl unit in 8 serves as a hydroxy surrogate and is converted into an alcohol via the Tamao oxidation after the allylboration reaction. The allylsilane products of asymmetric allylboration reactions of the dimethylphenylsilyl reagent 7 are readily converted into optically active 2-butene-l, 4-diols via epoxidation with dimethyl dioxirane followed by acid-catalyzed Peterson elimination of the intermediate epoxysilane. Although several chiral (Z)-y-alkoxyallylboron reagents were described in Section 1.3.3.3.3.1.4., relatively few applications in double asymmetric reactions with chiral aldehydes have been reported. One notable example involves the matched double asymmetric reaction of the diisopinocampheyl [(Z)-methoxy-2-propenyl]boron reagent with a chiral x/ -dialkoxyaldehyde87. 

Intramolecular oxonium ylide formation is assumed to initialize the copper-catalyzed transformation of a, (3-epoxy diazomethyl ketones 341 to olefins 342 in the presence of an alcohol 333 . The reaction may be described as an intramolecular oxygen transfer from the epoxide ring to the carbenoid carbon atom, yielding a p,y-unsaturated a-ketoaldehyde which is then acetalized. A detailed reaction mechanism has been proposed. In some cases, the oxonium-ylide pathway gives rise to additional products when the reaction is catalyzed by copper powder. If, on the other hand, diazoketones of type 341 are heated in the presence of olefins (e.g. styrene, cyclohexene, cyclopen-tene, but not isopropenyl acetate or 2,3-dimethyl-2-butene) and palladium(II) acetate, intermolecular cyclopropanation rather than oxonium ylide derived chemistry takes place 334 ). 

The epoxidation of nonconjugated olefins is slow123,124 and shows reduced enantioselectivity as compared with the epoxidation of conjugated olefins. For example, enantioselectivities from the epoxidation of (Z)-l-cyclohexyl-1-propene, 3,3-dimethyl-l-butene, and geranyl acetate are 82% (with (34)), 70% (with (34)),123 and 53% (6,7-epoxide, with (26)),124 respectively, and yields of the epoxides are modest. 

Long-chain derivatives of pyrazolyl pyridines coordinated to MoO(02)2 as 35 may efficiently replace the conventional Mo(CO)e in the oxidation of several double-bond typologies with TBHP, in non-polar hydrocarbon solvents . The epoxidation of cyclopentene and 2,3-dimethyl-2-butene led to the corresponding epoxides, notoriously sensitive to ring opening, in 100% and 87% yield respectively, in isoctane, with 1 hour reaction time. Recent advances in the epoxidation of a-pinene and other terpenes using the Mo-TBHP system have been reported. ... 

Dimethyl-2-butene, primary ozonide, 720 Dimethylcarbonyl oxide, ethylene epoxidation,... 

This mechanism is consistent with the observation of significant yields of epoxide products and N02 for some alkenes (Olzmann et al., 1994). For example, Fig. 6.7 shows the infrared spectrum of the minor products from the reaction of N03 with 2,3-dimethyl-2-butene at... 

Skov, H Th. Benter, R. N. Schindler, J. Hjorth, and G. Restelli, Epoxide Formation in the Reactions of the Nitrate Radical with 2,3-Dimethyl-2-butene, cis- and trans-2-Butene, and Isoprene, Atmos. Environ., 28, 1583-1592 (1994). 

A detailed study271 on the reaction of 2,3-dimethyl-2-butene with ozone revealed that epoxide formation strongly depends on alkene concentration and temperature. Under appropiate reaction conditions (neat alkene, 0°C) the corresponding tetra-methyloxirane was the main product. Dimethyldioxirane formed from energy-rich acetone oxide (a cleavage product of the alkene) was postulated to be responsible for epoxidation. 

Oxidation of 2,4-dimethyl- 2 -pentane gave the desired epoxide in high yield- (Eq. 109), and no other products were isolated,7 7 The reaction was conducted at 0° in a mixture of acetic anhydride and carbon disulfide. Under these conditions 2-methyl-2-butene. in which a... 

As cyano-substituted ozonides were easily reduced by triphenylphosphine, also p-tolyl sulfide can be used as a reducing agent and the corresponding sulfoxide could be isolated in quantitative yield. Alternatively, the 3-cyano-3-phenyl-ozonide 103 can oxidize 2,3-dimethyl-2-butene to the corresponding epoxide (Scheme 34). 

Carbenes or carbenoids have also been reported to deoxygenate epoxides. To generate these species, dimethyl diazomalonate/rhodium(II) acetate and 9-diazofluorene 44 have been employed both reagents show high stereoselectivity. For example, ciJ-2-butene oxide is converted to cir-alkene with more than 93% retention under irradiation (350 nm) using 9-diazofluorene, and functional groups, such as carbonyl, can survive using diazomalonate and rhodium(II) acetate (equation 49). 

Problem 28.9 The following reactions have all been found to yield a mixture of pinacol and pinacolone, and in the same proportions treatment of 3-amino-2,3-dimethyl-2-butanol with nitrous acid treatment of 3-chloro-2,3-dimethyl-2-butanol with aqueous silver ion and acid-catalyzed hydrolysis of the epoxide of 2,3-dimethyl-2-butene. What does this finding indicate about the mechanism of the pinacol rearrangement ... 

The products of the ozonizotion of 2-butene in acetic acid and of 2,3-dimethyl-2-butene in isopropyl alcohol are compared with known substances. The monomeric ozonides of methyl trimethylacrylate and of trimethylacrolein are described. Some unsymmetri-cally disubstituted ethylenes give epoxides instead of ozonides, when ozonized in inert solvents. 

C. Mukoid, S. Hawker, J. P. S. Badyal, R. M. Lambert, Molecular mechanism of alkene epoxidation A model study with 3,3-dimethyl-l-butene on Ag(lll), Catal. Lett. 4 (1990) 57. 

The Ti-Al-Beta catalyzed epoxidation of 2,3-dimethyl-2-butene 1 with H2O2 (30 wt% aqueous molar ratio 1 H2O2 = 2.4 1), via the epoxide 2 to pinacol 3 (Scheme 3), using different types of solvents, i.e. methyl-/er/-butylether (MTBE), acetone, r-BuOH, /-PrOH, diethyleneglycoldimethylether (diglyme) and 1,4-dioxane was studied in detail (Table 1). 

Then we changed over to the isomer allylic alcohol, to 3-methyl-2-buten-l-ol (prenol). Being a primary alcohol, it was smoothly epoxidized under both stoichiometric and catalytic Sharpless conditions. While the stoichiometric method provides only moderate yields as the dimethyl glycidol is fairly watersoluble, the catalytic method affords the double yield. The e.e. amounts to 90% in both cases. Optical purity and e.e. of the 3,3-dimethyl glycidol were determined by polarimetry and -NMR in the presence of chiral europium shift-reagent [22]. 

Evidence for epoxide formation from NO3 reactions with alkenes has been reported (Hjorth, Schindler). These results show that oxirane formation occurs via a radical adduct, in which rotation about the C-C bond can occur before elimination of NO2. Reactions of NO3 with isoprene and 2-butene at low pressure and at low O2 concentrations gave mainly oxiranes, whereas in air at atmospheric pressure, oxirane yields were negligible. However, even at atmospheric pressures, the reaction of NO3 with 2,3-dimethyl-2-butene gave an oxirane yield of around 20 %. Thus, it is apparent that, at least with some alkenes, oxirane formation may be important under tropospheric conditions. 

H. Skov, Th. Benter, R.N. Schindler, J. Hjorth, G. Restelli Epoxide formation in the reactions of the nitrate radical with 2,3-dimethyl-2-butene, cis- and rran5-2-butene and isoprene, Atmoj. Environ. 28A (1994) 1583. 

Epoxide formation in the reactions of nitrate radical with 2,3-2-dimethyl-2-butene, cis- and trans-2-butQn and isoprene,... 

Thus, epoxides (epoxyethane in the case of C2H4) are formed from the NOs-alkene adducts (Renter et al. 1994 Skov et al. 1994). The lifetime of the adduct is long enough to allow molecular rotation around C-C bond, and cis- and trans-epoxides are formed in the same ratio irrespective of starting with either cis- or trans-asymmetrical alkenes such as cis- and trans-2-butenes (Renter et al. 1994). The yields of epoxides are reported to be 0.50, 0.95, 0.20 for cis-, tran-2-butene. The yields of epoxides are 0.50, 0.95 and 0.20 for 2,3-dimethyl-2-butene, and isoprene, respectively (Skov et al. 1994). 

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