T-Butylethylene oxide

It seems likely that the observed differences in crystalline properties between the optically active and racemic PEL polymers clearly indicates that the crystalline regions in the latter are not simply formed from physically-separated blocks of R units and S units. Nevertheless, such block arrangements of chiral units could still be present in the polymer and form a different type of crystal lattice than the separate R or S polymers as was found in the crystal structure determination of isotactic, racemic poly(t-butylethylene oxide)(4). 

The Importance of this particular chelation is supported by the observations that -methoxy and -methyl groups increase the yield of crystalline isotactic polymer, while -chloro or 2,6-dimethyl groups decrease the isotactic fraction (14). The general importance of the chelation in establishing stereochemistry is supported by the observations that addition of dicyclohexyl 18-crown-6 ether in an amount equivalent to catalyst, or of solvents coordinating strongly with K., such as dimethyl-sulfoxide or hexamethylphosphortriamide (HMPT), markedly decrease the crystalline polymer from either t-butylethylene oxide or phenyl glycidyl ether (14),... 

Limited examples of nontransannular C-H insertions occurring in metalated epoxides exist. Treatment of trons-di-tert-butylethylene oxide 56 with t-BuLi predominantly gave the diastereomeric alcohols 58 and 59 (Scheme 5.13) [27]. Mioskowski... 

Di-t-butylethylene [5] has one unique property in comparison with other spin traps, in that it cannot be excited under normal photolysis conditions (Amax = 185 nm). Imidyl-[5] are formed by UV photolysis of ImX-[5] solutions, and it is obvious that the mechanism must involve excitation of ImX to ImX around 205 nm, followed by either homolytic cleavage of the excited state or oxidation of [5] (Table 3) [E°(ImX /ImX ) is estimated to be very high, 6 V] to give [5] + and create conditions for inverted spin trapping. 

A plausible mechanism involves the reaction of the dihydride precursor with t-butylethylene to the 14-e complex [Ir(C6H3-2,6 CH2P-f-Bu2 2)]> which undergoes the oxidative-addition reaction of the alcohol to afford a hydride alkoxide complex. Further /i-hydride ehmination gives the alde-hyde/ketone and regenerates the dihydride active species [55]. In the particular case of 2,5-hexanediol as the substrate, the product is the cycHc ketone 3-methyl-2-cyclopenten-l-one. The formation of this ketone involves the oxidation of both OH groups to 2,5-hexanedione followed by an internal aldol reaction and further oxidation as in the final step of a Robinson annotation reaction [56]. 

These isomerizations, rearrangements, and cleavages are best explained by a carbonium-ion mechanism. Vapor-phase dehydration of alcohols over aluminum oxide greatly reduces the tendency for isomerization and rearrangement. The alcohol vapors are passed over the catalyst at 300-420°. In this manner, pure 1-butene is prepared from re-butyl alcohol and t-butylethylene is obtained from methyl-/-butylcatbinol (54%). The relative rates of dehydration of the simpler alcohols over alumina have been studied. The main side reaction is dehydration to ethers (method 118). 

Tsuruta, T. Hasebe, Y. Stereocontrol mechanism of an organozineeomplex having ehain-type structure in the polymerization of ferf-butylethylene oxide comparison with propylene oxide. Macromol. Chem. Phys. 1994,195, 427-438. 

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