T-butylethylene

Twenty years later, by studying the chlorination of cis- and trans-di-t-butylethylenes, Fahey (1966) showed that halogen bridging is a general rule. It is expected that, owing to steric repulsions between the two branched groups, the cis-alkene would prefer to react via an open / -chlorocarbocation [14] where free rotation can occur rather than via a chloronium ion [15]. 

Fig. 14 Typical log k/YBr plots for assisted and unassisted alkene brominations. Allylbenzene and 1-pentene, less crowded than cis-methyl-t-butylethylene and methylideneadamantane, exhibit the smallest m-values. The points corresponding to acetic acid (O) and trifluoroethanol (A), two weakly nucleophilic solvents, are below the regression line for water, methanol, ethanol and their aqueous mixtures ( ) of similar nucleophilicity. In contrast, they are on the line for the branched alkenes where steric crowding inhibits nucleophilic assistance by alcoholic solvents (Ruasse et al, 1991, Ruasse and Motallebi, 1991).

For a long time, it was considered that the formation of a bromonium ion from olefin and bromine is irreversible, i.e. the product-forming step, a cation-anion reaction, is very fast compared with the preceding ionization step. There was no means of checking this assumption since the usual methods—kinetic effects of salts with common and non-common ions—used in reversible carbocation-forming heterolysis (Raber et al., 1974) could not be applied in bromination, where the presence of bromide ions leads to a reacting species, the electrophilic tribromide ion. Unusual bromide ion effects in the bromination of tri-t-butylethylene (Dubois and Loizos, 1972) and a-acetoxycholestene (Calvet et al, 1983) have been interpreted in terms of return, but cannot be considered as conclusive. 

Ta(CHCMe3)(0CMe3)2(PMe3)Cl reacts with ethylene, styrene, or 1-butene to give largely t-butylethylene (equation 3). 

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. 

I. Conversion of t-Butylethylene, unsym.-Methylisopropylcthylcnc, and Tetramethylethylene to Equilibrium Mixtures of the Three Olefins. J. Amer. chem. Soc. 56, 1395 (1934). 

A related dehydrogenation of primary and secondary alcohols to the corresponding aldehydes/ketones has been achieved using the dihydride iridium compound [IrH2(C6H3-2,6 CH2P-t-Bu2 2)j as the precursor s catalyst and t-butylethylene as hydrogen acceptor (Eq. 13). The reactions are carried out at 200 °C with a 99% yield in 18 h (alcohol/Rh = 10/1) [55]. 

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]. 

Frequently, steric effects also play an important role in determining the orientation of the azido function t-butylethylene (73) leads to vinyl azide (74) rather than the azide (75) expected from electronic considerations. 

A similar mechanism was recently suggested for the hydrochlorination of styrene and t-butylethylene by Fahey and McPherson (1969). The proposed mechanistic scheme appears reasonable in a weakly dissociating solvent, such as acetic acid, although it seems somewhat surprising that the product distribution and the stereochemistry are insensitive to addition of diluents such as formic acid up to 1 1m. 

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). 

Cis- and ra 5-di-/-butylthiiranium tetrafluoroborates (14) and (15) were generated from cis- and tra 5-di-t-butylethylene, respectively (Scheme 7), on reaction with methyl-bis(methylthio)sulfonium tetrafluoroborate in liquid SO2 at —78 °C. Their reaction with water was studied and different reaction modes were found. ... 

The use of preformed boron hydrides is advantageous. Thus, treatment of 1,2-di-t-butylethylene with 0.5 equiv. B2H6 followed by heating the mixture for 20 h at 160-165°C gives IV ... 

Neutralization processes of ions in the radiolysis of ethane or ethylene with SFg have been shown to lead to the formation of the SF5 radical. Compounds of the type RSF5 are formed as a result of the recombination reactions with hydrocarbon radicals. A kinetic e.s.r. study of the self-reaction of SF5, and a spectroscopic and kinetic e.s.r. study of its reaction with 1,1-di-t-butylethylene, have been reported. The radical undergoes self-reaction by a second-order process and adds to 1,1-di-t-butylethylene to give BU2CCH2SF5, which decomposes by a first-order process. 

The alkoxo-neopentylidene complex, Ta(CHCMe3)(OCMc3)2Cl(PMe3), reacts with ethylene to give t-butylethylene and propylene ... 

In the cleavage of olefins by ozone the first product is an unstable primary ozonide, as was proved experimentally by Criegee and Schroder19 for ionization of frprimary ozonide decomposes exothermally to an aldehyde or ketone and a peroxidic zwitterion. It is only by reunion of the two fragments that the ozonides are formed (see various reviews20,21) ... 

---