3.4- Dimethyl-l,5-hexadiene

The reaction of thioacetyl cations with 2,5-dimethyl-l,5-hexadiene under low-pressure conditions in an FT-ICR mass spectrometer leads to elimination of propene. At variance from the [4 + 2+] polar cycloadditions observed under high-pressure conditions in the QqQqQ instrument, Caserio and coworkers220 invoked electrophilic attack of the CE CS"1"... 

On the other hand 2,5-dimethyl-l,5-hexadiene can be converted to dimethylhexanes, ( v50% selectivity), and cyclic alkanes when reacted with a good hydride donor in concentrated H2SO4 indicating that multiple protonation and hydride transfer occurs faster than the rearrangement to trimethylpentane. 

The first example of the rearrangement of a cyclopropyl radical to an allyl radical in solution was observed in the thermal decomposition of l-methyl-2,2-diphenylcyclo-propanecarbonyl peroxide The radical reacted by abstracting hydrogen from solvent or by rearranging to the l,l-diphenyl-2-methylpropenyl radical which dimerized to yield l,l,6,6-tetraphenyl-2,5-dimethyl-l,5-hexadiene (89). The proportion of dimeric product to that of cyclopropane is dependent on the solvent. If a good radical scavenger is used, such as chloroform, carbon tetrachloride or thiophenol, then only the unrearranged cyclopropane derivative is obtained. This is also the case when a radical trap such as iodine is added to a benzene solution. 

Vapor pressure osmometry in chloroform. Dlolefine = 2,5-dimethyl-l,5-hexadiene. DiolefinG = 2,4-dimethyl-l, 4-pentadiene. 

With 2,5-dimethyl-l,5-hexadiene this reaction occurs quantitatively to give thermally stable organoaluminum compounds with a quaternary /3-carbon atom (139) ... 

Before the modern era of organotransition metal reactivity, it was observed that nickel carbonyl reacted with 2-methallyl chloride in methanol to give methyl 3-methyl-3-butenoate and 2,5-dimethyl-l,5-hexadiene as a by-product. In THF at 25 °C, the diene was the exclusive product. This mild formation of a carbon-carbon bond, and the interest in the synthesis of terpene-based natural products led to efforts to test the scope and limitations of the process. An obvious pathway involves stepwise oxidative addition of each allyl unit followed by Reductive Elimination. As discussed below, the key intermediates (left vague in Scheme 48) are likely to involve Ni -NP couples. 

Dimethyl-l,5-hexadiene reacts with H2B2(C2Hs)4 in the cold to form a 1 1 mixture of the cis and tram isomers of B-ethyl-3,6-dimethyl-boracycloheptane (XII, XIII) (25). 

As indicated earlier, one of the diene double bonds can be substituted by a triple bond. The resulting cyclic product then has an additional double bond. When these new bonds are conjugated with other olefinic linkages, a further adduct is formed. Thus, 2,5-dimethyl-l,5-hexadiene-3-yne 23 reacts with 2 moles of MA to give product 24. ... 

Dimethyl-l,5-Hexadiene (cont) 100 50 >30 6 Resistant -0.3-2 85-115 Solef Solvay Polymers Specimen Solef 1008, 1010 and 1012, 2 mm thick test pieces... 

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