2,3-Dimethy 1-2-butene

Because one might expect steric hindrance to be important, it is worth mentioning that the metathesis of alkenes branched at the double bond has been reported. Thus, isobutene gives (small) quantities of 2,3-dimethy 1-2-butene and ethene (16, 17) ... 

SAMPLE SOLUTION (a) Dehydration of 2,3-dimethyl-2-butanol can lead to either 2,3-dimethyl-1-butene by removal of a C-1 hydrogen or to 2,3-dimethy 1-2-butene by removal of a C-3 hydrogen. 

A mixture of three alkenes was obtained in 80% yield, having the composition shown. The alkene having the same carbon skeleton as the starting alcohol, 3,3-dimethyl-1-butene, constituted only 3% of the alkene mixture. The two alkenes present in greatest amount, 2,3-dimethy 1-2-butene and 2,3-dimethyl-1-butene, both have carbon skeletons different from that of the starting alcohol. 

Mechanistic investigations by Chapman and co-workers (99) indicated that these reactions occurred via a nonfluorescent singlet exciplex intermediate. While the rate constant for quenching of - -t5 by 2,3-dimethy 1-2-butene is slower than the rate of diffusion (Table 8), the limiting quantum yield for cycloaddition is 1.0. Thus, highly efficient exciplex cycloaddition may account for the absence of exciplex fluorescence, as in the case of t-1 photodimerization. Photochemical [2+2] cycloaddition reactions have also been observed to occur upon irradiation of the cyclic c-1 analogues diphenylcyclobutane (7) and diphenyl-vinylene carbonate (10) with 2,3-dimethyl-2-butene (96) however, the mechanistic aspects of these reactions have not been investigated. 

Oxidathedetuageefeyek openes. 1,3,3-Trimethylcyclopropene (1) is converted into l,l-diacetoxy-2,3-dimethy 1-2-butene (2) by oxidation with mercuric acetate in methylene chloride at room temperature. Reaction of (1) with thallium triacetate or... 

In the hope of preparing a more stable octasilacubane, we then synthesized thexyl-(l,l,2-tri-methylpropyl)-substituted octasilacubane, 2 [3b]. Because of the shorter length of Si-C than that of Si-Si, the thexyl group was expected to shield the cubane framework more effectively than silyl substituents without much sacrificing its reactivity. The procedure is shown in Scheme 2. Starting thexyltrichlorosilane was obtained by the reaction of trichlorosilanes with 2,3-dimethy 1-2-butene,... 

Thexylborane (ThxBH2, 1,1,2-trimethylpropylborane) is readily prepared by treating BHj THF or BH3 SMe2 in THF with 2,3-dimethy 1-2-butene in a 1 1 ratio. Although this monoalkylborane is crowded, it will hydroborate two additional alkenes provided they are not too hindered. 

Reactivities of various acceptors (values of hz relative to k- for 2,3-dimethy 1-2-butene), calculated by the method of Ingold and Shaw 18) (as discussed in the introduction) are assembled in Table VII. Values... 

The percentages shown were determined by analyzing the NMR of the tmns-2-pentene produced in this hydrogenation. The substrate 2,3-dimethyl-1,3-butadiene is hydrogenated under these conditions to a mixture containing 80% 2,3-dimethy 1-2-butene and 20% 2,3-dimethyl-1-butene. Note that because the hydrogenation carried out in micellar solution yields exclusively 2,3-dimethyl-l-butene (Table II), either of the possible hydrogenation products can be obtained by proper choice of reaction conditions. 

Hydroboration of representative olefins—such as 1-octene, 1-decene, styrene, o -methyl-styrene, 2-methyl-1-pentene, c/5 -4-methyl-2-pentene, 2-methy 1-2-butene, of-pinene, cyclohexene, 3-carene, 1-pheny 1-2-methyl-1-propene, 2,3-dimethy 1-2-butene and 1,2-dimethylcyclopentene—with dioxane-BH2Cl was carried out in dioxane and dichloromethane solvents. The procedure followed for all the olefins in both the solvents are same. The procedure followed for 1-decene in dichloromethane is representative. 

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