2.5- Dimethylhexa-2,4-diene, reaction

However, side reactions due to rearrangements are often observed. Thus, defluorination of perfluoro(3,4-dimethylhex-3-ene) gives perfluoro(3,4-dimethylhexa-2,4-diene) and its cyclobutene isomer.119,120 The latter is formed by an eleetrocyclic reaction. 

The reaction of perfluoro-3,4-dimethylhexa-2,4-diene with calcium hypochlorite leads to the formation of a diepoxide, rearranging at 200 °C into the corresponding derivative of 1,4-dioxane (96RCI703). 

NaBH4 (20 mmol), 2,5-dimethylhexa-2,4-diene (50 mmol) and 20 ml diglyme were mixed, cooled in an ice bath, methylsulfate (20 mmol) added, and the reaction stirred 3 hours. The resulting product suspension was used directly without purification. 

Previously we have shown that nido-2,3,5-tricarbahexaboranes(7) are formed by hydroboration reactions of l,3-dihydro-l,3-diborafulvenes 1 and of 4,5-diisopropylidene-1,3-diborolenes 3, obtained by ring-closure of cis-diborylethenes with (Me3Sn)2C=CMe2 and of 3,4-dilithio-2,5-dimethylhexa-2,4-diene-diid with diborylmethane derivatives1,2. The stability of the 2,3,5-tricarbahexaboranes 2 depends on the substituents in the basal positions of the carboranes. 

Some Diels-Alder reactions have only modest rate responses to changes in solvent,and when contrasted with a [2 + 2] addition exhibiting a strong dependence on solvent polarity, a neat mechanistic demarcation may be drawn distinctions between concerted versus nonconcerted reactions, and between early and late transition states, may be advanced. The large solvent effect in the [2 + 2] addition may be ascribed to solvent stabilization of a zwitterionic intermediate. However, when similar reactants, one set giving Diels-Alder product, the other [2 + 2] product, are examined for solvent effects on reaction rates, the dependencies may be virtually identical. A case in point is provided by the reactions of TCNE with 9,10-dimethylanthracene (Diels-Alder reaction) and with 2,5-dimethylhexa-2,4-diene ([2 + 2] cycloaddition). 

The Simmons-Smith reaction seems to be of little value for transfer of an alkoxycarbonyl-carbene to alkenes. Thus, reaction of the reagent formed from ethyl diiodoacetate and zinc-copper couple with 2,5-dimethylhexa-2,4-diene (reflux, 14 days) furnished ethyl 2,2-dimethyl-3-(2-methylprop-l-enyl)cyclopropane-l-carboxylatein only 12% yield, and ethyl dichloroacetate was an even less suitable starting material. ... 

With the ruthenium(I) catalyst [(OC)4Ru2(OAc)2]n (see Section 1.2.1.2.4.2.6.3.1.), cis selectivity was observed in cyclopropanation of trisubstituted alkenes (e.g. 2-methylbut-2-ene, 2,5-dimethylhexa-2,4-diene) with methyl diazoacetate. Furthermore, the interplay between steric, electronic, and lipophilic interactions can occasionally result in enhanced cis selectivity for an individual reaction. Notably, certain homoallyl chlorides were consistently cyclo-propanated by diazoacetates with pronounced cis selectivity in the product cyclopropanes 4 with various catalysts. 

Yang has shown that the initial concentration of the arene has a large effect on product ratios ([4 + 4] versus [4 + 2]) in the reaction of 9,10-difluoro-anthracene with 2,5-dimethylhexa-2,4-diene, and this effect is also found with anthracene (61) and cyclohexa-1,3-diene, which [like 9-phenylanthracene (59) and cyclohexa-1,3-diene] gives a minor product involving [2 - - 2]addition to a... 

Since then, a whole host of catalysts have been pubhshed, e.g. by Masamune, Kanemasa, Scott and Itagaki, for the enantioselective [2+l]-cycloadddition, but only a few give good yields for the reaction of 2,5-dimethylhexa-2,4-diene and the readily available t-butyl diazoacetate. [76] In the meantime, systematic optimisation work at Sumitomo has made highly active catalysts available, not only of the copper-salicylaldimine type, but also with bisoxazohne ligands, which enable excellent yields and selectivities. 

The alkoxy ir -allylic derivatives underwent alkoxyl exchange very readily when treated with the appropriate alcohol containing a little mineral acid (10" M)(e.g. methoxy-ethoxy and vice versa). These reactions are believed to go via an intermediate carbonium ion stabilised by the delocalised electron system of the tt-allylic group. Methoxy tt-allylic complexes derived from 2,5-dimethylhexa-2,4-diene, cyclohepta-1,3-diene and cycloocta-1,3-diene on heating lost methanol irreversibly to give a8-unsaturated tr-allylic complexes e.g. cyclohepta-1,3-diene first gave a tt-methoxycycloheptenyl and then a TT -cycloheptadienyl complex. 

Cycloocta-1,3-diene merely rearranges to the 1,5-isomer, norbornadiene is polymerised, and no reaction occurs with 2,5-dimethylhexa-2,4-diene. Disubstituted alkenes, RCH=CHR, afford isomerised terminal 1 1 adducts. Similarly, terminal alkenes RCH CH2 gave RCH2CH2SiX2 (X = Ph, OEt) or a mixture of... 

This mechanism has been disputed. There was no reaction with butadiene itself, although ARs were formed when NO was added. However, a variety of substituted butadienes did react with pure NO. Dilute solutions of 2,3-dimethylbuta-l,3-diene in inert solvents reacted very rapidly to give ARs having a quintet of triplets in the ESR spectrum indicative of four equivalent protons = 1.42 mT = 0.95 mT. In 2,5-dimethylhexa-2,4-diene, ARs have the typical value of isotropic HFI constant... 

Some investigations have been done on the reaction of several dienes with NO [70, 71]. In these experiments, a solution of NO in an organic solvent was added slowly to a stirred solution of the organic substrate in the same solvent at room temperature. The products obtained from conjugated 2,5-dimethylhexa-2,4-diene are shown in the scheme ... 

Ring synthesis by radical-radical coupling, as well as intramolecular radical substitution, is an alternative method for producing rings, which does not rely on the addition of a radical to an unsaturated bond. Cyclopropanes have been prepared from diiodides by the reaction of a catalytic amount of a fluorinated tin hydride with NaCNBHs in a fluorinated-organie solvent mixture. The rate constant for the reaction was determined using PhsSiH as a chain carrier and found to be 5 x 10 at 80 °C (Scheme 18). The cyclization of 2,2-diethylpropane-1,3-thiol and 4,4-diethyl-1,2-dithiolane in the presence of 2,5-dimethylhexa-2,4-diene and AIBN has been shown to proceed via a radical-chain mechanism (Scheme 19). ... 

Chambers RD, Gray WK, Mullins SJ, Kom SR (1997) Reactions involving fluoride ion. Part 42 Heterocyclic compounds from perfluoro-3,4-dimethylhexa-2,4-diene. J Chem Soc Perkin... 

A similar reaction of 3-trimethylsilyloxy-3,5-dimethylhexa-1,5-diene afforded 5-methylhex-5-en-2-one (eq 191). ... 

The formation of dodecamethyl[6]radialene (72) by a Ni(0)-mediated [2+2+2] cycloaddition of 2,5-dimethylbuta-2,3,4-triene (70) has already been mentioned (see Section 4.2.2). Much better yields could be obtained, when 3,4-dibromo(or diiodo)-2,5-dimethylhexa-2,4-diene was exposed to a Ni(0) complex. Here, the [3]cumulene 70 is a likely reaction intermediate, and the product distribution ([4]radialene 71, [6]radialene 72, and its isomer 73 see Scheme 4.14) depends strongly on the solvent, with donor solvents favoring the formation of 72. With DMF as the solvent and in s/fw-generated Ni(PPh3)4 as a mediator, a yield of 63 and 50% could be achieved for 72 from the dibromo- and the diiododiene, respectively [65, 66]. 

The preference for the four-centre transition state (Fig. 6.3(a)) was deduced by Doering and Roth (1963) by their classical work on the dimethylhexa-1,5-dienes. The thermolysis (225°) of fliejo-3,4-dimethylhexa-l,5-diene yielded cij,t/i Zf7i -octa-2,4-diene, whereas with ( ) 3,4-dimethylhexa-l, 5-diene the rearrangement products obtained at 180° were the transjrans- and cis.cis-octa-2,4-dienes (ratio (9 1). Both processes were highly stereospecific for example, only about 0-3 per cent of the rra/i, fra/ts-octa-2,4-diene was detected in the reaction of the meso-compound, The reaction pathways are illustrated in Equation (6.103). 

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