5-Methyl-l,4-hexadiene

Cyclopolymerization of Nonconjugated Dienes. Cyclopolymerization is an addition polymerization that leads to introduction of cyclic structures into the main chain of the polymer. Nonconjugated dienes are the most deeply studied monomers for cyclopolymerization and for cyclocopolymerizations with alkene monomers 66 In general, (substituted and unsubstituted) dienes with double bonds that are linked by less than two or more than four atoms cannot undergo efficient cyclization and result in crosslinked materials.12 In fact, efficient cyclopolymerization processes have been described, for instance, for a,oo-dienes like 1,5-hexadiene, 2-methyl-l,5-hexadiene, 1,6-heptadiene, and 1,7-octadiene,67 73 which lead to formation of homopolymers and copolymers containing methylene-1,3-cycloalkane units. 

Figure 3.50 Cyclopolymerisation of 2-methyl-l,5-hexadiene with metallocene-based catalysts...

Chain release by /3-CH3 transfer to the metal is unimolecular (Scheme 16)32,207,259 ancj obviously limited to the presence of propylene or other 2-methyl-substituted a-olefins, such as isobutene,260 and 2-methyl-l,5-hexadiene.261 No /3-alkyl transfer has been reported for higher alkyls, except for /3-trimethylsilyl transfer262 and cases in which a strained ring is formed.263-265 /3-Methyl transfer is an important and sometimes prevalent cause of molecular mass depression in the case of propylene polymerization with sterically hindered metallocenes262,266,267 or high polymerization temperatures combined with low propylene concentrations.268 Eisen reported this mechanism to be the... 

Cyclopolymerization of 2-methyl-l,5-hexadiene is catalyzed by a cationic zir-conocene complex [75]. Isolation of methylenecyclopentane derivatives 55-57 from the low molecular weight oligomeric products provides convincing evidence for chain transfer via P-methyl elimination. 

The competition of a triple bond and a double bond for the ketocarbenoid is poorly selective similar to the situation in copper-catalyzed reactions . Alternatively, the carbenoid derived from 2-bromoethyl diazoacetate and Rh2 OAc)4 (25 °C) or CU/CUSO4 (100 °C) reacted with 2-methyl-l,5-hexadien-3-yne at the double bonds exclusively The same holds true for the synthesis of bis(l-methylcyclopropyl)acetylene from 2,5-dimethy -l,5-hexadien-3-yne and diazomethane copper(II) bis (N-a-phenylethylsahcylaldiminate) has been recommended there as an efficient catalyst... 

If there is only enough electrophilic reagent to add to one of the double bonds, it will add preferentially to the more reactive double bond. For example, in the reaction of 2-methyl-l,5-hexadiene with HCl, addition of HCl to the double bond on the left forms a secondary carbocation, whereas addition of HCl to the double bond on the right forms a tertiary carbocation. Because the transition state leading to formation of a tertiary carbocation is more stable than that leading to a secondary carbocation, the tertiary carbocation is formed faster (Section 4.4). So in the presence of a limited amount of HCl, the major product of the reaction will be 5-chloro-5-methyl-l-hexene. 

See 2-Methyl-l 5-hexadiene. Methyldiallylcarbinol 4t-Methyl- 6-hepta-dienolA)... 

Schrock s molybdenum catalyst [Mo] 2, however, produced a low molecular weight polymer when exposed to 2-methyl-l,5-hexadiene [61]. Interestingly, it was shown that the monomer initially dimerized to 2,9-dimethyl-l,5,9-decatriene through metathesis of the unsubstituted vinyl group. Over time, however, the substituted vinyl groups underwent CM with the internal olefins to produce 1,4-polyisoprene. This was the first example of the condensation of... 

P-Carbon elimination of early transition metals has been applied to ring opening polymerization of methylenecyclopropanes [51] and methylenecyclobutenes [52]. Cyclopolymerization of 2-methyl-l,5-hexadienes [53] and isomerization of 1,4-dienes [54] also involve P-carbon elimination. 

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