Cyclic nonconjugated diene

The tandem reaction of allyl electrophiles with alkynes and MejAl or Mc2Zn occurs in the presence of Ni(acac)2 to give a regioisomeric mixture of the three-component coupling products [234]. The reaction can also proceed intramolecu-larly to give cyclic nonconjugated dienes. 

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. 

The ionic chain polymerization of unsaturated linkages is considered in this chapter, primarily the polymerization of the carbon-carbon double bond by cationic and anionic initiators (Secs. 5-2 and 5-3). The last part of the chapter considers the polymerization of other unsaturated linkages. Polymerizations initiated by coordination and metal oxide initiators are usually also ionic in nature. These are called coordination polymerizations and are considered separately in Chap. 8. Ionic polymerizations of cyclic monomers is discussed in Chap. 7. The polymerization of conjugated dienes is considered in Chap. 8. Cyclopolymerization of nonconjugated dienes is discussed in Chap. 6. 

Epoxidation of various acyclic and cyclic perfluorinated dienes is accomplished with an aqueous hypohalogenitc and acetonitrile as a cosolvent. The reactivity of a C = C bond toward this reagent is enhanced by the presence of the trifluoromethyl group. This activating effect is nicely illustrated by perfluoro(l-methylcyclohexa-l,4-diene), which reacts smoothly with sodium hypochlorite to give a diepoxide 11 in 58% yield,73 while the oxidation system failed for perfluorocyclohexadienes. Nonconjugated perfluorocyclohepta-1,4-diene (12) is oxidized to the corresponding diepoxide 13 by sodium hypobromite.74... 

The reaction of nonconjugated dienes such as 1,4-pentadiene and 1,5-hexadiene yields cyclopentanone derivatives, while 1,6-heptadiene gives only traces of ketone (equation 47). -2 80 The yields in these reactions are low, 1,4-pentadiene giving only 10% of cyclic ketone product. 

The fully delocalized n electron system of the benzene ring remains intact during electrophilic aromatic substitution reactions. However, in the Birch reduction, this is not the case. In the Birch reduction, benzene, in the presence of sodium metal in liquid ammonia and methyl alcohol, produces a nonconjugated diene system. This reaction provides a convenient method for making a wide variety of useful cyclic dienes. 

When nonconjugated dienes react with carbon monoxide and water in the presence of dicobalt octacarbonyl, saturated and unsaturated cyclic ketones are produced (55, 77). This appears to be due to the formation of unsaturated acylcobalt carbonyls followed by cyclization, as discussed in Section II, B,3. 

Hydroboration of acyclic, symmetrical, nonconjugated dienes with one equiv. of 9-BBN-H produces almost statistical mixtures of mono- and di-hydroborated species, but cyclic analogs may show substantial deviations from the statistical mixture. For example, monohydroboration of 1,5-cyclooctadiene occurs to the extent of 85% using 1 1 stoichiometry (equation 31), ° whereas disiamylborane gives predominantly dihydroboration product under such conditions. 

In the epoxidation of olefins not bearing a complexing group, there is not a great difference in stereoselectivity in comparison with the peracids. The c/s-oxirane is formed from cis-butene-2 and the trans-oxirane from trans-butene-2. Due to steric hindrance, regioselectivity may be observed for nonconjugated dienes. °° ° In terpenes, the attack takes place from the less hindered side. Double bonds in bridged cyclic systems have an effect on the reaction rate. ... 

Some nonconjugated dienes are converted to cyclic ketoesters. 5-Aiyl-1,2,4-oxadiazoles are formed in the carbonylation of aryl halides when RC(=NOH)NH2 are present. 

The copolymerization of ethylene with nonconjugated dienes is of significant interest due to its applicability to ethylene-propylene-diene rubber (EPDM) [84]. The cyclic dienes such as 1,3-cyclopentadiene, dicyclopen-tadiene, and vinylcyclohexane copolymerize with ethylene catalyzed by rac-Et(Ind)2ZrCl2/MAO (Eq. 16) [85]. 

Coordination polymerization of dienes has progressed significantly within the last decade. Selective polymerization of 1,3-dienes is reinforced by conventional transition metal catalysts and by new organolanthanide catalysts. Nonconjugated dienes also polymerize selectively to produce polymers with cyclic units or vinyl pendant groups. Living polymerization of dienes has become common, which enabled preparation of block copolymers of dienes with alkenes and other monomers. Another new topic in this field is the polymerization of allenes and methylenecycloalkanes catalyzed by late transition metal complexes. These reactive dienes and derivatives provide polymers with novel structure as well as functionalized polymers. The precision polymerization of 1,2-, 1,3-, and l,n-dienes, achieved in recent years, will be developed to construct new polymer materials with olefin functionality. 

The most recent application of olefin metathesis to the synthesis of polyenes has been described by Tao and Wagener [105,117], They use a molybdenum alkylidene catalyst to carry out acyclic diene metathesis (ADMET) (Fig. 10-20) on either 2,4-hexadiene or 2,4,6-octatriene. The Wagener group had earlier demonstrated that, for a number of nonconjugated dienes [118-120], these polymerizations can be driven to high polymer by removal of the volatile product (e. g., 2-butene). To date, insolubility limits the extent of polymerization of unsaturated monomers to polyenes containing 10 to 20 double bonds. However, this route has some potential for the synthesis of new substituted polyacetylenes. Since most of the monomer unit is preformed before polymerization, it is possible that substitution patterns which cannot be incorporated into an alkyne or a cyclic olefin can be built into an ADMET monomer. 

As one might expect, dialdehydes can be polymerized to yield polymers with cyclic ether linkages. This resembles polymerizations of nonconjugated dienes ... 

Examples of intra intermolecular polymerizations are cyclic polymerizations of nonconjugated dienes. This can resemble cyclopolymerization by free-radical mechanism ... 

Cyclopolymerization. As discussed earlier, nonconjugated dienes can be polymerized with metallocene-based catalysts to afford cyclopol5miers. In contrast to linear polyolefins which have only two microstructures of maximum order (isotactic and syndiotactic), cyclic polymers have four microstructures due to the possibility of configurational isomerism (cis vs trans) in the main chain (Fig. 16). Of these the frares-diisotactic structure contains no mirror planes of S5unmetry and is chiral by virtue of its main-chain stereochemistry (481). Two criteria for chirality of this microstructure are the presence of trans rings and isotacticity (the same... 

Copolymerizations of ethylene and/or propylene with nonconjugated dienes using various metallocene catalysts are a useful method to synthesize polyolefins with cyclic backbones. 

Polyolefins with cyclic units in the backbone show high TgS and high transparencies, and thus are suitable for optical and medical applications." " Even though they can be prepared by the copolymerization of ethylene and cyclic olefins (such as norbomene) using metallocene catalysts, the cyclopolymerization of nonconjugated dienes offers another access route into cyclopolymer materials. 

Nonconjugated dienes could have double bonds in which one is more reactive than the other [450-453] (e.g., 1,4-hexadiene and 5,7-dimethyl-1,6-octadiene). In this case only the reactive double bond is polymerized to give linear polymer chains. There are nearly no cyclic rings in the polymer. The situation is different if both double bonds have similar reactivities (e.g., 1,5-hexadiene and 1,6-heptadiene) [454-461]. In this case polymers with a high proportion of cyclic units are found ... 

At a polymerization temperature of 22 °C, approximately 80% of the cyclopentane rings in the polymer are trans. Table 23 shows some other examples of the polymerization of nonconjugated dienes to cyclic units [320]. 

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