Butadiene-piperylene

Ahern and Gokel (1979) briefly mention that (jE -arenediazocyanides also react with a variety of dienes (cyclopentadiene, cyclohexadiene, butadiene, ( )-piperylene, etc.) in a [4+ 2]-cycloaddition reaction with formation of tetrahydropyridazines (Scheme 6-31). Here the two azo nitrogen atoms of the diazocyanide react as a dieneophile in a bis-aza Diels-Alder reaction. 

The isothiocyanate (21) reacted with dienes to give the phosphoranes (22) more rapidly than did the corresponding fluoride and chloride, but less rapidly than did the bromide. The rates of reactions of (21) with various dienes were in the order isoprene > butadiene > piperylene > chloroprene. These data support the previous suggestion that attack on the diene is an electrophilic process. 

The synthesis of transtactic structures is based on catalysts in which the transition metal belongs to the 3d block (Ti, Cr, V, Ni). Particular emphasis is devoted to the synthesis of trans butadiene/piperylene copolymers and to their blends with synthetic cis-l,4-polyisoprene, with the aim of increasing the "green strength" of the latter. 

Figure 15. Behavior under strain of an unvulcanized tire ply (conventional recipe) based on NR (natural rubber 100%), 1R (synthetic cis-7,4-polyisoprene 100%), BP/1R (a 50/50 blend of IR and txans-butadiene-piperylene copolymer).

Figure 16. Processibility and green strength of trans-butadiene-piperylene copolymers as a function of melting point and Mooney viscosity.

A number of other specific reactions have been studied. For example, Diels-Alder reactions of the unsaturated 5(4//)-oxazolone derived from piperonal with 2-ferf-butyldimethylsilyloxy-1,3-butadiene, piperylene, 1-acetoxy-1,3-butadiene, and Danishefsky s diene have been described. In these cases, the results are variable and are dependent on the diene with poor yields often obtained even at high temperatures. Moreover, the stereochemical outcome of these reactions has not been determined. " ... 

Addition of propargyl chlorides to l -dienes.1 The homogeneous catalyst zinc chloride-diethyl ether effects the addition of propargyl chlorides to acyclic 1,3-dienes at low temperatures. The products undergo cyclization at higher temperatures. An example is the addition of the propargyl chloride (1) to isoprene (equation I). Similar reactions are obtained on reaction of 1 with 1,3-butadiene, piperylene, and 2,3-dimethyl-1,3-butadiene. 

In fact, the cycloaddition of butadiene to ethylene, as well as cycloadditions of similar non-polar dienes to non-polar alkenes seem experimentally to be cases where concerted and stepwise (biradical or biradicaloid) mechanisms compete. We have recently discussed a number of cases, such as the dimerization of butadiene, piperylene, and chloroprene, the cycloadditions of butadiene or methylated dienes to halogenated alkenes, and others, where non-stereospecificity and competitive formation of [2 + 2] adducts indicate that mechanisms involving diradical intermediates compete with concerted mechanisms10). Alternatively, one could claim, with Firestone, that these reactions, both [4 + 2] and [2 + 2], involve diradical intermediates1 In our opinion, it is possible to believe that a concerted component can coexist with the diradical one , and that both mechanisms can occur in the very same vessel 1 ). Bartlett s experiments on diene-haloalkene cycloadditions have also been interpreted in this way12). 

Arbuzov and Kataev40 obtained selenophene and its methyl homologs from dienes (butadiene, piperylene, or hexadiene) and metallic selenium at 380°-420°C. 

A strain-crystallizing material like NR shows much better autohesion. It can be processed to a relatively low viscosity for easy wetting on contact, and still exhibit green strength due to strain-induced crystallization. Several other strain-crystallizable elastomers have been synthesized and shown to exhibit autohesion and green strength comparable or superior to that of NR. These include rran.s-polypen-tenamer, fran -butadiene-piperylene elastomers, and uranium-catalyzed polybutadiene. 

Through the years other monomers have been investigated. The diene commonly employed is 1,3-butadiene, although isoprene, 2-ethyl butadiene, 2,3-dimethyl butadiene, piperylene, and other substituted dienes have been investigated. The nitrile commonly employed is acrylonitrile. It has been reported that when part of the acrylonitrile is replaced by methacrylo-nitrile or ethacrylonitrile, the cement-making properties of the rubber are improved. Small proportions of a third monomer may also be used in conjunction with the two principal components. Hycar 1072, which employs methacrylic acid as the third monomer, is occasionally used in adhesive applications. Other monomers including ethyl acrylate, methyl methacrylate, styrene, vinylidene chloride, acrylic acid, N-vinyl-2-pyrrolidone, and vinyl acetate have been employed in varying amounts to adjust the adhesive and elastomeric properties. 

G-5—G-9 Aromatic Modified Aliphatic Petroleum Resins. Compatibihty with base polymers is an essential aspect of hydrocarbon resins in whatever appHcation they are used. As an example, piperylene—2-methyl-2-butene based resins are substantially inadequate in enhancing the tack of 1,3-butadiene—styrene based random and block copolymers in pressure sensitive adhesive appHcations. The copolymerization of a-methylstyrene with piperylenes effectively enhances the tack properties of styrene—butadiene copolymers and styrene—isoprene copolymers in adhesive appHcations (40,41). Introduction of aromaticity into hydrocarbon resins serves to increase the solubiHty parameter of resins, resulting in improved compatibiHty with base polymers. However, the nature of the aromatic monomer also serves as a handle for molecular weight and softening point control. 

Conjugated dienes Butadiene 1,3-cyclohexadiene Piperylene Phenylbutadienes... 

Strong effects of the catalyst on the regioselectivity have been observed in the cycloadditions of a variety of heterocyclic dienophiles. Some results of the BF3-catalyzed reactions of quinoline-5,8-dione (21) and isoquinoline-5,8-dione (22) with isoprene (2) and (E)-piperylene (3) [25], and of the cycloadditions of 4-quinolones (23a, 23b) as well as 4-benzothiopyranone (23c) with 2-piperidino-butadienes, are reported [26] in Scheme 3.8 and Equation 3.2. The most marked... 

An example of stereocontrol by high pressure is given by the regio- and diastereoselective synthesis of hydrophenanthrenones [18] which are useful intermediates for synthesizing diterpenes and steroids, by EtAlCli-catalyzed cycloadditions of heteroannular bicyclic dienone 50 with (E)-piperylene (24) and 2,3-dimethyl-1,3-butadiene (51) (Scheme 5.4). 

The explanations for the relative rates of reaction have been based on three factors (1) The rate of reaction increases as the electron density in the diene system increases thus isoprene reacts faster than butadiene and a complex electron-rich 2-silylmethylbutadiene reacts even faster. (2) The rate of reaction increases as the steric hindrance due to the diene substituents decreases thus frans-piperylene reacts more slowly than dimethylbu-tadiene or isoprene. (3) A decrease in the equilibrium concentration of the cisoid conformer results in a slower reaction rate thus cw-piperylene or cis/trans-2,4-hexadiene react more slowly than /rans-piperylene or transltrans-2,4-hexadiene, respectively.175177... 

Isoprene and piperylene undergo photochemical cross-addition to olefins to yield products similar to those observed for butadiene<27) ... 

Figure 13. Melting points of lTans-poIy(butadiene co-piperylene) as a function of composition. Data from Ref. 30.

Copper-catalyzed monoaddition of hydrogen cyanide to conjugated alkenes proceeded very conveniently with 1,3-butadiene, but not with its methyl-substituted derivatives. The most efficient catalytic system consisted of cupric bromide associated to trichloroacetic acid, in acetonitrile at 79 °C. Under these conditions, 1,3-butadiene was converted mainly to (Z )-l-cyano-2-butene, in 68% yield. A few percents of (Z)-l-cyano-2-butene and 3-cyano-1-butene (3% and 4%, respectively) were also observed. Polymerization of the olefinic products was almost absent. The very high regioselectivity in favor of 1,4-addition of hydrogen cyanide contrasted markedly with the very low regioselectivity of acetic acid addition (vide supra). Methyl substituents on 1,3-butadiene decreased significantly the efficiency of the reaction. With isoprene and piperylene, the mononitrile yields were reduced... 

Depending on the trapping reagents, various reactions have been observed an ene reaction between propene, isobutene, and 2231 or 27,34 a [2 + 4] cycloaddition between butadiene and 12,21 22,31 and 27,34 or both an ene reaction and a [2 + 4] cycloaddition between 2,3-dimethylbutadiene and 2231 or 27,34 and between piperylene or hexadiene and 22.31 Some of these reactions are summarized in Scheme 8. By contrast, 27 does not react with the C = C double bond of an alkene such as CH2 = CH-OMe.34... 

Butadiene, isoprene, piperylene, chloroprene, or 2,3-dimethyl-1,3-butadiene with HSiCI3, HSiMeCl2, HSiEtCI2, or HSi(OEt)3 108... 

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