1.3- butadiene/higher dienes

Amine telomers are obtained from butadiene and secondary amines with nickel or palladium catalysts3. Highly regioselective (end on) and stereoselective E telomerization of butadiene and diethylamine to form ( )-A .A-diethyI-2,7-octadienamine (1) is achieved if the reaction is catalyzed by paIIadium(II) acetate, triphenylphosphane and triethylaluminum with an optimum Pd/P/Al ratio of 1 1 2X 3. While increasing the amount of triethylaluminum favors a high E/Z ratio, higher diene concentration leads to lower EiZ ratios and formation of higher telomers (C16). 

While the intermolecular reactions of butadiene and related methyl or simple alkyl-substituted dienes have been investigated extensively, relatively few examples of the Pd-catalyzed linear dimerization of higher dienes have been reported. Brun and co-work-ers in an isolated paper reported that, under palladium catalysis, reaction of methyl 2,4-pentadienoate (Scheme 9, 28) affords the linear dimer 29 in high yield (95%). Two aspects of this reaction are of particular interest, (i) The dimerization yields essentially only the tail-to-tail dimer 29, not the head-to-tail or head-to-head isomers (30 or 31, respectively). This is in contrast to the behavior of alkyl-substituted dienes under similar conditions vide infra), (ii) Although no details are given, the authors imply that 29 is... 

In order to make these oxidative reactions of 1,3-dienes catalytic, several reoxidants are used. In general, a stoichiometric amount of benzoquinone is used. Furthermore, Fe-phthalocyanine complex or Co-salen complex is used to reoxidize hydroquinone to benzoquinone. Also, it was found that the reaction is faster and stereoselectivity is higher when (phenylsulflnyl)benzoquinone (383) is used owing to coordination of the sulfinyl group to Pd, Thus the reaction can be carried out using catalytic amounts of PdfOAcji and (arylsulfinyl)benzoquinone in the presence of the Fe or Co complex under an oxygen atmosphere[320]. Oxidative dicyanation of butadiene takes place to give l,4-dicyano-2-butene(384) (40%) and l,2-dicyano-3-butene (385)[32l]. 

Chiral BOX-zinc(II) complexes can also catalyze the cycloaddition reaction of glyoxylates with, e.g., 2,3-dimethyl-l,3-butadiene and 1,3-cyclohexadiene [36]. The reaction gave for the former diene a higher cycloaddition product/ene product ratio compared with the corresponding chiral copper(II) complexes the ee, however, was slightly reduced. For the reaction of 1,3-cyclohexadiene slightly lower yield and ee were also found. 

Electrophilic addition to a conjugated diene at or below Toom temperature normally leads to a mixture of products in which the 1,2 adduct predominates over the 1,4 adduct. When the same reaction is carried out at higher temperatures, though, the product ratio often changes and the 1,4 adduct predominates. For example, addition of HBr to 1,3-butadiene at 0°C yields a 71 29 mixture of 1,2 and 1,4 adducts, but the same reaction carried out at 40 °C yields a 15 85 mixture. Furthermore, when the product mixture formed at 0 °C is heated to 40 °C in the presence of HBr, the ratio of adducts slowly changes from 71 29 to 15 85. Why ... 

Butadiene and isoprene give rise to mixtures of what are usually called telom-ers, namely 1 1 telomers between the amine and the 1,3-diene (trae hydroamination products), 1 2 telomers and even higher homologs together with oligomers of the diene as exemplified in Eq. (4.41). 

The conjugated diene (including the trans-trans, trans-cis, and cis-cis isomers) can further add ethylene to form Cg olefins or even higher olefins (/). The mechanism of isomerization is proposed to be analogous to butene isomerization reactions (4, 8), i.e., 1-butene to 2-butene, which involves hydrogen shifts via the metal hydride mechanism. A plot of the rate of formation of 2,4-hexadiene vs. butadiene conversion is shown in Fig. 2. 

Ionizing radiation leads also to formation of excited molecules in the triplet state. Okazaki and coworkers74 calculated the yield of the triplets and found that the yields for conjugated dienes are significantly higher than those of monoalkenes. The yield for 1,3-butadiene is 2.66, whereas the values for 1-butene, 2-butene and 2-methylpropene are 1.51, 1.55 and 1.54, respectively. 

From their crystal structures, (l,3-diene)CrL4 complexes46 are found to be approximately octahedral coordinate. The low temperature (—90 °C) 13C NMR spectrum of (butadiene)Cr(CO)4, which consists of 3 M-CO signals (1 2 1 ratio), is consistent with this static structure. At higher temperature, these coalesce into a single signal20. The chiral complex (2-ethyl-l,3-butadiene)Cr(CO)4 (8) shows similar behavior, however... 

Carboxylation of dienes and trienes, which takes place in a stepwise fashion, affords mono- or dicarboxylated products.146 Cobalt carbonyl,147 palladium chloride,148 149 and palladium complexes150 were used. 1,4 Addition to 1,3-butadiene gives the corresponding unsaturated tram ester (methyl trans-3-pentenoate) in the presence of [Co(CO)4]2 and a pyridine base.147 The second carboxylation step requires higher temperature than the first one to yield dimethyl adipate. In a direct synthesis (110°C, 500 atm, then 200°C, 530 atm) 51% selectivity was achieved.147... 

The oxidation of butadiene, diallyl carbonate, or diallyl ether gives the products of monoepoxidation with selectivities of 85% and higher when the ratio diene/H202 is 2.5 (Table VIII). The diepoxides are formed in larger amounts when the diene/H202 ratio is 1. 

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