Telomerization, conjugated dienes

Dimerization and Telomerization of Conjugated Dienes and Related Reactions... 

Telomerization is the reaction of olefins having conjugated double bonds (conjugated dienes) in the presence of a nucleophile (telogen). The main... 

The higher stability of primary anion 37 as compared to secondary anion 38 explains the predominant formation of branched isomers. The high reactivity of conjugated dienes and styrenes compared with that of monoolefins is accounted for by the formation of new resonance-stabilized anions (39 and 40). Base-catalyzed alkylation with conjugated dienes may be accompanied by telomerization. The reason for this is that the addition of a second molecule of diene to the 39 monoadduct anion competes with transmetallation, especially at lower... 

In addition to the industrial developments listed above, much academic efforts have also been devoted over the years to (1) the expansion of the scope of the telomerization reaction, (2) the elucidation of the details of the reaction mechanism and (3) process modifications that allow more efficient production and separation of the desired products. The scope of substrates that can be used in this reaction has indeed been shown to be very broad. 1,3-Butadiene is most often used as the conjugated diene, since it is cheap, readily available and provides a linear octadienyl chain. The use of other dienes, such as isoprene [13-16], piperylene [17] and myrcene [18,19], has also been described, but they have been far less commonly studied. Such substituted telogens come with an additional selectivity challenge as many more isomers can potentially be obtained, which is illustrated for isoprene in Fig. 1. 

Drent E, Jager WW (2004) Process for the telomerization of conjugated dienes. EP 1671940... 

Hill K, Weese KJ (1993) Telomerization of a conjugated diene with a sugar as telogen. DE 4242467... 

Table 17. Possible telomerization of non-conjugated dienes with functional telogens...

Palladium-catalyzed 1,4-hydroamination of conjugated dienes is usually accompanied by large amounts of 2 1 telomerization product [21,22]. It was shown that the use of an amine hydrochloride as a cocatalyst increased the selectivity for the 1,4-hydroamination product [23]. Thus, 1,3-butadiene and 2-3-dimethylbuta-1,3-diene gave a fair yield in the palladium-catalyzed 1,4-amination shown in [Eq.(5)]. 

Although 2 1 telomerization reactions can be considered as a special case of 1,4-addition to a conjugated diene by a carbon nucleophile and a second nucleophile [Eq.(14)], these reactions will not be covered by this chapter. The reader is advised to consult Refs. [8] and... 

Butadiene is a very inexpensive and attractive molecule for the industrial chemist. Several products can be made from butadiene and carbon monoxide under specific conditions. Subtle effects control the outcome of palladium-catalyzed carboxyla-tion of conjugated dienes such as butadiene. Depending on the reaction conditions, monocarboxylate, dicarboxylate, or telomerized products could be obtained (Scheme 4, cf. Section 2.3.5). 

Reactions of the second type are carried out with palladium compounds or complexes of either bivalent or zero-valent states. Since these reactions proceed catalyti-cally without using reoxidants they are more useful than the stoichiometric processes. Telomerization of conjugated dienes, reactions of allylic and alkenyl esters and ethers, and various organic halides belong to this type. 

Many other examples of transition metal catalyzed reactions such as oxidation, dimerization or telomerization of conjugated diene have been performed in these borderline anions-based ionic liquids and are described in recent reviews [4]. 

Transition metal carbohalogenation with polyhalomethanes can also be applied to non-conjugated dienes, leading to formal telomerization products. In an early example, this reaction was applied to the addition of carbon tetrachloride to norbornadiene, mediated by pentacar-bonyliron and trimethylamine iV-oxide. Stereoisomeric nortricylane products 12 were obtained with moderate stereoselectivity31-32. 

Telomerization of butadiene with 1,1,1-trichloroethane and 1,1,1,3-tetrachloro-propane was achieved. Butadiene acts as conjugated diene in this reaction, but only 1 1 and 2 1 adducts were isolated [36] (Fig. 39). 

Various natural products have been synthesized from telomers prepared by a Pd or Nickel catalyzed telomerization of conjugated dienes such as butadiene and isoprene. 

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