Telomerization of 2,3-Dimethylbutadiene

3-Dimethylbutadiene is a symmetrical molecule like butadiene and, therefore, only three isomeric telomers can be expected. However, this diene is a very inactive one and only in one case has telomerization been reported. The reaction of 2,3-dimethyl-l,3-butadiene with ethylacetoacet-ate in the presence of a [PdCl2(PPh3)2]/NaOPh catalyst results in the formation of ethyl-2-acetyl-2,3,6,7-tetramethyl-2,7-decadienoate (31) with a yield of 7% [37, 38]. 

In other experiments the formation of 1 1 adducts was observed. For instance, when the reaction of 2,3-dimethylbutadiene with methyl aceto-acetate is carried out in the presence of a catalyst composed of palladium dichloride and 3-methyl-1-phenyl-A -phospholene the 1 1 adduct 3-car-bomethoxy-5,6-dimethyl-5-hepten-2-one is formed (Equation 32). Alkali decomposition of this ketone gives 5,6-dimethyl-5-hepten-2-one, a key intermediate for the synthesis of a-irone [39]. 

There are different possibilities to synthesize functionalized fine products using dimerization reactions. A list of important examples is given in the following  

This reaction is often accompanied by the formation of longer-chained products, e.g.  

The products formed by reaction (37) often contain a similar structure to the telomers described in Section 1. 

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