1.4- Dien-3-ones chlorides 2 molecules

The titanium trichloride-diethylaluminum chloride catalyst converted butadiene to the cis-, trans,-trans-cyclododecatriene. Professor Wilke and co-workers found that the particular structure is influenced by coordination during cyclization between the transition metal and the growing diene molecules. Analysis of the influence of the ionicity of the catalyst shows effects on the oxidation and reduction of the alkyls and on the steric control in the polymerization. The lower valence of titanium is oxidized by one butadiene molecule to produce only a cis-butadienyl-titanium. Then the cationic chain propagation adds two trans-butadienyl units until the stereochemistry of the cis, trans, trans structure facilitates coupling on the dialkyl of the titanium and regeneration of the reduced state of titanium (Equation 14). 

It was also demonstrated that organosilylstannanes can be used as the trimethylsilyl anion source. In this case, the acid chlorides gave poor results and it was found that aryl iodides were suitable substrates. Reaction of buta-1,3-diene with Phi and BujSnSiMej gave the 1,4-carbosilylation product in 50% yield as an E/Z 84 16 mixture. The use of phenyl triflate as the aryl source did not give the desired 1,4-addition product but afforded the 2 1 telomerization product from two molecules of diene and one trimethylsilyl group, in good yield. 

When the tt electrons of the diene abstract D" from a molecule of undissociated DCl, the chloride ion can better stabilize the positive charge at C-2 than at C-4 simply because when the chloride ion is first produced, it is closer to C-2 than to C-4. So it is a proximity effect that causes the 1,2-addition product to be formed faster. A proximity effect is an effect caused by one species being close to another. 

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