Two-Step Transannular Reactions

Purely randomly occurring transannular reactions cannot lead to very long sequences of transannular rings [see, for example, (23-19)] since a maximum yield may not be exceeded. The case of a two-step transannular reaction caused by a polymerization reaction is more favorable. 

In the first step a polymer chain with regularly ordered substituents is produced, and in the second step the substituents themselves are polymerized. An example of this is the polymerization of butadiene to 1,2-poly(butadiene), which is then cyclized by polymerization of the vinyl groups  

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