Why This Topic Should be Treated Separately

Generally speaking, the construction of a cyclic molecule composed of carbon atoms is nothing more than a particular case of carbon-carbon bond formation. Why is it necessary, then, to examine the ring-forming reactions in a special section The answer to this question becomes apparent if we consider briefly the specific features of the transformations that should occur in order to form a cyclic structure. 

It is easy to see that in a molecule of this type the interaction between the terminal groups may proceed in an mframolecular fashion, leading to the desired closed-ring product 269, or as an iwrermolecular process to form oligomers 270. Relative rates of reaction for these two processes may vary within broad limits, depending mainly upon the structure of the substrate. This difference can be easily understood if one takes into account some obvious ramifications of the intramolecular mode of interaction required for the ring closure. 

Owing to these peculiarities, the relative ease of intra- versus iwler-molecular processes may differ dramatically, depending upon the ring size of the target system. Below we will examine some specific problems and solutions which are typically encountered in the synthesis of various cyclic structures. 

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