General Aspects of Retrosynthetic Analysis

First we accentuate that the most important retrosynthetic mle is related to the basic property of the C-C bond, electronic structure and electronic charges of the fragments that emerge on disconnection of this bond. The mle states that disconnection should follow the correct mechanism. Products of disconnection are synthons—anionic or cationic fragments or radicals. Behind synthons, however, real molecules should exist, denoted as reagents or synthetic equivalents. 

If in the cyclic TM III we contemporaneously disconnect two C-C bonds, two synthons, TM Ilia and TM Illb, are obtained. Again, if one or both TMs of this second generation are complex structures, retrosynthetic consideration continues. 

Disconnection resulting in more than two synthons represents a multicomponent reaction in the synthetic direction. In such a reaction three or more reagents form three or more new bonds in a one-pot reaction. Some long-known reactions belong to this group and are discussed in the Sects. 6.2.1 and 6.2.2. 

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