Synthons are idealized reagents

Disconnections must correspond to known, reliable reactions 

The chemists who first made amelfolide chose to make it from an amine and an acyl chloride because they knew that this reaction, the standard way of making an amide, had a very good chance of success. They chose to disconnect the C-N bond because this disconnection corresponds to a reliable reaction in a way that no other possible disconnection of this molecule does. 

Now that you ve seen the principle of retrosynthetic analysis at work, you should be able to suggest a reasonable disconnection of this compound, which is known as daminozide. 

You probably spotted immediately that daminozide is again an amide, so the best disconnection is the C-N bond, which could take us back to acyl chloride and dimethylhydrazine. This time we ve written C-N amide above the retrosynthetic arrow as a reminder of why we ve made the disconnection and we advise you to follow this practice. 

in fact, there is a problem with this acyl chloride—it would be unstable as it can cyclize to an anhydride. But this poses no problem for the synthesis of daminozide—we could just use the anhydride instead, since the reaction should be just as reliable. A better retrosynthesis therefore gives the anhydride and indeed this is how daminozide is made. 

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Synthon II, an analog of I with an oxygen atom at a lower oxidation state, is also conceivable. Here, the positive charge can be compensated intramolecularly by an electron pair from an oxygen atom, i.e., by the formation of epoxide. In other words, epoxides are ideal reagents for illogical synthons II ... 

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