Enamines pyrroles from 2 molecules

The salicylic acid functionality incorporated in a rather complex molecule interestingly leads to a compound that exhibits much the same activity as the parent. The 1,4 diketone required for formation of the pyrrole ring can be obtained by alkylation of the enamine from 2-tetralone (38) with phenacyl bromide. Condensation of the product, 39, with salicylic acid derivative 40 leads to the requisite heterocyclic system (41). The acid is then esterified (42) and the compound dehydrogenated to the fully aromatic system (43). Saponification affords fendosal (44). ... 

We indicated in the introduction that the trimerization of pyrrole involves, in the reaction of the third molecule of pyrrole, the interaction with a protonated enamine. Such an intermediate could also be generated by protonation of an imine. Although few examples of intermolecular reactions have been reported, it is clear that this is another method that is capable of further exploitation. Acyclic and cyclic im-ines have been shown to interact successfully with nucleophilic aromatic substrates such as indole. In the case of the cyclic imines they may be generated in situ from relatively stable trimers. 

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