Analogical approaches ring closure

The available ingenious and preparatively convenient methods for the synthesis of 1 and its analogs 2-4 have played a considerable role in the development of their chemistry. These approaches include thiophene ring closure based on pyridine derivatives and the pyridine ring closure based on thiophene derivatives. 

The next two approaches for synthesizing structurally defined ladder-type oligomers and polymers, discussed in sects. 4.3. and 4.4., rest on the formation of the single-stranded intermediates via polycondensation of (aromatic) monomers, again followed by a polymer-analogous ring-closure sequence. 

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