Diels Alder reaction polyphenylene synthesis

The above methods of synthesis have already used existent ring systems like difunctionalized benzene or cyclohexadienes as starting compounds. In an alternative approach one can generate benzene rings as part of the polymerization reaction, for example, by repetitive Diels-Alder reactions [100] or by valence isomerization [101]. Typical examples of the former include the combination of bisdienes, such as 54 and bisdienophiles, such as 55, whereby the formation of the benzene ring proceeds by extrusion of carbon monoxide from the original Diels-Alder products (scheme 9). The reaction thereby produces a mixture of para- and meto-linked polyphenylenes. 

Both the organometallic methods of phenyl-phenyl coupling (PPP synthesis) and the repetitive Diels-Alder reaction between tetraphenylcyclopentadienones and arylacetylenes toward branched polyphenylenes can be modified for the synthesis of structurally related oligomers (see also section 1.4.). Thus,... 

Scheme 9 Synthesis of polyphenylenes via Diels-Alder reaction.

Figure 8.6 Divergent synthesis of polyphenylene dendrimers through Diels-Alder reaction (Morgenroth et al, 1998). (Reproduced from F. Morgenroth, A.J. Berresheim, M. Wagner and K. Mullen, Spherical polyphenylene dendrimers via Diels-Alder reactions The first example of an A(4)B building block in dendrimer chemistry, Chemical Communications, 1139-1140,1998, by permission of the Royal Society of Chemistry.

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