Intramolecular Diels-Alder Reaction of a Biphenyl Group in a Strained meta -Quaterphenylene Acetylene.

At elevated temperatures, a strained, cyclic meta -quaterphenylene acetylene undergoes an intramolecular cyclization reaction to form benz[ e ]indeno[1,2,3- hi ]acephenanthrylene. This reaction represents an example of a Diels-Alder reaction at the 2-, 1-, 1'-, and 2'-positions of a biphenyl derivative, a region analogous to the bay regions of perylene and other periacenes. The reaction proceeds cleanly with high conversion. Kinetics studies of a methylated derivative reveal that the Δ G ‡ for the reaction is ∼40-41 kcal/mol, and computational models predict a similar value of G rel for the transition state of a concerted [4 + 2]-cycloaddition.