Intramolecular Diels–Alder Reaction of a Biphenyl Group in a Strained <i>meta</i>-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 ΔG‡ for the reaction is ∼40–41 kcal/mol, and computational models predict a similar value of Grel for the transition state of a concerted [4 + 2]-cycloaddition.