How aromatic are the benzene rings in biphenylene? The synthesis and NMR properties of a biphenyleno fused dihydropyrene

The synthesis of the biphenylene fused dihydropyrene 2 is described by cycloaddition of dibromobenzocyclobutadiene with the oxa[17]annulene 3 and deoxygenation of the adduct with Ti(0). Analysis of the NMR data indicates that biphenylene has about 55% of the relative bond fixing ability of benzene, which is equated to relative aromaticity. The experimentally determined Dewar resonance energy is 1.59 times that of benzene, while Dewar calculates 1.55 times benzene.