DIHYDROPYRENES - FURTHER INSIGHT INTO EFFECTS OF ANNULENOANNELATION, BENZANNELATION, CONJUGATION AND ISOANNELATION

A series of [e]-annelated derivatives of dimethyldihydropyrene 1 have been synthesized and their relative diatropicities studied. The high pi-bond orders of the annelated bonds in 4 and 5 clearly result in relatively smaller effects on the diatropicities of the respective [14]annulenes compared to benzoannelaton in 2. The derivative 11 shows a strong effect of conjugation on the diatropicity of the [14]annulene. A linear relationship between the diatropicity of dihydropyrene and the resonance energy of the annelated benzenoid system is observed based on a discussion of either the effect of benzannelation or the effect of conjugation. The first example of an isoannelated aza[18]annulene, namely 14, unambiguously indicates a more effective participation of nitrogen compared with oxygen in sustaining a ring current. Adverse steric interactions in 22 and 23 result in a deviation from planarity of the dihydropyrene periphery leading to a further decrease in diatropicity in addition to the effect of benzannelation. The anthroannelated system 24 is the first derivative of 1 which apparently shows no appreciable ring current. A comparison of the relative diatropicities of 23 and 26 suggests that the effective aromaticities of isoquinoline and pyridine are very similar to those of naphthalene and benzene respectively.