Aromatic Rings and Aromatic Rods: Nonplanar Character of an Indeno-dehydro[14]annulene

Since the concept of aromaticity has been proposed to be generalizable to acetylenic rods (‘linear ring’ of [2]annulene), p -diisopropyl-tetraphenyl- carbo -benzene (C 48 H 34 ) and an indenone-fused isopropyl-triphenyloctadehydro[14]annulene (C 42 H 26 O) can be regarded as based on heptacyclic aromatic cores. The formation and X-ray crystal structures of both products are described. The latter has been obtained as a reductive rearrangement product of a transient isopropyl-pentaoxy[5]pericyclyne devised as a putative precursor of a carbo -fulvene target. A mechanism accounting for this peculiar transformation is proposed. Deviation from global planarity is measured by a 6° angle between the mean plane of the indenone bicycle and that of 13 atoms of the [14]annulenic macrocycle, forming dihedral angles with the local plane of the isopropyl-substituted sp 2 vertex of 16° and 15°, respectively. The magnetic aromaticity of the carbo -benzene and indeno-octadehydro[14]annulene products is evaluated by NICS calculations.