No abstract

Syntheses, properties, and some reactions of a novel centropolycyclic hydrocarbon, centropentaindan (1) , are described. The molecular structure of 1 consists of a tetrabenzo[5.5.5.5]fenestrane bearing a fifth centrically fused indan unit. Independent syntheses have been developed employing i) twofold cyclodehydrogenation of tribenzotriquinacene (7) with PdjC at 500 "C, which gives 1 in 50 % yield, and ii) a two-step procedure by tetrabromination of di-fuso-centrotriindan (8) followed by condensation with two molecules of benzene, which provides 1 in 88 % yield. Some bridgehead-substituted centropentaindans are described, including the highly labile dibromo derivative 19, and the centrohexacyclic, topologically nonplanar endo-peroxide 26 and endodisulfide 28. The notably rigid ring fusion in the molecular framework of 1 is shown both by X-ray structural analysis and by particular steric interactions of the two mutually compressed bridgehead substituents.

The solid-state molecular structure of centrohexaindane (), a unique hydrocarbon comprising six benzene rings clamped to each other in three dimensions around a neopentane core, and the molecular packing in crystals of ·CHCl3 are reported. The molecular Td-symmetry and the Cartesian orientation of the six indane wings of in the solid state have been confirmed. The course and limitation of electrophilic aromatic substitution of are demonstrated for the case of nitration. Based on nitration experiments of a lower congener of , tribenzotriquinacene , the six-fold nitrofunctionalisation of has been achieved in excellent yield, giving four constitutional isomers, two nonsymmetrical ( and ) and two C3-symmetrical ones ( and ), all of which contain one single nitro group in each of the six benzene rings. The relative yields of the four isomers (∼3 : 1 : 1 : 3) point to a random electrophilic attack of the electrophiles at the twelve formally equivalent outer positions of the aromatic periphery of , suggesting electronic independence of its six aromatic π-electron systems. In turn, the pronounced conformational rigidity of the centrohexacyclic framework of enables the unequivocal structural identification of the isomeric hexanitrocentrohexaindanes by (1)H NMR spectroscopy.

The oxidative degradation of benzo nuclei of various higher contropolyindanes with ruthenium (VIII) oxide or ozone was studied to further explore the chemistry of partially benzoanellated centrohexaquinanes. Besides the two tribenzotri‐quinacenes 12 and 15 which were used as model substrates for oxidation with RuVIII, centrohexaindane 1 was converted to the corresponding centrohexacyclic diketone 19 by using either RuO4 in stoichiometric amounts or O3 in dichloro‐methane/pyridine. Subsequent Wolff‐Kishner reduction of 19 gave pentabenzohexaquinane 4. Correspondingly, tribenzocentrohexaquinane 2 was degraded by sequential ozonolysis/reduction to the C2v‐symmetrical dibenzocentrohexaquinane 10 and monobenzocentrohexaquinane 11 in low yields (8–9% in each sequence). Due to the low efficiency of the ozonolyses, the parent centrohexaquinane 3 has remained elusive, yet. The deeply red centrohexacyclic 1,2‐diketone 19 was subjected to single‐crystal X‐ray structural analysis and found to bear an almost perfectly syn‐coplanar α‐dicarbonyl chromophore with a strong and extremely low‐energy UV/Vis absorption (λmax = 512 and 531 nm).

No abstract