Partially Benzoanellated Centrohexaquinanes: Oxidative Degradation of Centropolyindanes by Using Ruthenium(VIII) Oxide and Ozone

Abstract

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).

Functionalized aromatics aligned with the three Cartesian axes: Extension of centropolyindane chemistry

“…Such a complete bridging would generate centrohexaquinane if six ethylene (1,2-ethano, -CH 2 -CH 2 -) bridges, and the likewise elusive centrohexaquinacene, if six vinylene (1,2-etheno, -CH=CH-) bridges were incorporated. Notably, a related C 3 -symmetrical triether bearing three -CH 2 -O-units has been known since 1981 [15][16][17]. Bridging neopentane 1 by six ortho-phenylene ("ortho-benzeno", 1,2-c-C 6 H 4 ) groups leads to the highest member of the centropolyindanes, centrohexaindane 3 [18], which can be synthesized in gram amounts through three independent routes [19] and represented the first, topologically nonplanar, "K 5 " hydrocarbon [20].…”

“…The "propellane" route provides an alternative access to the centrohexaindane framework and, in fact, has also proven most useful for the closest preparative approach to the parent centropolycyclane, the still elusive centrohexaquinane, because it opens the access to a tribenzo and a dibenzo derivative and, albeit in very minor yields, even to the monobenzo analog of the latter [17,38]. Recently, the propellane route enabled us to synthesize the first twelve-fold functionalized centrohexaindane, 27 (Scheme 4) [39].…”

An Elusive Nonaromatic Goal behind the Centropolyindanes: Aufbau of Veratrolo‐Annelated Centropolyquinanes and Ozonolytic Abbau

“…Other electron‐rich centropolyindane precursors for the oxidative dismantling of the aromatic nuclei may offer additional chances to reach these goals. Some of these approaches have already been tested or demonstrated . From our present point of view, combined strategies involving the synthesis of partially benzo‐ (or veratrolo‐) annelated centropolyquinanes, such as tribenzocentrohexaquinane 5 and the corresponding methoxy‐substituted derivatives, appear most promising.…”

“…The other family is that of the partially benzoannelated centropolyquinanes , the members of which bear the centrohexaquinane core of 1 with one to six annelated benzene units . Pentabenzocentrohexaquinane ( 3 ) and the corresponding 1,2‐diketone 4 are known, as are the C 3 v ‐symmetry tribenzocentrohexaquinane 5 and its C 3 ‐symmetrical, and thus chiral, triketone 6 (Figure ) . We have also reported the preparation of a dibenzo‐ ( 7 ) and the monobenzocentrohexaquinane ( 8 ), the latter of which was obtained in minute amounts through twofold oxidative degradation/reduction of 5 via 7 .…”

“…Pentabenzocentrohexaquinane ( 3 ) and the corresponding 1,2‐diketone 4 are known, as are the C 3 v ‐symmetry tribenzocentrohexaquinane 5 and its C 3 ‐symmetrical, and thus chiral, triketone 6 (Figure ) . We have also reported the preparation of a dibenzo‐ ( 7 ) and the monobenzocentrohexaquinane ( 8 ), the latter of which was obtained in minute amounts through twofold oxidative degradation/reduction of 5 via 7 . Notably, the parent nonaromatic hydrocarbon 1 has remained elusive since Simmons’ and Paquette's papers of 1981 on this topic…”