BENZOANNELATED CENTROPOLYQUINANES .21. CENTROHEXAINDANE - 3 COMPLEMENTARY SYNTHESES OF THE HIGHEST MEMBER OF THE CENTROPOLYINDANE FAMILY

The syntheses of centrohexaindane 1, a unique hydrocarbon bearing six mutually fused indane units in a centrohexacyclic. T-d symmetrical, an d topologically nonplanar framework is reported in full detail. Three independent and complementary synthetic routes have been developed mak ing use of derivatives of the readily accessible centrotriindanes 9, 1 0 and 11 (R = CH3) and centrotetraindane 13 (fenestrindane). The most efficient synthesis gives the title compound 1 in seven steps starting from indane-1,3-dione 15 in 40% yield, involving the 'broken' fenestr ane 10 ('broken-fenestrane route'). Also starting from dione 15, an ev en shorter route furnishes our target molecule 1 in six steps via trip tindanetrione 24 in 25% yield ('propellane route'). Both of these rout es surpass our first synthesis reported in 1988 via fenestrindane 13 w hich comprises eleven steps and gives a 7.5% overall yield from indane dione 15 ('fenestrane route'). The three routes allow the six benzene rings of compound 1 to be introduced in complementary ways, thus promi sing the synthesis of centrohexaindane derivatives with various substi tution patterns. Particularly remarkable key steps of the syntheses of compound 1 are, inter alia: (i) single and two-fold condensation of b enzene by AlBr3-catalysed Friedel-Crafts reaction of cyclic 1,3-dibrom ides, (ii) unusual three-fold addition of phenyllithium to a 1,3,3'-tr iketone (compound 24), (iii) two-fold and even three-fold cyclodehydra tion. Finally, a low-yield formation of compound 1, among other produc ts, has been observed upon cyclodehydrogenation of 10-methyl-1,4,7-tri phenyltribenzotriquinacene 32, which is obtained in two steps from 10- methyltribenzotriquinacene 11 (R = Me). with Pd/C at 500 degrees C, Th e spectroscopic properties of compound 1 are presented along with some unique structural features of its rigid centrohexacyclic framework.