CENTROPENTAINDAN, A FENESTRANE BEARING 5 MUTUALLY FUSED INDAN UNITS -SYNTHESES, MOLECULAR-STRUCTURE, AND BRIDGEHEAD SUBSTITUTION

Syntheses, properties, and some reactions of a novel centropolycyclic hydrocarbon, centropentaindan (1), are described. The molecular struct ure of 1 consists of a tetrabenzo[5.5.5.5]fenestrane bearing a fifth c entrically fused indan unit. Independent syntheses have been developed employing i) twofold cyclodehydrogenation of tribenzotriquinacene (7) with Pd/C at 500 degrees C, which gives 1 in 50 % yield, and ii) a tw o-step procedure by te-trabromination of di-fuso-centrotriindan (8) fo llowed by condensation with two molecules of benzene, which provides 1 in 88% yield. Some bridgehead-substituted centropentaindans are descr ibed, including the highly labile dibromo derivative 19, and the centr ohexacyclic, topologically nonplanar endo-peroxide 26 and endo-disulfi de 28. The notably rigid ring fusion in the molecular framework of 1 i s shown both by X-ray structural analysis and by particular steric int eractions of the two mutually compressed bridgehead substituents.