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The syntheses of a novel tetraindan 6, containing two contiguous quaternary central carbon atoms, and of a number of other derivatives of the (unknown) "irregular" centrotriindan 5, is reported. Two-fold bridgehead benzylation of the C2-symmetrical diindandione 7 followed by reduction leads to the dibenzyldiindandiols 11, which undergo 2-fold acid-catalyzed cyclodehydration (H3POr/ chlorobenzene) in moderate yield (22 5% ) to 6. In contrast, use of xylene as the solvent gives rise to a Wagner-Meerwein rearrangement along with a single cyclodehydration step producing benzylidenetriindan 14 in good yield (70 5% 1. Monobenzyldiindandiols 10 incorporate a solvent molecule upon cyclodehydration in p-xylene to give triindan 12, whereas use of chlorobenzene yields complex mixtures of triindene 13 and its oligomers. These results shed some light on the relatively high strain of the tetraquinane skeleton of 6 and, in particular, on the reactivity of bridgehead [A(9b,lO)ldiindenes, in line with previous results. An independent attempt to generate 6 from 2,2'-biindanyltetrol 16 gave the dibenzodioxatetraquinane 17 in low yield.In 1981, Gund and Gund2 published a classification scheme of complex polycyclic organic ring systems bearing a carbon atom which is shared by all of the rings. Among these centropolycyclanes,2 centropolyquinunes, Le., those congeners bearing mutually fused cyclopentane units, have been of particular interest because of their relation to naturally occurring314 and non-natural m o d e F systems and because of the favorable steric fit of centrically fused five-membered rings.Centropolyindans, the benzoannelated analogues of centropolyquinanes, obey the same classification scheme.8 During the past decade, all higher members of the family of "regular" centropolyindans have been synthesized in our laboratory,"ll including various centrotriindans and centrotetraindans (e.g., l,lonJld and, respectively, 21°bJld and 319 and the highest possible congeners, centropentaindan12 and ~entr0hexaindan.l~ (2) Gund, P.; Gund, T. M.

Iodine/silver(I) oxide (I(2)/Ag(2)O) reacts highly stereoselectively in the single, double, and triple anti epoxidation of the spherical 1,4,7-triene, 10-methyl-2,3:5,6:8,9-tris(cyclohexano)triquinacene 1. All of the three epoxides 3, 4, and 5 obtained with this reagent contain the epoxy groups at the convex side of the triquinacene framework. The stereochemical course of the epoxidation with I(2)/Ag(2)O is clearly distinct from that observed with m-chloroperbenzoic acid (MCPBA), which gives the same monoepoxide (3) but exclusively anti,syn di- and triepoxides (6-8) bearing at least one epoxy group at the concave side of the triquinacene framework. Epoxidation of the related three-fold 1,4-cyclohexadiene, tris(cyclohexeno)triquinacene 2, with MCPBA occurs similarly to the conversion of 1, whereas I(2)/Ag(2)O reacts with high regioselectivity at the less electron-rich peripheral double bonds of 2 giving triepoxides 12 and 13. The molecular structure of triepoxide 8 has been elucidated in detail by X-ray crystal structure analysis.

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