Irregular Centropolyindanes: Synthesis of 4b,9,13b,18-Tetrahydroindeno[1,2-a]indeno[2'',1''-b']indeno[1',2'-b]indene and Other Novel Centrotriindanes

Abstract

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 C-2-symmetrical diindandione 7 followed by reduction leads to the dibenzyldiindandiols 11, which undergo 2-fold acid-catalyzed cyclodehydration (H3PO4/chlorobenzene) in moderate yield (22%) 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%). 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 [Delta(9b,10)]-diindenes, in line with previous results. An independent attempt to generate 6 from 2,2'-biindanyltetrol 16 gave the dibenzodioxatetraquinane 17 in low yield.