IRREGULAR CENTROPOLYINDANS - SYNTHESIS OF 4B,9,13H,18-TETRAHYDROINDENO[ 1,2-A]INDENO[2'',1''-B']INDENO[1',2'-B]INDENE AND OTHER NOVEL CENTROTRIINDANS

The syntheses of a novel tetraindan 6, containing two contiguous quate rnary central carbon atoms, and of a number of other derivatives of th e (unknown) ''irregular'' centrotriindan 5, is reported. Two-fold brid gehead benzylation of the C-2-symmetrical diindandione 7 followed by r eduction leads to the dibenzyldiindandiols 11, which undergo 2-fold ac id-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 ste p producing benzylidenetriindan 14 in good yield (70%). Monobenzyldiin dandiols 10 incorporate a solvent molecule upon cyclodehydration in p- xylene to give triindan 12, whereas use of chlorobenzene yields comple x 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)]-dii ndenes, in line with previous results. An independent attempt to gener ate 6 from 2,2'-biindanyltetrol 16 gave the dibenzodioxatetraquinane 1 7 in low yield.