trijiuso - Centrotetraindan - Two Syntheses of a New Centropolyindan *

Two independent syntheses of the new centrotetraindan 2, a "trifuso", C,-symmetrical isomer of fenestrindan 1, are described. The first approach is based on the "endo"-phenyldiindanone 7, which is converted into 2 by benzylation to ketone 8 and subsequent cyclodehydration with polyphoshoric acid. The second, more efficient approach is based on the diindandione 17, which is converted into ketol 19 in two steps, which, in turn, is subjected to a three-step cyclodehydration-reduction-cyclodehydration sequence via 26 and 27 to give 2 in 8% overall yield. Some limits of the cyclodehydration of diindan alcohols and ketones are demonstrated with regard to effects of steric crowding and fragmentation of the carbon skeleton. The steric hindrance of "endo"-phenyl-substituted diindans is demonstrated in the case of ketone 26.