BENZOANELLATED CENTROPOLYQUINANES .14. SYNTHESIS OF TRIBENZOTRIQUINACENE BY STEREOCONTROLLED CYCLIZATION OF PHENYL-SUBSTITUTED C-S-DIINDANSLPHA,9,9A-ALPHA,10-TETRAHYDROINDENO[1,2-A]INDENES)

The synthesis of tribenzotriquinacene 4 by a stepwise cyclization stra tegy involving phenyl-substituted diindan intermediates is discussed i n detail. Based on the determination of the anti (a) stereochemistry o f the previously known phenyldiindanone 8 by standard electron impact mass spectrometry as well as on synthetical evidence (8 --> 12 --> 14) , the conversion of 8 to the syn (beta) phenyl-substituted isomer 20 b y means of dehydrogenation-rehydrogenation sequences has been achieved . In particular, the preparation of the isomeric diindenones 15 and 16 as key synthetic intermediates by thermal syn elimination of the corr esponding phenylsulfinyl and phenylseleninyl ketones 22 and 25 is desc ribed and contrasted to a bromination/dehydrobromination approach adop ted from a previous report. The synthesis is completed by reduction of 20 to diindanol 27 followed by cyclodehydration, giving 4 in 14-19% o verall yield from 8. Non-cyclizing dehydration of 27 and the isomeric diindanol 9 gives the Delta(4b,9)-diindene 30 as the most stable non-c yclized isomer of 4. The steric effect of the syn- or anti-oriented ph enyl substituents on the preferred conformation of the diindan skeleto n is deduced from the contrasting vicinal H-1-H-1 spin coupling observ ed for the stereoisomers, e.g. the (9)-phenyldiindans 28 and 29.