PUB - Publikationen an der Universität Bielefeld

The synthesis of tribenzotriquinacene 4 by a stepwise cyclization strategy involving phenyl-substituted diindan intermediates is discussed in detail. Based on the determination of the anti () stereochemistry of 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 () phenyl-substituted isomer 20 by 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 corresponding phenylsulfinyl and phenylseleninyl ketones 22 and 25 is described and contrasted to a bromination/dehydrobromination approach adopted from a previous report. The synthesis is completed by reduction of 20 to diindanol 27 followed by cyclodehydration, giving 4 in 14-19% overall yield from 8. Non-cyclizing dehydration of 27 and the isomeric diindanol 9 gives the 4b,9-diindene 30 as the most stable non-cyclized isomer of 4. The steric effect of the syn- or anti-oriented phenyl substituents on the preferred conformation of the diindan skeleton is deduced from the contrasting vicinal 1H-1H spin coupling observed for the stereoisomers, e.g. the 9-phenyldiindans 28 and 29.