PUB - Publikationen an der Universität Bielefeld

The synthesis of [3.3.3]propellanes 18, 19, and 3 bearing one, two, or three [1,10]-fused phenanthrene units instead of a simple benzene ring has been performed. Starting from tryptindan-9-one 4, the hitherto unknown tryptindane-9,10-dione 5 and tryptindane-9,10,11-trione 10, the corresponding mono-, di-, and tribenzylidenetriptindanes 7, 9, and 13 have been prepared. In all three cases. the stereoisomers bearing cis-oriented benzylidene groups. i.e., (Z)-stilbene units. are formed predominantly. The monostilbene (Z)-7 and the tristilbene (Z,Z,Z)-13 were obtained in pure form and their stereochemistry was fully characterized. Photocyclodehydrogenation of 7 under Mallory-Katz conditions gave dibenzo(phenanthro-[1,10])[3.3.3]propellane 18 in an almost quantitative yield, irrespective of the stereoisomeric composition of 7. In contrast, photocyclodehydrogenation of distilbene 9 gave the unusual propellane-fused elassovalene 20 in a moderate yield, and the expected benzodi-(phenanthro-[1,10])[3.3.3]propellane 19 was only obtained in a low yield. As an extreme case, tristilbene (Z,Z,Z)-13 eluded the desired threefold photolytic cyclodehydrogenation; however, catalytic cyclodehydrogenation by Pt/Al2O3/Ti at 310 degrees C furnished the threefold acephenanthrylene 3 in a yield of 18%.