S8-mediated cyclotrimerization of 4,5-dihydrobenz[l]acephenanthrylene: trinaphthodecacyclene (C60H30) isomers and their propensity towards cyclodehydrogenation

It is shown using (high-resolution) mass spectrometry that treatment of 4,5-dihydrobenz[l]acephenanthrylene (2, C20H14) and S8 in the melt gives the insoluble 532 a.m.u. (C40H20S) and 750 a.m.u. (C60H30) bisbenz[l]acephenanthrothiophenes (4a–c) and, trinaphtho[2,1-b,2,1-m,2,1-x]- (3a) and trinaphtho[2,1-b,2,1-m,1,2-a′]decacyclene (3b), respectively (estimated ratio 4a–c/3a–b 20:1). Whereas 3a fits the `C60 Schlegel diagramʹ and might be converted into C60 (720 a.m.u.) after full cyclodehydrogenation, 3b can only give a curved C60H12/C60H10 (732:730 a.m.u.). MALDI time-of-flight mass spectrometry shows that cyclodehydrogenations of 3a–b down to 732:730 a.m.u. occur; no evidence for C60 formation was found. This is attributed to the preferred formation of 3b, the lack of cyclodehydrogenation selectivity and the occurrence of C2 extrusions.