J. Chem. Research (S), 1997, 46–47 J. Chem. Research (M), 1997, 0430–0436 Triphenyltruxenene: a C48 Polycyclic Buckybowl Precursor M. John Plater,* Marapaka Praveen and Alan R. Howie Department of Chemistry, University of Aberdeen, Meston Walk, Aberdeen AB24 3UE, UK The synthesis and X-ray crystal structure of the title compound are reported. The discovery of the fullerenes has led to a renaissance of interest in the synthesis of strained non-planar fragments whose structures represent sections of the buckminsterfullerene surface.1 Most notable is the synthesis by Rabideau of the C30 fragment semibuckminsterfullerene or hemifullerene by the pyrolysis of a mixture of tri- and tetra-chlorotruxenenes 1.2 This key fragment represents half of the C60 surface and has the correct carbocyclic framework for two enantiomeric halves to dimerise into the C60 cage.3 A previous attempt to prepare hemifullerene by the pyrolysis of truxenene 2 proved unsuccessful.4 Truxenene derivatives and their chemistry are clearly of great interest as a route to ‘buckybowl’ precursors.With this in mind we have prepared triphenyltruxenene 6 and obtained an X-ray crystal structure. Truxenequinone 4 was prepared (see Scheme) by the acidcatalysed cyclotrimerisation of indane-1,3-dione 3.4 Addition of benzylmagnesium bromide to truxenequinone 4 gave a mixture of the two isomeric alcohols 5 which were readily dehydrated to give triphenyltruxenene 6 by treatment with toluene-p-sulfonic acid in refluxing benzene.In contrast to the poor stability of truxenene 2 and the difficulty in preparing it owing to the reactive exocyclic methylene groups,4 triphenyltruxenene 6 is a thermally stable crystalline solid. Owing to the successful pyrolytic synthesis of hemifullerene from 1 by three consecutive ring couplings, the X-ray crystal structure of compound 6 was of particular interest to determine the distances between the coupling sites and to determine the preferred ground-state geometry.Truxenenes can exist in two diastereoisomeric conformations with the lowestenergy conformer calculated to have the three exocyclic alkenes projecting on the same face.4 For truxenene 2 the conformer with two alkenes projecting on one face and the other on the opposite side was calculated at the ab initio 3-21G level to be 2.52 kcal molµ1 less stable. The perspective drawing of the X-ray crystal structure (Figure) shows the molecules to possess a three-fold symmetry axis perpendicular to the best plane of the central six-membered ring.Each alkene group projects onto the same face, as expected from the calculations for truxenene 2,4 and the alkene bond C(9)·C(10) makes a dihedral angle of 22° to the bond C(2ii)·C(1) of the central benzene ring [C(2ii) ·C(1) ·C(9)·C(10)]. The carbon atoms of the ring-coupling position C(4)·C(10i) are fairly close at 3.221(15) Å. Interestingly, the central benzene ring A displays a regular alternation in the bond lengths with C(1)·C(2), C(1i) ·C(2), C(1)i)·(C2i) and (C1ii)·C(2ii) all 1.418(6) Å and C(1)·C(2ii), C(1)i)·C(2) and C(1ii)·C(2i) all 1.387(6) Å.We are currently continuing our studies into the synthesis of halogenated polycyclic derivatives of triphenyltruxenene 6 which may serve as useful precursors to the hemifullerene core. Crystal Data for 6.·C48H30, Mr=606, F(000)=1908, rhombohedral, a=17.457(5), c=19.134(6) Å, V=5050 Å3, space group R3c, (No. 161), Z=6, Dx=1.197 g cmµ3, m(MoKa)=0.063 mmµ1. The experimental data were collected at room temperature on a Nicolet P3 diffractometer using a graphite monochromator with MoKa radiation 46 J. CHEM. RESEARCH (S), 1997 *To receive any correspondence (e-mail: m.j.plater@abdn.ac.uk). Scheme Reagents, conditions and yields: i, conc. H2SO4, room temp., 24 h, 75%; ii, PhCH2MgBr, THF, room temp., 8 h, 99%; iii, TsOH, C6H6, heat, 2 h, 56% Figure Perspective drawing of triphenyltruxenene showing the crystallographic atom-numbering scheme and 40% probability thermal vibration ellipsoids(l=0.71069 Å).The structure was solved by direct methods.5 The final R value was 0.062 (Rw=0.043). The estimated standard deviations for the geometrical parameters involving non-hydrogen atoms lie within the following ranges: bond lengths 0.006–0.015 Å; bond angles 0.6–1.0°. This work was supported by the Enginering and Physical Sciences Research Council (EPSRC) of the United Kingdom. Techniques used: IR, 1H and 13C NMR, mass spectrometry, X-ray crystallography References: 9 Schemes: 1 Table 1: Atomic coordinates and Ueq values for non-hydrogen atoms Table 2: Interatomic distances and angles Received, 14th October 1996; Accepted, 1st November 1996 Paper E/6/06989D References cited in this synopsis 1 P. W. Rabideau and A. Sygula, Acc. Chem. Res., 1996, 29, 235. 2 A. H. Abdourazak, Z. Marcinow, A. Sygula, R. Sygula and P. W. Rabideau, J. Am. Chem. Soc., 1995, 117, 6410. 3 M. J. Plater, H. S. Rzepa and S. Stossel, J. Chem. Soc., Chem. Commun., 1994, 1567. 4 F. Fabris, O. De Lucchi and F. Sbrogio, Synlett., 1994, 761. 5 G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467. J. CHEM. RESEARCH (S), 1996 47