99.18 (2), ~, = 95.67 (1) °, V= 750.1 (3) A 3, Z= 2, Dx = 1.286 g cm -3, a(Mo Ka) = 0.71069 A, /z = 0.67cm-1, F(000)=316, T=298K, R=0.063 for 2387 reflections. The trishomocubane moieties can be considered as formed from three multiply fused norbornane groups. The strained homocubane systems have nine C--C--C angles between 94.1 and 98.8 ° and 18 between 102.7 and 105.8 ° . There are three distinct classes of bond lengths which average 1.518 (5), 1.527 (8) and 1.567 (5) A in the three structures. The X-ray parameters are compared with those from the Cambridge Structural Database and with theoretical calculations of trishomocubane using the programs MM3, AM1 and GA USSIAN90. These parameters are also compared with those from experimental and theoretical studies of norbornane. The density of the o,e-isomer (2b) is significantly larger than that of the meso-isomer (2a).
IntroductionAs part of a general investigation of the synthesis and chemistry of novel polycyclic cage systems (Marchand, 1989), we recently reported the synthesis of mesoand D,L-D3-trishomocubylidene-D3-trishomocubane [(l a) and (lb), respectively] along with the results obtained via addition of biparticulate electrophiles (i.e., CF3CO2H and Br2) to the C=C double bond in each of these novel alkenes . More recently, we initiated an investigation of the corresponding addition of uniparticulate electrophiles (Paquette, Allen & Broadhurst, 1971) to these systems (see scheme below). In the first study, we investigated the epoxidation of the C=C double bond in (la) and (lb) by using m-chloroperbenzoic acid (MCPBA). Each epoxidation reaction proceeded smoothly, thereby affording the corresponding meso-epoxide [(2a) (2a) and (2b), as well as the fully saturated reference compound (3), are reported. In addition, the bond lengths and angles in trishomocubane (4) have been investigated theoretically through the use of MM3 (Allinger, Yuh & Li, 1989), AMPAC (Dewar, Zoebisch, Healy & Stewart, 1985) and GA USSIAN90 (Frisch et al., 1990). These values are compared with those obtained from the three X-ray structures and from an analysis of literature data. Since trishomocubane can be considered to be composed of three highly fused norbornane moieties, (5), these data are compared with those reported for norbornane.
ExperimentalAll compounds were obtained by synthesis. Crystal data and data collection and refinement parameters are given in Table 1. Data for compounds (2a) and (2b) were collected on two Rigaku AFC-6s diffractometers while data for (3) were collected on a Nicolet R3M//z update of a Syntex P21 diffractometer. Lorentz and polarization corrections and a 0-scan absorption correction were applied. The structures were solved by direct methods and refined by full-matrix least-squares techniques. from the Cambridge Structural Database (Allen, Kennard & Taylor, 1983; references for the structural fragments are given in Table 5) while Table 6 lists selected valence angles for the three compounds.Figs. 1, 2 and 3 are thermal ellipsoid plots of the three co...