The course of the hydrogenation of [5]- and [6]metacyclophane (1b and 1c) and their thermochemistry is described. Both compounds are hydrogenated rapidly (within 10 s) to furnish the bridgehead olefins 13b and 12c. The accompanying hydrogenation enthalpies are -220 and -141 kJmol(-1), respectively. Strain energies (SE) and olefinic strains (OS) of a number of bridgehead olefins have been evaluated by DFT calculations; it was concluded that 13b belongs to the class of hyperstable olefins which correlates nicely with its reluctance to undergo hydrogenation. By combining experimental hydrogenation enthalpies and DFT calculations, SE of 187 and 121 kJmol(-1) were derived for 1b and 1c.

No abstract

The synthesis of several 9,11,11-trihalo[5.3.1]propellanes and their 4-dimethylsila analogues is described. They solvolyze under formation of the corresponding isomeric 7,9,11- trihalobicyclo[5.3.l]undec-1(11)-enes which are "anti-Bredt" olefins with a strained trans double bond in a bridged eight-membered ring; in the presence of nucleophiles such as water or ethanol, the corresponding 7-hydroxy or 7-ethoxy derivatives, respectively, are obtained. On the basis of the X-ray crystal structures of four of these compounds (1a, 9a, 15, 17b), the effect of strain and of the substitution pattern on the degree of twisting and pyramidalization of the double bond is discussed.

boron atoms as framework species can be prepared. The presence of oxygen-atom vacancies in the framework is also notable, and may facilitate substitution reactions with the Zn/B/O framework itself. Experimental ProcedureSynthesis: The hydrothermal reaction (sealed teflon pouch, ZOO'C, 4 d, pH ca. 8.5) of 3.814 g of borax (Na,B,O, .10H,O), 3.440 g of 4 M NaOH solution, 6.43 g of Zn(NO,),, and 10 mL of water resulted in a highly crystalline, white powder, which could be indexed "by hand" on a rhombohedra1 basis with approximate lattice constants of u = 9.910 8, and 1 = 48.62" (hexagonal setting: u % 8.160 A. c T 26.156 %.). The systematic absences of the powder data (rhombic setting: hhl, I = 2n; hhh, A = 2n) indicated space groups R3c or R%, and no extra lines were left unindexed. The powder was tested for nonlinear optical activity by a powder-second-harmonic-generation (PSHG) test [lo] which gave a null response, indicating that the material probably crystallizes in centrosymmetric space group. The space group R3c (No. 167) was thus assumed for this material and confirmed by the successful course of the structure refinement. Thermogravimetric analysis indicated no weight loss for this material below 600°C.S/ructure Determinulion. Thecrystal structure of Zn,O(BO,), was solved by a b initio methods from laboratory X-ray powder data [I 1.12,13]. High-resolution data were collected for a flat-plate sample of Zn,O(BO,), over 12 h on a Scintag PAD-X automated diffractometer (0-0 geometry, 16' < 2 0 0) were obtained from the data and corrected for Lorentz. polarization. and multiplicity effects, the maximum possible number of Kit values observable within the (sin$)/>. limit was 230. These Fhx,

No abstract