William Clegg

Towards [6.5]coronane - fivefold cyclobutylmethyl-cyclopentyl rearrangement in a pentaspiroheneicosanal

Abstract The synthesis and successful rearrangement of the pentaspirane 4 yields the hexacyclic 11 , whose stereochemistry was unequivocally established as all- cis by X-ray analysis of a single epoxide 12 derived therefrom. A synthesis of [6.5]coronane 5 thus seems feasible.

Die Kristallstrukturen von KCd(N3)3 H2O und K2Cd(N3)4

K C d ( N 3 ) 3 H 2 0 crystallizes in space group Pnma with a = 11.991(2), b = 3.712(1), c = 17.292(2)Â and Ζ = 4. K2Cd(N3)4 crystallizes in space group C2/m with a = 14.272(2), b = 3.787(1), c = 8.887(2), β = 92.83(2)° and Ζ = 2. The structures have been determined from single crystal X-ray data. The final Ä-values are 0.074 and 0.063 respectively. In both structures cadmium is surrounded octahedrally by six azide groups; the Cd(N3)6-octahedra share edges. Potassium is coordinated by seven azide groups and two water molecules in KCd(N3)3 · H 2 0 and by eight azide groups in K2Cd(N3)4. In both structures all azide groups are approximately parallel, with mean Ν —Ν = 1.17(5) À.

Sterically crowded cyclohexanes - 81). Synthesis, crystal structure, conformation and dynamics of pentaspiro[2.0.2.0.2.0.2.0.2.1]hexadecane, pentaspiro[3.0.2.0.3.0.2.0.3.1]- nonadecane and pentaspiro[3.0.3.0.3.0.3.0.3.1] heneicosane

Abstract The synthesis, crystal structure (7,8), conformation and dynamics of pentaspiro[2.0.2.0.2.0.2.0.2.1] hexadecane 6, pentaspiro [3.0.2.0.3.0.2.0.3.1] nonadecane 7 and pentaspiro [3.0.3.0.3.0.3.0.3.1] heneicosane 8 are described. Chair conformations have been found in the solid state (7,8) and in solution (6,7,8). The activation parameters of the chair-to-chair interconversion have been determined from bandshape analyses of exchange broadened 1H-NMR (6,7) and13 C-NMR spectra (8), respectively. The results were as follows: 6: ΔH‡ = 48.9 ± 0.8 kJ/mol, ΔS‡ = -20.7 ± 2.8 J/mol, grd, ΔG‡298 = 55.0 ± 0.1 kJ/mol; 7: ΔH‡=51.2±0.7 kJ/mol, ΔS‡ = -12.0±2.4 J/mol, grd, ΔG‡298 = 54.8±0.1 kJ/mol; 8: ΔH‡ - 74.2±0.6 kJ/mol, ΔS‡ =-21.9 ± 1.5 J/mol, grd, ΔG‡298 = 80.7 ± 0.2 kJ/mol. On the basis of these values the barrier of inversion of the still unknown hexaspirane 5 is predicted to exceed 160 kJ/mol.