Scheme 1 geometry is presented in Figure 1. The polyketal 7 contains a 12-crown-6 moiety incorporated with a [ 16] orthocyclophane inside the macrocycle. The up-down-up conformation of the six oxygen atoms gives rise to a preorganized spherical cavity of diameter 1.02 A. The six benzylic carbon atoms in 7 form a plane (rms 0.0085 A), from which oxygen atoms deviate by about 0.8 A.Inspection of the CPK model of hexaketone 5 indicates that the preferred conformation has an up-down-up arrangement of the six carbonyl functions, causing serious steric strain in the molecule. It appears therefore that, as soon as it is produced, 5 undergoes rapid rearrangement, probably via the oxonium ion 6, resulting in sp2-to-sp3 rehybridization in each ketonic carbon to give the strain-free 7. This is an unprecedented reaction. The cyclic hexaketal 7 is a novel coronand containing the 2n-crown-n moiety. When viewed from above, the oxygen atoms of 7 form a six-pointed star. Although a number of coronands have been synthesized7 8 during the last two decades, in most cases the oxygens are separated by hydrocarbon spacers having two or more bridging atoms, such as dimethylene, trimethylene, or oor m-phenylene (7) X-ray analysis: 7 crystallizes in the monoclinic space group Fife (No. 14); a = 15.813( 6), b = 13.108(1), c = 20.257(7) A; 0 = 109.35(2)°; V = 3961.6 A•'; 4C[kd = 1.25 g/cm3; Z = 4. Data were collected on an Enraf-Nonius CAD4 diffractometer. Of the 5142 unique data collected with Mo Ka radiation ( = 0.71073 A), the 4212 with F0 > l.Ou(f) were used in the least-squares refinement to yield R = 5.2%, = 6.9% after an empirical absorption correction based on -scan data was applied.
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