PREPARATION, STRUCTURE AND STEREODYNAMICS OF PHOSPHORUS-BRIDGED CALIXARENES

The pyrolysis of several dialkylphosphate ester derivatives of calix[4 ]arenes yielded the same phosphorus bridged compound 7. Under the pyro lytic conditions the phosphate groups may be cleaved or intermolecular ly transferred. X-ray crystallography of the bridged calixarenes 7 and 8 shows that they exist in a chiral 'flattened cone' (fc) conformatio n. The bridged calixarenes undergo in solution a dynamic process with a barrier of about 10.1 kcal mol(-1) for 7 and 8 and 13.1 kcal mol(-1) for 10, respectively. The dynamic processes result in enantiomerizati on of the systems. Pyrolysis of partially phosphorylated calix[6]arene s resulted in the formation of two products (11 and 12), each consisti ng of two subunits of three proximal rinks bridged by a phosphate grou p. The rotational barriers for 11 and 12 are 14.4 and 8.8 kcal mol(-1) , indicating that the bridged calix[6]arene system 12 is appreciably m ore flexible than 11.