The pyrolysis of several dialkylphosphate ester derivatives of calixarenes yielded the same phosphorus bridged compound 7. Under the pyrolytic conditions the phosphate groups may be cleaved or intermolecularly transferred. X-ray crystallography of the bridged calixarenes 7 and 8 shows that they exist in a chiral 'flattened cone' (fc) conformation. 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 enantiomerization of the systems. Pyrolysis of partially phosphorylated calixarenes resulted in the formation of two products (11 and 12), each consisting of two subunits of three proximal rings bridged by a phosphate group. The rotational barriers for 11 and 12 are 14.4 and 8.8 kcal mol-1, indicating that the bridged calixarene system 12 is appreciably more flexible than 11.
|Original language||American English|
|Number of pages||20|
|Journal||Journal of Inclusion Phenomena and Molecular Recognition in Chemistry|
|State||Published - Mar 1994|