Cyclization and Reductive Cleavage of Monospirodienone Calix[4]arene Derivatives. Trihydroxy-p-tert-butylcalix[4]arene Revisited

The monospirodienone derivative of 5,11,17,23-tetra-terf-butyl-25,26,27,28-tetrahydroxycalix[4]arene (2) undergoes in the presence of an ammonium tribromide salt a spiroannulation reaction at the α-position to the carbonyl. Reaction of 2 with an equimolar amount of LDA followed by treatment with a phosphorylating agent yielded a monosubstituted spirodienone. Reductive cleavage of the latter (K/NH₃) afforded 5,11,17,23-tetra-tert-butyl-25,26,27-trihydroxycalixarene (10). The structure of 10 was corroborated indirectly by X-ray crystallography of its bromo dispiro derivative 11. It is concluded that the compound obtained by cleavage of the bis(diethyl phosphate) ester derivative 13, and previously described by us as 10, is 5,11,17,23-tetra-tert-butyl-25,27-dihydroxy-26-monoaminocalix[4] arene (12). The latter readily forms a tosylate salt in CDCl₃ solution. Considering this reassignment, the inversion barriers of several OH-depleted aminocalixarenes and their salts are reexamined.