Hydrazine-mediated C-O bond reductive cleavage in some bis- and mono- O -substituted derivatives of 4- tert -butylcalix[4]arene

Novel di- and tetra-substituted calix[4]arene derivatives bearing diacetylene moieties at the lower rim of macrocycle were synthesized via the Mitsunobu and Williamson reactions. The dealkylation of diacetylene moieties of calix[4]arene was for the first time discovered in the DMSO—hydrazine hydrate system. An important role in the dealkylation of diacetylene moieties is played by neighboring unsubstituted OH groups at the macrocycle. Blocking of OH groups with butyl substituents and elongation of the linker between the butadiynyl fragments and the macrocyclic platform significantly reduce the affinity of macrocycle to reductive cleavage. The unique reactivity of calix[4]arene in its reaction with hydrazine hydrate was demonstrated in comparison with a model conjugate of diacetylene with 4- tert -butylphenol. The reductive cleavage may proceed via the formation of pyrazole derivative of calix[4]arene. Pyrazole derivatives were the most reactive ones in the reaction with hydrazine hydrate among the studied isostructural calixarenes containing an active α-arylmethyleneoxy moiety. Results of performed quantum chemical calculations allowed us to propose a scheme for the reductive cleavage of oxymethylene derivatives of pyrazole with hydrazine hydrate.