Regioselective deuteration of 25,27-dialkoxycalix[4]arenes

A direct deuteration of the upper rim of calix[4]arene has been carried out for the first time. 25,27-Dialkoxy derivatives of calix[4]arene (R = Me, Et, n-Pr, n-Bu) were regioselectively deuterated at the para positions of unsubstituted phenolic rings using DCl/D2O in tetrachloroethane. Interestingly, identical reaction conditions do not lead to deuteration of mono- or tri-substituted derivatives where only simple cleavage of alkyl substituents was observed.