Source of the intraannular hydrogens in the dehydroxylation of calix [4] arene diethyl phosphate ester derivatives

The different possible sources of the intraannular hydrogens in the dehydroxylated calixarenes obtained by reductive cleavage of the calix [4] arene diethyl phosphate esters 2 and 6 are analysed. Two calixarene diethyl phosphate esters (4 and 5) full deuterated in the ethyl groups were synthesized. Reductive cleavage of 4 and 5 (potassium‐ammonia) resulted in the formation of the OH‐depleted calixarenes 3 and 7, respectively, which did not incorporate any deuterium at the intraannular positions, as judged by integration of the NMR signals. Quenching with D₂O of the reaction mixture of either 2 or 6 and potassium‐ammonia did not result in any deuterium incorporation in the products. The labelling experiments rule out the possibility that the source of the intraannular hydrogens is the diethyl phosphate ester groups or the quencher. It is concluded that the most probable sources of the hydrogen atoms in the OH‐depleted calixarenes is the ammonia molecule.