Synthesis, characterization and conformational study of new α,β-unsaturated acylhydrazones based on calix [4]arene backbone

A series of six new p-tert-butylcalix [4]arene-1,3-N,N′-diacylhydrazone derivatives 1–6 have been synthesized starting from β-chloro-α,β-unsaturated aldehydes and p-tert-butylcalix [4]arene hydrazide. They were characterized by IR, (1H, 13C, 19F) NMR and HRMS. In addition of the E/Z isomers around the C C bond of the starting aldehydes, the NMR data showed three conformers due to N C(O) bond rotation: transamid/transamid; Cisamid/transamid and Cisamid/Cisamid resulting from the disubstitution of calix [4]arenes. The rotational barriers around N C(O) bond for most compounds were measured in dimethylsulfoxide using dynamic NMR spectroscopy (DNMR). The results are discussed and compared with those previously reported for related β-chloro-α,β-unsaturated acylhydrazones.