Synthesis and dynamic 1H NMR study of dialkyl-2-[N-acetyl-N-(alkyl or aryl)carbamoyl]butandioate derivatives

The 1:1 adduct intermediate of alkyl or aryl isocyanides and dialkyl acetylenedicarboxylates were protonated by acetic acid to produce dialkyl-2-[N-acetyl-N-(alkyl or aryl)carbamoyl]butandioate derivatives and dynamic 1H NMR effects were observed in these compounds. The calculated free-energy of activation (?G?) for restricted rotation around the aryl-nitrogen single bonds in dimethyl-2-[N-acetyl-N-(2, 6-dimethyphenyl)carbamoyl]butandioate (3d) amounts to 58.2 ± 2 kJ.mol-1 with first order rate constant (k=189.3 s-1) at appropriate temperature.