Synthesis of sterically congested 1,3,4-oxadiazole derivatives from aromatic carboxylic acids, N,N-dicyclohexylcarbodiimide and (N-isocyanimino)triphenylphosphorane.

Reactions of (N-isocyanimino)triphenylphosphorane with N,N-dicyclohexylcarbodiimide in the presence of aromatic (or heteroaromatic) carboxylic acids proceed smoothly at room temperature and in neutral conditions to afford sterically congested 1,3,4-oxadiazole derivatives in high yields. The reaction proceeds smoothly and cleanly under mild conditions, and no side reactions were observed.