Metal-free access of bulky N,N′-diarylcarbodiimides and their reduction: bulky N,N′-diarylformamidines†
A metal-free synthesis of symmetrical and unsymmetrical bulky N,N′-diaryl carbodiimides from the dehydrosulfurisation of their corresponding N,N′-diarylthiourea with 4-dimethylaminopyridine (DMAP) and iodine under mild reaction conditions with moderate to excellent yields has been established. In the literature, the classical method of dehydrosulfurisation of bulky N,N′-diarylthiourea to N,N′-diarylcarbodiimide has been reported using toxic metal oxide (HgO) and magnesium sulphate (MgSO4) under harsh reaction conditions. Furthermore, easy access to 1,3-disubstituted symmetric and unsymmetrical N,N′-diaryl formamidines involving the reaction of symmetrical and unsymmetrical N,N′-diaryl carbodiimides with sodium borohydride is described. The widely used method for the preparation of bulky N,N′-diaryl formamidines is the treatment of primary amines with triethylorthoformate in the presence of acid under high temperature reaction conditions.