Improved Synthetic Methodology, Substrate Scope and X‐ray Crystal Structure for N, N’‐disubstituted Guanidines

Guanidine is a privileged scaffold in drug discovery. Herein we report our investigations into the acid promoted amination of pyrimidine‐bearing cyanamide to produce N, N’‐disubstituted guanidines. Hydrochloric acid was found to be a suitable catalyst, and the substrate scope using conventional heating was investigated with 23 aniline derivatives. The highest yield was obtained with anilines having pKa in the range of 2–4. Further, a microwave synthesis was developed using 3‐chloroaniline as a model substrate increasing the yield from 68 to 93 %. The microwave method was especially suited for increasing yields with anilines having pKa > 3. The structure of the pyrimidine‐bearing guanidines was confirmed by NMR spectroscopy, and one representative compound has been evaluated by X‐ray crystallography, showing the trans‐isomer as the only tautomer in solid form.