Synthesis of Unprotected Guanidines Using Polymer-Bound Pyrazole Derivatives

Significance

Synthetic methods of guanidines have been well studied, while isolation of guanidines is often difficult due to their high water solubility and high polarity. The authors have developed a polymer-bound 1H-pyrazole-1-carboxamidine 1 for the one-step transformation of primary and secondary amines into the corresponding guanidines. Thus, the reaction of amines with 1 and triethylamine was carried out in THF at 60 °C to give the corresponding guanidines in 31-99% yields. The reaction was drastically accelerated under microwave-assisted conditions to give comparable yields of the guanidines (see scheme).