Copper(II) chloride promoted transformation of amines into guanidines and asymmetrical N,N′-disubstituted guanidines

We present a concise, less-toxic and broadly applicable method for coupling weakly nucleophilic amines with N,N′-di-(tert-butoxycarbonyl)thiourea, N-(tert-butxoycarbonyl), N′-alkyl/arylsubstituted-thioureas and N,N′-di-(tert-butoxycarbonyl)imidazolidine-2-thione in the presence of copper(II) chloride. Subsequent removal of Boc protecting groups affords guanidines, di-substituted guanidines and 2-aminoimidazolines in modest to excellent overall yields.