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Six general methods for the synthesis of acyclic and cyclic guanidines, of structures 1 and 2 and bearing a variety of substituents, are described. These guanidines may be symmetrical or unsymmetrical, and the substituents they bear provide the basis for further chemical manipulation. The acyclic guanidines are derived from single carbon intermediates, such as 3, 9, 13, and 14, and the appropriately substituted amine. The cyclic guanidines result from the functionalization of a 2-p-toluenesulfonamidopyrimidine which is subsequently hydrogenated. Use of the tosyl as B protecting group reduces the effects of the strongly alkaline guanidine moiety, and its facile removal is achieved with hydrogen fluoride. Detosylation of the tosyl-protected guanidino diester 12 resulted in formation of the imidazolin-4-one 51; this reaction proved to be general for the guanidines 1, 2 = 1, and 2, z = 1, 2. These imidazolinones underwent deuterium exchange for which a mechanism involving the formation of a mesoionic intermediate is proposed.