Guanidine polysubstituted

Polysubstituted pyrimidines were synthesized from in situ generated a,p-unsaturated imines and the corresponding amidine or guanidine derivatives in a convenient one-pot procedure. It was proposed that the described transformations proceed via the initial formation of o,P-imsaturated imine that undergo nucleophilic attack by a bidentate nucleophile (amidine or guanidine). This step is then followed by elimination of ammonia and aromatization to yield the observed polysubstituted pyrimidine. 

Van der Eycken s group [27] also recently reported a flexible synthesis toward polysubstituted 2-aminoimidazoles (see Scheme 9). A key step in their synthesis involved the use of silver (I) as a catalyst to heterocyclize guanidine derivatives to provide the desired 1,4,5-trisubstituted 2-aminoimidazole derivatives. 

An efficient procedure for the preparation of polysubstituted guanidines has been reported using ecofriendly bismuth-based catalyst and oxidant reactant instead of the highly toxic HgCl2--based methodology reported previously (Equation 57) [130]. 

Polysubstituted pyrimidines 39 can be obtained from a,P-unsaturated imines 38 and amidines or guanidines in a one-pot procedure [270]. The imines 38 are generated in situ in a sequential three-component process from methyl phosphonate, nitriles, and aldehydes (both preferentially aromatic for the utihty of 38 in pyridine synthesis, cf p. 373) ... 

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