A simple synthesis of the fused tetrahydro-imidazopyridine 13 was accomplished via selective addition of protected guanidine to N-carbomethoxy-1, 2-dihydropyridine in the presence of bromine. Base-mediated semicleavage of the aminal gave 4-substituted 2- aminoimidazole 14. With this new method, natural marine metabolite 3-amino-1-(2- aminoimidazol-4-yl)-prop-1-ene (1) and derivatives may now be prepared from pyridine. ...