[reaction: see text] 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. Ab initio calculations of the energies of tautomers I-IV and deuteration experiments have provided insight into their reactivity.
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