Ethyl amidinoacetates in the synthesis of pyrazines

Abstract

Ethyl ethoxycarbonylacetimidate (1a) hydrochloride was converted by a one-stage process into ethyl 2-amidino-2-nitroso-(2a) or 2-amidino-2-phenylazo-acetate (2b). Reduction of these intermediates to ethyl 2-amidino-2-aminoacetate (2g) dihydrochloride followed by cyclisation with 1,2-dicarbonyl reagents in the presence of a suitable base, yielded ethyl 3-aminopyrazine-2-carboxylates (3a–d). Phenylglyoxal afforded ethyl 3-amino-5-phenylpyrazine-2-carboxylate (3d) in contrast to 3-amino-6-phenylpyrazine-2-carboxamide (3g) which is formed with this reagent and 2-amidino-2-aminoacetamide (2h). The pyrazine-2-carboxylates were converted into a number of 3-aminopyrazine-2-(N-alkyl)carboxamides (3i–x).