Abstract: Cimetidine, namely N-cyano-N'-methyl-N"-[2-((4-methyl-5-imidazolyl) methylthio) ethyl] guanidine which is useful as an antagonist of H.sub.2 -receptor is prepared by reacting 4-methyl-5-[(2-aminoethyl) thiomethyl] imidazole, which is obtained by the reaction of 4-methyl-5-hydroxymethylimidazole on 2-aminoethanethiolsulfuric acid, with O-alkyl-S-alkyl-cyanothioimidocarbonate to give N-cyano-N'-[2-((4-methyl-5-imidazolyl) methylthio) ethyl]-O-alkylisourea, which is reacted with monomethylamine. According to the present process, cimetidine can be prepared in good yield and desired purity with very reduced amount of methyl mercaptan released from the reaction.

Abstract: Novel amidoxime derivatives having the following structural formula (IV) or (IV'): ##STR1## wherein R.sub.1 represents methyl or ethyl group and R.sub.2 represents hydrogen or methyl group, useful as a raw material for 3-amino-5-methyl isoxazole, are prepared from .beta.-amino crotonitrile. Said isoxazole, useful as an intermediate for various medicines, may be prepared without producing any by-products of isomer.