It was found that the compounds having the general formula RCH(X)-C≡C-R'gave thiazole derivatives by reaction with thiourea. The relationship between the structure of thiazoles and substituent groups was clarified as follows : (1) When R=R'=Ph, 2-amino-4-benzyl-5-phenylthiazole (IId) is obtained, (2) When R=alkyl, R'=H, two kinds of thiazoles are obtained ; and (3) when R=R'=alkyl, thiazole derivative is not obtained. Similarly, propargyl bromide and phenylpropargyl bromide, when reacted with ammonium dithiocarbamate, afforded 2-mercapto-4-methylthiazole (XX) and 2-mercapto-4-benzylthiazole (XXIII), respectively. Further, 2-amino-4-methylimidazole (XXV) was obtained from guanidine and propargyl bromide.