1-Ethyl-4-thiocyanato-3-oxo-2-arylhydrazonobutanoates in heterocyclization reactions. x-ray structural study of 2-imino-5-[1-(4-methoxyphenylhydrazono)-2-ethoxyoxalyl]-4,5-dehydro-1,3-oxathiolane and 2-chloro-4-[1-(3-trifluoromethylhydrazono)-2-ethoxyoxalyl]-4,5-dehydro-1,3-thiazole |