The Acid-catalyzed Decomposition of Diazo Carbonyl Compounds. II. Synthesis of 2- or 5-Heteroatom-substituted Oxazoles

The BF3-catalyzed decomposition of m- and p-substituted α-diazoacetophenones in excess of methyl thiocyanate and ethyl thiocyanate gave the corresponding 2-methylthio-, and 2-ethylthio-5-aryloxazoles, respectively in good yields along with s-alkyl-n-aroylmethylthiocarbamates and α-ethoxyacetophenones. However, yields of 2-dimethylamino-5-aryloxazoles by the reaction of dimethylcyanamide with α-diazoacetophenones were poor. 5-Dimethylamino- or 5-alkoxy-4-aryl-2-methyloxazoles were prepared by the reaction of N,N-dimethyl-α-(p-nitrophenyl)diazoacetamide or alkyl aryldiazoacetates with nitriles. When ethyl phenyldiazoacetate or methyl p-chlorophenyldiazoacetate were used, ketazines of alkyl arylglyoxylates were obtained together with oxazoles.