Abstract
O-Acetoacetylbenzamide oxime derivatives (2) were prepared from benzamide oxime derivatives (1) and diketene at low temperature in almost quantitative yields. Cyclization of 2 in the presence of a strong base proceeded with elimination of acetone to afford 3-aryl-1, 2, 4-oxadiazolin-5-one derivatives (4) in 77-95% yields. However, in the cases of the o-, m-, and p-nitrobenzamide oxime derivatives (2f-h), the reaction proceeded with dehydration even in the presence of a strong base to afford 5-acetonyl-3-aryl-1, 2, 4-oxadiazole derivatives (3f-h) in moderate yields. Possible mechanisms of these cyclization are discussed.
