alpha-Oxoketene O,N-acetals were prepared from beta-oxothiono esters and primary amines in the presence of triethylamine at room temperature within several hours in good yields.
A New Two-Step Synthesis of α-Oxoketene<i>O,N</i>-Acetals
A new synthesis of α-oxoketene O,N-acetals has been developed from β-oxothioxo esters. Thus, the reaction of 2a-c with alkyl, allyl or cyclic primary amines in refluxing toluene and formic acid led to α-oxoketene O,N-acetals 3a-i in good yields.
3-Ethoxyisoxazoles and 3-ethoxy-1H-pyrazoles were obtained in high yields from β-oxo thionoesters. The reaction of the ethyl β-oxo thionoesters with hydroxylamine hydrochloride in the presence of triethylamine at room temperature for 2 h gave the ethyl 3-oxopropiohydroximates and their hemiacetals, which were easily converted to the 3-ethoxyisoxazoles by refluxing for 3 h at pH 3—5. On the other hand, the reaction of the ethyl β-oxo thionoesters with hydrazine derivatives in the presence of triethylamine for 3—8 h at room temperature directly yielded the 3-ethoxy-1H-pyrazoles.