In Situ Generated Difluoroketene as a C1 Synthon for the [4 + 1] Annulation to 5-Difluoromethyl-1,2,4-oxadiazoles

Herein, we report an efficient synthesis of 5-difluoromethyl-1,2,4-oxadiazoles through a [4 + 1] annulation process, utilizing in situ generated difluoroketene from readily accessible difluorobromoacetylsilane as the one-carbon building block. This method features simple operation, mild reaction conditions, and broad substrate compatibility with respect to amidoximes. Furthermore, the practicality and robustness of this protocol are further underscored by successful gram-scale reactions and downstream synthetic transformations.