Silver-catalyzed carboxylative cyclization of alkynic hydrazones with carbon dioxide

Abstract

The development of new catalytic methodologies to synthesize heterocyclic fine chemicals using carbon dioxide as a synthon has attracted considerable attention. Herein, we report the silver(I)-catalyzed carboxylative cyclization of a variety of alkynic hydrazones with carbon dioxide to produce the corresponding 1,3,4-oxadiazin-2-ones under mild reaction conditions. In this reaction, silver(I) salts play a π-Lewis acid role for the highly efficient activation of the alkyne moiety in the hydrazone substrates. Single-crystal X-ray analysis and NOE experiments confirm that the newly formed oxadiazinone products exhibit Z configuration. Based on control experiments and NMR studies, a mechanism including the formation of a reactive carbazate intermediate, electrophilic cyclization, and subsequent protonation is proposed. This study offers an efficient and atom-economical method for the synthesis of biologically important 1,3,4-oxadiazin-2-ones.