7‐Oxa‐4‐thia‐1‐aza‐bicyclo[3.2.1]octane 4,4‐Dioxides: Mechanochemical Synthesis by Tandem Michael Addition–1,3‐Dipolar Cycloaddition of Aldoximes and Evaluation of Antibacterial Activities

Abstract

A solvent‐free, green, and efficient mechanochemical method for the synthesis of a series of bridged bicyclo aza‐sulfone derivatives, namely 7‐oxa‐4‐thia‐1‐aza‐bicyclo[3.2.1]octane 4,4‐dioxides through tandem Michael addition–1,3‐dipolar cycloaddition of aldoximes was developed. Mechanochemical grinding/milling facilitates quick formation of aldoximes from corresponding aldehydes and hydroxylamine, which upon reaction with divinyl sulfone in a mixer mill affords 7‐oxa‐4‐thia‐1‐aza‐bicyclo[3.2.1]octane 4,4‐dioxide derivatives in good overall yields. The newly synthesized bicyclo aza‐sulfone derivatives 4 were screened for antibacterial activities. Mostly bicyclo aza‐sulfones derived from electron‐rich aromatic aldehydes inhibit the growth of Mycobacterium smegmatis (mc2155) and those from aliphatic aldehydes the growth of Escherichia coli (DH5α) in moderate to good effect. However, butyraldehyde‐derived compound 4r was very effective against both M. smegmatis and E. coli. The key advantages of this mechanochemical method are catalyst‐ and solvent‐free conditions, shorter reaction time, and formation of a new series of 7‐oxa‐4‐thia‐1‐aza‐bicyclo[3.2.1]octane 4,4‐dioxide derivatives, which are good antibacterial agents against M. smegmatis and E. coli.