N-Heterocyclic carbene catalyzed base assisted C–C bond cleavage of cyclopropenones: an approach towards diastereoselective synthesis of azetidinones and benzoxazepines

Abstract

N-Heterocyclic carbene catalyzed base assisted diastereoselective ring opening of diphenyl-cyclopropenone followed by ring-closing through [3 + 1] or [3 + 4] addition with o-aminophenol furnished biologically important scaffolds azetidinones or benzoxazepines, respectively. The unique feature of this reaction is that the key intermediate acylazolium species is generated through C–C bond cleavage of cyclopropenone rather than routine substrates such as conjugated enals, ynals and acyl halides. Interestingly, this reaction involves an α-aryl substituted acylazolium species, which has never been reported so far with respect to N-heterocyclic carbene catalysis.