Higher-Order Cycloaddition of N-Aromatic Zwitterions and Ketenes to Access Diazepine Derivatives

A series of N-aromatic zwitterions that could undergo higher-order dipolar cycloadditions were prepared by a rhodium(II)-catalyzed reaction between heteroaromatic compounds and 1-sulfonyl-1,2,3-triazoles. NICS(0) and structural calculations revealed a strong correlation between the aromaticity and stability of N-aromatic zwitterions. The initial success of [5+2] cycloadditions of N-aromatic zwitterions and ketene is expected to advance their application in medicinal chemistry.