Cobalt(II)-catalyzed remote C5-selective C-H sulfonylation of quinolines via insertion of sulfur dioxide

A novel and simple method for C-H sulfonylation of quinolines based on an inexpensive cobalt catalyst via insertion of sulfur dioxide is established. Excellent selectivity in the C5-position of quinolines is observed. This transformation has no need of oxidant and additive, affording sulfonated products in moderate to good yields. Furthermore, aromatic amines can displace aryldiazonium tetrafluoroborates as original materials via the in situ diazotization. The results of control experiments indicate that a radical pathway is involved in this sulfonylation.