Cobalt-Catalyzed C-H Nitration of Indoles by Employing a Removable Directing Group.

A mild and efficient C(sp2 )-H nitration of 3-substituted indoles, by using the economical and non-toxic cobalt nitrate hexahydrate [Co(NO3 )2 ⋅6 H2 O] as a catalyst and tert-butyl nitrite (TBN) as the nitro source, is reported. This approach provides a unique methodology involving a site-selective C-N bond formation for preparation of C-2 substituted nitro indoles. Utilization of the tBoc as the removable directing group enhances the synthetic utility of the method.