Reaction of some 4,6-dimethoxyindoles with nitric acid: nitration and oxidative dimerisation

Some 3-substituted-4,6-dimethoxyindoles can be nitrated using nitric acid in acetonitrile, to give 7-nitro and 2-nitro-indoles. Some undergo oxidative dimerisation at C7, if 2,3-disubstituted, and at C2, if N-methylated and unsubstituted at C2.