An efficient iron-catalyzed C3-selective formylation of free (N–H) or N-substituted indoles was developed by employing formaldehyde and aqueous ammonia, with air as the oxidant. This new method gave 3-formylindoles in moderate to excellent yields with fairly short reaction times. Moreover, this procedure for catalytic formylation of indoles can be applied to gram-scale syntheses.
An efficient iodine-catalyzed chemoselective 3-formylation of free (N–H) and N-substituted indoles was achieved by using hexamethylenetetramine (HMTA) in the presence of activated carbon under air atmosphere. This new method could provide 3-formylindoles in moderate to excellent yields with fairly short reaction times. Moreover, this catalytic formylation of indoles procedure can be applied to gram-scale