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
The simultaneous construction of both rings of indole from primary amines and MBH acetate of cyclohexenone is established. This method employed montmorillonite K10 as a cheap catalyst and diethyl carbonate as a green solvent. The scope of the reaction was scouted, in which 37 N-substituted indoles including 1,1′-bisindole were obtained.