Silica-supported ceric ammonium nitrate catalyzed chemoselective formylation of indoles

Selective formylation of free (N-H) indoles at C3 can be achieved by using formylating species generated from hexamethylenetetramine (HMTA) and silica-supported ceric ammonium nitrate (CAN-SiO2). The use of a catalytic amount of this solid-supported reagent was found to be compatible with a range of substituents on the indoles and generated the corresponding products with good yields. A plausible mechanism for the formylation involving an electron transfer process is discussed. (C) 2014 Elsevier Ltd. All rights reserved.