Synthesis of 3‐Substituted Chalcogenophene‐Fused Indoles from 2‐Alkynylindoles

Abstract The intramolecular electrophilic cyclization of 3‐organoselanyl‐2‐alkynylindoles providing the synthesis of 3‐iodo‐selenophene‐fused indoles is reported herein. The strategy was extended to the preparation of 3‐iodo‐thiophene‐fused indoles in a one‐pot iodine‐promoted thiolation of 2‐alkynylindoles, followed by an electrophilic cyclization sequence. Besides, the synthesis of 3‐butylselanyl‐selenophene‐fused indoles from 3‐butylselanyl‐2‐alkynylindoles was also developed using iron(III) chloride and dibutyl diselenide to promote the cyclization and functionalization of the heterocycle. The identification of the alkyl halide intermediate afforded evidence to the proposed mechanism, which indicated that the reactions proceed through the formation of an iodonium ion, followed by a selenium 5‐ endo ‐dig cyclization, to afford the indole derivatives. The 3‐iodo‐selenonophene‐fused indoles prepared were applied as substrates in copper‐catalyzed cross‐coupling reactions with thiols to give the Ullmann type products in good yields. magnified image