Palladium‐Catalyzed Enantioselective Domino Heck–Cyanation Sequence: Development and Application to the Total Synthesis of Esermethole and Physostigmine

Abstract

An efficient synthesis of functionalized 3-alkyl-3-cyanomethyl-2-oxindole 1 by a palladium-catalyzed domino Heck–cyanation reaction has been developed. Reaction of ortho-iodoanilide 5 with potassium ferro(II)cyanide, K₄[Fe(CN)₆], dissolved in DMF in the presence of palladium acetate and sodium carbonate afforded oxindole 1 in good to excellent yields. An enantioselective domino Heck–cyanation process has been developed for the first time using (S)-DIFLUORPHOS as a chiral supporting ligand, and an enantioselectivity of up to 79 % ee in the enantiomerically enriched oxindole was obtained under optimized conditions. A concise total synthesis of esermethole and physostigmine, powerful inhibitors of acetyl- and butyryl-cholinesterase, is documented.