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, K(4)[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.
[reaction: see text] A highly efficient palladium-catalyzed synthesis of unsymmetrically substituted 3-(diarylmethylenyl)indolinones from readily accessible starting materials is developed. The domino reaction involves a sequence of intermolecular carbopalladation, C-H activation, and C-C bond formation. A plausible mechanistic pathway for the reaction is discussed on the basis of the kinetic isotope effect [K(H)/K(D) (intermolecular) = 1, K(H)/K(D) (intramolecular) = 2.7] as well as the electronic effect.
3‐3‐1 Formation: [Pd(PPh3)4]/CuI serves as an efficient catalyst for the reaction of three readily available starting materials to give 3‐(diarylmethylene)indolin‐2‐ones 3 through a sequence of intermolecular Sonagashira reaction/intermolecular carbopalladation/CH activation/CC bond formation (see scheme). Three CC bonds are thereby formed as a result of three distinct catalytic cycles with one catalyst. DMF=N,N‐dimethylformamide.
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