Cobalt-Catalyzed C8-H Sulfonylation Of 1-Naphthalamine Deritatives

An efficient protocol for cobalt-catalyzed C8-H sulfonylation of 1-naphthylamine derivative with sodium sulfonate has been developed.The reaction has good functional group compatibility and high regioselectivity.Both aromatic and aliphatic sodium sulfonate can be coupled effectively with 1-naphthylamine derivatives.Catalytic amount NFSI can remarkably improve the yield of the target product,and the addition of trace water to this reaction system can effectively reduce the generation of C4-H sulfonylation byproducts(Scheme 1).When 2 equivalent of radical inhibitor 2,2,6,6-tetramethylpiperidine N-oxide(TEMPO)was added to the system,the target product was not obtained.Similarly,2 equivalent of 2,6-ditert-butyl-4-methylphenol(BHT)could also surpress the reaction,and an adduct of BHT with benzene sulfonyl group was successfully detected by 1H NMR spectroscopy,which suggested that the reaction may involve a free radical process.In addition,the kinetic isotope experiment was also explored and KIE value(1.3)indicated that C8-H bond activation step may not be the rate-determining step.