Selective Cross-Dehydrogenative Coupling of N-Phenyltetrahydroisoquinolines in Aqueous Media Using Poly(Aniline Sulfonic Acid)/Gold Nanoparticles

Abstract

Selective cross-dehydrogenative coupling ofN-phenyltetrahydroisoquinoline with carbon nucleophiles such as dimethyl malonate, ethyl acetoacetate, and nitromethane was demonstrated in complete aqueous media using poly(2-methoxyaniline-5-sulfonic acid)/gold nanoparticles under molecular oxygen.Catalytic oxidative C-H bond functionalizations, particularly C-C bond forming reactions, have attracted significant interest. 1Among them, catalytic cross-dehydrogenative coupling of tert-amines such as N-phenyltetrahydroisoquinoline (1) with carbon nucleophiles has received much attention. 2Concerning about the terminal oxidant, molecular oxygen is favorable due to the following reasons: available from atmosphere, low cost, easy separation, low toxic, ecological, safer than peroxides, and so on.Some transition metals such as Cu catalyze this reaction effectively under molecular oxygen. 3Recently, it was revealed that gold nanoparticles (Au NPs) exhibit efficient catalytic activity. 4This reaction is considered to involve the oxidation of tert-amine 1 to produce the iminium cation species 2, and the subsequent nucleophilic addition, giving the corresponding product.The byproducts of this reaction are just water and/or hydrogen peroxide when molecular oxygen is employed as a terminal oxidant.Therefore, this reaction is considered to be atom economic.On the other hand, organic reactions in aqueous media are required for sustainable chemistry. 5From this point of view, the difficulty of this cross-dehydrogenative coupling is much raised because water can attack to the iminium cationic intermediate 2 and the further oxidation of 3 leads to the lactam 4 (Scheme 1).In fact, only a few examples have achieved the selective