Gold nanoclusters stabilized by poly(N-vinyl-2-pyrrolidone) (Au:PVP) are active and selective catalysts for N-formylation of amines under aerobic oxidation using methanol or formalin as a formyl source.Direct formation of amides from alcohols or aldehydes with amines has recently received attention from the viewpoint of the development of environmentally benign processes.1 In particular, N-formylation of amines using MeOH or formaldehyde (especially formalin) is very important. The use of simple reactants makes it possible to understand the reaction mechanism. Furthermore, the starting materials are both economical and the formamide derivatives produced in the reaction are important intermediates in organic synthesis. Until now though, only a few examples of this transformation have been reported. Cu hydroxy salts have been used in the presence of hydrogen peroxide.2 Aerobic oxidation has been achieved with nanosizedgold supported on metal oxide 3 with MeOH, and formylation of dimethylamine with formaldehyde has been carried out using metallic gold 4 or silver 5 surfaces as a catalyst. Practical procedures for N-formylation by aerobic oxidation that tolerate a wide scope of amines are still needed.Nanosized-gold metal has recently attracted a great deal of interest because of its high activity 6 and potential application in the emerging area of green oxidation chemistry. We have recently demonstrated that gold nanoclusters stabilized by poly(N-vinyl-2-pyrrolidone) (Au:PVP) act as an excellent quasi-homogenous catalyst for the aerobic oxidation of benzylic alcohols, 7 generation of H 2 O 2 in the presence of ammonium formate, 8 homocoupling reaction of arylboronic acids, 9 and other cyclization reactions.10 Herein, we wish to report highly selective direct Nformylation using MeOH or formalin as a formyl source in the presence of Au:PVP under aerobic conditions. Given our recent achievements in the aerobic oxidation of alcohol by Au:PVP, 7 we decided to conduct an N-formylation reaction similar to those used for methanol oxidation. NFormylation of N-methylaniline was screened in MeOH/H 2 O and the results are listed in Table 1.The reaction did not proceed without either base (Entry 1) or Au:PVP (Entry 2). The basic conditions are important for oxidation of MeOH to generate the key intermediate for Nformylation. The best results were obtained when 200 mol % of LiOH was used and LiOH was included in all further reactions. 11Reaction temperature was then evaluated. The reaction proceeded smoothly in the presence of 10 atom % of Au:PVP under reflux conditions (Entry 3), 12 giving N-formyl-N-methylaniline (2a) in 94% yield along with the formation of N-formylaniline (3a) in 5% yield, which is produced via oxidative demethylation followed by N-formylation. The reaction also proceeded at 50°C and the yields of the products, 2a, 3a, and aniline (4a) after 4 h were 80%, 2%, and 2% yields, respectively with 1a also recovered in 16% yield (Entry 4). No reaction was observed at 27°C (Entry 5). The importance of water and the ...

Gold nanoclusters stabilized by poly(N-vinyl-2-pyrrolidone) (Au:PVP) are active and selective catalysts under aerobic conditions for oxidation of cyclic secondary amines at the a-position of the nitrogen atom. The catalyst accelerates the formation of the imines by oxidation of the amines in aqueous solvent to afford the corresponding lactams.

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For the title reaction an active and selective catalyst is presented under basic conditions.

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