Lewis Acid Character of Zero-valent Gold Nanoclusters under Aerobic Conditions: Intramolecular Hydroalkoxylation of Alkenes

Abstract

Gold nanoclusters stabilized by poly(N-vinyl-2-pyrrolidone) (Au:PVP NCs, φ = 1.3 nm) behave as Lewis acid catalyst in aqueous media under aerobic conditions, to promote the intramolecular hydroalkoxylation of unactivated alkenes. Molecular oxygen generates a reaction center having the Lewis acidic character on the surface of Au NCs in which constituent gold atoms are formally in zero-valence state.

Gold Nanoclusters as a Catalyst for Intramolecular Addition of Primary Amines to Unactivated Alkenes under Aerobic Conditions

“…As proposed in previous studies, 1,7,11,12 the reaction is initiated by the adsorption of O 2 onto the surface of the Au nanoclusters as a key intermediate (A) that possesses electrondeficient site (Scheme 1). The most important difference from the previous reactions, such as cyclization of alcohols and toluenesulfonamides, is that the reaction should be carried out under neutral to slightly acidic conditions.…”

“…To elucidate the hydrogen source for the product and the role of the formic acid derivatives, 1a was treated with 1000 mol % of HCO 2 NH 4 or DCO 2 NH 4 in D 2 O and/or EtOH-d 6 (condition A), and the results are listed in Table 3. For the cyclization of alcohol 11 and toluenesulfonamide, 1 the hydrogen at the terminal methyl group of the products was introduced from the formyl group of DMF and the ethyl group of EtOH, both of which were used as a solvent, respectively. In contrast, EtOH was not a major hydrogen source in the case of the primary amines, as shown in Entries 13.…”

Catalytic activity of gold nanoclusters in intramolecular hydroamination of alkenes and alkynes with toluenesulfonamide under aerobic and basic conditions

“…In fact, cyclization did not occur under carefully degassed conditions, or with the use of larger clusters of Au:PVP (average size: 9.5 nm), which indicates that molecular oxygen plays an essential role in both the hydroamination and hydroalkoxylation reactions (Eq. (3)) [3].…”

“…The first example reaction was the intramolecular hydroalkoxylation of unactivated alkenes (Eq. (1)) [3]. The reaction was carried out under aerobic and basic conditions similar to those used in typical aerobic oxidation reactions [4].…”

Aluminium Triflate Catalysed Cyclisation of Unsaturated Alcohols: Novel Synthesis of Rose Oxide and Analogues

“…[2] These atom-economic processes, known to be catalysed by Brønsted acids in super-stoichiometric amounts, have been recently reported by the use of strong Lewis acids in catalytic amounts. [3] Thus, Sn IV [4] and Al III [5] triflates as well as Pt II /PR 3 , [6] Fe III [7] and Au derivatives [8] have shown interesting catalytic activities in the formation of cyclic ethers from nonactivated olefins. The high activity of the metallic triflate catalysts is due to the strongly electron-withdrawing trifluoromethanesulfonate group.…”