A Flexible and Stereoselective Synthesis of Azetidin‐3‐ones through Gold‐Catalyzed Intermolecular Oxidation of Alkynes

Optimizing P,N‐Bidentate Ligands for Oxidative Gold Catalysis: Efficient Intermolecular Trapping of α‐Oxo Gold Carbenes by Carboxylic Acids

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A few years ago we reported [1] that gold-catalyzed [2] intermolecular oxidation of alkynes offered an expedient access to synthetically versatile a-oxo gold carbene intermediates (Scheme 1 a). This strategy circumvents the use of hazardous and potentially explosive a-diazo ketone precursors [3] and has led to the development of various efficient synthetic methods, by us [1,4] and others, [5] based on intramolecular trapping of aoxo gold carbene intermediates. The intermolecular counterpart, which is likely to be of exceptional synthetic utility, however, proves to be very challenging because of the highly electrophilic nature of the carbene center and is often plagued with overoxidation, reactions with solvents, [4b,g] and intractable side reactions.

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Gold‐Catalyzed 1,2‐Oxoarylations of Nitriles with Pyridine‐Derived Oxides

“…as thriving topics in current gold and platinum catalysis. [1][2][3][4][5] These oxidations lead to 1,2-oxofunctionalization products by two paths. With pyridine-derived N-oxides, the oxidations typically generate a-oxo carbenes which can be functionalized with a tethered or external nucleophile.…”

“…With pyridine-derived N-oxides, the oxidations typically generate a-oxo carbenes which can be functionalized with a tethered or external nucleophile. [2,3] For sulfoxides and some nitrones, the initial intermediates (I and II, respectively) undergo 3,3-sigmatropic shifts to afford the 1,2-oxoarylation products 2 and 3, respectively (Scheme 1 a). [4,5] Although nitriles and alkynes are two common triple-bond motifs, catalytic oxidations of nitriles with organic or inorganic oxides still remain a formidable task.…”

“…Our initial trial with AuCl 3 (5 mol %) in hot 1,2dichloroethane (80 8C, 12 h) resulted in an incomplete conversion, from which the double oxidation product 5 a was isolated in 22 % yield, together with unreacted 4 a (55 %; entry 1). We switched to cationic gold catalysts such as PPh 3 AuCl/AgSbF 6 , P(tBu) 2 (o-biphenyl)AuCl/AgSbF 6 , and IPrAuCl/AgSbF 6 (IPr = 1,3-bis(diisopropylphenyl)imidazol-2-ylidene), which provided 5 a in 48, 75, and 82 % yield, respectively (entries [2][3][4]. Different counter anions to IPrAuCl/AgX (X = OTf and NTf 2 ) maintained satisfactory product yields (entries 5 and 6).…”

Gold‐Catalyzed 1,2‐Oxoarylations of Nitriles with Pyridine‐Derived Oxides

“…[1][2][3][4][5] These oxidations lead to 1,2-oxofunctionalization products by two paths. [1][2][3][4][5] These oxidations lead to 1,2-oxofunctionalization products by two paths.…”