Electrophilicity of α-oxo gold carbene intermediates: halogen abstractions from halogenated solvents leading to the formation of chloro/bromomethyl ketones

Abstract

α-Oxo gold carbenes generated via intermolecular oxidation of terminal alkynes are shown to be highly electrophilic and can effectively abstract halogen from halogenated solvents such as 1,2-dichloroethane or 1,2-dibromoethane. Chloro/bromomethyl ketones are prepared in moderate efficiencies in one step using Ph(3)PAuNTf(2) as the catalyst and 8-methylquinoline N-oxide as the oxidant.

Gold‐Catalyzed Redox Synthesis of Imidazo[1,2‐a]pyridines using Pyridine N‐Oxide and Alkynes

“…The resulting vinylgold intermediate can rearrange to form a gold-carbenoid intermediate. [24] This intermediate may form an α-chloro and α-mesylate ketones [25] that are known to be converted to imidazo[1,2- a ]pyridine; however, neither of these α-functionalized ketones were detected in our investigations. In contrast, the mass consistent with the proposed pyridinium intermediate in Scheme 3 was identified by crude LCMS analysis of the reaction mixture.…”

Gold-catalyzed regioselective oxidation of propargylic carboxylates: a reliable access to α-carboxy-α,β-unsaturated ketones/aldehydes

“…By using pyridine N- oxides [1] and later 8-substituted quinoline N -oxides [2] as the external oxidants, this approach permits a safe and efficient access to α-oxo gold carbenes without resorting to the dediazotization strategy [3–5] using hazardous and potentially explosive diazo substrates (Scheme 1). Since then an array of versatile synthetic methods has been developed based on the general approach by us [2,6–12] and other researchers [13–20], thus making it an exciting area for further advancing gold chemistry.…”

Meeting the Challenge of Intermolecular Gold(I)‐Catalyzed Cycloadditions of Alkynes and Allenes

“…The oxidation of alkynes coordinated to gold(I) complexes using pyridine- or quinoline- N -oxide-type oxidants has been proposed to form highly electrophilic α-oxo gold(I)–carbenes 47. 48 The synthesis of α-functionalized ketones through this process circumvents the use of hazardous α-diazoketones.…”

“…48 The synthesis of α-functionalized ketones through this process circumvents the use of hazardous α-diazoketones. The resulting α-oxo gold–carbenes can be trapped intramolecularly by formal O–H,47a, 49 N–H,50 and C–H48b, 51 insertions or by other nucleophilic partners 52. 53 However, it is important to note that in other related cases, the initial involvement of α-oxo gold(I)–carbene has been questioned 54.…”