Gold-Catalyzed Intermolecular Oxidation of Terminal Alkynes: Simple and Efficient Synthesis of α-Mesyloxy Ketones

Abstract

A variety of terminal alkynes were efficiently converted into the corresponding α-mesyloxy ketones through gold-catalyzed intermolecular oxidation in the presence of 3,5-dichloropyridine N-oxide as the oxidant. The reaction is proposed to proceed via α-oxo gold carbene intermolecular O–H insertion.

Key words

alkynes - homogenous catalysis - gold - α-oxo gold carbine - α-mesyloxy ketones

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For some gold-catalyzed oxidative reactions, the possible alkenyl gold mechanism was also proposed, see:
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• 21 General Procedure N-Oxide 4f (0.39 mmol, 63.96 mg), MsOH (0.36 mmol, 34.60 mg) and Cy₃PAuNTf₂ (11.1 mg, 0.015 mmol) were added to a solution of the alkyne 1 (0.30 mmol) in chlorobenzene (6 mL) at r.t. The reaction mixture was stirred at r.t., and the progress of the reaction was monitored by TLC. The reaction typically took 8 h. Upon completion, the mixture was concentrated, and the residue was purified by chromatography on silica gel (eluent: hexanes–EtOAc) to afford the desired product 2. 2-Oxo-2-phenylethyl Methanesulfonate (2a) Compound 2a was prepared in 79% yield according to the general procedure and its spectroscopic data match well with with those reported. ¹H NMR (400 MHz, CDCl₃): δ = 7.90 (d, J = 8.0 Hz, 2 H), 7.66 (t, J = 8.0 Hz, 1 H), 7.52 (t, J = 8.0 Hz, 2 H), 5.53 (s, 2 H), 3.30 (s, 3 H). ¹³C NMR (100 Mz, CDCl₃): δ = 191.09, 134.41, 133.45, 129.04, 127.76, 70.19, 39.15. IR (neat): 2956, 1702, 1560, 1338, 1156, 801 cm^–1. HRMS (EI): m/z calcd for C₉H₁₀O₄S: 214.0300; found: 214.0297.