Pd-Catalyzed α-Arylation of Trimethylsilyl Enol Ethers with Aryl Bromides and Chlorides: A Synergistic Effect of Two Metal Fluorides as Additives

✍ Scribed by Weiping Su; Steven Raders; John G. Verkade; Xuebin Liao; John F. Hartwig

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 127 KB
• Volume: 118
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/ange.200601887

✦ Synopsis

Ketone enolates are among the most common nucleophiles in organic chemistry, and transition-metal-catalyzed cross-coup ling reactions are among the most commonly used catalytic processes. [1] However, the combination of these two chemistries-cross-coupling of enolate nucleophiles-has been developed only recently. [2-6] Moreover, coupling of silyl enol ethers, which temper the high basicity and nucleophilicity of alkali metal enolates, [7] is undeveloped. [8-11] The first example of the cross-coupling of silyl enol ethers was reported in 1982 by Kuwajima and Urabe, and the reactions of related tin enolates were reported by Kosugi and co-workers in 1984. [9] The reactions of silyl enol ethers were limited to the enolates of methyl ketones, and the activation of the silyl enol ether was conducted with stoichiometric tributyltin fluoride. Over the next twenty years, the scope and utility of the coupling of silyl or stannyl enol ethers has advanced only slightly. [10-12] The cross-coupling of silyl enol ethers offers several advantages over the coupling of alkali-metal enolates of ketones. The reduced basicity should improve functionalgroup compatibility; the defined structure of the main-group enolate could allow coupling at the more hindered site of a ketone with two enolizable positions; and conditions for the coupling of silyl enol ethers could ultimately allow the development of enantioselective processes to form acidic tertiary stereocenters.