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Pd-catalyzed arylation of silyl enol ethers of substituted alpha-fluoroketones.

Organic & biomolecular chemistry (2009-04-04)
Yong Guo, Brendan Twamley, Jean'ne M Shreeve
ABSTRACT

Alpha-fluoro-alpha-aryl-ketones were synthesized by the Pd-catalyzed cross-coupling of aryl bromides with either alpha-fluoroketones or their corresponding silyl enol ethers. The direct arylation with an alpha-fluoroketone requires a strong base, such as potassium tert-butoxide, and under these conditions the presence of a base-sensitive functional group is not compatible. However, good functional tolerance was achieved when the anionic coupling moieties were generated from the silyl enol ethers obtained by reacting alpha-fluoroketones with tetrabutylammonium (tripheny1silyl)difluorosilicate (TBAT) as the fluoride source under nearly neutral conditions. The aryl halides with a carbmethoxy, nitro, cyano or carbonyl group were used. The reaction with nonfluorinated silyl enol ether 1h gave a cross-coupling product in low yield.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Potassium tert-butoxide solution, 1.0 M in THF
Sigma-Aldrich
Potassium tert-butoxide, sublimed grade, 99.99% trace metals basis
Sigma-Aldrich
Potassium tert-butoxide, reagent grade, ≥98%