Synthesis of Trifluoromethyl Ketones by Palladium-Catalyzed Cross-Coupling Reaction of Phenyl Trifluoroacetate with Organoboron Compounds

Abstract

Cross-coupling reaction of aryl trifluoroacetates with organoboron compounds catalyzed by palladium complexes gives trifluoromethyl ketones in moderate to excellent yields under mild conditions. The catalytic process has been designed on the basis of fundamental studies dealing with oxidative addition of phenyl trifluoroacetate to a Pd(0) complex to give a (phenoxo)(trifluoroacetyl)palladium(II) complex and its subsequent reaction with phenylboronic acid to liberate phenyl trifluoromethyl ketone. The catalytic cycle is proposed to be composed of (a) oxidative addition of the ester to give acyl(aryloxo)palladium intermediate, (b) the subsequent transmetallation with arylboron compounds, and (c) reductive elimination. Palladium(0) complexes, as well as catalysts prepared in situ from palladium acetate and 3 molar amounts of tributylphosphine or phosphite at room temperature, serve as convenient and effective catalysts. The process is applicable to a wide range of phenyl- and naphthylboronic acids to give various aryl trifluoromethyl ketones under mild conditions. Aryl perfluoroalkyl ketone derivatives can be similarly prepared in high yields from various phenyl perfluoroalkanecarboxylates and arylboronic acids.

Metal‐Catalyzed Cross‐Coupling Reactions of Organoboron Compounds with Organic Halides

“…The reactions of allyl acetate or phenoxide [108], propargyl carbonates [109], 1,3-butadiene monoxide [110], phenyl trifluoroacetate [111], and carboxylic acid anhydrides [112] proceed in the absence of bases, because oxidative addition yields RO-Pd species (87)(88)(89)(90)(91) which can transmetallate with organoboron compounds. Among these intermediates, the reaction of phenylboronic acid with 91 has been shown to occur at room temperature under neutral conditions [111]. PMe 3 is not suitable for the catalytic process, but it is an excellent ligand to prepare phosphine-bound model intermediates due to its high basicity and small steric hindrance toward oxidative addition.…”

Cross-coupling reaction of organoboron compounds via base-assisted transmetalation to palladium(II) complexes

“…Cross-coupling reactions of allyl phenoxide [22], propargyl carbonates [23], 1,3-butadiene monoxide [24], and phenyl trifluoroacetate [25] were carried out in the absence of a base. Such transmetalation may involve a rate-determining coordination of the R"O ligand to the boron atom [23].…”

Synthetic Design of Carbonyl-Group-Containing Compounds Based on C−O Bond Cleavage Promoted by Pd Complexes

“…As discussed in the previous section dealing with stoichiometric processes involving the acylÀO bond cleavage, aryl trifluoroacetates oxidatively add to the reactive, coordinatively unsaturated complex [Pd(styrene)(PMe 3 ) 2 ] to give trans-(aryloxo)(trifluoroacetyl)bis(trimethylphosphine)palladium(II) complexes (Scheme 4). Scheme Treatment of the (trifluoroacetyl)palladium complex with phenylboronic acid was found to afford phenyl trifluoromethyl ketone probably through transmetallation and the ensuing reductive-elimination processes (Scheme 19) [50].…”