Preparation and Addition−Elimination Reactions of Benzyl α,β,β-Trifluoroacrylate. A New Stereoselective Approach to (<i>Z</i>)-β-Substituted α,β-Difluoroacrylates
Benzyl α,β,β-trifluoroacrylate (1) was prepared in good yield via the reductive Br−F elimination of benzyl 2-bromo-2,3,3,3-tetrafluoropropanoate or the palladium-catalyzed cross-coupling reaction of 1,2,2-trifluorovinylstannane with benzyl chloroformate. On treating 1 with various Grignard reagents or dialkylzinc reagents in the presence of copper(I) salt, the corresponding β-substituted α,β-difluoroacrylates
On treating readily prepared benzyl 2,3,3-trifluoroacrylate with various Grignard reagents, e.g., aryl-, alkyl-, or alkenylmagnesium halide, in the presence of a catalytic amount of copper(I) salt in THF at -78 degrees C for 1 h, the corresponding alpha,beta-difluoroacrylates were obtained in 54-98% yields with high Z-selectivity.
Highly Diastereoselective Reductive Coupling of 2-Bromo-2,3,3,3-tetrafluoropropanamide with Aldehydes Promoted by Triphenylphosphine−Titanium(IV) Isopropoxide. An Efficient Route to the Synthesis of <i>e</i><i>rythro</i>-α-Fluoro-α-(trifluoromethyl)-β-hydroxy Amides
The reductive coupling reaction of N-methoxy-N-methyl-2-bromo-2,3,3,3-tetrafluoropropanamide (Weinreb amide) with various aldehydes under the influence of the combined reagent, 1.2 equiv each of triphenylphosphine and titanium(IV) isopropoxide, took place smoothly at ambient temperature to give the corresponding alpha-fluoro-alpha-(trifluoromethyl)-beta-hydroxy amides in a highly erythro-selective manner. The high erythro selectivity was also obtained even by employing a combination of triphenylphosphine (1.2 equiv) and a catalytic amount of titanium(IV) isopropoxide.