Zinc-mediated Coupling Reaction of 2-Bromo-2,3,3,3-tetrafluoropropanoate with Various Chiral Imines. Simple and Effective Access to Optically Active α-Fluoro-α-(trifluoromethyl)-β-amino Esters
The reactions of benzyl 2-bromo-2,3,3,3-tetrafluoropropanoate with various types of chiral imines in the presence of zinc in THF at room temperature were revealed to afford the threo- and erythro-isomers of α-fluoro-α-(trifluoromethyl)-β-amino esters with high diasteremeric excesses in fair to good chemical yields.
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.