Asymmetric Catalytic Synthesis of -Aryl--Hydroxy Esters with Chiral Rhodium-NHC type Catalysts

Abstract

Herein we describe for the first time the enantioselective catalytic arylation of ethyl glyoxalate using phenylboron reagents and chiral rhodium(I)-NHC catalysts. (KOBu)-Bu-t was the base of choice, along with tert-amyl alcohol as the solvent. A novel chiral bis-imidazolium salt was synthesized and evaluated for the first time in this catalytic transformation. Although moderate enantioselectivities (up to 34% ee) were obtained for the phenylation reaction, despite the excellent yields, very low enantioselectivities were obtained using other arylboronic acids with a variety of chiral rhodium(I)-NHC catalysts.