Chiral dirhodium(II) carboxamidate-catalyzed [2+2]-cycloaddition of TMS-ketene and ethyl glyoxylate

The [2+2]-cycloaddition reaction between ethyl glyoxylate and trimethylsilylketene is reported. Enantiomeric excesses up to 83% have been achieved with the use of only 1.0 mol % of a previously unreported chiral imidazolidinone-ligated dirhodium(II) carboxamidate catalyst. An extensive survey of chiral catalysts has shown that enantiocontrol for cycloaddition increases as the steric bulk of the ligand is increased. However, enantioselectivity is increased to 99% ee by the addition of 1.0 mol % of quinine as a co-catalyst with a chiral dirhodium(II) azetidinone-ligated catalyst, and there is a significant decrease in reaction time.