<i>Tropos</i>Ligands in Asymmetric Rhodium(I)-Catalyzed Addition of Arylboronic Acids to Enones: How a Tunable Coordination Gives Different Reaction Products

Abstract

Different tropos deoxycholic acid derived biphenylphosphites were used as Rh(I) chiral ligands, at P/Rh 1:1 and 2:1 molar ratios, to obtain mono- or disubstituted Rh(I) complexes, which act as catalytic precursors in the asymmetric conjugate addition of arylboronic acids to cyclic enones, giving the addition products in high to quantitative yields and ee’s up to 92%. In addition, using an excess of arylboronic acid only the disubstituted complexes gave diastereomerically pure 1,3-diarylcyclohexanols with ee’s up to 94%. The tropos nature of the complexes, as well as the coordination mode, was investigated by 31P NMR spectroscopy. A disubstituted rhodium complex was isolated, and its X-ray molecular structure was determined.