Download or read book Applications of Planar-chiral Heterocycles in Asymmetric Catalysis written by Beata Tao and published by . This book was released on 2002 with total page 440 pages. Available in PDF, EPUB and Kindle. Book excerpt: (Cont.) By increasing the steric demand of the bottom ring, we found that the selectivity increases significantly. Thus, bulky derivative 3c affords 92% ee in the ring opening of cis-stilbene oxide at -85 C.A number of epoxides can be desymmetrized in very good yield and high stereoselectivity under these conditions (up to 98% ee). ... In addition, we have also synthesized a new family of planar-chiral N, P-ligands (4). The ligand design allows incorporation of different substituents on the phosphorus atom and on the C5R5 bottom ring, thereby providing a means for tuning catalyst enantioselectivity. We chose the asymmetric hydrosilylation of ketones to test the effectiveness of our ligand design. In general, sterically demanding silanes such as MesPhSiH2 and (o-tol)2SiH2 furnish better enantioselectivities than simple silanes like Ph2SiH2. Among the planar-chiral ligands tested, we found that ligand 4a gives the best yields and enantioselectivities for a wide array of substrates (arylalkyl ketones: up to 99% ee; dialkyl ketones: up to 96% ee). Deuterated benzaldehyde-l-d can also be reduced with excellent enantioselectivity (95% ee). Access to chiral silanes is also possible using the same ligand.