Asymmetric 1,4-Reductions of Hindered β-Substituted Cycloalkenones Using Catalytic SEGPHOS-Ligated CuH
Bruce H. Lipshutz,* Jeff M. Servesko, Tue B. Petersen, Patrick P. Papa and Andrew A. Lover
*Department of Chemistry and Biochemistry, University of California, Santa
Barbara, California 93106, Email: lipshutz
chem.ucsb.edu
B. H. Lipshutz, J. M. Servesko, T. B. Petersen, P. P. Papa, A. A. Lover, Org. Lett., 2004, 6, 1273-1275.
DOI: 10.1021/ol0400185
Abstract
Catalytic amounts of copper hydride ligated by a nonracemic SEGPHOS ligand leads in situ to an extremely reactive species capable of effecting asymmetric hydrosilylations of conjugated cyclic enones with very high enantioselectivity.
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Details
The study by Lipshutz et al. explores the use of catalytic copper hydride (CuH) ligated by a nonracemic SEGPHOS ligand for asymmetric hydrosilylations of conjugated cyclic enones. This method achieves high enantioselectivities and unprecedented substrate-to-ligand (S/L) ratios, up to 275,000:1. The research highlights the effectiveness of DTBM-SEGPHOS in accelerating these reductions, even for sterically hindered substrates, compared to other bis-phosphines. The reactions, conducted in toluene at low temperatures, yield high enantioselectivities and can be optimized further by adjusting the base-to-CuCl ratio. Alternative solvents like THF and THF/dioxane mixtures also enhance enantioselectivity. The study demonstrates that using pinocolborane instead of PMHS can simplify the process by eliminating the need for hydrolytic workup. The findings suggest that SEGPHOS-ligated CuH is a highly effective catalyst for asymmetric reductions, offering mild conditions, high yields, and superior enantioselectivities. The research was supported by the NSF and benefited from the provision of ligands by Takasago and Roche. The detailed procedures and spectral data for new products are available online.
Asymmetric 1,4-Hydrosilylations of α,β-Unsaturated Esters
B. H. Lipshutz, J. M. Servesko, B. R. Taft, J. Am. Chem. Soc., 2004, 126, 8352-8353.
Key Words
1,4-Reduction, Enones, PMHS, CuH
ID: J54-Y2004-340
