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Enantioselective Addition of Allyl Bromides to Ketones
J. J. Miller, M. S. Sigman*
University of Utah, Salt Lake City, USA
24 April 2007 (online)
As an extension of the author’s previously reported enantioselective Nozaki-Hiyama-Kishi reaction (J.-Y. Lee, J. J. Miller, S. S. Hamilton Org. Lett. 2005, 7, 1837-1839), this communication highlights the first example of a chromium-catalyzed enantioselective addition of allylic bromides to ketones. The ligand used is synthesized in three steps from a protected valine. For aryl ketones, the scope is broad and encompasses various substitution types (electron-withdrawing, -donating, or neutral) and placements (ortho, meta, or para) on the aromatic ring with good to excellent ee values and yields. Halide-substituted aryl ketones are also well tolerated. Methylallyl- and crotylbromides can also be used as the nucleophilic components; modest diastereoselection (3.8:1) is seen for crotylbromide addition. Poor enantiomeric ratios are observed for aliphatic ketones and the facial selectivity is reversed.