ORGN 175 |
Asymmetric synthesis of highly substituted 1,2-dihydroquinolines and 2H-1-benzopyrans via chiral nonracemic palladacycles with a metal-bonded stereogenic carbon
| Helena C. Malinakova and Genliang Lu. Department of Chemistry, University of Kansas, 1251 Wescoe Hall Drive, 2010 Malott Hall, Lawrence, KS 66045 |
Transition metal-mediated reactions provide powerful tools for the construction of carbon-carbon bonds. Traditionally, intermediates possessing a sp2-hybridized metal-bonded carbon participate in these transformations. A new strategy would arise, if organometallics featuring a metal-bonded sp3-hybridized stereogenic carbon could be generated in a high enantiomeric purity from achiral organic substrates, and subsequently participate in the formation of new carbon-carbon bonds with retention of the stereochemical information. Aiming to validate this concept, we have been exploring asymmetric synthesis of stable palladacycles 1, and the development of their synthetic applications. Herein, we describe studies on the mechanism of asymmetry transfer from homochiral ligands L (N,N,N’N’-tetramethyl-(1R,2R)-diaminocyclohexane) into the metal-bonded sp3-hybridized stereogenic carbon in oxa- and azapalladacycles 1. Palladacycles 1 generated in 60-92% de, participated in a regioselective reaction with unsymmetrical activated alkynes to afford good yields of contiguously substituted 2H-1-benzopyrans 2 in 30-60% ee, and 1,2-dihydroquinolines 2 in 80-92% ee.  |
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