Co-metal-free enantioselective conjugate addition reactions of zinc reagents.
Asymmetric conjugate addition of diethylzinc to cinnamaldehyde in a co-metal-free fashion by using N,O-ligands with planar and central chirality is described. Different modulations of the ligand structure, including several combinations of the chiral units, indicate that a [2.2]paracyclophane backbone is essential for the activity and the enantioselectivity of the generated active catalyst. By using the optimized ligand, an isolated yield of 90 % was obtained with up to 99 % ee.
Ay
Sefer
S
Institute of Organic Chemistry, University of Karlsruhe (TH), Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany.
Nieger
Martin
M
Bräse
Stefan
S