Highly enantioselective michael additions of indole to benzylidene malonate using simple bis(oxazoline) ligands: importance of metal/ligand ratio.
[Structure: see text] Simple bis(oxazoline) ligands, especially azabis(oxazolines), can catalyze the copper-catalyzed addition of indoles to benzylidene malonates in up to >99% ee, provided that excess of chiral ligand is avoided. The paradigm followed in many asymmetric catalyses that an excess of chiral ligand with respect to the metal should improve enantioselectivity because a background reaction by free metal is suppressed, is not applicable here, which might call for revisiting some of the many copper(II)-bis(oxazoline)-catalyzed processes known.
Rasappan
Ramesh
R
Institut für Organische Chemie, Universität Regensburg, Universitätsstr. 31, 93053 Regensburg, Germany.
Hager
Markus
M
Gissibl
Anja
A
Reiser
Oliver
O
D001597:Benzylidene Compounds / Q000737:chemistry*; D007211:Indoles / Q000737:chemistry*; D008024:Ligands; D008670:Metals / Q000737:chemistry*; D008958:Models, Molecular; D013237:Stereoisomerism; D014961:X-Ray Diffraction
D001597:Benzylidene Compounds; D007211:Indoles; D008024:Ligands; D008670:Metals; C030374:indole