Complexes of Schiff bases and intermediates in the copper-catalyzed oxidative heterocyclization by atmospheric oxygen.
After complexation with copper(II) ions, Schiff bases 1a-d may undergo an oxidative ring closure using atmospheric oxygen to give a number of imidazo[1,5-a]pyridines 2, an imidazo[1,5-a]imidazole 3, and an imidazo[5,1-a]isochinoline 4. This ligand oxidation can be performed with catalytic amounts of copper ions in the reaction. A catalytic cycle for the copper-catalyzed oxidative heterocyclization will be presented together with isolated copper complexes of Schiff bases 1a,b and intermediates 5 and 8 that were found by X-ray structure analyses which confirm this reaction scheme.
Bluhm
Martin E
ME
Institute for Technical Chemistry (ITC-CPV), Forschungszentrum Karlsruhe, P.O. Box 3640, 76021 Karlsruhe, Germany.
Ciesielski
Michael
M
Görls
Helmar
H
Walter
Olaf
O
Döring
Manfred
M
D002384:Catalysis; D003300:Copper / Q000737:chemistry*; D003500:Cyclization; D007093:Imidazoles / Q000138:chemical synthesis*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D011725:Pyridines / Q000138:chemical synthesis*; D012545:Schiff Bases / Q000737:chemistry; D014961:X-Ray Diffraction
D007093:Imidazoles; D011725:Pyridines; D012545:Schiff Bases; D003300:Copper; D010100:Oxygen