Frustrated Lewis Pair Catalyzed Dehydrogenative Oxidation of Indolines and Other Heterocycles.
An acceptorless dehydrogenation of heterocycles catalyzed by frustrated Lewis pairs (FLPs) was developed. Oxidation with concomitant liberation of molecular hydrogen proceeded in high to excellent yields for N-protected indolines as well as four other substrate classes. The mechanism of this unprecedented FLP-catalyzed reaction was investigated by mechanistic studies, characterization of reaction intermediates by NMR spectroscopy and X-ray crystal analysis, and by quantum-mechanical calculations. Hydrogen liberation from the ammonium hydridoborate intermediate is the rate-determining step of the oxidation. The addition of a weaker Lewis acid as a hydride shuttle increased the reaction rate by a factor of 2.28 through a second catalytic cycle.
Institute of Organic Chemistry, University of Paderborn, Warburger Strasse 100, 33098, Paderborn, Germany.
Alexander F G
AF
Maier
Institute of Organic Chemistry, University of Paderborn, Warburger Strasse 100, 33098, Paderborn, Germany.
Sebastian
S
Tussing
Institute of Organic Chemistry, University of Paderborn, Warburger Strasse 100, 33098, Paderborn, Germany.
Tobias
T
Schneider
Institute of Inorganic Chemistry, University of Paderborn, Warburger Strasse 100, 33098, Paderborn, Germany.
Ulrich
U
Flörke
Mulliken Center for Theoretical Chemistry, Institut für Physikalische und Theoretische Chemie, University of Bonn, Beringstrasse 4, 53115, Bonn, Germany.
Zheng-Wang
ZW
Qu
Mulliken Center for Theoretical Chemistry, Institut für Physikalische und Theoretische Chemie, University of Bonn, Beringstrasse 4, 53115, Bonn, Germany. grimme@thch.uni-bonn.de.
Stefan
S
Grimme
Institute of Organic Chemistry, University of Paderborn, Warburger Strasse 100, 33098, Paderborn, Germany. jan.paradies@uni-paderborn.de.
Jan
0000-0002-3698-668X
J
Paradies
1,2-dihydroquinolines; 1,4-dihydropyridines; acceptorless dehydrogenation; frustrated Lewis pairs; indolines