A Ruthenium Catalyst with Unprecedented Effectiveness for the Coupling Cyclization of γ‑Amino Alcohols and Secondary Alcohols

The
ruthenium complex (8-(2-diphenylphosphinoethyl)­aminotrihydroquinolinyl)­(carbonyl)­(hydrido)­ruthenium
chloride exhibited extremely high efficiency toward the coupling cyclization
of γ-amino alcohols with secondary alcohols. The corresponding
products, pyridine or quinoline derivatives, are obtained in good
to high isolated yields. On comparison with literature catalysts whose
noble-metal loading with respect to γ-amino alcohols reached
0.5–1.0 mol % for Ru and a record lowest of 0.04 mol % for
Ir, the current catalyst achieves the same efficiency with a loading
of 0.025 mol % for Ru. The mechanism of acceptorless dehydrogenative
condensation (ADC) was proposed on the basis of DFT calculations;
in addition, the reactive intermediates were determined by GC-MS,
NMR, and single-crystal X-ray diffraction. The catalytic process is
potentially suitable for industrial applications.