In the presence of triphenylphosphine as a mild reductant,
the
use of catalytic amounts of Mo(CO)6 and an ortho-quinone ligand enables the intermolecular reductive coupling of
aromatic aldehydes and the intramolecular coupling of aromatic ketones
to produce functionalized alkenes. Diaryl- and diheteroaryl alkenes
are synthesized with high (E)-selectivity and a tolerance
toward bromide, iodide, and steric hindrance. Intramolecular coupling
of dicarbonyl compounds under similar conditions affords mono- and
disubstituted phenanthrenes