Palladium-Catalyzed Ligand-Controlled Regioselective Nucleophilic Aromatic Substitution of 1‑(Chloromethyl)naphthalenes with Arylacetonitriles

The
palladium-catalyzed reaction of 1-(chloromethyl)­naphthalenes 1 with (hetero)­aryl­acetonitriles 2 gives either para- or ortho-acylated
naphthalenes (3 or 4) in good to high yields.
The regioselectivity can be controlled by the ligand of a palladium
catalyst. A sterically bulky ligand, tBuPPh2, affords para-acylated products 3, whereas a sterically less bulky ligand, Me2PPh,
provides ortho-acylated products 4.
Further, direct substitution product 5 at the benzylic
position is not obtained essentially, although such a reaction at
the benzylic position is favorable in ordinary nucleophilic substitutions.
In this paper, it was revealed that the benzylpalladium intermediate
could react through a different mode (η3-benzylpalladium
intermediate or η1-benzylpalladium intermediate)
in nucleophilic aromatic substitution. In addition to the interesting
mechanistic aspect, the present reaction provides a facile synthetic
method for a wide range of diaryl ketones, some of which are not easily
available through the previously known procedures.