Regioselective
CH Bond Activation on Stabilized Nitrogen
Ylides Promoted by Pd(II) Complexes: Scope and Limitations
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Abstract
The orthopalladation of N-ylides [H<sub><i>x</i></sub>C<sub><i>y</i></sub>N–CHC(O)Ar] (H<sub><i>x</i></sub>C<sub><i>y</i></sub>N = pyridine, benzylamine,
imidazole,
aniline, and phenylpyridine; Ar = aryl) has been studied. The incorporation
of the Pd atom to these substrates is regioselective, since the orthopalladation
is produced, in most of the cases, only at the aryl ring of the benzoyl
group with concomitant C-bonding of the N-ylide. The X-ray structure
of one representative example is reported. Factors governing the observed
orientation are discussed, because this regioselectivity is worthy
of note, considering the deactivating nature of the carbonyl group.
Two exceptions to the general trend have been observed. The first
one is the double metalation of the ylide [PhMe<sub>2</sub>NCHC(O)Ph],
which incorporates one Pd at each Ph. The second one is the palladation
of the phenylpyridine derivative, which occurs at the pyridinic 2-phenyl
ring and produces a six-membered palladacycle
