Аннотация: Previously we have shown that interaction of the simplest N,N-dimethylbenzylaminate palladacycle with chlorine dioxide results in the formation of a 3-chlorinated palladacycle instead of the expected hydroxylation product.[1] It was reasonably to assume that this transformation includes the Pd–C bond chlorination of the CN-palladacycle followed by repeated cyclopalladation of ortho-Cl-substituted ligand thus formed. This guess was verified stereochemically using optically active palladacycle (R)-1 derived from prochiral benzylamine ligand (Scheme).
At preliminary stage this reaction has been conducted on the dimer rac-1. The formation of the intermediate Pd-coordinated 2-chlorinated amine (R)-I/II and its further ortho-palladation at unsubstituted phenyl ring was unambiguously confirmed by X-ray study of the PPh3-adduct rac-2. The most important evidences in support of the proposed mechanistic pathway are: i) inversion of the alpha-C*-stereocentre configuration at the first stage of this process [from (R)-1 to (S)-2], evident from opposite sign of the specific rotation, and ii) its complete racemization at the second step of the prochiral 2,2'-dichlorinated benzylamine cyclopalladation [from (S)-2 to (R,S)-3] ([alpha]D = 0).
Authors thanks RFBR grant 04-03-32986-a, for financial support of this research.
[1]. Dunina V.V., Gorunova O.N., et al, Russ. Chem. Bull. 2005, 54, 2073-2082.