Norbornene hydroarylation catalyzed by ferrocene palladacycle complexes

The ligand (-)-2D-hydroxypinan-3-one diphenylmethylimine was synthesized and studied. New dinuclear CN-palladacycles and their mononuclear triphenylphosphine derivatives were obtained. It was shown that ortho-palladation of terpene diphenylmethylimines produced pure stereoisomers.Natural monoterpenoids that are isolated from renewable plant sources are convenient chiral starting materials for synthesizing important classes of compounds, in particular, for preparing chiral cyclopalladated complexes, which are being applied more and more widely in asymmetric synthesis [1,2]. They were used successfully as catalysts for cross-coupling reactions [3,4], alkene hydroarylation [5], and allyl alkylation [6].We selected the bicyclic monoterpenoids D-pinene and camphor as the starting materials for synthesizing homochiral ligands. This was due to their commercial availability and facile chemical modification. It was especially noteworthy that ligands could possibly be obtained as pure enantiomers.Oxidation of (+)-D-pinene produced (-)-2D-hydroxypinan-3-one (1) [7], condensation of which with diphenylmethylamine synthesized the (1S,2S,5S)-diphenylmethylimine (2) in 54% yield (Scheme 1). We reported previously the synthesis of the (1R,2R,5R)-enantiomer of 2D-hydroxypinan-3-one diphenylmethylimine [8].Cyclopalladation of 2D-hydroxypinan-3-one and camphor benzylimines was studied before [8-10]. The 2D-hydroxypinan-3-one derivatives, in contrast with bornane ligands, were rather easily cyclopalladated upon reaction with Li 2 PdCl 4 . The new dinuclear palladacycle 3 was synthesized in 58% yield under these conditions (Scheme 1).The structure of 3 was confirmed by NMR spectroscopy. The ortho-disubstituted aromatic ring was identified by characteristic NMR resonances in the region of aromatic protons that included four non-equivalent proton resonances with a characteristic splitting. The multiplicity and integrated intensity of proton resonances for the second mono-substituted benzene ring persisted in the PMR spectra.

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“…They were used successfully as catalysts for cross-coupling reactions [3,4], alkene hydroarylation [5], and allyl alkylation [6].…”

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confidence: 99%