Palladium-Catalyzed Asymmetric Arylation, Vinylation, and Allenylation of tert-Cyclobutanols via Enantioselective C−C Bond Cleavage

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Abstract
A novel enantioselective C−C bond cleavage has been achieved using palladium catalysts and chiral N,P-bidentate ligands in the asymmetric arylation, vinylation, and allenylation of tert-cyclobutanols. In these reactions, the enantioselective β-carbon elimination of Pd(II) alcoholate formed in situ is the key step. Treatment of tert-cyclobutanols with arylating reagents in toluene in the presence of Pd(OAc)2, a chiral ferrocene-containing N,P-bidentate ligand, and Cs2CO3 affords optically active γ-arylated ketones in excellent yields with high enantioselectivity (up to 95% ee). When vinylating reagents are used in place of arylating ones, the asymmetric vinylation also proceeds to afford optically active γ-vinylated ketones in high yields with good to high enantioselectivity. When propargylic acetates are used, which are known to generate (σ-allenyl)palladium complexes with Pd(0) species, asymmetric allenylation occurs to afford optically active γ-allenylated ketones in moderate to good yields with moderate to high enantioselectivity.

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