The palladium-catalyzed arylation of alpha,alpha-disubstituted arylmethanols with aryl halides proceeds not only via C-H bond cleavage at the ortho-position, but also via cleavage of the sp(2)-sp(3) C-C bond with the liberation of ketones (beta-carbon elimination) to give the corresponding biaryls. Both reactions appear to occur through common arylpalladium(II) alcoholate intermediates. The results of systematic studies with respect to which C-C or C-H bond is preferentially cleaved in the arylation are reported. Among the important findings is the selective elimination of ortho-substituted aryl groups even from aryl(diphenyl)methanols due to steric reasons. Thus, various biaryls having ortho-substituents can be produced efficiently by treatment of the corresponding aryl(diphenyl or dimethyl)methanols with aryl bromides and chlorides.

Triarylmethanols are effectively dehydroarylated and reacted with some unsaturated compounds by using an appropriate palladium catalyst system such as Pd(OAc)2-P(1-Nap)3 (1-Nap = 1-naphthyl) to give the corresponding arenes and hydroarylation products, respectively, along with diaryl ketones.

Polyphenyl derivatives Polyphenyl derivatives Q 0700Palladium-Catalyzed Arylation of α,α-Disubstituted Arylmethanols via Cleavage of a C-C or a C-H Bond to Give Biaryls. -The palladium-catalyzed arylation of α,α-disubstituted arylmethanols with aryl halides can proceed not only by C-H bond cleavage at the ortho-position but also by cleavage of the C(sp 2 )-C(sp 3 ) bond to generate ketones (β-carbon elimination) and biaryl compounds. The preferential cleavage of C-H bond or C-C bond strongly depends on the nature of arylmethanol substrate as well as on the bulkiness of phosphine ligand. Thus, using bulky PCy 3 as ligand, bulky o-substituted aryl groups are selectively cleaved from arylmethanols even in the presence of two phenyl groups in α-position [cf. (XIb) vs. (XId), (XIV)]. Electronic effects are less influential. C-H Bond cleavage is observed mainly for α,α-disubstituted biphenylmethanols, e.g. (XXII) or (IX), and the corresponding o,o'-diarylated products are preferentially achieved even with bulky aryl halides [cf. (XXIV)]. -(TERAO, Y.; WAKUI, H.; NOMOTO, M.; SATOH, T.; MIURA*, M.; NOMURA, M.; J. Org.

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Polyphenylalkane derivatives Q 0720Palladium-Catalyzed Dehydroarylation of Triarylmethanols and Their Coupling with Unsaturated Compounds Accompanied by C-C Bond Cleavage. -In the presence of Pd(O-Ac)2/P(Nap)3, triarylmethanols undergo dehydroarylation yielding diaryl ketones and arenes. Addition of unsaturated compounds to the reaction mixture leads to hydroarylated products such as (VII), (X), and (XII). -(TERAO, Y.; NOMOTO, M.; SATOH, T.; MIURA*, M.; NOMURA, M.; J. Org. Chem. 69 (2004) 20, 6942-6944; Dep. Appl. Chem., Fac. Eng., Osaka Univ., Suita, Osaka 565, Japan; Eng.) -Jannicke 06-100