Palladium‐catalyzed oxidative homocoupling and hydroxylation of 3‐arylbenzo[d]isoxazoles have been developed via direct C(sp2)−H bond activation using benzoisoxazoles as a new directing group. The protocols offer a divergent approach to functionalized, synthetically useful benzoisoxazoles in good yields. Critically, 1‐iodo‐4‐methoxybenzene functions as an oxidant to mediate the dehydrogenative homocoupling and minimize the cross‐coupling. A dual‐core dimeric palladacycle intermediate is confirmed by X‐ray crystallography, and serves as an active catalytic species in the catalytic cycles.magnified image

A catalytic cascade has been developed for the synthesis of biaryl‐2‐methyl acetates via a palladium‐catalyzed ortho‐C(sp2)−H bond arylation of pyruvate O‐arylmethyl ketoximes with aryl iodides followed by a solvolysis, in which the pyruvic ketoxime ester as a new auxiliary is employed to direct the C(sp2)−H bond activation. The straightforward treatment of O‐arylmethyl hydroxylamines and ethyl pyruvate with aryl iodides also provides the target products in a one‐pot fashion. Furthermore, the new palladacycle intermediate is unambiguously confirmed by single‐crystal X‐ray diffraction analysis. A plausible reaction pathway is proposed for the Pd‐catalyzed arylation‐acetolysis sequence.magnified image

A palladium-catalyzed Csp3–H bond mono-aroyloxylation of O-alkyl substituted oxime ethers has been developed by using 2,4,6-trimethoxybenzaldoxime as an exo-type directing group with exclusive site-selectivity. With the wide range of masked aliphatic alcohol substrates and aromatic acid coupling partners, the protocol allows rapid access to various 2-alkyl substituted glycol derivatives in synthetically useful to good yields. The employed directing group is readily removed, accordingly affording valuable functionalized aliphatic alcohols. When the solvent from hybrid DCE/HFIP to CH3CN, non-directed oxidative cross-coupling is observed between the electron-rich aromatic ring of substrates and aromatic acid partners.

A palladium-catalyzed ortho-C(sp 2)-H bond iodination of 4-arylthiazoles has been developed. Through screening of directing groups and optimazation of reaction parameters, the most efficient reaction conditions for mono-ortho-position iodination were obtained, which were applied to synthesize a series of 4-(2-iodoaryl)thiazoles with broad scope of 4-arylthiazole substrates. Furthermore, the iodine group can be easily transformed into other organic functional groups, which improved the application value of this methodology. At last, plausible mechanism was proposed based on an intermolecular deuterium labeling kinetic experiment and radical inhibition experiments. Keywords palladium-catalyzed; 4-arylthiazoles; mono-selectivity; C(sp 2)-H bond; iodination 2 Results and discussion Given our recent success in thiazole-directed C(sp 2)-H Chinese Journal of Organic Chemistry ARTICLE