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

Palladium-catalyzed direct olefination of 6-electron-withdrawing group substituted 3-arylbenzo[d]isoxazoles has been developed with exclusive site-selectivity and excellent E-stereoselectivity.

The palladium-catalyzed oxidative acyloxylation of 5-alkyl-4-aryl-thiazole-2-carboxylates via ad irect ortho-Csp 2 ÀHb ond activationh as been described with an ewly reported radicalm echanism. Based on the late-stage functionalizationo ft he highlys ubstituted thiazoles, the reaction delivered multifarious valuable acyloxylated products with moderate-to-excellent yields. The transformationa ffords highly functionalized substrates, has broad scope of carboxylic acidc oupling partners, excellent site-selectivity, rapid reaction rates, simple operation and mild conditions. The diversea cyloxylationr eactiona llows rapid access to ap lethora of mono-acyloxylated products from the functionalized thiazoles. Results and DiscussionTo gain insighti nto as uitable thiazole directing group, we explored 4-aryl-thiazole-2-carboxylates (1)a ss ubstrates to achieve the acetoxylation (Scheme 2). The reactionw as first performed with 4-phenyl-thiazole-2-carboxylate (1a,0 .3 mmol), Scheme1.Previousrelatedw ork and present late-stageacyloxylation of 5alkyl-4-aryl-thiazole-2-carboxylates.

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 highly site-selective palladium-catalyzed ortho-mono-aroyloxylation of O-aralkyl substituted acetoxime ethers via direct Csp2–H bond activation has been developed with simple exo-acetoxime as a directing group.