Palladium-Catalyzed Oxidative Diarylating Carbocyclization of Enynes

A mild and efficient palladium-catalyzed oxidative diarylating carbocyclization of enynes is described. The reaction tolerates a range of functionalized arylboronic acids to give diarylated products in good yields. Control experiments suggest that the reaction starts with an arylpalladation of the alkyne, followed by carbocyclization, transmetalation, and reductive elimination to afford the diarylated product

Kinetics and Mechanism of the Palladium-Catalyzed Oxidative Arylating Carbocyclization of Allenynes

Pd-catalyzed C–C bond-forming reactions under oxidative conditions constitute a class of important and widely used synthetic protocols. This Article describes a mechanistic investigation of the arylating carbocyclization of allenynes using boronic acids and focuses on the correlation between reaction conditions and product selectivity. Isotope effects confirm that either allenic or propargylic C–H activation occurs directly after substrate binding. With an excess of H₂O, a triene product is selectively formed via allenic C–H activation. The latter C–H activation was found to be turnover-limiting and the reaction zeroth order in reactants as well as the oxidant. A dominant feature is continuous catalyst activation, which was shown to occur even in the absence of substrate. Smaller amounts of H₂O lead to mixtures of triene and vinylallene products, where the latter is formed via propargylic C–H activation. The formation of triene occurs only in the presence of ArB­(OH)₂. Vinylallene, on the other hand, was shown to be formed by consumption of (ArBO)₃ as a first-order reactant. Conditions with sub-stoichiometric BF₃·OEt₂ gave selectively the vinylallene product, and the reaction is first order in PhB­(OH)₂. Both C–H activation and transmetalation influence the reaction rate. However, with electron-deficient ArB­(OH)₂, C–H activation is turnover-limiting. It was difficult to establish the order of transmetalation vs C–H activation with certainty, but the results suggest that BF₃·OEt₂ promotes an early transmetalation. The catalytically active species were found to be dependent on the reaction conditions, and H₂O is a crucial parameter in the control of selectivity

Automated, Capsule-Based Suzuki–Miyaura Cross Couplings

The development of an automated process for Suzuki–Miyaura cross couplings is described, in which the complete reaction, workup, and product isolation are effected automatically with no user involvement, aside from loading of the starting materials and reaction capsule. This practical and simple method was successfully demonstrated to provide the desired biaryl products using a range of aryl bromides and boronic acids and is also effective for the late-stage functionalization of aryl halides in bioactive molecules