Effects of Ring Size and Steric Encumbrance on Boron-to-Palladium Transmetalation from Arylboronic Esters.

The structure of the diol from which an arylboronic ester is derived dramatically influences the rate of transmetalation in the Suzuki-Miyaura cross-coupling reaction. Some esters undergo transmetalation more than 20 times faster than the parent arylboronic acid. Herein, investigations into the influence of arylboronic ester ring size and steric properties on the mechanism of transmetalation in the Suzuki-Miyaura reaction are described.

Heteroaryl-Heteroaryl, Suzuki-Miyaura, Anhydrous Cross-Coupling Reactions Enabled by Trimethyl Borate.

Reaction conditions have been developed for refractory heteroaryl-heteroaryl Suzuki-Miyaura cross-couplings. The reported method employs neopentyl heteroarylboronic esters as nucleophiles, heteroaryl bromides and chlorides as the electrophiles, and the soluble base potassium trimethylsilanolate (TMSOK) under anhydrous conditions. The addition of trimethyl borate enhances reaction rates by several mechanisms, including (1) solubilization of -generated boronate complexes, (2) preventing catalyst poisoning by the heteroatomic units, and (3) buffering the inhibitory effect of excess TMSOK.

Potassium Trimethylsilanolate Enables Rapid, Homogeneous Suzuki-Miyaura Cross-Coupling of Boronic Esters.

Herein, a mild and operationally simple method for the Suzuki-Miyaura cross-coupling of boronic esters is described. Central to this advance is the use of the organic-soluble base, potassium trimethylsilanolate, which allows for a homogeneous, anhydrous cross-coupling. The coupling proceeds at a rapid rate, often furnishing products in quantitative yield in less than 5 min.