Application of cooperative iron/copper catalysis to a palladium-free borylation of aryl bromides with pinacolborane.

A new cooperative copper/iron catalysis for the borylation of various aryl bromides with pinacolborane, at -10 °C, is reported. Use of the toxic, precious metal Pd is avoided. The mechanism of the protodebromination side reaction is discussed.

Fast Pd- and Pd/Cu-catalyzed direct C-H arylation of cyclic nitrones. Application to the synthesis of enantiopure quaternary α-amino esters.

Cocatalysis by pivalic acid or copper bromide allows a very fast, clean, and high-yielding palladium-catalyzed coupling of a large array of aryl, thienyl, and pyridyl halides with cyclic nitrones, including DMPO. The study of the reaction conditions, scope, and mechanism is presented. Applied to the chiral nitrone MiPNO, this transformation provides a straightforward access to enantiopure α-methyl α-arylglycine esters.

An opportunity for Mg-catalyzed Grignard-type reactions: direct coupling of benzylic halides with pinacolborane with 10 mol % of magnesium.

Mg in catalytic amounts as the only metal permits the reductive coupling between benzyl halides and pinacolborane. HBpin acts both as an electrophile and as a reducing agent to regenerate an organomagnesium species in situ. An hydride oxidation mechanism is proposed on the basis of DFT calculations.