Escape from Palladium: Nickel-Catalyzed Catellani Annulation.

While Catellani reactions have become increasingly important for arene functionalizations, they have been solely catalyzed by palladium. Here we report the first nickel-catalyzed Catellani-type annulation of aryl triflates and chlorides to form various benzocyclobutene-fused norbornanes in high efficiency. Mechanistic studies reveal a surprising outer-sphere concerted metalation/deprotonation pathway during the formation of the nickelacycle, as well as the essential roles of the base and the triflate anion.

Ligand-Controlled Site- and Enantioselective Carbene Insertion into Carbon-Silicon Bonds of Benzosilacyclobutanes.

We report herein a highly efficient palladium-catalyzed carbene insertion into strained Si-C bonds of benzosilacyclobutanes, which provides an efficient method to access α-chiral silanes. With a sterically hindered ligand, carbene insertion into the C(sp )-Si bond of benzosilacyclobutanes occurred in excellent site- and enantioselectivity, while C(sp )-Si bond insertion occurred selectively with less sterically hindered ligands. Reaction mechanism, in particular the roles of the chiral ligands in controlling the site-selectivity of the insertion reactions, are elucidated by using hybrid density functional theory.

Palladium-Catalyzed Enantioselective Carbene Insertion into Carbon-Silicon Bonds of Silacyclobutanes.

We report herein a highly efficient palladium-catalyzed carbene insertion into strained Si-C bonds with excellent enantioselectivity, which provides a rapid and distinct method to access silacyclopentanes with a three- or four-substituted stereocenter asymmetrically. Mechanistic studies using hybrid density functional theory suggest a catalytic cycle involving oxidative addition, carbene migratory insertion, and reductive elimination. In addition, roles of the chiral ligands in controlling the reaction enantioselectivity are also elucidated.

Synthesis of Alkenylboronates from -Tosylhydrazones through Palladium-Catalyzed Carbene Migratory Insertion.

The palladium-catalyzed oxidative borylation reaction of -tosylhydrazones has been developed. The reaction features mild conditions, broad substrate scope, and good functional group tolerance. It thus represents a highly efficient and practical method for the synthesis of di-, tri-, and tetrasubstituted alkenylboronates from readily available -tosylhydrazones.

Palladium-catalyzed oxidative borylation of conjugated enynones through carbene migratory insertion: synthesis of furyl-substituted alkenylboronates.

A palladium-catalyzed oxidative borylation reaction of conjugated enynones is developed. This reaction represents a new method for the synthesis of furyl-substituted alkenylboronates. The reaction works well with a series of conjugated enynones.

Regioselective copper-catalyzed aminoborylation of styrenes with bis(pinacolato)diboron and diazo compounds.

A Cu(i)-catalyzed aminoborylation reaction of styrenes is reported. In this transformation, diazo compounds are used as the electrophilic amination agent. The in situ generated benzylcopper species is trapped by the electrophilic nitrogen terminus of the diazo substrate to afford borylated hydrazones in a regioselective manner.

Palladium(0)-catalyzed C(sp)-Si bond formation via formal carbene insertion into a Si-H bond.

Pd(0)-Catalyzed formal carbene insertion into Si-H bonds has been achieved as an efficient method for C(sp3)-Si bond formation. The reaction, which uses readily available N-tosylhydrazones as the diazo precursors, is highly efficient and shows a wide substrate scope. Rh(ii) and Cu(i) salts, which are the widely used catalysts for carbene insertion reactions, have been proved to be ineffective for the current reaction.