Generating Active "L-Pd(0)" via Neutral or Cationic π-Allylpalladium Complexes Featuring Biaryl/Bipyrazolylphosphines: Synthetic, Mechanistic, and Structure-Activity Studies in Challenging Cross-Coupling Reactions.

Two new classes of highly active yet air- and moisture-stable π-R-allylpalladium complexes containing bulky biaryl- and bipyrazolylphosphines with extremely broad ligand scope have been developed. Neutral π-allylpalladium complexes incorporated a range of biaryl/bipyrazolylphosphine ligands, while extremely bulky ligands were accommodated by a cationic scaffold. These complexes are easily activated under mild conditions and are efficient for a wide array of challenging C-C and C-X (X = heteroatom) cross-coupling reactions. Their high activity is correlated to their facile activation to a 12-electron-based "L-Pd(0)" catalyst under commonly employed conditions for cross-coupling reactions, noninhibitory byproduct release upon activation, and suppression of the off-cycle pathway to form dinuclear (µ-allyl)(µ-Cl)Pd2(L)2 species, supported by structural (single crystal X-ray) and kinetic studies. A broad scope of C-C and C-X coupling reactions with low catalyst loadings and short reaction times highlight the versatility and practicality of these catalysts in organic synthesis.

Benzylation of nitroalkanes using copper-catalyzed thermal redox catalysis: toward the facile C-alkylation of nitroalkanes.

The C-alkylation of nitroalkanes under mild conditions has been a significant challenge in organic synthesis for more than a century. Herein we report a simple Cu(I) catalyst, generated in situ, that is highly effective for C-benzylation of nitroalkanes using abundant benzyl bromides and related heteroaromatic compounds. This process, which we believe proceeds via a thermal redox mechanism, allows access to a variety of complex nitroalkanes under mild reaction conditions and represents the first step toward the development of a general catalytic system for the alkylation of nitroalkanes.

Palladium-Catalyzed N-Arylation of Cyclopropylamines.

A general method has been developed for the previously challenging arylation of cyclopropylamine and N-arylcyclopropylamines. Highly active, air-stable, and commercially available R-allylpalladium precatalysts provide access to a wide range of (hetero)arylated cyclopropylanilines in high yields. Precatalysts [(tBuBrettPhos)Pd(allyl)]OTf and [(BrettPhos)Pd(crotyl)]OTf, deliver monoarylated products, while (PtBu3)Pd(crotyl)Cl is suited for preparing unsymmetrical diarylated products. The developed conditions tolerate a range of functional groups and heterocycles, allowing access to an array of arylated cyclopropylamines, a motif present in prominent drug molecules.

Copper-Catalyzed Alkylation of Nitroalkanes with α-Bromonitriles: Synthesis of ß-Cyanonitroalkanes.

Copper catalysis now enables the efficient C-alkylation of nitroalkanes with α-bromonitriles. Using a simple and inexpensive catalyst, this process provides access to ß-cyanonitroalkanes. The method is highly tolerant of various functional groups and substitution patterns. These functionally dense products serve as orthogonally masked 1,3-diamines, which can be revealed selectively for access to differentially substituted diamines. These products can also be exploited for the formation of complex cyanoalkenes and 5-aminoisoxazoles.

General route for preparing ß-nitrocarbonyl compounds using copper thermal redox catalysis.

Using a simple copper catalyst, the alkylation of nitroalkanes with α-bromocarbonyls is now possible. This method provides a general, functional group tolerant route to ß-nitrocarbonyl compounds, including nitro amides, esters, ketones, and aldehydes. The highly sterically dense, functional group rich products from these reactions can be readily elaborated into a range of complex nitrogen-containing molecules, including highly substituted ß-amino acids.