Tandem C/N-Difunctionalization of Nitroarenes: Reductive Amination and Annulation by a Ring Expansion/Contraction Sequence.

A synthetic method for the reductive transformation of nitroarenes into ortho-aminated and -annulated products is reported. The method operates via the exhaustive deoxygenation of nitroarenes by an organophosphorus catalyst and a mild terminal reductant to access aryl nitrenes, which after ring expansion, are trapped by amine nucleophiles to give dearomatized 2-amino-3H-azepines. Treatment of these ring-expanded intermediates with acyl electrophiles triggers 6π electrocyclization to extrude the nitrogen atom and restore aromaticity of the phenyl ring, which delivers via C-H functionalization 2-aminoanilide and benzimidazole products.

Asymmetric Allylic C-H Alkylation via Palladium(II)/ cis-ArSOX Catalysis.

We report the development of Pd(II)/ cis-aryl sulfoxide-oxazoline ( cis-ArSOX) catalysts for asymmetric C-H alkylation of terminal olefins with a variety of synthetically versatile nucleophiles. The modular, tunable, and oxidatively stable ArSOX scaffold is key to the unprecedented broad scope and high enantioselectivity (37 examples, avg. > 90% ee). Pd(II)/ cis-ArSOX is unique in its ability to effect high reactivity and catalyst-controlled diastereoselectivity on the alkylation of aliphatic olefins. We anticipate that this new chiral ligand class will find use in other transition metal catalyzed processes that operate under oxidative conditions.

Allylic C-H amination cross-coupling furnishes tertiary amines by electrophilic metal catalysis.

Intermolecular cross-coupling of terminal olefins with secondary amines to form complex tertiary amines-a common motif in pharmaceuticals-remains a major challenge in chemical synthesis. Basic amine nucleophiles in nondirected, electrophilic metal-catalyzed aminations tend to bind to and thereby inhibit metal catalysts. We reasoned that an autoregulatory mechanism coupling the release of amine nucleophiles with catalyst turnover could enable functionalization without inhibiting metal-mediated heterolytic carbon-hydrogen cleavage. Here, we report a palladium(II)-catalyzed allylic carbon-hydrogen amination cross-coupling using this strategy, featuring 48 cyclic and acyclic secondary amines (10 pharmaceutically relevant cores) and 34 terminal olefins (bearing electrophilic functionality) to furnish 81 tertiary allylic amines, including 12 drug compounds and 10 complex drug derivatives, with excellent regio- and stereoselectivity (>20:1 linear:branched, >20:1 E:Z).

A new biarylphosphine ligand for the Pd-catalyzed synthesis of diaryl ethers under mild conditions.

A new bulky biarylphosphine ligand (L8) has been developed that allows the Pd-catalyzed C-O cross-coupling of a wide range of aryl halides and phenols under milder conditions than previously possible. A direct correlation between the size of the ligand substituents in the 2', 4', and 6' positions of the nonphosphine containing ring and the reactivity of the derived catalyst system was observed. Specifically, the rate of coupling increased with the size of these substituents.