A redox-enabled strategy for intramolecular hydroamination

Palladium-catalyzed annulation and intermolecular hydroamination involving norbornene derivatives: synthesis of indanones and N-alkylamines

A palladium-catalyzed divergent reaction of primary benzamides using norbornene (NBE) derivatives as a controlled switch is reported. When NBE is used as a mediator, indanones are synthesized with moderate to good yields via a Catellani reaction that involves sequential ortho-C-H alkylation and ipso-C-N bond cleavage annulation of primary benzamides. Employing norbornadiene (NBD) instead of NBE enables the assembly of N-alkylamines by an intermolecular hydroamination reaction.

EDA-Enabled Three-Component Polarity-Crossover Cyclization: Modular Installation of Fully Substituted γ-Lactams

A photoinduced three-component radical addition-aminalization cascade was accomplished, enabling rapid assembly of a wide range of densely functionalized γ-lactams. Key to this transformation is the electron-donor-acceptor (EDA) generation of enamine and in situ trapping of an iminium intermediate with bromodifluoroacetamide. This rationally designed protocol fully takes advantage of the polarity crossover (enamine-iminium) in the process, providing the modular assembly of previously inaccessible scaffolds. The reaction proceeds under mild reaction conditions with excellent regio- and diastereoselectivity, which is amenable to structurally varied substrates and pharmaceuticals.

Enabling Unfavorable Hydroamination Reactions Using a Chemoselective N-O Bond Reduction

Despite major advances, intramolecular alkene hydroamination reactions often face limitations. Herein, a redox-enabled process featuring oxidation of an amine to a hydroxylamine, a concerted hydroamination step, followed by catalytic reduction of N-oxide is shown to be broadly applicable. Catalyst screening and optimization showed that a K2OsO2(OH)4-pinacol complex rapidly and chemoselectively reduces the N-oxide cycloadduct in the presence of hydroxylamine and dimethyl sulfoxide. This selectivity was exploited to drive the equilibria toward complex products.

Oxidative Syntheses of N,N-Dialkylhydroxylamines

Despite the wide utility of hydroxylamines in organic synthesis, relatively few are commercially available, and there is a need for direct, efficient, and selective methods for their synthesis. Herein, we report two complementary methods to accomplish direct oxidation of secondary amines using UHP as an oxidant. The first method uses 2,2,2-trifluoroethanol (TFE) and a large excess of amine. Isolation of hydroxylamine products is enabled by selective salt formation, and recovery of excess amine is demonstrated. The second method uses hexafluoroacetone as an additive and is highlighted by the 1:1 stoichiometry between the oxidant and amine.