Iridium-Catalyzed Reductive (3+2) Annulation of Lactams Enabling the Rapid Total Synthesis of (±)-Eburnamonine

Total Synthesis of Isodaphlongamine H by Iridium-Catalyzed Reductive [3 + 2] Cycloaddition of N-Hydroxylactam

The total synthesis of isodaphlongamine H based on a lactam strategy, which enables quick access to complex cyclic amines, is described. The strategy begins with alkylation of a chiral lactam and subsequent N-oxidation via an imino ether to afford the N-hydroxylactam. For the key transformation to functionalize the amide carbonyl, an iridium-catalyzed reductive [3 + 2] cycloaddition of the N-hydroxylactam provides a tricyclic isoxazolidine in a one-pot process. After the coupling reaction with an allylic silane fragment, the total synthesis is accomplished through intramolecular Hosomi-Sakurai allylation to construct a pentacyclic core. The deoxygenated pentacyclic intermediate shows higher cytotoxicity against HeLa and U937 cell lines than isodaphlongamine H, and might become a lead compound for further biological study.

Catalytic Reductive Amination and Tandem Amination-Alkylation of Esters Enabled by a Cationic Iridium Complex

Reported herein is a convenient and efficient method for one-pot, catalytic reductive amination, as well as the first multi-component tandem reductive amination-functionalization of bench-stable and readily available common carboxylic esters. This method is based on the cationic [Ir(COD)2]BArF-catalyzed chemoselective hydrosilylation of esters, followed by one-pot acid-mediated amination and nucleophilic addition. The reaction was conducted under mild conditions at a very low catalyst loading (0.1 mol % of Ir), which could be further reduced to 0.001 mol %, as demonstrated by a reaction at a 15 g scale. The method is highly versatile, allowing the use of esters with or without α-protons for the N-mono-alkylation of primary and secondary amines to produce diverse secondary and tertiary amines, as well as α-branched/functionalized amines. The method is highly chemoselective and tolerates a variety of functional groups such as bromo, trifluoromethyl, ester, and cyano groups. The value of the method was demonstrated by the one-step catalytic synthesis of two bio-relevant N-mono-methyl α-amino esters and the antiparkinsonian agent piribedil, as well as by the use of two shorter chain triglycerides as alkylating feedstock.

Merging SOMO activation with transition metal catalysis: Deoxygenative functionalization of amides to β-aryl amines

Singly occupied molecular orbital (SOMO) activation of in situ generated enamines has achieved great success in (asymmetric) α-functionalization of carbonyl compounds. However, examples on the use of this activation mode in the transformations of other functional groups are rare, and the combination of SOMO activation with transition metal catalysis is still less explored. In the area of deoxygenative functionalization of amides, intermediates such as iminium ions and enamines were often generated in situ to result in the formation of α-functionalized amines. In contrast, the direct deoxygenation of amides to β-functionalized amines is highly appealing yet remains scarcely investigated. Here, a deoxygenative arylation of amides with aryl halides was developed via multicatalysis of iridium/photoredox/nickel/iridium, affording β-aryl amines in high efficiency. The key to the success of this reaction is the SOMO activation of enamine in synergy with a Ni-catalyzed arylation, which is in conjunction with two compatible Ir-catalyzed reduction processes.

Transition-Metal-Free Radical Relay Cascade Annulation of Amides: Access to Antitumor Active Benzo[b]azepine and Oxindole Derivatives

Efficient transition-metal-free synthesis of benzo[b]azepines and oxindoles is achieved via a radical relay cascade strategy employing halogen atom transfer (XAT) for aryl radical generation followed by intramolecular hydrogen atom transfer (HAT). Optimization yielded moderate to substantial yields under visible light irradiation. Preliminary biological assessments revealed promising anti-tumor activity for select compounds. This study underscores the potential of XAT-mediated radical relay cascades in medicinal chemistry and anticancer drug discovery.

Deoxygenative Nucleophilic Phosphonation and Electrophilic Alkylation of Secondary Amides: A Facile Access to Quaternary α-Aminophosphonates

The widespread occurrence and synthetic accessibility of amides render them valuable precursors for the synthesis of diverse nitrogen-containing compounds. Herein, we present a metal-free and streamlined synthetic strategy for the synthesis of quaternary α-aminophosphonates. This approach involves sequential deoxygenative nucleophilic phosphonation and versatile electrophilic alkylation of secondary amides in a one-pot fashion. Notably, this method enables the direct bis-functionalization of secondary amides with both nucleophiles and electrophiles for the first time, with simple derivatization leading to valuable free α-aminophosphonates by hydrolysis. The protocol has the advantages of operational simplicity, broad functional-group compatibility, environmental friendliness, and scalability to multigram quantities.