Aziridine Opening via a Phenonium Ion Enables Synthesis of Complex Phenethylamine Derivatives

Transition Metal Catalysis for the Asymmetric Synthesis of 2-Arylethylamines: A Review of the New Millennium

The 2-arylethylamine motif is very well-known in medicinal chemistry because of its interesting properties when it comes to interacting with the Central Neural System thanks to its ability to pass the blood-brain barrier. This nitrogen-containing family of compounds is of great interest in synthetic organic chemistry and, when it comes to its asymmetric synthesis, great challenges can be faced in order to obtain the chiral purity required in the drug industry. Thus, we provide a concise transition metal review presenting the recent advances in the synthesis of chiral 2-arylethylamines using transition metals as the main catalysts in the introduction of chirality. Both conventional and photocatalysis methods will be covered, considering the main transition metal used in the studies.

Electrochemical Ring Opening and [3 + 2] Cycloaddition of Aziridines: Access to 1,2-Bifunctionalized Products and Imidazolines

Herein, we report an electricity-driven activation of aziridine via direct anodic oxidation to give N-heterocycles and 1,2-bifunctionalized products by excluding any oxidant/reductant or metal catalyst. Many structurally modified aziridines were employed in the presence of different nitriles. A large variety of nucleophiles were screened to furnish chemoselectively O-alkylated and C-alkylated products. Late-stage derivatization of aziridine with natural and medicinally active compounds has also been done. Remarkably, our strategy was found to be a greener, sustainable, and atom-economical approach (E-factor = ca. 0.8). Azetidine was also found to be compatible with our protocol and generated six-membered N-heterocycles. The detailed mechanistic study highlighted that the reaction is driven via the generation of an aziridine radical cation followed by the SN2 nucleophilic attack.

Magic Blue-Initiated SN2-Type Ring Opening of Activated Aziridines: Friedel-Crafts-Type Alkylation of Electron-Rich Arenes/Heteroarenes

A transition metal-free, atom-economical, and highly stereospecific synthetic approach to Friedel-Crafts-type alkylation of arenes/heteroarenes has been developed. The protocol involves the catalytic aminium radical-cation salt (Magic Blue)-initiated SN2-type nucleophilic ring opening of activated aziridines with arenes/heteroarenes to give the corresponding 2,2-diarylethylamines up to 99% yield and 85% ee (for nonracemic aziridines) in a very short reaction time. Moreover, on reaction with 1,3-dimethylindole and benzofuran, aziridines undergo domino-ring-opening cyclization (DROC) to give the various biologically significant heterocyclic scaffolds in moderate to good yields.

Catalytic Aminium Radical-Cation Salt (Magic Blue)-Initiated SN2-Type Nucleophilic Ring-Opening Transformations of Aziridines

A simple and atom economic protocol for the construction of C-X/C-C bonds via catalytic aminium radical-cation salt (Magic Blue)-initiated SN2-type nucleophilic ring-opening transformations of racemic and nonracemic aziridines with different hetero and carbon nucleophiles to afford various amino ethers, thioethers, and amines in up to 99% yield, and with perfect enantiospecificity for some substrates but reduced ee with others (for nonracemic aziridines), is developed. This aminium radical-cation salt-initiated, SN2-type nucleophilic ring-opening strategy, along with various cyclization protocols, is employed to synthesize various biologically significant compounds.

Reductive Opening of Oxetanes Catalyzed by Frustrated Lewis Pairs: Unexpected Aryl Migration via Neighboring Group Participation

B(C₆F₅)₃ was found to catalyze an unusual double reduction of oxetanes by hydrosilane with aryl migration via neighboring group participation. Control experiments suggested that the phenonium ion serves as the key intermediate. Minor modification of this protocol also led to simple hydrosilylative opening of oxetanes.