TfOH-promoted Classical Nazarov-type Cyclization of Benzofulvenes: Synthesis of Polycyclic 5H,10'H-spiro[benzo[k]phenanthridine-5,6'-dibenzopentalenes]

Copper complexes for the chemoselective N-arylation of arylamines and sulfanilamides via Chan-Evans-Lam cross-coupling

Copper(II) complexes with tridentate NNN-ligands were utilized for Chan-Evans-Lam (CEL) cross-coupling reactions to enable the N-arylation of multifarious N-nucleophiles through the activation of aryl boronic acids. A condition-specific methodology was developed to chemoselectively target the amine versus sulfonamide N-arylation of 4-aminobenzenesulfonamide using new catalysts. Two different pyridine-based ligands and corresponding copper(II) complexes were characterized using 1H and 13C-NMR, FTIR, and UV-vis spectroscopy, HRMS, single-crystal X-ray diffraction, and cyclic voltammetry. Solvent and base-controlled cross-coupling reactions were observed, which led to the optimization of selective conditions for targeted C-N bond formation of sulfanilamides. Beyond the chemoselective processes reported here, a breadth of N-nucleophiles including sulfanilamides and arylamines were screened for arylation by this CEL catalyst.

Sodium Trifluoroacetate mediated Copper-Catalyzed aza-Michael addition of α,β-unsaturated olefins with aromatic amines

We present a sodium trifluoroacetate (CF3CO2Na) mediated copper-catalyzed aza-Michael addition of aromatic amines with activated olefins under mild, aqueous reaction conditions. This simplistic protocol employs a copper catalyst (10 mol%) and water as solvent. This transformation occurs precisely with aromatic substituted amines containing both electron-donating (EDG) and electron-withdrawing (EWG) groups. A broad range of substrates were tested under the optimized conditions, which are producing good to moderate yields.

One-Pot Double Intramolecular Cyclization Approach to Tetralin-Based Cis-Fused Tetracyclic Compounds

Presented herein is a BF₃·OEt₂-mediated, diastereoselective one-pot double cyclization of 4-aryl-2-[(arylthio)methyl]butanals leading to the formation of cis-tetrahydro-6H-naphtho[2,1-c]thiochromenes for the first time. Mechanistically, the formation of the title products involves the one-pot intramolecular Friedel-Crafts hydroxyalkylation/intramolecular Friedel-Crafts alkylation cascade. This synthetic methodology is featured by its high atom economy, broad substrate scope, mild transition-metal-free reaction conditions, capability to assemble two new rings in one pot, and moderate to high yields (up to 94% yield). It was then applied in the synthesis of a thia analogue of brazilane and a chromeno[3,4-c]chromene derivative. Moreover, the methodology was successfully extended to the synthesis of cis-hexahydrobenzo[c]phenanthrenes. Specifically, 1,5-diarylpentan-3-ones were first subjected to the Corey-Chaykovsky reaction, and the resulting epoxides, without being chromatographically isolated, were treated with BF₃·OEt₂ to afford the cyclized products in high yields (up to 84% yield over two steps).