Divergent Regioselective Csp2-H Difluoromethylation of Aromatic Amines Enabled by Nickel Catalysis

Metal-free synthesis of difluoro/trifluoromethyl carbinol-containing chromones via tandem cyclization of o-hydroxyaryl enaminones

We herein propose a HFIP-promoted tandem cyclization reaction for the synthesis of difluoro/trifluoromethyl carbinol-containing chromones from o-hydroxyphenyl enaminones at room temperature. This protocol provides a facile and efficient approach to access diverse difluoro/trifluoromethylated carbinols in good to excellent yields. In addition, gram-scale and synthetic derivatization experiments have also been performed.

Copper-Catalyzed C-C Cross-Couplings of Tertiary Alkyl Halides with Anilines Enabled by Cyclopropenimine-Based Ligands

Catalytic cross-couplings of tertiary alkyl electrophiles with carbon nucleophiles offer a powerful platform for constructing quaternary carbon centers, which are prevalent in bioactive molecules. However, these reactions remain underdeveloped primarily because of steric challenges that impede efficient bond formation. Herein, we describe the copper-catalyzed synthesis of such centers through the C(sp3)-C(sp2) bond-forming reaction between tertiary alkyl halides and arene rings of aniline derivatives, enabled by the strategic implementation of bidentate bis(cyclopropenimine) ligands. The copper catalyst bound by two imino-nitrogen atoms of these ligands, which have never been employed in metal catalysis previously, is highly effective in rapidly activating tertiary halides to generate alkyl radicals, allowing them to react with aryl nucleophiles under mild conditions with remarkably short reaction times (1-2 h). Various tertiary halides bearing carbonyl functional groups can be coupled with secondary or primary anilines, furnishing a range of quaternary carbon centers in good yields. Several mechanistic observations support the generation of copper(II) species and alkyl radicals which as a result elucidate the steps in the proposed catalytic cycle.

Synthetic strategies for the construction of C3-fluorinated oxindoles

C3-fluorinated oxindoles are important scaffolds known to demonstrate various biological properties. As bio-isosteres of oxindoles, these compounds have shown tremendous potential in drug research discovery programs. Besides, they also serve as starting materials for synthesizing other fluorine-containing new architectures, thus launching research for developing new methods for their synthesis. Consequently, various approaches have been developed over the years to synthesize C3-fluorinated oxindoles. This review highlights the strategies developed to date to access C3-difluoro and monofluorooxindoles via intermolecular and intramolecular approaches. The key findings of the strategies developed are discussed along with the prevailing mechanism.

Transition-Metal-Catalyzed C-H Bond Activation for the Formation of C-C Bonds in Complex Molecules

Site-predictable and chemoselective C-H bond functionalization reactions offer synthetically powerful strategies for the step-economic diversification of both feedstock and fine chemicals. Many transition-metal-catalyzed methods have emerged for the selective activation and functionalization of C-H bonds. However, challenges of regio- and chemoselectivity have emerged with application to highly complex molecules bearing significant functional group density and diversity. As molecular complexity increases within molecular structures the risks of catalyst intolerance and limited applicability grow with the number of functional groups and potentially Lewis basic heteroatoms. Given the abundance of C-H bonds within highly complex and already diversified molecules such as pharmaceuticals, natural products, and materials, design and selection of reaction conditions and tolerant catalysts has proved critical for successful direct functionalization. As such, innovations within transition-metal-catalyzed C-H bond functionalization for the direct formation of carbon-carbon bonds have been discovered and developed to overcome these challenges and limitations. This review highlights progress made for the direct metal-catalyzed C-C bond forming reactions including alkylation, methylation, arylation, and olefination of C-H bonds within complex targets.

Iron-catalysed reductive coupling for the synthesis of polyfluorinated compounds

Iron-catalysed reductive cross-coupling of difluorobromo acetic acid derivatives with trifluoromethyl olefins to afford polyfluorinated molecules, containing a difluorenyl and difluoroalkyl group, with a broad substrate scope.