Access to Difluoromethylene-Skipped 1,4-Diynes with gem-Difluoropropargyl Bromide

Palladium-catalyzed alkynylation of allylic gem-difluorides

Herein, a palladium-catalyzed regioselective alkynylation, esterification, and amination of allylic gem-difluorides via C-F bond activation/transmetallation/β-C elimination or nucleophilic attack has been achieved. This innovative protocol showcases an extensive substrate range and operates efficiently under mild reaction conditions, resulting in high product yields and Z-selectivity. Particularly noteworthy is its exceptional tolerance towards a wide array of functional groups. This developed methodology provides effective and convenient routes to access a diverse array of essential fluorinated enynes, esters and amines.

Recent Advances in the Synthesis of Propargyl Derivatives, and Their Application as Synthetic Intermediates and Building Blocks

The propargyl group is a highly versatile moiety whose introduction into small-molecule building blocks opens up new synthetic pathways for further elaboration. The last decade has witnessed remarkable progress in both the synthesis of propargylation agents and their application in the synthesis and functionalization of more elaborate/complex building blocks and intermediates. The goal of this review is to highlight these exciting advances and to underscore their impact.

Palladium-Catalyzed Defluorinative Coupling of Difluoroalkenes and Aryl Boronic Acids for Ketone Synthesis

The transition-metal-catalyzed carbonylation reaction is a useful approach for ketone synthesis. However, it is often problematic to use exogenous carbonyl reagents, such as gaseous carbon monoxide. In this manuscript, we report a novel palladium-catalyzed coupling reaction of gem-difluoroalkenes and aryl boronic acids that yields bioactive indane-type ketones with an all-carbon α-quaternary center. Characterization and stoichiometric reactions of the key intermediates RCF₂ Pd^II support a water-induced defluorination and cross-coupling cascade mechanism. The vinyl difluoromethylene motif serves as an in situ carbonyl precursor which is unprecedented in transition-metal-catalyzed coupling reactions. It is expected to raise broad research interest from the perspectives of ketone synthesis, fluoroalkene functionalization, and rational design of new synthetic protocols based on the unique reactivity of difluoroalkyl palladium(II) species.

Access to Divergent Fluorinated Enynes and Arenes via Palladium-Catalyzed Ring-Opening Alkynylation of gem-Difluorinated Cyclopropanes

Herein, we describe a palladium-catalyzed alkynylation of gem-difluorinated cyclopropanes via C-C bond activation/C-F bond cleavage, followed by C-C(sp) coupling. The new approach proceeds with broad substrate scope under mild reaction conditions, whereas both 1,1-disubstituted and complex-molecule-modified gem-difluorinated cyclopropanes react smoothly with high stereoselectivity. The developed method provides efficient and convenient ways access to diversity of important fluorinated enynes and arenes by slightly modification of the reaction conditions.

Silver-promoted decarboxylative radical addition/annulation of oxamic acids with gem-difluoroolefins: concise access to CF2-containing 3,4-dihydroquinolin-2-ones

Described is a silver-promoted decarboxylative radical addition/annulation of oxamic acids with gem-difluoroalkenes. This reaction proceeded under mild reaction conditions with broad functional group compatibility, enabling the convenient synthesis of various structurally diverse CF2-containing 3,4-dihydroquinolin-2-ones that might find applications in medical chemistry.

Diastereoselective synthesis of cyclopropanes bearing trifluoromethyl-substituted all-carbon quaternary centers from 2-trifluoromethyl-1,3-enynes beyond fluorine elimination

Highly diastereoselective cyclopropanations of trifluoromethylenynes with sulfur ylides deliver cyclopropanes bearing trifluoromethyl-substituted all-carbon quaternary centers.

Transition-Metal (Cu, Pd, Ni)-Catalyzed Difluoroalkylation via Cross-Coupling with Difluoroalkyl Halides

Difluoroalkylated compounds play a remarkably important role in life and materials sciences because of the unique characteristics of the difluoromethylene (CF₂) group. In particular, precise introduction of a CF₂ group at the benzylic position can dramatically improve the biological properties of the corresponding molecules. As a consequence, difluoroalkylation of aromatic compounds has become a powerful strategy in modulating the bioactivities of organic molecules. However, efficient strategies to selectively synthesize difluoroalkylated arenes had been very limited before 2012. Traditional synthetic methods in this regard suffer from either harsh reaction conditions or narrow substrate scope, significantly restricting their widespread applications, particularly for late-stage difluoroalkylation of bioactive molecules. To overcome these limitations, a straightforward route to access these valuable difluoroalkylated skeletons is the direct introduction of the difluoroalkylated group (CF₂R) onto aromatic rings through transition-metal-catalyzed cross-coupling. However, because of the instability of some difluoroalkylated metal species, which are prone to protonation, dimerization, and/or generation of other unknown byproducts, it is difficult to selectively control the catalytic cycle to suppress these side reactions. In this context, we proposed the use of low-cost and widely available difluoroalkyl halides as fluoroalkyl sources for transition-metal-catalyzed difluoroalkylation reactions via cross-coupling. In this Account, we summarize our major efforts on copper-, palladium-, and nickel-catalyzed difluoroalkylations of aromatics with low-cost and widely available difluoroalkyl halides as fluoroalkyl sources. Four modes of catalytic difluoroalkylation reactions, including nucleophilic difluoroalkylation, electrophilic difluoroalkylation, radical difluoroalkylation, and metal-difluorocarbene coupling (MeDiC), have been demonstrated through careful modulation of the catalytic systems. Among these reactions, the MeDiC reaction represents a new mode of fluoroalkylation. These processes enable difluoroalkylation of a variety of aryl halides and arylboron reagents under mild reaction conditions. A wide range of difluoroalkyl halides, including activated difluoroalkyl halides (Cl/BrCF₂R, R = π system), unactivated difluoroalkyl halides (BrCF₂R, R = alkyl, H), and especially the inert and inexpensive industrial chemical chlorodifluoromethane (ClCF₂H), are applicable to these reactions, providing straightforward and facile routes to a diverse range of difluoroalkylated (hetero)arenes. These difluoroalkyl halide-based strategies can also be applied to prepare difluoroalkylated alkenes, alkynes, and alkanes and feature impressive advantages over conventional methods for the synthesis of difluoroalkylated compounds in terms of synthetic efficiency, functional group tolerance, and structural diversity. In particular, the late-stage difluoroalkylation of bioactive molecules through these processes offers good opportunities for the synthesis and development of new medicinal agents without the need for multistep de novo syntheses.

Nickel-Catalyzed Regioselective C(2)-H Difluoroalkylation of Indoles with Difluoroalkyl Bromides

Regioselective C(2)-H difluoroalkylation of C-3 unsubstituted indoles with commonly available fluoroalkyl bromides is successfully achieved employing a simple nickel catalyst system, (DME)NiCl₂ /Xantphos. This methodology shows excellent regioselectivity and exhibits a broad substrate scope. Various functional groups, such as -OMe, -F, and -Br, are tolerated on the indole backbone to give the difluoroalkylated products in moderate to good yields. Preliminary mechanistic findings demonstrate that the reaction is homogeneous in nature and involves a radical manifold. Synthetic utility of this nickel-catalyzed method is demonstrated by synthesizing melatonin receptor antagonist Luzindole derivative.

meta-Selective C–H difluoromethylation of various arenes with a versatile ruthenium catalyst

A ruthenium-enabled meta-selective C–H difluoromethylation of arenes has been developed.

Nonconventional difluoroalkylation of C(sp2)–H bonds through hydroarylation

A nonconventional difluoroalkylation of the C(sp²)–H bond is achieved by Rh(iii)-catalyzed hydroarylation of 2,2-difluorovinyl arenesulfonate.