Nucleophilic difluoromethylation and trifluoromethylation using tetrakis(dimethylamino)ethylene (TDAE) reagent

TBAF-Mediated [3+1] Cycloaddition of Difluorocarbene to Access gem-Difluorinated 1,2-Diazetidine Analogues as Potent Anticancer Agents

The facile synthesis of gem-difluorinated 1,2-diazetidines was achieved by metal-free [3+1] annulation between C,N-cyclic azomethine imines with difluorocarbene. A library of 30 compounds benefiting from the TBAF-mediated cyclization process could be directly assembled in moderate to good yield under mild conditions. A plausible mechanism involving the difluorocarbene pathway was proposed based on carbene trapping and control experiments. Many compounds exhibited dramatic antiproliferative activity in 4T1, A549, and HeLa tumor cell lines.

Metal-Free SF6 Activation: A New SF5 -Based Reagent Enables Deoxyfluorination and Pentafluorosulfanylation Reactions

The activation of SF₆ , a potent greenhouse gas, under metal-free and visible light conditions is reported. Herein, mechanistic investigations including EPR spectroscopy, NMR studies and cyclic voltammetry allowed the rational design of a new fluorinating reagent which was synthesized from the 2-electron activation of SF₆ with commercially available TDAE. This new SF₅ -based reagent was efficiently employed for the deoxyfluorination of CO₂ and the fluorinative desulfurization of CS₂ allowing the formation of useful fluorinated amines. Moreover, for the first time we demonstrated that our SF₅ -based reagent could afford the mild generation of Cl-SF₅ gas. This finding was exploited for the chloro-pentafluorosulfanylation of alkynes and alkenes.

Synthesis of Difluorinated Heterocyclics through Metal-Free [8+1] and [4+1] Cycloaddition of Difluorocarbene

With Ph₃P⁺CF₂COO^- or TMSCF₂Br as the difluorocarbene sources, a facile metal-free cycloaddition between heteroconjugated alkenes and difluorocarbene was developed for the highly convergent synthesis of novel difluorinated heterocyclics, including gem-difluorinated azetidines and 2,3-dihydrobenzofurans. The cycloaddition features high reactivity and regioselectivity, as well as good tolerance of various electron-donating or electron-withdrawing substituents on azaheptafulvenes and o-quinone methides.

Neutral Organic Super Electron Donors Made Catalytic

Neutral organic super electron donors (SEDs) display impressive reducing power but, until now, it has not been possible to use them catalytically in radical chain reactions. This is because, following electron transfer, these donors form persistent radical cations that trap substrate-derived radicals. This paper unlocks a conceptually new approach to super electron donors that overcomes this issue, leading to the first catalytic neutral organic super electron donor.

Metal-free and light-promoted radical iodotrifluoromethylation of alkenes with Togni reagent as the source of CF3 and iodine

Iodotrifluoromethylation of alkenes is effectively conducted by combining benzophenone, “black light”, isopropanol and Togni reagent 1 as the source of both the CF₃ group and iodine atom.

n-Dopants Based on Dimers of Benzimidazoline Radicals: Structures and Mechanism of Redox Reactions

Dimers of 2-substituted N,N'-dimethylbenzimidazoline radicals, (2-Y-DMBI)2 (Y=cyclohexyl (Cyc), ferrocenyl (Fc), ruthenocenyl (Rc)), have recently been reported as n-dopants for organic semiconductors. Here their structural and energetic characteristics are reported, along with the mechanisms by which they react with acceptors, A (PCBM, TIPS-pentacene), in solution. X-ray data and DFT calculations both indicate a longer C-C bond for (2-Cyc-DMBI)2 than (2-Fc-DMBI)2 , yet DFT and ESR data show that the latter dissociates more readily due to stabilization of the radical by Fc. Depending on the energetics of dimer (D2 ) dissociation and of D2 -to-A electron transfer, D2 reacts with A to form D(+) and A(-) by either of two mechanisms, differing in whether the first step is endergonic dissociation or endergonic electron transfer. However, the D(+) /0.5 D2 redox potentials-the effective reducing strengths of the dimers-vary little within the series (ca. -1.9 V vs. FeCp2 (+/0) ) (Cp=cyclopentadienyl) due to cancelation of trends in the D(+/0) potential and D2 dissociation energy. The implications of these findings for use of these dimers as n-dopants, and for future dopant design, are discussed.

Organocatalytic direct difluoromethylation of aldehydes and ketones with TMSCF2H

Organocatalytic direct difluoromethylation of aldehydes and ketones with TMSCF₂H.

Trifluoromethylation of alkenes with concomitant introduction of additional functional groups

The trifluoromethyl group is found in many synthetic bioactive compounds, and the difunctionalization of a C=C bond, as a powerful strategy for the construction of compounds with various functional groups, has been intensively investigated. Therefore, the difunctionalizing trifluoromethylation of alkenes has attracted growing interest because of the potential of the products as building blocks for bioactive molecules. In this review, we focus on recent advances in the trifluoromethylation of alkenes with concomitant introduction of additional functional groups.

Introduction of fluorine and fluorine-containing functional groups

Over the past decade, the most significant, conceptual advances in the field of fluorination were enabled most prominently by organo- and transition-metal catalysis. The most challenging transformation remains the formation of the parent C-F bond, primarily as a consequence of the high hydration energy of fluoride, strong metal-fluorine bonds, and highly polarized bonds to fluorine. Most fluorination reactions still lack generality, predictability, and cost-efficiency. Despite all current limitations, modern fluorination methods have made fluorinated molecules more readily available than ever before and have begun to have an impact on research areas that do not require large amounts of material, such as drug discovery and positron emission tomography. This Review gives a brief summary of conventional fluorination reactions, including those reactions that introduce fluorinated functional groups, and focuses on modern developments in the field.

A Novel Organic Electron Donor Derived from N-Methylisatin

We report the reactivity of an electron donor derived from N-methylisatin on reduction by sodium amalgam. Transfer of a clear supernatant solution to iodoarenes affords the products of two-electron reduction. Reductions of sulfones, activated arenesulfonamides, and Weinreb amides are also reported.

Hybrid super electron donors - preparation and reactivity

Neutral organic electron donors, featuring pyridinylidene–imidazolylidene, pyridinylidene–benzimidazolylidene and imidazolylidene–benzimidazolylidene linkages are reported. The pyridinylidene–benzimidazolylidene and imidazolylidene–benzimidazolylidene hybrid systems were designed to be the first super electron donors to convert iodoarenes to aryl radicals at room temperature, and indeed both show evidence for significant aryl radical formation at room temperature. The stronger pyridinylidene–imidazolylidene donor converts iodoarenes to aryl anions efficiently under appropriate conditions (3 equiv of donor). The presence of excess sodium hydride base has a very important and selective effect on some of these electron-transfer reactions, and a rationale for this is proposed.

Fragmentations observed in the reactions of α-methoxy-γ-alkoxyalkyl iodide substrates with super-electron-donors derived from 4-DMAP and N-methylbenzimidazole

Reactions of super-electron-donors (SEDs) derived from 4-dimethylaminopyridine and from N-methylbenzimidazole with α-methoxy-γ-alkoxyalkyl iodides lead to liberation of the γ-alkoxy groups as their alcohols. This is consistent with generation of alkyl radicals from the alkyl halide precursors, and trapping of these radicals by the radical-cation of the SED, followed by a heterolytic fragmentation.

Copper-mediated fluoroalkylation reactions with iododifluoroacetamides: controlling the selectivity among cross-coupling, intramolecular cyclization, and homocoupling reactions

Cu-mediated fluoroalkylation reactions with iododifluoroacetamides 1 have been systematically investigated. It was found that three types of reactions may coexist in Cu-mediated reactions between iododifluoroacetamides and aryl/alkenyl iodides: cross-coupling, intramolecular cyclization, and homocoupling reactions. The selectivity among these three types of reactions could be controlled by tuning the substituents on the nitrogen atom of iododifluoroacetamides, and/or by removing the cross-coupling reaction partner (aryl/alkenyl halides). The general rule is as follows: (a) in the presence of proper aryl/alkenyl iodides, the cross-coupling products 2 (or 6) are generally formed as the major products; (b) in the absence of aryl/alkenyl iodides, and when R(1) = alkyl and R(2) = aryl groups, or when R(1) = R(2) = aryl groups, the intramolecular cyclization products 3 can be formed predominantly; and (c) in the absence of aryl/alkenyl iodides, and when R(1) = R(2) = alkyl groups, or when R(1) = H and R(2) = alkyl, aryl groups, the homocoupling products 4 can be formed dominantly. Our experimental results also indicate that in many cases when cross-coupling, homocoupling, and intramolecular cyclization reactions coexist in the Cu-mediated reaction system, the reactivity decreases in the following order: cross-coupling > intramolecular cyclization > homocoupling.