2-Fluoro-1,3-benzodithiole-1,1,3,3-tetraoxide: A Reagent for Nucleophilic Monofluoromethylation of Aldehydes

The Acidities of Nucleophilic Monofluoromethylation Reagents: An Anomalous α-Fluorine Effect

Fluorine incorporation into organic molecules is expected to lower the pK_a of neighboring functionality via its strong electron-withdrawing effect, and this strategy has been widely exploited in diverse disciplines. Herein, we report a striking anomalous α-fluorine substitution effect on the α-C_sp3 -H acidity. We have experimentally measured the pK_a values of a series of popular nucleophilic monofluoromethylating reagents α-fluoro(phenylsulfonyl)methane derivatives as well as their C-H analogues by Bordwell's overlapping indicator method in dimethyl sulfoxide solution. Contrary to expectations, we found that α-fluorine substituent does not generally enhance but rather weaken the α-C_sp3 -H acidity of most (phenylsulfonyl)methane derivatives. DFT computations reproduce and provide insight into the anomalous α-fluorine effect. A correlation was identified between the C-H pK_a of (phenylsulfonyl)methane derivatives and Mayr's nucleophilicity parameter (N) of the corresponding carbanions.

Reagents for Selective Fluoromethylation: A Challenge in Organofluorine Chemistry

The introduction of a monofluoromethyl moiety has undoubtedly become a very important area of research in recent years. Owing to the beneficial properties of organofluorine compounds, such as their metabolic stability, the incorporation of the CH2 F group as a bioisosteric substitute for various functional groups is an attractive strategy for the discovery of new pharmaceuticals. Furthermore, the monofluoromethyl unit is also widely used in agrochemistry, in pharmaceutical chemistry, and in fine chemicals. The problems associated with climate change and the growing need for environmentally friendly industrial processes mean that alternatives to the frequently used CFC and HFBC fluoromethylating agents (CH2 FCl and CH2 FBr) are urgently needed and also required by the Montreal Protocol. This has recently prompted many researchers to develop alternative fluoromethylation agents. This Minireview summarizes both the classical and new generation of fluoromethylating agents. Reagents that act via electrophilic, nucleophilic, and radical pathways are discussed, in addition to their precursors.

Sulfones as Chemical Chameleons: Versatile Synthetic Equivalents of Small-Molecule Synthons

Sulfones are flexible functional groups that can act as nucleophiles, electrophiles, or even radicals. Changing the reaction conditions can completely alter the reactivity of a sulfonyl group, and as a result, molecules bearing multiple sulfones are versatile building blocks. This Review highlights the unique ability of 1,1- and 1,2-bis(sulfones) to masquerade as a vast array of reactive synthons including methane polyanions, vinyl cations, and all-carbon dipoles that would be difficult or impossible to access directly.

The Nucleophilicity of Persistent α-Monofluoromethide Anions

α-Fluorocarbanions are key intermediates in nucleophilic fluoroalkylation reactions. Although frequently discussed, the origin of the fluorine effect on the reactivity of α-fluorinated CH acids has remained largely unexplored. We have now investigated the kinetics of a series of reactions of α-substituted carbanions with reference electrophiles to elucidate the effects of α-F, α-Cl, and α-OMe substituents on the nucleophilic reactivities of carbanions.

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.