Perrhenate Esters as Intermediates in Molecular Complexity-Increasing Reactions

Allylic alcohols form perrhenate esters upon reaction with Re2O7 or HOReO3. These species undergo nonstereospecific and nonregiospecific alcohol-transposition reactions through cationic intermediates. Sequencing these nonselective processes with reversible trapping by electrophiles results in cyclization reactions where regio- and stereocontrol are dictated by thermodynamics. The cationic intermediates can also be utilized as electrophiles in intra- or intermolecular dehydrative reactions with nucleophiles. These processes serve as the basis for applications in catalytic syntheses of a wide range of heterocyclic and carbocyclic structures that often show considerable increases in molecular complexity. This Account describes a sequence of events that started from a need to solve a problem for the completion of a natural product synthesis and evolved into a central element in the design of numerous new transformations that proceed under mild conditions from readily accessible substrates.1 Introduction2 Exploratory Studies3 Application to Spiroketal Synthesis4 Reactions with Epoxides as Trapping Agents5 Development of Dehydrative Cyclizations6 Bimolecular Reactions7 Spirocyclic Ether Formation8 Conclusions

Bifluoride Ion Mediated SuFEx Trifluoromethylation of Sulfonyl Fluorides and Iminosulfur Oxydifluorides

Sulfur-Fluoride Exchange (SuFEx) is the new generation click chemistry transformation exploiting the unique properties of S-F bonds and their ability to undergo near-perfect reactions with nucleophiles. We report here the first SuFEx based protocol for the efficient synthesis of pharmaceutically important triflones and bis(trifluoromethyl)sulfur oxyimines from the corresponding sulfonyl fluorides and iminosulfur oxydifluorides, respectively. The new protocol involves the rapid exchange of the S-F bond with trifluoromethyltrimethylsilane (TMSCF₃) upon activation with potassium bifluoride in anhydrous DMSO. The reaction tolerates a wide selection of substrates and proceeds under mild conditions without need for chromatographic purification. A tentative catalytic mechanism is proposed supported by DFT calculations, involving formation of the free trifluoromethyl anion followed by nucleophilic displacement of the S-F through a five-coordinate intermediate. The preparation of a benzothiazole derived bis(trifluoromethyl)sulfur oxyimine with cytotoxic selectivity for MCF7 breast cancer cells demonstrates the utility of this methodology for the late-stage functionalization of bioactive molecules.<br>

Bifluoride Ion Mediated SuFEx Trifluoromethylation of Sulfonyl Fluorides and Iminosulfur Oxydifluorides

Sulfur-Fluoride Exchange (SuFEx) is the new generation click chemistry transformation exploiting the unique properties of S-F bonds and their ability to undergo near-perfect reactions with nucleophiles. We report here the first SuFEx based protocol for the efficient synthesis of pharmaceutically important triflones and bis(trifluoromethyl)sulfur oxyimines from the corresponding sulfonyl fluorides and iminosulfur oxydifluorides, respectively. The new protocol involves the rapid exchange of the S-F bond with trifluoromethyltrimethylsilane (TMSCF₃) upon activation with potassium bifluoride in anhydrous DMSO. The reaction tolerates a wide selection of substrates and proceeds under mild conditions without need for chromatographic purification. A tentative catalytic mechanism is proposed supported by DFT calculations, involving formation of the free trifluoromethyl anion followed by nucleophilic displacement of the S-F through a five-coordinate intermediate. The preparation of a benzothiazole derived bis(trifluoromethyl)sulfur oxyimine with cytotoxic selectivity for MCF7 breast cancer cells demonstrates the utility of this methodology for the late-stage functionalization of bioactive molecules.<br>

Bifluoride Ion Catalyzed Late-Stage SuFEx Trifluoromethylation of Sulfonyl Fluorides and Iminosulfur Oxydifluorides

Sulfur-Fluoride Exchange (SuFEx) is a new generation click chemistry transformation that exploits the unique properties of S-F bonds and their ability to undergo near-perfect reactions with nucleophiles. We report here the first SuFEx based protocol for the efficient late-stage synthesis of pharmaceutically important trifluoromethyl sulfones and bis(trifluoromethyl)sulfur oxyimines from the corresponding sulfonyl fluorides and iminosulfur oxydifluorides, respectively. The new protocol involves the rapid exchange of the S-F bond with trifluoromethyltrimethylsilane (TMSCF₃, Ruppert’s reagent), upon activation with catalytic potassium bifluoride in anhydrous DMSO. The reaction tolerates a wide selection of substrates and proceeds under mild conditions without need for chromatographic purification. DFT calculations provide the first reported mechanism of anhydrous SuFEx reactivity, which confirms catalytic bifluoride behaviour with a five-coordinate sulfur intermediate. The preparation of a benzothiazole derived bis(trifluoromethyl)sulfur oxyimine with cytotoxic selectivity for MCF7 breast cancer cells demonstrates the utility of this methodology for the late stage functionalization of bioactive molecules.

Bifluoride Ion Catalyzed Late-Stage SuFEx Trifluoromethylation of Sulfonyl Fluorides and Iminosulfur Oxydifluorides

Sulfur-Fluoride Exchange (SuFEx) is a new generation click chemistry transformation that exploits the unique properties of S-F bonds and their ability to undergo near-perfect reactions with nucleophiles. We report here the first SuFEx based protocol for the efficient late-stage synthesis of pharmaceutically important trifluoromethyl sulfones and bis(trifluoromethyl)sulfur oxyimines from the corresponding sulfonyl fluorides and iminosulfur oxydifluorides, respectively. The new protocol involves the rapid exchange of the S-F bond with trifluoromethyltrimethylsilane (TMSCF₃, Ruppert’s reagent), upon activation with catalytic potassium bifluoride in anhydrous DMSO. The reaction tolerates a wide selection of substrates and proceeds under mild conditions without need for chromatographic purification. DFT calculations provide the first reported mechanism of anhydrous SuFEx reactivity, which confirms catalytic bifluoride behaviour with a five-coordinate sulfur intermediate. The preparation of a benzothiazole derived bis(trifluoromethyl)sulfur oxyimine with cytotoxic selectivity for MCF7 breast cancer cells demonstrates the utility of this methodology for the late stage functionalization of bioactive molecules.

The structure of ortho-(trifluoromethyl)phenol in comparison to its homologues – A combined experimental and theoretical study

The molecular and crystal structure of commercially-availableortho-(trifluoromethyl)phenol were determined by means of single-crystal X-ray diffractometry (XRD) and represent the first structural characterization of anortho-substituted (trihalomethyl) phenol. The unexpected presence of a defined hydrate in the solid state was observed.Intermolecular contacts and hydrogen bonding were analyzed. The compound was further characterized by means of multi-nuclear nuclear magnetic resonance (NMR) spectroscopy (1H,13C{1H},19F) and Fourier-Transform infrared (FT-IR) vibrational spectroscopy. To assess the bonding situation as well as potential reaction sites for reactions with nucleophiles and electrophiles in the compound by means of natural bonding orbital (NBO) analyses, and density functional theory (DFT) calculations were performed for the title compound as well as its homologous chlorine, bromine and iodine compounds. As far as possible, experimental data were correlated to DFT data.

4-Selective Pyridine Functionalization Reactions via Heterocyclic Phosphonium Salts

Pyridines are widely used across the chemical sciences in applications ranging from pharmaceuticals, ligands for metal complex and battery technologies. Direct functionalization of pyridine C–H bonds is an important strategy to make useful pyridine derivatives, but there are few ways to selectively transform the 4-position of the scaffold. We recently reported that pyridines can be converted into heterocyclic phosphonium salts that can serve as generic handles for multiple subsequent bond-forming processes. Reactions with nucleophiles and transition-metal cross-couplings will be described to make C–O, C–S, C–N, and C–C bonds in a diverse range of pyridines including those embedded in complex pharmaceuticals.1 Introduction2 Direct, Regioselective Functionalization of Pyridines3 4-Position Selectivity via Metal Catalysis4 Versatile Functional Groups versus Specific Bond Constructions5 Phosphonium Salts as Reagents for Pyridine Functionalization6 Conclusions

Recent Advances in Magnesium Carbenoid Chemistry

Magnesium carbenoids are a class of organomagnesium species possessing a halo group at the α-position. The reactions of magnesium carbenoids can be classified into the following three categories: nucleophilic reactions resembling Grignard reagents, electrophilic reactions resembling organic halides, and rearrangements resembling carbenes. This short review summarizes recent studies on magnesium carbenoids reported between 2010 and 2016, and milestone studies reported before 2010 according to the classification of the reactions into the aforementioned three categories.1 Introduction2 Structures of Magnesium Carbenoids3 Reactions of Magnesium Carbenoids as Nucleophiles3.1 Nucleophilic Reactions of Magnesium Carbenoids3.2 Nucleophilic Reactions of Magnesium Alkylidene Carbenoids3.3 Nucleophilic Reactions of Cyclopropylmagnesium Carbenoids4 Electrophilic Reactions of Magnesium Carbenoids4.1 Reactions with Nucleophiles Followed by Electrophiles4.2 Reactions with Nucleophiles Possessing Electrophilic Functional Groups4.3 Nucleophilic Substitution Followed by β-Elimination5 Rearrangements of Magnesium Carbenoids5.1 1,2-Shifts of Magnesium Carbenoids5.2 1,3-C–H Insertions of Magnesium Carbenoids5.3 1,5-C–H Insertions of Magnesium Carbenoids5.4 [2+1] Cycloaddition of a Magnesium Carbenoid6 Conclusion and Outlook