4-Trifluoromethoxy proline: synthesis of stereoisomers and lipophilicity study

All four stereoisomers of 4-CF3O-proline have been synthesized through a fluorodesulfurization approach using the corresponding 4-hydroxyprolines as starting materials. The investigation of their lipophilicity characteristics and comparison with those of other 4-substituted proline analogs demonstrated a similar impact of CF3 and CF3O groups on log D.

Reactivity of [AuF3 (SIMes)]: Pathway to Unprecedented Structural Motifs

We report on a comprehensive reactivity study starting from [AuF3 (SIMes)] to synthesize different motifs of monomeric gold(III) fluorides. A plethora of different ligands has been introduced in a mono-substitution yielding trans-[AuF2 X(SIMes)] including alkynido, cyanido, azido, and a set of perfluoroalkoxido complexes. The latter were better accomplished via use of perfluorinated carbonyl-bearing molecules, which is unprecedented in gold chemistry. In case of the cyanide and azide, triple substitution gave rise to the corresponding [AuX3 (SIMes)] complexes. Comparison of the chemical shift of the carbene carbon atom in the 13 C{1 H} NMR spectrum, the calculated SIMes affinity and the Au-C bond length in the solid state with related literature-known complexes yields a classification of trans-influences for a variety of ligands attached to the gold center. Therein, the mixed fluorido perfluoroalkoxido complexes have a similar SIMes affinity to AuF3 with a very low Gibbs energy of formation when using the perfluoro carbonyl route.

Direct Allylic C(sp3 )-H and Vinylic C(sp2 )-H Thiolation with Hydrogen Evolution by Quantum Dots and Visible Light

Direct allylic C-H thiolation is straightforward for allylic C(sp³ )-S bond formation. However, strong interactions between thiol and transition metal catalysts lead to deactivation of the catalytic cycle or oxidation of sulfur atom under oxidative condition. Thus, direct allylic C(sp³ )-H thiolation has proved difficult. Represented herein is an exceptional for direct, efficient, atom- and step-economic thiolation of allylic C(sp³ )-H and thiol S-H under visible light irradiation. Radical trapping experiments and electron paramagnetic resonance (EPR) spectroscopy identified the allylic radical and thiyl radical generated on the surface of photocatalyst quantum dots (QDs). The C-S bond formation does not require external oxidants and radical initiators, and hydrogen (H₂ ) is produced as byproduct. When vinylic C(sp² )-H was used instead of allylic C(sp³ )-H bond, the radical-radical cross-coupling of C(sp² )-H and S-H was achieved with liberation of H₂ . Such a unique transformation opens up a door toward direct C-H and S-H coupling for valuable organosulfur chemistry.

Tertiary-Amine-Initiated Synthesis of Acyl Fluorides from Carboxylic Acids and CF3 SO2 OCF3

A convenient method for deoxyfluorination of aromatic and aliphatic carboxylic acids with CF₃ SO₂ OCF₃ in the presence of a suitable base at room temperature has been developed. The reaction allows a straightforward access to a variety of acyl fluorides and proves that CF₃ SO₂ OCF₃ is an effective deoxyfluorination reagent for carboxylic acids. The method features simplicity, expeditiousness, high efficiency, ease of handling, good functional group tolerance, a wide range of substrates, excellent yields of products, compatibility of many amine initiators, use of environmentally friendly reagents, and effortless removal of byproducts. This reaction represents the first utilization of trifluoromethyl trifluoromethanesulfonate as a fluorination reagent.

Visible-Light Photoredox-Catalyzed and Copper-Promoted Trifluoromethoxylation of Arenediazonium Tetrafluoroborates

We report the development of photoredox-catalyzed and copper-promoted trifluoromethoxylation of arenediazonium tetrafluoroborates, with trifluoromethyl arylsulfonate (TFMS) as the trifluoromethoxylation reagent. This new method takes advantage of visible-light photoredox catalysis to generate the aryl radical under mild conditions, combined with copper-promoted selective trifluoromethoxylation. The reaction is scalable, tolerates a wide range of functional groups, and proceeds regioselectively under mild reaction conditions. Furthermore, mechanistic studies suggested that a Cs[Cu(OCF₃ )₂ ] intermediate might be generated during the reaction.

Redox-Active Reagents for Photocatalytic Generation of the OCF3 Radical and (Hetero)Aryl C-H Trifluoromethoxylation

The trifluoromethoxy (OCF3 ) radical is of great importance in organic chemistry. Yet, the catalytic and selective generation of this radical at room temperature and pressure remains a longstanding challenge. Herein, the design and development of a redox-active cationic reagent (1) that enables the formation of the OCF3 radical in a controllable, selective, and catalytic fashion under visible-light photocatalytic conditions is reported. More importantly, the reagent allows catalytic, intermolecular C-H trifluoromethoxylation of a broad array of (hetero)arenes and biorelevant compounds. Experimental and computational studies suggest single electron transfer (SET) from excited photoredox catalysts to 1 resulting in exclusive liberation of the OCF3 radical. Addition of this radical to (hetero)arenes gives trifluoromethoxylated cyclohexadienyl radicals that are oxidized and deprotonated to afford the products of trifluoromethoxylation.

Intermolecular Allylic C-H Etherification of Internal Olefins

Herein we report on the development of an oxidative allylic C-H etherification reaction, utilizing internal olefins and alcohols as simple precursors. Key advances include the use of RhCp* complexes to promote the allylic C-H functionalization of internal olefins and the compatibility of the oxidative conditions with oxidatively sensitive alcohols, enabling the direct etherification reaction. Preliminary mechanistic studies, consistent with C-H functionalization as the rate determining step, are presented.

Silver-Promoted Oxidative Benzylic C-H Trifluoromethoxylation

A silver-promoted oxidative benzylic C-H trifluoromethoxylation has been reported for the first time. With trifluoromethyl arylsulfonate as the trifluoromethoxylation reagent, various arenes, having diverse functional groups, undergo trifluoromethoxylation of their benzylic C-H bonds to form trifluoromethyl ethers under mild reaction conditions. In addition, the trifluoromethoxylation and the fluorination of methyl groups of electron-rich arenes have been achieved to prepare α-fluorobenzyl trifluoromethyl ethers in one step.

Radical Trifluoromethoxylation of Arenes Triggered by a Visible-Light-Mediated N-O Bond Redox Fragmentation

A simple trifluoromethoxylation method enables non-directed functionalization of C-H bonds on a range of substrates, providing access to aryl trifluoromethyl ethers. This light-driven process is distinctly different from conventional procedures and occurs through an OCF₃ radical mechanism mediated by a photoredox catalyst, which triggers an N-O bond fragmentation. The pyridinium-based trifluoromethoxylation reagent is bench-stable and provides access to synthetic diversity in lead compounds in an operationally simple manner.

Catalytic C-H Trifluoromethoxylation of Arenes and Heteroarenes

The intermolecular C-H trifluoromethoxylation of arenes remains a long-standing and unsolved problem in organic synthesis. Herein, we report the first catalytic protocol employing a novel trifluoromethoxylating reagent and redox-active catalysts for the direct (hetero)aryl C-H trifluoromethoxylation. Our approach is operationally simple, proceeds at room temperature, uses easy-to-handle reagents, requires only 0.03 mol % of redox-active catalysts, does not need specialized reaction apparatus, and tolerates a wide variety of functional groups and complex structures such as sugars and natural product derivatives. Importantly, both ground-state and photoexcited redox-active catalysts are effective. Detailed computational and experimental studies suggest a unique reaction pathway where photoexcitation of the trifluoromethoxylating reagent releases the OCF3 radical that is trapped by (hetero)arenes. The resulting cyclohexadienyl radicals are oxidized by redox-active catalysts and deprotonated to form the desired products of trifluoromethoxylation.

A Radical Revolution for Trifluoromethoxylation

The study of OCF₃ -substituted molecules is somewhat hampered by a lack of diverse synthetic methods to access them. By introducing a new mild and practical reaction system for accessing the ^. OCF₃ radical, a recent study by Liu, Ngai, and co-workers has the potential to dramatically expand the scope of direct trifluoromethoxylation. The features of this ground-breaking system are discussed and placed into context with other recent advances on nucleophilic trifluoromethoxylation.

Direct Dehydroxytrifluoromethoxylation of Alcohols

The first example of a direct dehydroxytrifluoromethoxylation of alcohols has been developed. This method generated an alkyl fluoroformate in situ from alcohols, followed by nucleophilic trifluoromethoxylation with trifluoromethyl arylsulfonate (TFMS) as the trifluoromethoxylation reagent. The reaction is operationally simple and scalable, and it proceeds under mild reaction conditions to provide access to a wide range of trifluoromethyl ethers from alcohols. In addition, this method is suitable for the late-stage trifluoromethoxylation of complex small molecules.