Samarium-Oxo/Hydroxy Cluster: A Solar Photocatalyst for Chemoselective Aerobic Oxidation of Thiols for Disulfide Synthesis.

Oxidation contributes as a secondary driver of the prevailing carbon emission in the chemical industries. To address this issue, photocatalytic aerobic oxidation has emerged as a promising alternative. However, the challenge of achieving satisfactory chemoselectivity and effective use of solar light has hindered progress in this area. In this context, the present study introduces a novel homogeneous photocatalyst, [Sm6O(OH)8(H2O)24]I8(H2O)8 cluster (Sm-OC), via a unique auxiliary ligand-free oxidative hydrolysis. Using Sm-OC as catalyst, a solar photocatalyzed aerobic oxidation of thiols has been developed for the synthesis of valuable disulfides. Remarkably, this catalyst manifested a significant turnover number ≥2000 under tested conditions. Sm-OC-catalyzed aerobic oxidation showcased remarkable chemoselectivity. In thiol oxidations, despite the vulnerability of disulfides toward overoxidation, overoxidized byproducts or oxidation of nontarget functional groups was not detected across all 28 tested substrates. This investigation presents the first application of a lanthanide-oxo/hydroxy cluster in photocatalysis.

Single Electron Transfer Reductive Deuteration of Acyl Chlorides for the Synthesis of Deuterated Alcohols with a High Deuterium Atom Economy.

We present a highly deuterium atom economical approach for the synthesis of deuterated alcohols via the single electron transfer (SET) reductive deuteration of acyl chlorides. Cost-effective sodium dispersion and EtOD-d1 were used as the single electron donor and deuterium donor, respectively. Our approach achieved up to 49% deuterium atom economy, which represents the highest deuterium atom economy yet achieved in SET reductive deuteration reactions. With all 20 tested substrates, excellent regioselectivity and >92% deuterium incorporations were obtained. Furthermore, we demonstrated the potential of this methodology by synthesizing four deuterated analogues of pesticides.

Photocatalytic Dehalogenative Deuteration of Halides over a Robust Metal-Organic Framework.

Deuterium labelling of organic compounds is an important process in chemistry. We report the first example of photocatalytic dehalogenative deuteration of both arylhalides and alkylhalides (40 substrates) over a metal-organic framework, MFM-300(Cr), using CD3 CN as the deuterium source at room temperature. MFM-300(Cr) catalyses high deuterium incorporation and shows excellent tolerance to various functional groups. Synchrotron X-ray powder diffraction reveals the activation of halogenated substrates via confined binding within MFM-300(Cr). In situ electron paramagnetic resonance spectroscopy confirms the formation of carbon-based radicals as intermediates and reveals the reaction pathway. This protocol removes the use of precious-metal catalysts from state-of-the-art processes based upon direct hydrogen isotope exchange and shows high photocatalytic stability, thus enabling multiple catalytic cycles.

Reductive Deuteration of Acyl Chlorides for the Synthesis of α,α-Dideuterio Alcohols Using SmI2 and D2O.

The synthesis of α,α-dideuterio alcohols has been achieved via single electron transfer reductive deuteration of acyl chlorides using SmI2 and D2O. This method is distinguished by its remarkable functional group tolerance and exquisite deuterium incorporation, which has also been applied to the synthesis of valuable deuterated agrochemicals and their building blocks.

Suzuki-Miyaura Cross-Coupling of Aryl Fluorosulfonates Mediated by Air- and Moisture-stable [Pd(NHC)(µ-Cl)Cl]2 Precatalysts: Broad Platform for C-O Cross-Coupling of Stable Phenolic Electrophiles.

A highly efficient protocol for the Suzuki-Miyaura cross-coupling of aryl fluorosulfonates by selective -OF cleavage using well-defined, air- and moisture-stable NHC-Pd(II) chloro dimers is presented. The reaction proceeds in excellent yields and with broad functional group tolerance using 0.10-0.20 mol % of [Pd] in the presence of mild K3PO4 base under aqueous conditions. A variety of sensitive functional groups are tolerated in this operationally trivial protocol for C-O bond activation. Selectivity studies and gram scale cross-coupling are presented. The method advances well-defined and highly reactive Pd(II)-NHCs to the cross-coupling of readily available, orthogonal, and bench-stable fluorosulfonates as aryl halide surrogates.

One-Pot Sequential Hydrogen Isotope Exchange/Reductive Deuteration for the Preparation of α,ß-Deuterated Alcohols using Deuterium Oxide.

An efficient one-pot sequential hydrogen isotope exchange (HIE)/reductive deuteration approach was developed for the preparation of α,ß-deuterated alcohols using ketones as the precursors. The HIE step can also be used for the synthesis of α-deuterated ketones. This method has been applied in the synthesis of four deuterated drug and MS internal standards.

Sequential Iron-Catalyzed C(sp2)-C(sp3) Cross-Coupling of Chlorobenzamides/Chemoselective Amide Reduction and Reductive Deuteration to Benzylic Alcohols.

Benzylic alcohols are among the most important intermediates in organic synthesis. Recently, the use of abundant metals has attracted significant attention due to the issues with the scarcity of platinum group metals. Herein, we report a sequential method for the synthesis of benzylic alcohols by a merger of iron catalyzed cross-coupling and highly chemoselective reduction of benzamides promoted by sodium dispersion in the presence of alcoholic donors. The method has been further extended to the synthesis of deuterated benzylic alcohols. The iron-catalyzed Kumada cross-coupling exploits the high stability of benzamide bonds, enabling challenging C(sp2)-C(sp3) cross-coupling with alkyl Grignard reagents that are prone to dimerization and ß-hydride elimination. The subsequent sodium dispersion promoted reduction of carboxamides proceeds with full chemoselectivity for the C-N bond cleavage of the carbinolamine intermediate. The method provides access to valuable benzylic alcohols, including deuterium-labelled benzylic alcohols, which are widely used as synthetic intermediates and pharmacokinetic probes in organic synthesis and medicinal chemistry. The combination of two benign metals by complementary reaction mechanisms enables to exploit underexplored avenues for organic synthesis.

Acyl fluorides as direct precursors to fluoride ketyl radicals: reductive deuteration using SmI2 and D2O.

A highly chemoselective reductive deuteration of acyl fluorides to provide α,α-dideuterio alcohols with exquisite levels of deuterium incorporation was developed using SmI2 and D2O as the deuterium source. This method introduces acyl fluorides as attractive radical precursors for the generation of reactive acyl-type fluoride ketyls that should find widespread application in many synthetic strategies involving single electron transfer processes.

Synthesis of α-Deuterated Primary Amines via Reductive Deuteration of Oximes Using D2O as a Deuterium Source.

Selective introduction of the deuterium atom into the α-position of amines is important for the development of all types of novel deuterated drugs and agrochemicals due to the pervasive presence of amines. In this study, we report the first general single-electron-transfer reductive deuteration of both ketoximes and aldoximes using SmI2 as an electron donor and D2O as a deuterium source for the synthesis of α-deuterated primary amines with excellent levels of deuterium incorporations (>95% [D]). This protocol exhibits excellent chemoselectivity and tolerates a variety of functional groups. The potential application of this new method was showcased in the synthesis of deuterated drugs, such as rimantadine-d4, the tebufenpyrad analogue, derivatives of nabumetone and pregnenolone, and a series of building blocks for the rapid and general assembly of deuterated drugs and pesticides.

Pentafluorophenyl Esters: Highly Chemoselective Ketyl Precursors for the Synthesis of α,α-Dideuterio Alcohols Using SmI2 and D2O as a Deuterium Source.

We report the first highly chemoselective synthesis of α,α-dideuterio alcohols with exquisite incorporation of deuterium (>98% [D2]) using pentafluorophenyl esters as ketyl radical precursors, SmI2 as a mild reducing agent, and D2O as the deuterium source. This system tolerates a variety of functional groups, offering rapid entry to valuable α,α-dideuterated alcohol building blocks. More generally, this report introduces pentafluorophenyl esters as the most reactive O-ketyl precursors reported to date.

Selective C-N σ Bond Cleavage in Azetidinyl Amides under Transition Metal-Free Conditions.

Functionalization of amide bond via the cleavage of a non-carbonyl, C-N σ bond remains under-investigated. In this work, a transition-metal-free single-electron transfer reaction has been developed for the C-N σ bond cleavage of N-acylazetidines using the electride derived from sodium dispersions and 15-crown-5. Of note, less strained cyclic amides and acyclic amides are stable under the reaction conditions, which features the excellent chemoselectivity of the reaction. This method is amenable to a range of unhindered and sterically encumbered azetidinyl amides.

A Practical and Chemoselective Ammonia-Free Birch Reduction.

A novel protocol for a significantly improved, practical, and chemoselective ammonia-free Birch reduction mediated by bench-stable sodium dispersions and recoverable 15-crown-5 ether is reported. A broad range of aromatic and heteroaromatic compounds is reduced with excellent yields.

Reduction and Reductive Deuteration of Tertiary Amides Mediated by Sodium Dispersions with Distinct Proton Donor-Dependent Chemoselectivity.

A practical and scalable single electron transfer reduction mediated by sodium dispersions has been developed for the reduction and reductive deuteration of tertiary amides. The chemoselectivity of this method highly depends on the nature of the proton donor. The challenging reduction via C-N bond cleavage has been achieved using Na/EtOH, affording alcohol products, while the use of Na/NaOH/H2O leads to the formation of amines via selective C-O scission. Sodium dispersions with high specific surface areas are crucial to obtain high yields and good chemoselectivity. This new method tolerates a range of tertiary amides. Moreover, the corresponding reductive deuterations mediated by Na/EtOD- d1 and Na/NaOH/D2O afford useful α,α-dideuterio alcohols and α,α-dideuterio amines with an excellent deuterium content.

Transition-Metal-Free, Selective Reductive Deuteration of Terminal Alkynes with Sodium Dispersions and EtOD- d1.

A transition-metal-free single electron transfer reaction has been developed for the synthesis of [D3]-alkenes from terminal alkynes using sodium dispersions as the electron donor and EtOD- d1 as the deuterium source. Both reagents are cost-effective and bench-stable. This practical method exhibits remarkable terminal alkyne selectivity and exclusive alkene selectivity. Excellent deuterium incorporations and yields were achieved across a broad range of terminal alkynes without olefin isomerization. Of note, this reaction is highly solvent dependent. n-Hexane provides unique enhancement to this reductive deuteration process.

Development of a Modified Bouveault-Blanc Reduction for the Selective Synthesis of α,α-Dideuterio Alcohols.

A modified Bouveault-Blanc reduction has been developed for the synthesis of α,α-dideuterio alcohols from carboxylic acid esters. Sodium dispersions are used as the electron donor in this electron transfer reaction, and ethanol-d1 is employed as the deuterium source. This reaction uses stable, cheap, and commercially available reagents, is operationally simple, and results in excellent deuterium incorporation across a broad range of aliphatic esters, which provides an attractive alternative to reactions mediated by expensive pyrophoric alkali metal deuterides.