Rhenium-catalyzed deoxygenation of epoxides without adding any reducing agent

This work reports a novel method for the deoxygenation of epoxides catalyzed by oxo-rhenium (V) and (VII) complexes without adding any reducing agent. This eco-friendly methodology was successfully applied to the deoxygenation of several epoxides with tolerance of different functional groups and high reusability of the catalysts ReIO₂(PPh₃)₂ and ReOCl₃(PPh₃)₂.     

Highly efficient and chemoselective reduction of sulfoxides using the system silane/oxo-rhenium complexes

This work reports a novel method for the reduction of sulfoxides with silanes catalyzed by high valent oxo-rhenium(V) and (VII) complexes. The catalytic system PhSiH₃/ReIO₂(PPh₃)₂ (1 mol %) proved to be highly efficient for the reduction of a wide range of sulfoxides in excellent yields under mild conditions. This novel methodology is also highly chemoselective, tolerating several functional groups such as –CHO, –CO₂R, –Cl, –NO₂, and double or triple bonds.     

Silica–PSCl3: A Mild and Efficient Reagent for Deoxygenation of Sulfoxides

A new solid supported reagent, silica–PSCl₃, has been developed for deoxygenation of sulfoxides. With this reagent, conversion of sulfoxides to sulfides occurred cleanly and efficiently at room temperature. Facile isolation of the product was achieved by simple filtration of the by‐products without any extensive workup.     

Lewis acid-promoted electron transfer deoxygenation of epoxides, sulfoxides, and amine N-oxides: the role of low-valent niobium complexes from NbCl5 and Zn

A mild and operationally simple deoxygenation of epoxides, sulfoxides, and amine N-oxides is described using a sub-stoichiometric amount of low-valent niobium complexes generated in situ from commercially available NbCl₅ and zinc dust. The deoxygenation proceeds by a reductive cleavage of polarized O-C/O-N/O-S bonds through a single electron transfer from zinc metal to the niobium-substrate complex due to the high oxophilic nature of the niobium species. The presence of adjacent radical-stabilizing groups is beneficial to epoxide substrates; however the similar prerequisite does not apply to sulfoxides and amine N-oxides, where a broad range of substrates are efficiently deoxygenated in excellent yields.     

The deoxygenation of sulfoxide mediated by the Ph3P/Lewis acid combination and the application to the kinetic resolution of racemic phosphines using optically active sulfoxide

It was found that the combination of Ph₃P/TiCl₄ was an effective promoter for the deoxygenation of sulfoxides and gave the corresponding sulfides in good yield (up to 97%) under mild conditions. This method was applied to the reaction between racemic phosphines and (R)-methyl p-tolyl sulfoxide, and it was found that the kinetic resolution was achieved in moderate selectivities.     

Reduction of sulfoxides catalyzed by oxo-complexes

This work reports the catalytic activity of the oxo-complexes HReO₄, MoO₂(acac)₂, WO₂Cl₂, and VO(acac)₂ in the reduction of sulfoxides with PhSiH₃ or HBcat. The results obtained showed that the catalyst systems PhSiH₃/HReO₄ (5 mol %) and HBcat/HReO₄ (5 mol %) are highly efficient for the deoxygenation of sulfoxides. The complex MoO₂(acac)₂ was also efficient, but the reactions required more time and heating. Finally, the complexes WO₂Cl₂ and VO(acac)₂ showed a moderate activity.     

Homolytic Cleavage of a B−B Bond by the Cooperative Catalysis of Two Lewis Bases: Computational Design and Experimental Verification

Density functional theory (DFT) investigations revealed that 4‐cyanopyridine was capable of homolytically cleaving the B?B σ bond of diborane via the cooperative coordination to the two boron atoms of the diborane to generate pyridine boryl radicals. Our experimental verification provides supportive evidence for this new B?B activation mode. With this novel activation strategy, we have experimentally realized the catalytic reduction of azo‐compounds to hydrazine derivatives, deoxygenation of sulfoxides to sulfides, and reduction of quinones with B₂(pin)₂ at mild conditions.     

Mild and Efficient Deoxygenation of Sulfoxides to Sulfides Using HfCl4/KBH4 System

HfCl₄/KBH₄ was found to be a facile, efficient, convenient, and chemoselective system for the deoxygenation of dialkyl, diaryl, and aryl alkyl sulfoxides, especially for the reduction of dibenzyl sulfoxide to the corresponding sulfides under mild conditions. In addition, the HfCl₄/KBH₄ system could be used in reduction of some other sulfur-bearing substrates to the corresponding sulfides, such as 2,2′-dibenzothiazolyl disulfide, but this reducing system could not reduce sulfolane, diphenyl sulfone, p-toluenesulfonic acid, and p-toluenesulfonyl chloride to their corresponding thiophenols.     

Efficient Organic Transformations Mediated by ZrOCl2·8H2O in Water

Abstract

Operationally simple and environmentally benign methods for some organic transformations comprising reductive coupling of sulfonyl chlorides, chemoselective deoxygenation of sulfoxides, and halogenation of alcohols mediated by ZrOCl₂·8H₂O/MX in water have been developed.

GRAPHICAL ABSTRACT     

A Sulfoxide Reduction Method Using Low Valent Molybdenum Acetates

It has been demonstrated that molybdenum(III) ion is effective for deoxygenation of sulfoxides.¹ However, since this reagent was generated by treatment of molybdenyl chloride with zinc dust, the role of some suspended metal in the sulfoxide reduction cannot be assessed. In order to conclusively establish the reducing capability of low-valent molybdenum ions for sulfoxides we have carried out experiments with Mo species obtained in a manner that the suspicion of active metal participation is exonerated.     

The syntheses of sulfides by deoxygenation of sulfoxides using Woollins’ reagent

Woollins’ reagent (WR) acts as a deoxygenation reagent for a wide range of sulfoxides affording the corresponding sulfides in good to excellent yields (up to 99% isolated yield) under mild conditions.     

A novel efficient and chemoselective method for the reduction of nitriles using the system silane/oxo-rhenium complexes

This work reports the reduction of nitriles to the corresponding primary amines with silanes catalyzed by oxo-rhenium complexes. The catalytic system PhSiH₃/ReIO₂(PPh₃)₂ (10 mol %) reduced efficiently a series of nitriles in the presence of a wide range of functional groups such as -Cl, -F, -Br, -I, -CF₃, -OCH₃, -SCH₃, -SO₂CH₃ and -NHTs.     

Highly regio- and stereoselective PdCl2(MeCN)2-catalyzed cross coupling of 1,2-allenylic sulfoxides with allyl bromide

2-Allyl-1(E),3(E)-dienyl sulfoxides were prepared highly stereoselectively via the PdCl₂(MeCN)₂-catalyzed coupling reaction of 1,2-allenylic sulfoxides and allyl bromide. A rationale was proposed for this transformation.     

Hydrogen activation by high-valent oxo-molybdenum(VI) and -rhenium(VII) and -(V) compounds

The high-valent oxo-molybdenum(VI) and -rhenium(VII) and -(V) derivatives MoO2Cl2, ReCH3O3 (MTO) and ReIO2(PPh3)2 catalyze the selective hydrogenation of alkynes to alkenes at 80 degrees C under 40 atm of pressure. The reduction of sulfoxides to sulfides has also been performed by oxo-rhenium and -molybdenum complexes using hydrogen as a reducing agent. Activation of hydrogen by MoO2Cl2 and MoO2(S2CNEt2)2 was shown by means of DFT calculations to proceed by H-H addition to the Mo=O bond, followed by hydride migration to yield a water complex.     

The Stereospecific Tert-Butyllithium Reduction of Triene Sulfoxides: Improved Levels of Deuterium Incorporation

Treatment of triene sulfoxides with t-BuLi and methanol-O-d₁ in D₂O-wet ether leads to trienes with practical levels (96%) of deuterium incorporation. Alternatively, successive treatment of triene sulfoxides dwith CH₃Li and then t-BuLi followed by methanol-O-d₁ quench affords similar levels of label incorporation.     

Sulfoxide-controlled SN2′ displacements between cuprates and vinyl and alkynyl epoxy sulfoxides

The S_N2′ displacement of readily available vinyl epoxy sulfoxides with organocopper reagents takes place in good yields with high anti selectivity and a good degree of E/Z stereocontrol to produce enantiopure α-hydroxy vinyl sulfoxides. A second allylic displacement on the related mesyloxy vinyl sulfoxides allows for the asymmetric construction of two adjacent chiral centers. In addition, cuprate mediated S_N2′ addition to alkynyl epoxy sulfoxides affords α-hydroxy allenyl sulfoxides in good yields.     

Electrophilic Chlorine from Chlorosulfonium Salts: A Highly Chemoselective Reduction of Sulfoxides

Herein, we describe a selective late-stage deoxygenation of sulfoxides based on a novel application of chlorosulfonium salts and demonstrate a new process using these species generated in situ from sulfoxides as the source of electrophilic chlorine. The use of highly nucleophilic 1,3,5-trimethoxybenzene (TMB) as the reducing agent is described for the first time and applied in the deoxygenation of simple and functionalized sulfoxides. The method is easy to handle, economic, suitable for gram-scale operations, and readily applied for poly-functionalized molecules, as demonstrated with more than 45 examples, including commercial medicines and analogues. We also report the results of competition experiments that define the more reactive sulfoxide and we present a mechanistic proposal based on substrate and product observations.     

Studies on the highly regio- and stereoselective selenohydroxylation of 1,2-allenylic sulfoxides with PhSeCl

The selenohydroxylation of 1,2-allenyl sulfoxides with PhSeCl in MeCN/H₂O (10/1) afforded E-3-hydroxy-2-phenylseleno-1-alkenyl sulfoxides in good yields and high regio-/stereoselectivities.     

Synthesis and equilibrium studies of new dihydrothiophene sulfoxides

Oxidation of the Knoevenagel condensation products 2 of 3-oxo- tetrahydrothiophene (1) and active methylene compounds of the type Z-CH₂-COOH with an H₂O₂/V₂O₅/t-BuOH reagent furnishes the corresponding sulfoxides 3 in excellent yields. The isomer distributions of the sulfides 2 and the sulfoxides 3 reflect peculiarities of hydrothiophenes as compared to similar open-chain systems and establish that the stabilizing effect of the sulfoxide group on β, γ-double bonds is greater than the corresponding effect of so strongly stabilizing groups as CN and COOR.     

Theoretical study on the reaction mechanism of NO and CO catalyzed by Rh atom

The gas-phase reaction mechanism of NO and CO catalyzed by Rh atom has been systematically investigated on the ground and first excited states at CCSD(T)//B3LYP/6-311+G(2d), SDD level. This reaction is mainly divided into two reaction stages, NO deoxygenation to generate N₂O and then the deoxygenation of N₂O with CO to form N₂ and CO₂. The crucial reaction step deals with the NO deoxygenation to generate N₂O catalyzed by Rh atom, in which the self-deoxygenation of NO reaction pathway is kinetically more preferable than that in the presence of CO. The minimal energy reaction pathway includes the rate-determining step about N–N bond formation. Once the NO deoxygenation with CO catalyzed by rhodium atom takes place, the reaction results in the intermediate RhN. Then, the reaction of RhN with CO is kinetically more favorable than that with NO, while both of them are thermodynamically preferable. These results can qualitatively explain the experimental finding of N₂O, NCO, and CN species in the NO + CO reaction. For the N₂O deoxygenation with CO catalyzed by rhodium atom, the reaction goes facilely forward, which involves the rate-determining step concerning CO₂ formation. CO plays a dominating role in the RhO reduction to regenerate Rh atom. The complexes, OCRhNO, RhON₂, RhNNO, ORhN₂, RhCO₂, RhNCO, and ORhCN, are thermodynamically preferred. Rh atom possesses stronger capability for the N₂O deoxygenation than Rh⁺ cation.