Two Distinct Mechanisms of Alkyne Insertion into the Metal–Sulfur Bond: Combined Experimental and Theoretical Study and Application in Catalysis

The present study reports the evidence for the multiple carbon–carbon bond insertion into the metal–heteroatom bond via a five‐coordinate metal complex. Detailed analysis of the model catalytic reaction of the carbon–sulfur (C? S) bond formation unveiled the mechanism of metal‐mediated alkyne insertion: a new pathway of C? S bond formation without preliminary ligand dissociation was revealed based on experimental and theoretical investigations. According to this pathway alkyne insertion into the metal–sulfur bond led to the formation of intermediate metal complex capable of direct C? S reductive elimination. In contrast, an intermediate metal complex formed through alkyne insertion through the traditional pathway involving preliminary ligand dissociation suffered from “improper” geometry configuration, which may block the whole catalytic cycle. A new catalytic system was developed to solve the problem of stereoselective S? S bond addition to internal alkynes and a cost‐efficient Ni‐catalyzed synthetic procedure is reported to furnish formation of target vinyl sulfides with high yields (up to 99 %) and excellent Z/E selectivity (>99:1).     

Synthesis and Diversification of Macrocyclic Alkynediyl Sulfide Peptides

The synthesis of rare macrocyclic alkynediyl sulfides by a Cu-catalyzed C_sp−S cross-coupling is presented. The catalytic protocol (Cu(MeCN)₄PF₆/dtbbpy) promotes macrocyclization of peptides, dipeptides and tripeptides at ambient temperature (14 examples, 23→73 % yields) via thiols and bromoalkynes, and is chemoselective with regards to terminal alkynes. Importantly, the underexplored alkynediyl sulfide functionality incorporates a rigidifying structural element and opens new opportunities for diversification of macrocyclic frameworks through S oxidation, halide addition and azide–alkyne cycloaddition chemistries to integrate sulfones, halides or valuable fluorophores (7 examples, 37→92 % yields).     

One-Step Synthesis of Unsymmetrical Sulfides Bearing Hexafluorocumyl Moiety

A facile and convenient one-pot synthesis of novel unsymmetrical sulfides, 2′-alkylthio- and 2′-arylthio-1,1,1,3,3,3-hexafluoro-2-phenylpropan-2-oles 1a–k, is presented. Physicochemical characterization; IR infrared; ¹H, ¹³C, and ¹⁹F NMR; and mass spectral analyses of the obtained compounds are discussed as well.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]     

Reaction of 2-imino-2H-chromene-3-carboxamide with phosphorus sulfides: Synthesis of novel 2-sulfido-2,3-dihydro-4H-chromeno[2,3-d][1,3,2]diaza-phosphinines

Abstract

Novel 2-sulfido-2,3-dihydro-4H-chromeno[2,3-d][1,3,2]diazaphosphinines are obtained in a simple one-pot procedure via treatment of 2-imino-2H-chromene-3-carboxamide with various phosphorus sulfides. Possible reaction mechanisms are proposed. The structure of the obtained products is confirmed by elemental analyses and spectral tools.     

Asymmetric oxidation of sulfides catalyzed by chiral (salen)Mn(III) complexes with a pyrrolidine backbone

Catalytic properties of a series of chiral (pyrrolidine salen)Mn(III) complexes for asymmetric oxidation of aryl methyl sulfides were evaluated. Moderate activity, good chemical selectivity and low enantioselectivity were attained with iodosylbenzene as a terminal oxidant. Enantioselectivity of sulfide oxidation was affected slightly by polar solvent and the sulfoxidation carried out in THF for thioanisole and in CH₃CO₂Et for electron‐deficient sulfides gave better enatioselctivities. The addition of the donor ligand PPNO (4‐phenylpyridine N‐oxide) or MNO (trimethylamine N‐oxide) only has a minor positive effect on the enantioselectivity. Also explored was the steric effect of the N_aza‐substituent in the backbone of (pyrrolidine salen)Mn(III) complexes on the enantioselectivity of sulfide oxidation. The sulfides' access pathway is discussed based on the catalytic results. Copyright © 2006 John Wiley & Sons, Ltd.     

Palladium‐Catalyzed Amination of Aryl Sulfides with Anilines

A combination of a palladium–NHC catalyst and potassium hexamethyldisilazide enables the amination of aryl sulfides with anilines to afford a wide variety of diarylamines. The reaction conditions are versatile enough for the reaction of even bulky ortho‐substituted aryl sulfides. This amination can be applied to the modular synthesis of N‐aryl carbazoles from the corresponding ortho‐bromothioanisoles. As aryl sulfoxides undergo extended Pummerer reactions to afford ortho‐substituted aryl sulfides, the Pummerer products are thus useful substrates for the amination to culminate in efficient syntheses of a 2‐anilinobenzothiophene and an indole as proof‐of‐principle of the utility of the extended Pummerer reaction/amination cascade.     

Metal-Free Highly Efficient Aerobic Oxidation of Sulfides to Sulfoxides Catalyzed by DBDMH/TBN/H2O

A highly efficient metal-free catalytic system, 1,3-dibromo-5,5-dimethylhydantoin (DBDMH)–tert-butylnitrite (TBN)–H₂O, has been developed for an environmentally friendly and economical aerobic acid-free oxidation of sulfides. TBN was identified as an efficient NO equivalent for the activation of molecular oxygen. Under optimal conditions, a variety of sulfides substrates were converted into their corresponding sulfoxides in good yields by molecular oxygen.     

Stereoselective Synthesis of Substituted 2-(Z-Styrylsulfonyl)-1H-imidazoles and Benzothiazole

A novel method has been reported involving the synthesis of z-styryl sulfides by the reaction of phenylacetylene with 2-mercpto benzimidazoles and benzthiazole using NaOH as a base in absolute ethanol. On further oxidation with H₂O₂, these resulted in the formation of the desired styryl sulfones in good yields with retention of stereochemistry.     

Syntheses and Antimicrobial Activity of Some Novel 6‐Substituted Dibenzo[d,f][1,3,2]dioxaphophepin‐6‐oxides,Sulfides, and Selenides

6‐Substituted‐dibenzo[d, f][1,3,2]dioxaposphepin‐6‐oxides, sulfides, and selenides (5a–i, 6a–d, and 7a–d) were synthesized by reacting 2,2′‐biphenol (1) with phosphorus tribromide in the presence of triethylamine at 0–30°C and subsequent reaction of the monobromide (2) with different Grignard reagents (3) at room temperature. The products (4) were converted to corresponding oxides, sulfides, and selenides (5a–i, 6a–d, and 7a–d) by oxidation with H₂O₂ at room temperature and refluxing with sulfur and selenium respectively. The chemical structures of all the products were confirmed by analytical, IR, NMR (¹H, ¹³C, and ³¹P), and mass spectral data. Most of these compounds exhibited moderate antimicrobial activity.     

Mechanism of (Salen)manganese(III)‐Catalyzed Oxidation of Aryl Phenyl Sulfides with Sodium Hypochlorite

The oxidation of 4‐substituted phenyl phenyl sulfides was carried out with several oxo(salen)manganese(V) complexes in MeCN/H₂O 9 : 1. The kinetic data show that the reaction is first‐order each in the oxidant and sulfide. Electron‐attracting substituents in the sulfides and electron‐releasing substituents in salen of the oxo(salen)manganese(V) complexes reduce the rate of oxidation. A Hammett analysis of the rate constants for the oxidation of 4‐substituted phenyl phenyl sulfides gives a negative ρ value (ρ=?2.16) indicating an electron‐deficient transition state. The log k₂ values observed in the oxidation of each 4‐substituted phenyl phenyl sulfide by substituted oxo(salen)manganese(V) complexes also correlate with Hammett σ constants, giving a positive ρ value. The substituent‐, acid‐, and solvent‐effect studies indicate direct O‐atom transfer from the oxidant to the substrate in the rate‐determining step.     

Hemin-Promoted Direct C−H Thiolation in the Synthesis of Diaryl Sulfides

Diaryl sulfides are a class of important synthetic chemical units. Herein, we report a new method for direct preparation of diphenyl sulfides using P-toluenesulfonyl chloride as an effective thiophenyl radical precursor with assistance from Hemin. Various substituted anisoles and benzenesulfonyl chlorides are well tolerated, resulting in moderate to good yields of diaryl sulfides. The potential of the proposed method is validated by good yields obtained in gram scale reactions.     

Photocatalytic activity of nanoparticles of metal sulfides in the degradation of organic dyes

The photocatalytic degradation of dyes at the nanosized sulfides of transition metals in aqueous solutions was investigated. The rate of degradation increases with decrease in the synthesis temperature of the nanoparticles and with the addition of alcohol. The substitution of Cd²⁺ cations by Ag⁺ or Cu²⁺ leads to a decrease in the photoactivity of the CdS, while substitution by In³⁺ leads to an increase. The substitution of Ni²⁺ and Co²⁺ cations in the corresponding sulfides by Cd²⁺ leads to an increase in the rate of degradation. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 5, pp. 276–280, September–October, 2006.     

Catalytic reaction of methanol with alkanethiols

Methanol reacts with primary alkanethiols (R=C₁–C₃) over alumina catalysts to yield dialkyl sulfides. Methanethiol is completely converted to dimethyl sulfide. Ethane-and 2-propanethiols give methyl alkyl sulfides. However, the process is complicated by side reactions producing olefins and dimethyl sulfide. If mixed thiols are used, their transformations hinder each other.     

Selective Oxidation of Sulfides to Sulfoxides and Sulfones Using n -Butyltriphenylphosphonium Dichromate (Bu n PPh3)2Cr2O7 in the Presence of Aluminium Chloride in Solution and Under Microwave Irradiation

A wide variety of sulfides are efficiently oxidized to their corresponding sulfoxides and sulfones in excellent yields using n-butyltriphenylphosphonium dichromate (BTPPDC) in the presence of aluminium chloride in acetonitrile solution and under microwave irradiation. In addition, selective oxidation of sulfides in the presence of functional groups such as a carbon–carbon double bond, ketone, oxime, aldehyde, ether, and acetal can be considered as a noteworthy advantage of this method.     

Highly diastereoselective addition of allyltitanocenes to α-chiral ketones

The addition of allyltitanium reagents, generated by the desulfurizative titanation of allylic sulfides with the titanocene(II) reagent Cp₂Ti−1-butene, to α-chiral ketones produced tertiary homoallylic alcohols bearing three adjacent chiral centers with high diastereoselectivity.     

Silicon-Directed Nazarov Cyclizations. Part VI. The anomalous cyclization of vinyl dienyl ketones

Reactions, of various vinyl dienyl ketones (see la – e , li ) with FeCl, give rise to β,γ-unsaturated α-vinyl-cyclo-pentenones (see 2a – e , 2i , Table 2). The reaction succeeds for vinyl dienyl ketones with substituents on either double bond. Aryl dienyl and alkyl dienyl ketones (see 1f – h ) do not cyclize cleanly. The effects of substituents on the rate of reaction is discussed in terms of the mechanism of the rearrangement. A ¹³C-labeling study establishes the pathway as an unusual 1-hydroxypentadienyl-cation electrocyclization to a cyclopentenyl cation which collapses via a pinacol rearrangement to the α-vinyl ketone.     

One-Pot Synthesis and Asymmetric Oxidation of 2-Nitro-4-(Trifluoromethyl)Benzene Containing Sulfides

Abstract

An efficient one-pot method for the preparation of 2-nitro-4-(trifluoromethyl)benzene containing sulfides from 1,1′-disulfanediylbis[2-nitro-4-(trifluoromethyl)benzene] is proposed. The corresponding enantiomerically enriched sulfoxides with up to 78% enantiomeric excess are prepared by the asymmetric oxidation of sulfides using a modified Sharpless method. The yield of sulfoxides is shown to decrease with an increase in the bulk of the aliphatic group and with a decrease of the inductive effect of the hydrocarbonic moiety on the sulfur atom.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

GRAPHICAL ABSTRACT      

Synthesis and Antitumor Activity of Novel 2-(Thymin-1 ′ -ylmethoxy)ethyl Alkyl Sulfides and Their Oxidation Products

A series of novel 2-(thymin-1′-ylmethoxy)ethyl alkyl sulfides have been synthesized in three steps from thymine. They have been oxidized into sulfoxide and sulfone derivatives by means of NaIO ₄ and H ₂ O ₂ 30%/diethyl azodicarboxylate (DEAD), respectively, in high yields. All products were characterized by ¹ H NMR and IR spectra and elemental analyses. The preliminary bioassay indicates that the compound 6g exhibited potential antitumor activity.     

Imination of Sulfides and Sulfoxides with Sulfonylimino‐λ3‐Bromane under Mild,Metal‐Free Conditions

Exposure of sulfides and sulfoxides to trifluoromethanesulfonylimino(aryl)‐λ³‐bromane in dichloromethane at 0 °C results in a facile transfer of the sulfonylimino group to sulfur atoms and affords N‐triflylsulfilimines and ‐sulfoximines in high yields under transition‐metal‐free conditions. Imination of (R)‐methyl p‐tolyl sulfoxide proceeded with predominant retention of configuration at the stereogenic sulfur center. The Hammett plot afforded ρ values of ?0.58 for para‐substituted thioanisoles and ?0.49 for their equivalent sulfoxides, which suggests a buildup of positive charge on the sulfur atoms of sulfides and sulfoxides in the transition state. Calculations suggest a bimolecular nucleophilic‐substitution mechanism on the negatively charged nitrogen atom of the sulfonylimino‐λ³‐bromane, which involves the attack of a sulfide from the opposite side to bromine(III).     

Selective oxidation of sulfides to sulfoxides and sulfones at room temperature using H2O2 and a Mo(VI) salt as catalyst

Selective oxidation of sulfides to sulfoxides and sulfones is achieved by H₂O₂ using MoO₂Cl₂ as the catalyst. Various substituted sulfides having functional groups such as methyl, methoxy, bromo, nitro, alkene, alkyne, alcohol, ester, aldehyde and remarkably an oxime are successfully and selectively oxidized without affecting the sensitive functionalities.