Sulfides, unsaturated, oxidation

The kinetics of formation and hydrolysis of /-C H OCl have been investigated (262). The chemistry of alkyl hypochlorites, /-C H OCl in particular, has been extensively explored (247). /-Butyl hypochlorite reacts with a variety of olefins via a photoinduced radical chain process to give good yields of aUyflc chlorides (263). Steroid alcohols can be oxidized and chlorinated with /-C H OCl to give good yields of ketosteroids and chlorosteroids (264) (see Steroids). /-Butyl hypochlorite is a more satisfactory reagent than HOCl for /V-chlorination of amines (265). Sulfides are oxidized in excellent yields to sulfoxides without concomitant formation of sulfones (266). 2-Amino-1, 4-quinones are rapidly chlorinated at room temperature chlorination occurs specifically at the position adjacent to the amino group (267). Anhydropenicillin is converted almost quantitatively to its 6-methoxy derivative by /-C H OCl in methanol (268). Reaction of unsaturated hydroperoxides with /-C H OCl provides monocyclic and bicycHc chloroalkyl 1,2-dioxolanes. 

As already mentioned above, sulfides are oxidized to the corresponding sulfoxides with alkyl hydroperoxides in the presence of various metal catalysts like Mo, W, Ti and V. In the presence of excess hydroperoxide further oxidation to the sulfone occurs. Sulfides are generally oxidized much faster than alkenes, which is reflected in the selective oxidation of unsaturated sulfides exclusively at the sulfur atom. During the last years many asymmetric versions of this reaction have been developed and can be mainly divided... 

The reaction of enolates with dimethyl disulfides (MeSSMe) or diphenyl disulfides (PhSSPh) leads to the corresponding sulfides. Their oxidation to sulfoxides followed by heating provides a route to functionally substituted alkenes, such as a,[3-unsaturated carbonyl compounds. In the example below, the exocyclic alkene is formed since that is the only possible yn-elimination product. 

Various methods can be used to analy2e succinic acid and succinic anhydride, depending on the characteristics of the material. Methods generally used to control specifications of pure products include acidimetric titration for total acidity or purity comparison with Pt—Co standard calibrated solutions for color oxidation with potassium permanganate for unsaturated compounds subtracting from the total acidity the anhydride content measured by titration with morpholine for content of free acid in the anhydride atomic absorption or plasma spectroscopy for metals titration with AgNO or BaCl2 for chlorides and sulfates, respectively and comparison of the color of the sulfide solution of the metals with that of a solution with a known Pb content for heavy metals. 

The highly ionic thaHic nitrate, which is soluble in alcohols, ethers, and carboxyhc acids, is also a very useful synthetic reagent. Oxidation of olefins, a,P-unsaturated carbonyl compounds, P-carbonyl sulfides, and a-nitrato ketones can aH be conveniently carried out in good yields (31,34—36). 

Sodium sulfide or hydrosulfide can be used in double Michael additions thus the bridged thiopyran (11) is formed from 2,7-cyclooctadienone (12),12 and dihydrodithiin oxides (13) and related compounds are similarly produced from unsaturated sulfoxides (14).13... 

Carbon, activated Chlorates Calcium hypochlorite, all oxidizing agents, unsaturated oils Ammonium salts, acids, metal powders, sulfur, finely divided organic or combustible materials, cyanides, metal sulfides, manganese dioxide, sulfur dioxide, organic acids... 

The reaction described is of considerable general utility for the preparation of benzoyloxy derivatives of unsaturated hydrocarbons.2"8 Reactions of 2-butyl perbenzoate with various other classes of compounds in the presence of catalytic amounts of copper ions produce benzoyloxy derivatives. Thus this reaction can also be used to effect one-step oxidation of saturated hydrocarbons,9, 10 esters,6,11 dialkyl and aryl alkyl ethers,12 14 benzylic ethers,11,15 cyclic ethers,13,16 straight-chain and benzylic sulfides,12, 17-19 cyclic sulfides,11,19 amides,11 and certain organo-silicon compounds.20... 

Different nucleophiles such as methanol, allylsilanes, silyl enol ethers, trimethylsilyl-cyanide, and arenes can be used in this process [62]. When the sulfide itself contains an unsaturated or aromatic fragment and the process is carried out in the absence of a nucleophile, an intramolecular anodic sub-stitution/cyclization might occur [61-63]. Methyl esters of 2-benzothiazolyl-2-alkyl or aryl-acetic acid, oxidized in MeOH/Et4 NCIO4 or H2SO4 in the presence of CUCI2, form 2,2-dimethoxy products (Eq. 7) [64]. 

Presumably, 1,4-addition of sulfide to each unsaturated system occurs which is followed by elimination of methoxide and bromide leading to an intermediate such as 99, which then cyclizes under oxidative conditions to give 32. 

Bromination of the enol ether product with two equivalents of bromine followed by dehydrobromination afforded the Z-bromoenol ether (Eq. 79) which could be converted to the zinc reagent and cross-coupled with aryl halides [242]. Dehydrobromination in the presence of thiophenol followed by bromination/dehydrobromination affords an enol thioether [243]. Oxidation to the sulfone, followed by exposure to triethylamine in ether, resulted in dehydrobromination to the unstable alkynyl sulfone which could be trapped with dienes in situ. Alternatively, dehydrobromination of the sulfide in the presence of allylic alcohols results in the formation of allyl vinyl ethers which undergo Claisen rearrangements [244]. Further oxidation followed by sulfoxide elimination results in highly unsaturated trifluoromethyl ketonic products (Eq. 80). 

Because of the mechanism of action of DDQ, sulfides and selenides are expected not to react with DDQ during the mild conditions used in the oxidation of unsaturated alcohols. There is one published example in which an alcohol is oxidized with DDQ in the presence of a selenide.130... 

It is notable that allyloxylation can also be performed in relatively good yields (Table 6) although allyl alcohols are easily oxidized anodically12. The allyloxylated sulfides thus obtained are easily converted into the corresponding ft, /-unsaturated ketones by a [2,3] Wittig rearrangement using bases as shown in equation 21. Anodic desilylation/carboxylation of a-thiomethylsilanes also takes place similarly as shown in an example in Table 6. 

The actions of photoexcited semiconductor particles on organic compounds under oxygen is of significant importance from both practical and basic aspects. Semiconductors like titanium dioxide and cadmium sulfide were shown to induce oxidation of olefins and aromatic hydrocarbons under oxygen, and also to sensitize isomerization of unsaturated systems. The mechanisms of these reactions are discussed. 

Unsaturated 1,5-dicarbonyl compounds. The phenylthioalkylation of silyl enol ethers of carbonyl compounds (9, 521-522) can be extended to the synthesis of unsaturated 1,5-dicarbonyl compounds. In a typical reaction the enol silyl ether of a ketone is alkylated with the unsaturated chloride 1 under ZnBr2 catalysis to give a homoallyl sulfide. Ozonolysis of the methylene group is accompanied by oxidation of the phenylthio group sulfoxide elimination results in an unsaturated 1,5-aldehydo ketone (equation I). Alkylation with 2 results in a methyl ketone (equation II). 

The rhodium-catalyzed hydroboration has opened the way to cyclization reactions starting from dienes [92], For instance, rhodium-catalyzed hydroboration of the terminal alkenyl group of an os/f-unsaturated lactone followed by reaction with the PTOC-OMe chain transfer reagent afforded the bicyclic a-S-pyridyl lactone in 63% yield (Scheme 39). After oxidation of the sulfide with m-CPBA, thermal elimination of the sulfoxide afforded the corresponding a-methylene lactone in 65% yield. Interestingly, such bicyclic a -methylenelactones are substructures that can be found in many natural products such as mirabolide [93]. 

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