Sulfines thioketones

Oxidation Reaction. Treatment of 2,2,4,4-tetramethyl-3-thioxocyclobutanone (1) with m-CPBA in diethyl ether (or dichloromethane) at 0 °C gives the colorless sulfine (thioketone 5-oxide, 2) in 80% yield (eq 1). The same product is reported to be formed by sensitized photochemical oxidation of 1 with 02/methylene blue in chloroform. ... 

No isolated derivatives of 1,2,3-dioxathietanes have been reported. It is reasonable to assume their intermediacy in the reaction of singlet oxygen with thioketones and sulfines to give ketones (71CC118, 70TL4683), and energy profiles have been calculated (CNDO/B) on the supposed 1,2,3-dioxathietane intermediate (80JCS(P2)188). 

The first unequivocal 1,3-dipolar cycloaddition of sulfines involves the reaction of 2,2,4,4-tetramethyl-3-thioxocyclobutanone S-oxide with diaryl thioketones to produce... 

For aliphatic thioketones, when an appreciable amount of enethiol is present, oxidation leads to divinyl disulfides397. However, Metzner409,410 has carried out the selective oxidation of symmetric and unsymmetrical aliphatic thioketones to afford quantitatively the corresponding sulfines (equation 105). 

In the case of carbonyl oxides 127, generated by ozonolysis of vinyl ethers 126, the addition to a number of thioketones affords thioozonides 128 in moderate yields461 (equation 134), although sometimes oxidation to sulfines was observed. 

Sulfines are obtained by oxidation of thioketones and, after some days, elemental sulfur is formed and the corresponding ketones are produced quantitatively. A possible mechanism is the thermally allowed electrocyclization of sulfines to give an intermediate oxathiirane 141 which, upon sulfur extrusion, affords the corresponding ketones409. 

Thiocarbonyl compounds (e.g., compound 237) can be oxidized by m-OI-C6H4-COd I to. Y-oxidcs (sulfines, e.g., compound 238) which as 1,3-dipoles react with thioketones yielding 1,2,4-oxadithioles 239-241. The structure of the cross-product 241 was confirmed by X-ray crystallography (Scheme 76) <2005HCA2624>. 

A third method of access to sulfines is the oxidation of thiocarbonyl compounds. When the starting material is available it is an attractive route. There has been some dispute in the past whether enethiolisable thiocarbonyl derivatives would lead to the corresponding sulfines or to divinyl disulfides [101, 102]. It is now clear from our research that, even if the C=S molecules bear highly acidic a-protons, oxidation occurs on C=S and does not touch the a-protons. There are many examples of this behaviour. The most easily enethiolised compounds are thioketones. We have shown that their reaction with a peroxycarboxylic acid, mCPBA, is very fast at 0°C and quantitatively provides the corresponding sulfines [103]. In many examples the aliphatic sulfines are not very stable and have to be used in subsequent reactions that will be faster than their decomposition (t1/2 from some hours to days). 

The dithiete isomers of bis(thioketones) have been oxidised [112] to afford the first a-bis(sulfines), fully characterised by X-ray analysis. The major isomers have an (E,E) structure. For the monoxidation, a dithiete monoxide was evidenced and shown to equilibrate with the a-thioxo sulfi-ne. These results confirm that oxidation of the C=S moiety stabilises this weak 2p-p double bond. 

Pentafluorophenyl thioketones are available [115] from the reaction of the corresponding fluoroketones with B2S3 formed in situ. Oxidation with monoperphthalic acid generated the sulfine, the X-ray structure of which revealed a dimer in the crystal lattice. 

Allyl silanes may also be employed for thiophilic addition to various sulfines, obtained by oxidation of thioketones, dithioesters [151] and trithio-carbonates [111]. It provides a new entry to allyl sulfoxides. 

The isomers of the now very popular dioxiranes, carbonyl oxides, are much less well-known species. However, the reaction of both isomers with two aliphatic thioketones was investigated [258]. A clear cut difference in reactivity was observed, with dioxiranes leading expectedly to the sulfines, while 5-membered ring thio-ozonides were produced from the reactions with carbonyl oxides, thus proving the possibility of a dipolar cycloaddition. 

The addition of ZnBr2 to the tandem 1,3-azaprotio cyclotransfer-cycloaddition of a ketoxime with divinyl ketone results in rate enhancement and the exclusive formation of l-aza-7-oxabicyclo[3.2.1]octan-3-ones7 The 1,3-dipolar cycloaddition of 1-aza-l-cyclooctene 1-oxide with alkenes produces the corresponding isoxazolidines in high yields with a minimum of polymeric material. The cycloaddition of thiophene-2-carhaldehyde oxime with acetonitrile and methyl acrylate produces the 1,3-dipolar adduct, suhstituted isoxazolidines, and not the previously reported 4 - - 2-adducts. Density functional theory and semi-empirical methods have been used to investigate the 3 + 2-cycloaddition of azoxides with alkenes to produce 1,2,3-oxadiazolidines. The 3 -h 2-cycloaddition of a-nitrosostyrenes (62) with 1,3-diazabuta-1,3-dienes (63) and imines produces functionalized cyclic nitrones (64) regioselectively (Scheme 22). The first imequivocal 1,3-dipolar cycloaddition of sulfines involves the reaction of 2,2,4,4-tetramethyl-3-thioxocyclobutanone S-oxide with diaryl thioketones to produce... 

The conversion of thioketones to sulfines (R2C=S=0) is difficult to categorize into the sections available, and it placed after oxidation of ketones and aldehydes. The reaction of a thioketone with hydrogen peroxide and a catalytic amount of MTO (methyl trioxorhenium) gives the sulfine. ... 

With 1,3-dienes like 2,3-dimethylbutadiene (48), sulfines (45) undergo the Diels-Alder reaction to form the [4 + 2] cycloadducts (49) (Scheme 25). In this reaction, sulfines behave similarly to thioketones and certain sulfenes (see Chapter 7, p. 117), although the latter generally show a greater tendency to form [2 + 2] cycloadducts. 

The stable dithiirane 5-oxide (4) is converted to sulfine (15) and triphenylphosphine sulfide upon treatment with triphenylphosphine (93JA4914). When heated, (4) decomposes to give thioketone (16), sulfine (15), and dicarbonyl compound (17). Compounds (16) and (15) result from loss of sulfur monoxide and sulfur, respectively, from (4). Thioketone (16) exists in equilibrium with oxathietane (18). The rate of thermal decomposition of (4) was found to be dependent on its concentration, with higher rates at higher concentrations. The authors suggest that this observation is indicative of a decomposition pathway involving the sulfur and sulfur monoxide products. Thermolysis of (4) also leads to isomerization of (12) in addition to the products described above. 

The reaction is believed to involve homolysis of the S—S bond to give a biradical which is intermediate to isomerization and product formation. Thermal decomposition of (4a) gives elemental sulfur and thioketone (16) <94AG(E)777>. Treatment of (4a) with triphenylphosphine also leads to (16) plus triphenylphosphine thiooxide. Oxidation of the dithiirane with MCPBA gives the sulfine (15). Heating of a dilute solution of (4a) in 1,2-dichloroethane gives the bicyclic 1,3,4-oxadithiolane (19) along with (16) and (18). 

Elimination of hydrogen chloride from sulfinyl chlorides by means of triethylamine709 has been used in a few cases to afford sulfines (an alternative method is the oxidation of diaryl thioketones by peracids710) ... 

Allenyl chloromethyl sulfoxide (57) reacts with m-CPBA to furnish allenyl chloromethyl sulfone (58) (eq 21). The enethi-olizahle thioketone (59) has been oxidized to the ( )-sulfine (60) (eq 22). The 2 -deoxy-4-pyrimidinone (62) has been prepared by reacting the 2-thiop3Timidine nucleoside (61) with m-CPBA (eq 23). Thioamides have been transformed to the amides in high yields. ... 

Peroxyacetic acid s. under H20 /0HgCOOH Peroxyphthalic acid Sulfines from thioketones... 

Hydrogen peroxide acetic acid HiOjCHgCOOH Sulfines from thioketones C S C S O with peroxyphthalic acid cf. 21, 130 with aq. in acetic acid, f. reactions of thioketones, s. A. Ohno et al., Chem. Lett. 1975, 983 ... 

Thioketones, R2C=S, can be oxidized to sulfines, R2C=S=0, and further oxidized to, ultimately, the ketones, R2C=0 (-1-SO2). Hydrogen peroxide can effect both reactions with catalysis by methyltrioxorhenium (MeReOs). The kinetics of the oxidation sequence have been studied for a range of symmetrically disubstituted thiobenzophen-ones, and for thiocamphor. The first step is favoured by electron-releasing substituents (Hammett p = -1.12), whereas the second process, which is slower, exhibits a U-shaped Hammett plot. Hence it appears that the sulfine oxidation involves a mechanism in which the direction of electron flow in the transition state changes with the electron demand of the substituents in the reactants. The first step of the second reaction converts the sulfine to sultine (99) and/or sulfone (R2CSO2). Although the... 

As a Carbon Nucleophile in Lewis Base-catalyzed Reactions. Allylation of alkyl iodides with allyltrimethylsilane proceeds in the presence of phosphazenium fluoride. Tetra-butylammonium triphenyldifluorosilicate (TBAT) is useful for allylation of aldehydes, ketones, imines, and alkyl halides with allyltrimethylsilane (eq 63). 55 Similarly, TBAHF2 is an effective catalyst for allylation of aldehydes. The homoallylamines are synthesized from allyltrimethylsilane and imines with a catalytic amount of TBAF (eq 64). The reactions of thioketones as well as sulfines with allyltrimethylsilane can be mediated by TBAF to give allylic sulfides and allyl sulfoxides, respectively. Besides fluoride ion, 2,8,9-triisopropyl-2,5,8,9-tetra-aza-1-phosphabi-cyclo[3.3.3]undecane promotes the allylation of aldehydes with allyltrimethylsilane as a Lewis base catalyst (eq 65). ... 

Thioaldehydes and thioketones oxidized at sulfur are additively named as thioaldehyde oxides, dioxides and thioketone oxides, dioxides, respectively. Besides, the traditional names sulfine and sulfene are still used for these species. 

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