Thiocarbonyl 5-oxides

Cycloaddition of thiocarbonyl 5-oxides was first observed in the reaction of dichloro-methanethione 5-oxide with diazo compounds77. This reaction initially gives an unstable 2,5-di-hydrothiadiazole 5-oxide which undergoes elimination of nitrogen to give three-membered cyclic sulfoxides 3. 

Thiocarbonyl 5-oxides behave as dienophiles and undergo cycloaddition with 1,3-dienes to form cyclic sulfoxides (cf. Houben-Weyl, 4th ed., Vol. Ell, p 940). Thus, dichloromethanethione 5-oxide and cyclopentadiene react exothermically at — 40 °C to form a mixture of unstable diastereomeric 3,3-dichloro-2-thiabicyclo[2.2.1]hept-5-ene 2-oxide (7)77. 

The cycloaddition reaction of chiral thiocarbonyl 5-oxides derived from terpene alcohols such as (—)-menthol, ( —)-borneol, (+)-a-fenchol and (—)-3-tWo-hydroxy-2-CTitfo-phenylbornane affords 2-substituted 2-alkoxysulfonyl-3,6-dihydro-4,5-dimethyl-2//-thiopyran 1-oxides IIA and 11B as a mixture of diastereomers85. 

In contrast, the cycloaddition reaction of ( )- or (Z)-lO-chloro-lO-thioformylcamphor S-oxide with 2,3-dimethyl-1,3-butadiene proceeds with complete asymmetric induction and affords in each case a single diastereomer 12 or 13 only differing in the reaction rate the (L)-thiocarbonyl 5-oxide reacts faster than the (Z)-isomer85. 

From the absolute configuration of the products, determined by X-ray diffraction, the stereochemical course of the cycloaddition can be inferred for the (Z)-isomer the diene approaches the plane of the thiocarbonyl 5-oxide group from the CRe,Ssi face which is the least hindered face in the conformation shown here85. 

Similarly, the cycloaddition of chiral thiocarbonyl 5-oxides, derived From optically active TV-substituted 5-phenyl- or S-(4-methylphenyl)-5-(l-trimethylsilylethyl)sulfoximides with 2,3-di-methyl-1,3-butadiene, is completely stereoselective affording TV-substituted 3,6-dihydro-2,4,5-tri-methyl-2-[(5)-5-phenyl- or 5-(4-methylphenyl)sulfonimidoyl)]-2//-thiopyran 1-oxides as single diastereomers, determined by 1H-NMR spectroscopy using shift reagents and analytical reverse-phase HPLC85,87. 

Finally, the benzyl ether 13 (and, similarly, the mesitylmethyl ether 14) were converted to chiral thiocarbonyl 5-oxides via sulfonamides, The thiocarbonyl 5-oxides are useful chiral dienophiles (Section D. 1.6.1.1.1.1.2.2.). The sulfonamides are obtained simply by the addition of the sulfonyl chlorides to the ethers in tetrahydrofuran18. 

The 1,3-dipolar cycloaddition of thiocarbonyl 5-oxides to thiones has been used to obtain... 

Thiocarbonyl oxides are a subject of active investigation. The natural occurrence of sulfines and related compounds in plants of the genus Allium (onion, garlic, etc.) is included in a superb and extensive review by Block [91]. Two detailed papers [92, 93] report the isolation of zwiebelanes from onions and their chemical synthesis involving intermediate sulfines produced by oxidation of di-l-propenyl disulfide, subsequent sulfoxide accelerated [3.3] sigmatropic shift and the [2+2] cycloaddition of the C=S and C=S=0 moieties. A further article [94] provides a great deal of information on the mechanism of formation of (Z)-propanethial S-oxide, the lachrymatory factor of the onion, as well as its chemical synthesis and reactions. Techniques of analysis of the volatiles of onions have been further improved [95]. 

A general way to achieve thiophilic addition is to use sulfines [149]. The sulfur atom of thiocarbonyl oxides is selectively attacked by carbanions. We have applied this property to aliphatic dithioester oxides and shown [150] that, despite the probably high acidity of the a-protons, thiophilic addition of alkyllithiums is observed, leading to stabilised carbanions. After treatment with electrophiles, dithioacetal oxides were obtained. From a synthetic point of view, it is worthy of note that these adducts are much more easily... 

Oxidation (with H2O2 and HOAc) of 2-methylthio-4-thioxobenzo[d]-[l,3]thiazine is reported to occur solely at the thiocarbonyl sulphur to give the corresponding thiocarbonyl oxide (67%). ... 

These reactions differ from those of sulfur tetrafluoride with carbonyl compounds in that a formal oxidation-reduction of the sulfur atoms m the thiocarbonyl compound and sulfur tetrafluoride molecule occurs, resulting in the formation of free sulfur and the complete utilization of the fluorine atoms in sulfur tetrafluoride. 

The mechanism for the redistribution in oxidation states begins similarly to that of the Paal thiophene synthesis. However, upon formation of dithione 38, nucleophilic addition of one thiocarbonyl into the other produces the intermediate zwitterion 39. A 1,3-tautomerization of hydrogen then gives... 

Exobidentate Coordination Dienic, Carbonyl, and Thiocarbonyl Derivatives of Metals in Higher Oxidation States... 

Conventional conversion of amide, lactam, imide, and urea carbonyl groups into enaminones, enamino esters, or enamino nitriles requires prior activation of the carbonyl groups either by alkylation to imino ethers, followed by reaction with activated methylene groups, or by thiation, e.g. with P2S5, to thiocarbonyl groups followed by alkylation (and possibly also oxidation), and, again, subsequent reac-... 

Tc(V) and Re(V) are thiols, thioethers and thiocarbonyl compounds and molecules containing combinations of their functional groups. There exist significant differences in the ability of the various groups to form stable complexes and in the kind of complexes formed. Unlike thiols, a neutral S-donor shows a preference for the metals in oxidation states lower than +5. 

Common synthesis of disulfonium dications involves formation of a S-S bond by oxidative coupling of two sulfide moieties. Involving for oxidative generation of S-S bond, thiocarbonyl compounds can lead to new-type dications containing disulfide moieties between two positively charged fragments. There are several disulfide dications of this type derived from thioureas, thiocarbon-ates and thioketones as well as selenium derivatives.137 148... 

Nitrosonium tetrafluorobprate was used later as oxidant for convertion of dithiolanthione 150 to dication 151.151 This technique was found to be general for oxidation of number of thiocarbonyl compounds (Scheme 56).146... 

Direct oxidation of thiocarbonyl compound by triflic anhydride results in stable dication salts containing disulfide framework. For example, reaction of thiocarbonate 155 with Tf2Q yields the dication salt 156 (Scheme 58).154... 

I.3.4.2.5. Carbonyl and Thiocarbonyl Compounds a-(Hydroxyimino)phenyl-acetonitrile oxide (generated in situ at room temperature from PhC( NOH)C ( NOH)Cl in the presence of NaHC03 or Et3N) reacts with simple aldehydes and ketones R1R2CO to give 1,4,2-dioxazoles 180 (347). Related dioxazoles, formed by cycloaddition of benzonitrile oxide to aromatic aldehydes, upon treatment with I-BuOK, undergo cyclo-reversion, allowing direct conversion to substituted benzoic acids or their esters (348). 

Oxidation of sulfur atom of pyrazolo[l,5-c]thiazole 64 into sulfoxide 65 followed by Pummerer-type dehydration furnished the transient nonclassical pyrazolo[ 1,5-c]thiazole, the thiocarbonyl ylide 67, which could react with various dipolarophiles such as Ar-pheny 1 ma 1 eiinide (Equations 27 and 28) <2000T10011>. In an excess of oxidizing agent, pyrazolo[l,5-c]thiazole 64 was readily converted to sulfone 66 (Equation 27) <2001J(P1)1795>. 

Treatment of Fischer-type carbene complexes with different oxidants can lead to the formation of carbonyl compounds [150,253]. Treatment with sulfur leads to the formation of complexed thiocarbonyl compounds [141]. Conversion of the carbene carbon atom into a methylene or acetal group can be achieved by treatment with reducing agents. Treatment of vinylcarbene complexes with diborane can also lead to demetallation and formation of diols [278]. The conversion of heteroatom-substituted carbene complexes to non-heteroatom-substituted carbene complexes... 

Conversion of the thiocarbonyl group into carbonyl has been reviewed. In general, hydrolytic methods catalysed by metal ions are recommended over oxidative methods, as the former are typically cleaner and more easily worked up. 

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