1.3- Dithianes oxidative cleavage

Suda and coworkers described the anodic oxidation of 2-silyl-l,3-dithianes which have two sulfur atoms on the carbon adjacent to silicon [42], In this case, however, the C Si bond is not cleaved, but the C-S bonds are cleaved to give the corresponding acylsilanes (Scheme 12). Although the detailed mechanism has not been clarified as yet, the difference in the anode material seems to be responsible for the different pathway of the reaction. In fact, a platinum plate anode is used in this reaction, although a carbon anode is usually used for the oxidative cleavage of the C-Si bond. In the anodic oxidation of 2-silyl-l,3-dithianes the use of a carbon anode results in a significant decrease in the yield of acylsilanes. The effects of the nature of the solvent and the supporting electrolyte may also be important for the fate of the initially formed cation radical intermediate. Since various 2-alkyl-2-silyl-l,3-dithianes can be readily synthesized, this reaction provides a convenient route to acylsilanes. 

Cyelobutanone has been prepared by (1) reaction of diazomethane with ketene,4 (2) treatment of methylenecyclobutane with performic acid, followed by cleavage of the resulting glycol with lead tetraacetate,s (3) ozonolysis of methylenecyclobutane, (4) epoxidation of methylene-cyclopropane followed by acid-catalyzed ring expansion,7 and (5) oxidative cleavage of cyclobutane trimethylene thioketal, which in turn is prepared from 2-(co-chloropropyl)-l,3-dithiane.8... 

Diethyl-3,5-octadiene 174 Dithiane oxides alkylation of 84 carbanions of 84 Dithianes alkylation of 76,79 as acyl anion equivalents 75 carbanions of 76,79 cleavage of 14-18.76,79 desulfurization of 78 oxidation of 23... 

Oxidative hydrolysis of 1,3-ditkiane derivatives. The oxidative cleavage of 1,3-dithiane derivatives to the parent carbonyl compounds can be effected by reaction with Pb02 in aqueous THF in the presence of BF3 etherate or HC104 (equation I).1... 

Oxidative cleavage. Recovery of carbonyl compounds from 2-substituted 1,3-dithianes is achieved by mixing with Cu(N03)2 2.5H2O/montmorillonite-K10 in the air and irradiation with ultrasound. ... 

A carbonyl group can be protected as a sulfur derivative—for example, a dithio acetal or ketal, 1,3-dithiane, or 1,3-dithiolane—by reaction of the carbonyl compound in the presence of an acid catalyst with a thiol or dithiol. The derivatives are in general cleaved by reaction with Hg(II) salts or oxidation acidic hydrolysis is unsatisfactory. The acyclic derivatives are formed and hydrolyzed much more readily than their cyclic counterparts. Representative examples of formation and cleavage are shown below. 

Bohman and Allenmark resolved a series of sulphoxide derivatives of unsaturated malonic acids of the general structure 228. The classical method of resolution via formation of diastereoisomeric salts with cinchonine and quinine has also been used by Kapovits and coworkers " to resolve sulphoxides 229, 230, 231 and 232 which are precursors of chiral sulphuranes. Miko/ajczyk and his coworkers achieved optical resolution of sulphoxide 233 by utilizing the phosphonic acid moiety for salt formation with quinine. The racemic sulphinylacetic acid 234, which has a second centre of chirality on the a-carbon atom, was resolved into pure diastereoisomers by Holmberg. Racemic 2-hydroxy- and 4-hydroxyphenyl alkyl sulphoxides were separated via the diastereoisomeric 2- or 4-(tetra-0-acetyl-D-glucopyranosyloxy)phenyl alkyl sulphoxides 235. The optically active sulphoxides were recovered from the isolated diastereoisomers 235 by deacetylation with base and cleavage of the acetal. Racemic 1,3-dithian-l-oxide 236... 

The stereospecific base-cleavage of the trimethylsilyl group in 1,3-dithiane 1-oxides 499 enables to obtain the specifically deuteriated products 500 (equation 303), A nitro group in y-nitroalkyl sulphoxides 501 (obtained by the Michael addition of nitroalkanes to a, j8-unsaturated sulphoxides) is replaced by hydrogen by means of tributyltin hydride (equation 304). This reagent does not affect the sulphinyl function. The overall procedure provides an efficient method for the conjugate addition of alkyl groups to a, -unsaturated sulphoxides . ... 

Typical examples for type 1 are the anodic cleavages of two carbon-sulfur bonds in 1,3-dithianes [46] or dithiolanes [47]. This reaction is especially effective if performed under the conditions of indirect electrolysis using triarylamine cation radicals as regenerable oxidative mediators [47] ... 

Dithianes and gemdithioacetals could be alternatively oxidized indirectly by means of the redox catalysis method. The technique appeared to be particularly mild and mainly avoided inhibition and adsorption phenomena relative to the anode platinum interface. Thus aromatic hydrocarbons (e.g. 9,10-diphenylanthracene) [83] and judiciously substituted triphenylamines [84] afford quite stable cation radicals used homogeneously as oxidants. Their standard potential, E°x, will determine the rate of electron exchange with the concerned sulfur compound. The cleavage of a C—S bond in any dithiane can be regarded as fast enough to draw the redox catalysis process to the indirect oxidation. 

During the course of an aldehyde oxidation with NaC102, it was observed that a dithiane was cleaved during the reaction. Optimization of the conditions led to a cleavage process that gave 61-97% yields of ketones and aldehydes. ... 

A new non-oxidative ring cleavage which should find application in steroids occurred when the bicyclic keto-dithian (392) was treated with sodium methoxide in DMSO. 

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