Sulphoxides 3-keto

Peroxomonosulphate and peroxodisulphate have also been used to oxidize sulphoxides to sulphones in good yields at room temperature. Potassium persulphate (KHS05) readily oxidizes a range of sulphoxides to sulphones at 0°C in yields greater than 90%, in the presence of hydroxy, keto and alkene groups82-84. The mechanism is similar to that observed for other peroxy species, as discussed above. Peroxomonosulphate oxidation has been used as an analytical procedure for the estimation of dimethyl sulphoxide84. 

Benzyltriethylammonium permanganate has also been used for the mild oxidation of sulphoxides to sulphones at — 10 °C in methylene chloride in the presence of keto, amino and ester groups in > 65% yields142. 

Direct sulphanylation of activated methylene groups to form methyl thioethers is possible under basic conditions, when the stabilized carbanion reacts with 5-methyl methanethiosulphonate. The reaction has been applied successfully in, for example, reactions with p-keto sulphoxides [59] and a-sulphonyl acetic esters [60] (Scheme 4.13). 

The activated methylene compound (2 mmol), TEBA-Cl (46 mg, 0.2 mmol) and powdered K2C03 (0.55 g) in CH2Cl2 or PhH (10 ml) are stirred at room temperature for ca. 1 h. MeSS02Me (0.25 g, 2 mmol) in CH2C12 (3 ml) is added, and the mixture is stirred for 2-6 h and then filtered. The solid is washed with CH2C12 (20 ml) and the combined solutions are washed with H20 (2 x 20 ml), dried (MgS04), and evaporated to yield the methyl thioether ( a 1 1 mixture of CH2C12 and PhH is preferred for the p-keto sulphoxides). 

Although there are other convenient procedures for the conversion of sulphides into sulphoxides and sulphones, the phase-transfer catalysed reaction using Oxone has the advantage that the oxidation can be conducted in the presence of other readily oxidized groups, such as amines, alkenes, and hydroxyl groups, and acid-labile groups, such as esters and carbamates [6, 7], Hydrolysis of very acid-labile groups, such as ketals, can result in production of the keto sulphone. 

Abbreviations KMB, 2-keto-methylthiobutyric acid DMPO, the spintrap, 5,5-dimethyl- 1 -pyroline-A -oxide ESR, electron-spin resonance (=electron paramagnetic resonance, EPR) spectroscopy DMSO, dimethyl sulphoxide Phe, phenylalanine Tyr, tyrosine HPLC, high-performance liquid chromatography. 

Other useful p-menthane syntheses of no great novelty are of cis- and trans-piperitol from 2a,3o -epoxycarane (silica-catalysed rearrangement to ds-p-menth-2-en-l,8-diol is also reported), of ( )-dihydrocarvone, isopulegone, and p-menthofuran via /S-keto-sulphoxides, of p-mentha-l,4(8)-diene via a bromination-dehydrobromination sequence, and of trans-carveol by benzoyl peroxide-CuCl oxidation of a-pinene. Further details for the conversion of (-)-(142) into (+)-(142), via its epoxide, are reported (Vol. 5, p. 25 cf. Vol. 3, p. 44). " ... 

Butenolides [e.g. (435)] have been synthesized from /8-keto-sulphoxides by alkylation with methyl bromoacetate, followed by reduction and lactonization (Scheme 14). The required /3-keto-sulphoxide (432) was prepared by reaction between the methyl etienate and dimsyl potassium (MeSOCHiK ). ... 

The 8-aza-steroid (467 R = OMe) has been converted by a series of high yielding reactions involving Pummerer rearrangement of the )3-keto-sulphoxide (467 R = CHj SO Me) into its corticoid analogue (467 R = CH2OAC). 

Further examples of asymmetric reactions involving chiral monoterpenoids include the formation of chiral /S-keto-sulphoxides from (-)-menthyl carboxy-lates, " synthesis of diastereomeric tetrahedral molybdenum complexes,the enantioselective hydrosilylation of ketones,and the preparation of the chiral l-amino-2-phenylethylphosphonic acids. 

The chiral hydroxy-sulphoxides (420) and the epimeric alcohols can both be obtained from the same B-keto-sulphoxide by a judicious choice of reducing agent oxidation to the sulphone, double... 

Syntheses of /(-(-i-)-myoporone (em-12) and / -(-H)-10,l 1-dehydromyoporone (ent-14) have been published recently (22). These rely on the use of methyl 5-citronellate as the source of the asymmetric carbon (Scheme 3). Of more general interest and application is an approach (23) which leads to the stereospecific synthesis of 9-dihydromyoporone, which contains two asymmetric centres. This synthesis formally constitutes a synthesis of myoporone. Still and Darst (23) have shown that hydroboration of -2,6-dimethylhepta-1,4-diene with thexylborane leads, with high diastereoselectivity, to the diastereomeric 1,4-diols (Scheme 4). Appropriate transformation of the yn-diol to the electrophilic iodo compound, followed by alkylation of the P-keto sulphoxide, gives... 

The 8-keto-sulphoxide dianion (152) cyclizes intramolecularly to 2-phenyl-sulphinylcyclopentadecanone (153) in 70% yield. Thermolysis of (153) and treatment of the resultant a/3-unsaturated ketone with excess lithium dimethylcuprate produces d/-muscone in excellent yield. 

Keto 1,3-dithianes are susceptible to nucleophilic attack at the carbonyl with subsequent cleavage occurring preferentially between the carbonyl and the dithiane functions In the one instance reported, the keto dithiane (27) was cleaved with sodium methoxide in dimethyl sulphoxide to acid (28). The explanation as to why the acid is formed instead of the... 

The synthesis of ketones from j9-keto-sulphoxides shows the comparability of these compounds with j8-dicarbonyl compounds. " Other synthetic uses include the formation of a-chloro-oximes RC(Cl)=NOH on nitrosation... 

Functional Groups.—Kinetic studies of dehydrochlorination reactions in the gas phase reveal participation of neighbouring groups in aliphatic 2-chloroethyl sulphides. Physical studies indicate interactions of functional groups in /ff-keto-sulphides and in the corresponding nitriles. A more unusual example of participation by sulphur is the enhanced rate of reduction by 1 of y-(methylthio)alkyl methyl sulphoxides. ... 

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