Dimethyl sulfide, conversion

Usually, organoboranes are sensitive to oxygen. Simple trialkylboranes are spontaneously flammable in contact with air. Nevertheless, under carefully controlled conditions the reaction of organoboranes with oxygen can be used for the preparation of alcohols or alkyl hydroperoxides (228,229). Aldehydes are produced by oxidation of primary alkylboranes with pyridinium chi orochrom ate (188). Chromic acid at pH < 3 transforms secondary alkyl and cycloalkylboranes into ketones pyridinium chi orochrom ate can also be used (230,231). A convenient procedure for the direct conversion of terminal alkenes into carboxyUc acids employs hydroboration with dibromoborane—dimethyl sulfide and oxidation of the intermediate alkyldibromoborane with chromium trioxide in 90% aqueous acetic acid (232,233). 

Reduction of 3,5,5-tris-aryl-2(5// )-furanones 115 (R, R, R = aryl) with dimethyl sulfide-borane led to the formation of the 2,5-dihydrofurans 116 in high yields. However, in the case of 3,4-diaryl-2(5//)-furanones 115 (R, R = aryl R = H or r = H R, R = aryl), the reduction led to a complicated mixture of products of which only the diarylfurans 117 could be characterized (Scheme 36) (88S68). It was concluded that the smooth conversion of the tris-aryl-2(5//)-furanones to the corresponding furan derivatives with the dimethylsulfide-borane complex in high yields could be due to the presence of bulky aryl substituents which prevent addition reaction across the double bond (88S68). 

Similar data for sulfate have been reported in many studies. Figure 9.36, for example, shows overall average sulfate distributions measured in marine areas as well as at continental sites (Milford and Davidson, 1987). The marine data show two modes, a coarse mode associated with sea salt and a fine mode associated with gas-to-particle conversion. Sulfate in seawater, formed, for example, by the oxidation of sulfur-containing organics such as dimethyl sulfide, can be carried into the atmosphere during the formation of sea salt particles by processes described earlier and hence are found in larger particles. The continental data show only the fine particle mode, as expected for formation from the atmospheric oxidation of the S02 precursors. 

Additions to a,fa-acetylenic esters. Piers et alhave prepared a number of these reagents, and conclude that (trimethylstannyl)copper(I)-dimethyl sulfide, (CH3),SnCu-S(CH3)2 (1), is the best reagent of this type for conversion of 1-alkynes to 2-trimethylstannyl-l-alkenes (equation I) or for addition to ethyl 2-butynoate to... 

White peach scale. Several scale sex pheromones have now been elucidated each of them possesses an asymmetric center and usually a trisubstituted alkene link within an isoprenoid framework (43). The structure of the white peach scale pheromone, R,Zb-II (Figure 8), lent itself to synthesis with another chiral starting material, namely limonene (44). Selective ozonlysis followed by workup with dimethyl sulfide-methanol provided a ketoacetal, III. Wittig methylenation followed by hydrolytic cleavage of the acetal gave a dienaldehyde, IV. Conversion of the aldehyde via the acid to an amide (45) with enantiomerically pure ot-methylbenzylamine permitted chromatographic assessment of the purity of the diene aldehyde (and the limonene). The required R-isomer of the diene aldehyde was >48% ee. 

Bromobis[2,3-butanedione dioximato( 1 -)] (4-terf-butylpyridine)cobalt(lIl) is a tan, microcrystalline solid with greatly enhanced solubility in organic solvents compared to the chloro(pyridine) analogue. It is also the compound of choice in preparing alkylcobaloximes by the subsequent procedure because of the ease of isolation of the resultant products. In addition, the bromo(4-ferf-bupy) species react directly with electron-rich olefins, such as ethyl vinyl ether, in the presence of ethanol to yield, in this case, bis[2,3-butanedione dioximato(l-)]-(2,2-diethoxyethyl)(pyridine)cobalt(III).1J Conversion of the dimethyl sulfide compound to the pyridine derivatives is readily detected by a characteristic infrared absorption at 1600 cm 1 (pyridine stretch). The H nmr spectrum of bromobis[2,3-butanedione dioximato(1 -)] (4-ferf-butylpyridine)cobalt (III) has absorptions in the alkane region in the ratio of 3 4 at 6 1.25 ppm [Py—C (CH3)3 ] and 6 2.43 ppm (dh—CH3) from tetramethylsilane. 

Epoxyannelation. The enolate of cyclohexanone reacts with this reagent (1) to form the a,(3-unsaturated epoxide 2, with displacement of dimethyl sulfide, and a mixture of two sulfur-containing products (3). The reaction to give an epoxide is general for enolates of unhindered, cyclic ketones, but is not observed with enolates of acyclic ketones. However, it is possible with enolates of aldehydes. An example is the conversion of phenylacetaldehyde into 4 and 5, in somewhat low yield. 

An indirect conversion of halides to alcohols involved triethylborane. The reaction of an a-iodo ester with BEt3, followed by reaction with dimethyl sulfide in methanol, gave an a-hydroxy ester. 

Selective conversion ofailylic and benzylic alcohols into halides It was noted above that ailylic or benzylic alcohols are not oxidized by the N-chlorosuccinimide-dimethyl sulfide reagent but instead are converted into chlorides. Corey el al. now report that this procedure can be used to form ailylic and benzylic chlorides in high yield if the sulfoxonium intermediate corresponding to (3, above) is allowed to decompose in methylene chloride without addition of a tertiary amine. For example, the ailylic or benzylic alcohol is treated with the complex of N-chlorosuccinimide-dimethyl sulfide as above in methylene chloride and then allowed to stand for 4 hr. at — 25°. In the case of benzhydrol [(C6H5)2CHOH], benzhydryl chloride can be obtained in > 95% yield. 

While a number of synthetic routes are available to various sulfoxides, the primary methods for commercial production of DMSO involve oxidation of dimethyl sulfide by oxides of nitrogen or by air in the presence of NO cat-alyst.f Dimethyl sulfoxide is both the product and the reaction solvent. To alleviate the potential for exothermic, and potentially explosive, runaway reactions in these oxidations, the feed rate for dimethyl sulfide is adjusted to ensure complete conversion and, thus, low instantaneous concentrations at any time. Alternate oxidants for the conversion of sulfides to sulfoxides include nitric acid, H202/acetic acid, peracids, and halogen/water. ... 

An important aspect is the oxidation of side-chain methyl to hydroxymethyl or aldehyde oxidation levels. The former can be achieved by reaction of the lithiated species with molecular oxygen, then qnenching with dimethyl sulfide in acetic acid. Conversion of methyl to the aldehyde oxidation level (see also 8.2) can be achieved by dibromination, then hydrolysis. ... 

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