Alkyl sulphides, reduction

Van t Hoff t-factors 565 Vinylallenes rearrangement of 748 synthesis of 737 Vinyl carbonium ions 620 17a-Vinyl-17/f-hydroxysteroids, epimerization of 735 Vinyl sulphides, as alkyl sulphoxide reduction products 930, 932 Vinyl sulphones - see also Alkenyl... 

An efficient one-pot procedure for the iV-monomethylation of primary amines has been reported the method involves formylation with acetic formic anhydride followed by borane methyl sulphide reduction. The reaction sequence is applicable to even very weakly basic and sterically hindered amines, and the products are uncontaminated by over-alkylation. In addition, the transition-metal-catalysed j V-monoalkylation of amines by alcohols has been previously reported (c/. Vol. 6, p. 198) as a method to overcome problems associated with over-alkylation. A similar procedure for the preparation of unsymmetrical secondary (and tertiary) amines utilises a ruthenium catalyst, and is particularly suitable for the synthesis of cyclic amines. ... 

An alternative route to sulphones utilizes the reaction of the appropriate activated halide with sodium dithionite or sodium hydroxymethanesulphinite [6], This procedure is limited to the preparation of symmetrical dialkyl sulphones and, although as a one-step reaction from the alkyl halide it is superior to the two-step oxidative route from the dialkyl sulphides, the overall yields tend to be moderately low (the best yield of 62% for dibenzyl sulphoxide using sodium dithionite is obtained after 20 hours at 120°C). The mechanism proposed for the reaction of sodium hydroxymethanesulphinite is shown in Scheme 4.20. The reaction is promoted by the addition of base and the best yield is obtained using Aliquat in the presence of potassium carbonate. It is noteworthy, however, that a comparable yield can be obtained in the absence of the catalyst. The reaction of phenacyl halides with sodium hydroxy-methane sulphinite leads to reductive dehalogenation [7]. 

Generation of aryl radicals by reduction of aryl halides in the presence of some nucleophiles, particularly alkyl or aryl sulphide ions and cyanide ions, leads to bond formation with the generation of a new radical-anion. Overall, a reaction between the initial aryl halide and a nucleophile is triggered at the cathode and is an equivalent of the Sr I process. It proceeds in stages according to Scheme 4.6 [156] and requires only a catalytic concentration of radical-anion. The reaction can... 

The lower members of the homologous series of 1. Alcohols 2. Aldehydes 3. Ketones 4. Acids 5. Esters 6. Phenols 7. Anhydrides 8. Amines 9. Nitriles 10. Polyhydroxy phenols 1. Polybasic acids and hydro-oxy acids. 2. Glycols, poly-hydric alcohols, polyhydroxy aldehydes and ketones (sugars) 3. Some amides, ammo acids, di-and polyamino compounds, amino alcohols 4. Sulphonic acids 5. Sulphinic acids 6. Salts 1. Acids 2. Phenols 3. Imides 4. Some primary and secondary nitro compounds oximes 5. Mercaptans and thiophenols 6. Sulphonic acids, sulphinic acids, sulphuric acids, and sul-phonamides 7. Some diketones and (3-keto esters 1. Primary amines 2. Secondary aliphatic and aryl-alkyl amines 3. Aliphatic and some aryl-alkyl tertiary amines 4. Hydrazines 1. Unsaturated hydrocarbons 2. Some poly-alkylated aromatic hydrocarbons 3. Alcohols 4. Aldehydes 5. Ketones 6. Esters 7. Anhydrides 8. Ethers and acetals 9. Lactones 10. Acyl halides 1. Saturated aliphatic hydrocarbons Cyclic paraffin hydrocarbons 3. Aromatic hydrocarbons 4. Halogen derivatives of 1, 2 and 3 5. Diaryl ethers 1. Nitro compounds (tertiary) 2. Amides and derivatives of aldehydes and ketones 3. Nitriles 4. Negatively substituted amines 5. Nitroso, azo, hy-drazo, and other intermediate reduction products of nitro com-pounds 6. Sulphones, sul-phonamides of secondary amines, sulphides, sulphates and other Sulphur compounds... 

Reductive alkylation of esters of thioarsinic acids and arsine sulphides... 

In the preparation of various unsaturated amides, the dianion of -phenyl-2-(phenyIsulphonylmethyl)propenamide (49) proved to be a versatile synthon. Borohydride reduction of alkylation products of the dianion occurred in high yield to afford moderate overall yields of ,B-unsaturated amides.The dianion of the corresponding phenyl sulphide alkylated poorly giving small amounts of oth a- and y-alkylation products, whereas the sulphone-ester corresponding to (49) was found to be labile under the deprotonation conditions. Compound (49) was also employed in the development of a general strategy for the synthesis of 3,4-epoxy-2-methylene-alkanoic acid amides (Scheme 29). ... 

Reductive cleavage of sulphides, selenides, and tellurides on Raney nickeP and cleavage by lithium in THE, leading to secondary or tertiary alkyl-lithium compounds, are useful synthetic operations novel variations are involved in the cleavage of dialkenyl sulphides with EtjSiH (giving low yields of silyl sulphides) and of alkenyl, aryl, and allyl sulphides and selenides with PPhj and... 

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. ... 

A small number of papers that cover mechanistic aspects deal with the factors that stabilize the developing carbonium ion in the hydrolysis of 0,S-thioacetaIs. An electron-transfer, mild reduction system (iron polyphthalocyanine) has been shown to reduce benzil dithioacetal to the / -keto-sulphide [PhCOCPh(SPh)2 PhCOCHPhSPh]. Homolysis of dithioacetals on heating with BuKDOBu in PhCI followed by a 1,2-shift of an alkylthio-group leads to l,2-bis-(alkylthio)alkyl compounds/ ... 

Several bi- and tri-cyclic thiepan derivatives were obtained by autoxidation of the cyclobutadiene (111) or by various reactions with strained sulphur-containing acetylenes, e.g.. the dithiet (112). The ylides derived from cis- and trans-ill) were alkylated stereoselectively at low temperatures, and they reacted with carbonyl compounds to give ring-opened oxirans (113). Reduction of the 6-methoxy-carbonyl derivative of (72) afforded the ten-membered cyclic sulphide (114). ... 

Reductive Methods.—Aldehydes from Acid Equivalents. In a two-step process which formally constitutes a reduction, carboxylic acids are first reduced to the corresponding alkyl borate ester by the borane-dimethyl sulphide complex, which in turn is oxidized in high overall yield to the aldehyde [equation (1)]. ... 

Reactions of Enolates and Enolate Equivalents.—Several papers have appeared on the use of enolates released from silyl enol ethers by Lewis acids. Fleming reports the regiospecific alkylation of either the thermodynamic or the kinetic silyl enol ethers with chloromethyl phenyl sulphide in the presence of titanium(iv) chloride. Oxidative or reductive removal of the sulphur gives a-methylene- or a-methyl-ketones respectively (Scheme 69). ... 

When a thiol ester with at least one hydrogen alpha to the carbonyl group is treated with a strong, non-nucleophilic base, thiol anion is rapidly and quantitatively released subsequent reaction with an alkylating agent provides the basis of a synthesis of sulphides under non-aqueous conditions (Scheme 160). The reduction of sulphoxides to sulphides with sodium hydrogen sulphite has been subjected to mechanistic investigation. ... 

Corey has reported a novel method for the introduction of two alkyl appendages at the carbonyl carbon of ketones. Ketones react with the anion of diethyl allylthiomethylphosphonate (155) to give vinyl allyl sulphides such as (156) heating in the presence of mercury(ii) oxide induces a thio-Claisen rearrangement to yield the aldehyde (157), which can be further elaborated by various oxidation-reduction sequences to give, for example, the spiro-enone (158). 

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