Thioethers, alkylation

The reactivity of a series of thioethers has also been examined. It was found that the enantioselectivity is a function of the thioether alkyl group. The highest ee values were obtained with methyl and benzyl groups. Interestingly, X-ray analysis revealed that the stereochemistry of the reaction was the opposite of that obtained with analogous ether complexes (Scheme 49)90. 

Thioethers. Alkylation of thiols with alcohols under the Mitsunobu reaction conditions is catalyzed by imidazole. 

Other sulfur-bonding adducts of the Rhj core have been reported for thiols, thioethers, alkyl sulfides,thiourea derivatives, " and benzothiadiazole. Reaction of NCX (X = S, Se) with [Rh2(02CMe)4] is reported to lead to the anionic 1 1 adduct [Rh2(02CMe)4(NCX)] A structure has not been reported, but based on analytical data, one-dimensional chains with bridging NCX anions were proposed. ... 

Alkyl 2,4-dinitrophenyl thioether (Alkyl 2.4-dinitrophenyl sulfide). 

The alkyl sulphides or thioethers, the sulphur analogues of the ethers, are conveniently obtained by boiling alkyl halides with anhydrous sodium sulphide in alcoholic solution, for example ... 

Alkyl (or Aryl) 2 4-dinitrophenyl-sulphides (or thioethers) and the corresponding sulphones. Mercaptans react with 2 4-dinitrochlorobenzene in alkaline solution to yield crystalhne thioethers (2 4-dinitrophenyl-sulphides) (I) ... 

Anions of allylic thioethers may also be alkylated with alkyl bromides in high yield. The thioether groups can subsequently be removed by hydrogenolysis (F.W. Sum, 1979). 

The nucleophUic reactivity in neutral medium has been used extensively to prepare various thioethers of thiazole (122). In acidic medium, alkylation may be performed with alcohols (123, 124). An unexpected reaction encountered was the decarboxylation of 2-mercapto-4-methyl-5-thiazolecarboxyhc acid (60) when treated with butyl alcohol under acidic conditions (Scheme 27) (123). Reaction between A-4-thiazoline-2-thione... 

The methylthio group is removed by treatment with zinc powder in HCl (276) to give the 2-unsubstituted thiazole. The action of aluminum-mercury amalgam in methanol on various thioethers is reported to yield the expected thiazole (108) when Rj is an alkyl group and the corresponding A-4-thiazoline-2-thione (109) when Rj PhCH - (Scheme 55) (169). 

Sulfur Substituents. Acetylation and alkylation of pyridinethiones usually take place on sulfur (39). An exception to this is 4-pyridinethione [19829-29-9] which is acetylated on nitrogen. Displacement of thioethers can be achieved with hydroxide or amines (eq. 13) (40). Thioether functional groups can also be removed by reduction (39). 

Sulfur is reactive ia many forms. Mercaptides are alkylated to thioethers, and thioethers react further to give sulfonium salts, R2S" CH20S0 2-Suitable thiones also alkylate. Thioachdone (34) and thiourea (35) are examples the first gives the alkylmetcaptoacridine and the second gives the isothiourea. 

Pyrrolethiols, readily obtained from the corresponding thiocyanates by reduction or treatment with alkali, rapidly oxidize to the corresponding disulfides. They are converted into thioethers by reaction with alkyl halides in the presence of base. Both furan- and thiophene-thiols exist predominantly as such rather than in tautomeric thione forms. 

S-Benzyl and substituted S-benzyl derivatives, readily cleaved with sodium/ammonia, are the most frequently used thioethers. n-Alkyl thioethers are difficult to cleave and have not been used as protective groups. Alkoxymethyl or alkylthio-... 

Typical of these materials are the poly(vinyl thioethers), the poly(vinyl isocyanates), the poly(vinyl ureas) and the poly(alkyl vinyl ketones). Methyl isopropenyl ketone and certain vinylpyridine derivatives have been copolymerised with butadiene to give special purpose rubbers. 

A-Acetylmetbionine Derivative(Chart 9). Cleaved by alkylation of the thioether with iodoacetamide followed by cyclization. 

Pyrazine-2-thione (213) and quinoxaline-2-thione (214) probably exist in the thione form since their ultraviolet spectra are different from those of the 2-methylthio analogs. The basicity of quinoxaline-2-thione is 1.4 pK units less than that of 2-methylthio-quinoxaline, and the ultraviolet spectra of the cations are dissimilar. Presumably quinoxaline-2-thione and its 2-methylthio derivative do not form similar cations (215, P = alkyl, H), and it would appear that either the thione gives the cation 216 or the 2-thioether gives the cation 217. Similar considerations apply to pyrazine-2-thione. 

The same diamine, when treated with carbon disulfide in alkaline medium, yielded 2-mercapto- l//-imidazo[4,5-/]quinoline (88PS267,88SC973,86IJC264), which, on treatment with alkyl, aralkyl, and acid halides, gave the corresponding thioethers and thioesters 111, respectively (88PS267, 86IJC264). 

A great advantage of catalyst 24b compared with other chiral Lewis acids is that it tolerates the presence of ester, amine, and thioether functionalities. Dienes substituted at the 1-position by alkyl, aryl, oxygen, nitrogen, or sulfur all participate effectively in the present asymmetric Diels-Alder reaction, giving adducts in over 90% ee. The reaction of l-acetoxy-3-methylbutadiene and acryloyloxazolidinone catalyzed by copper reagent 24b, affords the cycloadduct in 98% ee. The first total synthesis of ewt-J -tetrahydrocannabinol was achieved using the functionalized cycloadduct obtained [23, 33e] (Scheme 1.39). 

Inclusion of iodine in the thiouracyl molecule similarly proves compatible with antithyroid activity. Alkylation of thiouracyl proper (85) with benzyl chloride affords the thioether,... 

So far, hexasubstituted derivatives 135 have been prepared with aryl and alkyl thiolates, phenolates as well as oxo- and thioether precursors [220]. 

Thioethers (sulfides) can be prepared by treatment of alkyl halides with salts of thiols (thiolate ions). The R group may be alkyl or aryl and organolithium bases can be used to deprotonate the thiol. As in 10-37, RX cannot be a tertiary halide, and sulfuric and sulfonic esters can be used instead of halides. As in the Williamson... 

This reaction is analogous to 10-16. Primary and secondary alcohols can be converted to alkyl aryl sulfides (ROH RSAr) in high yields by treatment with BU3P and an V-(arylthio)succinimide in benzene. Thioethers RSR can be prepared from an alcohol ROH and a halide R Cl by treatment with tetra-methylthiourea Me2NC(=S)NMe2 followed by NaH. ... 

Symmetrical thioethers can also be prepared by treatment of an alkyl halide with sodium sulfide, or with S(MgBr)2 with allylic halides. ... 

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