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药学英语，求帮忙翻译一下，论文要用
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Synthesis of β-keto sulfones The synthesis of β-keto sulfones can be carried out in several ways. The most available and broadly used synthetic routes to β-keto sulfones include acylation of methyl sulfones [3,4] (Method 1), alkylation of metallic arene sulfinates with α-halo ketones [5,6] (Method 2) and oxidation of β-keto sulfides (Method 3). Acylation of methyl sulfones with excess amounts of either esters or carboxylic acid chlorides in the presence of base such as n−butyllithium, LDA or sodium hydride (Method 1) (Scheme 1) is the most explored and demanded method to provide β-keto sulfones to date. Recently, Nacylbenzotriazoles have been found to be effective C-acylation reagents for this purpose, which can be used in stoichiometric ratios affording high yields of β-keto sulfones。 Scheme 1. General routes to β-keto sulfones. Heteryl β-keto sulfones containing benzothiazole or phenyltetrazole heterocyclic core were prepared by theacylation of the corresponding heteryl methyl sulfones using lithium trimethyl silyl azide as a base (Scheme 2).The use of such non-nucleophilic base is derived from the presence of electrophilic center within the heterocyclic core of methyl sulfone that can react with nucleophilic bases present in the reaction mixture furnishing side products. Scheme 2. Synthesis of heteryl β-keto sulfones. β-Keto sulfone having triple bond within the alkyl chain at carbonyl moiety was obtained by the Claisen-type condensation reaction of cyclic vinilogous carboxylic acid triflate with anion of dimethyl sulfone . Scheme3. Synthesis of β-keto sulfone containing triple bond using cyclic vinilogous carboxylic acid triflate. For the synthesis of β-keto sulfones bearing C4F9 group at sulfonyl moiety as starting compound, commercially available nonafluorobutanesulfonyl fluoride was used. The latter was reduced with hydrazine to the sulfinicacid that was methylated with MeIto give methyl nonaflate. Subsequent deprotonation of methyl sulfone with LDA followedby acylation with acetyl chloride afforded the corresponding β-keto perfluorobutylsulfone in 76% yield. Scheme 4. Synthesis of nonaflyl acetone starting from nonafluorobutanesulfonyl fluoride. Acylation of Grignard reagents of sulfones, exemplified by para-tolylsulfonylmethyl magnesium bromide, with esters was also used as a method for the preparation of β-keto sulfones. Scheme 5. Synthesis of β-keto sulfones from p-tolylsulfonylmethyl magnesium bromide. β-Keto sulfones with alkyne moiety at carbonyl group were prepared by the oxidation of βhydroxy sulfones with PCC. The corresponding β-hydroxy sulfones were obtained from aryl methyl sulfones and prop-2-ynals via Grignard reagents . Scheme6. Synthesis of β-keto sulfones with alkynemoiety by oxidation of β-hydroxy sulfones. Another way to construct β-keto sulfone moiety involves sulfonylation of methyl ketones. In particular, such an approach was used in the synthesis of chiral[2.2]paracyclophane derivatives of β-keto sulfones, as potential ligands for asymmetric catalysis, by reactions of 4-hydroxy-5acyl[2.2]paracyclophane with sodium hydride and triflic anhydride or nonafluorobutanesulfonyl fluoride . Scheme 7. Synthesis of β-keto sulfones with paracyclophane moiety. Synthetic approaches to β-keto sulfones based on the alkylation of arene sulfinates metal salts with α-halo ketones (Method 2) (Scheme 1) are constantly being upgraded in order to enhance effectiveness and numerous modifications of this method arise in the literature. It was reportedthat reactions of this type were promoted by PEG-400 and ionic liquids as reaction media. β-Heteryl β-keto sulfones with coumarine fragment at C=O g roup were obtained using this method under solvent-free conditions. Microwave-assisted synthesis of β-keto sulfones by the alkylation of arene sulfinates with the corresponding halo derivatives was used for rapid preparation of parallel synthetic libraries for studying QSAR. Alkylation of trifluoromethylsulfinates with α-bromomethyl ketones was used as a method for the preparation of β-keto trifluromethylsulfones (triflones) . Scheme 8. Synthesis of β-keto trifluromethylsulfones (triflones) by alkylation of trifluoromethylsulfinates with α-bromomethyl ketones. Besides α-haloketones, α-tosyloxy ketones generated in situ from the readily available methyl ketones upon the action of HTIB have also been used in reactions with arene sulfinates for the efficient synthesis of β-keto sulfones . Scheme 9. Alkylation of trifluoromethylsulfinates with in situ generated α-tosyloxy ketones. Since the presence of the carbonyl group has no essential influence on the oxidative ability of sulfuratom,oxidation of β-keto sulfides constitutes another wide spread method for the synthesis of β-keto sulfones (Method 3). As oxidants, the same reagents as for the oxidation of sulfides to sulfones are usually used, as described by Trost.Peroxides or peroxy acids are the most common oxidants in the sereactions. However, the presence of the functionalities on the sulfide substrate often complicates the oxidation due to the competing reactions of the functional groups, thus requiring specific reaction conditions. In particular, for the synthesis of β-keto glycosyl sulfone derivative bearing sulfur atom at the anomeric carbon, soft oxidation of the corresponding thioglycoside using HOF·MeCN complex at room temperature was used. Scheme 10. Oxidation of β-keto glycosyl sulfide using HOF-MeCN complex. Another β-keto sulfone containing glycoside counterpart at sulfur was obtained from the corresponding allene sulfone by treating with base and subsequent instantaneous hydrolysis of the intermediate enamino sulfone . Sulfonyl-containing C-glucoside endo-glycal was obtained by the reaction of C-glucosyl vinyl sulfone with reactive α-halo acetophenone in the presence of sodium methoxide involving basecatalyzed migration of the double bond prior to transsulfonylation . As a method to synthesize β-keto sulfones, free-radical rearrangement of enol sulfonates was also described. During recent decades, a number of novel alternative approaches for the synthesis of β-keto sulfones appeared, apart from the common methods described above. The purposes of the newly arising approaches are to overcome the drawbacks generally associated with the poor availability of the starting substrates, inconvenience of the synthetic procedure, low tolerance of the employed Scheme 11. Synthesis of β-keto sulfone from sulfonyl allene. Scheme 12. Acylation of C-glucosyl vinyl sulfone with α-halo acetophenone. |
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