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jiangchen077木蟲(chóng) (小有名氣)
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[求助]
求助：一段英文翻譯
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Amines and their derivatives are important functionalities invarious natural products and important synthetic targets.Theyare widely used as basic intermediates to prepare solvents,fine chemicals,pharmaceuticals,agrochemicals and catalysts for polymerization.1 As a result,the development of new methods to prepare these compounds has become the goal of many research groups over the ears.Traditionally,amines are alkylated in solution phase using inorganic acids as the catalysts and alkyl halides or dimethyl sulfate as the alkylating agents,2 besides methanol3 and dimethyl carbonate.4 However, yields or products selectivity(mono-or bis-alkylations)are,with few exceptions,low and depend on the nature of the catalysts and on the reaction conditions.From a methodological viewpoint,direct nucleophilic attack of amines to alkyl halides is the most straightforward procedure for the alkylation of amines.5 The major synthetic problem for direct alkylation procedure is the competing over-alkylation,which leads to mixtures of secondary and tertiary amines and even quaternary ammonium salts,and the prevention of over-alkylation becomes more difficult when highly reactive alkylating agents such as methyl,ethyl,benzyl,and allyl halides are used as alkylating agents.6 Thermal reaction between alkyl halides and amines in the presence of a base requires longer reaction time period and affords lower yields of desired product.7 Inorganic bases like NaH,8 K2CO3,9 CsOH·H2O,10 Cs2CO311 have been employed in N-alkylation of amines.Recently,Varma and his co-workers studied the formation of tertiary amines via N-alkylation in aqueous alkaline medium under microwave irradiation to evolve a greener procedure.12 Use of strong inorganic bases,however, can lead to undesired products in the presence of base-sensitive functional groups and hydrolysis of the corresponding alkyl halides may also result.Copper-catalyzed Ullmann and Gold-berg reactions13 or Pd-catalyzed Buchwald–Hartwig reaction14 have been established as versatile C–N bond-forming reactions.However,transition metal-free amination of electron-rich benzyl halides has remained largely unexplored.15 Although most of the methods are apparently useful,many of them are limited byharsh reaction conditions,low yields,long reaction times and use of toxic solvents or catalysts.N-alkylations promoted on solid phase are often associated with strong basicity of the surface limiting the scopes of recyclability and selectivity.16 Further-more,the possibility of the concomitant over-alkylations,when the amine is employed as the limiting substrate,often reduces the application of these methods.17 Therefore,development of mild,efficient,selective and environmentally benign method of N-alkylation of amines including diamines and heterocyclic compounds bearing acidic hydrogen atom attached to nitrogen has been a major challenge in organic synthesis. |
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云和風(fēng)清
金蟲(chóng) (著名寫(xiě)手)
- 翻譯EPI: 4
- 應(yīng)助: 0 (幼兒園)
- 金幣: 3463.1
- 散金: 28
- 紅花: 2
- 帖子: 2069
- 在線: 201.5小時(shí)
- 蟲(chóng)號(hào): 430842
- 注冊(cè): 2007-08-11
- 性別: GG
- 專業(yè): 傳遞過(guò)程
【答案】應(yīng)助回帖
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wypward(金幣+1):歡迎新蟲(chóng) 2010-07-01 20:25:57
wypward(金幣+1):歡迎新蟲(chóng) 2010-07-01 20:25:57
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胺類及其衍生物是在許多的天然產(chǎn)物和重要的合成目標(biāo)產(chǎn)物中的重要的功能化合物。 它們被廣泛用作制備溶劑、精細(xì)化學(xué)品、藥物、農(nóng)業(yè)化學(xué)品及聚合反應(yīng)的催化劑的基礎(chǔ)中間體[1]。因此，制備這類產(chǎn)物的新方法的進(jìn)展已經(jīng)成為眾多研究機(jī)構(gòu)的目標(biāo)。通常意胺類是在液相中烷基化的，使用無(wú)機(jī)酸作催化劑，鹵代烷或硫酸二甲酯作烷基化試劑[2]，此外烷基化試劑還有甲醇[3] 和碳酸二甲酯[4]。但是，除少數(shù)例外外，產(chǎn)率或產(chǎn)物的選擇性(單-或重烷基化)不太好，且依賴于催化劑的性質(zhì)和反應(yīng)條件。 從方法論角度上講，如胺類直接親核攻擊鹵代烷則將是胺類烷基化最直接的方式[5]， 直接烷基化面臨的最重大的合成困難是如何應(yīng)對(duì)過(guò)度烷基化，其可能會(huì)導(dǎo)致仲銨鹽、叔胺鹽甚至季銨鹽產(chǎn)生，特別使用甲基、乙基、芐基和烯丙基鹵化物等高活性試劑作為烷基化試劑時(shí)，避免過(guò)度的烷基化就會(huì)變得更加困難[6]。烯丙基鹵化物與胺類在堿存在條件下的熱反應(yīng)需要較長(zhǎng)的反應(yīng)時(shí)間且理想產(chǎn)物的產(chǎn)率較低[7]，無(wú)機(jī)堿如NaH[8]，K2CO3[9]，CsOH•H2O[10]，Cs2CO3[11]也已被用于胺類的N-烷基化。最近，Varma及其合作者研究了微波輻射條件下經(jīng)由N-烷基化合成叔胺的形成過(guò)程，給我們提供了一條綠色的合成途徑[12]。但是由于使用強(qiáng)的無(wú)機(jī)堿，在堿敏感基團(tuán)存在條件下可能會(huì)產(chǎn)生非理想產(chǎn)物，也可能會(huì)導(dǎo)致相應(yīng)的鹵代烷水解。銅催化的Ullmann和Gold-berg 反應(yīng)[13]或鈀催化的Buchwald–Hartwig反應(yīng)[14]被公認(rèn)為通用的C–N鍵合成反應(yīng)，但是，富電荷的芐基鹵代物的在無(wú)過(guò)渡金屬條件下的胺化則尚未充分研究[15]，盡管很明顯這些方法中大多數(shù)是很有用的，但其中很多由于反應(yīng)條件嚴(yán)苛，產(chǎn)率低、反應(yīng)時(shí)間長(zhǎng)和使用的溶劑或催化劑有毒性而使其應(yīng)用受到限制。固相上的改進(jìn)N-烷基化通常是與表面的強(qiáng)堿性相聯(lián)系，這就制約了再生性和選擇性[16]。進(jìn)一步講，但胺類充當(dāng)限制性物質(zhì)時(shí)，過(guò)度烷基化伴生的可能性通常會(huì)降低應(yīng)用這些方法的可行性[17]。因此，開(kāi)發(fā)出一種溫和、高效、選擇性好、環(huán)境友好的胺類(包含二胺類和具有與氮原子相連的酸性H原子的雜環(huán)化合物)N-烷基化的方法已經(jīng)成為有機(jī)合成中重要的研究課題。 翻譯的不太好，有些翻譯很不盡人意，有點(diǎn)難以理解 |
2樓2010-07-01 20:03:46
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