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2. Palladium-Catalyzed Intramolecular Cyclization Reaction Abell and co-workers recently developed a new synthetic method for trisubstituted imidazoles, 2-substituted 1-benzyl-4- methylimidazoles 2, based on the palladium-catalyzed intramolecular amino-Heck reaction of amidoximes 1 (Scheme 1).[15] With the success of the catalytic imidazole synthesis by the Pd-catalyzed intramolecular cyclization reaction, which employed relatively simple amidoximes, Abell and co-workers applied this transformation to the substrates prepared from amino acids to introduce an imidazole moiety as a stable ester isostere at the C terminus of peptidomimetics[23] (Scheme 2). 3. Palladium-Catalyzed Multicomponent Coupling Reaction Siamaki and Arndtsen succeeded in developing a direct synthesis of imidazoles by the palladium-catalyzed multicomponent coupling reaction (MCR) starting from two imines 3 and 5 and acid chlo- ACHTUNGTRENUNGrides 4 under CO atmosphere (Scheme 4).[16] In the early stages of the investigation, Siamaki and Arndtsen suffered low yields of the desired imidazole due to the formation of undesired a-sulfonylamide 7 and amide 8 (Scheme 5). 4. d10（10为上标）-Metal-Catalyzed Cycloaddition Reaction As shown in Scheme 7, only two examples were reported. The reaction of isocyanides 9a and 9b afforded the corresponding imidazoles 10 a and 10b in excellent yields. During the course of our research on the copper-catalyzed synthesis of pyrroles starting from isocyanides and acetylenes conjugated with an electron- withdrawing group (EWG),[31] we encountered homodimerization of ethyl isocyanoacetate (12 a, EWG=CO2Et; Scheme 9) with a catalytic amount of Cu2O and 1,10-phen- ACHTUNGTRENUNGanthroline (phen) to produce 1-(ethoxycarbonylmethyl)-4- (ethoxycarbonyl)imidazole (10 c, R=Et; Scheme 7) in 49% yield. 5. Lewis AcidCatalyzedMulticomp onent Coupling Reaction In this context, Sharma et al. investigated a Lewis acid catalyzed synthesis of imidazoles. They surveyed the three-component coupling reaction (TCR) of benzil, aldehydes 14, and NH4OAc in the presence of a catalytic amount of ZrCl4 and observed a dramatic acceleration in imidazole formation (Scheme 11).[19] The ZrCl4-catalyzed four-component coupling reaction (FCR) was further examined with benzil, benzaldehyde, primary amine 16, and NH4OAc to synthesize the fully substituted imidazoles 17 (Scheme 12). 6. Thiazolium-CatalyzedThree-Com ponent Coupling Reaction Frantz et al. developed the one-pot synthesis of imidazoles through the synthesis of a-ketoamides (N) via the thiazolium- catalyzed addition of aldehydes 19 to acylimines generated from a-sulfonylamides 18[39] and subsequent treatment with amines 20 (Scheme 13).[20] |
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肚而家
木虫 (小有名气)
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RXMCDM: 金币+1, 多谢应助！ 2014-03-12 02:06:00
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2.钯催化分子间成环反应。 Abell和其同事最近在钯催化脒肟类分子内氨基Heck反应的基础上研制了一种新的合成三取代咪唑（2-取代 1-苄基-4-甲基咪唑）的方法。（图1） 随着用相对简单的脒肟类钯催化分子内成环反应催化合成咪唑的成功，Abell和其同事把这种反应应用于氨基酸制成的衬底以引入咪唑基元并用其作为肽链C端的稳定酯类异构体。（图2） 3.钯催化多组分偶联反应 Siamaki和Arndtsen使用钯催化多组分偶联反应（MCR）成功用一步法合成了咪唑。反应在CO气氛下使用两份亚胺和 XXX 和酰氯反应。（图4） 在研究的早期阶段，Siamaki和Arndtsen经历了极低的咪唑产率，这主要是因为产生了α-磺酰胺和酰胺。（图5） 4.d10金属催化环加成反应。 如表7所示，只有两个实例见诸报导。9a和9b的异腈反应为10a和10b中相应咪唑的生成提供了极好的产率。 在我们对于 反应物为异腈和与吸电子基团共轭的炔烃的 铜催化合成吡咯的研究过程中，我们遭遇了异腈基乙酸乙酯(12a, EWG=CO2Et; 图 9)的同二聚作用，当时使用了催化剂量的Cu2O和1,10-邻二氮杂菲（邻二氮菲）来制备1-乙酸乙酯基-4-乙酯基咪唑(10 c, R=Et; 图7) ，产率为49%。 5.路易斯酸催化多组分偶联反应 在这种情况下，Sharma等人研究了咪唑的路易斯酸催化合成。他们进行了四氯化锆催化二苯乙二酮、乙醛、醋酸铵三组分偶联反应（TCR）并观察到咪唑的的加速形成。 ZrCl4催化四组分偶联反应（FCR）被进一步用二苯乙二酮、苯甲醛、伯胺、醋酸铵等组分合成全取代咪唑。（图12） 6.噻唑催化三组分偶联反应 Frantz等人开发了咪唑的一锅法合成。它经过两步：1. 噻唑催化乙醛和由α-磺酰胺生成的酰亚胺反应生成α-酮酰胺。2. 所得产物与胺反应。（图13） |
2楼2014-03-11 21:53:35
肚而家
木虫 (小有名气)
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3楼2014-03-11 21:58:04
