Development of Solvent-Driven Iron-Catalyzed Reactions
摘要:
The possibility of solvent-driven iron-catalyzed reactions has been investigated using ionic liquids and acetonitrile as key solvents. Three iron-catalyzed reactions, the intramolecular cyclization of cyclopropane dithioacetals, the [2+2]-cycloaddition of (trans)-anethole, and the [2+3]-type cycloaddition of styrene derivatives with 1,4-benzoquinone, were first developed using acetonitrile as solvent in the presence of 3 similar to 5 mol% of Fe(ClO4)(3)center dot Al2O3 or Fe(BF4)(2)center dot 6H(2)O under air conditions. In particular, we found the rapid cycloaddition of iron-catalyzed [2+3]-type cycloaddition of styrene derivatives with 1,4-benzoquinone when the reaction was carried out in an ionic liquid which contained [PF6] or [Tf2N] anion. Homo-coupling reaction of aryl or alkynyl Grignard reagent was next discovered using 1 mol% of FeCl3 as catalyst and the reaction also proceeded very rapidly in an ionic liquid. We also found that 3-5 mol% of Fe(ClO4)(2)center dot Al2O3 or Fe(BF4)(2)center dot 6H(2)O-successfully catalyzed Friedel-Crafts type alkylation of indoles or pyrroles with vinyl ketones or alpha-aryl-beta-silylalcohol. In particular, the reaction of chiral alpha-aryl-beta-silylalcohol with indole using Fe(ClO4)(3)center dot nH(2)O as catalyst proceeded with retention of the configuration of stereochemistry of the hydroxyl group. Then, we discovered the first example of iron-catalyzed enantioselective C-S bond formation via Michael addition of thiols to (E)-3-crotonoyloxazolidin-2-one using 10 mol% of Fe(BF4)(2)/Pybox. We further demonstrated that Fe(ClO4)(3)center dot Al2O3-catalyzed the Nazarov type cyclizations of thiophene, pyrrole, indole, benzofuran, and benzo[b]thiophene derivatives using ionic liquids as solvent. Solvents have been recognized as a by-player in chemical reactions in the process of "optimization of reaction conditions". However, further investigation of the solvent-driven iron-catalyzed reaction will allow discovery of useful reactions for organic syntheses.
The Nazarov cyclization of two types of pyrrole derivatives was effectively catalyzed by 5 mol% alumina-supported iron(III) perchlorate [Fe(ClO4)3⋅Al2O3 ] which provided the desired cyclization with high trans selectivity in good to excellent yield. The cyclized product was next reacted with a vinyl ketone in the presence of the same iron salt to afford the corresponding Michael product. A sequential
两种类型的吡咯衍生物的环化纳扎罗夫被有效5摩尔%的氧化铝担载铁(III),高氯酸催化的[Fe(CLO 4)3 ⋅Al 2 ö 3 ],其提供高的所需的环化反式选择性良好至优异的屈服。然后在相同的铁盐存在下使环化产物与乙烯基酮反应,得到相应的迈克尔产物。吡咯衍生物的Nazarov / Michael顺序反应也已经完成。4,5-二氢环戊[ b ]吡咯-6(1 H)-一衍生物5或5,6-二氢环戊[ b ] pyrrol-4(1 )的合成途径因此已经使用非常经济的铁催化剂建立了H)一衍生物6。
Brønsted acid-catalyzed Nazarov cyclization of pyrrole derivatives accelerated by microwave irradiation
作者:Prabhakar Bachu、Takahiko Akiyama
DOI:10.1016/j.bmcl.2009.04.109
日期:2009.7
The Bronsted acid-catalyzed Nazarov cyclization of pyrrole derivatives was developed. Microwave irradiation accelerated the Nazarov cyclization significantly at 40 degrees C to give cyclopenta[b] pyrrole derivatives in excellent yields with high trans selectivity. (C) 2009 Elsevier Ltd. All rights reserved.