DEVELOPMENT OF SOLVENT-DRIVEN IRON-CATALYZED REACTIONS

作者：Itoh Toshiyuki^*

来源：Heterocycles, 2016, 92(8): 1373-1395.

DOI：10.3987/REV-16-842

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.

• 出版日期2016-8-1