title: A Simple, Effective, Green Method for the Regioselective 3-Acylation of Unprotected Indoles.
abstract: A fast and green method is developed for regioselective acylation of indoles in the 3-position without the need for protection of the NH position. The method is based on Friedel-Crafts acylation using acid anhydrides. The method has been optimized, and Y(OTf)₃ in catalytic amounts is found to be the best catalyst together with the commercially available ionic liquid [BMI]BF₄ (1-butyl-3-methylimidazolium tetrafluoro-borate) as solvent. The reaction is completed in a very short time using monomode microwave irradiation. The catalyst can be reused up to four times without significant loss of activity. A range of substituted indoles are investigated as substrates, and thirteen new compounds have been synthesized.
authors.affiliation: Department of Organic Chemistry, Faculty of Chemistry, University of Science, Vietnam National University, Ho Chi Minh City 70000, Vietnam. thphuong15@yahoo.com.
authors.forename: Phuong Hoang
authors.initials: PH
authors.lastname: Tran
authors.affiliation: Department of Organic Chemistry, Faculty of Chemistry, University of Science, Vietnam National University, Ho Chi Minh City 70000, Vietnam. sidoantruong@gmail.com.
authors.forename: Hai Ngoc
authors.initials: HN
authors.lastname: Tran
authors.affiliation: Department of Science, Systems and Models, Roskilde University, POB 260, Roskilde DK-4000, Denmark. Poulerik@ruc.dk.
authors.forename: Poul Erik
authors.initials: PE
authors.lastname: Hansen
authors.affiliation: Department of Organic Chemistry, Faculty of Chemistry, University of Science, Vietnam National University, Ho Chi Minh City 70000, Vietnam. dhnmai@gmail.com.
authors.forename: Mai Hoang Ngoc
authors.initials: MH
authors.lastname: Do
authors.affiliation: Department of Organic Chemistry, Faculty of Chemistry, University of Science, Vietnam National University, Ho Chi Minh City 70000, Vietnam. lenthach@yahoo.com.
authors.forename: Thach Ngoc
authors.initials: TN
authors.lastname: Le
mesh_terms: D000215:Acylation; D002384:Catalysis; D055772:Green Chemistry Technology; D007211:Indoles / Q000138:chemical synthesis* / Q000737:chemistry*; D008872:Microwaves; D015394:Molecular Structure; D013237:Stereoisomerism
chemical_list: D007211:Indoles
keywords: Friedel-Crafts acylation; indole derivatives; ionic liquids; metal triflate; microwave irradiation