InBr3-catalyzed Friedel-Crafts addition of indoles to chiral aromatic epoxides: a facile route to enantiopure indolyl derivatives

Nucleophilic Transformations of Lewis Acid-Activated Disubstituted Epoxides with Catalyst-Controlled Regioselectivity

Due to their inherent ring strain and electrophilicity, epoxides are highly attractive building blocks for fundamental organic reactions. However, controlling the regioselectivity of disubstituted epoxide transformations is often particularly challenging. Most Lewis acid-mediated processes take advantage of intrinsic steric or electronic substrate bias to influence the site of nucleophilic attack. Therefore, the scope of many of these systems is frequently quite limited. Recent efforts to generate catalysts that can overcome substrate bias have expanded the synthetic utility of these well-known reactions. In this Perspective, we highlight various regioselective transformations of disubstituted epoxides, emphasizing those that have inspired the production of challenging, catalyst-controlled processes.

Friedel-Crafts alkylation with α-bromoarylacetates for the preparation of enantioenriched 2,2-diarylethanols

Highly enantioenriched 2,2-diarylethanols can be efficiently synthesized through the Friedel-Crafts alkylation of (hetero)arenes with configurationally labile α-bromoarylacetates. The substitution of highly diastereoenriched α-bromoarylacetates occurs in the presence of AgOTf, and the subsequent reduction affords diverse 2,2-diarylethanols with high yields and enantioselectivities up to 99 : 1 er. In addition, the application of this asymmetric synthetic methodology to the preparation of highly enantioenriched dihydrobenzofuran and indoline derivatives is demonstrated.

Tryptophol and derivatives: natural occurrence and applications to the synthesis of bioactive compounds

This report presents some fundamental aspects related to the natural occurrence and bioactivity of tryptophol as well as the synthesis of tryptophols and their utilization for the preparation of naturally occurring alkaloid metabolites embedding the indole system.

Regio- and enantioselective friedel-crafts reactions of indoles to epoxides catalyzed by graphene oxide: a green approach

Graphene oxide efficiently promotes high regio- and enantioselective ring opening reactions of aromatic epoxides by indoles addition, in solvent- and metal-free conditions. The Friedel-Crafts products were obtained with enantioselectivity up to 99 % ee. The complete inversion of stereochemistry indicates the occurrence of SN 2-type reaction, which assures high level of enantioselectivity.

Indium(III) triflate — a catalyst for greener aromatic alkylation reactions

An environmentally friendly method for alkylating aromatic compounds with simple alcohols in the presence of a catalytic amount of indium(III) triflate is reported. Ionic liquids are used as solvents and energy-efficient heating is provided by microwave radiation. Good yields are obtained with benzyl, secondary, and tertiary alcohols. Simple primary alcohols are not effective alkylating agents under these conditions. With tertiary alcohols, activated aromatic compounds such as toluene and anisole must be used to obtain good yields. The catalyst, which is immobilized in a water-insoluble ionic liquid, can be easily recycled without significant loss of activity.

Ultrasound promoted efficient method for the cleavage of 3-aryl-2,3-epoxyl-1-phenyl-1-propanone with indole

An efficient synthesis of 3-aryl-3-hydroxy-2-(1H-indol-3-yl)-1-phenyl-1-propanone via the cleavage of epoxides with indole promoted by ultrasound irradiation was carried out in good yields by using montmorillonite K10-ZnCl(2) within 2-5h at room temperature. This method provides several advantages such as operational simplicity, high yield and mild conditions.

Regio- and stereoselective ring-opening reactions of epoxides with indoles and pyrroles in 2,2,2-trifluoroethanol

Aliphatic and aromatic epoxides react regio- and stereoselectively with indoles and pyrroles in 2,2,2-trifluoroethanol without the use of a catalyst or any other additive. While aromatic epoxides are selectively attacked at the benzylic position, aliphatic epoxides react at the less-substituted position. Chiral epoxides react with >99 % ee (ee=enantiomeric excess).

Remarkably mild and efficient intramolecular Friedel-Crafts cyclization catalyzed by In(III)

[structure: see text]. Indium(III) salts were found to be highly effective catalysts for the intramolecular Friedel-Crafts reaction of simple allylic bromides and arenes. In(III) salts appear to be the most general and possess unique halophilic properties as a Lewis acid for this reaction among the catalysts evaluated to date. Deactivated arenes possessing chloride, bromide, and fluoride underwent smooth reaction when activated by InCl3.

A simple, highly regioselective and efficient reaction of indole with epoxides under solvent-free conditions

Lithium perchlorate has been found to be an inexpensive and efficient catalyst for the ring opening of epoxides by indole and N-methylindole, which provides an environmentally friendly method for the synthesis of substituted indoles. A complete regioselectivity in favor of nucleophilic attack at the benzylic carbon atom of aromatic epoxides, such as styrene oxide, is observed. However, aliphatic unsymmetrical alkene oxides undergo selective nucleophilic attack at the sterically less-hindered carbon atom. This catalyst offers several advantages, such as short reaction time, high yields, lower catalytic loading, simple experimental procedure, and easy isolation of the products, under solvent-free conditions.

A Study of 5-Nitroindole Alkylation

A detailed study of the 5-nitroindole alkylation, the key step in the synthesis of Zafirlukast, is presented. A broad distribution of alkyl derivatives has been found. 2,3- And 1,3-dialkylindoles can be selectively obtained in a ZnBr2-catalyzed reaction. Structure of all the products was fully assigned.

Reactions of indole derivatives with oxiranes and aziridines on silica. Synthesis of beta-carbolin-1-one mimic of pancratistatin

[reaction: see text] Indole and several indoles functionalized at C-2 were condensed with oxiranes, vinyloxiranes, aziridines, and vinylaziridines in the solid state on the surface of silica. The yields of these reactions were compared to those obtained from Lewis acid-catalyzed ring-opening reactions performed in solution and found to be superior in each case. The solid-phase aziridine opening constituted a key step in the synthesis of the beta-carbolin-1-one mimic of pancratistatin. Methyl 2-indolecarboxylate was found to react on the silica gel surface with N-tosylvinylaziridine in 68% yield. A nine-step synthesis of the pancratistatin mimic has been attained. The additional key transformation in this synthesis involved silica gel-catalyzed opening of an epoxide and hydrolysis of an acetonide. Detailed experimental procedures and full characterization are reported for all new compounds.