Trityl Chloride as a Novel and Efficient Organic Catalyst For Room Temperature Preparation of Bis(indolyl)methanes under Solvent-Free Conditions in Neutral Media

Green and sustainable approaches for the Friedel-Crafts reaction between aldehydes and indoles

The synthesis of indoles and their derivatives, more specifically bis(indolyl)methanes (BIMs), has been an area of great interest in organic chemistry, since these compounds exhibit a range of interesting biological and pharmacological properties. BIMs are naturally found in cruciferous vegetables and have been shown to be effective antifungal, antibacterial, anti-inflammatory, and even anticancer agents. Traditionally, the synthesis of BIMs has been achieved upon the acidic condensation of an aldehyde with indole, utilizing a variety of protic or Lewis acids. However, due to the increased environmental awareness of our society, the focus has shifted towards the development of greener synthetic technologies, like photocatalysis, organocatalysis, the use of nanocatalysts, microwave irradiation, ball milling, continuous flow, and many more. Thus, in this review, we summarize the medicinal properties of BIMs and the developed BIM synthetic protocols, utilizing the reaction between aldehydes with indoles, while focusing on the more environmentally friendly methods developed over the years.

Multicomponent synthesis of pyrimido[4,5-b] quinolines over a carbocationic catalytic system

Trityl chloride (TrCl) was efficiently used as a neutral catalyst for the multicomponent cyclization reaction of an aldehyde with dimedone and 6-amino-1,3-dimethyluracil for the preparation of pyrimido[4,5-b] quinolines in chloroform under reflux condition.

Simple iodoalkyne-based organocatalysts for the activation of carbonyl compounds

A novel approach for the formation of bisindolylmethane derivatives (BIMs) is described as a proof of concept to evaluate the catalytic capacity of iodoalkynes. The use of these derivatives is reported as an example of simple halogen bond-based organocatalyst. This kind of activation has not been used before for the synthesis of bisindolylmethane derivatives 3. Interestingly, the preparation of 3-(1H-indol-3-yl)-1-phenylbutan-1-one (8) has been also achieved for the first time with an iodoalkyne derivative. We prove the efficiency of this family of new catalysts by developing a simple and easy operational methodology, opening the door to the development of alternative catalysts in the area of halogen bond-based organocatalysts.

Solvent-Free Addition of Indole to Aldehydes: Unexpected Synthesis of Novel 1-[1-(1H-Indol-3-yl) Alkyl]-1H-Indoles and Preliminary Evaluation of Their Cytotoxicity in Hepatocarcinoma Cells

New 1-[1-(1H-indol-3-yl) alkyl]-1H-indoles, surprisingly, have been obtained from the addition of indole to a variety of aldehydes under neat conditions. CaO, present in excess, was fundamental for carrying out the reaction with paraformaldehyde. Under the same reaction conditions, aromatic and heteroaromatic aldehydes afforded only classical bis (indolyl) aryl indoles. In this paper, the role of CaO, together with the regiochemistry and the mechanism of the reaction, are discussed in detail. The effect of some selected 3,3′- and 1,3′-diindolyl methane derivatives on cell proliferation of the hepatoma cell line FaO was also evaluated.

Multicomponent Facile Synthesis of Highly Substituted [1,2,4]Triazolo[1,5-a] Pyrimidines

A simple and convenient method for one-pot synthesis of a series of potentially biologically active [1,2,4]triazolo[1,5- a]pyrimidine-6-carboxamide derivatives has been developed in solvent-free conditions using maltose as a commercially available, cheap and eco-friendly catalyst. The salient features of the present protocol are mild reaction conditions, good to excellent yields, high atom economy, benign environmental conditions, easy isolation of products without column chromatography and clean reaction profiles.

Trityl chloride promoted the synthesis of 3-(2,6-diarylpyridin-4-yl)-1H-indoles and 2,4,6-triarylpyridines by in situ generation of trityl carbocation and anomeric based oxidation in neutral media

An efficient protocol for the synthesis of 2,4,6-triarylpyridines and 3-(2,6-diarylpyridin-4-yl)-1H-indoles by the one-pot pseudo four component condensation reaction of aldehydes with acetophenones and ammonium acetate in the presence of Ph3CCl under neutral and solvent-free conditions has been reported. Mechanistically, it is interesting that trityl chloride by in situ generation of trityl carbocation (Ph3C+) promotes the reaction. In this work, seven products have been reported for the first time.

Solvent-free preparation of amidoalkyl phenols catalyzed by trityl chloride under neutral media

A one-pot, multicomponent condensation reaction of phenols, aromatic aldehydes, and amides in the presence of catalytic amount of trityl chloride as a homogeneous organocatalyst under solvent-free condition to prepare amidoalkyl phenols has been reported. It is interesting that trityl chloride by in situ generation of trityl carbocation with inherent instability catalyzes the reaction.

A new approach for the synthesis of bisindoles through AgOTf as catalyst

A novel approach for the catalyzed formation of bisindolylmethane derivatives (BIMs) is described. This methodology is the unique example where AgOTf has been successfully used for the activation of aldehydes, giving easy access to a broad range of bisindolyl derivatives with excellent results. Moreover, the simplicity and easy operational methodology using a small amount of commercially available AgOTf (1-3 mol %), one of the lowest catalytic charge used in this process to date, makes this procedure an alternative approach for this interesting and appealing reaction.

Synthesis of 3-substituted indoles via reactive alkylideneindolenine intermediates

Elimination of suitable leaving groups from 3-substituted indoles under basic or acidic conditions readily provides alkylideneindolenine intermediates that may react with a large variety of nucleophilic reagents. This article highlights some recent developments of this synthetic approach for the preparation of functionalized indole derivatives.