Current Organic Synthesis - Volume 18, Issue 3, 2021

Background: The thiocyanation of indoles is a direct way for carbon-sulfur bond formation to access 3-thiocyanato-indoles. 3-thiocyanato-indoles exhibit potent biological and pharmacological activities and also serve as building blocks to synthesize many biologically active sulfur-containing indole derivatives. Objective: The aim of this review is to highlight different approaches for the thiocyanation of indoles focusing on its scope and mechanism. Conclusion: In this review, we have summarized various methods for the thiocyanation of indoles. Selection of new methods for the preparation of 3-thiocyanato-indoles will be done. The mechanistic aspects and significance of the methods are also briefly discussed.

Heterocyclic compounds containing the quinoline ring play a significant role in organic synthesis and therapeutic chemistry. Polyfunctionalized quinolines have attracted the attention of many research groups, especially those who work on drug discovery and development. These derivatives have been widely explored by the research biochemists and are reported to possess wide biological activities. This review focuses on the recent progress in the synthesis of heterocyclic compounds based-quinoline and their potential biological activities.

Background: This review elaborates the updated synthetic and pharmacological approaches of a known group of dihydropyrimidinones/thiones from the multi-component reaction like Biginelli reaction, which was named Pietro Biginelli in 1891. This review consists of the reaction of an aromatic aldehyde, urea and ethyl acetoacetate leading to dihydropyrimidinone/thione. Currently, the scientific movement to develop economically viable green methods using compounds that are reusable, non-volatile, easily obtained, etc. Objective: This review covers the recent synthesis and pharmacological advancement of dihydropyrimidinones/ thiones moiety, along with covering the structure-activity relationship of the most potent compounds, which may prove to become better, more efficacious and safer agents. Thus, this review may help the researchers in drug designing and development of new Dihydropyrimidinones entities. Conclusion: This review focuses on the wide application of dihydropyrimidinone/thione review reports the design, synthesis and pharmacological activities of nitrogen-sulphur containing dihydropyrimidinone moiety by using multi-component reaction. Dihydropyrimidinones (DHPM) pharmacophore is an important heterocyclic ring in medicinal chemistry. It is derived from multi-component reactions, “Biginelli reaction” and plays a critical role as anticancer, antioxidant, antimicrobial, anti-inflammatory, anti-HIV-1, antimalarial, anti-inflammatory, antihypertensive and anti-tubercular agents. Exhaustive research has led to its vast biological profile, with a wide range of therapeutic application.

Objective: Aminomethylphenol molecules have wider applications in pharmaceuticals, agrochemicals, plant protection and promising functional materials. The development of an efficient and practical method to prepare this class of compound is highly desirable from both environmental and economical points of view. Materials and Methods: In order to establish an effective synthetic method for preparing aminomethylphenol derivatives, the Petasis borono-Mannich reaction of salicylaldehyde, phenylboronic acid and 1,2,3,4- tetrahydroisoquinoline was selected as a model reaction. A variety of reaction conditions are investigated, including solvent and temperature. The generality and limitation of the established method were also evaluated. Results and Discussion: It was found that model reaction can be carried out in cyclopentyl methyl ether at 80 °C under catalyst-free conditions. This protocol, with broad substrate applicability, the reaction of various arylboronic acid, secondary amine and salicylaldehyde proceeded smoothly under optimal reaction conditions to afford various aminomethylphenol derivatives in high yields. A practical, scalable, and high-yielding synthesis of aminomethylphenol derivatives was successfully accomplished. Conclusion: A catalyst-free practical method for the synthesis of minomethylphenol derivatives based on Petasis borono–Mannich (PBM) reaction of various arylboronic acid, secondary amine and salicylaldehyde in cyclopentyl methyl ether has been developed. The salient features of this protocol are avoidance of any additive/catalyst and toxic organic solvents, use of cyclopentyl methyl ether as the reaction medium, clean reaction profiles, easy operation, and high to excellent yield.

Background: A rapid, efficient, and environmentally benign procedure for the synthesis of novel furo [2,3-c]phenazine derivatives has been developed via reactions of 2-hydroxynaphthalene-1,4-dione, arylglyoxals, and indole in the presence of TiO2-SO3H-catalyst (TSAC) as a recyclable heterogeneous catalyst under solventfree conditions using microwave irradiation. Introduction: This study describes a successful approach for the synthesis of 2-(4-bromophenyl)-1-(1H-indol-3- yl) benzo[a]furo[2,3-c] phenazine in the presence of TiO2-SO3H-catalyst using microwave irradiation. Objectives: In this paper, we report an efficient and convenient method for the synthesis of phenazine derivatives from benzo[a]phenazin-5-ol, arylglyoxal derivatives, and indoles in the presence of TiO2-SO3H-catalyst under microwave irradiation. Materials and Methods: All reagents and solvents were purchased from Merck and Aldrich and used without further purification. 1H NMR spectra (DMSO) were recorded on the Gemini-500 MHz spectrophotometer with TMS as an internal standard. Results and Discussion: To investigate the reaction conditions for the synthesis of 2-(4-bromophenyl)-1-(1Hindol- 3-yl) benzo[a]furo [2, 3-c] phenazine derivatives, we performed a reaction between 2-hydroxynaphthalene- 1,4-dione (1 mmol) and aromatic 1,2-diamines (1 mmol) as a model. Conclusion: We demonstrated a green and straightforward procedure for the efficient synthesis of novel benzo[ a]furo[2, 3-c] phenazine derivatives in high yields via a one-pot, four-component domino protocol by using TiO2-SO3H as a mild, effective, non-toxic, and inexpensive solid acid catalyst without the addition of an organic co-solvent.

Aims and Objectives: Benzoxazoles are valuable bicyclic aromatic compounds; the construction of benzoxazoles via C-O cross-coupling reactions has attracted more and more attention. Materials and Methods: The best condition of C-O bond formation from o-haloanilides was carried out, taking Cu(OTf)2 (5 mol%) and vasicine (10 mol%) as the catalysts in EtOH in the presence of K2CO3 (2 eq.) for 12 h at 90°C. Results: A series of 2-substituted benzoxazoles have been prepared in high yields from 2-bromoanilides and 2- iodioanilides under mild conditions. Conclusion: We have developed an efficient Cu-vasicine catalytic system for intramolecular C-O bond formation. This strategy is applicable to the synthesis of a wide variety of 2-substituted benzoxazoles by intramolecular O-arylation of o-haloanilides.