An overview of recent advances in the catalytic synthesis of substituted pyrans

Abstract

Substituted pyrans (4H‐Chromenes) are the most significant structural scaffolds in synthetic and medicinal chemistry. They are found in an array of natural products, medicines, and phytochemical compounds, bearing an explicit of pharmacological activities. The structural importance of substituted pyrans has elicited a huge upsurge in the field of synthesis and biology. Different synthetic approaches of 4H‐chromene scaffolds have been discussed systematically to emphasize their significance in the scientific world. The present article summarizes the different synthetic strategies of substituted pyran derivatives via acid‐base catalysis, ionic liquids, nanomaterials, deep eutectic solvents, bio‐based, visible light, metal catalyzed, and so forth developed in the last decade. Moreover, this article will definitely contribute to the scientific world for developing synthetically and biologically important pyran analogs.

Oxygen vacancy enhanced catalytic activity in a Pt nanoparticle decorated GO–CexOycatalyst for the efficient synthesis of pyran based derivatives

“…This electronic interaction could also signify that disorder occurred in the structures after nanoparticle decoration. 60 Oxygen vacancies in metal oxides are regarded as the most active sites which increases the ability to adsorb reactants molecules on their surface. 61 Oxygen vacancies normally change the periodic arrangement of crystals as well as the electronic environment around those vacancies.…”

“…This could be due to the electron withdrawing nature of the NO 2 group which activates the aldehyde ring. [86][87][88] To confirm the heterogeneity of the prepared catalyst, a hot filtration test was done. A hot filtration test was performed by taking aromatic benzaldehyde (1 mmol), malono nitrile (1 mmol) and ethyl acetoacetate (1 mmol) followed by addition of the catalyst.…”

“…This electronic interaction could also signify that disorder occurred in the structures after nanoparticle decoration. 60…”

Advancements in the Preparation of 4H‐Chromenes: An Overview

“…Generally, these established methods can be classified into three categories, namely the nucleophilic functionalization of 2 H ‐chromene derivatives like 1‐benzopyrylium ion or 2‐iminochromene, the 4 H ‐chromene ring formation involved cycloaddition or cyclization reactions, and miscellaneous reactions. Although base‐catalyzed tandem reactions of salicylaldehydes or salicyclic imines with α,β‐unsaturated compounds, [3] and enantioselective organocatalyzed, [4a] ionic liquid‐assisted [4b] and recently published MCRs (multicomponent reactions) based on aldehydes [4c] for the synthesis of 2‐amino‐4 H ‐chromenes have been published to introduce protocols for the synthesis of 4 H ‐chromenes, these reviews covered only small parts based on transformations on salicylaldehydes or salicyclic imines. In addition, some recently developed catalytic asymmetric methods are rarely included.…”

Tandem phospha-Michael addition/cyclization/dehydration of 2-hydroxychalcones with H-phosphine oxides for the synthesis of 4-phosphorylated 4H-chromenes

“…The importance of 4 H -chromenes in synthetic chemistry-included fields attracted a number of chemists to develop new and improved methods for their synthesis. 2,4–8 Among these reported protocols, the tandem Michael addition/cyclization/dehydration of 2-hydroxychalcones turned out to be a promising strategy for the preparation of 4-functionalized 4 H -chromenes (Scheme 1, eqn (1)). 7 Under the catalysis of a Brønsted or Lewis acid, 2-hydroxychalcones undergo intermolecular Michael addition with nucleophiles to afford the Michael addition adduct, which can further undergo intramolecular cyclization of the hydroxy group with a ketone moiety to give a hemiketal intermediate under suitable conditions.…”