Caffeinium Hydrogen Sulfate: A Green Solid Acid Catalyst for Selective One‐Pot Domino Knoevenagel‐Michael Transformations

Abstract

A green, water soluble and efficient solid acid catalyst Caffeinium Hydrogen Sulfate (CHS) is prepared by sulfonation of caffeine and characterized by 1H‐NMR, 13C‐NMR, FTIR spectroscopy, elemental and thermal analysis. The catalytic application of the prepared catalyst for the selective one‐pot domino Knoevenagel‐Michael synthesis of bis‐cyclohexenones and 1,8‐dioxooctahydroxanthenes is investigated. This report demonstrate the selectivity of CHS to synthesise bis‐cyclohexenone and xanthenes at different temperature conditions. The proposed methodology put forward various advantages such as cost effectiveness, excellent yields of the targeted products, clean and mild reaction profile, negligible waste generation, eliminate the use of harmful organic solvents and corrosive reagents, reusability of the catalytic system and afford pure products without any extraction and purification steps.

Advancement in synthetic strategies of bisdimedones: Two decades study

“…An eco-benign and effective approach has been developed for the synthesis of bisdimedone derivatives through the reaction of dimedone and different aldehydes using Caffeinium Hydrogen Sulfate (10 mol%) as a catalyst in the water: ethanol (4:1) medium at 30 C by Agarwal and colleagues [84]. This procedure has several advantages such as high yields of product (80%-94%), mild reaction conditions, avoidance of harmful solvents and reagents, and easy separation of product.…”

Green Lewis Acid Catalysis in Organic Reactions

“…[5,6] Due to their good selectivity, non-corrosive nature, high recyclability, and low toxicity, these catalysts have emerged as cost-effective alternatives for various organic transformations. [7,8] In general, these acid catalysts have good turnover numbers and are easily separated from the reaction medium. Depending on their arrangement and structure, these catalysts differ in nature.…”

A Facile and Green Pathway for One‐Pot Multicomponent Synthesis of Functionalized Spiroxyindoles using Caffeinium Hydrogen Sulfate as a Catalyst.

“…With the advancement of green chemistry solid acid catalysts have been extensively investigated over traditional harsh liquid mineral acids for the synthesis of diverse fine and bulk organic molecules ,. Owing to their significant properties like excellent selectivity, non‐corrosive nature, good recyclability and negligible toxicity these catalysts served as economically suitable options for various organic transformations ,. These acid catalysts generally have high turnover numbers and are easily separable from reaction media .…”

“…Owing to their significant properties like excellent selectivity, non‐corrosive nature, good recyclability and negligible toxicity these catalysts served as economically suitable options for various organic transformations ,. These acid catalysts generally have high turnover numbers and are easily separable from reaction media . Recently, MCR's have become an excellent strategy for the construction of C−C bonds and are extensively utilized for the synthesis of a vast library of functionally diverse organic molecules and drug candidates .…”

“…In continuation of our efforts concerned with the development of green strategies for the preparation of various biologically important heterocyclic compounds, we recently developed a green solid acid catalyst Caffeinium hydrogen sulfate and used it for selective synthesis of biscyclohexenones and xanthenes at different temperature conditions . To extend the catalytic efficiency and applicability of our catalyst, we herein report a step‐economic, efficient and mild strategy for the preparation of spiroxyindoles [spiro(2‐amino‐4H‐pyrans)] via domino Knoevenagel‐Michael‐cyclization reaction of isatin, C−H active acids with malononitrile in the presence of CHS as a green, water soluble and a versatile catalyst.…”