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

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. An eco‐friendly, high yielding and efficient protocol for domino Knoevenagel‐Michael synthesis of bis‐cyclohexenones and 1,8‐dioxooctahydroxanthenes using Caffeinium Hydrogen Sulfate (CHS) as a green solid acid catalyst at different temperature range is reported. The advantages of proposed methodology include high selectivity, practicability, cost effectiveness, broad substrate scope, high yields of desired products, operational simplicity, and reusability of the catalytic system and isolation of products without using extraction and chromatographic techniques. [ABSTRACT FROM AUTHOR]