Highly economic and waste valorization strategy for multicomponent and Knoevenagel reactions using water extract of tamarind seed ash

WEPA: a reusable waste biomass-derived catalyst for external oxidant/metal-free quinoxaline synthesisviatandem condensation–cyclization–oxidation of α-hydroxy ketones

“…1,3 In connection with this, the ashes of waste biomass and their water extracts have been reported to be wonderful catalysts, reagents, and (or) aqueous media for conducting organic reactions. 1,4 Solid organic biomass-derived ashes have been substantiated to be outstanding heterogeneous catalysts in biodiesel production via the transesterification process of edible/non-edible/microorganism-derived oils and methanol/ethanol. 1,5 Recently, aqueous extracts of waste biomass ashes were used for conducting several state-of-the-art chemical transformations, including C–C coupling reactions, multicomponent processes to access heterocycles, decarboxylative transformations of organic acids, dehydrative synthesis of multiple bonds and halogenations.…”

“…1,5 Recently, aqueous extracts of waste biomass ashes were used for conducting several state-of-the-art chemical transformations, including C–C coupling reactions, multicomponent processes to access heterocycles, decarboxylative transformations of organic acids, dehydrative synthesis of multiple bonds and halogenations. 1,4 These reactions are highly efficient, economical, sustainable, practical, and, most importantly, biomimetic, and are excellent alternatives to non-renewable resource-based catalysts and other materials.…”

Catalyst-free mechanochemistry as a versatile tool in synthetic chemistry: a review

“…Knoevenagel condensation is a versatile chemical transformation used in synthetic chemistry to create a vast range of organic compounds with multiple functional groups that can be used as substrates in many synthetic protocols. 25 Hence, the development of new synthetic methodologies that can be operated under catalyst, solvent-free conditions would have great impact in organic synthesis. 25 In this regard, Kaupp et al developed a catalyst, solvent-free mechanochemical (ball milling) procedure for the Knoevenagel reaction of stoichiometric quantities of barbituric acid/its derivative ( 14 ) or Meldrum's acid ( 15 ) with solid aldehydes ( 13 ) to access polyfunctionalized olefins 16 and 17 (Scheme 8).…”

“…25 Hence, the development of new synthetic methodologies that can be operated under catalyst, solvent-free conditions would have great impact in organic synthesis. 25 In this regard, Kaupp et al developed a catalyst, solvent-free mechanochemical (ball milling) procedure for the Knoevenagel reaction of stoichiometric quantities of barbituric acid/its derivative ( 14 ) or Meldrum's acid ( 15 ) with solid aldehydes ( 13 ) to access polyfunctionalized olefins 16 and 17 (Scheme 8). 26 The reaction of dimedone ( 18 ) with solid aldehyde ( 13 ) produced the bis-enol derivative 19 (Scheme 9), involving Knoevenagel condensation of 13 and 18 followed by a nucleophilic addition (Michael addition) of 18 with the resultant Knoevenagel condensation product.…”

“…In current organic synthesis, one-pot, multicomponent reactions have shown great advantages like pot-economy, step-economy and the avoidance of the separation of intermediate substances and purification steps, thereby saving time, energy and chemicals; hence these are considered to be green techniques in the hands of synthetic chemists. Although several green/sustainable catalysts have been invented for multicomponent reactions, 1 c ,25 the development of new multicomponent protocols under catalyst-free, energy-efficient conditions is a highly anticipated task for the construction of a variety of organic compounds. 42…”