A Green, Novel and Efficient Protocol for the Preparation of Diverse 4H-Pyrans: The First Report on the Catalytic Activity of Water Extract ofElaeagnus angustifoliaLeaves in Organic Reactions

Zn (II)‐Schiff base covalently anchored to CaO@SiO2: A hybrid nanocatalyst for green synthesis of 4H‐pyrans

“…The plausible mechanism for the synthesis of dihydropyrano[ c ]chromene derivatives 6 in the presence of CaO@SiO 2 ‐NH 2 ‐Sal‐Zn is similar to that reported in the literature. [ 29 ] As illustrated in Scheme 3, a Knoevenagel condensation between malononitrile and catalyst‐activated aldehyde generates arylidene malononitrile (intermediate I) . The nucleophilic attack of 4‐hydroxycoumarin on intermediate I, via Michael addition, affords the intermediate II .…”

Waste-to-wealth transition: application of natural waste materials as sustainable catalysts in multicomponent reactions

“…Dried powdered leaves of Elaeagnus angustifolia ( E. Angustifolia ) were extracted and used in the synthesis of 3,4-dihydropyrano[ c ]chromenes 82 or 1,4-dihydropyrano[2,3- c ]pyrazoles 17 by the treatment of aldehydes 1 , malononitrile 10 , 4-hydroxycoumarin 81 , or 3-methyl-1-phenyl-2-pyrazoline-5-one 16 , respectively (Scheme 45). 93…”

“…92 BFE has been used as a catalyst in the Knoevenagel reaction between malononitrile 10 and 2-hydroxybenzaldehyde 1. The plausible mechanism entails the formation of intermediate 77 93 The plausible mechanism suggests the formation of intermediate 83 via Knoevenagel condensation between aldehydes 1 and malononitrile 10. Then, intermediate 84 was obtained via the Michael addition of compound 81 to intermediate 83.…”

4‐Hydroxycoumarin: A Versatile Substrate for Transition‐metal‐free Multicomponent Synthesis of Bioactive Heterocycles

“…In all the cases, good to high yields was observed (Table 1). [104][105][106][107][108][109][110][111][112] Another type of pyran fused coumarin derivatives 110 via an organocatalytic three-component reaction of 4-hydroxycoumarin 1, aldehydes 31, and 3-bromo-4-hydroxycoumarin 109 has been synthesized in 2013 by Ahadi et al, (Scheme 44). [113] In the presence of 30 mol% of DBU (1,8-Diazabicyclo[5.4.0]undec-7-ene) as the organocatalyst; various aryl, heteroaryl, and alkylsubstituted aldehydes were found to smoothly undergo the reaction to deliver the desired pyranocoumarin hybrids 110 in 60-96% yield.…”