Fruit juice of Citrus limon (lemon juice) has been utilized as a natural and renewable catalyst for the green and environmentally friendly preparation of 3,4-disubstituted isoxazol-5(4H)-one derivatives and 6-amino-1,4-dihydropyrano[2,3-c]-pyrazole-5-carbonitrile derivatives in hydroalcoholic media at 90 °C. A one-pot three-component reaction of β-oxoesters with hydroxylamine hydrochloride and various aromatic aldehydes afforded 3,4-disubstituted isoxazole-5(4H)-one derivatives in excellent yields. The rate constant (K = 6.12 × 10−2 min−1 at 25 °C) for the formation of isoxazole derivative (1g) was also calculated. Similarly, a four-component reaction of ethyl acetoacetate, hydrazine hydrate, aryl aldehydes, and malononitrile gives pyrano[2,3-c]-pyrazole derivatives in very good yields. After completion of the reaction, the products were isolated by simple filtration. A simple work-up process, high product yields, short reaction times, and the use of an inexpensive and biodegradable catalyst are the advanced rewards of the present protocol.

Fruit juice of Citrus limon as a biodegradable and reusable catalyst for facile, eco-friendly and green synthesis of 3,4-disubstituted isoxazol-5(4H)-ones and dihydropyrano[2,3-c]-pyrazole derivatives

A green and efficient approach for synthesis of some new 4H-pyran derivatives is reported, catalyzed by green recyclable poly(4-vinylpyridine)-supported copper iodide nanoparticle catalyst in water. This procedure has many advantages such as operational simplicity, short reaction time, clean procedure, and high product yield.

Aqua-mediated multicomponent synthesis of various 4H-pyran derivatives catalyzed by poly(4-vinylpyridine)-supported copper iodide nanoparticle catalyst

The widespread biological properties of dihydropyrano[3,2-c]chromenes, 2-amino-4-aryl-4H-benzo[h]chromenes, and 3-amino-1-aryl-1H-benzo[f]chromenes have led to increasing efforts for the development of tremendously effective synthetic protocols aimed at their synthesis. In this contribution, sodium malonate was employed for the first time as an efficient catalyst for the one-pot, three-component tandem Knoevenagel–cyclocondensation reaction of 4-hydroxycoumarin (or naphthols), malononitrile/ethyl cyanoacetate, and various aldehydes. These compounds underwent Knoevenagel–Michael–Thorpe–Ziegler cyclization upon heating at 70 °C in water to give the respective medicinally relevant dihydropyrano[3,2-c]chromenes and amino-benzochromenes. The method is versatile and amenable to many substrates as it requires no specialized devices such as microwave, ultrasound and ball-milling. Also, the salient features of this high-yielding protocol are green reaction conditions, the use of commercially available catalyst, easy purification processes by a simple filtration, and relatively shorter reaction times.

Aqua one-pot, three-component synthesis of dihydropyrano[3,2-c]chromenes and amino-benzochromenes catalyzed by sodium malonate

The efficacy of thiourea dioxide (TUD) as an efficient, inexpensive, and readily accessible organocatalyst for the synthesis of 1,4-dihydropyrano[2,3-c]-pyrazole-5-carbonitrile derivatives via a four-component reaction of ethyl acetoacetate, hydrazine hydrate, aryl aldehydes, and malononitrile is described. Upon completion of the reaction, the product was isolated by filtration, and the remaining aqueous TUD solution could be reused several times with consistent catalytic activity. High yields, simple work-up process, avoiding the use of organic solvents, short reaction time, and recyclable catalyst are the superior advantages of the present protocol.

A green and one-pot synthesis of a library of 1,4-dihydropyrano[2,3- c ]-pyrazole-5-carbonitrile derivatives using thiourea dioxide (TUD) as an efficient and reusable organocatalyst

Preparation, characterization and catalytic application of molybdenum Schiff‐base complex immobilized on silica‐coated Fe3O4 as a reusable catalyst for the synthesis of pyranopyrazole derivatives

Poly(4-vinylpyridine) is used as a green, commercially available and recyclable basic catalyst for the multicomponent synthesis of benzopyrans and dihydropyranochromenes by one-pot condensation of aromatic aldehydes, 3-methyl-1-phenyl-2-pyrazolin-5-one, and malononitrile or 4-hydroxycoumarin in ethanol at reflux temperature. This procedure provides several advantages such as mild reaction conditions, short reaction times, simple work-up and high yields.

Efficient synthesis of benzopyrans and dihydropyranochromenes catalyzed by poly(4-vinylpyridine) as a green and commercially available basic catalyst.

A green and highly efficient procedure is reported for the one pot synthesis of tetrahydrobenzo(b)pyran derivatives catalyzed by poly(4-vinylpyridine) as a heterogenous and recyclable basic catalyst under solvent-free conditions. This procedure provides many advantages such as recyclability of the catalyst, simple work-up, clean procedure, short reaction times and high yields of the products.

Efficient synthesis of tetrahydrobenzo(b)pyran derivatives catalyzed by poly(4- vinylpyridine) as a green and heterogeneous recyclable basic catalyst under solvent-free condtions

Fatemeh Akbari Balout-Bangan

Papers

Efficient synthesis of benzopyrans and dihydropyranochromenes catalyzed by poly(4-vinylpyridine) as a green and commercially available basic catalyst.

Efficient synthesis of tetrahydrobenzo(b)pyran derivatives catalyzed by poly(4- vinylpyridine) as a green and heterogeneous recyclable basic catalyst under solvent-free condtions