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

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 degrees C. A one-pot three-component reaction of beta-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 9 10(-2) min(-1) at 25 degrees 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. [GRAPHICS] .