Nano-ZnO Catalyzed Multicomponent One-Pot Synthesis of Novel Spiro(indoline-pyranodioxine) Derivatives

Table 2

Comparison of catalytic activity of ZnO nanoparticles in the synthesis of compounds 4a and 5a by conventional heating (Δ) and microwave irradiation method (MW).

Entry	Conditions	Type of catalysts	Reaction time; (hrs/min.)	Yield; (%)
4a	MW; MW; Δ; Δ	No catalyst; ZnO; No catalyst; ZnO	35 min.; 9 min.; 25 hrs; 10 hrs	traces; 87; traces; 62
5a	MW; MW; Δ; Δ	No catalyst; ZnO; No catalyst; ZnO	28 min.; 10 min.; 25 hrs; 10 hrs	traces; 84; traces; 65

Amount of Reactants: Meldrum acid (1.0 mmol), isatin (1.0 mmol), and malononitrile/ethylcyanoacetate
(1.0 mmol); reaction under microwave irradiation was carried out at 420 watts.