In this paper, calcium iodate nanoparticles were first synthesized by the modified reaction of Ca(NO 3 ) 2 and KIO 3 in an aqueous medium under ultrasonic irradiation. The structure of nanocatalyst was then characterized by FT-IR, FESEM, EDX, XRD, and BET techniques. Afterward, the fabricated Ca(IO 3 ) 2 was applied as a nanocatalyst in the facile synthesis of heterocycles including quinoxalines, 5,6-dicyano pyrazines, and pyrido[2,3-b]pyrazines. For this purpose, the feasibility of the reaction in the presence of different catalyst amounts, solvents, and temperatures was first investigated. Next, the target compounds were obtained by the condensation reaction of aryl-1,2-diamines or 2,3-diaminomaleonitrile with 1,2-diketones in the presence of a catalytic amount of Ca(IO 3 ) 2 in ethanol or acetic acid solvents at ambient temperature in good to excellent yields. One of the salient advantages of this work is the synthesis of calcium iodate nanoparticles by chemical precipitation method and its application as a heterogeneous nanocatalyst for the first time in the synthesis of organic compounds. The other important benefits of this process are the use of an inexpensive, safe, stable and recyclable catalyst, high product yields, short reaction times, and easy isolation of the product in pure form. Supplementary Information The online version contains supplementary material available at 10.1007/s11164-022-04914-3.

In this paper, calcium iodate salt nanoparticles were first synthesized by the modified reaction of Ca(NO3)2 and KIO3 in aqueous media and under ultrasonic irradiation. The structure of nano-catalyst was then identified by FT-IR, FESEM, EDX, XRD, and BET techniques. Afterward, the fabricated Ca(IO3)2 was applied as a nanocatalyst in the facile synthesis of heterocycles including quinoxalines, 5,6-dicyano pyrazines, and pyrido[2,3-b]pyrazines. For this purpose, the feasibility of the reaction in the presence of different catalyst amounts, solvents and temperatures was first investigated. Next, the target compounds were obtained by the condensation reaction of aryl-1,2-diamines or 2,3-diaminomaleonitrile with 1,2-diketones in the presence of catalytic amount of Ca(IO3)2 in ethanol or acetic acid solvents at ambient temperature in good to excellent yields. One of the salient advantages of this work is the synthesis of calcium iodate nanoparticles by chemical precipitation method and its application as a heterogeneous nanocatalyst for the first time in the synthesis of organic compounds. The other important benefits of this process are the use of an inexpensive, safe, stable and recyclable catalyst, high yields, short reaction times, easy isolation of the product in pure form.