An efficient and green approach for the synthesis of 2,4-dihydropyrano[2,3-<i>c</i>]pyrazole-3-carboxylates using Bi₂O₃/ZrO₂ as a reusable catalyst

Abstract

A novel material of bismuth loaded on zirconia (Bi₂O₃/ZrO₂) is synthesized by simple wet-impregnation method and characterized by several techniques (P-XRD, TEM, SEM, BET, <i>etc.</i>). Bi₂O₃/ZrO₂ proved to be a good catalyst for the four-component, one-pot reaction to produce a new series of 2,4-dihydropyrano[2,3-<i>c</i>]pyrazole-3-carboxylate derivatives with excellent yields (91 to 98%) under mild conditions at RT with short reaction times (≈20 min). The structures of the target molecules were confirmed by ¹H NMR, ¹³C NMR, ¹⁵N NMR, HRMS and FT-IR. The catalyst is easily separable and can be reused for six cycles without ostensible loss of activity. This method is inexpensive, atom-efficient and no chromatographic separations are needed.