**1. Introduction**

Coumarin (2H-chromen-2-one) derivatives have spawn great interest over the years because of their significant biological importance [1]. They are associated with various biological activities viz. antiviral [2, 3], antibacterial [4, 5], antimicrobial [6], anticoagulant [7], anti-inflammatory [8, 9], anticancer [10, 11], anticonvulsant [12], antioxidant [13], antifungal [14, 15], and anti-HIV [16]. They also possess the properties like inhibition of platelet aggregation [17] and inhibition of steroid 5α-reductase [18]. Besides, they are attracting considerable attention of chemists due to their wide range of applications such as optical brighteners [19], photosensitizers [20], fluorescent and laser dyes [21], and additives [22] in food, perfumes, cosmetics, and pharmaceuticals. The novel compounds are also utilized in drug and pesticidal preparations [23]. Considering these multifarious activities of coumarins, synthetic chemists are actively engaged in developing new and superior methods for the isolation of coumarin derivatives. The most widely used method for their synthesis is Pechmann reaction [24–27], which involves the condensation between phenols and β-keto esters, in the presence of an acid catalyst. This method employs both homogeneous catalysts such as concentrated H2SO4 [24, 25], trifluoroacetic acid (TFA) [28], and Lewis acids (LA) such as AlCl3 [29], ZnCl2 [30], ZrCl4 [31], TiCl4 [32], etc. and heterogeneous catalysts such as cation-exchange resins [33], Nafion resin/ silica composites [34], zeolite H-BEA (H-beta, SiO2/Al2O3 = 14) [35], and other solid acids.
