3.1.2. Synthesis of Compounds **6a–d**

Syntheses were carried out from resorcinol **4** and appropriate β-keto esters (**5a–d**) in accordance with [46]. Conc. H2SO<sup>4</sup> (2 mL, 37.6 mmol) was added dropwise to cooled (0–5 ◦C) solution of resorcinol **4** (2.3 g, 21 mmol) and appropriate β-keto esters (**5a–d**) (21 mmol) in dry ethanol (5 mL) with vigorously stirring. The reaction mixture was stirred at room temperature for 15 min, and then heated at 60 ◦C until it congealed. It was then left overnight at room temperature. Finally, it was poured into ice water (50 mL). The resulting solid was filtered off and crystallized from ethanol–water. The yields of **6a, 6b, 6c,** and **6d** were 81%, 79%, 73%, and 63% respectively.
