ZrCl4 is an efficient catalyst in the Pechmann condensation of phenols with ethyl acetoacetate and propynoic acid under solvent free conditions leading to formation of coumarins in very good yields.
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Typical experimental procedure for compounds: A mixture of 4-methoxynaphthol (10 mmol) and ethyl acetoacetate (10 mmol) was stirred at room temperature in the presence of ZrCl4 (10 mol%) for 20 min with a guard tube. After completion of the reaction (TLC), the crude product was subjected to column chromatography to give 6-methoxy-4-methyl-2H-benzo [h] chromene-2-one (5) in 98% yield as colourless crystals, m.p. 134–136°C. 1H NMR (CDCl3, 200 MHz): δ 2.52 (s, 3H, CH3), 4.06 (s, 3H, OCH3), 6.36 (s, 1H), 6.74 (s, 1H, aromatic), 7.58–7.68 (m, 2H, aromatic), 8.20–8.22 (m, 1H, aromatic), 8.52–8.58 (m, 1H, aromatic). Mass (m/z): 240 (M+), 226, 198, 142, 115, 76 and 39. The other compounds were prepared in a similar manner.
