A mixture of 4-(4-phenylbutoxy)bromobenzene (0.50 g, 1.64 mmole), 8-amino-4-oxo-2-(tetrazol-5-yl)-4H-1-benzopyran (0.75 g, 3.28 mmole), bis-(triphenylphospine)palladium (II) chloride (0.135 g, 0.19 mmole) and 1,8-diazabicyclo[5.4.0]undec-7-ene (0.87 g, 5.74 mmole) was stirred in N-methylpyrrolidinone (10 ml) at 100-110° C. under an atmosphere of carbon monoxide at atmospheric pressure for 4.5 hours. The reaction mixture was diluted with water (15 ml) and acidified using concentrated hydrochloric acid (5 ml). The precipitate was filtered, washed with water and methanol and then stirred in concentrated hydrochloric acid (8 ml) to dissolve unreacted 8-amino-4-oxo-2-(tetrazol-5-yl)-4H-1-benzopyran. The undissolved solid was filtered, washed with concentrated hydrochloric (2×1.5 ml), water, then methanol. The damp cake was stirred with sodium acetate (0.15 g, 1.83 mmole) in methanol (10 ml) and the solution filtered. The supernatant liquor was acidified with concentrated hydrochloric acid (0.2 ml), and the product filtered, washed with methanol and dried to give the title compound (422 mg, 53%).
