Example Compound I-51 was synthesized through the following steps: ##STR88## 1.61 g (40.3 m mole) of sodium hydroxide was dissolved in 10.7 ml of water, followed by cooling at -7.5--5° C. on ice-common salt bath. To the solution, 0.66 ml (25.6 m mole) of bromic acid was added dropwise under stirring, followed by cooling at ca. -5° C. To the mixture solution, 4.2 ml of dioxane was added dropwise under stirring to prepare sodium hypobromite solution. In a 200 ml three-neck flask, 1.50 g (3.81 m mole) of (4-decyloxyphenyl)-5-acetylbenzooxazole synthesized in Example 3, 30 ml of dioxane and 2.5 ml of water were placed, followed by keeping inner temperature below 5° C. under cooling with ice and stirring. To the mixture solution, the above-mentioned sodium hypobromite solution was added dropwise, and the reaction temperature was raised up to 45° C. and maintained for 90 minutes. After the reaction, the reaction mixture was poured into 150 ml of water. To the resultant reaction mixture, 3.2 ml of chloric acid was added to show pH=1 to precipitate a crystal. The crystal was filtered and washed with water, followed by recrystallizing from a mixture solvent of acetone-methanol to obtain 1.13 g of 2-(4-decyloxyphenyl)-5-carboxybenzooxazole (Yield: 75.0%).
