The general procedure for the synthesis of 9,9-dimethylfluorene-2,7-diboronic acid from triisopropyl borate and 2,7-dibromo-9,9-dimethylfluorene was as follows: 2,7-dibromo-9,9-dimethylfluorene (14.8 g, 42.4 mmol) was placed in a three-necked flask, 100 mL of tetrahydrofuran (THF) was added, and the reaction was cooled under nitrogen protection to -78 °C and maintained for 30 min. Subsequently, 21 mL of n-butyllithium (2.5 M) solution was added slowly and reacted for 1 hour. Next, triisopropyl borate (14 g) was added and the reaction was continued at low temperature for 1 hour, after which it was gradually warmed to room temperature. After completion of the reaction, the pH was adjusted to 4-5 by adding 2 M hydrochloric acid to the reaction mixture. the aqueous layer was extracted with ethyl acetate, the organic layers were combined and dried over anhydrous sodium sulfate, and concentrated under reduced pressure to give Intermediate A1 (9.5 g, 80% yield).
