Yield:1522117-83-4 31%

Reaction Conditions:

with caesium carbonate

Steps:

General Methods

3',6'-bis((4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyl)oxy)-3H-spiro[isobenzofuran-1,9'-xanthen]-3-one (FBBBE):
Fluorescein (2.45 g, 7.3 mmol) was dissolved in 50 mL MeCN.
To this was added Cs₂CO₃ (7.21 g, 22.1 mmol) followed by 4-bromomethylphenyl boronic acid pinacol ester (6.57 g, 22.1 mmol).
The reaction was held at reflux for 18 h under nitrogen.
The mixture was then cooled to room temperature, filtered, and rinsed with CH₂Cl₂.
The solvent was removed and the product was purified by silica gel chromatography, eluting with 20-30% EtOAc in hexanes to afford FBBBE in 31% yield (1.72 g, 2.3 mmol).
¹H NMR (400 MHz, CDCl₃): δ=8.01 (d, J=7.6 Hz, 1H), 7.85 (d, J=7.6 Hz, 4H), 7.62 (m, 2H), 7.43 (d, J=7.6 Hz, 4H), 7.15 (d, J=7.6 Hz, 1H), 6.82-6.81 (m, 2H), 6.70-6.67 (m, 4H), 5.11 (s, 4H), 1.35 (s, 24H).
¹³C NMR (100 MHz, CDCl₃): δ=169.7, 160.5, 153.4, 152.6, 139.6, 135.3, 135.2, 129.9, 129.4, 127.0, 126.7, 125.2, 124.2, 112.5, 111.7, 102.1, 84.1, 83.4, 70.4, 25.1. ESI-MS (+): m/z 765.44 [M+H]⁺, 787.37 [M+Na]⁺.

References:

US2014/248218,2014,A1 Location in patent:Page/Page column