A Convenient Method for the Removal of Tetrabutylammonium Salts from Desilylation Reactions

Abstract

4-Bromophenol (2). A single-necked (24/40 joint) 250 mL round-bottomed flask is equipped with a Teflon-coated magnetic stir bar (3.0 x 1.5 cm, footballshaped). The apparatus is flame-dried under reduced pressure and cooled to 23 °C under an atmosphere of nitrogen. The flask is then equipped with a rubber septum and then placed under positive pressure of nitrogen using a nitrogen inlet. To the flask is then added (4-bromophenol)(tertbutyl)dimethylsilane (1) (4.5 g, 3.8 mL, 16 mmol, 1.0 equiv) (Note 2) via syringe. Then, dry THF (30 mL) (Note 3) is added at 23 °C to the flask via syringe and stirring is started (300 rpm). After one min of stirring, tetrabutylammonium fluoride solution (19 mL, 1.0 M in THF, 19 mmol, 1.2 equiv) (Note 4) is added via syringe dropwise over five min (Figure 1A). The reaction mixture is then allowed to stir (300 rpm) at 23 °C for 30 min (Note 5). Then, the rubber septum is removed, and calcium carbonate (8.2 g, 82 mmol, 5.3 equiv) (Note 6) is added in one portion followed by Dowex 50WX8, 200–400 mesh, ion exchange resin (24 g) (Note 7) in two equal portions using a funnel to assist with the addition. To the reaction mixture is then added methanol (60 mL) (Figure 1B) (Note 8), the rubber septum is Br OTBS i. TBAF, THF, 23 °C