Synthesis of Aryl Stannanes from Silyl Triflates via Aryne Intermediates

Abstract

Aryl stannanes are easily accessible from o-silylated aryl triflates in the presence of KF and Bu₃SnH. The corresponding arynes are formed in situ, and undergo clean hydrostannation to give a mixture of the regioisomeric aryl stannanes. The whole reaction sequence can also be carried out as a one-pot reaction under microwave irradiation.

Key words

arynes - aryl stannanes - hydrostannation - one-pot reaction - Stille coupling

References and Notes

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15

General procedure for the synthesis of aryl stannanes 2: In a Schlenk flask, silyl triflate 1 (0.33 mmol) was dissolved in THF (3 mL) and hydroquinone (0.033 mmol, 3.6 mg), tributyltin hydride (0.10 mL, 0.39 mmol), 18-crown-6 (174 mg, 0.660 mmol), and KF (37 mg, 0.66 mmol) were added sequentially. The resulting mixture was stirred at 20 ˚C for 2-3 h. The reaction mixture was then diluted with ethyl acetate, filtered through Celite, and concentrated. Column chromatography on silica gel (pentane or hexane with 1 vol% Et₃N) gave aryl stannanes 2 as colorless oils.
One-pot synthesis of phenyl stannane and Stille coupling with benzoyl chloride: In a microwave vial, silyl triflate 1a (100 mg, 0.330 mmol) was dissolved in THF (2.0 mL) and hydroquinone (0.033 mmol, 3.6 mg), tributyltin hydride (0.089 mL, 0.33 mmol), 18-crown-6 (174 mg, 0.660 mmol), and KF (37 mg, 0.66 mmol) were added sequentially. The resulting mixture was subjected to microwave irradiation for 15 min at 100 ˚C (max. 200 W). Separately, in a round-bottom flask, [(allyl)PdCl]₂ (0.0033 mmol, 1.2 mg) and Ph₃P (3.5 mg, 0.013 mmol) were dissolved in THF (2 mL) and stirred at r.t. for 5 min. The resulting solution and benzoyl chloride (70 mg, 0.49 mmol) were added to the crude reaction mixture in the microwave vial, which was subjected to further microwave irradiation at 150 ˚C for 30 min (max. 200 Watt). The reaction mixture was diluted with saturated aq KF (3 mL) and stirred for 30 min. The mixture was extracted with Et₂O and the combined organic layers were dried with NaSO₄, filtered and concentrated under reduced pressure. Purification of the residue by column chromatography on silica gel (hexane-EtOAc, 19:1) afforded benzophenone as a colorless solid (37 mg, 60%).