Copper-Catalyzed Cross- and Carbonylative Coupling Reactions of ­Alkynyliodonium Salts with Organoboronic Acids and Organostannanes

Abstract

Copper-catalyzed cross- and carbonylative coupling ­reactions have been achieved in the reaction of a variety of alkynyl­iodonium salts with arylboronic acids and organostannanes under the mild reaction conditions in high yield. Our investigation shows that the alkynylidonium tetrafluoroborates are more efficient than those of triflates and tosylates.

copper catalyst - iodonium salt - organoboronic acid - coupling - organostannane

References

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Typical Procedure for the Synthesis of 3a.
A flame-dried flask containing CuI (7.6 mg, 0.04 mmol), K₂CO₃ (133 mg, 0.96 mmol), and PhB(OH)₂ (2a, 107 mg, 0.88 mmol) was evacuated and carefully purged with N₂ and then charged with freshly purified mixed solvent (4 mL, DME-DMF-H₂O, 3:1:1). After stirring at 20 °C for 10 min, 1a (297 mg, 0.8 mmol) in a mixed solvent (2 mL) was added over 10 min to the resulting mixture. After stirring at 20 °C for 1 h, the resulting mixture was quenched by addition of a 10% aq NH₄Cl (5 mL) solution, and then extracted with Et₂O (3 ×). The combined organics were washed with H₂O (1 ×) and brine (1 ×). The organic layer was dried over anhyd MgSO₄, filtered, and concentrated under reduced pressure. The crude product was purified by flash column chromatography (EtOAc-hexane, 1:15) to give 3a (115 mg, 0.727 mmol, 91%) as a colorless liquid.

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Typical Procedure for the Synthesis of 5a.
A flame-dried Schlenk flask containing CuI (7.6 mg, 0.04 mmol), K₂CO₃ (133 mg, 0.96 mmol), and PhB(OH)₂ (2a, 107 mg, 0.88 mmol) was evacuated and carefully purged with CO three times using a balloon and then charged with a mixed solvent (freshly purified and degassed, 4 mL, DME-H₂O, 4:1). After stirring at 20 °C for 10 min, 1a (297 mg, 0.8 mmol) in a mixed solvent (2 mL) was added over 10 min. Reaction was allowed to proceed for an additional 2 h. After removal of CO balloon carefully, the resulting mixture was quenched by addition of a 10% aq NH₄Cl (5 mL) solution, and then extracted with Et₂O (3 ×). The combined organics were washed with H₂O (1 ×) and brine (1 ×). The organic layer was dried over anhyd MgSO₄, filtered, and concentrated under reduced pressure. The crude product was purified by flash column chromatography (EtOAc-hexane, 1:10) to give 5a (124 mg, 0.67 mmol, 83%) as a colorless liquid.

<A NAME="RU23005ST-16">16</A> General discussion for the mechanistic aspects of coupling reactions, see: Echavarren AM. Cardenas DJ. In Metal-Catalyzed Cross-Coupling Reactions   2nd ed., Vol. 1:  de Meijere A. Diederich F. Wiley-VCH; Weinheim: 2004.  p.1-40