Pd-Catalyzed Addition of Organoboronic Acids to Alkynes at Room Temperature

Abstract

Combination of Pd(OAc)₂ with 2-bromo-1,3-bis-[diphenylphosphenomethyl)]benzene (1) or 2-bromo-1,3-bis-[di-tert-butylphosphenomethyl)]benzene (3) catalyzed hydroarylations and hydroalkenylations of various alkynes more efficiently in terms of reaction time and temperature.

Key words

palladium - organoboronic acids - alkynes - catalyst - hydroarylation - hydroalkenylation

References

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8

Preparation of Compound 7; General Procedure
A 10 mL round-bottomed flask was charged with an alkyne 5a-f (0.40 mmol), organo boronic acid 6a-c (0.48 mmol), ligand 1 (3 mol%), Pd(OAc)₂ (3 mol%) and then 1,4-dioxane (1.0 mL) at 0 °C. The reaction mixture was purged with dry argon gas and was treated with HOAc (0.04 mmol) via a 10 µL gastight syringe at 0 °C. The mixture was stirred at 25 °C as described in Table [2] . On completion of the reaction, the mixture was cooled to 0 °C, quenched with H₂O, and then extracted with Et₂O. The organic portion was washed with sat. NaCl solution, dried over anhyd MgSO₄, and concentrated in vacuo. The residue thus obtained was purified by flash chromatography (EtOAc-hexane = 1:10) to give product 7. All the isolated products were characterized by IR, ¹H NMR, ¹³C NMR and HRMS.

9

Preparation of Compounds 9 and 10; General Procedure
A 10 mL round-bottomed flask was charged with an alkyne carboxylate 8a-e, (0.40 mmol), organoboronnic acid 6a-c (0.48 mmol), Pd(OAc)₂ (5 mol%), ligand 3 (5 mol%), NaOAc (2.1 equiv, 0.48 mmol) and 0.95 mL of ethylene dichloride and 0.05 mL of H₂O. The reaction mixture was stirred vigorously until the absence of starting material was observed on TLC. Then the mixture was diluted with Et₂O (10 mL) plus H₂O (5 mL) and extracted twice with Et₂O (2 × 10 mL). The combined organic portion was washed with a sat. brine solution, dried over anhyd MgSO₄, and concentrated in vacuo. Finally, the residue was purified by flash chromatography (EtOAc-hexane = 1:10) to get 9 and/or 10. The product structure was assigned by IR, ¹H NMR, ¹³C NMR and HRMS.