Enantioselective Rhodium-Catalyzed [2+2+2] Cycloaddition of Pentenyl Isocyanate and 4-Ethynylanisole: Preparation and Use of Taddoi-pyrrolidine Phosphorarnidite

摘要

Taddol-pyrrolidine phosphoramidite. A 250-mL single-necked, round-bottomed flask equipped with an egg-shaped magnetic stir bar (12.7 x 25.4 mm) is flame-dried under vacuum. After cooling to 23 °C, (R,R)-Taddol (2.0 g, 4.29 mmol) (Note 1) is added to the round-bottomed flask, a rubber septum is fitted, the reaction flask is put under an atmosphere of N2, and tetrahydrofuran (75 mL) (Note 2) is added via syringe. To this clear, colorless solution, triethylamine (2.4 mL, 17.2 mmol, 4 equiv) (Note 3) is added via syringe resulting in a clear solution with a slight yellow color. The reaction mixture is cooled to 0 °C with an ice bath and phosphorous trichloride (0.39 mL, 4.5 mmol, 1.05 equiv) (Note 4) is added dropwise over 2 min via syringe resulting in a white suspension. The ice bath is removed, the reaction is allowed to warm to 23 °C and stirred for 1 h.