Cu-Catalyzed Highly Stereoselective Syntheses of (E)-δ-Vinyl-homoallylic Alcohols
Jiaming Liu, Bo Su* and Ming Chen*
*Nankai University, Tianjin, China; Auburn University, Auburn, Alabama 36849, United States, Email: subonankai.edu.cn, mzc0102auburn.edu
J. Liu, B. Su, M. Chen, Org. Lett., 2021, 23, 6035-6040.
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Cu-catalyzed allylation of aldehydes or ketones with α-vinyl allylboronate provides secondary or tertiary δ-vinyl-homoallylic alcohols with high E-selectivities. It is proposed that the reaction operates under the Curtin-Hammett principle via the intermediacy of an α-vinyl allylic copper species.
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General procedure for Cu-catalyzed aldehyde allylation
To a reaction vial containing a Teflon-coated magnetic stirring bar was added CuCl (1 mg, 0.01 mmol, 10 mol %), Xantphos (7 mg, 0.012 mmol, 12 mol %), NaOtBu (14 mg, 0.15 mmol, 1.5 equiv) and THF (0.5 mL) in an argon-filled glove box. The mixture was stirred for 15 min at ambient temperature in the glove box. Then allylboronate (29 mg, 0.15 mmol, 1.5 equiv) was added. After stirring for 5 min, aldehyde (0.10 mmol, 1.0 equiv) was added and the resulting mixture was stirred at ambient temperature in the glove box. After complete consumption of the aldehyde, the reaction vial was removed from the glove box. A solution of 3 N NaOH (1 mL) was added to the reaction mixture followed by slow addition of 30% H2O2 (0.5 mL) at 0 °C. The resulting mixture was stirred vigorously for 3 h. Brine (1 mL) and Et2O (1 mL) were added, the organic layer was separated and the aqueous layer was extracted with Et2O (3 x 1 mL). The combined organic layers were dried over anhydrous magnesium sulfate, filtered, and concentrated under reduced pressure. Purification of the crude product was performed by flash column chromatography (gradient elution with hexane and Et2O) to provide product.