Ir-Catalyzed Asymmetric Allylic Alkylation of Dialkyl Malonates Enabling the Construction of Enantioenriched All-Carbon Quaternary Centers
Farbod A. Moghadam, Elliot F. Hicks, Zachary P. Sercel, Alexander Q. Cusumano, Michael D. Bartberger and Brian M. Stoltz*
*Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E. California Blvd., MC 101-20, Pasadena, California 91125, United States, Email: stoltzcaltech.edu
F. A. Moghadam, E. F. Hicks, Z. P. Sercel, A. Q. Cusumano, M. D. Bartberger, B. M. Stoltz, J. Am. Chem. Soc., 2022, 144, 7983-7987.
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An enantioselective iridium-catalyzed allylic alkylation of malonates with trisubstituted allylic electrophiles at ambient temperature provides all-carbon quaternary stereocenters. The quaternary products can be readily converted to several valuable building blocks such as vicinal quaternary products and β-quaternary acids.
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Iridium-Catalyzed Allylic Alkylation Reactions: General Procedure
In a nitrogen-filled glovebox, a catalyst solution of [Ir(COD)Cl]2 (6.5 mg/mL), ligand (10 mg/mL), and TBD (7 mg/mL) in THF was stirred for 20 min at 25 °C. In separate vials, solutions of (E)-allylic carbonate (0.5 mmol/mL) and of malonate nucleophile (0.5 mmol/mL) were prepared in THF. During that time, the reaction vial was charged with ZnI2 (63.8 mg, 0.2 mmol, 2.0 equiv) and NaHMDS (36.7 mg, 0.2 mmol, 2.0 equiv). 0.2 mL of the nucleophile solution (0.1 mmol, 1.0 equiv) was added to the reaction vial and stirred for 5 min, followed by 0.2 mL of catalyst solution, and finally 0.2 mL of allylic carbonate solution (0.1 mmol, 1.0 equiv). The vial was sealed with a Teflon-lined cap, removed from the glovebox, and stirred at 21 °C for 18 h unless noted otherwise. After 18 h, 3 mL 0.5 M HCl was added to the crude reaction mixture, which was then extracted three times with ethyl acetate, dried over MgSO4, concentrated, and purified by silica gel flash chromatography to provide the desired alkylation product.