Chiral Bifunctional Phosphine Ligand-Enabled Cooperative Cu Catalysis: Formation of Chiral α,β-Butenolides via Highly Enantioselective γ-Protonation
Xinpeng Cheng, Tianyou Li, Kaylaa Gutman and Liming Zhang*
*Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, California 93106, United States, Email: zhangchem.ucsb.edu
X. Cheng, T. Li, K. Gutman, L. Zhang, J. Am. Chem. Soc., 2021, 143, 10876-10881.
A Cu(I)-ligand cooperative catalysis enables the synthesis of α,β-butenolides with ≥96% enantiomeric excess from β,γ-butenolides. The chiral biphenyl-2-ylphosphine ligand features a remote tertiary amino group. DFT studies support the cooperation between the metal center and the ligand basic amino group during the initial soft deprotonation and the key asymmetric γ-protonation.
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Synthesis of α,β-butenolides:
To a 2-dram vial with substrate (0.3 mmol) under argon protection, [(S)-L2Cu(MeCN)]+PF6- (13.8 mg, 5 mol %) in 1.2 mL DCM was added and the reaction solution was stirred at room temperature for the indicated time. The solvent was removed, and the residue was purified by flash column chromatography (hexanes/EtOAc = 10/1, 7/1, or 5/1) to afford the desired product.