Understanding Halide Counterion Effects in Enantioselective Ruthenium-Catalyzed Carbonyl (α-Aryl)allylation: Alkynes as Latent Allenes and Trifluoroethanol-Enhanced Turnover in The Conversion of Ethanol to Higher Alcohols via Hydrogen Auto-transfer
Eliezer Ortiz, Jonathan Z. Shezaf, Yu-Hsiang Chang, Théo P. Gonçalves, Kuo-Wei Huang* and Michael J. Krische*
*KAUST, Thuwal 23955-6900, Saudi Arabia; Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States, Email: kuowei.huangkaust.edu.sa, mkrischemail.utexas.edu
E. Ortiz, J. Z. Shezaf, Y.-H. Chang, T. P. Gonçalves, K.-W. Huang, M. J. Krische, J. Am. Chem. Soc., 2021, 143, 16709-16717.
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In RuI(CO)(η3-C3H5)(JOSIPHOS) catalyzed anti-diastereo- and enantioselective C-C couplings of primary alcohols with 1-aryl-1-propynes, a non-classical hydrogen bond between iodide and the aldehyde formyl CH bond stabilizes the favored transition state for carbonyl addition. An improved catalytic system provides previously unattainable products of carbonyl anti-(α-aryl)allylation.
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To a dried pressure tube equipped with a magnetic stir bar under an argon atmosphere, charged with ethanol (12 µL, 0.2 mmol, 100 mol%), alkyne (0.3 mmol, 150 mol%), RuI(CO)3(η3-C3H5) (3.2 mg, 0.01 mmol, 5 mol%), ligand (5.5 mg, 0.01 mmol, 5 mol%), trifluoroethanol (57 µL, 0.8 mmol, 400 mol%), was added DME (0.4 mL, 0.5 M). The tube was sealed with a PTFE lined cap and the reaction mixture was allowed to stir for 48 hours at 80 °C. After reaching ambient temperature, the solvent was removed in vacuo and the residue was subjected to flash column chromatography (SiO2) under the noted conditions to furnish the products. The diastereomeric ratios were determined by 1H NMR of crude reaction mixtures and the enantiomeric excesses were determined by HPLC using chiral columns.
T. Liang, K. D. Ngyuen, W. Zhang, M. J. Krische, J. Am. Chem. Soc., 2015, 137, 3161-3164.