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TCI Practical Example: The Z-Selective Horner-Wadsworth-Emmons Reaction Using Ethyl Diphenylphosphonoacetate
We are proud to present the Z-selective Horner-Wadsworth-Emmons reaction of p-tolualdehyde using ethyl diphenylphosphonoacetate (Ando method). Ethyl diphenylphosphonoacetate can be used to easily introduce (Z)-α,β-unsaturated esters.
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Used Chemicals
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Procedure
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Sodium hydride (64 mg, 1.6 mmol, 1.6 eq.) was added to a solution of ethyl diphenylphosphonoacetate (481 mg, 1.5 mmol, 1.5 eq.) in dry THF (5 mL) at -78 °C. The mixture was stirred at same temperature for 30 minutes. Then p-tolualdehyde (120 mg, 1.0 mmol) was added to the reaction mixture at -78 °C and stirred 2 hours at same temperature. After that the reaction mixture was quenched with water (15 mL). The solution was extracted with ethyl acetate (15 mL x 3) and the organic layer was washed with 2 mol/L HCl aq. (10 mL), sat. NaHCO3 aq. (10 mL), and brine (10 mL), dried over sodium sulfate and filtered. The solvent was removed under reduced pressure and the residue was purified by column chromatography (on silica gel, hexane:ethyl acetate = 20:1) to give 1 as a pale yellow oil (157 mg, 83% yield, E:Z = 1 : 3.67).
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Experimenter’s Comments
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The reaction mixture was monitored by UPLC.
The ratio of E-form and Z-form was estimated from 1H-NMR.
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Analytical Data
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Compound 1
1H NMR (400 MHz, CDCl3);
1-Z: δ 7.52 (d, J = 8.4 Hz, 2H), 7.16 (d, J = 8.0 Hz, 2H), 6.90 (d, J = 12.8 Hz, 1H), 5.89 (d, J = 12.8 Hz, 1H), 4.19 (q, J = 7.2 Hz, 2H), 2.36 (s, 3H), 1.26 (t, J = 7.2 Hz, 3H).
1-E: δ 7.62 (d, J = 16 Hz, 2H), 7.43 (d, J = 8.0 Hz, 2H), 7.19 (d, J = 8.0 Hz, 1H), 6.40 (d, J = 16.0 Hz, 1H), 4.26 (q, J = 6.8 Hz, 2H), 2.37 (s, 3H), 1.34 (t, J = 6.8 Hz, 3H).
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Lead Reference
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- Highly Selective Synthesis of Z-Unsaturated Esters by Using New Horner−Emmons Reagents, Ethyl (Diarylphosphono)acetates
