Preparation of Magnesium Enolates of α-Keto Esters and Synthetic Applications

Abstract

The reaction between α-chloroglycidic esters 1 and magnesium iodide in the presence of an excess of active magnesium led to magnesium α-ketoester enolates 3. Some synthetic applications of these new reagents are reported.

Key words

pyruvic ester - α-keto esters - magnesium enolate - α-chloroglycidic esters - β-iodo-α-ketoesters

References

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1

Present address: Laboratoire de Chimie Biomoléculaire, UMR CNRS - UM II - Mayoly Spindler 5032 - ERT 5, Université Montpellier II, ENSCM, 8 Rue de l"Ecole Normale, 34296 Montpellier, France.

9

Experimental Procedure: In a typical experiment to obtain 5d, Mg (powder 325 mesh, 20.3 mmol) was poured onto anhyd Et₂O (65 mL). Iodine (10.15 mmol) was added onto the mixture. After stirring at 35 °C during 3 h in the absence of light, the mixture MgI₂-activated Mg was allowed to warm to r.t. and was added dropwise, at -60 °C under stirring, to the α-chloroglycidic ester 1 (10.15 mmol) at the concentration of 0.05 M in Et₂O-toluene 4:1. [10] The mixture was allowed to warm up to -30 °C. After stirring during 120 min, HMPA (40.60 mmol) and Et₃N (30.15 mmol) were added before adding a solution of CH₃OCH₂Cl (20.30 mmol) in Et₂O (10 mL). The resulting mixture was stirred for 6 h at r.t. and H₂O (15 mL) was added. The mixture was extracted with Et₂O (2 × 15 mL), the combined organic extract was dried with MgSO₄, the solvent was removed under reduced pressure, and the residue purified by silica gel column chromatography to afford 5.
Analytical Data of ( Z )-5d: FTIR (KBr plate): 1721, 1660 cm^-1. ¹H NMR (250 MHz, CDCl₃): δ = 1.26 (d, 3 H, J = 6 Hz), 1.27 (d, 3 H, J = 6 Hz), 1.32, 1.47, 1.66 (3 s, 12 H), 3.47 (s, 3 H), 4.25 (dd, 1 H, J = 7.9 Hz, J = 1.6 Hz), 4.30 (dd, 1 H, J = 4.7 Hz, J = 2.0 Hz), 4.60 (dd, 1 H, J = 2.0 Hz, J = 7.9 Hz), 4.89 (dd, 1 H, J = 1.6 Hz, J = 8.3 Hz), 4.90-5.15 (2 m, 3 H), 5.52 (d, J = 4.7 Hz), 6.27 (d, 1 H, J = 8.3 Hz). ¹³C NMR (62.9 MHz, CDCl₃): δ = 21.4, 24.0, 24.6, 25.6, 57.1, 63.1, 68.7, 70.1, 70.5, 72.5, 96.1, 97.0, 108.3, 109.0, 122.6, 143.9, 162.2. MS (FAB+): m/z = 403 (65) [M + 1].