Samarium Diiodide as an Efficient Catalyst for the Conversion of N-Acyloxazolidinones into Esters

Abstract

The transformation of N-acyloxazolidinones into esters is readily performed using catalytic amounts of samarium diiodide in tetrahydrofuran at room temperature. This method allows the isolation of various esters without racemization in the case of scalemic substrates and the recovery of oxazolidinones in good yields.

Key words

samarium diiodide - catalysis - deprotection - N-acyloxazolidinones - esters

References and Notes

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14

In a typical experiment to THF (5 mL) was added a solution of SmI₂ (0.1 N) in THF (0.1 mmol, 1 mL) and EtOH (10 mmol, 600 µL) followed by a solution of N-dodecanoyl-oxazolidinone (1b, 1 mmol, 269 mg) in THF (2 mL). The reaction mixture turned from blue to light yellow within a few minutes. The reaction was monitored by TLC, which indicated total conversion of the starting product after 2 h. The reaction was hydrolyzed with 1 N HCl, extracted by CH₂Cl₂, and dried over MgSO₄. The crude product was purified by column chromatography on silica gel to afford ethyl dodecanoyl ester [2c, heptane-EtOAc (90:10), 223 mg, 98% yield] and oxazolidinone 3a [CH₂Cl₂-MeOH (90:10), 58 mg, 67%]. For reactions in the presence of acid-sensitive groups, workup was performed with H₂O.
Diethyl 2-(4-Methoxyphenylamino)succinate (2i) ¹H NMR (250 MHz, CDCl₃): δ = 6.81 (d, J = 8.8 Hz, 2 H), 6.69 (d, J = 8.8 Hz, 2 H), 4.35-4.45 (m, 1 H), 4.14-4.38 (m, 4 H), 3.77 (s, 3 H), 2.85 (d, J = 6.3 Hz, 2 H), 1.25-1.31 (m, 6 H) ppm. ¹³C NMR (62.9 MHz, CDCl₃): δ = 172.6, 170.6, 153.1, 140.4, 115.7, 114.8, 61.5, 60.9, 55.6, 55.0, 53.4, 37.6, 14.1 ppm. ESI-HRMS: m/z calcd for [C₁₅H₂₁NO₅ + Na]⁺: 318.1312; found: 318.1323.
Ethyl 3-(2-Methoxyphenylamino)butanoate (2j)
¹H NMR (400 MHz, CDCl₃): δ = 6.85 (t, J = 7.6 Hz, 1 H), 6.75 (d, J = 8.1 Hz, 1 H), 6.27-6.67 (m, 2 H), 4.32 (br s, 1 H), 4.12 (q, J = 7.3 Hz, 2 H), 3.90-3.95 (m, 1 H), 3.81 (s, 3 H), 2.67 (dd, J ₁ = 5.1 Hz, J ₂ = 14.9 Hz, 1 H), 2.36 (dd, 1 H, J ₁ = 7.6 Hz, J ₂ = 14.9 Hz, 1 H), 1.28 (d, J = 6.3 Hz, 3 H), 1.23 (t, J = 7.3 Hz, 3 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 171.8, 146.9, 136.6, 121.3, 116.5, 110.4, 109.6, 60.4, 55.4, 45.5, 41.3, 20.7, 14.2 ppm. ESI-HRMS: m/z calcd for [C₁₃H₁₉NO₃ + Na]⁺: 260.1257; found: 260.1254.
Ethyl 3-(4-Methoxyphenylamino)-2-methylpropanoate (2k) ¹H NMR (250 MHz, CDCl₃): δ = 6.76 (d, J = 8.8 Hz, 2 H), 6.55 (d, J = 8.8 Hz, 2 H), 4.10 (q, J = 6.9 Hz, 2 H), 3.72 (s, 3 H), 3.35 (dd, J ₁ = 8.3 Hz, J ₂ = 12.8 Hz, 1 H), 3.14 (dd, J ₁ = 5.3 Hz, J ₂ = 12.8 Hz, 1 H), 2.72-2.80 (m, 1 H), 1.18-1.30 (m, 6 H) ppm. ¹³C NMR (62.9 MHz, CDCl₃): δ = 175.4, 152.3, 141.9, 114.9, 114.4, 60.5, 55.8, 48.1, 39.3, 15.0, 14.2 ppm. ESI-HRMS: m/z calcd for [C₁₃H₁₉NO₃ + Na]⁺: 260.1257; found: 260.1252.