A Simplified Procedure for the Efficient Conversion of Aromatic Aldehydes into Esters

Abstract

A mild, efficient conversion of aromatic aldehydes into their corresponding methyl (or ethyl) esters was achieved by treatment with manganese dioxide and sodium cyanide in methanol (or ethanol) but without the use of acetic acid.

Notes

Unpublished results; aldehyde 1a was synthesized in nine steps from indoline.

Methyl ester 1b: a pale brown oily liquid; R_f 0.38 (EtOAc-hexanes, 1:2); ¹H NMR (CDCl₃) δ 9.16 (s, broad, 1 H, NH), 8.06 (d, J = 7.7 Hz, 1 H), 7.95 (d, J = 3.0 Hz, 1 H), 7.20 (t, J = 7.2-8.1 Hz, 1 H), 7.06 (d, J = 7.2 Hz, 1 H), 5.50 (t, 1 H), 3.92 (s, 3 H), 3.65 (d, J = 7.1 Hz, 2 H), 3.62 (s, 3 H), 2.54 (t, J = 6.1-6.5 Hz, 2 H), 2.42 (t, J = 6.1-6.6 Hz, 2 H), 1.84 (s, 3 H); ¹³C NMR (CDCl₃) δ 174.75, 166.56, 136.26, 135.99, 132.06, 126.67, 124.87, 123.49, 123.23, 122.54, 119.93, 108.91, 52.20, 51.57, 35.09, 32.64, 31.23, 16.58; IR (neat) 3333, 2952, 1733, 1705, 1535, 1442, 1245, 1193, 1159 cm⁻¹. Anal. calcd for C₁₀H₂₁NO₄: C, 68.55; H, 6.71; N, 4.44. Found: C, 68.32; H, 6.70; N, 4.38.

Methyl benzoate: ¹H NMR (CDCl₃) δ 8.02 (d, J = 7.1 Hz, 2 H), 7.52 (t, J = 7.5 Hz, 1 H), 7.42-7.37 (t, J = 7.2-7.7 Hz, 2 H), 3.88 (s, 3 H); Ethyl benzoate: ¹H NMR (CDCl₃) δ 8.04 (d, J = 7.2 Hz, 2 H), 7.55 (t, J = 7.4 Hz, 1 H), 7.44-7.39 (t, J = 7.3-7.8 Hz, 2 H), 4.39 (q, J = 7.2 Hz, 2 H), 1.38 (t, J = 7.2 Hz, 3 H); Methyl m-anisate: ¹H NMR (CDCl₃) δ 7.60-7.57 (dt, J = 1.0-1.4, 7.5 Hz, 1 H), 7.51 (dd, J = 1.3-1.4, 2.6 Hz, 1 H), 7.28 (t, J = 7.0-7.9 Hz, 1 H), 7.06-7.02 (ddd, J = 1.0, 2.7, 8.3 Hz, 1 H), 3.86 (s, 3 H), 3.78 (s, 3 H); Ethyl m-anisate: ¹H NMR (CDCl₃) δ 7.64-7.61 (dt, J = 1.1-1.5, 7.3-7.7 Hz, 1 H), 7.56 (dd, J = 1.4-1.6, 2.5-2.6 Hz, 1 H), 7.34 (t, J = 7.8-8.0 Hz, 1H), 7.11-7.07 (ddd, J = 1.0, 2.7, 8.2-8.3 Hz, 1 H), 4.37 (q, J = 7.1-7.2 Hz, 2 H), 3.85 (s, 3 H), 1.39 (t, J = 7.1-7.2 Hz, 3 H); Methyl p-bromobenzoate: ¹H NMR (CDCl₃) δ 7.88 (d, J = 8.7 Hz, 2 H), 7.56 (d, J = 8.7 Hz, 2 H), 3.90 (s, 3 H); Methyl m-nitrobenzoate: ¹H NMR (CDCl₃) δ 8.84 (s, 1 H), 8.42-8.34 (m, 2 H), 7.65 (t, J = 8.0 Hz, 1 H), 3.98 (s, 3 H).