Rhenium-Catalyzed Highly Efficient Oxidations of Tertiary Nitrogen ­Compounds to N-Oxides Using Sodium Percarbonate as Oxygen Source

Abstract

Sodium percarbonate was found to be an ideal and efficient oxygen source for the oxidation of tertiary nitrogen compounds to N-oxides in excellent yields in presence of various rhenium-based catalysts under mild reaction conditions.

rhenium - solid oxidants - sodium percarbonate - oxidation - N-oxides

Reference and Notes

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The use of SPC as oxidant with water donor for oxidation of tertiary nitrogen compounds to N-oxides has been reported:

<A NAME="RD08906ST-6A">6a</A> Rosenau T. Potthast A. Kosma P. Synlett  1999,  1972 

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<A NAME="RD08906ST-7">7</A>

Typical Experimental Procedure: To a stirred solution of 4-picoline (10 mmol, 0.93 g), in MeCN (3 mL) were added SPC (3.12 g, 20 mmol) and MTO (25 mg, 1 mol%) and the mixture was heated to 50 °C under nitrogen atmosphere. AcOH (20 mol%) was added dropwise over a period of 15 min at 50 °C to this vigorously stirred solution. A vibrant yellow color appeared in the reaction mixture upon addition of AcOH. The progress of the reaction was monitored by TLC (SiO₂). After completion, the solvent was evaporated and the residue was dissolved in CH₂Cl₂. The organic layer was washed with water (2 ×) and dried over anhyd Na₂SO₄. The solvent was evaporated under reduced pressure and the residue thus obtained was purified by passing through a short silica gel column using EtOAc-hexane (4:6) as eluent. Evaporation of the solvent under reduced pressure yielded pure 4-picoline N-oxide (1.02 g, 92%); mp 180-181 °C (Lit. [9] 182 °C). IR: 3033, 1470, 1250, 1176 cm^-1. ¹H NMR: δ = 2.39 (s, 3 H), 7.10-7.22 (d, 2 H), 8.09-8.20 (d, 2 H).

<A NAME="RD08906ST-8">8</A>

Product Characterization Data.Pyridine N -Oxide (Table [2] , entry 1): mp 60-61 °C (Lit. [9] 62-63 °C). IR: 3076, 1388, 1265, 1176 cm^-1. ¹H NMR: δ = 7.42-7.45 (m, 3 H), 8.25-8.40 (m, 2 H).2-Picoline N -Oxide (Table [2] , entry 4): Hygroscopic oil. IR: 3030, 1482, 1252, 1190 cm^-1. ¹H NMR: δ = 2.42 (s, 3 H), 7.10-7.19 (m, 3 H), 8.10-8.23 (m, 1 H).4-Cyanopyridine N -Oxide (Table [2] , entry 5): mp 180-182 °C (Lit. [9] 182-183 °C). IR: 3076, 2247, 1492, 1282, 1176 cm^-1. ¹H NMR: δ = 7.89-8.00 (d, 2 H), 8.42-8.46 (d, 2 H).Nicotinamide N -Oxide (Table [2] , entry 6): mp 289-290 °C (decomp.). IR: 3350, 3060, 1694, 1450, 1140 cm^-1. ¹H NMR: δ = 7.37-7.45 (m, 2 H), 8.27-8.40 (m, 2 H).3-Picoline N -Oxide (Table [2] , entry 7): Hygroscopic oil. IR: 3030, 1470, 1252, 1162 cm^-1. ¹H NMR: δ = 2.35 (s, 3 H), 7.11-7.21 (m, 2 H), 8.18-8.20 (m, 2 H).Quinoline N -Oxide (Table [2] , entry 8): mp 50-52 °C (Lit. [9] 52-53 °C). IR: 3030, 1484, 1298, 1176 cm^-1. ¹H NMR: δ = 7.21-7.35 (m, 4 H), 8.10-8.19 (m, 2 H), 8.40 (m, 1 H).N , N -Diethylaniline N -Oxide (Table [2] , entry 9): Hygroscopic solid. IR: 3013, 2941, 1369, 1219, 1190 cm^-1. ¹H NMR: δ = 1.2 (t, 6 H), 3.3 (q, 2 H), 6.9 (m, 3 H), 7.3 (m, 2 H).N , N -Dimethylaniline N -Oxide (Table [2] , entry 10): Hygroscopic solid. IR: 3010, 2941, 1367, 1219, 1175 cm^-1. ¹H NMR: δ = 3.32 (s, 6 H), 7.22-7.28 (m, 3 H), 7.49-7.55 (m, 2 H).Triethylamine N -Oxide (Table [2] , entry 11): Hygroscopic solid. IR: 2940, 2870, 1470, 1250 cm^-1. ¹H NMR: δ = 1.12 (t, 9 H), 3.30 (q, 6 H).

<A NAME="RD08906ST-9">9</A> Prasad MR. Kamalkar G. Madhavi G. Kulkarni SJ. Raghavan KV. J. Mol. Catal. A: Chem.  2002,  186:  109