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Synlett 2006(16): 2661-2663  
DOI: 10.1055/s-2006-951487
LETTER
© Georg Thieme Verlag Stuttgart · New York

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

Suman L. Jain, Jomy K. Joseph, Bir Sain*
Chemical and Biotechnology Division, Indian Institute of Petroleum, Dehradun 248005, India
Fax: +91(135)2660202; e-Mail: birsain@iip.res.in;
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Publication History

Received 28 March 2006
Publication Date:
22 September 2006 (online)

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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.

Key words

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

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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).

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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).