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Synlett 2006(3): 0395-0398  
DOI: 10.1055/s-2006-926269
LETTER
© Georg Thieme Verlag Stuttgart · New York

An Efficient and General Method for the Deoxygenation of Organic N-Oxides Using Zn(OTf)2 and Cu(OTf)2

Anil Saini, Sanjay Kumar, Jagir S. Sandhu*
Department of Chemistry, Punjabi University, Patiala-147 002, India
Fax: +91(175)2283073; e-Mail: j_sandhu2002@yahoo.com;
Further Information

Publication History

Received 2 November 2005
Publication Date:
06 February 2006 (online)

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Abstract

A mild and efficient general method for the deoxygenation of organic N-oxides such as azoxybenzenes, N-arylnitrones, and N-heteroarene N-oxides using Zn(OTf)2 and Cu(OTf)2 in excellent yields is described.

Key words

deoxygenation - metal triflates - nitrones - N-heteroarene N-oxides - azoxybenzenes

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Deoxygenation of Nitrones; Typical Procedure
To a stirred solution of benzaldehyde N-phenylnitrone (3a, 0.39 g, 2 mmol) in CH3CN (15 mL) was added Zn(OTf)2 (2 mmol, 1 equiv) and the resulting mixture was stirred at 80 °C for 70 min. After completion of the reaction (monitored by TLC), the solvent was removed under reduced pressure, and the residue was treated with H2O (3 × 30 mL). The resultant mixture was extracted with CH2Cl2, the organic layer was dried (Na2SO4), and the solvent removed by distillation to give the crude product, which was purified by column chromatography (silica, hexane-EtOAc) to afford benzylidine aniline 4a, in 74% yield; mp 51-52 °C (Lit.26 mp 52 °C). 1H NMR (200 MHz): δ = 8.35 (s, 1 H, CH=N), 7.30-7.60 (m, 10 H, Ar). 13C NMR (50 MHz): δ = 122.0, 12.3, 127.0, 128.4, 128.6, 129.0, 129.1, 129.6, 129.8, 130.8, 131.2, 153.2 (Ar), 163.4 (CH).

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Deoxygenation of Heteroarene N -Oxides: Typical Procedure
To a stirred solution of pyridine N-oxide (5a, 0.19g, 2 mmol) in CH3CN (15 mL) was added Zn(OTf)2 (2 mmol, 1 equiv) and the resulting mixture was stirred at 80 °C for 60 min. The solvent was removed under reduced pressure and H2O (50 mL) was added. The pH was adjusted to >7 by the addition of 25% aq NH3 and the product extracted with Et2O (3 × 50 mL). The organic layer was dried (Na2CO3) and evaporated to give the crude product, which after purification afforded pyridine 6a in 89% yield; bp 113-115 °C (Lit.27 bp 115.5 °C); picrate mp 163-164 °C (Lit.27 mp 164-65 °C). 1H NMR (200 MHz): δ = 7.20 (dd, 2 H, J = 8.2 Hz), 7.55 (dd, 1 H, J = 8.2 Hz), 8.50 (d, 2 H, J = 6.2 Hz). 13C NMR (50 MHz): δ = 123.2, 123.7, 135.4, 149.6, 149.7.