Synlett 2008(16): 2529-2531  
DOI: 10.1055/s-2008-1078218
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

A Mild and Clean Method for Oxidative Formation of Amides from Aldehydes and Amines

Chen Fang, Weixing Qian*, Weiliang Bao*
Department of Chemistry, Zhejiang University, Xi Xi Campus, Hangzhou, Zhejiang 310028, P. R. of China
Fax: +86(571)88273814; e-Mail: wlbao@css.zju.edu.cn;
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Publikationsverlauf

Received 16 April 2008
Publikationsdatum:
22. August 2008 (online)

Abstract

A metal-free direct oxidative formation of amides from aldehydes and amines using a hypervalent iodine(III) reagent or an ion-supported hypervalent iodine(III) reagent as a recyclable oxidant under mild conditions is reported.

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All reagents and solvents were pure analytical grade materials purchased from commercial sources and were used without further purification, if not stated otherwise. All melting points are uncorrected. The NMR spectra were recorded in CDCl3 on a Bruker Avance 400 MHz instrument with TMS as internal standard. TLC was carried out with 0.2 mm thick silica gel plates (GF254). The columns were hand packed with silica gel 60 (200-300 µm). All products were confirmed by ¹H NMR and ¹³C NMR. Unknown compounds were additionally confirmed by elemental analysis.
Typical Procedure for the Oxidative Amidation of Aldehydes with Amines by DIB: A solution of aldehyde (0.50 mmol, 1.0 equiv), DIB (0.75 mmol, 1.5 equiv), and two drops of H2O in CHCl3 (1 mL) was cooled to 0 ˚C under an inert atmosphere (N2) and the amine (0.65 mmol, 1.3 equiv) was slowly added (about one drop in 1 h for 3 h). The reaction vessel was capped and the reaction mixture was stirred for 3 h at 0 ˚C and then for 17 h at r.t. The crude reaction mixture was purified by column chromatography on silica gel (EtOAc-hexane, 1:4). 3,4,5-Trimethoxy- N -propylbenzamide (Table 2, entry 9): white solid; mp 108 ˚C. ¹H NMR (400 MHz, CDCl3): δ = 7.00 (s, 2 H), 6.25 (br, 1 H), 3.89 (s, 6 H), 3.87 (s, 3 H), 3.40 (q, J = 6.8 Hz, 2 H), 1.60-1.69 (m, 2 H), 0.98 (t, J = 8.0 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 167.3, 153.1, 140.7, 130.3, 104.3, 60.8, 56.2, 41.8, 22.9, 11.4. Anal. Calcd for C13H19NO4: C, 61.64; H, 7.56; N, 5.53; O, 25.27. Found: C, 61.60; H, 7.65; N, 5.60.

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The ionic liquid [dibmim]+[BF4]- was recovered and recycled in our previous work. Please refer to ref. 12.