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

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.

(diacetoxyiodo)benzene - ion-supported hypervalent iodine(III) reagent - direct oxidative formation of amides - amines - aldehydes

References and Notes

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<A NAME="RW06108ST-17">17</A>

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.

<A NAME="RW06108ST-18">18</A>

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

<A NAME="RW06108ST-19">19</A> Gao J. Wang G.-W. J. Org. Chem.  2008,  73:  2955