Synlett 2007(9): 1455-1457  
DOI: 10.1055/s-2007-980349
LETTER
© Georg Thieme Verlag Stuttgart · New York

Thiourea-Catalyzed Transfer Hydrogenation of Aldimines

Zhiguo Zhang, Peter R. Schreiner*
Institut für Organische Chemie, Justus-Liebig-Universität Giessen, Heinrich-Buff-Ring 58, 35392 Giessen, Germany
Fax: +49(641)9934309; e-Mail: prs@org.chemie.uni-giessen.de;
Further Information

Publication History

Received 20 February 2007
Publication Date:
23 May 2007 (online)

Abstract

The present letter reports on the thiourea-catalyzed transfer hydrogenation of imines through hydrogen-bonding activation with Hantzsch 1,4-dihydropyridine as the hydrogen source. A ­variety of aromatic as well as aliphatic aldimines can be reduced to give the respective amines under acid- and metal-free reaction conditions.

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13

Since it is difficult to avoid the formation of carboxylic acids generated from aldehydes during the reaction, 10 mol% of NaHCO3 was added.

14

General Procedure for the Thiourea-Catalyzed Transfer Hydrogenation of Aldimines
In a typical experiment the aldimine 1 (1.0 mmol), thiourea 3 (1 mol%) and Hantzsch dihydropyridine 2 (1.1 equiv) were suspended in anhyd CH2Cl2 (5 mL) in a flask. The resulting mixture was allowed to stir at r.t. for 15 h. The solvent was removed under reduced pressure and the residue was purified by column chromatography on silica gel using mixtures of PE and Et2O to afford the pure corresponding amine 4. All compounds were fully characterized on the basis of IR, 1H NMR, 13C NMR and HRMS.
Compound 4a: light yellow oil. IR (film): 3418, 1699, 1602, 1505, 1179, 1064 cm-1. 1H NMR (400 MHz, CDCl3): δ = 4.20 (s, 2 H), 6.50-6.52 (d, 2 H, J = 8.71 Hz), 6.59-6.63 (t, 1 H, J = 7.41 Hz), 7.04-7.09 (t, 2 H, J = 7.40 Hz), 7.14-7.27 (m, 5 H). 13C NMR (100 MHz, CDCl3): δ = 48.2, 112.8, 117.5, 127.1, 127.4, 128.5, 129.2, 139.4, 148.1. HRMS: m/z calcd for C13H13N: 183.10425; found: 183.10347.