Synlett 2008(12): 1837-1839  
DOI: 10.1055/s-2008-1078509
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Hydrophosphorylation of Imines Catalyzed by Tosyl Chloride for the Synthesis of α-Aminophosphonates

Babak Kaboudin*, Elaheh Jafari
Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), Gava Zang, Zanjan 45195-1159, Iran
Fax: +98(241)4214949; e-Mail: kaboudin@iasbs.ac.ir;
Further Information

Publication History

Received 18 February 2008
Publication Date:
19 June 2008 (online)

Abstract

A simple, efficient, and general method has been developed for the synthesis of α-aminophosphonic esters using TsCl as an efficient catalyst. α-Aminophosphonic acids were obtained in good to high yields (65-85%) and purity under mild conditions by the reaction of diethyl phosphite with imines in the presence of TsCl.

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TsCl (1 mmol, 0.18 g) was added to a stirred mixture of diethyl phosphite (0.012 mol) in CH2Cl2 (10 mL) at r.t. Imine (0.01 mol) was added to the reaction mixture and the mixture was stirred for 2-4 h at r.t. H2O (50 mL) was added to the reaction mixture and the organic layer was extracted with EtOAc (4 × 50 mL), dried with CaCl2, and the solvent was evaporated to give the crude product. Chromatography on silica gel with EtOAc-n-hexane (1:9 → 5:5) and evaporation of the solvent under reduced pressure gave the pure products in 65-85% yields. All the products gave satisfactory spectral data in accordance with the assigned structures and literature reports. [¹²a] [¹6b] Diethyl[phenyl(phenylamino)methyl]phosphonate (2a): ¹H NMR (250 MHz, CDCl3): δ = 1.13 (t, J = 7.0 Hz, 3 H), 1.29 (t, J = 7.0 Hz, 3 H), 3.60-3.75 (m, 1 H), 3.85-4.01 (m, 1 H), 4.03-4.22 (m, 2 H), 4.76 (d, J HP = 24.2 Hz, 1 H), 6.59 (d, J = 8.5 Hz, 2 H), 6.69 (t, J = 7.2 Hz, 1 H), 7.11 (t, J = 8.3 Hz, 2 H), 7.22-7.52 (m, 5 H). ³¹P NMR (101.2 MHz, CDCl3, H3PO4): δ = 23.31. ¹³C NMR (62.9 MHz, CDCl3): δ = 16.2 (d, J PC = 6.3 Hz), 16.4 (d, J PC = 6.3 Hz), 56.1 (d, J PC = 150.3 Hz), 63.1, 63.2, 113.8, 118.3, 127.9 (d, J PC = 5.7 Hz), 128.5 (d, J PC = 2.5 Hz), 129.2, 136.0 (d, J PC = 2.5 Hz), 146.3 (d, J PC = 14.5 Hz).