Fast racemization and dynamic kinetic resolution of primary benzyl amines

Tetrahedron Letters

Volumn 51, Issue 42, 2010, Pages 5581-5584

  Kim, Yunwoong ^a   Park, Jaiwook ^a   Kim, Mahn Joo ^a  

^a Pohang University of Science and Technology (POSTECH)   (South Korea)

Author keywords

[No Author keywords available]

Indexed keywords

BENZYLAMINE DERIVATIVE; NANOPARTICLE; PALLADIUM COMPLEX; TRIACYLGLYCEROL LIPASE;

ARTICLE; CATALYST; HIGH PERFORMANCE LIQUID CHROMATOGRAPHY; KINETICS; NANOCATALYST; RACEMIZATION; REACTION ANALYSIS; THERMOSTABILITY;

EID: 77956652753     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/j.tetlet.2010.08.050     Document Type: Article

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38. 2 (33 mg, 0.147 mmol) and ethanol (10 mL, 170 mmol) were added to a 50 mL round-bottomed flask and stirred at room temperature for 10 min followed by the addition of AlO(OH) (1.54 g). The resultant mixture was further stirred at room temperature for 1 h to allow the spontaneous reduction of Pd(II) to Pd(0) nanoparticles adsorbed on AlO(OH) powder. The heterogeneous mixture was filtered, washed with acetone, and dried at 80 °C under a reduced pressure to give 2 as dark powder (Pd on AlO(OH); 1.46 g). The ICP analysis indicated that the Pd nanocatalyst contained 0.85 wt % of Pd.
39. 1H NMR spectroscopy and HPLC (Kromasil-5-CellCoat, n-hexane/2-propanol/diethyl amine = 90:10:0.1, flow rate = 1.5 mL/min, UV 220 nm): (R)-3a = 5.57 min, (S)-3a = 6.57 min.
40. 5a
41. In general, the racemization of benzyl amines takes place through a two-step process, dehydrogenation and hydrogenation via an imine intermediate. The observation that the racemizations of 3b-g took place slowly relative to that of 3a in DKR indicates that racemization is retarded by both electron-donating and electron-attracting groups on the benzene ring.
42. In racemization, the dehydrogenation step should be rate determining with electron-attracting groups while the hydrogenation step should be rate determining with electron-donating groups. Accordingly, the life time of imine intermediate in the latter case is long relative to that in the former case. This explains the reason why the amounts of byproducts resulting from the side reactions of imine intermediate (including its reaction with amine substrate) are significantly larger in the DKR of 3d with an electron-donating group than in the DKR of 3b with an electron-attracting group.