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DOI: 10.1055/s-2002-19354
An Efficient Approach to α-Aryl β-Amino Esters through 1,2-Aryl Migration of p-Toluenesulfonic Acid Mediated Diazo Decomposition
Publikationsverlauf
Publikationsdatum:
01. Februar 2007 (online)
Abstract
A new method for the synthesis of α-aryl β-amino esters has been developed. The key step in this preparation is the chemoselective 1,2-aryl migration of diazo carbonyl compounds catalyzed by TsOH.
Key words
diazo compounds - 1,2-aryl migration - amino acids - hydrogenations - α-aryl β-amino esters
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References
General procedure for the TsOH catalyzed diazo decomposition: To a solution of TsOH (1 mg) in anhydrous CH2Cl2 (20 mL) at 0 °C under N2, was added dropwise a solution of diazo compound in anhydrous CH2Cl2 (5 mL). The reaction was complete within 30 min as indicated by TLC check. Solvent was removed by evaporation, and the residue was purified by flash column chromatography to give cis and trans α-aryl-β-enamino esters as a mixture.
11General procedure for the hydrogenation of a-aryl-b-enamino esters: To a solution of α-aryl-β-enamino esters (50 mg, cis and trans mixture) in absolute MeOH (25 mL) was added 10% Pd/C catalyst (10 mg). The reaction mixture was stirred for 10 h under 1 atm hydrogen atmosphere. Then catalyst was removed by filtration and solvent was evaporated to give a residue, which was purified by flash column chromatography. 3a: 1H NMR (200 MHz, CDCl3): δ 1.13 (t, 3 H), 2.36 (s, 3 H), 3.19-352 (m, 2 H), 3.79-3.86 (q, 1 H), 4.04-4.17 (m, 2 H), 5.13 (t, 1 H), 7.13 (m, 7 H), 7.72 (d, 2 H); 13C NMR (50 MHz, CDCl3): δ 13.88, 21.42, 45.62, 51.72, 61.27, 126.91, 127.82, 127.84, 128.88, 129.68, 135.63, 136.86, 143.40, 172.34; MS m/z (relative intensity): 347 (M+, 17%), 118 (100%). 3b: 1H NMR (200 MHz, CDCl3) δ 1.18 (t, 3H), 2.42 (s, 3 H), 3.16-3.50 (m, 2H), 3.77-3.81 (m, 1 H), 3.79 (s, 3H), 4.04-4.17 (m, 2 H), 5.07 (t, 1 H), 6.83 (d, 2 H), 7.06 (d, 2 H), 7.29 (d, 2 H), 7.72 (d, 2 H); 13C NMR (50 MHz, CDCl3): δ 13.90, 21.41, 45.67, 50.82, 55.14, 61.18, 114.25, 126.91, 127.60, 128.90, 129.65, 136.90, 143.36, 159.14, 172.56; MS m/z (relative intensity): 377 (M+, 10%), 194 (100%). 3c: 1H NMR (200 MHz, CDCl3) δ 1.19 (t, 3 H), 2.39 (s, 3 H), 3.21-3.55 (m, 2 H), 3.84-3.91(q, 1 H), 4.04-4.20 (m, 2 H), 5.07 (t, 1 H), 7.20-7.57 (m, 1 1H), 7.71 (d, 2 H); 13C NMR (50 MHz, CDCl3): δ 13.96, 21.45, 45.65, 51.40, 61.39, 126.95, 127.45, 127.60, 128.30, 129.71, 134.60, 136.89, 140.26, 140.82, 143.45, 172.36. m/z (relative intensity): 423 (M+, 11%), 240 (100%). 3d: 1H NMR (200 MHz, CDCl3) δ 1.17 (t, 3 H), 2.42 (s, 3 H), 3.15-3.50 (m, 2 H), 3.78-3.85 (q, 1 H), 4.04-4.18 (m, 2 H), 5.20 (t, 1 H), 6.92-7.30 (m, 6 H), 7.70 (d, 2 H); 13C NMR (50 MHz, CDCl3): δ 13.87, 21.41, 45.57, 50.92, 61.37, 115.55, 115.98, 126.89, 129.44, 129.60, 129.69, 136.79, 143.47, 172.19. m/z (relative intensity): 365 (M+, 24%), 182 (100%). 3e: 1H NMR (200 MHz, CDCl3) δ 1.18 (t, 3 H), 2.42 (s, 3 H), 3.20-3.55 (m, 2 H), 3.87-3.94 (q, 1 H), 4.04-4.17 (m, 2 H), 5.13 (t, 1 H), 7.29 (m, 2 H), 7.31-7.56 (m, 4 H), 7.70 (m, 2 H); 13C NMR (50 MHz, CDCl3): δ 13.84, 21.42, 45.44, 51.55, 61.61, 124.74, 124.81, 126.91, 129.42, 131.44, 136.68, 136.78, 143.62, 171.70. m/z (relative intensity): 415 (M+, 8%) 184 (100%). 3f: 1H NMR (200 MHz, CDCl3) δ 1.22 (t, 3 H), 1.97 (m, 2 H), 2.39 (s, 3 H), 2.83 (t, 2 H), 3.89 (d, 2 H), 4.02-4.20 (m, 4 H), 5.15 (t, 1 H), 7.23 (d, 2 H), 7.68 (d, 2 H); 13C NMR (50 MHz, CDCl3): δ 14.32, 21.40, 23.74, 31.15, 39.35, 59.84, 72.16, 76.36, 76.99, 77.63, 98.03, 127.10, 129.11, 137.59, 142.79, 167.55, 173.76. m/z (relative intensity): 339 (M+, 14%), 184 (100%).
12For the α-aryl-β-enamino esters 5f and 6f, the hydrogenation gave a product with the furanyl moiety being partially hydrogenated. The structure of the 3f (Figure) is as follows.