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16
Typical Procedure for the Synthesis of N-Protected β-Amino Ketones
To a solution of HPAs (5 mol%) in MeCN (1.0 mL) were added ethyl carbamate (1.5 mmol), benzaldehyde (1.0 mmol), and acetophenone (2.0 mmol) successively at r.t. After the mixture was stirred for 24 h, a sat. aq NaHCO3 solution (5 mL) and brine (5 mL) were added, and the mixture was extracted with EtOAc. The organic phase was dried (anhyd Na2SO4) and filtered. The filtrate was evaporated under reduced pressure. The crude product was purified by silica gel chromatography and gave the desired product.
Compound 4d: mp 96-97 °C. 1H NMR (600 MHz, CDCl3): δ = 7.89 (d, J = 7.4 Hz, 2 H), 7.53 (t, J = 7.4 Hz, 1 H), 7.42 (t, J = 8.0 Hz, 2 H), 7.20 (t, J = 8.0 Hz, 1 H), 6.76-6.93 (m, 3 H), 5.70 (br s, 1 H), 5.25 (dd, J
1 = 6.0 Hz, J
2 = 13.6 Hz, 1 H), 4.08 (dd, J
1 = 7.0 Hz, J
2 = 14.1 Hz, 2 H), 3.77 (s, 3 H), 3.65 (m, 1 H), 3.40 (dd, J
1 = 5.8 Hz, J
2 = 16.7 Hz, 1 H), 1.20 (t, J
1 = 6.7 Hz, J
2 = 14.0 Hz, 3 H). 13C NMR (150 MHz, CDCl3): δ = 197.8, 159.8, 155.9, 143.2, 136.7, 133.3, 129.7, 128.7, 128.1, 118.6, 112.7, 112.4, 60.9, 55.2, 51.7, 44.0, 14.6. ESI-HRMS: m/z calcd for [C19H21NO4 + Na]+: 350.3641; found: 350.3638.
Compound 4j: mp 116-117 °C. 1H NMR (600 MHz, CDCl3): δ = 8.24 (s, 1 H), 8.08 (d, J = 8.0 Hz, 1 H), 7.88 (d, J = 7.4 Hz, 2 H), 7.73 (d, J = 7.2 Hz, 1 H), 7.56 (t, J = 7.4 Hz, 1 H), 7.44-7.50 (m, 3 H), 5.99 (br s, 1 H), 5.38 (dd, J
1 = 5.6 Hz, J
2 = 13.0 Hz, 1 H), 4.09 (dd, J
1 = 7.0 Hz, J
2 = 14.2 Hz, 2 H), 3.72-3.75 (m, 1 H), 3.50 (dd, J
1 = 5.4 Hz, J
2 = 17.4 Hz, 1 H), 1.23 (t, J
1 = 6.4 Hz, J
2 = 14.2 Hz, 3 H). 13C NMR (150 MHz, CDCl3): δ = 197.3, 156.0, 148.5, 144.0, 136.3, 133.8, 132.9, 129.5, 128.8, 128.1, 122.4, 121.4, 61.3, 50.9, 43.5, 14.5. ESI-HRMS: m/z calcd for [C18H18N2O5 + Na]+: 365.3358; found: 365.3460.
Compound 4s: mp 81-82 °C. 1H NMR (600 MHz, CDCl3): δ = 7.86 (d, J = 7.7 Hz, 2 H), 7.52 (t, J = 7.1 Hz, 1 H), 7.40 (t, J = 7.6 Hz, 2 H), 7.19-7.31 (m, 6 H), 6.88 (t, J = 7.7 Hz, 2 H), 6.75 (dd, J
1 = 2.2 Hz, J
2 = 8.2 Hz, 1 H), 5.86 (br s, 1 H), 5.28 (dd, J
1 = 6.2 Hz, J
2 = 13.1 Hz, 1 H), 5.05-5.10 (m, 2 H), 3.74 (s, 3 H), 3.65 (m, 1 H), 3.39 (dd, J
1 = 5.2 Hz, J
2 = 16.5 Hz, 1 H). 13C NMR (150 MHz, CDCl3): δ = 197.8, 159.8, 155.7, 136.7, 136.5, 133.4, 129.7, 128.7, 128.5, 128.1, 118.6, 112.8, 112.4, 66.8, 55.2, 51.8, 44.0. ESI-HRMS: m/z calcd for [C24H23NO4 + Na]+: 412.4335; found: 412.4330.
Compound 4w: mp 143-144 °C. 1H NMR (600 MHz, CDCl3): δ = 8.15 (d, J = 8.4 Hz, 2 H), 7.86 (d, J = 7.6 Hz, 2 H), 7.34-7.54 (m, 10 H), 6.08 (br s, 1 H), 5.40 (d, J = 6.2 Hz, 1 H), 5.10-5.15 (m, 2 H), 3.73-3.76 (m, 1 H), 3.49 (dd, J
1 = 4.6 Hz, J
2 = 17 Hz, 1 H). 13C NMR (150 MHz, CDCl3): δ = 197.3, 155.7, 148.8, 147.1, 136.2, 133.9, 128.8, 128.3, 127.0, 123.8, 51.2, 43.2. ESI-HRMS: m/z calcd for [C23H20N2O5 + Na]+: 427.4052; found: 427.4055