3000
K. Schwekendiek, F. Glorius
PAPER
13C NMR (75 MHz, CDCl3): d = 10.4 (CH2CH3), 19.7 (Ar-o-CH3),
21.3 (Ar-p-CH3), 29.0 (CH2CH3), 68.5 (NCHEt), 71.8 (OCH2),
126.4 (CAr), 128.8 (CAr), 136.9 (CAr), 139.1 (CAr), 164.0 (OC=N).
127 (15), 126 (3), 125 (35), 117 (2), 113 (3), 111 (13), 103 (2), 102
(20), 89 (6), 76 (5), 75 (17), 51 (4), 50 (4), 43 (4), 41 (8), 39 (8), 29
(3), 28 (20), 27 (11).
MS (EI+): m/z (%) = 218 (15), 217 (3), 217 (100) [M]+, 189 (4), 188
(84), 172 (20), 162 (9), 161 (31), 160 (80), 158 (3), 148 (5), 147
(86), 146 (63), 145 (17), 144 (6), 133 (41), 132 (6), 131 (10), 130
(21), 119 (11), 118 (7), 117 (18), 116 (5), 115 (13), 104 (3), 103
(10), 91 (40), 78 (3), 77 (17), 65 (8), 55 (4), 53 (3), 52 (2), 51 (5),
43 (7), 41 (50), 39 (40), 32 (5), 29 (28), 28 (52), 27 (57).
MS (ESI+, MeOH): m/z = 218.2 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C14H20NO: 218.1539; found:
HRMS (ESI): m/z [M + H]+ calcd for C11H13ClNO: 210.0680;
found: 210.0680.
Methyl 4-(4-Ethyl-4,5-dihydrooxazol-2-yl)benzoate (1l)
Oxazoline 1l was prepared according to general procedure 1 using
( )-2-aminobutan-1-ol (89 mg, 1.0 mmol, 1.0 equiv), methyl 4-
formylbenzoate (164 mg, 1.0 mmol, 1.0 equiv), and NBS (178 mg,
1.0 mmol, 1.0 equiv) in CH2Cl2. The crude product was purified by
column chromatography (pentane–MTBE–Et3N, 90:20:1) The
product was obtained as a white solid; yield: 193 mg (83%); Rf =
0.27 (pentane–MTBE–Et3N, 90:20:1).
218.1539.
4-Ethyl-2-tolyl-4,5-dihydrooxazole (1j)
IR (KBr): 2962, 2918, 1716, 1646, 1611, 1508, 1441, 1409, 1383,
1359, 1283, 1195, 1116, 1066, 1019, 967, 949, 871, 783, 710 cm–1.
1H NMR (300 MHz, CDCl3): d = 1.01 (t, J = 7.4 Hz, 3 H, CH3),
1.60–1.85 (m, 2 H, CH2CH3), 3.94 (s, 3 H, OCH3), 4.08 (t,
J = 8.0 Hz, 1 H, OCH2), 4.24–4.34 (m, 1 H, NCHEt), 4.53 (dd,
J = 8.4 Hz, J = 9.2 Hz, 1 H), 8.00–8.10 (m, 4 H, ArH).
13C NMR (75 MHz, CDCl3): d = 9.1 (CH3), 27.7 (CH2CH3), 51.4
(OCH3), 67.3 (NCHR), 71.5 (OCHEt), 127.3 (CAr), 128.6 (CAr),
131.1 (CAr), 131.5 (CAr), 161.8, 164.2.
Oxazoline 1j was prepared according to general procedure 1 using
( )-2-aminobutan-1-ol (89 mg, 1.0 mmol, 1.0 equiv), 2-methyl-
benzaldehyde (116 mL, 1.0 mmol, 1.0 equiv), and NBS (178 mg,
1.0 mmol, 1.0 equiv) in CH2Cl2. The crude product was purified by
column chromatography (pentane–MTBE–Et3N, 98:2:1). The prod-
uct was obtained as a colorless oil; yield: 176 mg (93%); Rf = 0.31
(pentane–MTBE–Et3N, 98:2:1).
IR (KBr): 3027, 2963, 2925, 1645, 1603, 1575, 1492, 1456, 1383,
1350, 1328, 1305, 1265, 1241, 1137, 1043, 951, 898, 775, 729 cm–1.
1H NMR (300 MHz, CDCl3): d = 1.01 (t, J = 7.4 Hz, 3 H, CH3),
1.56–1.83 (m, 2 H, CH2CH3), 2.58 (s, 3 H, CH3), 4.02 (dd,
J = 7.6 Hz, J = 7.9 Hz, 1 H, OCH2), 4.22–4.32 (m, 1 H, NCHEt),
4.42 (dd, J = 7.9 Hz, J = 9.4 Hz, 1 H, OCH2), 7.18–7.35 (m, 3 H,
ArH), 7.75–7.78 (m, 1 H, ArH).
13C NMR (75 MHz, CDCl3): d = 10.1 (CH3), 21.7 (ArCH3), 28.9
(CH2CH3), 68.4 (NCHEt), 71.6 (OCH2), 125.6 (CAr), 127.6(CAr),
129.9 (CAr), 130.5 (CAr), 131.2 (CAr), 138.8 (CAr), 164.2 (OC=N).
MS (EI): m/z (%) = 233 (7) [M]+, 205 (11), 204 (2), 204 (100), 103
(2), 202 (4), 188 (5), 176 (5), 163 (5), 162 (7), 149 (2), 145 (2), 132
(3), 117 (5), 105 (5), 104 (2), 103 (6), 102 (2), 90 (3), 77 (2), 76 (5),
75 (4), 59 (19), 50 (3), 43 (4), 41 (4), 39 (3), 29 (4), 28 (14), 27 (10).
HRMS (EI): m/z [M]+ calcd for C13H15NO3: 233.1046; found:
233.1055.
4-Ethyl-2-(4-nitrophenyl)-4,5-dihydrooxazole (1m)
Oxazoline 1m was prepared according to general procedure 2 using
( )-2-aminobutan-1-ol (89 mg, 1.0 mmol, 1.0 equiv), 4-nitrobenz-
aldehyde (151 mg, 1.0 mmol, 1.0 equiv), K3PO4 (636 mg,
3.0 mmol, 3 equiv), and NBS (178 mg, 1.0 mmol, 1.0 equiv) in tol-
uene. The crude product was purified by column chromatography
(pentane–MTBE–Et3N, 90:10:1). The product was obtained as a
pale yellow solid; yield: 150 mg (68%); Rf = 0.21 (pentane–MTBE–
Et3N, 90:10:1).
MS (EI): m/z (%) = 190 (5), 189 (100) [M]+, 161 (14), 161 (2), 166
(76), 144 (16), 134 (5), 133 (3), 132 (31), 130 (2), 119 (14), 118 (5),
117 (6), 116 (3), 106 (2), 105 (32), 104 (2), 103 (2), 91 (26), 90 (13),
89 (9), 77(3), 65 (12), 63 (2), 51 (2), 41 (8), 39 (13), 32 (5), 29 (4),
28 (42), 27 (9).
MS (ESI+, MeOH): m/z = 190 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C12H16NO: 190.1226; found:
190.1228.
IR (film): 2971, 2894, 1647, 1597, 1520, 1471, 1410, 1345, 1287,
1263, 1104, 1070, 1010, 969, 956, 897, 862, 851, 704, 654 cm–1.
2-(2-Chlorophenyl)-4-ethyl-4,5-dihydrooxazole (1k)
Oxazoline 1k was prepared according to general procedure 2 with
( )-2-aminobutan-1-ol (89 mg, 1.0 mmol, 1.0 equiv), 2-chloro-
benzaldehyde (140 mg, 1.0 mmol, 1.0 equiv), K3PO4 (636 mg,
3.0 mmol, 3 equiv), and NBS (178 mg, 1.0 mmol, 1.0 equiv) in tol-
uene. The crude product was purified by column chromatography
(pentane–MTBE–Et3N, 90:10:1). The product was obtained as a
yellowish oil; yield: 146 mg (69%); Rf = 0.19 (pentane–MTBE–
Et3N, 90:10:1).
1H NMR (300 MHz, CDCl3): d = 1.02 (t, J = 7.4 Hz, 3 H, CH3),
1.57–1.85 (m, 2 H, CH2CH3), 4.11 (dd, J = 8.0 Hz, J = 8.0 Hz, 1 H,
OCH2), 4.25–4.35 (m, 1 H, NCHEt), 4.54 (dd, J = 8.2 Hz,
J = 9.5 Hz, 1 H), 8.09–8.14 (m, 2 H, ArH), 8.24–8.28 (m, 2 H,
ArH).
13C NMR (75 MHz, CDCl3): d = 10.1 (CH3), 28.7 (CH2CH3), 68.6
(NCHR), 72.0 (OCHEt), 123.6 (CAr), 129.4 (CAr), 133.9 (CAr),
149.6 (CArNO2), 161.8 (OC=N).
IR (film): 3070, 2974, 2932, 1652, 1594, 1570, 1479, 1436, 1355,
1329, 1305, 1240, 1129, 1094, 1035, 945, 900, 766, 735 cm–1.
MS (EI): m/z (%) = 220 (5) [M]+, 192 (12), 192 (2), 191 (100), 175
(5), 163 (11), 117 (13), 104 (2), 103 (5), 90 (6), 76 (8), 75 (2), 43
(4), 41 (3), 39 (2), 32 (4), 28 (46), 27 (3).
HRMS (EI): m/z [M]+ calcd for C11H12N2O3: 220.0842; found:
220.0844.
1H NMR (300 MHz, CDCl3): d = 1.02 (t, J = 7.4 Hz, 3 H, CH3),
1.59–1.86 (m, 2 H, CH2CH3), 4.09 (dd, J = 7.7 Hz, J = 7.8 Hz, 1 H,
OCH2), 4.26–4.35 (m, 1 H, NCHEt), 4.49 (dd, J = 8.0 Hz,
J = 9.5 Hz, 1 H), 7.28–7.45 (m, 3 H, ArH), 7.72–7.75 (m, 1 H,
ArH).
13C NMR (75 MHz, CDCl3): d = 10.0 (CH3), 28.6 (CH2CH3), 68.4
(NCHR), 72.3 (OCHEt), 126.6 (CAr), 128.0 (CAr), 130.7 (CAr),
131.4 (CAr), 131.6 (CAr), 133.5 (CAr), 161.8 (OC=N).
(4S,5R)-2-tert-Butyl-4-methyl-5-phenyl-4,5-dihydrooxazole (1s)
Oxazoline 1s was prepared according to general procedure 1 using
L-norephedrine (151 mg, 1.0 mmol, 1.0 equiv), pivalaldehyde
(110 mL, 1.0 mmol, 1.0 equiv), and NBS (178 mg, 1.0 mmol,
1.0 equiv) in CH2Cl2. The product was obtained as a colorless oil;
yield: 197 mg (91%); [a]D21 –214 (c 1.01, CHCl3); Rf = 0.50 (pen-
tane–MTBE–Et3N, 90:10:1).
MS (EI): m/z (%) = 211 (3) [M]+, 209 (15) [M]+, 183 (5), 182 (48),
181 (17), 180 (9), 180 (100), 179 (7), 166 (5), 164 (23), 154 (8), 153
(3), 152 (27), 151 (2), 141 (4), 140 (4), 139 (15), 138 (21), 137 (2),
Synthesis 2006, No. 18, 2996–3002 © Thieme Stuttgart · New York