(S)-2-(2-Methoxyphenyl)-2-oxo-1-phenylethyl acrylate (1b).
Prepared from (S)-5b and acryloyl chloride in 83% yield; white
crystals; mp 96.9–98.7 °C. 1H NMR (300 MHz, CDCl3): δ
(ppm) 3.83 (s, 3H) 5.88 (dd, 1H, J1 = 10.3 Hz, J2 = 1.4 Hz),
6.25 (dd, 1H, J1 = 17.4 Hz, J2 = 10.3 Hz), 6.50 (dd, 1H, J1 =
17.4 Hz, J2 = 1.4 Hz), 6.87 (d, 1H, J = 8.3 Hz), 6.96 (t, 1H, J =
7.7 Hz), 7.13 (s, 1H), 7.31–7.45 (m, 6H), 7.78 (dd, 1H, J1 = 7.7
Hz, J2 = 1.6 Hz). 13C NMR (75.5 MHz, CDCl3): δ (ppm) 55.6,
80.9, 111.8, 121.1, 125.9, 128.3, 128.8, 129.0, 129.1, 131.5,
131.7, 134.5 (broad), 158.5, 165.7, 195.1. MS (EI, m/z): 296 (2),
161 (10), 135 (100), 77 (30), 55 (30). FTIR (KBr, cm−1): 3068,
2937, 2837, 1714, 1674, 1597, 1485, 1404, 1292, 1238, 1201,
1022, 976, 756, 698. Anal. calcd for C18H16O4: C, 72.96; H,
5.44%. Found: C, 73.06; H, 5.66%.
the products were extracted to dichloromethane (25 mL). The
organic layer was separated and dried over MgSO4, and dichlor-
omethane was removed under reduced pressure.
(c) Catalyzed reaction. A catalyst (1 or 2 eq, Table 1) was
added dropwise to a solution of a dienophile (1, 1 mmol) in dry
solvent (25 mL) at the given temperature (Table 1), and the
mixture was stirred for 20 min. A solution of cyclopentadiene
(170 μL, 2 mmol) in the same dry solvent (5 mL) was added
dropwise. The mixture was stirred at the given temperature (until
the starting material was consumed; TLC) and subsequently
treated according to the following procedures.
SnCl4. The reaction mixture was quenched with the addition
of aq HCl (10%, 30 mL). The organic layer was separated,
washed with aq Na2CO3 (10%, 25 mL), water (2 × 20 mL) and
brine (20 mL), and dried over MgSO4. The solvent was evapor-
ated under reduced pressure.
2-Oxo-1,2-diphenylethyl acetate (6a). Prepared from 5a and
1
acetyl chloride in 95% yield; white solid; mp 85.3–87.1 °C. H
NMR (300 MHz, CDCl3): δ (ppm) 2.22 (s, 3H), 6.87 (s, 1H),
7.35–7.55 (m, 8H), 7.92–7.97 (m, 2H). 13C NMR (75.5 MHz,
CDCl3): δ (ppm) 21.0, 77.9, 128.8, 128.9, 129.0, 129.3, 129.5,
133.7, 133.9, 134.9, 170.7, 194.0. MS (EI, m/z): 254 (1), 211
(4), 195 (1), 194 (1), 165 (10), 167 (2), 149 (25), 107(30), 105
(100), 77 (25), 43 (30). FTIR (KBr, cm−1): 3062, 2956, 1730,
1691, 1593, 1448, 1369, 1230, 1051, 986, 758, 696, 523. UV
(CH3OH): ε313 = 1200 dm3 mol−1 cm−1. Anal. calcd for
C16H14O3: C, 75.57; H, 5.55%. Found: C, 75.12; H, 5.55%.
TiCl4. The reaction mixture was quenched with saturated aq
NaHCO3 (25 mL). The organic phase was separated and washed
with water (2 × 20 mL) and brine (20 mL), and dried over
MgSO4. The solvent was removed under reduced pressure.
EtAlCl2. The reaction mixture was quenched with aq NaOH
(10%, 25 mL). The organic layer was separated and washed with
water (2 × 20 mL) and brine (20 mL), and dried over MgSO4.
The solvent was evaporated under reduced pressure.
Finally, the product 2 (four stereoisomers) was purified by
column chromatography (diethyl ether/petroleum ether, 3 : 7) in
all procedures.
(S)-2-(2-Methoxyphenyl)-2-oxo-1-phenylethyl acetate (6b).
Prepared from (S)-5b and acetyl chloride in 92% yield; white
solid; mp 109.5–112.1 °C. 1H NMR (300 MHz, CDCl3): δ
(ppm) 2.18 (s, 3H), 3.81 (s, 3H), 6.86 (d, 1H, J = 8.4 Hz), 6.95
(dt, 1H, J1 = 7.6 Hz, J2 = 1.0 Hz), 7.01 (s, 1H), 7.28–7.43 (m,
6H), 7.75 (dd, 1H, J1 = 7.8 Hz, J2 = 1.8 Hz). 13C NMR
(75.5 MHz, CDCl3): δ (ppm) 20.9, 55.3, 80.6, 111.6, 120.8,
127.8, 128.5, 128.8, 128.9, 131.3, 134.2, 134.6, 158.2, 170.8,
198.8. MS (EI, m/z): 284 (3), 241 (2), 225 (2), 210 (3), 181 (4),
149 (1), 135 (100), 107 (10), 77 (30), 43 (25). FTIR (KBr,
cm−1): 3070, 1969, 2937, 2839, 1734, 1676, 1595, 1483, 1367,
(S)-2-Oxo-1,2-diphenylethylbicyclo[2.2.1]hept-5-ene-2-carbox-
ylate (2a). Prepared from 1a; yield 85–95%; white solid; mp
1
89.7–96.5 °C; a mixture of diastereomers (Table 1). H NMR
(300 MHz, CDCl3): δ (ppm) 1.29 (d, 1H, J = 8.3 Hz), 1.40–1.55
(m, 2H), 1.87–2.01 (m, 1H), 2.92 (bs, 1H), 3.07–3.19 (m, 1H),
3.26 (bs, 0.4H), 3.39 (bs, 0.6H), 5.85 (dd, 0.4H, J1 = 5.4 Hz, J2
= 2.8 Hz), 6.08 (dd, 0.6H, J1 = 5.4 Hz, J2 = 2.8 Hz), 6.18 (dd,
1H, J1 = 5.3 Hz, J2 = 2.9 Hz), 6.80 (d, 1H, J = 5.9 Hz),
7.33–7.42 (m, 5H), 7.44–7.53 (m, 3H), 7.92 (d, 2H, J = 7.6 Hz).
13C NMR (75.5 MHz, CDCl3): δ (ppm) 29.5, 29.6, 42.8, 42.8,
43.2, 43.4, 46.0, 46.6, 49.9, 77.4, 77.5, 128.7, 128.8, 129.0,
129.2, 129.3, 132.5, 132.9, 133.5, 133.5, 134.1, 134.2, 135.1,
135.1, 137.6, 138.0, 174.5, 174.5, 194.4, 194.4. FTIR (KBr,
cm−1): 3062, 2976, 2870, 1736, 1687, 1595, 1448, 1338, 1225,
1176, 1105, 943, 756, 698, 538. Anal. calcd for C22H20O3: C,
79.50; H, 6.06%. Found: C, 79.15; H, 6.13%. HRMS (MS
ES+): cald for C22H21O3 (M + H+) 333.1491, found 333.1485.
1238, 1045, 1020, 862, 760, 704, 536. UV (CH3OH): ε313
=
5500 dm3 mol−1 cm−1. HRMS (APCI−): calcd for C17H15O4
(M–H+) 283.0976, found 283.0980. Anal. calcd for C17H16O4:
C, 71.82; H, 5.67%. Found: C, 71.88; H, 5.81%.
General procedures for asymmetric Diels–Alder reaction
between chiral benzoin acrylates (1a, b) and cyclopentadiene
(a) Non-catalyzed reaction (toluene). A solution of cyclopen-
tadiene (170 μL, 2 mmol) in dry toluene (5 mL) was added to a
solution of 1 (1 mmol) in dry toluene. The reaction mixture was
vigorously stirred at the given temperature (Table 1) until the
starting material was consumed (TLC). The solvent was
removed under reduced pressure, and the residue was dissolved
in dichloromethane (25 mL) and washed with water (20 mL) and
brine (20 mL). The organic layer was dried over MgSO4 and
dichloromethane was removed under reduced pressure.
(S)-2-(2-Methoxyphenyl)-2-oxo-1-phenylethyl
bicyclo[2.2.1]
hept-5-ene-2-carboxylate (2b). Prepared from 1b; yield 85–95%;
white crystals; mp 51.9–59.8 °C; a mixture of diastereomers
1
(Table 1). H NMR (300 MHz, CDCl3): see Fig. S9 (ESI‡). 13C
NMR (75.5 MHz, CDCl3): δ (ppm) major diastereomer (endo):
29.2, 42.6, 42.9, 46.3, 49.5, 55.3, 80.1, 111.5, 120.7, 126.9,
128.4, 128.5, 128.6, 131.0, 132.8, 133.9, 134.2, 137.0, 158.1,
174.1, 195.1; minor diastereomer (exo): 29.3, 42.5, 43.1, 46.3,
49.5, 55.3, 80.2, 111.4, 120.7, 126.8, 128.4, 128.4, 128.5, 131.0,
132.3, 133.9, 134.5, 137.5, 158.0, 174.0, 195.3. FTIR (KBr,
cm−1): 3059, 2976, 2941, 1872, 2834, 1730, 1676, 1595, 1485,
1460, 1288, 1246, 1171, 1022, 758, 704. UV (CH3OH):
(b) Non-catalyzed reaction (water). Cyclopentadiene (170 μL,
2 mmol) and 1 (1 mmol) were added to water (20 mL). The reac-
tion mixture was vigorously stirred at the given temperature
(Table 1) until the starting material was consumed (TLC), and
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Photochem. Photobiol. Sci., 2012, 11, 500–507 | 505