S. Onitsuka et al. / Tetrahedron 57 -2001) 6003±6009
6007
yields are summarized in Table 1. The products 2a, 2d, and
2e were further puri®ed and recrystallized from methanol.
diated using a 250 W halogen lampat 0 8C for 5 min with
dry air bubbling. The solvent was removed in vacuo and the
1H NMR spectrum of the residue was immediately
measured in deuteriochloroform. The spectrum showed
the existence of the endoperoxide A. Upon standing for
12 h at 238C, the spectrum changed to that of the oxirane 2a.
4.3.1. 2,2-Diacetyl-3-benzoyloxirane (2a). Colorless
needles 2from methanol); mp91.5±92.0 8C 2lit,14 mp88±
908C); IR 2CHCl3) n 1717, 1693 2CvO); 1H NMR
2CDCl3) d 7.95±7.45 25H, m, arom H), 4.61 21H, s, H-3),
2.34 23H, s, Ac), 2.32 23H, s, Ac); 13C NMR 2CDCl3) 199.7,
199.2, 190.3 2CvO), 134.8 2arom C), 134.7, 129.1 22C),
128.5 22C) 2arom CH), 69.4 2.C,), 60.6 2.CH-), 28.8,
25.9 2Ac); FABMS m/z 2rel intensity) 233 2100, M11),
217 218), 191 222), 120 218), 105 280). Anal. calcd for
C13H12O4: C, 67.23; H, 5.21. Found: C, 67.53; H, 5.51.
4.4.1. 5-Acetyl-4-methyl-1-phenyl-2,3,7-trioxabicyclo-
[2.2.1]hept-5-ene (A).27 1H NMR 2CDCl3) d 7.90±7.35
25H, m, arom H), 7.20 21H, s, H-6), 2.35 23H, s, Ac), 2.05
23H, s, Me). cf. 3-Acetyl-2-methyl-5-phenylfuran 21a)23
colorless needles 2from ethanol); mp50±51 8C 2lit,23 mp
1
50±518C); IR 2CHCl3) n 1646 2CvO); H NMR 2CDCl3)
d 7.41 25H, m, arom H), 6.80 21H, s, H-4), 2.62 23H, s, Me),
2.41 23H, s, Ac); 13C NMR 2CDCl3) d 193.8 2CO), 157.6
2C-5), 151.5 2C-2), 129.7 2arom C), 128.6 22C), 127.6 22C),
123.5 2arom CH), 123.1 2C-3), 104.9 2C-4), 28.9 2Ac), 14.3
2Me); MS m/z 2rel intensity) 200 272, M1), 185 287), 157
239).
4.3.2. 2,2-Diacetyl-3-(4-¯uorobenzoyl)oxirane (2b). Color-
less oil; IR 2CHCl3) n 1720, 1693 2CvO); 1H NMR
2CDCl3) d 7.99 22H, m, arom H), 7.19 22H, m, arom H),
4.55 21H, s, H-3), 2.34 23H, s, Ac), 2.33 23H, s, Ac); 13C
NMR 2CDCl3) 199.7, 199.1, 188.8 2CvO), 166.6 2d, J
259.2 Hz, arom CF), 131.4 22C, d, J11.1 Hz, arom CH),
131.2 2arom C), 116.4 22C, d, J22.1 Hz, arom CH), 69.3
2.C,), 60.6 2.CH-), 28.8, 26.0 2Ac); FAB HRMS
2MeOH±NBA±NaI) Found: m/z 273.0542. Calcd for
C13H11FO4Na: M, 273.0539.
4.5. Photooxygenation of furans (method 2)
A similar reaction was carried out using a 250 W halogen
lampat 0 8C for 5 min with dry air bubbling 2¯ow rate:
120 dm3 min21). After irradiation, the reaction mixture
was poured into water 230 mL) at room temperature and a
solid precipitated. The solid was dissolved with stirring for
1 h at room temperature, and additional water 250 mL) was
added to the aqueous mixture. The extraction with diethyl
ether 230£3 mL) followed by ¯ush chromatographic sepa-
ration on silica gel 2Fuji Silysia BW-300 silica gel) with
hexane/ethyl acetate 24:1 v/v) gave a mixture of 2 and 3.
4.3.3. 2,2-Diacetyl-3-(4-chlorobenzoyl)oxirane (2c). Color-
less oil; IR 2CHCl3) n 1722, 1692 2CvO); 1H NMR
2CDCl3) d 7.88 22H, m, arom H), 7.48 22H, m, arom H),
4.54 21H, s, H-3), 2.33 23H, s, Ac), 2.31 23H, s, Ac); 13C
NMR 2CDCl3) d 199.5, 199.1, 189.2 2CvO), 141.4, 133.1
2arom C), 129.9 22C), 129.5 22C) 2arom CH), 69.3 2.C,),
60.6 2.CH-), 28.8, 26.0 2Ac); FABMS m/z 2rel intensity)
267 250, M11), 225 220), 139 2100). Anal. calcd for
C13H11ClO4: C, 58.55; H, 4.16. Found: C, 58.53; H, 4.14.
1
The ratio and the yields were determined by the H NMR
spectra 2Table 1). The products 3 were unstable in aceto-
nitrile solution and polymerized at 238C until 24 h.
4.3.4. 2,2-Diacetyl-3-(4-methylbenzoyl)oxirane (2d).
Colorless needles 2from methanol); mp70.4 8C; IR
4.5.1. 3-Acetyl-1-phenyl-2-pentene-1,4-dione (3a). A pale
yellow needle; mp68.5 8C 2lit,14 mp69±71 8C); IR 2CHCl3)
n 1706, 1666 2CvO), 1597 2CvC±CvO); 1H NMR
2CDCl3) d 8.00±7.40 25H, m, arom H), 7.59 21H, s,
vCH±), 2.46 23H, s, Ac), 2.42 23H, s, Ac); 13C NMR
2CDCl3) d 202.9, 196.4, 189.9 2CvO), 151.9 2C,),
136.1 2arom C), 134.4 2arom CH), 130.2 2vCH±), 129.0
22C), 128.7 22C) 2arom CH), 30.7, 27.2 2Ac). Anal. calcd for
C13H12O3: C, 72.21; H, 5.59. Found: C, 72.37; H, 5.59.
1
2CHCl3) n 1720, 1690 2CvO); H NMR 2CDCl3) d 7.84
22H, m, arom H), 7.30 22H, m, arom H), 4.57 21H, s, H-3),
2.43 23H, s, Me), 2.34 23H, s, Ac), 2.32 23H, s, Ac); 13C
NMR 2CDCl3) 199.8, 199.2, 189.7 2CvO), 146.0, 132.4
2arom C), 129.8 22C), 128.7 22C) 2arom CH), 69.3
2.C,), 60.8 2.CH-), 28.8, 26.1 2Ac), 21.9 2Me);
FABMS m/z 2rel intensity) 247 250, M11), 231 214), 205
220), 161 214), 134 215), 119 2100). Anal. calcd for
C14H14O4: C, 68.28; H, 5.73. Found: C, 68.57; H, 5.80.
4.5.2. 3-Acetyl-1-(4-¯uorophenyl)-2-pentene-1,4-dione
(3b). Yellow oil; IR 2CHCl3) n 1705, 1668 2CvO), 1605
2CvC±CvO); 1H NMR 2CDCl3) d 8.01 22H, m, arom H),
7.54 21H, s,vCH±), 7.19 22H, m, arom H), 2.46 23H, s, Ac),
2.44 23H, s, Ac); 13C NMR 2CDCl3) d 202.7, 195.9, 188.3
2CvO), 166.5 2d, J257.4 Hz, arom CF), 152.2 2C,),
132.7 2arom C), 131.6 22C, d, J9.2 Hz, arom CH), 129.8
2CH±), 123.2 22C, d, J22.1 Hz, arom CH), 30.7, 27.4
2Ac). FAB HRMS Found: m/z 235.0793. calcd for
C13H12FO3: M11, 235.0770.
4.3.5. 2,2-Diacetyl-3-(4-methoxybenzoyl)oxirane (2e).
Colorless needles 2from methanol); mp89.5 8C; IR
1
2CHCl3) n 1720, 1681 2CvO); H NMR 2CDCl3) d 7.94
22H, m, arom H), 6.97 22H, m, arom H), 4.54 21H, s, H-3),
3.89 23H, s, MeO), 2.34 23H, s, Ac), 2.32 23H, s, Ac); 13C
NMR 2CDCl3) d 199.9, 199.2, 188.3 2CvO), 164.8 2arom
C), 131.1 22C, arom CH), 127.9 2arom C), 114.4 22C, arom
CH), 69.3 2.C,), 60.8 2.CH-), 55.7 2MeO), 28.8 2Ac),
26.2 2Ac); FABMS m/z 2rel intensity) 263 265, M11), 221
218),150 220), 135 2100). Anal. calcd for C14H14O5: C,
64.12; H, 5.38. Found: C, 64.10; H, 5.47.
4.5.3. 3-Acetyl-1-(4-chlorophenyl)-2-pentene-1,4-dione
(3c). Yellow oil; IR 2CHCl3) n 1710, 1667 2CvO), 1595
2CvC±CvO); 1H NMR 2CDCl3) d 7.91 22H, m, arom H),
7.54 21H, s,vCH±), 7.48 22H, m, arom H), 2.47 23H, s, Ac),
2.43 23H, s, Ac); 13C NMR 2CDCl3) d 202.7, 196.1, 188.7
2CvO), 152.2 2C,), 141.0, 134.4 2arom C), 130.1 22C,
4.4. Detection of the endoperoxide A
Furan 1a 20.5 mmol) was dissolved in acetonitrile 210 mL)
containing Rose Bengal 25 mg) in a quartz cell and irra-