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Y.-J. Chen et al. / Tetrahedron 69 (2013) 9591e9599
acetate/hexanes, 1:1) to obtain 4 (146 mg), 14 (41 mg, 23%), and
dimers 12a,b (36 mg, 20%).
28.8, 23.6, 14.7; MS (EI, 75 eV) m/z (rel intensity) 280 (Mþ, 0.2), 238
(14), 223 (2),196 (100),181 (21),167 (13),121 (8),113 (50), 93 (7), 55
(10); HRMS m/z (Mþ) calcd for C13H19O3F3 280.1286, found
280.1284.
5.9.3.1. 20-Hydroxyethyl-3-oxocyclopentanecarboxylate (14). IR
(KBr): 3415, 2945, 1728, 1398, 1198, 1080, 1028, 894 cmꢂ1; 1H NMR
(400 MHz, C6D6):
2.45 (dd, J¼18.1, 7.7 Hz, 1H), 2.15 (dd, J¼18.1, 7.7 Hz, 1H), 2.06w2.11
(m, 1H), 1.75w1.87 (m, 3H); 13C NMR (100 MHz, C6D6)
: 215.0,
174.4, 66.4, 60.8, 40.9, 40.8, 37.0, 26.5; MS (EI, 75 eV) m/z (rel in-
tensity) 172 (Mþ, 10), 144 (31), 128 (6), 111 (48), 100 (96), 84 (100),
72 (7), 55 (96); HRMS (EI) Calcd for C8H12O4:172.0736,
Found:172.0725.
d
3.59 (br s, 2H), 2.87 (br s, 1H), 2.73 (m, 1H),
5.9.8. Irradiation of 5d. Dimethoxycyclohexenone 5d (33.8 mg,
0.11 mmol) in TFE (11.3 mL) was irradiated for 1.3 h. After solvent
workup, the residue was purified in a column (hexanes/ethyl ace-
tate, 10:1) to afford a yellowish liquid 19 (11 mg, 27%).
d
5.9.8.1. 4-Methoxy-4-(20,20,20-trifluoroethoxy)-2-(tert-butyldime-
thylsiloxymethyl)-2-cyclohexenone (19). IR (neat) 2938, 1685, 1463,
1277, 1148, 1067, 1008, 972, 928, 846, 779 cmꢂ1; 1H NMR (400 MHz,
5.9.4. Irradiation of 4 in 2,2,2-trifluoroethanol (0.010 M). Under
C6D6)
d
6.98 (m, 1H), 4.60 (dd, J¼3.2, 2.0 Hz, 2H), 3.60 (qd, J¼8.8,
similar photochemical conditions, irradiation of
4
(312 mg,
0.8 Hz, 2H), 3.06 (s, 3H), 2.43e2.39 (m, 2H), 1.76e1.71 (m, 1H), 1.66
ꢂ1.61 (m, 1H), 1.02 (s, 9H), 0.10 (s, 6H); 13C NMR (100 MHz, C6D6)
2.03 mmol) in TFE (0.010 M) and separation of photoproduct in
a silica gel column (ethyl acetate/hexane, 2:1) afforded 14 (273 mg,
78%) as the sole product.
d
196.0, 140.4, 138.2, 122.8, 97.8, 59.5, 58.9, 48.5, 34.3, 31.3, 25.6,
25.5, 25.4, 18.0, ꢂ6.0; MS (EI) m/z (%) 368 (Mþ, 1), 337 (9), 311 (69),
279 (12), 249 (22), 211 (12), 197 (15), 181 (20), 169 (31), 155(7), 137
(7),109 (8), 73 (27), 57 (100); HRMS m/z (Mþ) calcd for C15H27O4F3Si
368.1631, found 368.1634.
5.9.4.1. Ethyl-3-oxocyclopentanecarboxylate (15). A solution of
14 (240 mg, 1.39 mmol) and K2CO3 (20 mg, 0.14 mmol) in ethanol
(14 mL) was stirred at 42 ꢁC for 3 h, after which the solution was
quenched with HCl (0.30 M) and extracted with ethyl acetate
several times; the organic layer was collected, washed with sat-
urated NaCl, dried (MgSO4), concentrated under reduced pressure,
and chromatographed in silica gel column (ethyl acetate/hexanes,
2:3) to afford a colorless oil 15 (173 mg, 79%). IR (KBr): 2974, 1737,
5.9.9. Irradiation of 6a. A solution of 6a (110.4 mg, 0.99 mmol) in
TFE (100 mL) was irradiated for 40 h. After solvent workup, the
crude photoproduct was separated in a silica gel column (hex-
anes/ethyl acetate, 2:1) to afford a colorless liquid 2028 (87.9 mg,
80%).
1462, 1405, 1375, 1199, 1158, 1031 cmꢂ1 1H NMR (400 MHz,
;
CDCl3):
d
4.05 (q, J¼7.2 Hz, 2H), 3.03 (quintet, J¼7.9 Hz, 1H),
5.9.10. Irradiation of 6b. Cyclohexenone 6b (105.5 mg, 0.84 mmol)
in TFE (84 mL) was irradiated for 52 h to furnish a colorless liquid
2114 (74.6 mg, 80%) and recover a small amount of 6b (15.0 mg,
14%).
1.98w2.42 (m, 6H), 1.16 (t, J¼7.2 Hz, 3H); 13C NMR (100 MHz,
CDCl3)
d: 216.4, 174.0, 60.7, 40.9, 40.7, 37.1, 26.3, 13.9; MS (EI,
75 eV) m/z (rel intensity) 156 (Mþ, 13), 128 (66), 111 (27), 100 (58),
83 (67), 73 (9), 55 (100), 45 (5).
5.9.11. Irradiation of 6c. Cyclohexenone 6c (109.8 mg, 0.49 mmol)
in trifluoroethanol (49 mL) was irradiated for 32 h to afford a col-
orless liquid stereoisomers 22a,b (79.4 mg, 53%).
5.9.5. Irradiation of 5a. Vinyl ketone 5a (170.1 mg, 0.93 mmol) in
TFE (93 mL) was irradiated for 16 h to furnish a colorless liquid 16
(142.7 mg, 90%) and recover a small amount of 5a (10.8 mg, 6%). IR
(neat) 2964, 1727, 1453, 1328, 1223, 1128, 1076, 1032, 924 cmꢂ1; 1H
5.9.11.1. 3-[{[1-(tert-Butyl)-1,1-dimethylsily]oxy}(2,2,2-
NMR (400 MHz, C6D6)
d
3.06 (s, 3H), 3.09e3.00 (m, 1H), 2.96 (s, 3H),
trifluoroethoxy)methyl]-1-cyclopentanones (22a). IR (neat) 2946,
2.78 (apparent q, J¼5.6 Hz, 1H), 2.68e2.65 (m, 1H), 2.60 (dd, J¼8.2,
2860, 1745, 1405, 1278, 1162, 1071, 1002, 839, 780 cmꢂ1 1H NMR
;
3.0 Hz, 2H), 2.55e2.50 (m, 1H), 2.26 (ddd, J¼11.1, 7.2, 5.2 Hz, 1H),
(400 MHz, CDCl3)
d
4.87 (d, J¼4.7 Hz, 1H), 3.92e3.72 (m, 2H),
1.60 (d, J¼11.1 Hz, 1H); 13C NMR (100 MHz, C6D6)
d
208.9, 102.9,
2.46e2.42 (m, 1H) 2.38e2.30 (m, 1H), 2.24 (d, J¼8.1 Hz, 2H),
2.18e2.03 (m, 2H), 1.85e1.79 (m, 1H), 0.89 (s, 9H), 0.13 (s, 3H), 0.10
49.9, 49.6, 49.5, 47.6, 38.4, 36.3, 32.7, 27.1; MS (EI, 75 eV) m/z (rel
intensity) 182 (Mþ, 3), 154 (34), 139 (19), 128 (8), 123 (40), 107 (13),
101 (100), 88 (46), 79 (35), 75 (3); HRMS m/z (Mþ) calcd for
(s, 3H); 13C NMR (100 MHz, CDCl3)
d 218.4, 124.0, 100.2, 63.0, 42.2,
39.0, 37.6, 25.6, 24.3, 18.0, ꢂ4.5, ꢂ4.6; MS (EI) m/z (%) 325 (Mþꢂ1,
0.4), 269 (43), 243 (13), 227 (15), 169 (36) 157 (7), 115 (16), 113 (25),
95 (15), 77 (100), 67 (58), 57 (31); HRMS m/z (Mþ) calcd for
C
10H14O3 182.0942, found 182.0945.
5.9.6. Irradiation of 5b. Dimethyldimethoxy cyclohexenone 5b
(45.1 mg, 0.25 mmol) in TFE (25 mL) was irradiated for 1.6 h. After
solvent workup, the residue was purified in a column (hexanes/
ethyl acetate, 8:1) to furnish a white solid 1713 (16.9 mg, 45%).
C
14H25O3F3Si 326.1526, found 326.1530.
5.9.11.2. 3-[{[1-(tert-Butyl)-1,1-dimethylsily]oxy}(2,2,2-
trifluoroethoxy)methyl]-1-cyclopentanones (22b). IR (neat) 2946,
2860, 1745, 1468, 1407, 1276, 1071, 1158, 1002, 841, 780 cmꢂ1 1H
NMR (400 MHz, CDCl3)
;
5.9.7. Irradiation of 5c. Butyldimethoxy cyclohexenone 5c
(123.4 mg, 0.l58 mmol) in TFE (58 mL) was irradiated for 27 h. After
removing the solvent in a rotavap, the residue was purified in
a column (hexanes/ethyl acetate, 15:1) to afford a colorless liquid 18
(51.1 mg, 26%).
d
4.85 (d, J¼4.9 Hz, 1H), 3.92e3.75 (m, 2H),
2.46e2.43 (m, 1H), 2.31e2.25 (m, 2H), 2.16e2.03 (m, 3H), 1.95e1.88
(m, 1H), 0.89 (s, 9H), 0.12 (s, 3H), 0.11 (s, 3H); 13C NMR (100 MHz,
CDCl3)
d 218.3, 124.0, 100.1, 63.0, 42.1, 40.2, 37.7, 25.5, 23.2, 17.9,
ꢂ4.6, ꢂ4.7; MS (EI) m/z (%) 325 (Mþꢂ1, 3), 309 (51), 269(100), 249
(8), 227 (13) 193 (6), 171 (7), 127 (6), 113 (21), 95 (12), 67 (51), 55
(19); HRMS m/z (Mþ) calcd for C14H25O3F3Si 326.1526, found
326.1530.
5.9.7.1. 5-n-Butyl-4-methoxy-4-(20,20,20-trifluoroethoxy)-2-
cyclohexenone (18). IR (neat) 2943, 1691, 1462, 1417, 1383, 1281,
1165, 1124, 1071, 968 cmꢂ1 1H NMR (400 MHz, C6D6)
; d 6.00 (dd,
J¼10.4, 2.0 Hz, 1H), 5.90 (dd, J¼10.4, 0.8 Hz, 1H), 3.57e3.48 (m, 1H),
3.37e3.28 (m, 1H), 2.95 (s, 3H), 2.75 (ddd, J¼17.2, 4.6, 1.6 Hz, 1H),
2.49 (ddd, J¼17.2, 3.2, 1.2 Hz, 1H), 2.06e2.03 (m, 1H), 1.45e1.40 (m,
1 H) 1.32e0.92 (m, 5H), 0.86 (t, J¼7.2 Hz, 3H); 13C NMR (100 MHz,
5.9.12. Transformation of 22a,b to 20. To a solution of 22a,b
(32.2 mg, 0.10 mmol) in MeCN (0.8 mL) was added 48% HF (0.2 mL)
at room temperature. The reaction mixture was stirred for 1 h and
then quenched with water (1 mL). The solution was extracted with
CHCl3 (3.0 mLꢀ3) and the organic layer collected, worked up, and
C6D6)
d 197.3, 144.2, 132.8, 125.4, 100.8, 61.0, 48.5, 41.5, 39.5, 30.2,