Kabanyane et al.
273
that no excess diazomethane remained, and the solution was
then washed successively with saturated NaHCO3 solution
and brine. It was then dried over MgSO4 and the amorphous
material remaining after removal of solvent in vacuo was
purified by flash chromatography on a column of silica gel
(hexane:EtOAc, 5:1), affording the pure cyclopentanone, 7
(2.04 g, 98%) as fine crystals, mp 101–103°C; IR (CHCl3)
νmax: 2989, 1780, 1750, 900, and 750 cm–1; 1H NMR
(400 MHz, CDCl3) δ: 3.84 (3H, s), 3.10–3.00 (1H, m), 2.75
(1H, dd, J = 18.9 and 8.9 Hz), 2.05 (1H, dd, J = 19.0 and
11.1 Hz), 1.60–1.20 (4H, m), 0.90 (3H, t, J = 7.4 Hz) and
0.25 (9H, s); 13C NMR δ: 198.7, 167.9, 87.2, 87.0, 52.5,
38.9, 36.4, 32.5, 20.7, 14.1, and 1.6; HREIMS m/z (ion):
340.0665, M+, (calcd. for C13H22O4Si35Cl2: 340.0664).
enol ether, 9, (1.00 g, 2.43 mmol) in dichloromethane
(20 mL) was gradually added from a dropping funnel over a
1 h period. The reaction mixture was stirred at –78°C for 4 h
and was then allowed to warm up to ambient temperature. A
cold saturated solution of NH4Cl (30 mL) was added and the
mixture was extracted with ether (3 × 50 mL). The extracts
were washed with brine, dried (MgSO4), and evaporated to
dryness in vacuo. The residue was purified by flash chroma-
tography on a column of silica gel (hexane:EtOAc, 10:1)
furnishing the allylic phenyl selenide (980 mg, 82%) as a
pale yellow oil; IR (film) νmax: 2959, 1740, 1738, 1520, and
1
840 cm–1; H NMR (400 MHz, CDCl3) δ: 7.4 (5H, m), 5.72
(1H, s), 3.66 (3H, s), 3.58 (1H, t, J = 6.7 Hz) 1.90–1.70
(2H, m), 0.90 (3H, t, J = 7.0 Hz), and 0.36 (9H, s); LREIMS
m/z (relative intensity) (ion): 492 (8) (M+), 477 (16)
(M–CH3)+, 434 (3) (MH–CO2CH3)+, 336 (23) (M–PhSe)+,
322 (47), 294 (41) (M–C3H6PhSe)+, 278 (100), 156 (37)
(PhSe)+, 93 (33), 89 (25), (OSiMe3)+,73 (82) (SiMe3)+.
The γ-phenyl selenide product (500 mg, 1.01 mmol) was
dissolved in dry THF (10 mL). To the resulting solution,
cooled to 0°C, was added 30% H2O2 solution (0.9 mL,
~7.9 mmol) and the mixture was set aside at 0°C with stir-
ring for 2 h. The reaction mixture was then diluted by addi-
tion of ether (20 mL), and the solution was washed with
saturated NaHCO3 solution (2 × ~20 mL), dried (MgSO4),
and evaporated to dryness under reduced pressure. The resi-
due was purified by chromatography on a column of silica
gel (hexane:EtOAc, 10:1), furnishing the pure dienone, 10
(202 mg, 60%) as a pale yellow oil; IR (film) νmax: 3440,
2954, 1740, 1738, 1600, 1200, and 956 cm–1; UV λmax
Methyl 5,5-dichloro-4-oxo-2-n-propyl-1-trimethylsilyloxy-
cyclopent-2-ene carboxylate, 8: A mixture of cyclopentanone
(7) (1.0 g, 2.93 mmol) and selenium dioxide (467 mg,
4.21 mmol) in toluene was heated under reflux in an atmo-
sphere of argon for 12 h. The reaction mixture was allowed
to attain room temperature, and was then diluted by addition
of hexane (50 mL) and filtered through Celite. The filtrate
was evaporated to dryness in vacuo, and the residue was pu-
rified by chromatography on a column of silica gel (hex-
ane:EtOAc, 10:1), affording cyclopentenone 8 (767 mg,
77%) as a pale yellow oil; IR (film) νmax: 2960, 1755, 1743,
and 851 cm–1; UV λmax (EtOH): 246 nm (⑀ = 10,900);
1H NMR (400 MHz, CDCl3) δ: 6.20 (1H, t, J = 1.5 Hz),
3.76 (3H, s), 2.25 (2H, ddd, J = 5.4, 7.3, and 16.5 Hz), 1.55
(2H, dt, J = 7.3 and 16.8 Hz), 0.98 (3H, t, J = 7.4 Hz) and
0.30 (9H, s); 13C NMR δ: 189.9, 175.5, 168.8, 125.3, 124.9,
87.7, 53.4, 30.8, 19.8, 13.6, and 2.1; HREIMS m/z (ion):
323.0281, (M–CH3)+, (calcd for C12H17O4Si35Cl2: 323.0273).
1
(EtOH): 282 nm (⑀ = 16,800); H NMR (400 MHz, CDCl3)
δ: 6.65 (1H, dt, J = 6.9 and 16.0 Hz), 6.30 (1H, s), 6.28 (1H,
d, J = 15.8 Hz), 3.68 (3H, s), 1.90 (3H, d, J = 6.8 Hz), and
0.34 (9H, s); 13C NMR δ: 189.8, 169.1, 165.9, 142.2, 123.2,
122.8, 89.6, 88.2, 53.5, 19.7, and 1.8; LREIMS m/z (relative
intensity) (ion): 336 (8) (M+), 320 (39) (M–CH3-H)+, 278
(75) (MH-CO2CH3)+, 276 (79) (M–CO2CH3-H)+, 242 (25)
(C7H12O3Si35Cl2), 149 (100), 73 (82) (SiMe3)+.
Preparation of silyl enol ether, 9: A solution of cyclopen-
tenone, 8 (1.01 g, 2.98 mmol) and chlorotrimethylsilane
(0.5 mL, 428 mg, 3.94 mmol) in dry tetrahydrofuran
(10 mL) was added dropwise to a mixture of dry
triethylamine (0.6 mL, 4.30 mmol) and sodium hydride (cf.
17) (7.2 mg, 0.30 mmol) in tetrahydrofuran (20 mL). The
mixture was set aside with stirring at ambient temperature
under an argon atmosphere for 30 min, and was then heated
under reflux for 15 h. The reaction mixture was allowed to
attain room temperature and was then diluted by addition of
ether (100 mL) and filtered through Celite. The filtrate was
washed successively with cold 5% HCl solution, saturated
NaHCO3 solution, and brine and then dried over MgSO4.
The solvent was removed under reduced pressure to yield
the silyl enol ether, 9 (1.09 g, 89%) sufficiently pure to be
Methyl 5-chloro-4-oxo-2-propenyl-1-trimethylsilyloxy-cyclopent-
2-ene carboxylate, 11: The dienone 10 (300 mg, 0.99 mmol)
was dissolved in 1:1 acetic acid-water (20 mL). Zinc powder
(57 mg, 0.87 mg-atom) was added in one portion and the
mixture was set aside with stirring at ambient temperature
for 10 min. It was then diluted by addition of water (50 mL)
and the mixture was extracted with ether (3 × 50 mL). The
extracts were washed with saturated NaHCO3 solution (3 ×
~25 mL) and brine and then dried (MgSO4) and evaporated
to dryness under reduced pressure. The residue was purified
by chromatography on a column of silica gel (hex-
ane:EtOAc, 10:1), affording methyl 5-chloro-4-oxo-2-
propenyl-1-trimethylsilyloxy-cyclopent-2-ene carboxylate,
11, as a single epimer (183 mg, 68%); IR (film) νmax: 2958,
used directly for the subsequent reaction; IR (film) νmax
:
2936, 1742, and 1225 cm–1; H NMR (400 MHz, CDCl3) δ:
5.58 (1H, s), 5.20 (1H, t, J = 3.9Hz), 3.65 (3H, s), 2.10–2.00
(2H, m), 0.95 (3H, t, J = 7.0 Hz), 0.35 (9H, s), and 0.31
(9H, s); LREIMS m/z (relative intensity) (ion): 339 (6)
(M–35Cl–H35Cl)+, 321 (5) (M–OSiMe3)+, 295 (16), 279 (11),
205 (21), 89 (33) (OSiMe3)+, 73 (100) (SiMe3)+, 59 (21)
(CO2CH3)+.
1
1
2878, 1762, 1750, 1620, and 844 cm–1; H NMR (400 MHz,
CDCl3) δ: 6.80–6.60 (1H, m), 6.27 (1H, s), 6.20 (1H, d, J =
1.6 Hz), 4.45 (1H, s), 3.80 (3H, s), 1.95 (3H, dd, J = 1.6 and
5.9 Hz), and 0.24 (9H, s); 13C NMR δ: 194.5, 169.5, 167.6,
141.5, 126.1, 123.4, 67.7, 67.5, 53.0, 19.6, and 1.0;
LREIMS m/z (relative intensity) (ion): 303 (3) (MH+), 287
(17) (M–CH3)+, 259 (6) (M–C3H7)+, 243 (31) (M–CO2CH3)+,
73 (100) (SiMe3)+.
Preparation of dienone, 10: To a solution of phenylselenenyl
chloride (464 mg, 2.42 mmol) in dichloromethane (10 mL),
cooled to –10°C, was added 1 M TiCl4 (2.5 mL, 2.5 mmol).
The mixture was cooled to to –78°C and a solution of silyl
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