Regiospecific Formation of Cyclic Silyl Enol Ethers
J . Org. Chem., Vol. 66, No. 26, 2001 8991
resulting mixture was partitioned between ether and water.
The organic layer was washed with brine, dried (MgSO4), and
concentrated in vacuo. The residual oil was chromatographed
with MPLC over a Lobar size B column (eluted with hexane/
ethyl acetate, 95/5) to give 2.39 g (88%) of 40 as a greenish
yellow oil: IR (neat) 1623 cm-1; 1H NMR (CDCl3, 300 MHz) δ
0.89 (s, 3 H), 1.38-1.45 (m, 1 H), 1.45-1.60 (m, 2 H), 1.66-
1.84 (m, 3 H), 3.27 (t, J ) 6.7 Hz, 2 H), 3.86 (t, J ) 7.0 Hz, 1
H), 7.03 (br d, J ) 7.0 Hz, 2 H), 7.10-7.23 (m, 3 H), 7.34-
7.48 (m, 6 H), 7.62-7.70 (m, 4 H); 13C NMR (CDCl3, 75 MHz)
δ -3.9 (q), 25.7 (t), 27.2 (t), 32.4 (t), 33.2 (t), 60.5 (d), 127.9
(d), 128.0 (d), 128.1 (d), 128.8 (d), 130.0 (d), 131.5 (s), 132.8
(s), 133.0 (d), 135.2 (d), 231.9 (s). Anal. Calcd for C25H27BrOSSi:
C, 62.10; H, 5.63. Found: C, 61.16; H, 5.61.
by gas chromatography. The yield of 50 determined this way
was 99%: tR ) 16.06 min (column temperature ) 210 °C, flow
rate ) 19 mL/min).
Ra d ica l Cycliza tion of 53. 5-Meth yl-1-(m eth yld ip h e-
n ylsiloxy)cyclop en ten e (54). Similar as the cyclization of
49, the cyclization of 53 was analyzed with gas chromatogra-
phy using tetradecane as internal standard. The yield of 54
was determine as 92%: tR ) 12.40 min (column temperature
) 220 °C, flow rate ) 18 mL/min). Characteristic 1H NMR
signals of 54: (CDCl3, 200 MHz) δ 0.70 (s, 3 H), 1.06 (d, J )
7 Hz, 3 H), 2.50-2.62 (m, 1 H), 4.43 (br s, 1 H), 7.30-7.50 (m,
6 H), 7.56-7.70 (m, 4 H).
2-Met h yl-5-[1-(m et h yld ip h en ylsilyl)-2,6-d it h ia cyclo-
h exyl]bu ta n ol (59). A mixture of 1.43 g (3.57 mmol) of 57
and 162 mg (4.28 mmol) of sodium borohydride in 6 mL of
ethanol and 1 mL of dichloromethane was stirred in an ice/
water bath for 2 h and then partitioned between ether and
water. The organic layer was washed with brine, dried
(MgSO4), and concentrated in vacuo. The residue was chro-
matographed over silica gel (eluted with hexane/ethyl acetate,
8/2) to give 1.26 g (88%) of 59 as a pale yellow oil: IR (neat)
Gen er a l P r oced u r e for th e Oxid a tion of r-P h en ylsu fe-
n yla cylsila n es. 6-Br om o-1-(m eth yld ip h en ylsilyl)-2-p h e-
n ylsu lfon yl-1-h exa n on e (41). To a mixture of 2.39 g (4.94
mmol) of 40 and 4.15 g (49.4 mmol) of sodium bicarbonate in
33 mL of dichloromethane cooled in an ice/water bath was
added 2.68 g (10.9 mmol) of MCPBA (70%). The resulting
mixture was stirred at 0 °C for 30 min, quenched by stirring
with 146 mg (0.987 mmol) of sodium thiosulfate for 5 min, and
then partitioned between dichloromethane and water. The
organic layer was dried (MgSO4) and concentrated in vacuo.
The residual oil was chromatographed with MPLC over a
Lobar size B column (eluted with hexane/ethyl acetate, 9/1 and
then 8/2) to give 2.16 g (85%) of 41 as a greenish yellow oil:
1
3622, 3482 (br) cm-1; H NMR (CDCl3, 300 MHz) δ 0.72 (d, J
) 6.6 Hz, 3 H), 0.76 (s, 3 H), 1.10-1.28 (m, 1 H), 1.30-1.52
(m, 3 H), 1.81-2.05 (m, 2 H), 2.08-2.30 (m, 2 H), 2.43 (dt, J
) 14, 4 Hz, 2 H), 2.98 (br t, J ) 14 Hz, 2 H), 3.23-3.30 (m, 2
H), 7.25-7.48 (m, 6 H), 7.79 (d, J ) 6 Hz, 4 H); 13C NMR
(CDCl3, 75 MHz) δ -3.8, 16.4, 23.9, 24.7, 30.3, 35.0, 36.0, 39.1,
67.7, 127.5, 129.7, 134.2, 135.8; HRMS calcd for C22H30OS2Si
m/z 402.1507, found 402.1507.
1
IR (neat) 1640 cm-1; H NMR (CDCl3, 300 MHz) δ 0.91 (s, 3
H), 1.07 (q, J ) 7.5 Hz, 2 H), 1.48-1.70 (m, 3 H), 1.75-1.90
(m, 1 H), 3.05-3.15 (m, 2 H), 4.66 (dd, J ) 10.3, 3.8 Hz, 1 H),
7.35-7.50 (m, 10 H), 7.55-7.65 (m, 5 H); 13C NMR (CDCl3, 75
MHz) δ -4.9 (q), 25.3 (t), 25.6 (t), 32.1 (t), 32.6 (t), 74.6 (d),
128.2 (d), 128.4 (d), 128.9 (d), 129.3 (d), 130.4 (d), 130.5 (d),
131.5 (s), 134.0 (d), 135.3 (d), 135.4 (d), 137.0 (s), 237.7 (s).
Anal. Calcd for C25H27BrO3SSi: C, 58.24; H, 5.28. Found: C,
58.10; H, 5.46.
5-B r o m o -4-m e t h y l-1-(m e t h y ld ip h e n y ls ily l)-1-p e n -
ta n on e (60). To a solution of 1.60 g (3.97 mmol) of 59 and
1.58 g (4.77 mmol) of carbon tetrabromide in 4 mL of dichlo-
romethane cooled in an ice/water bath was added over 20 min
a solution of 1.24 g (4.77 mmol) of triphenylphosphine in 5
mL of dichloromethane. The reaction mixture was stirred at
the same temperature for 2 h and then directly filtered over a
short pad of silica gel (eluted with ether). The filtrate was
concentrated in vacuo, and the residue was dissolved in 3 mL
of dry THF. This THF solution was added to a mixture of 1.72
g (7.95 mmol) of red mercury oxide, 1.72 g of Celite, and 1 mL
(7.95 mmol) of borontrifluoride etherate in aqueous THF (H2O/
THF ) 3 mL/17 mL). The resulting mixture was stirred at
room temperature for 2 h and filtered. The filtrate was
partitioned between ether and water. The organic layer was
washed with brine, dried (MgSO4), and concentrated in vacuo.
The residue was chromatographed over silica gel (eluted with
hexane/ethyl acetate, 95/5) to give 0.95 g (63%) of 60 as a
yellow oil: IR (neat) 1641 cm-1; 1H NMR (CDCl3, 300 MHz) δ
0.76 (s, 3 H), 0.89 (d, J ) 7 Hz, 3 H), 1.43 (dq, J ) 14, 7 Hz,
1 H), 1.55-1.75 (m, 2 H), 2.66 (t, J ) 7 Hz, 2 H), 3.17 (dd, J
) 9.5, 6 Hz, 2 H), 3.25 (dd, J ) 9.5, 4.5 Hz, 1 H), 7.33-7.50
(m, 6 H), 7.67 (d, J ) 7 Hz, 4 H); 13C NMR (CDCl3, 75 MHz)
δ -5.0, 18.5, 27.1, 34.5 40.7, 46.7, 128.2, 130.1, 132.6, 134.9,
243.7; HRMS calcd for C19H23BrOSi m/z 376.0702, found
376.0699.
Ra d ica l Cycliza tion of 41. Meth od (A). 1-(Meth yl-
d ip h en ylsiloxy)cycloh exen e (42). To a refluxing mixture
of 394 mg (0.763 mmol) of 41 and 642 mg (7.64 mmol) of finely
ground sodium bicarbonate in 10.2 mL of benzene was added
via syringe pump over 2 h a solution of 0.25 mL 0.916 mmol)
of tributyltin hydride and 12.5 mg (0.076 mmol) of AIBN in 5
mL of benzene. The resulting mixture was stirred at 80 °C for
another 2 h, filtered, and concentrated in vacuo. The residue
was mixed with 0.1 mL of anhydrous triethylamine and
chromatographed over silica gel (eluted with hexane) to give
109 mg (88%) of 42 as a colorless liquid: IR (neat) 1670 cm-1
;
1H NMR (CDCl3, 300 MHz) δ 0.70 (s, 3 H), 1.38-1.50 (m, 2
H), 1.55-1.65 (m, 2 H), 1.87-1.98 (m, 2 H), 1.98-2.05 (m, 2
H), 4.85-4.89 (m, 1 H), 7.30-7.42 (m, 6 H), 7.56-7.63 (m, 4
H); 13C NMR (CDCl3, 75 MHz) δ -2.5 (q), 22.2 (t), 23.1 (t),
23.8 (t), 29.8 (t), 105.1 (d), 127.8 (d), 129.8 (d), 134.3 (d), 136.3
(s), 150.2 (s). Meth od (B). To a refluxing mixture of 118 mg
(0.228 mmol) of 41 and 87.0 µL (0.273 mmol) of allyl(tributyl)-
stannane in 3.9 mL of benzene was added via syringe pump
over 1 h a solution of 7.0 µL (0.023 mmol) of tributyltin hydride
and 3.7 mg (0.023 mmol) of AIBN in 0.7 mL of benzene. The
resulting mixture was stirred at 80 °C for another 3 h and
concentrated in vacuo, and the residue was chromatographed
over silica gel (eluted with hexane) to give 53 mg (79%) of 42.
Further elution with hexane/ethyl acetate (9/1 and then 8/2)
gave 34 mg (81%) of allyl phenyl sulfone.38
Ra d ica l Cycliza tion of 62. 4-Meth yl-1-(m eth yld ip h e-
n ylsiloxy)cyclop en ten e (30). Similar to the cyclization of
49, the cyclization of 62 was analyzed with gas chromatogra-
phy using tetradecane as internal standard. The yield of 30
was determined as 85%: tR ) 10.40 min (column temperature
) 220 °C, flow rate ) 24 mL/min). Characteristic 1H NMR
signals of 30: (CDCl3, 300 MHz) δ 0.72 (s, 3 H), 0.98 (d, J )
6 Hz, 3 H), 1.78 (br d, J ) 13 Hz, 1 H), 1.89 (br d, J ) 13 Hz,
1 H), 2.20-2.50 (m, 3 H), 4.45-4.53 (m, 1 H), 7.35-7.50 (m, 4
H), 7.56-7.70 (m, 4H).
Ra d ica l Cycliza tion of 49. 1-(Meth yld ip h en ylsiloxy)-
cyclop en ten e (50). According to the procedure for the cy-
clization of 41, 200 mg (0.399 mmol) of 49 reacted with 0.13
mL (0.48 mmol) of tributyltin hydride, 6.4 mg (0.039 mmol) of
AIBN, and 0.503 g (5.98 mmol) of sodium bicarbonate.
Purification of the product through silica gel column chroma-
tography (eluted with hexane) gave 59 mg (52%) of 50 as a
Ack n ow led gm en t . Financial support by the
National Science Council of the Republic of China is
gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Characterization
data for compounds 9b,c, 10b,c, 11a ,c, 12a ,c, 14, 15, 17, 23,
48, 49, 52, 53, 56-58, 61, and 62 and copies of 1H and 13C
NMR spectra of new compounds. This material is available
colorless liquid: IR (neat) 1645 cm-1 1H NMR (CDCl3, 200
;
MHz) δ 0.75 (s, 3 H), 1.81 (quartet, J ) 5.9 Hz, 2 H), 2.16-
2.35 (m, 4 H), 4.55-4.62 (m, 1 H, vinyl CH), 7.30-7.50 (m, 6
H, ArH), 7.56-7.70 (m, 4 H, ArH). In another experiment, 2
equiv of decane was added to the reaction mixture as an
internal GC standard, and the resulting solution was analyzed
J O010883S