Photochemically RemoVable Silyl Protecting Groups
J. Am. Chem. Soc., Vol. 123, No. 16, 2001 3643
127.46, 122.37, 121.08, 116.79, 21.07. IR (CH2Cl2, cm-1): 1772, 1468,
1428. Anal. Calcd for C13H9F3O5S: C, 46.71; H, 2.71. Found: C, 46.75;
H, 2.73.
and treated with an excess of cyanide on Amberlyst (3 mmol/g). The
solvent was poured off the beads and removed in vacuo. The resulting
oil was purified using flash chromatography on silica gel eluting with
5:95 EtOAc:hexane to give 37 mg (78%) of the desired compound as
2-(Trimethylsilylethynyl)-3-acetoxynaphthalene. To a solution of
compound 30 (4.70 g, 14.0 mmol) in 100 mL DMF was added
dichlorobis(triphenylphosphine)palladium(II) (196 mg, 0.28 mmol)
followed by triethylamine (3.90 mL, 28.0 mmol). After stirring for 5
min, trimethylsilylacetylene (2.97 mL, 21.0 mmol) was added to the
mixture. The mixture was stirred for 30 min, and the temperature was
brought to 90 °C. After stirring for 10 h, the solvent was removed in
vacuo. The residue was redissolved in diethyl ether and washed with
30 mL 1 N HCl and brine. The organic phase was dried over MgSO4,
and the solvent was removed in vacuo. The residue was purified by
flash chromatography on silica gel using ethyl acetate and hexane (9:
1) as eluent. A white solid (3.32 g, 84%) was obtained. Mp 123 °C.
1H NMR (CDCl3): δ 8.05 (1H, s), 7.78 (2H, m), 7.53 (1H, s), 7.48
(2H, m), 2.39 (3H, s), 0.29 (9H, s). 13C NMR (CDCl3): δ 160.80,
148.07, 133.57, 133.13, 130.85, 127.42, 127.25, 127.20, 126.11, 119.19,
116.14, 99.87, 99.21, 20.84, -0.06. IR (CH2Cl2, cm-1): 2962, 2355,
2161, 1766. Anal. Calcd for C17H18O2Si: C, 72.30; H, 6.42. Found:
C, 72.21; H, 6.47.
1
a clear oil. H NMR (CDCl3): δ 1.12 (12H, m), 1.20 (2H, m), 4.89
(2H, s), 5.07 (1H, s), 6.51 (1H, d, J ) 20 Hz), 7.23-7.39 (8H, m),
7.44 (1H, d, J ) 20 Hz), 7.59 (1H, d, J ) 8.4 Hz), 7.23 (1H, d, J )
8.4 Hz), 7.85 (1H, s). 13C NMR (CDCl3): δ 12.63 (CH), 17.64 (CH3),
65.39 (CH2), 110.05 (CH), 123.89 (CH), 125.28 (CH), 125.86 (CH),
126.11 (CH), 126.57 (CH), 126.97 (CH), 127.77 (C), 127.99 (CH),
128.28 (CH), 128.98 (C), 134.27 (C), 141.36 (C), 141.53 (CH), 151.35
(C). HRMS (FAB, MH+) calcd for C25H31O2Si, 391.2093; found,
391.2090.
Photolysis of 27g. 2,2-Diisopropyl-2H-1-oxa-2-sila-anthracene
(32). Compound 27g (0.07 g, 0.19 mmol) was dissolved in 14 mL
(0.013 M) of methanol and irradiated for 45 min in a Rayonet
photochemical reactor (350 nm phosphor lamps). The solvent was
removed in vacuo, and the photoproduct was isolated using flash
chromatography on silica gel eluting with 2:98 EtOAc:hexanes to give
1
35.0 mg (66%) of a clear oil. H NMR (CDCl3): δ 1.01 (14H, m),
1.12 (2H, m), 6.00 (1H, d, J ) 14.4 Hz), 7.23 (1H, s), 7.25 (1H, m),
7.34 (1H, m), 7.52 (1H, s), 7.55 (1H, d, J ) 14.4 Hz), 7.61 (1H, d, J
) 8.0 Hz), 7.68 (1H, d, J ) 8.0 Hz). 13C NMR (CDCl3): δ 13.42
(CH), 16.65 (CH3), 113.78 (CH), 121.26 (CH), 123.66 (CH), 126.20
(CH), 126.50 (CH), 127.76 (CH), 128.81 (C), 130.29 (CH), 134.61
(C), 147.44 (CH), 152.48 (C). HRMS (FAB, MH+): calcd for C18H23-
OSi, 283.1518; found, 283.1510.
2-Ethynyl-3-acetoxynaphthalene (23). To a solution of 2-(tri-
methylsilylethynyl)-3-acetoxynaphthalene (300 mg, 1.06 mmol) in 50
mL of dichloromethane was added tetrabutylammonium fluoride (1.25
mmol fluoride/g on silica gel) (4.42 g, 5.30 mmol). The mixture was
allowed to stir at room temperature for 2 h and was poured into 50 mL
of saturated aqueous ammonium chloride. The mixture was extracted
with ethyl acetate. The organic phase was dried over MgSO4, and the
solvent was removed in vacuo. The residue was purified by flash
chromatography on silica gel using ethyl acetate and hexane (9:1) as
eluent. A white solid (192 mg, 86%) identified as compound 23 was
General Procedure for the Protection of Alcohols. The alkyne
23 (108 mg, 0.51 mmol) was azeotroped from toluene and taken up in
5.0 mL diethyl ether. An aliquot (30 µL) of a prepared solution (0.10
M in 2-propanol) of hydrogen hexachloroplatinate(IV) hydrate was
added to 1.0 mL of diethyl ether, and to this solution was added chloro-
diisopropylsilane (0.20 mL, 1.17 mmol). This solution was stirred for
5 min followed by the addition of the alkyne solution. The reaction
was stirred for 10 h at room temperature, and the solvent was removed
in vacuo. The flask was refilled with nitrogen. The resulting oil was
taken up in 5 mL of tetrahydrofuran, and the solution was cooled to 0
°C. Diisopropylethylamine (0.18 mL, 1.03 mmol) and alcohol (0.46
mmol) were added to the reaction mixture. The mixture was allowed
to stir overnight. The solution was poured into ethyl acetate, washed
with brine, and dried over MgSO4. The solvent was removed in vacuo.
The residue was purified by flash chromatography on silica gel using
ethyl acetate and hexane (9:1) as eluent. This intermediate acetate (0.35
mmol) was dissolved in 4 mL of methanol and treated with an excess
of cyanide (1.40 mmol) on Amberlyst (3 mmol cyanide/g). The solvent
was poured off the beads and removed in vacuo. The residue was
purified by flash chromatography on silica gel using ethyl acetate
and hexane (7:1) as eluent. Evaporation of solvent afforded com-
pounds 27.
1
obtained. Mp 115 °C. H NMR (CDCl3): δ 8.08 (1H, s), 7.79 (2H,
m), 7.55 (1H, s), 7.48 (2H, m), 3.29 (1H, s), 2.40 (3H, s). 13C NMR
(CDCl3): δ 169.00, 148.00, 134.12, 133.29, 130.77, 127.39, 127.27,
126.21, 119.36, 115.10, 81.45, 78.87, 20.87. IR (CH2Cl2, cm-1): 3248,
2355, 1760, 1537. Anal. Calcd for C14H10O2: C, 79.98; H, 4.79.
Found: C, 79.80; H, 4.91.
Hydrosilylation of 23. 2-Acetoxy-3-[trans-diisopropyl(benzyloxy)-
silyl)vinyl] Naphthalene. The alkyne 23 (0.35 g, 1.66 mmol) was
azeotroped from acetonitrile and taken up in 6.0 mL of diethyl ether.
An aliquot (50 µL) of a prepared solution (0.10 M in 2-propanol) of
hydrogen hexachloroplatinate(IV) hydrate was added to 1.0 mL of
diethyl ether, and to this solution was added chlorodiisopropylsilane
(0.65 mL, 3.81 mmol). This solution was stirred for 5 min followed
by the addition of the alkyne solution. The reaction was stirred for 3
h at room temperature, and the solvent was removed in vacuo. The
flask was refilled with argon, the resulting oil was taken up in 5 mL of
tetrahydrofuran, and the solution was cooled in an ice bath. Diisopro-
pylethylamine (1.66 mL, 9.50 mmol) and benzyl alcohol (1.97 mL,
19.04 mmol) were added to the reaction mixture that was allowed to
stir overnight. The solution was poured into EtOAc, washed with water,
and dried over NaSO4. The desired compound was obtained following
flash chromatography on silica gel eluting with 5:95 EtOAc:hexane to
give 0.04 g of a clear oil that was slightly impure. The oil was further
purified on silica gel eluting with a gradient of 0:100 to 2:98 diethyl
General Procedure for the Deprotection of Silyl Ethers 27. The
protected alcohol (0.20 mmol) 27 was dissolved in 10 mL of methanol
and irradiated for 45 min in a Rayonet photochemical reactor (350 nm
phosphor lamps). The solvent was removed in vacuo, and the residue
was purified by flash chromatography on silica gel using ethyl acetate
and hexane (15:1) as eluent.
1
ether:pentane to give 0.40 g (58%) of a clear oil. H NMR (CDCl3):
Acknowledgment. Financial support provided by NIH GM-
46720. The assistance of L. LaBean in administrative support
of this work is greatly appreciated.
δ 1.22-1.27 (14H, m), 2.32 (3H, s), 5.01 (2H, s), 6.65 (1H, d, J )
19.5 Hz), 7.32-7.62 (9H, m), 7.87 (1H, m), 7.95 (1H, m), 8.15 (1H,
s). 13C NMR (CDCl3): δ 12.59 (CH), 17.52 (CH3), 17.46 (CH3), 20.64
(CH3), 65.23 (CH2), 119.58 (CH), 125.77 (CH), 125.92 (CH), 125.99
(CH), 126.12 (CH), 126.59 (CH), 126.92 (CH), 127.27 (CH), 127.99
(CH), 128.25 (CH), 130.48 (C), 131.66 (C), 133.40 (C), 140.65 (CH),
141.27 (C), 146.27 (C), 169.37 (C). HRMS (FAB, MH+): calcd for
C27H33O3Si, 433.2200; found, 433.2204.
Supporting Information Available: Experimental descrip-
tions and/or spectral data for 14, 15, 17-19, 20a-c, 21, 22,
24, 25, 27a-f; UV/vis spectrum of 32; 1H and 13C NMR spectra
of compound 27b-f (PDF). This material is available free of
2-Hydroxy-3-[trans-diisopropyl (benzyloxy)silyl)vinyl]naphtha-
lene (27g). 2-Acetoxy-3-[trans-diisopropyl (benzyloxy)silyl)vinyl]-
naphthalene (0.04 g, 0.10 mmol) was dissolved in 4 mL of methanol
JA002370T