7454 J . Org. Chem., Vol. 66, No. 22, 2001
Manoso and DeShong
atmosphere of argon. Triethoxysilane (277 µL, 1.5 mmol) was
added, causing formation of yellow foam and a darkening of
the reaction mixture. The reaction was heated at 60 °C (12
h). The black reaction mixture was extracted with 5 × 25 mL
of pentane. The combined extracts were washed with 3 × 25
mL water to remove NMP, dried over MgSO4, filtered, and
concentrated. The resulting yellow oil was purified by bulb-
to-bulb distillation (100 °C, 0.5 Torr) to give 184 mg (68% yield)
of 4-(triethoxysilyl)anisole as a colorless oil. The IR and 1H
and 13C NMR data were identical to published spectral data.14
4-(Tr ieth oxysilyl)tolu en e: colorless oil. The IR and 1H
and 13C NMR data were identical to published spectral data.14
4-(Tr ieth oxysilyl)-1,2-(m eth ylen ed ioxy)ben zen e: color-
less oil; IR (CCl4) 2976 (s), 2926 (m), 2886 (s), 1613 (w), 1503
(w), 1487 (m), 1422 (m), 1237 (m), 1168 (m), 1080 (s), 1045
(m) cm-1; 1H NMR (CDCl3) δ 1.24 (t, J ) 6.8, 9H), 3.85 (q, J )
6.8, 6H), 5.95 (s, 2H), 6.86 (d, J ) 7.6, 1H), 7.12 (s, 1H), 7.19
(d, J ) 7.6, 1H); 13C NMR (CDCl3) δ 18.1, 59.9, 100.8, 108.8,
114.2, 123.9, 129.6, 147.6, 149.7; MS m/z 284 (100), 239 (39),
226 (28), 211 (10), 195 (14), 183 (25), 167 (18), 153 (13), 149
(24), 148 (14), 147 (75), 135 (12); HRMS for C13H20O5Si calcd
284.1080, found 284.1083.
ligand (4) is crucial. Although aryl iodides remain the
substrates of choice for silylation, an acceptable yield of
arylsiloxane may be obtained from the corresponding
bromide. This is an advantage since aryl bromides are
generally less expensive and more widely available.
The scope of the silylation protocol has been fully
defined: the synthesis of aryl and heteroaryl siloxanes
using HSi(OEt)3 and a Pd catalyst is limited generally
to electron-rich, para- and meta-substituted aryl bro-
mides and iodides. This silylation method (Scheme 3) is
an excellent companion to the more traditional organo-
metallic approach (Scheme 2). Case in point, ortho-
substituted arylsiloxanes are readily synthesized from
the Grignard or lithium reagent.15,20 Last, unlike the
metalation approach, the Pd-catalyzed silylation tech-
nique can be performed in the presence of a wide range
of functional groups, including carbonyl-containing elec-
trophiles and protic moieties such as a phenol or primary
amine.
4-(Tr ieth oxysilyl)a ceta n ilid e: colorless oil. The IR and
1H and 13C NMR data were identical to published spectral
data.14
4-(Tr ieth oxysilyl)a n ilin e: colorless oil; IR (neat) 3469 (m),
3372 (s), 3223 (w), 2974 (s), 2926 (s), 2885 (s), 1624 (s), 1601
(s), 1509 (m), 1390 (m), 1295 (m), 1166 (s), 1074 (vs) cm-1; 1H
NMR (CDCl3) δ 1.23 (t, J ) 7.0, 9H), 3.79 (s, 2H), 3.84 (q, J )
7.0, 6H), 6.67 (d, J ) 8.3, 2H), 7.46 (d, J ) 8.3, 2H); 13C NMR
(CDCl3) δ 18.3, 28.6, 114.4, 118.4, 136.3, 148.6; MS m/z 255
(100), 210 (48), 153 (11), 147 (34), 136 (9), 135 (3); HRMS for
Exp er im en ta l Section
Gen er a l Meth od s. All 1H and 13C NMR spectra were
recorded on a 400 MHz instrument in CDCl3, unless otherwise
noted. Coupling constants (J ) are given in Hz. Dimethylfor-
mamide (DMF) was distilled from molecular sieves. 1-Methyl-
2-pyrrolidinone (NMP), toluene, pyridine, and acetonitrile
(MeCN) were each distilled from calcium hydride. Tetrahy-
drofuran (THF) was distilled from sodium-benzophenone
ketyl. Glassware used in the reactions was dried overnight in
an oven at 120 °C. All reactions were performed under an
atmosphere of argon.
Bis(dibenzylideneacetone)palladium (Pd(dba)2) was pur-
chased from Acros and used as received. 2-(Di-tert-butylphos-
phino)biphenyl (P(t-Bu)2(o-biphenyl)) was purchased from
Strem Chemical Co. and recrystallized from methanol (MeOH)
prior to use. 2-(Dicyclohexylphosphino)biphenyl (P(cyh)2(o-
biphenyl)) was purchased from Strem Chemical Co. and
recrystallized from absolute ethanol (EtOH) prior to use. All
other phosphines and triphenylarsine were purchased from
Aldrich, stored under argon, and used as received. Triethoxy-
silane (HSi(OEt)3), diisopropylethylamine (i-Pr2NEt), triethyl-
amine (Et3N), potassium acetate (KOAc), cesium carbonate
(CsCO3), 2,6-lutidine, and 1,8-diazabicyclo[5.4.0]undec-7-ene
(DBU) were purchased from Aldrich, stored in a desiccator,
and used as received. N-(4-Bromophenyl)acetamide,21 2-iodo-
pyridine,22 3-iodopyridine,23 and 5-bromo-2-methoxypyridine24
were each prepared according to the literature procedure. All
other aryl halides were purchased from Aldrich and used as
received. All compounds were determined to be >95% pure
by GC and 1H NMR unless otherwise noted. CAUTION!
Triethoxysilane should be handled in a well-ventilated hood,
and proper eye protection should be worn to prevent severe
eye damage.
C
12H21O3NSi calcd 255.1291, found 255.1292.
4-Acetoxy(tr ieth oxysilyl)ben zen e: colorless oil. The IR
1
and H and 13C NMR data were identical to published spectral
data.14
4-(Tr ieth oxysilyl)p h en ol: colorless oil; IR (CCl4) 3606 (s),
3356 (vs), 2976 (s), 2926 (s), 2885 (s), 1602 (m), 1582 (w), 1506
(m), 1390 (w), 1261 (w), 1167 (m), 1125 (s), 1107 (s), 1080 (s)
cm-1; 1H NMR (CDCl3) δ 1.24 (t, J ) 7.2, 9H), 3.87 (q, J ) 7.2,
6H), 6.23 (s, 1H), 6.85 (d, J ) 8.3, 2H), 7.55 (d, J ) 8.3, 2H);
13C NMR (CDCl3) δ 18.3, 59.0, 115.4, 121.2, 137.0, 158.1; MS
m/z 256 (100), 241 (13), 220 (12), 211 (43), 210 (40), 183 (13),
167 (11), 163 (17), 155 (14), 147 (55), 119 (18); HRMS for
C
12H20O4Si calcd 256.1131, found 256.1135.
Tr ieth oxyp h en ylsila n e: colorless oil. The IR and H and
1
13C NMR data were identical to an authentic sample, as well
as published spectral data.14
4-(Tr ieth oxysilyl)a cetop h en on e: colorless oil; IR (neat)
2975 (s), 2927 (s), 2890 (s), 1728 (m), 1689 (s), 1497 (w), 1443
(m), 1390 (m), 1360 (m), 1263 (s), 1167 (s), 1079 (vs) cm-1; 1H
NMR (CDCl3) δ 1.26 (t, J ) 7.0, 9H), 2.61 (s, 3H), 3.89 (q, J )
7.0, 6H), 7.79 (d, J ) 8.0, 2H), 7.95 (d, J ) 8.0, 2H); 13C NMR
(CDCl3) δ 18.3, 26.8, 59.0, 127.4, 135.2, 137.4, 138.4, 198.5;
MS m/z 282 (8), 268 (22), 267 (100), 239 (15), 238 (67), 237
(57), 223 (16), 209 (18), 193 (13), 181 (20), 165 (19), 163 (24),
147 (16), 138 (12), 135 (9); HRMS for
282.1287, found 282.1288.
C14H22O4Si calcd
Gen er a l P r oced u r e for Syn t h esis of Siloxa n es (2).
Siloxane preparations and product isolations were performed
under identical reaction conditions, the only variable being the
reaction time and temperature as indicated in Tables 2-4. The
following example is illustrative.
4-(Tr ieth oxysilyl)a n isole. 4-Bromoanisole (126 µL, 1.00
mmol) and i-Pr2NEt (523 µL, 3.00 mmol) were added to a
stirring solution of Pd(dba)2 (17 mg, 0.03 mmol) and (t-Bu)2P-
(o-biphenyl)(4)(18 mg, 0.06 mmol) in 4 mL of NMP under an
4-Ch lor o(tr ieth oxysilyl)ben zen e: colorless oil. An au-
thentic sample was prepared in 76% isolated yield from
4-chloroiodobenzene using the general procedure for the
1
synthesis of siloxanes given above; the IR and H and 13C NMR
data were identical to published spectral data.14 By GC, the
reaction of 4-bromochlorobenzene with triethoxysilane using
the general procedure for the synthesis of siloxanes given
above yielded none of the desired product.
4-Br om o(tr ieth oxysilyl)ben zen e: colorless oil; IR (neat)
2975 (s), 2926 (s), 2887 (s), 1575 (m), 1481 (m), 1442 (m), 1390
(20) Ahn, C.; Soheili, A.; Manoso, A. S.; DeShong, P. Manuscript in
preparation.
(m), 1379 (m), 1295 (w), 1165 (s), 1073 (vs) cm-1 1H NMR
;
(21) Bjornestedt, R.; Zhong, G.; Lerner, R. A.; Barbas, C. F., III. J .
Am. Chem. Soc. 1996, 118, 11720-11724.
(22) Corcoran, R. C.; Bang, S. H. Tetrahedron Lett. 1990, 31, 6757-
6758.
(23) Coudret, C. Synth. Commun. 1996, 26, 3543-3547.
(24) Kunishima, M.; Friedman, J . E.; Rokita, S. E. J . Am. Chem.
Soc. 1999, 121, 4722-4723.
(CDCl3) δ 1.24 (t, J ) 7.2, 9H), 3.86 (q, J ) 7.2, 6H), 7.50-
7.55 (m, 4H); 13C NMR (CDCl3) δ 18.4, 59.0, 125.5, 130.1, 132.3,
136.6; MS m/z 320 (5), 318 (5), 275 (26), 273 (22), 239 (16),
231 (11), 219 (11), 217 (12), 201 (10), 195 (33), 163 (12), 162
(18), 149 (11), 148 (21), 147 (100), 137 (10), 135 (32); HRMS
for C12H19O379BrSi calcd 318.0287, found 318.0295.