Synthesis of silylboronic esters functionalized on silicon

Article abstract of DOI:10.1021/om0609867

New silylpinacolboranes bearing chloro, fluoro, alkoxy, and dialkylamino groups on silicon were synthesized in high yields via derivatization of[(diethylamino)diphenylsilyl]pinacolborane, which was prepared by reaction of [(diethylamino)diphenvlsilyl]lithium with (isopropoxy)pinacolborane, and (chlorodimethylsilyl)pinacolborane, prepared by reaction of (dimethylphenylsilyl)pinacolborane with hydrogen chloride in the presence of a catalytic amount of aluminum chloride.

Full text of DOI:10.1021/om0609867

Organometallics 2007, 26, 1291-1294
1291
Notes
Synthesis of Silylboronic Esters Functionalized on Silicon
Toshimichi Ohmura, Kohei Masuda, Hideki Furukawa, and Michinori Suginome*
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering,
Kyoto UniVersity, Katsura, Kyoto 615-8510, Japan
ReceiVed October 25, 2006
Summary: New silylpinacolboranes bearing chloro, fluoro,
alkoxy, and dialkylamino groups on silicon were synthesized
in high yields Via deriVatization of [(diethylamino)diphenylsilyl]-
pinacolborane, which was prepared by reaction of [(diethyl-
amino)diphenylsilyl]lithium with (isopropoxy)pinacolborane,
and (chlorodimethylsilyl)pinacolborane, prepared by reaction
of (dimethylphenylsilyl)pinacolborane with hydrogen chloride
in the presence of a catalytic amount of aluminum chloride.
offering convenient access to organometallic compounds con-
taining both boryl and silyl groups in regio- and stereodefined
manners. Silaboration reactions that are accompanied by either
C-C bond formation or cleavage have also been developed,
providing new access to boron- and silicon-containing organic
2b,4a,6,7
compounds with rather complex structures.
Recent studies
also revealed that those catalytic reactions can be successfully
applied to catalytic asymmetric synthesis, leading to new
4c,5d,f,g,8
enantioenriched organoboron compounds.
Even with no
Introduction
transition metal catalysts, silylboranes exhibit interesting reac-
9
tivities. Noncatalytic insertion reactions of isocyanides and
In recent years, silylboranes have received much attention in
organic and organometallic chemistry. Extensive studies on
silaboration of unsaturated organic molecules using transition
10
carbenoids to the Si-B bond have provided new routes to
organoboron compounds that are otherwise difficult to synthe-
size. Silylboranes have also been utilized for the generation of
1
metal catalysts have been reported. Group 10 transition metal
11
12
13
silyl anions, silyl radicals, and borylenes. Further research
efforts have been focused on their physical properties, including
complexes have been established as efficient catalysts for
2
3
4
5
silaboration of alkynes, alkenes, 1,3-dienes, and allenes,
14
absorption and fluorescence emission in the visible region.
In the course of our study on silaboration, we were interested
in silylboranes bearing heteroatom substituents on silicon. Our
major concern was enhancement of reactivity, which may allow
us not only to make the existing reactions proceed more
efficiently and selectively but also to find new reaction systems,
including intramolecular reactions, in which reacting groups are
*
(
Corresponding author. E-mail: suginome@sbchem.kyoto-u.ac.jp.
1) For reviews, see: (a) Beletskaya, I.; Moberg, C. Chem. ReV. 1999,
9, 3435. (b) Han, L.-B.; Tanaka, M. Chem. Commun. 1999, 395. (c)
9
Suginome, M.; Ito, Y. Chem. ReV. 2000, 100, 3221. (d) Suginome, M.; Ito,
Y. J. Organomet. Chem. 2003, 680, 43. (e) Beletskaya, I.; Moberg, C. Chem.
ReV. 2006, 106, 2320.
(2) (a) Suginome, M.; Nakamura, H.; Ito, Y. Chem. Commun. 1996, 2777.
3
b
(
(
5
b) Onozawa, S.-y.; Hatanaka, Y.; Tanaka, M. Chem. Commun. 1997, 1229.
c) Suginome, M.; Matsuda, T.; Nakamura, H.; Ito, Y. Tetrahedron 1999,
5, 8787. (d) Da Silva, J. C. A.; Birot, M.; Pillot, J.-P.; P e´ traud, M. J.
Organomet. Chem. 2002, 646, 179. (e) Suginome, M.; Noguchi, H.; Hasui,
T.; Murakami, M. Bull. Chem. Soc. Jpn. 2005, 78, 323.
introduced to the silicon atom. Such reactivity enhancement
by introduction of heterosubstituents on silicon is reasonably
expected from observations in catalytic hydrosilylation.15 How-
ever, synthetic accessibility of silylboranes has not been fully
(3) (a) Suginome, M.; Nakamura, H.; Ito, Y. Angew. Chem., Int. Ed.
16
exploited, resulting in the lack of a practical method for the
Engl. 1997, 36, 2516. (b) Ohmura, T.; Furukawa, H.; Suginome, M. J. Am.
Chem. Soc. 2006, 128, 13366.
synthesis of silylboranes functionalized on silicon. Although
silylboranes having various functional groups on the boron atom
suchaschloro,amino,andalkoxygroupshavebeenprepared,2
(4) (a) Suginome, M.; Nakamura, H.; Matsuda, T.; Ito, Y. J. Am. Chem.
c,5d,16c,d,f,g
Soc. 1998, 120, 4248. (b) Suginome, M.; Matsuda, T.; Yoshimoto, T.; Ito,
Y. Org. Lett. 1999, 1, 1567. (c) Gerdin, M.; Moberg, C. AdV. Synth. Catal.
005, 347, 749.
the silyl groups are limited to triorganosilyl groups such as
2
(
5) (a) Suginome, M.; Ohmori, Y.; Ito, Y. Synlett 1999, 1567. (b)
Onozawa, S.; Hatanaka, Y.; Tanaka, M. Chem. Commun. 1999, 1863. (c)
Suginome, M.; Ohmori, Y.; Ito, Y. J. Organomet. Chem. 2000, 611, 403.
d) Suginome, M.; Ohmura, T.; Miyake, Y.; Mitani, S.; Ito, Y.; Murakami,
M. J. Am. Chem. Soc. 2003, 125, 11174. (e) Chang, K.-J.; Rayabarapu,
D.-K.; Yang, F.-Y.; Cheng, C.-H. J. Am. Chem. Soc. 2004, 127, 126. (f)
Ohmura, T.; Suginome, M. Org. Lett. 2006, 8, 2503. (g) Ohmura, T.;
Taniguchi, H.; Suginome, M. J. Am. Chem. Soc. 2006, 128, 13682.
(10) (a) Hata, T.; Kitagawa, H.; Masai, H.; Kurahashi, T.; Shimizu, M.;
Hiyama, T. Angew. Chem., Int. Ed. 2001, 40, 790. (b) Shimizu, M.;
Kitagawa, H.; Kurahashi, T.; Hiyama, T. Angew. Chem., Int. Ed. 2001, 40,
4283. (c) Kurahashi, T.; Hata, T.; Masai, H.; Kitagawa, H.; Shimizu, M.;
Hiyama, T. Tetrahedron 2002, 58, 6381. (d) Shimizu, M.; Kurahashi, T.;
Kitagawa, H.; Hiyama, T. Org. Lett. 2003, 5, 225. (e) Shimizu, M.;
Kurahashi, T.; Kitagawa, H.; Shimono, K.; Hiyama, T. J. Organomet. Chem.
2003, 686, 286. (f) Murakami, M.; Usui, I.; Hasegawa, M.; Matsuda, T. J.
Am. Chem. Soc. 2005, 127, 1366.
(
(
(
6) Suginome, M.; Matsuda, T.; Ito, Y. Organometallics 1998, 17, 5233.
7) (a) Suginome, M.; Matsuda, T.; Ito, Y. J. Am. Chem. Soc. 2000, 122,
1
1015. (b) Suginome, M.; Matsuda, T.; Yoshimoto, T.; Ito, Y. Organo-
metallics 2002, 21, 1537. (c) Pohlman, T.; de Meijere, A. Org. Lett. 2000,
, 3877.
(11) (a) Kawachi, A.; Minamimoto, T.; Tamao, K. Chem. Lett. 2001,
1216. (b) Kajiwara, T.; Takeda, N.; Sasamori, T.; Tokitoh, N. Chem.
Commun. 2004, 2218.
2
(
8) Rh-catalyzed asymmetric 1,4-addition of silylborane to R,â-unsatur-
(12) Matsumoto, A.; Ito, Y. J. Org. Chem. 2000, 65, 5707.
(13) Pachaly, B.; West, R. Angew. Chem., Int. Ed. Engl. 1984, 23, 454.
(14) Pillot, J.-P.; Birot, M.; Bonnefon, E.; Dunogu e` s, J.; Rayez, J.-C.;
Rayez, M.-T.; Liotard, D.; Desvergne, J.-P. Chem. Commun. 1997, 1535.
(15) For examples: (a) Kiso, Y.; Kumada, M.; Tamao, K.; Umeno, M.
J. Organomet. Chem. 1973, 50, 297. (b) Tsuji, J.; Hara, M.; Ohno, K.
Tetrahedron 1974, 30, 2143.
ated ketones and esters giving enantioenriched â-silyl ketones and esters,
see: Walter, C.; Auer, G.; Oestreich, M. Angew. Chem., Int. Ed. 2006, 45,
675.
(
19. (b) Suginome, M.; Fukuda, T.; Ito, Y. J. Organomet. Chem. 2002,
43-644, 508.
5
9) (a) Suginome, M.; Fukuda, T.; Ito, Y. Organometallics 2000, 19,
7
6
1
0.1021/om0609867 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 01/27/2007

1
292 Organometallics, Vol. 26, No. 5, 2007
Notes
trimethylsilyl and dimethylphenylsilyl groups. Some silylboranes
having heteroatom functional groups have been prepared with
very bulky groups on the silicon atoms, which made it difficult
to utilize them for synthetic applications.16m The lack of practical
methods for the synthesis of silylboranes that are functionalized
on the silicon atom prompted us to establish new synthetic routes
to produce them. Herein, we describe a high-yield synthesis of
silylboronic esters 1 bearing heteroatom substituents on silicon
via derivatization of [(diethylamino)diphenylsilyl]pinacolborane,
which was prepared by reaction of [(diethylamino)diphenylsilyl]-
lithium with (isopropoxy)pinacolborane, and (chlorodimethyl-
silyl)pinacolborane, prepared by reaction of (dimethylphenylsilyl)-
pinacolborane with hydrogen chloride in the presence of a
The amino group of silylboronic ester 4 could be converted
into a chloro group by the reaction with acetyl chloride or
hydrogen chloride. Use of the latter was found to be practical,
because in the former case removal of N,N-diethyl acetamide
by distillation was not trivial. Pure 5 was isolated in 94% yield
by filtration followed by distillation, when using hydrogen
chloride (eq 2).
17
catalytic amount of aluminum chloride.
Results and Discussion
Synthesis of XMe2Si-B(pin) (X ) Cl, F, RO, R2N). The
reaction of [(dialkylamino)diphenylsilyl]lithium with boron
electrophiles described above cannot be applied to the synthesis
of the corresponding dimethylsilyl derivatives, because genera-
tion of [(dialkylamino)dimethylsilyl]lithium is not possible by
reductive metalation. We found that reaction of (dimethylphe-
Synthesis of XPh2Si-B(pin) (X ) Et2N, Cl). Our first
approach to the silylboranes having heteroatom substituents on
silicon was a reaction of boron electrophiles with silyllithium
that carries a dialkylamino group. Following the Si-B bond
formation, the amino groups on the silicon and boron atoms
could be substituted selectively by other functional groups. We
initially tried a reaction of [(diethylamino)diphenylsilyl]lithium
1
6i
nylsilyl)pinacolborane (6) with dry hydrogen chloride in the
presence of a catalytic amount (10 mol %) of aluminum chloride
afforded (chlorodimethylsilyl)pinacolborane (7), which is suit-
able for introduction of functional groups on the silicon atoms
18
(2) with bis(diethylamino)chloroborane and obtained the
corresponding silylborane, which bore three amino groups on
both the boron and silicon atoms. However, attempts using diols
or acetyl chloride for selective substitution of the silicon- or
boron-bound diethylamino groups all failed. We then focused
on the direct preparation of [(dialkylamino)silyl]pinacolborane
by the reaction of [(dialkylamino)silyl]lithiums with 2 equiv of
alkoxypinacolborane.1
2
0
(
eq 3). It should be remarked that the chlorodephenylation
occurred smoothly without cleavage of the Si-B bond, giving
in good yield by distillation. No reaction took place in the
7
absence of aluminum chloride.
6i
Silyllithium 2 was reacted with 2.4 equiv of (isopropoxy)-
1
9
pinacolborane (3) in THF at 0 °C to room temperature (eq 1).
The reaction proceeded cleanly to give [(diethylamino)diphe-
nylsilyl]pinacolborane (4) in 95% yield. Pinacolborane [HB-
(
pin)] could also be used as a boron electrophile for this
16i
reaction.
With the (chlorosilyl)borane 7 in hand, silylboronic esters
bearing other heteroatom substituents on silicon were prepared.
Fluorination of 7 was successfully achieved with SbF3 under
solvent-free conditions to afford (fluorodimethylsilyl)pinacol-
(
16) Reactions of silyl anions with boron electrophiles, see: (a) Seyferth,
D.; K o¨ gler, H. P. J. Inorg. Nucl. Chem. 1960, 15, 99. (b) Cowley, A. H.;
Sisler, H. H.; Ryschkewitsch, G. E. J. Am. Chem. Soc. 1960, 82, 501. (c)
N o¨ th, H.; H o¨ llerer, G. Angew. Chem., Int. Ed. Engl. 1962, 1, 551. (d) N o¨ th,
H.; H o¨ llerer, G. Chem. Ber. 1966, 99, 2197. (e) Biffar, W.; N o¨ th, H.;
Pommerening, H. Angew. Chem., Int. Ed. Engl. 1980, 19, 56. (f) Biffar,
W.; N o¨ th, H.; Schwerth o¨ ffer, R. Liebigs Ann. Chem. 1981, 2067. (g) Buynak,
J. D.; Geng, B. Organometallics 1995, 14, 3112. (h) Bonnefon, E.; Birot,
M.; Dunogu e` s, J.; Pillot, J.-P.; Courseille, C.; Taulelle, F. Main Group Metal
Chem. 1996, 19, 761. (i) Suginome, M.; Matsuda, T.; Ito, Y. Organome-
tallics 2000, 19, 4647. Wurtz type reductive coupling of Si-Cl with B-Cl,
see: (j) Blumenthal, A.; Bissinger, P.; Schmidbaur, H. J. Organomet. Chem.
2
1
borane (8) in 76% yield (eq 4).
1
993, 462, 107. See also refs 2e, 16c, and 16e. Insertion of silylene to
The reactions of 7 with alcohols proceeded cleanly in the
presence of pyridine in CH2Cl2 (eq 5). Under these conditions,
(alkoxysilyl)boranes 9a-d having methoxy, ethoxy, isopropoxy,
and tert-butoxy groups were synthesized in good yields (76-
0%).
Amination of 7 was achieved by the reaction with secondary
amines in the presence of triethylamine (eq 6). The reactions
of diethylamine, dimethylamine, and pyrrolidine gave the
corresponding (aminosilyl)boranes 10a-c in high yields (71-
boron containing a σ-bond such as B-C, B-H, B-B, and B-X (X ) Cl,
I), see: (k) Metzler, N.; Denk, M. Chem. Commun. 1996, 2657. (l) Takeda,
N.; Kajiwara, T.; Tokitoh, N. Chem. Lett. 2001, 1076. (m) Kajiwara, T.;
Takeda, N.; Sasamori, T.; Tokitoh, N. Organometallics 2004, 23, 4723.
See also ref. 11b. Transition metal-mediated coupling reactions, see: (n)
Jiang, Q.; Carroll, P. J.; Berry, D. H. Organometallics 1993, 12, 177. (o)
Lesley, G.; Nguyen, P.; Taylor, N. J.; Marder, T. B.; Scott, A. J.; Clegg,
W.; Norman, N. C. Organometallics 1996, 15, 5137.
9
(17) Synthesis of 4 and 5 and their transformation to borylsilanyl
homoallyl ethers has been described briefly in the Supporting Information
for ref 3b.
(
(
18) Tamao, K.; Kawachi, A.; Ito, Y. J. Am. Chem. Soc. 1992, 114, 3989.
19) Hoffmann, R. W.; Metternich, R.; Lanz, J. W. Liebigs Ann. Chem.
(20) Tamao, K.; Kumada, M. J. Organomet. Chem. 1971, 30, 339.
(21) Damrauer, R.; Danahey, S. E. Organometallics 1986, 5, 1490.
1
987, 881.

Notes
Organometallics, Vol. 26, No. 5, 2007 1293
filtration under nitrogen atmosphere, the filtrate was concentrated.
1
1
Recrystallization from pentane gave pure 4 (34.5 g, 95%). 4:
B
1
NMR (128 MHz, C
D
6 6
) δ 33.6; H NMR (400 MHz, CDCl
.60-7.62 (m, 4H), 7.33-7.35 (m, 6H), 2.94 (q, J ) 6.8 Hz, 4H),
.28 (s, 12H), 1.00 (t, J ) 6.8 Hz, 6H); 13C NMR (126 MHz,
) δ 137.8, 135.4, 128.8, 127.5, 83.4, 41.1, 25.0, 15.4.
Synthesis of 2-(Chlorodiphenylsilyl)-4,4,5,5-tetramethyl-1,3,2-
dioxaborolane (5, eq 2). To a CH Cl (60 mL) solution of 4 (25.1
g, 65.7 mmol) was added an Et O solution of hydrogen chloride
1.0 M, 145 mL, 145 mmol) at 0 °C. The mixture was stirred at
3
) δ
7
1
CDCl
3
2
2
90%). However, no reaction took place when diisopropylamine
2
(
was used under the same reaction conditions.
room temperature for 5 h. The white precipitate was removed by
filtration under nitrogen atmosphere, and the resulting filtrate was
concentrated. Bulb-to-bulb distillation under reducing pressure (190
1
1
°
C/1.5 mmHg) gave 5 as white solid (21.4 g, 94%). 5: B NMR
1
(
7
6 6 3
128 MHz, C D ) δ 32.3; H NMR (300 MHz, CDCl ) δ 7.69-
13
.73 (m, 4H), 7.36-7.47 (m, 6H), 1.32 (s, 12H); C NMR (75
MHz, CDCl
3
) δ 134.6, 134.0, 130.3, 128.1, 84.7, 25.0; HRMS (CI)
+
m/z calcd for C18
H23BO
2
ClSi (MH ) 345.1249, found 345.1255.
Synthesis of 2-(Chlorodimethylsilyl)-4,4,5,5-tetramethyl-1,3,2-
1
6i
dioxaborolane (7, eq 3). To a solution of 6 (9.73 g, 37.1 mmol)
Conclusion
in benzene (40 mL) was added aluminum chloride (0.495 g, 3.71
mmol), and the mixture stirred at room temperature. Aluminum
chloride was dissolved and the solution showed a pale yellow color.
Hydrogen chloride was passed through the solution via a Teflon
tube with vigorous stirring. The progress of the reaction was
checked by GC. The starting compound was consumed after
introducing ca. 30 equiv of hydrogen chloride. The reaction was
quenched with acetone (5 mL), and the resulting mixture was stirred
for 15 min. After removal of the volatile materials, the residue was
distilled under reducing pressure (47.5-49.0 °C/2.5 mmHg) to give
Practical synthetic methods for silylpinacolboranes bearing
chloro, fluoro, alkoxy, and amino groups on the silicon atom
were established. Functionalized diphenylsilyl derivatives were
prepared from the (aminosilyl)borane 4, which was prepared
by the reaction of (aminosilyl)lithium 2 with boron electrophiles
through Si-B bond formation. On the other hand, functionalized
dimethylsilyl derivatives were synthesized from the (phenyl-
silyl)borane 6 through electrophilic aromatic ipso-substitution,
which gave (chlorosilyl)borane 7. Conversion of the amino
group of 4 and the chloro group of 7 was achieved with the
same methods as those used in the conventional conversions.
It should be emphasized here that the new silylboronic esters
functionalized on silicon are expected not only to show higher
reactivity than the previously known triorganosilyl derivatives
but also to make possible further transformation of the silyl
group into other functionalities. Studies along this line are now
actively being undertaken in this laboratory.
11
7
as a colorless liquid (6.36 g, 78%). 7: B NMR (128 MHz,
1
CDCl
(
3
) δ 32.4; H NMR (400 MHz, CDCl
3
) δ 1.28 (s, 12H), 0.52
s, 6H); 13C NMR (75 MHz, CDCl
m/z calcd for C H19BClO Si (MH ) 221.0936, found 221.0934.
8 2
) δ 84.2, 24.9, 2.1; HRMS (CI)
3
+
Synthesis of 2-(Fluorodimethylsilyl)-4,4,5,5-tetramethyl-1,3,2-
dioxaborolane (8, eq 4). Antimony(III) fluoride (0.83 g. 4.6 mmol)
was placed in a two-necked round-bottomed flask equipped with a
magnetic stirring bar. The flask was cooled to -78 °C by acetone/
dry ice bath. Then 7 (2.63 g, 11.9 mmol) was added to the flask,
which immediately froze on the wall. After removal of the cooling
bath, the reagents were mixed with stirring at room temperature
for 3 h. The resulting dark brown solution was distilled (58-62
Experimental Section
General Comments. All reactions were carried out under a
1
1
°
C/10 mmHg) to afford 8 (1.84 g, 76%). 8: B NMR (128 MHz,
1
nitrogen or an argon atmosphere. H NMR spectra were recorded
1
CDCl
400 MHz, CDCl ) δ 1.27 (s, 12H), 0.36 (d, JHF ) 8.8 Hz, 6H);
3
) δ 32.3; 19F NMR (377 MHz, CDCl
6
) δ -176.3; H NMR
on Varian GEMINI-2000 (300.07 MHz) or Varian Mercury-400
400.44 MHz) spectrometers. 13C NMR spectra were recorded on
Varian GEMINI-2000 (75.45 MHz) or JEOL JNM-A500 (125.65
MHz) spectrometers. 11B NMR (128.48 MHz) and F NMR
3
(
3
(
1
3
2
C NMR (75 MHz, CDCl
HRMS (CI) m/z calcd for C
05.1225.
General Procedure for the Synthesis of (Alkoxysilyl)boranes
9 (eq 5). A solution of 7 in CH Cl (1.0 M) was cooled to 0 °C.
3
) δ 83.8, 25.0, 0.3 (d, JCF ) 14.0 Hz);
+
8
H19BFO
2
Si (MH ) 205.1231, found
19
2
(
376.87 MHz) spectra were recorded on a Varian Mercury-400
spectrometer. Chemical shifts were reported in ppm downfield from
1
13
11
2
2
tetramethylsilane (for H and C), BF
3
‚OEt
2 3
(for B), and CFCl
19
Pyridine (1.2 equiv) and an alcohol (1.1 equiv) were added to the
solution in this order. The reaction mixture was warmed to room
temperature and stirred for 3 h. After removal of the precipitation
by filtration, the filtrates were concentrated and purified by
distillation under reducing pressure.
(
for F). Elemental analyses were performed by Elemental Analysis
Center of Kyoto University. High-resolution mass spectra were
recorded on a JEOL JMS-MS700 (CI) spectrometer.
Hydrogen chloride was generated by the slow addition of
4
concentrated sulfuric acid to NH Cl. The gas was dried by passing
through concentrated sulfuric acid prior to introduction into the
reaction mixture.
Synthesis of 2-[(Diethylamino)diphenylsilyl]-4,4,5,5-tetra-
methyl-1,3,2-dioxaborolane (4, eq 1). To a solution of (isopro-
poxy)pinacolborane (3, 42.6 g, 229 mmol) in hexane (100 mL)
was added [(diethylamino)diphenylsilyl]lithium (2),18 which was
prepared from (diethylamino)diphenylsilyl chloride (27.6 g, 95.3
mmol) and lithium (2.65 g, 381 mmol) in THF (90 mL), dropwise
at 0 °C over 30 min. After the addition, the cooling bath was
removed. The mixture was stirred for 12 h at room temperature.
The volatiles were removed in Vacuo, and then the residue was
diluted with pentane. After removing the insoluble white solid by
2-(Methoxydimethylsilyl)-4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lane (9a). According to the general procedure, 7 (665 mg, 3.01
mmol) was reacted with MeOH (293 mg, 3.70 mmol). The product
9
a was isolated as a colorless liquid by bulb-to-bulb distillation
11
19
(90 °C/1.0 mmHg) in 76% yield (492 mg). 9a: B NMR (128
1
MHz, CDCl ) δ 33.1; H NMR (400 MHz, CDCl ) δ 3.46 (s, 3H),
3
3
1
5
2
.26 (s, 12H), 0.23 (s, 6H); 13C NMR (126 MHz, CDCl
1.1, 25.0, -1.2; HRMS (CI) m/z calcd for C
17.1431, found 217.1429. Anal. Calcd for C
3
) δ 83.4,
Si (MH )
+
9
H22BO
3
9 3
H21BO Si: C, 50.01;
H, 9.79. Found: C, 49.75; H, 9.62.
2-(Ethoxydimethylsilyl)-4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lane (9b). According to the general procedure, 7 (445 mg, 2.02

1294 Organometallics, Vol. 26, No. 5, 2007
Notes
mmol) was reacted with EtOH (117 mg, 2.53 mmol). The product
b was isolated as a colorless liquid by bulb-to-bulb distillation
precipitates, the filtrates were concentrated and purified by distil-
lation under reducing pressure.
2-[(Diethylamino)dimethylsilyl]-4,4,5,5-tetramethyl-1,3,2-di-
oxaborolane (10a). According to the general procedure, 7 (3.43
9
11
(
90 °C/1.0 mmHg) in 77% yield (359 mg). 9b: B NMR (128
1
3 3
MHz, CDCl ) δ 33.0; H NMR (400 MHz, CDCl ) δ 3.70 (q, J )
7
.2 Hz, 2H), 1.25 (s, 12H), 1.21 (t, J ) 7.2 Hz, 3H), 0.23 (s, 6H);
g, 15.6 mmol) was reacted with Et NH (1.25 g, 17.8 mmol) twice
2
1
3
C NMR (126 MHz, CDCl
CI) m/z calcd for C10
3
) δ 83.3, 59.3, 25.0, 18.5, -0.5; HRMS
3
(85% conversion after first reaction and 100% conversion after
+
(
H
24BO
Si (MH ) 231.1588, found 231.1586.
second reaction). The product 10a was isolated as a colorless liquid
by bulb-to-bulb distillation (115 °C/1.5 mmHg) in 90% yield (3.62
3
Anal. Calcd for C10H23BO Si: C, 52.18; H, 10.07. Found: C, 51.90;
g). 10a: 11B NMR (128 MHz, CDCl ) δ 33.8; H NMR (400 MHz,
1
H, 9.77.
3
2
-(Isopropoxydimethylsilyl)-4,4,5,5-tetramethyl-1,3,2-dioxa-
CDCl ) δ 2.82 (q, J ) 7.2 Hz, 4H), 1.24 (s, 12H), 0.99 (t, J ) 7.2
3
Hz, 6H), 0.13 (s, 6H); 13C NMR (75 MHz, CDCl ) δ 82.9, 41.2,
borolane (9c). According to the general procedure, 7 (1.02 g, 4.62
mmol) was reacted with i-PrOH (307 mg, 5.01 mmol). The product
3
25.0, 15.8, -0.7. Anal. Calcd for C H BNO Si: C, 56.03; H,
12
28
2
9
c was isolated as a colorless liquid by bulb-to-bulb distillation
10.97; N, 5.44. Found: C, 55.82; H, 10.69; N, 5.48.
11
(100 °C/1.5 mmHg) in 90% yield (1.01 g). 9c: B NMR (128
2-[(Dimethylamino)dimethylsilyl]-4,4,5,5-tetramethyl-1,3,2-di-
oxaborolane (10b). According to the general procedure, 7 (1.11
1
3 3
MHz, CDCl ) δ 33.1; H NMR (400 MHz, CDCl ) δ 3.99 (septet,
J ) 6.0 Hz, 1H), 1.25 (s, 12H), 1.17 (d, J ) 6.0 Hz, 6H), 0.22 (s,
g, 5.04 mmol) was reacted with Me NH (2.0 M THF solution, 2.77
2
6
H); 13C NMR (126 MHz, CDCl
HRMS (CI) m/z calcd for C11
45.1737. Anal. Calcd for C11
Found: C, 54.34; H, 10.07.
-(tert-Butoxydimethylsilyl)-4,4,5,5-tetramethyl-1,3,2-dioxa-
borolane (9d). According to the general procedure, 7 (468 mg,
.12 mmol) was reacted with t-BuOH (206 mg, 2.78 mmol). The
product 9d was isolated as a colorless liquid by bulb-to-bulb
3
) δ 83.2, 66.1, 25.6, 25.0, 0.06;
mL, 5.54 mmol) twice. The product 10b was isolated as a colorless
+
H
3
26BO Si (MH ) 245.1744, found
liquid by bulb-to-bulb distillation (110 °C/2.5 mmHg) in 71% yield
2
H25BO
3
Si: C, 54.10; H, 10.32.
(824 mg). 10b: 11B NMR (128 MHz, CDCl ) δ 33.7;
1
H NMR
3
(400 MHz, CDCl ) δ 2.46 (s, 6H), 1.24 (s, 12H), 0.12 (s, 6H); 13
3
C
2
NMR (75 MHz, CDCl ) δ 83.1, 38.9, 25.0, -2.6. Anal. Calcd for
3
C H BNO Si: C, 52.40; H, 10.55; N, 6.11. Found: C, 52.13; H,
10
24
2
2
10.26; N, 5.82.
2
-(Dimethylpyrrolidinosilyl)-4,4,5,5-tetramethyl-1,3,2-diox-
11
distillation (110 °C/1.0 mmHg) in 82% yield (447 mg). 9d:
NMR (128 MHz, CDCl
1
B
3
) δ
aborolane (10c). According to the general procedure, 7 (1.12 g,
1
3
) δ 33.4; H NMR (400 MHz, CDCl
5.09 mmol) was reacted with pyrrolidine (407 mg, 5.73 mmol).
.27 (s, 9H), 1.25 (s, 12H), 0.21 (s, 6H); 13C NMR (126 MHz,
The product 10c was isolated as a colorless liquid by bulb-to-bulb
CDCl
3
) δ 83.1, 72.1, 31.8, 24.9, 2.1; HRMS (CI) m/z calcd for
11
distillation (110 °C/0.6 mmHg) in 82% yield (1.06 g). 10c:
B
+
C
12
H26BO
3
Si [(M - H) ] 257.1744, found 257.1739. Anal. Calcd
1
NMR (128 MHz, CDCl
3
) δ 33.7; H NMR (400 MHz, CDCl
3
) δ
for C12 27BO
H
3
Si: C, 55.81; H, 10.54. Found: C, 55.77; H, 10.66.
2
6
.90-2.93 (m, 4H), 1.69-1.72 (m, 4H), 1.23 (s, 12H), 0.15 (s,
General Procedure for the Synthesis of (Aminosilyl)boranes
13
H); C NMR (75 MHz, CDCl
3
) δ 83.0, 47.6, 26.7, 25.0, -2.4.
10 (eq 6). A solution of 7 in hexane (0.50 M) was cooled to 0 °C.
Anal. Calcd for C12
6.68; H, 10.01.
2
H26BNO Si: C, 56.47; H, 10.27. Found: C,
Triethylamine (1.2 equiv) and dialkylamine (1.1 equiv) were added
to the solution in this order. The reaction mixture was warmed to
room temperature and stirred for 24 h. After removal of the
precipitation by filtration, the filtrates were treated with triethy-
lamine (1.2 equiv) and dialkylamine (1.1 equiv) again, since a small
amount of unreacted 7 was contained in the product of the first
5
Supporting Information Available: 1H and 13C NMR spectra
of new silylboronic esters. This material is available free of charge
via the Internet at http://pubs.acs.org.
1
reaction (checked by H NMR analysis). After filtration to remove
OM0609867