A mild synthesis of unsymmetrical bisalkoxysilanes through catalyzed alcoholysis of hydridosilanes containing C-C multiple bonds and aryl halides

Article abstract of DOI:10.1021/jo9022765

(Chemical Equation Presented) The synthesis of unsymmetrical bisalkoxysilanes containing unsaturated C-C bonds and alkyl and aryl bromides has been developed. This method is a modification of our previously reported two-step procedure that utilizes readily available catalysts (rhodium acetate dimer and manganese pentacarbonyl bromide) under mild neutral aprotic conditions. Good to moderate yields of the products were obtained in a short period. In this two-step synthesis, unsymmetrical bisalkoxysilanes with groups that can be further functionalized can be prepared effectively without the need to isolate the intermediates. 2009 American Chemical Society.

Full text of DOI:10.1021/jo9022765

pubs.acs.org/joc
reactions,1,2 protecting agents for many functional groups,3
A Mild Synthesis of Unsymmetrical Bisalkoxysilanes
through Catalyzed Alcoholysis of Hydridosilanes
Containing C-C Multiple Bonds and Aryl Halides
and anchoring reagents and substrates for solid support
synthesis.4
ꢀ
Bisalkoxysilanes (silyl ketals) are normally prepared from
the reaction of dichlorosilanes with an alcohol in the pre-
sence of base. These conditions, however, are not compatible
with many base labile compounds; therefore other methods
have been developed to address this problem. To make
unsymmetrical bisalkoxysilanes requires a selective method
that would allow for addition of two alcohols without a
statistical mixture of monoalkoxy and bisalkoxy products.
This requires selectively breaking the symmetry of the
dichlorosilane. This method becomes very important when
valuable synthetic intermediates are used, and time, effi-
ciency, and the need for less waste become crucial. We
reported the results of our search for catalysts that would
perform controlled alcoholysis of hydridosilanes to form
unsymmetrical bisalkoxysilanes.5 In a continuation of this
study, we evaluated catalysts that can achieve the same
results with alcohols that contain reactive functional groups
such as alkenes, alkynes, and aryl halides.
Colleen N. Scott* and Craig S. Wilcox
Department of Chemistry and Combinatorial Chemistry
Center, University of Pittsburgh, Pittsburgh, Pennsylvania
15260
cogst5@siu.edu
Received October 22, 2009
Reports in the literature where transition metals have been
used to catalyze alcoholysis of silanes are extensive.6 Reports
that include catalysts that are known to be compatible
with both alkenes and alkynes are Stryker’s catalyst
[PPh3CuH]6,6f Mn(CO)5Br, and its dimer [Mn(CO)4Br]2,6c
while Rh2(pfb)4 is known to be compatible only with alkenes.
To our knowledge, there have been no reports of transition
metal catalysts that were used in the presence of aryl halides.
Herein we report an efficient method for the synthesis of
unsymmetrical bisalkoxysilanes containing reactive func-
tional groups from dihydridosilanes in two consecutive
catalyzed alcoholysis reactions (Scheme 1).
In our previous paper, we demonstrated that rhodium
acetate dimer [Rh2(OAc)4] and 10% palladium on carbon
(10% Pd/C) were effective catalysts for the two-step synth-
esis of unsymmetrical bisalkoxysilanes; however, 10% Pd/C
was not compatible with some reactive functional groups in
the second step.5 We continue our study by looking for a
suitable catalyst to replace Pd/C in the second step that
would be compatible with reactive functional groups
(Scheme 2). We began this study by evaluating the catalysts
that were reported to be compatible with C-C multiple
bonds during silyl alcoholysis. We found that while the
[PPh3CuH] does catalyze the reaction of the second step,
the product was isolated in low yield, and there were many
byproduct. In our previous work, we found that the Rh2-
(pfb)4 does catalyze the reaction in the second step; however,
The synthesis of unsymmetrical bisalkoxysilanes contain-
ing unsaturated C-C bonds and alkyl and aryl bromides
has been developed. This method is a modification of our
previously reported two-step procedure that utilizes read-
ily available catalysts (rhodium acetate dimer and man-
ganese pentacarbonyl bromide) under mild neutral
aprotic conditions. Good to moderate yields of the pro-
ducts were obtained in a short period. In this two-step
synthesis, unsymmetrical bisalkoxysilanes with groups
that can be further functionalized can be prepared effec-
tively without the need to isolate the intermediates.
Organosilanes are vital to organic synthesis and therefore
the methods to synthesize them have become very important.
Formation of silyl ethers and silyl ketals are among the
examples. Over the years, there have been significant devel-
opments in silyl ether synthesis and their applications to
organic chemistry. Silyl ethers and ketals are important in
organic synthesis due to their versatility, compatibility with a
wide range of reaction conditions, safety, and ease to work
with. For these reasons, silyl ethers and silyl ketals have been
widely employed in organic synthesis. They are used in the
areas of tethering reactants for stereospecific intramolecular
(1) For reviews see: (a) Gauthier, D. R.; Zandi, K. S.; Shea, K. J.
Tetrahedron 1998, 54, 2289. (b) Fensterbank, L.; Malacria, M.; Sieburth,
S. McN. Synthesis 1997, 813. (c) Bois, M.; Skrydstrup, T. Chem. Rev. 1995,
95, 1253.
(2) (a) Hutchinson, J. H.; Daynard, T. S.; Gillard, J. W. Tetrahedron Lett.
1991, 32, 573. (b) Maas, G.; Gettwert, V. Tetrahedron 2002, 58, 3813.
(c) Hoye, T. R.; Promo, M. A. Tetrahedron Lett. 1999, 40, 1429.
(d) Denmark, S. E.; Hurd, A. R.; Sacha, H. J. J. Org. Chem. 1997, 62,
1668. (e) Garner, P.; Cox, P. B.; Anderson, J. T.; Protasiewicz, J.; Zaniewski,
R. J. Org. Chem. 1997, 62, 493.
(4) (a) Duboc, R.; Savignac, M.; Genet, J. J. Organomet. Chem. 2002,
643-644, 512. (b) Smith, E. Tetrahedron Lett. 1999, 40, 3285.
(5) Scott, C. N.; Wilcox, C. S. Synthesis 2004, 16, 2273.
(6) (a) Chang, S.; Scharrer, E.; Brookhart, M. J. Mol. Catal. A: Chem.
1998, 130, 107. (b) Doyle, M. P.; High, K. G.; Bagheri, V.; Pieters, R. J.;
Lewis, P. J.; Pearson, M. M. J. Org. Chem. 1990, 55, 6082. (c) Gregg, B. T.;
Cutler, A. R. Organometallics 1994, 13, 1039. (d) Luo, X. L.; Crabtree, R. H.
J. Am. Chem. Soc. 1989, 111, 2527. (e) Corriu, R. J. P.; Moreau, J. J. E.
J. Organomet. Chem. 1976, 120, 135. (f) Lorenz, C.; Schubert, U. Chem. Ber.
1995, 128, 1267. (g) Yamamoto, K.; Takemae, M. Bull. Chem. Soc. Jpn. 1989,
62, 2111. (h) Corriu, R. J. P.; Moreau, J. J. E. J. Chem. Soc., Chem. Commun.
1973, 38.
(3) (a) Rover, S.; Wipf, P. Tetrahedron Lett. 1999, 40, 5667. (b) Lalonde,
M.; Chan, T. H. Synthesis 1985, 831.
DOI: 10.1021/jo9022765
r
Published on Web 12/02/2009
J. Org. Chem. 2010, 75, 253–256 253
2009 American Chemical Society

Scott and Wilcox
JOCNote
SCHEME 1. A Two-Step Controlled Silyl Alcoholysis of
Hydridosilanes
TABLE 2. Bisalkoxysilanes Containing Alkyl and Aryl Bromides
SCHEME 2. Silyl Alcoholysis of an Alkenol Catalyzed by
Mn(CO)5Br
TABLE 1. Bisalkoxysilanes Containing C-C Multiple Bonds
aPercent isolated yield over two steps, based on (þ)-ethyl lactate.
susceptible to hydrosilylation during transition metal cata-
lyzed alcoholysis; however, these bonds remained intact
under these conditions.
We continued our evaluation of Mn(CO)5Br with alcohols
containing alkyl and aryl bromide functional groups. Mn(CO)5-
Br also catalyzes the reaction of 1 with alcohols containing alkyl
and aryl bromide functional groups in moderate to good yields
with no reduction side product detected (Table 2). To our
knowledge, this is the first example of silane alcoholysis with
alcohols containing alkyl and aryl bromide functional groups.
As we have reported, the yields for the manganese system
are lower compared with those of the palladium system. In
the manganese system, we observed the formation of a small
amount of side products (∼10-20%) resulting from alcohol
exchange between the second alcohol and the monoalkoxy
compound, resulting in the formation of a symmetrical
product and the desilylated (þ)-ethyl lactate. This was not
observed in the palladium system. We conducted several
experiments to decipher the problem; however, those results
will not be discussed here.7 The conclusion from those
experiments is that once the product is formed, it is stable
to the reaction conditions, and therefore, the side products
are being formed along the reaction pathway.
We have shown from our previous work that controlled
catalytic alcoholysis of dialkylsilanes can provide a practical
route to unsymmetrical silyl ketals. We have now developed
this method to include alcohols containing alkenes, alkynes,
and alkyl and aryl bromide functionality. There is continuing
work with this project to explore other reactive functional
groups, and the use of other catalysts to synthesize unsym-
metrical bisalkoxysilanes containing reactive functional
groups.
aPercent isolated yield over two steps, based on (þ)-ethyl lactate.
the reaction time was long, and therefore it was not evaluated
with this work. We then turned our interest to the manganese
catalysts reported by Cutler et al.6c We were pleased to find
that Mn(CO)5Br successfully catalyzes the reaction of the
monoalkoxysilane 1 with alcohols containing unsaturated
C-C bonds (Table 1).
Compared to the good yields that were obtained in our
previous work for primary, secondary, and tertiary alcohols,
only moderate yields were obtained over two steps for
primary and secondary alcohols, while slightly lower yields
were obtained for tertiary and benzyl alcohols. Alcohols
containing terminal double and triple bonds are usually
(7) Scott, C. N. Ph.D. Dissertation, University of Pittsburgh, 2005.
254 J. Org. Chem. Vol. 75, No. 1, 2010

Scott and Wilcox
JOCNote
þ
Experimental Section
HRMS (EI) m/z calcd for C13H25O4Si [M - CH(CH3)2
273.1522, found 273.1522.
]
All reactions were conducted with magnetic stirring in oven-
dried glassware. CH2Cl2 was dried over calcium hydride. Ethyl
(2S)-2-[(diisopropylsilyl)oxy]propanoate 1 was prepared ac-
cording to our previously reported procedure.5 All alcohols
were dried over calcium hydride and distilled before use. Mn-
(CO)5Br was commercially obtained and used without further
treatment.
Representative Formation of Bisalkoxysilanes (2a-f and
5a-e). To a solution of alcohol 2a-f and 5a-e (3.0 mmol)
and monoalkoxy silane 1 (2.0 mmol) in CH2Cl2 was added
Mn(CO)5Br (0.022 g, 4.0 mol %) and the reaction was allowed
to stir at room temperature for 2 h. The volatile components
were removed under reduced pressure and the crude mixture was
purified by flash column chromatography on silica gel eluting
with hexane (100 mL) followed by hexane:ethyl acetate (25:1) to
give the pure products as colorless liquids. The characteristic
data for 3a-f and 5a-e are presented below.
Ethyl (2S )-2-({diisopropyl[(1-phenylprop-2-en-1-yl)oxy]silyl}-
oxy)propanoate (3e), 2-diastereomers: 1H NMR (CD2Cl2) δ
7.55-7.34 (m, 10 H, 2 diastereomers), 6.11 (ddd, 1 H, J = 10,
6, 3 Hz, 1 diastereomer), 6.05 (ddd, 1 H, J = 10, 6, 3 Hz,
1 diastereomer), 5.53 (d, 2 H, J = 6 Hz, 1 diastereomer), {5.46
(dt, 1 H, J = 7, 2 Hz), 5.41 (dt, 1 H, J = 7, 2 Hz),
1 daistereomer}, 5.20 (dt, 1 H, J = 6, 2 Hz, 1 diastereomer),
5.17 (dt, 1 H, J = 6, 2 Hz, 1 diastereomer), 4.54 (q, 1 H, J =
7 Hz, 1 diastereomer), 4.53 (q, 1 H, J = 7 Hz, 1 diastereomer),
4.26 (qd, 2 H, J = 7, 1.3 Hz, 1 diastereomer), {4.21 (dq, 1 H, J =
11, 7 Hz), 4.13 (dq, 1 H, J =11, 7 Hz), 1 diastereomer}, 1.49 (d,
3 H, J = 7 Hz, 1 diastereomer), 1.40 (d, 3 H, J = 7 Hz,
1 diastereomer), 1.39 (t, 3 H, J = 7 Hz, 1 diastereomer), 1.33 (t,
3 H, J = 7 Hz, 1 diastereomer), 1.22-1.08 (m, 28 H,
2 diastereomers); 13C NMR (CD2Cl2) δ 173. 7, 173.6, 143.7,
143.6, 141.7, 141.6, 128.30, 128.26, 127.24, 127.15, 126.0, 125.9,
113.1, 112,9, 75.5, 67.9, 67.8, 60.7, 21.3, 21.2, 17.07, 17.01, 16.96,
16.91, 14.1, 14.0, 12.61, 12.54, 12.50; IR (cm-1) 3086, 3063,
2942, 2867, 1754, 1734, 1466, 1371, 1270, 1191, 1139, 1064, 1034,
988, 026, 884, 857, 753, 700; HRMS (EI) m/z calcd for
C17H25O4Si [M - CH(CH3)2þ] 321.1522, found 321.1524.
Ethyl (2S )-2-{[diisopropyl(prop-2-yn-1-yloxy)silyl]oxy}prop-
anoate (3f): 1H NMR (CD2Cl2) δ 4.52 (q, 1 H, J = 7 Hz), 4.43
(d, 2 H, J = 2 Hz), 4.30 (q, 2 H, J = 7 Hz), 2.44 (t, 1 H, J =
2 Hz), 1.42 (d, 3H, J = 7 Hz), 1.26 (t, 3 H, J = 7 Hz), 1.05 (br s,
14 H); 13C NMR (CD2Cl2) δ 173.5, 82.1, 72.6, 68.0, 60.8, 51.2,
21.2, 17.0, 14.0, 12.2; IR (cm-1) 3313, 3273, 2942, 2868, 1752,
1462, 1372, 1266, 1197, 1144, 1091, 1066, 1005, 886, 800, 69þ8;
Ethyl (2S )-2-{[(allyloxy)(diisopropyl)silyl]oxy}propanoate (3a):
1H NMR (CD2Cl2) δ 5.91 (ddt, 1 H, J = 17 Hz, 11 Hz, 4 Hz),
5.28 (dq, 1 H, J = 17, 2 Hz), 5.07 (dq, 1 H, J = 11, 2 Hz), 4.48
(q, 1 H, J = 7 Hz), 4.28 (dt, 2 H, J = 4, 2 Hz), 4.13 (q, 2 H, J =
7 Hz), 1.39 (d, 3 H, J = 7 Hz), 1.26 (t, 3 H, J = 7 Hz), 1.04-1.02
(m, 14 H); 13C NMR (CD2Cl2) δ 173.8, 137.5, 113.7, 68.1, 63.9,
60.8, 21.4, 17.21, 17.17, 17.13, 14.2, 12.54, 12.49; IR (cm-1
)
3088, 2946, 2864, 1752, 1736, 1462, 1372, 1270, 1144, 1033,
886, 809, 694; HRMS (EI) m/z calcd for C11H21O4Si [M -
CH(CH3)2þ] 245.1209, found 245.1216.
Ethyl (2S )-2-({diisopropyl[(1-methylpro-2-en-1-yl)oxy]silyl}-
1
oxy)propanoate (3b), two diastereomers: H NMR (CD2Cl2) δ
HRMS (EI) m/z calcd for C11H19O4Si [M - CH(CH3)2
]
6.01-5.88 (m, 2 H, 2 diastereomers), 5.28 (dt, 1 H, J = 5 Hz,
2 Hz, 1 diastereomer), 5.22 (dt, 1 H, J = 5, 2 Hz, 1 diastereomer),
5.08 (dt, 1 H, J = 6, 2 Hz, 1 diastereomer), 5.05 (dt, 1 H, J = 6,
2 Hz, 1 diastereomer), 4.65-4.54 (m, 4 H, J = 7 Hz, 2 dia-
stereomers), 4.22 (qd, 4 H, J = 7, 4 Hz, 2 diastereomers), 1.47
(d, 3 H, J = 7 Hz, 1 diastereomer), 1.46 (d, 3 H, J = 7 Hz,
1 diastereomer), 1.36-1.29 (m, 12 H, 2 diastereomers), 1.11 (br s,
28 H, 2 diastereomers); 13C NMR (CD2Cl2) δ 173.7, 173.7, 142.7,
142.6, 112.4, 112.3, 69.5, 69.4, 67.8, 67.8, 60.6, 24.2, 24.2, 21.3,
21.3, 17.0, 14.0, 12.6, 12.6, 12.5, 12.5; IR (cm-1) 3088, 2940, 2868,
1737, 1639, 1465, 1378, 1306, 1178, 1096, 1009, 912, 886, 810, 758,
243.1053, found 243.1051.
Ethyl (2S )-2-{[(2-bromoethoxy)(diisopropyl)silyl]oxy}prop-
anoate (5a): 1H NMR (CD2Cl2) δ 4.52 (q, 1 H, J = 7 Hz), 4.15 (q,
2 H, J = 7 Hz), 4.03 (t, 2 H, J = 6 Hz), 3.44 (t, 2 H, J =
6 Hz), 1.41 (d, 3 H, J = 7 Hz), 1.26 (t, 3 H, J = 7 Hz), 1.05-1.04
(m, 14 H); 13C NMR (CD2Cl2) δ 173, 68.2, 63.6, 60.9, 33.6, 21.4,
17.1, 14.2, 12.5; IR (cm-1) 2938, 2868, 1753, 1462, 1377, 1283,
1140, 1017, 976, 882, 788, 739, 690; HRMS (EI) m/z calcd for
C10H079BrO4Si [M - CH(CH3)2þ] 311.0314, found 311.0313.
Ethyl (2S )-2-{[[(2-bromobenzyl)oxy](diisopropyl)silyl]oxy}-
1
propanoate (5b): H NMR (CD2Cl2) δ 7.60 (dd, 1 H, J = 8,
687;
HRMS
(EI)
m/z
calcd
for
C12H23O4Si
1 Hz), 7.52 (dd, 1 H, J = 8, 1 Hz), 7.36 (ddd, 1 H, J = 8, 7, 1 Hz),
7.15 (ddd, 1 H, J = 8, 7, 1 Hz), 4.90 (s, 2 H), 4.54 (q, 1 H, J =
7 Hz), 4.11 (dq, 2 H, J = 3, 7 Hz), 1.42 (d, 3 H, J = 7 Hz), 1.22 (t,
3 H, J = 7 Hz), 1.12-1.09 (m, 14H); 13C NMR(CD2Cl2) δ 173.5,
140.0, 132.1, 128.3, 127.4, 121.0, 68.0, 64.5, 60.8, 21.2, 17.12,
17.09, 17.03, 14.0, 12.4, 12.3; IR (cm-1) 3064, 2945, 2865, 2725,
1751, 1571, 1462, 1442, 1367, 1268, 1203, 1138, 1093, 1028, 879,
820, 745, 691; HRMS (EI) m/z calcd for C15H2279BrO4Si
[M - CH(CH3)2þ] 373.0484, found 373.0471.
Ethyl (2S )-2-{[[2-(2-bromophenyl)ethoxy](diisopropyl)silyl]-
oxy}propanoate (5c): 1H NMR (CD2Cl2) δ 7.53 (dd, 1 H, J =
8, 1 Hz), 7.31 (dd, 1 H, J = 8, 2 Hz), 7.24 (ddd, 1 H, J = 8, 7,
1 Hz), 7.09 (ddd, 1 H, J = 8, 7, 2 Hz), 4.38 (q, 1 H, J = 7 Hz),
4.13 (q, 2 H, J = 7 Hz), 3.96 (t, 2 H, J = 7 Hz), 3.00 (t, 2 H, J =
7 Hz), 1.36 (d, 3 H, J = 7 Hz), 1.24 (t, 3 H, J = 7 Hz), 0.99 (br s,
14 H); 13C NMR (CD2Cl2) δ 173.7, 138.4, 132.7, 131.8, 128.1,
127.3, 124.6, 67.8, 62.4, 60.7, 39.4, 21.3, 17.0, 14.1, 12.3; IR
(cm-1) 3053, 2940, 2863, 1747, 1737, 1470, 1440, 1368, 1281,
1194, 1143, 1096, 1061, 1040, 886, 743, 687; HRMS (EI) m/z
calcd for C16H2479BrO4Si [M - CH(CH3)2þ] 387.0627, found
387.0627.
[M - CH(CH3)2þ] 259.1366, found 259.1366.
Ethyl (2S)-2-({diisopropyl[(1-vinylbut-3-en-1-yl)oxy]silyl}oxy)-
propanoate (3c), two diastereomers: 1H NMR (CD2Cl2) δ
5.94-5.73 (m, 4 H, 2 diastereomers), 5.20 (dt, 1 H, J = 5,
2 Hz, 1 diastereomer), 5.14 (dt, 1 H, J = 5, 2 Hz, 1 diastereomer),
5.10-5.00 (m, 4 H, 1 diastereomer, 2 H, 1 diastereomer), 4.50 (q,
2 H, J = 7 Hz, 2 diastereomer), 4.43-4.36 (m, 2 H,
2 diastereomers), 4.14 (qd, 4 H, J = 7, 4 Hz, 2 diastereomers),
2.41-2.23 (m, 4 H, 2 diastereomers), 1.40 (d, 3 H, J = 7 Hz,
1 diastereomer), 1.38 (d, 3 H, J = 7 Hz, 1 diastereomer) 1.26 (t,
3 H, J = 7 Hz, 1 diastereomer), 1.25 (t, 3 H, J = 7 Hz,
1 diastereomer), 1.08-0.95 (m, 28 H, 2 diastereomers); 13C
NMR (CD2Cl2) δ 173.7, 140.75, 40.67, 134.5, 116.9, 114.0,
113.9, 73.3, 73.2, 67.9, 42.7, 21.4, 17.0, 14.0, 13.9, 12.62, 12.56;
IR (cm-1) 3088, 2940, 2868, 1737, 1639, 1465, 1378, 1306, 1178,
1096, 1033, 886, 809, 694; HRMS (EI) m/z calcd for C14H25O4Si
[M - CH(CH3)2þ] 285.1522, found 285.1517.
Ethyl (2S )-2-{[[(1,1-dimethylprop-2-en-1-yl)oxy](diisopropyl)-
1
silyl]oxy}propanoate (3d): H NMR (CD2Cl2) δ 5.99 (dd, 1 H,
J = 17, 11 Hz), 5.15 (dd, 1 H, J = 17, 2 Hz), 4.92 (dd, 1 H, J =
11, 2 Hz), 4.50 (q, 1 H, J = 7 Hz), 4.14 (q, 2 H, J = 7 Hz), 1.38 (d,
3 H, J = 7 Hz), 1.36 (s, 6H), 1.25 (t, 3 H, J = 7 Hz), 1.05-0.95
(m, 14 H); 13C NMR (CD2Cl2) δ 173.8, 146.6, 110.3, 73.9, 67.9,
60.5, 29.8, 21.4, 17.3, 14.0, 13.6, 13.5; IR (cm-1) 3079, 2980,
2945, 2865, 1755, 1731, 1462, 1372, 1143, 1059, 880, 775, 680;
Ethyl (2S )-2-{[[(2,6-dibromobenzyl)oxy](diisopropyl)silyl]oxy}-
propanoate (5d): 1H NMR (CD2Cl2) δ 7.56 (d, 2 H, J = 8 Hz),
7.03 (t, 1 H, J = 8 Hz), 5.15 (d, 1 H, J = 11 Hz), 5.11 (d, 1 H, J =
11 Hz), 4.64 (q, 1 H, J = 7 Hz), 4.15 (q, 1 H, J = 7 Hz), 4.14 (q,
1 H, J = 7 Hz), 1.45 (d, 3 H, J = 7 Hz), 1.25 (t, 3 H, J = 7 Hz),
J. Org. Chem. Vol. 75, No. 1, 2010 255

Scott and Wilcox
JOCNote
1.09 (br s, 14 H); 13C NMR (CD2Cl2) δ 173. 7, 138.3, 132.6, 130.5,
16.96, 16.92, 14.0, 12.4; IR (cm-1) 3063, 2940, 2863, 1747, 1568,
1455, 1368, 1265, 1148, 1096, 1030, 958, 876, 794, 748; HRMS (EI)
m/z calcd for C19H3179BrO4Si [M - CH(CH3)2þ] 387.0627, found
387.0626.
126.1, 68.0, 65.8, 60.7, 21.4, 17.1, 14.1, 12.54, 12.46; IR (cm-1
2935, 2863, 1742, 1588, 1557, 1424, 1373, 1276, 1204, 1143, 1102,
974, 886, 784, 718; HRMS (EI) m/z calcd for C15H2179Br2O4Si
[M - CH(CH3)2þ] 450.9576, found 450.9574.
)
Ethyl (2S)-2-{[[(1S)-1-(2-bromophenyl)ethoxy](diisopropyl)silyl]-
oxy}propanoate (5e): 1H NMR (CD2Cl2) δ 7.65 (dd, 1 H, J = 8,
2 Hz), 7.48 (dd, 1 H, J = 8, 1 Hz), 7.34 (ddd, 1 H, J = 8, 8, 1 Hz),
7.11 (ddd, 1 H, J = 8, 8, 2 Hz), 5.39 (q, 1 H, J = 6 Hz), 4.43 (q, 1 H,
J=7Hz), 4.10(dq, 1H, J=11, 7Hz), 4.04(dq, 1H, J= 11, 7 Hz),
1.44 (d, 3 H, J = 6 Hz), 1.38 (d, 3 H, J = 7 Hz), 1.22 (t, 3 H, J =
7 Hz), 1.07-0.98 (m, 14 H); 13C NMR (CD2Cl2) δ 173. 5, 145.6,
132.3, 128.4, 127.7, 127.1, 120.7, 69.7, 67.9, 60.7, 25.5, 21.3, 17.02,
Acknowledgment. The authors thank the Office of the
Dean of the Faculty of Arts and Sciences, University of
Pittsburgh, for support of this investigation.
Supporting Information Available: Spectral copies of 1H
NMR and 13C NMR for all new compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
256 J. Org. Chem. Vol. 75, No. 1, 2010