Synthesis and hydrolytic stability of tert-butoxydimethylsilyl enol ethers

Article abstract of DOI:10.1081/SCC-100104840

tert-Butoxydimethylsilyl enol ethers derived from aldehydes and ketones were synthesized in good yields with high regio- and stereoselectivities, under thermodynamically and kinetically controlled conditions. The hydrolytic stability of tert-butoxydimethy

Full text of DOI:10.1081/SCC-100104840

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: http://www.tandfonline.com/loi/lsyc20
SYNTHESIS AND HYDROLYTIC STABILITY OF TERT-
BUTOXYDIMETHYLSILYL ENOL ETHERS
Zacharia A. Fataftah , Abdel-Monem M. Rawashdeh & Chariklia Sotiriou-
Leventis
To cite this article: Zacharia A. Fataftah , Abdel-Monem M. Rawashdeh & Chariklia Sotiriou-
Leventis (2001) SYNTHESIS AND HYDROLYTIC STABILITY OF TERT-BUTOXYDIMETHYLSILYL ENOL
ETHERS, Synthetic Communications, 31:15, 2379-2389, DOI: 10.1081/SCC-100104840
To link to this article: http://dx.doi.org/10.1081/SCC-100104840
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Date: 20 November 2015, At: 15:40

SYNTHETIC COMMUNICATIONS, 31(15), 2379–2389 (2001)
SYNTHESIS AND HYDROLYTIC STABILITY
OF TERT-BUTOXYDIMETHYLSILYL
ENOL ETHERS
1
,
2
Zacharia A. Fataftah, * Abdel-Monem M. Rawashdeh,
2
,
andChariklia Sotiriou-Leventis
*
1
Department of Chemistry, Yarmouk University, Irbid, Jordan
2
Department of Chemistry, University of Missouri-Rolla,
Rolla, MO 65409, USA
ABSTRACT
tert-Butoxydimethylsilyl enol ethers derived from aldehydes
and ketones were synthesized in good yields with high regio-
and stereoselectivities, under thermodynamically and kineti-
cally controlled conditions. The hydrolytic stability of tert-
butoxydimethylsilyl enol ether of cyclohexanone was studied
under acidic and basic conditions and compared to that of
trimethylsilyl, tert-butyldimethylsilyl and (2,4,6-tri-tert-butyl-
phenoxy)dimethylsilyl enol ethers.
Silyl enol ethers have shown to be useful enolate equivalents for the
1
2
3
synthesis of enones, a-hydroxy ketones, 1,4-diketones, and other functio-
nalized carbonyl compounds, which in turn are versatile intermediates for
the syntheses of some naturalproducts. Severalmethods for the preparation
4
5
,6
of silyl enol ethers have been reported. House described the preparation of
*
Corresponding authors.
2
379
Copyright & 2001 by MarcelDekker, Inc.
www.dekker.com

ORDER
REPRINTS
2
380
FATAFTAH, RAWASHDEH, AND SOTIRIOU-LEVENTIS
trimethylsilyl enol ethers (1) from aldehydes and ketones with trimethylsilyl
7
chloride. However, the utility of these enol ethers is limited by their suscept-
ibility to hydrolysis. This problem was overcome by the use of the tert-butyl-
8
dimethylsilyl derivatives (2). tert-Butyldimethylsilyl chloride, however, is
9
,10
considerably more expensive than trimethylsilyl chloride.
In an effort to
find a silylating agent which could provide hydrolytic stability similar to that
of the tert-butyldimethylsilyl moiety at a more reasonable cost, Rathke pre-
pared the solid (2,4,6-tri-tert-butylphenoxy) dimethylsilyl chloride (TPS, 3)
1
1
from 2,4,6-tri-tert-butylphenol. Here, we explore the possibility of using an
alkoxy dimethylsilyl chloride instead of the phenoxy analog 3. Therefore,
tert-butoxydimethylsilyl chloride (TBOSCI, 4), was chosen in our study.
TBOSCI is a colorless liquid that can be prepared readily and more inexpen-
sively than 3 from dichlorodimethylsilane and tert-butanolin the presence
1
2
of urea.
RESULTS AND DISCUSSION
Several tert-butoxydimethylsilyl enol ethers were prepared for the first
time in good to excellent yields (50–98%) from the reaction of tert-butoxy-
dimethylsilyl chloride with a number of ketones and aldehydes (eq. 1, Table 1)
by two distinctive methods based on thermodynamic and kinetic control.
Equation 1.
In the thermodynamically controlled method A (Table 1), a mixture of a
ketone, triethylamine, sodium iodide and the silylating agent 4 in acetonitrile,

ORDER
REPRINTS
TERT-BUTOXYDIMETHYLSILYL ENOL ETHERS
2381
was stirred at room temperature for 40–120 min, depending on the substrate.
Yields of TBOS enol ethers ranged from 70 to 98%. For aldehydes, the
reaction mixtures were refluxed (method B, Table 1). Since aldehyde enolates
7
are more reactive than ketone enolates toward aldol condesation, heat is
required to enhance the retroaldol reaction of aldehydes.
Table 1. Formation of tert-Butoxydimethylsilyl Enol Ethers
(
continued )

ORDER
REPRINTS
2
382
FATAFTAH, RAWASHDEH, AND SOTIRIOU-LEVENTIS
Table 1. Continued
a
In method A, the carbonylcompound was stirred at room temperature with a
mixture of Et N, TBOSCland NaI in CH CN. In method B, the reaction mixture
3
3
of method A was refluxed. In method C, the enolate formed by the reaction of the
cabonylcompound with LDA in THF, was quenched withTBOSC l. In method D,
b
LiTMP was used instead of LDA. GC yield.
The kinetically controlled methods C and D (Table 1), involve
initialformation of the enoalte ions via reaction of the carbonylcom-
pound either with a solution of lithium diisopropylamide (LDA, gene-
rated from diisopropylamine and n-butyllithium, method C) or lithium

ORDER
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TERT-BUTOXYDIMETHYLSILYL ENOL ETHERS
2383
2,2,6,6-tetramethylpiperidide (LiTMP, prepared from 2,2,6,6-tetramethylpi-
peridine and n-butyllithium, method D) in tetrahydrofuran (THF), under
nitrogen. Subsequent quenching of the produced enolate ions with tert-
butoxydimethylsilyl chloride produced the tert-butoxydimethylsilyl enol
ethers. The products were obtained within 15–72 min with yields in the
range of 50–97% (Table 1).
The regio- and stereoselectivity of the tert-butoxydimethylsilyl enol
ethers are influenced by the different methods used in their formation
(
thermodynamic vs. kinetic). As expected, kinetic controlfavors the forma-
tion of the E enolate, resulting from a-proton abstraction from the less
sterically hindered side (Table 1). The use of the more hindered base
LiTMP (method D) increases the ratio of E/Z enolates even further
1
3,14
(
Table 1, 5a, 5c, and 5f ).
The rate of hydrolysis of TBOS enol ether derived from cyclohexa-
none (5k, Table 2) was investigated under acidic and basic conditions.
Our experimental data were compared with the literature rates of hydrolysis
of TMS enolether 6, TBS enolether 7, and TPS enolether 8 derived from
7
cyclohexanone under the same reaction conditions (Table 2). It is clear that
TBOS enolether 5k is by far more resistant to acid hydrolysis than the TMS
derivative 6, and 5k is even slightly more resistant to acid hydrolysis than
the TBS derivative 7. Also, it may be noted that 5k is almost as resistant to
acid hydrolysis as the TPS enol ether 8. All three enol ethers 5k, 7, and 8 are
stable to base treatment.
In conclusion, the facile, inexpensive synthesis and easy handling of
tert-butoxydimethylsilyl chloride may rank it as the reagent of choice for the
synthesis of silyl enol ethers compared to (2,4,6-tri-tert-butylphenoxy)-
dimethylsilyl and tert-butyldimethylsilyl chloride which are more expensive.
The latter reagent is also more difficult to prepare. In addition, the hydro-
lytic stability of the resulting TBOS enol ethers is superior to TMS and
comparable to TBS and TPS enol ethers.
EXPERIMENTAL
IR spectra were recorded on a Pye-Unican SP-300 spectrometer.
H NMR spectra were obtained in CDCl with a Bruker WP 80 EY spectro-
1
3
meter. Mass spectra were recorded on a sector field double focusing unit VG
7070E GC-MS spectrometer at an accelerating voltage of 6k volts. Vapor
phase chromatographic analysis and preparative work were carried out on
Varian Aerographs 1400 and 3400 with thermalconductivity detectors.
Elemental analysis was performed by M-H-W Laboratories, Phoenix AZ.

ORDER
REPRINTS
2
384
FATAFTAH, RAWASHDEH, AND SOTIRIOU-LEVENTIS
a
Table 2. Hydrolysis of Silyl Enol Ethers
a
7 b
2
Hydrolysis of compounds 6, 7, and 8 are from literature. A, HOAc/THF/H O,
c
:10:1; B, THF/1 M HCl. 20 : 1; C, THF/1 M NaOH, 20:1. Determined by GC with
1
decane as internalstandard.
All starting materials and reagents were from Aldrich. Tetrahydrofuran was
distilled from lithium aluminum hydride, and triethylamine was distilled
from calcium hydride prior to use.
Preparation of tert-Butoxychlorodimethylsilane (4)
1
2
Following the procedure of Krovelets et al., urea (70 g, 1.2 mol) and
dichlorodimethylsilane (120 ml, 1 mol) were stirred vigorously for 15 min at
room temperature, under nitrogen, followed by the dropwise addition of tert-
butanol (94 ml, 1 mol). The reaction mixture was stirred for an
additional 1.5 h at room temperature followed by filtration (moisture
should be excluded during the filtration since urea hydrochloride is
very hygroscopic). The filtrate was subjected to fractional distillation to

ORDER
REPRINTS
TERT-BUTOXYDIMETHYLSILYL ENOL ETHERS
2385
ꢀ
12
give 4 as a colorless liquid. Yield: 86%; bp 100 C/760 mm Hg (lit. bp 107–
1
ꢀ
1
08 C/747 mm Hg); H NMR d 0.43 (6H, s), 1.32 (9H, s).
Preparation of tert-Butoxydimethylsilyl Enol Ethers (5a–n)
MethodA . Into a 10 mlround bottom flask, sodium iodide (3 mmo,l
.45 g), acetonitrile (3 ml), triethylamine (0.63 ml, 4.5 mmol), and tert-
0
butoxychlorodimethylsilane (0.6 ml, 3.3 mmol) were added followed by the
addition of ketone or aldehyde (3 mmol). The mixture was stirred at room
temperature, under nitrogen for 40–120 min, depending on the substrate
(
ether (40–60 C) and washed with cold saturated aqueous NaHCO
Table 1). The reaction mixture was then diluted with 6 ml of petroleum
ꢀ
3
(
trated in vacuo followed by the addition of an appropriate standard
2 ꢁ 3 ml). The organic layer was dried over anhydrous Na SO , concen-
2
4
0
0
0
(
n-C H to n-C H , 3 mmol), and GC analysis (10% SE-30, 1/8 ꢁ 5
1
1
24
16 34
00 0
or 1/8 ꢁ 20 column).
MethodB . Same as method A except that after the addition of alde-
hyde the reaction mixture was refluxed for the indicated time (Table 1).
MethodC . A 10 mlflask equipped with a magnetic stirring bar,
septum, gas inlet valve, and mercury bubbler was flame-dried under nitro-
gen. n-Butyllithium as a 1.6 M solution in hexane (1.3 ml, 2 mmol) was
added and the flask was immersed in an ice bath. Diisopropylamine
(
0.28 ml, 2 mmol) was added dropwise with stirring. After the evolution of
butane had ceased, hexane was removed under vacuum, which was broken
with nitrogen. LDA obtained as a white solid, was dissolved in 2 ml anhy-
drous THF, and 2 mmolof the carbonylcompound was added dropwise
ꢀ
with stirring at 0 C over 2 min. The reaction mixture was stirred for 10 min
ꢀ
at 0 C, then quenched with tert-butoxychlorodimethylsilane (0.36 ml,
ꢀ
2 mmol), and stirred for 5 min at 0 C. An appropriate standard (n-C H
to n-C H , 2 mmol) was added. The reaction mixture was stirred at
1
1
24
1
6
34
room temperature for the indicated time (Table 1), followed by GC analysis
0
0
0
(
(
10% SE-30, 1/8 ꢁ 5 column). For product isolation, petroleum ether
2 ml) was added to the reaction mixture and washed with cold saturated
aqueous NaHCO3 (2 ml). The organic layer was dried over anhydrous
sodium sulfate and concentrated in vacuo, followed by fractional vacuum
distillation.
MethodD . Same as method C except that 2,3,6,6-tetramethylpiper-
idine was used instead of diisopropylamine.
tert-Butoxydimethylsilyl enol ethers from 2-butanone (5a and5b)
ꢀ
Colorless liquid consisting of 5a (E and Z isomers) and 5b; bp 35 C
þ
(
9 mm Hg); d 0.851 g/ml; MS, m/e 187(M -15), 145, 129, 115, 86, 75,

ORDER
REPRINTS
2
386
FATAFTAH, RAWASHDEH, AND SOTIRIOU-LEVENTIS
5
1
7, 45. Anal. Calcd for C H SiO : C, 59.35; H, 10.96. Found: C, 59.28; H,
1
0.79. The regioisomers 5a and 5b were separated by preparative GC.
0
22
2
However, the E and Z isomers of 5a were inseparable by this technique.
À1
1
5
a (E þ Z ): IR 1670 cm (C ¼ C); H NMR d 0.17 (6H, s), 1.29
9H, s), 1.50 (3H, d, J ¼ 6.9 Hz), 1.80 (3H, s), 4.74 (q, J ¼ 7.2 Hz, E ),
.43 (q, J ¼ 6.4 Hz, Z ).
(
4
À1
1
5
b: IR 1620 cm (C ¼ C); H NMR d 0.18 (6H, s), 1.02 (3H, t,
J ¼ 7.2), 1.29 (9H, s), 1.96 (2H, q, J ¼ 7.3 Hz), 4.05 (1H, s), 4.16 (1H, s).
tert-Butoxydimethylsilyl enol ether from 3-pentanone (5c): Colorless
liquid consisting of E and Z isomers; bp 30 C (3 mm Hg), d 0.845 g/ml;
ꢀ
À1
IR 1650 cm (C ¼ C). The E and Z isomers were separated by preparative
1
GC. H NMR d E: 0.14 (6H, s), 1.0 (3H, t, J ¼ 7.6 Hz), 1.28 (9H, s), 1.52
(
(
(
3H, d, J ¼ 7.1 Hz), 2.1 (2H, q, J ¼ 7.6 Hz), 4.70 (1H, q, J ¼ 6.9 Hz); Z: 0.17
6H, s), 1.02 (3H, t, J ¼ 7.6 Hz), 1.29 (9H, s), 1.52 (3H, d, J ¼ 7.1 Hz), 2.10
þ
2H, q, J ¼ 7.6 Hz), 4.48 (1H, q, J ¼ 7.1 Hz); MS, m/e 201 (M -15), 159, 143,
75. Anal. Calcd for C H SiO : C, 61.06; H, 11.18. Found: C, 60.88;
H, 11.40.
11 24 2
tert-Butoxydimethylsilyl enol ether from 4-methyl-2-pentanone (5d):
ꢀ
À1
Colorless liquid; bp 65 C (8 mm Hg); d 0.815 g/ml; IR 1615 cm (C ¼ C);
1
H NMR d 0.17 (6H, s), 0.88 (7H, m), 1.29 (9H, s), 1.86 (2H, m), 4.01 (1H, s),
þ
4
.18 (1H, s); MS, m/e 230 (M ), 216, 215, 207, 188, 173, 159, 157, 75,
57. Anal. Calcd for C H SiO : C, 62.55; H, 11.37. Found: C, 62.43;
H, 11.33.
1
2
26
2
tert-Butoxydimethylsilyl enol ether from 3,3-dimethyl-2-butanone (5e):
ꢀ
À1
Colorless liquid; bp 42 C (3 mm Hg); d 0.826 g/ml; IR 1610 cm (C ¼ C);
1
H NMR d 0.17 (6H, s), 1.04 (9H, s), 1.29 (9H, s), 4.09 (2H, s); MS, m/e 230
þ
(
H, 11.37. Found: C, 62.34; H, 11.12.
M ), 215, 173, 159, 157, 77, 75. Anal. Calcd for C H SiO : C, 62.55;
1
2
26
2
tert-Butoxydimethylsilyl enol ether from 4-pentanone (5f ): Colorless
liquid consisting of E and Z isomers (inseparable by preparative GC); bp
ꢀ
À1
1
6
6 C (7 mm Hg); d 0.815 g/ml; IR 1660 cm (C ¼ C); H NMR d 0.16 (6H,
s), 0.89 (6H, t, J ¼ 6.3 Hz), 1.29 (9H, s), 1.37–1.58 (2H, m), 2.00 (4H, q,
J ¼ 7.3 Hz), 4.39 (1H, t, J ¼ 7.5 Hz, Z ), 4.74 (1H, t, J ¼ 7.6 Hz, E ); MS, m/e
þ
2
29 (M -15), 188, 187, 173, 171, 145, 75, 57. Anal. Calcd for C H SiO : C,
2
1
3
28
6
3.86; H, 11.55. Found: C, 63.93; H, 11.61.
tert-Butoxydimethylsilyl enol ether from 2,6-dimethyl-4-heptanone (5g):
Colorless liquid consisting of E and Z isomers (inseparable by preparative
ꢀ
À1
1
GC); bp 77 C (5 mm Hg); d 0.826 g/ml; IR 1650 cm (C ¼ C); H NMR
d 0.15 (6H, s), 0.92 (13H, m), 1.28 (9H, s); 1.91 (2H, m), 2.28 (1H, m),
þ
4
.23 (1H, d, J ¼ 9, Z ), 4.62 (1H, d, J ¼ 9.7 Hz, E ); MS, m/e 256 (M -16),
214, 200, 198, 109, 75, 57. Anal. Calcd for C H SiO : C, 66.11; H, 11.84.
Found: C, 66.13; H, 11.70.
1
5
32
2

ORDER
REPRINTS
TERT-BUTOXYDIMETHYLSILYL ENOL ETHERS
2387
tert-Butoxydimethylsilyl enol ether from pentanal (5h): Colorless liquid
À1
consisting of E and Z isomers; d 0.866 g/ml; IR 1660 cm (C ¼ C). The E
1
and Z isomers were separated by preparative GC. H NMR d E: 0.15 (6H,
s), 0.89 (3H, t, J ¼ 7 Hz), 1.28 (9H, s), 1.3–1.6 (2H, m), 2.06 (2H, q,
J ¼ 6.8 Hz), 5.0 (1H, dt, J
¼ 11.8 Hz, J ¼ 7.5 Hz), 6.23 (1H, d,
trans
J
¼ 11.8 Hz); Z: 0.15 (6H, s), 0.89 (3H, t, J ¼ 7 Hz), 1.28 (9H, s),
cis
trans
1
.3–1.6 (2H, m), 2.06 (2H, q, J ¼ 6.8 Hz), 4.45 (1H, dt, J ¼ 6.2 Hz,
J ¼ 7.5 Hz), 6.2 (1H, d, J ¼ 6.2 Hz). Anal. Calcd for C H SiO : C,
cis 11 24 2
6
1.06; H, 11.18. Found: C, 60.87; H, 10.99.
tert-Butoxydimethylsilyl enol ether from hexanal (5i): Colorless liquid
À1
consisting of E and Z isomers; d 0.875 g/ml; IR 1660 cm (C ¼ C). The E
1
and Z isomers were separated by preparative GC. H NMR d E: 0.15 (6H, s),
0
J
0
J
.88 (3H, t, J ¼ 6.5 Hz), 1.28 (9H, s), 1.0–2.22 (6H, m), 5.0 (1H, dt,
¼ 11.8 Hz, J ¼ 7.3 Hz), 6.25 (1H, d, J
trans trans
¼ 11.8 Hz); Z: 0.15 (6H, s),
.88 (3H, t, J ¼ 6.5 Hz), 1.28 (9H, s), 1–2.22 (6H, m), 4.46 (1H, dt,
¼ 6.2 Hz, J ¼ 7.3 Hz), 6.2 (1H, d, J ¼ 6.2 Hz). Anal. Calcd for
cis
cis
C H SiO : C, 62.55; H, 11.37. Found: C, 62.35; 11.32.
2
1
2
26
tert-Butoxydimethylsilyl enol ether from cyclopentanone (5j): Colorless
ꢀ
À1
1
liquid; bp 65 C (5 mm Hg); d 0.890 g/ml; IR 1630 cm (C ¼ C); H NMR d
0
.17 (6H, s), 1.28 (9H, s), 1.5–2.3 (4H, m), 2.23 (2H, q, J ¼ 5.9 Hz), 4.70 (1H,
þ
br s); MS, m/e 214 (M ), 199, 158, 157, 141, 133, 115, 75, 59, 57, 39. Anal.
Calcd for C H SiO : C, 61.63; H, 10.34. Found: C, 61.71; H, 10.39.
1
1
22
2
tert-Butoxydimethylsilyl enol ether from cyclohexanone (5k): Colorless
ꢀ
À1
1
liquid; bp 54 C (1 mm Hg); d 0.876 g/ml; IR 1650 cm (C ¼ C); H NMR
d 0.15 (6H, s), 1.28 (9H, s), 1.42–2.09 (8H, m), 4.89–4.97 (1H, m); MS, m/e
230 (M ), 216, 215, 207, 188, 173, 159, 157, 75, 57. Anal. Calcd for
C H SiO : C, 63.11; H, 10.60. Found: C, 63.16; H, 10.75.
þ
1
2
24
2
tert-Butoxydimethylsilyl enol ether from 4-methylcyclohexanone (5l):
ꢀ
À1
Colorless liquid; bp 59 C (1.5 mm Hg); d 0.869 g/ml; IR 1660 cm (C¼C);
1
H NMR d 0.14 (6H, s), 0.93 (3H, d, J ¼ 4.9 Hz), 1.29 (9H, s), 1.37–2.50 (7H,
þ
m), 4.92 (1H, m); MS, m/e 242 (M ), 227, 186, 185, 171, 169, 157, 144, 143,
1
6
29, 127, 75, 57. Anal. Calcd for C H SiO : C, 64.41; H, 10.81. Found: C,
13 28 2
4.33; H, 10.91.
tert-Butoxydimethylsilyl enol ether from cycloheptanone (5m): Colorless
ꢀ
À1
1
liquid; bp 45 C (1 mm Hg); d 0.906 g/ml; IR 1650 cm (C ¼ C); H NMR
d 0.14 (6H, s), 1.28 (9H, s), 1.44–2.31 (10H, m), 5.09 (1H, t, J ¼ 6.6 Hz); MS,
þ
m/e 241 (M -1), 226, 186, 185, 171, 169, 158, 157, 94, 75, 57. AnalCa lc d for
C H SiO : C, 64.41; H, 10.81. Found: C, 64.29; H, 10.98.
1
3
28
2
tert-Butoxydimethylsilyl enol ether from acetophenone (5n): Colorless
ꢀ
À1
1
liquid; bp 70 C (0.7 mm Hg); d 0.931 g/ml; IR 1610 cm (C ¼ C); H NMR
d 0.27 (6H, s), 1.33 (9H, s), 4.61 (1H, d, J ¼ 1.5 Hz), 4.93 (1H, d, J ¼ 1.4 Hz),
þ
7
.25–7.28 (3H, m), 7.34–7.59 (2H, m); MS, m/e 235 (M -15), 193, 179, 135,

ORDER
REPRINTS
2
388
FATAFTAH, RAWASHDEH, AND SOTIRIOU-LEVENTIS
1
6
05, 103, 75, 45. Anal. Calcd for C H SiO : C, 67.15; H, 8.86. Found: C,
22
1
4
2
6.96; H, 8.86.
Hydrolysis. The hydrolysis of the silyl enol ether derived from
cyclohexanone (5k) was investigated with the following solutions: A,
HOAc/THF/H O. 1:10:1 (v/v); B, THF/1 M HCl, 20:1 (v/v); C, THF/
2
1
M NaOH, 20:1 (v/v). For this purpose, silyl enol ether 5k (1 mmol) was
dissolved in 2.5 ml of solution A, B or C. After the indication time (Table 2),
the internalstandard, decane, was added, 10 mlof ether was used to extract
the solution, and the solution was washed with H O (5 ml), dried with
2
MgSO , and analyzed by GC.
4
ACKNOWLEDGMENT
C. Sotiriou-Leventis thanks the Petroleum Research Fund, admin-
istered by the American ChemicalSociety (Grant No. 35154-AC).
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1
2
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7
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9
. Stork, G.; Hudrlik, P.F. J. Am. Chem. Soc. 1968, 90, 4462.
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ity); tert-butyldimethylsilyl chloride ($226/mol, 99% purity). The latter
can be prepared from dimethylsilyl chloride and tert-butyllithium by
1
0
the method of Corey for approximately half of the selling cost.
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Received in the USA November 6, 2000

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