Tert-Butyldimethylsilyl Amine (TBDMS-NH2): A Mild and Green Reagent for the Protection of Benzyl Alcohols, Phenols, and Carboxylic Acids under Solvent-Free Conditions

Article abstract of DOI:10.1071/CH16097

Herein, we present the use of the tert-butyldimethylsilyl amine (TBDMS-NH2) as a silylating reagent for phenols, benzyl alcohols, and carboxylic acids. Unlike other silyl protection reactions, this reported process with TBDMS-NH2 does not involve the form

Full text of DOI:10.1071/CH16097

CSIRO PUBLISHING
Aust. J. Chem.
Full Paper
http://dx.doi.org/10.1071/CH16097
tert-Butyldimethylsilyl Amine (TBDMS-NH2):
A Mild and Green Reagent for the Protection of
Benzyl Alcohols, Phenols, and Carboxylic Acids
under Solvent-Free Conditions
A
A B
,
A B
,
Jeremy A. Duczynski, Rebecca Fuller,
and Scott G. Stewart
A
School of Chemistry and Biochemistry, The University of Western Australia (M310),
35 Stirling Highway, Crawley, WA 6009, Australia.
B
Corresponding authors. Email: rebecca.fuller@uwa.edu.au; scott.stewart@uwa.edu.au
Herein, we present the use of the tert-butyldimethylsilyl amine (TBDMS-NH2) as a silylating reagent for phenols, benzyl
alcohols, and carboxylic acids. Unlike other silyl protection reactions, this reported process with TBDMS-NH2 does not
involve the formation of HCl. Importantly, we report the efficacy of this reagent in operating under solvent-free conditions
and enabling short reaction times.
Manuscript received: 19 February 2016.
Manuscript accepted: 12 April 2016.
Published online: 11 May 2016.
Introduction
tert-Butyldimethylsilyl amine (TBDMS-NH2) was of interest
to us because of its corresponding basicity and the ability to
potentially generate gaseous ammonia as a product. This com-
pound has been used as the precursor to a nucleophilic reagent
specifically in several cases where a TBDMS-sulfinamide[12,13]
group has been required or where the TBDMS-NH2 is required as
a ligand.[14–19] The reagent has also been used in SnCl4-promoted
amidation reactions as an ammonia equivalent.[20] Additionally,
when TBDMS-NH2 has been used as a substrate in the formation
of more complex silicon compounds, often, multiple Si–N bonds
have been possible.[12,21,22] This reagent has been reported as a
silylating agent, however, only in rare instances. And in one
case, it has been used in conjunction with a strong acid.[23]
These reported preparations also include the formation of the
bis-tert-butyldimethylsilyl amine.[22] We had specific interest in
the behaviour of this reagent, particularly under solvent-free
conditions. A solvent-free system would simplify workup as
theoreticallytheonlyby-productisthevolatilegasammonia.[24,25]
The use of silicon-based protecting groups has historically been
an important facet in organic chemistry. Silicon-based protecting
groups have been successfully attached to various functional
groups including amines and imines but most importantly various
alcohols and phenols. The tert-butyldimethylsilyl (TBDMS)
ether has been used in synthetic programs encompassing total
synthesis, medicinal chemistry, and fine chemical synthesis.
Since the discovery of this group by Corey and Venkateswarlu in
1972,[1] a range of techniques have been proposed specifically for
the protection of oxygen-based functional groups.[2] It was
initially determined that imidazole was an excellent base for this
process; however, other bases such as triethylamine and DBU
have been used. Furthermore, in subsequent studies, it has been
reported that I2 can accelerate the reaction when the reagent
TBDMS-Cl is used.[3] Patschinski and Zipse have also recently
revisited the role of Lewis bases (additives such as 4-dimethyl-
aminopyridine) in various solvents along with reactions using
DMF alone.[4,5] Interestingly, the use of DMF has recently
been discovered to accelerate the reaction through a proposed
solvent-catalyzed pathway as opposed to a Lewis base-catalyzed
pathway.
Other useful TBDMS-based reagents for alcohols include
TBDMS-CN[6] and TBDMS-OTf,[7] which can be difficult to
prepare and are more expensive TBDMS-Cl. Silanes have
also been used as a protecting agent in combination with
[RuCl2(p-cymene)]2.[8] The silyl protection of phenols normally
mirrors that of alcohols with some articles detailing this reaction
specifically as part of detailed synthetic pathways.[9,10] Interes-
tingly, when dealing with more hindered phenols, Mitsunobu
reaction conditions (diethyl azodicarboxylate, triphenylpho-
sphine, and TBDMS-OH) have been reported to be more
successful.[11]
Results and Discussion
In order to carry out this study, a medium-scale synthesis of the
TBDMS-NH2 reagent was carried out following the procedure
of Wells et al.[26] As reported, simply bubbling ammonia
through a solution of the precursor TBDMS-Cl in pentane
afforded the reagent as well as solid ammonium chloride
(Scheme 1). It should be noted that for large amounts of
TBDMS-NH2, the workup procedure needed to be performed
under minimal contact with air because of the high vapour
pressure and hygroscopic nature of this reagent.
Initially, we investigated the protection of phenol with this
reagent in solvent-free conditions. Similarly, the group of
Mojtahedi reported the use of the hexamethyldisilazane under
Journal compilation Ó CSIRO 2016
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B
J. A. Duczynski, R. Fuller, and S. G. Stewart
Pentane
A
ꢀ
Table 1. Solvent effects for silyl protection using TBDMS-NH2
NH4Cl
ꢀ
2 NH3
Cl Si
H2N
Si
OH
O
1
2
rt
Si
ꢀ
Si
H2N
30 min
solvent
Scheme 1. Synthesis of TBDMS-NH2 reagent.[26]
4
2
5
Entry
Solvent
GC conversionB [%]
OH
1
2
3
4
5
6
THF
11
4
O
rt, neat
Si
NH
ꢀ
ꢀ
2-MeTHF
CH2Cl2
Ether
H2N
Si
3
30 min,
89 %
13
2
2
3
Water
Neat
6
85
Scheme 2. Protection of phenol under solvent-free conditions; rt denotes
room temperature.
AReactions conditions: alcohol (1.0 mmol), TBDMS-NH2 (1.0 mmol),
catalyst free, room temperature, 30 min.
BAll GC conversions are reported after 30 min reaction time.
Lewis acidic (Fe3O4 nanoparticles) and solvent-free conditions
for synthesis of the simpler and less stable TMS ethers.[27] In our
case, simply taking phenol and adding TBDMS-NH2 and
stirring for 30 min in an open flask resulted in an 89 % yield
of the TBDMS ether following a simple workup (Scheme 2).
Placing a pH indicator paper over the reaction outlet resulted in
an intense colour change, suggesting the evolution of ammonia.
Additionally, the reaction mixture reached homogeneity within
5 min.[25]
In order to determine if the solvent-free method was the most
compatible and efficient with this reagent, a series of reactions
with the 4-tert-butylphenol (4) was conducted (Table 1). In
THF, a solvent commonly used for the formation of silyl ethers,
the reaction conversion was poor. This result was also mirrored
with the environmentally friendly 2-MeTHF and the other
solvents i.e. DCM and ether. In order to determine the efficacy
of the reagent in a benign and polar solvent, a reaction in water
was conducted (Table 1, Entry 5). Unfortunately, this reaction
was also poor, only resulting in 6 % yield of the silyl ether under
the described conditions.
Given the success of the neat reaction at room temperature
after 30 min, a subsequent series of reactions involving other
phenols were conducted. Generally, the reported conversion of
the phenols, based on consumption of the starting material, was
excellent (Table 2). Importantly, the gas chromatography (GC)
conversion also mirrored the isolated yield (within minor error),
implying that products were stable to the workup conditions and
that GC was a valid technique for measuring conversions in
these systems. In this reaction study, under a short period of
time, phenols bearing electron-withdrawing groups (Table 2,
Entries 1 and 2) were readily converted into the corresponding
silyl ethers. Likewise, the aryl halide (Table 2, Entry 4) and
substrates bearing electron-withdrawing substituents (Table 2,
Entries 5–11) were effective. As reported by Liu et al.,[28] the
protection of the meta-hydroxylbenzaldehyde was more facile
than the ortho-analogue, probably due to intramolecular inter-
actions. The bicyclic systems hydroxyquinoline and naphthols
(Table 2, Entries 12 and 13) afforded a lower yield after 30 min;
however, over slightly longer reaction times, the yields were
good-to-excellent.
TBDMS-NH2 were realized when the ortho, ortho-bisisopropyl
phenol was determined to be unreactive.
In conjunction with this phenol protection study, two other
functional groups bearing acidic protons (carboxylic acids and
benzyl alcohols) were also investigated for their ability
to undergo silylation under these solvent-free conditions.
The protection of carboxylic acids has been investigated by
several groups[1,29,30] sometimes under catalytic conditions
(Ru3(CO)12/EtI).[31] This reaction is normally achieved using
standard conditions using TBDMS-Cl but can include additives
such as N-methylmorpholine. Also, TBDM-SH has been used
by Yamamoto and Takemae[30] and Thiemann et al.[32] with the
use of triphenylphosphine as catalyst. In this study (Table 3),
carboxylic acids bearing different electronic properties were
rapidly converted into the silyl ester, again under neat conditions
with only ammonia as the other product. Importantly, for silyl
esters, this protection procedure does not involve the formation
of HCl, instead relying on ammonia as the leaving group. A
solvent-free route to silyl esters has also been reported by Ojima
et al. using the carboxylic acid (p-cymene)ruthenium dichloride
and a silane.[8]
A short investigation involving the protection of benzyl
alcohols was also conducted (Table 3). It was clear that this
reaction required longer reaction times and more reagent possibly
due to the less acidic nature of the functional group in comparison
with other reactions in our study. In the two cases where electron-
donating groups adorned the ring system, the conversion was
excellent (Table 3, Entries 6 and 7). However, the halide-
substituted benzyl alcohol was less reactive (76 %) during this
short timeframe under the same reaction conditions.
A final study involving a series of competition experiments
were also conducted (Scheme 3). To begin with, a reaction
involving 3 equiv. of the TBDMS-NH2 reagent (to allow for
multiple protection of both the phenol and benzyl alcohol) led to
the bis-protected product in 76 % yield. Surprisingly, when
limiting the reagent to 1.2 equiv. (Scheme 3b), selectivity for
the benzyl alcohol (43 %) over the phenol (11 %) was observed
with the bis-protected product (28 %) also isolated. Further-
more, to confirm this selectivity a second experiment wherein
both the phenol and benzyl alcohol were treated with a stoichio-
metric amount of the silylating agent resulted in a 2 : 1 mixture
of the benzyl alcohol in favour of phenol. The selectivity
between a simple primary alcohol, heptanol, and phenol was
also examined resulting in a similar rate of protection of each of
The phenyl ether phenol system (Table 2, Entry 14) was also
high yielding. However, the more sterically encumbered ortho,
ortho-dimethoxy-substituted phenol produced only moderate
amounts of the silyl ether after 3 h. This result is in agreement
with earlier reports, which indicate a low conversion associated
with ortho–ortho di-substituted phenols (2,6-dimethylphenol)
and the need for Mitsunobu conditions.[11] The limitations of

tert-Butyldimethylsilyl Amine (TBDMS-NH2)
C
A
Table 2. (Continued)
Table 2. Protection of phenols using TBDMS-NH2
OH
O
Entry
13
Phenol
Time [min]
GC conversionB
rt, neat
Si
ꢀ
ꢀ NH3
H2N
Si
(isolated yield) [%]
R
R
2
180
91 (76)
Entry
1
Phenol
Time [min]
GC conversionB
OH
(isolated yield) [%]
14C
30
85
30
30
96 (86)
O
OH
OH
O
OH
OH
15C
180
(51)
2
3
85
O
O
16
180
0
30
97 (97)
OH
OH
CF3
AReactions conditions: phenol (0.5 mmol), TBDMS-NH2 (0.6 mmol), neat,
room temperature.
4
5
30
30
98 (98)
H
O
BReaction was monitored by GC and is reported as a conversion relative to
Cl
the starting material.
CTHF (0.2 mL) added as solvent.
100 (99)
OH
H
these moieties (Scheme 3d). Competition between phenol and
benzoic acid was also conducted, resulting in selectivity for the
carboxylic acid over the phenol in a ratio of roughly 2 : 1.
O
6
30
100 (91)
OH
Conclusion
O
In summary, we have developed a green protocol for the
protection of phenols, benzyl alcohols, and carboxylic acids
using the reagent tert-butyldimethylsilyl amine. This protocol
was found to be general, displaying a wide substrate scope and
functional group tolerance while providing good-to-excellent
yields of the silylated product. In following investigations, we
intend to use other silyl amines as protecting agents such
as TMS-NH2, triisopropylsilyl amine (TIPS-NH)2, and tert-
butyldiphenylsilyl amine (TBDPS-NH2) as well as examining
the mechanistic pathway of this interesting reagent.
H
7C
180
61
OH
O
H
8
9
30
30
100 (99)
OH
O2N
98
OH
OH
Experimental
General
NO2
NO2
All air-sensitive reactions were performed under nitrogen. All
non-aqueous solvents used in reactions were anhydrous unless
noted otherwise. Anhydrous solvents were distilled over the
appropriate drying agent or acquired from a Pure Solv 5-Mid
Solvent Purification System (Innovative Technology Inc.).
1H and 13C NMR spectra were acquired on a Bruker AV500
(500.13 MHz for 1H and 125.8 MHz for 13C) or a Bruker AV600
10
11
12
30
30
96
98
81
OH
1
(600.13 MHz for H and 150.9 MHz for 13C) spectrometer at
258C. All chemical shifts (d) were referenced to the residual
partially non-deuterated solvents and reported in parts per
million (ppm). Infrared spectra were measured directly with an
attenuated total reflectance (ATR) adaptor and acquired on a
PerkinElmer Spectrum One spectrometer at 2 cmꢀ1 resolution.
Mass spectroscopy (MS) was performed on a Waters GCT
Premier XE instrument for high-resolution (HR) electron
ionization (EI), Waters LCT Premier for atmospheric pressure
N
180
N
OH
(Continued)

D
J. A. Duczynski, R. Fuller, and S. G. Stewart
Table 3. Protection of carboxylic acids and benzyl alcohols using
A
TBDMS-NH2
Preparation of tert-Butyldimethylsilyl Amine
TBDMS-NH2 was prepared according to an existing proce-
dure.[33] tert-Butyldimethylsilyl chloride (15 g, 100 mmol) was
dissolved in pentane (20 mL), and the resulting mixture was
cooled to ꢀ788C. Anhydrous ammonia was bubbled through
this solution for 1 h, resulting in the immediate formation of a
white precipitate. The ensuing mixture was warmed to room
temperature and refluxed for 2 h to remove excess ammonia. The
resulting precipitate was removed by filtration under nitrogen,
and the solution was concentrated under reduced pressure to
afford tert-butyldimethylsilyl amine (10 g, 76mmol, 76 %).
O
O
Si
O
R
R
OH
OR
rt, neat
ꢀ
H2N Si
ꢀ NH3
OR
Si
2
OH
O
R
R
Entry
1
Substrate
Time [min]
30
GC conversionB
(isolated yield) [%]
General Procedure for the Protection of Phenols with
No Solvent
100
O
OH
The protection of phenols was carried out by the addition
of starting phenol (0.5 mmol) to magnetically stirred tert-
butyldimethylsilyl amine (0.6 mmol) in an open 3-mL reaction
vial. Reaction progress was monitored at various time points
by GC analysis. After the reaction was complete, the mixture
was immediately subjected to purification by preparative
TLC.
2
3
30
30
100 (99)
O
OH
O
100 (99)
O
O
tert-Butyldimethyl(phenoxy)silane (Scheme 2)
OH
Phenol (188mg, 2 mmol) was added to tert-butyldimethylsilyl
amine (315mg, 2.4mmol). The resulting solution was stirred for
30min at room temperature. After completion of the reaction, the
crude reaction mixture was purified by preparative TLC with
hexanes/ethyl acetate(EtOAc) 90: 10 (v/v) to afford the corres-
ponding silyl ether as a colourless oil (371 mg, 1.78 mmol, 89%).
The spectral data were in accordance with those reported in the
literature.[34] dH (CDCl3, 500 MHz) 7.22 (2H, t, J 7.8), 6.94 (1H, t,
J 7.3), 6.84 (2H, d, J 8.0), 0.98 (9H, s), 0.19 (6H, s).
O
O
4
5
30
100 (99)
OH
1200
0
HO
OH
Br
H2N
tert-Butyl(4-methoxyphenoxy)dimethylsilane
(Table 2, Entry 1)
O
6C
1200
93D
O
O
4-Hydroxyanisole (62 mg, 0.5 mmol) was added to tert-
butyldimethylsilyl amine (80 mg, 0.6 mmol). The resulting
solution was stirred for 30 min at room temperature. After
completion of the reaction, the crude reaction mixture was
purified by preparative TLC with hexanes/EtOAc 90 : 10 (v/v)
to afford the corresponding silyl ether as a colourless
oil (103 mg, 0.43 mmol, 86 %). The spectral data were in
accordance with those reported in the literature.[35] dH
(CDCl3, 500 MHz) 6.76 (4H, m), 3.76 (3H, s), 0.97 (9H, s),
0.16 (6H, s).
OH
O
7C
1200
1200
97D (81)
O
O
OH
8C
76D
I
OH
tert-Butyl(4-(tert-butyl)phenoxy)dimethylsilane
AReactions conditions: substrate (1.0 mmol), TBDMS-NH2 (1.2 mmol),
room temperature.
(Table 2, Entry 2)
The general procedure was followed using 4-tert-butylphenol
(75 mg, 0.5 mmol) to afford the corresponding silyl ether as
determined by GC analysis (86 % yield). The spectral data for
this compound were in accordance with those reported in the
literature.[36] dH (CDCl3, 500 MHz) 7.22 (2H, d, J 8.4), 6.75 (2H,
d, J 7.6), 1.29 (9H, s), 0.98 (9H, s), 0.19 (6H, s).
BReaction was monitored by GC and is reported as a conversion relative to
the starting material.
CTHF (0.2 mL) added as solvent.
DTBDMS-NH2 (1.5 mmol) was used.
tert-Butyldimethyl(3-(trifluoromethyl)phenoxy)silane
(Table 2, Entry 3)
chemical ionization (APCI), or a Shimadzu GCMS QP2010 for
low-resolution. Preparative TLC was performed with in-house
prepared plates, using silica gel 60 (0.04–0.063) supplied by
Merck, unless otherwise stated. The visualization of the
developed plates was achieved using a 254-nm or 365-nm
UV lamp.
3-(Trifluoromethyl)phenol (62 mL, 0.5 mmol) was added to
tert-butyldimethylsilyl amine (80 mg, 0.6 mmol). The resulting
solution was stirred for 30 min at room temperature. After
completion of the reaction, the crude reaction mixture was

tert-Butyldimethylsilyl Amine (TBDMS-NH2)
E
(a)
(b)
(c)
OH
OTBDMS
TBDMS-NH2 (3 equiv.)
rt, 180 min
OH
OTBDMS
76 %
OTBDMS
OH
OTBDMS
OH
TBDMS-NH2 (1.2 equiv.)
rt, 180 min
ꢀ
ꢀ
OTBDMS
H
O
OTBDMS
OH
43
11 %
%
28 %
OH
OH
OTBDMS
TBDMS-NH2 (1.2 equiv.)
rt, 30 min
ꢀ
ꢀ
OTBDMS
OH
:
1
2
(d)
(e)
OTBDMS
TBDMS-NH2 (1.2 equiv.)
rt, 30 min
H
O
OTBDMS
ꢀ
ꢀ
:
1
1
H
O
OTBDMS
O
O
TBDMS-NH2 (1.2 equiv.)
rt, 30 min
OH
OTBDMS
ꢀ
ꢀ
:
1
2
Scheme 3. Functional group competition experiments with the TBDMS-NH2 reagent.
purified by preparative TLC with hexanes/EtOAc 90 : 10 (v/v)
to afford the corresponding silyl ether as a yellow oil (134 mg,
0.49 mmol, 97 %). nmax (neat)/cmꢀ1 2933 (C–H), 1491, 1448,
1328 (C–F), 1125, 942. dH (CDCl3, 600 MHz) 7.34 (1H, t, J 7.9),
7.24–7.19 (1H, m), 7.08 (1H, t, J 1.7), 7.00 (1H, dd, J 8.2, 2.4),
1.00 (9H, s), 0.22 (6H, s). dC (CDCl3, 151 MHz) 156.0, 132.0
(q, JC–F 32.3), 130.1, 124.1 (q, JC–F 272.3), 123.5, 118.1 (q, JC–F
3.9), 117.2 (q, JC–F 3.8), 25.7, 18.3, ꢀ4.4. HRMS (EI) m/z
276.1155; [M]þ requires 276.1157.
3-((tert-Butyldimethylsilyl)oxy)benzaldehyde
(Table 2, Entry 6)
3-Hydroxybenzaldehyde (61 mg, 0.5 mmol) was added to
tert-butyldimethylsilyl amine (80 mg, 0.6 mmol). The resulting
solution was stirred for 30 min at room temperature. After
completion of the reaction, the crude reaction mixture was
purified by preparative TLC with hexanes/EtOAc 90 : 10 (v/v)
to afford the corresponding silyl ether as a pale yellow oil
(108 mg, 0.46 mmol, 91 %). The spectral data for this compound
were in accordance with those reported in the literature.[39] dH
(CDCl3, 500 MHz) 9.95 (1H, s), 7.43 (2H, dt, J 27.3, 7.6), 7.33
(1H, s), 7.11 (1H, d, J 6.2) 1.00 (9H, s), 0.22 (6H, s).
tert-Butyl(4-chlorophenoxy)dimethylsilane
(Table 2, Entry 4)
4-Chlorophenol (64 mg, 0.5 mmol) was added to tert-
butyldimethylsilyl amine (80 mg, 0.6 mmol). The resulting
solution was stirred for 30 min at room temperature. After
completion of the reaction, the crude reaction mixture was
purified by preparative TLC with hexanes/EtOAc 90 : 10 (v/v)
to afford the corresponding silyl ether as a pale yellow oil
(120 mg, 0.5 mmol, 99 %). The spectral data were in accor-
dance with those reported in the literature.[37] dH (CDCl3,
500 MHz) 7.17 (2H,d, J 8.5), 6.76 (2H, d, J 8.5), 0.97 (9H, s),
0.18 (6H, s).
2-((tert-Butyldimethylsilyl)oxy)benzaldehyde
(Table 2, Entry 7)
The general procedure was followed using 2-hydroxy-
benzaldehyde (61 mg, 0.5 mmol) and the addition of THF
(0.2 mL) to afford the corresponding silyl ether as determined
by GC analysis (61 % yield). The spectral data for this
compound were in accordance with those reported in the
literature.[40] dH (CDCl3, 500 MHz) 10.37 (1H, s), 7.71 (1H,
dd, J 9.3, 1.5), 7.36 (1H, dt, J 8.1, 1.9), 6.93 (1H, t, J 7.7), 6.78
(1H, d, J 8.3), 0.92 (9H, s), 0.18 (6H, s).
4-((tert-Butyldimethylsilyl)oxy)benzaldehyde
(Table 2, Entry 5)
tert-Butyldimethyl(4-nitrophenoxy)silane (Table 2, Entry8)
4-Hydroxybenzaldehyde (61 mg, 0.5 mmol) was added to
tert-butyldimethylsilyl amine (80 mg, 0.6 mmol). The resulting
solution was stirred for 30 min at room temperature. After
completion of the reaction, the crude reaction mixture was
purified by preparative TLC with hexanes/EtOAc 90 : 10 (v/v)
to afford the corresponding silyl ether as a colourless oil
(118 mg, 0.5 mmol, 100 %). The spectral data for this compound
were in accordance with those reported in the literature.[38]
dH (CDCl3, 500 MHz) 9.87 (1H, s), 7.79 (2H, d, J 8.4), 6.94 (2H,
d, J 8.4), 0.99 (9H, s), 0.25 (6H, s).
4-Nitrophenol (64 mg, 0.5 mmol) was added to tert-
butyldimethylsilyl amine (80 mg, 0.6 mmol). The resulting
solution was stirred for 30 min at room temperature. After
completion of the reaction, the crude reaction mixture was
purified by preparative TLC with hexanes/EtOAc 90 : 10 (v/v)
to afford the corresponding silyl ether as a yellow oil (125 mg,
0.49 mmol, 99 %). The spectral data for this compound were in
accordance with those reported in the literature.[41] dH (CDCl3,
500 MHz) 8.15 (2H, d, J 9.0), 6.90 (2H, d, J 9.0), 0.99 (9H, s),
0.26 (6H, s).

F
J. A. Duczynski, R. Fuller, and S. G. Stewart
tert-Butyldimethyl(3-nitrophenoxy)silane
(Table 2, Entry 9)
(CDCl3, 151 MHz) 158.0, 147.8, 146.7, 129.5, 125.0, 122.1,
122.1, 122.0, 121.8, 116.8, 25.6, 18.3, ꢀ4.4. m/z (HRMS APCI)
301.1632; [M þ H]þ requires 301.1624.
The general procedure was followed using 3-nitrophenol
(70 mg, 0.5 mmol) to afford the corresponding silyl ether as
determined by GC analysis (98 % yield). The spectral data for
this compound were in accordance with those reported in the
literature.[42] dH (CDCl3, 500 MHz) 7.79 (1H, d, J 8.1), 7.43 (1H,
t, J 7.8), 7.06–6.95 (2H, m), 1.01 (9H, s), 0.26 (6H, s).
tert-Butyl(2,6-dimethoxyphenoxy)dimethylsilane
(Table 2, Entry 16)
The general procedure was followed using 2,6-dimethoxy-
phenol (77 mg, 0.5 mmol) and the addition of THF (0.2 mL) to
afford the corresponding silyl ether determined by GC analysis
(51 % yield). nmax (neat)/cmꢀ1 2927 (C–H), 1595, 1501, 1476,
1251, 1110, 766. dH (CDCl3, 500 MHz) 6.85 (1H, t, J 6.8), 6.55
(2H, d, J 6.6), 3.79 (6H, s), 1.02 (9H, s), 0.13 (6H, s). dC (CDCl3,
126 MHz) 152.0, 134.6, 120.7, 105.5, 55.9, 26.0, 18.9, ꢀ4.5.
HRMS (EI) m/z 268.1507; [M]þ requires 268.1495.
tert-Butyldimethyl(2-nitrophenoxy)silane
(Table 2, Entry 10)
The general procedure was followed using 2-nitrophenol
(70 mg, 0.5 mmol) to afford the corresponding silyl ether as
determined by GC analysis (96 % yield). The spectral data for
this compound were in accordance with those reported in the
literature.[43] dH (CDCl3, 500 MHz) 7.80 (1H, d, J 8.1), 7.43
(1H, t, J 7.8), 7.02 (1H, t, J 7.7), 6.98 (1H, d, J 8.3), 1.01
(9H, s), 0.26 (6H, s).
tert-Butyldimethylsilyl Benzoate (Table 3, Entry 1)
The general procedure was followed using benzoic acid
(61 mg, 0.5 mmol) to afford the corresponding silyl ester deter-
mined by GC analysis (100 % yield). The silyl ester was purified
by preparative TLC with hexanes/EtOAc 90 : 10 (v/v). The
spectral data for this compound were in accordance with those
reported in the literature.[46] dH (CDCl3, 600 MHz) 8.04 (2H, dd,
J 8.3, 1.4), 7.54 (1H, dd, J 10.5, 4.4), 7.43 (2H, dd, J 10.9, 4.8),
1.03 (5H, s), 0.38 (3H, s).
4-((tert-Butyldimethylsilyl)oxy)benzonitrile
(Table 2, Entry 11)
The general procedure was followed using 4-cyanophenol
(60 mg, 0.5 mmol) to afford the corresponding silyl ether as
determined by GC analysis (98 % yield). The spectral data for
this compound were in accordance with those reported in
the literature.[44] dH (CDCl3, 500 MHz) 7.54 (2H, d, J 8.6),
6.89 (2H, d, J 8.6), 0.98 (9H, s), 0.23 (6H, s).
tert-Butyldimethylsilyl 4-Methoxybenzoate
(Table 3, Entry 2)
The general procedure was followed using 4-methoxybenzoic
acid (76 mg, 0.5 mmol), and the resulting solution was concen-
trated under reduced pressure to afford the corresponding ester as
a colourless oil (133 mg, 0.5 mmol, 100%). nmax (neat)/cmꢀ1
2955, 2931, 2858, 1693, 1605, 1286, 1251. dH (CDCl3, 500 MHz)
7.99 (2H, d, J 8.6), 6.91 (2H, d, J 8.6), 3.86 (3H, s), 1.02 (9H, s),
0.36 (6H, s). dC (CDCl3, 151 MHz) 166.5, 163.5, 132.3, 124.2,
113.7, 55.6, 25.8, 18.0, ꢀ4.6. HRMS (APCI) m/z 267.1427;
[Mþ H]þ requires 267.1416.
8-((tert-Butyldimethylsilyl)oxy)quinoline
(Table 2, Entry 12)
The generalprocedure was followed using 8-hydroxyquinoline
(73 mg, 0.5 mmol) to afford the corresponding silyl ether as
determined by GC analysis (81 % yield). nmax (neat)/cmꢀ1 3050
(C–H), 2928 (C–H), 1570, 1498, 1471, 1101, 824. dH (CDCl3,
600 MHz) 8.86 (1H, dd, J 4.1, 1.7), 8.09 (1H, dd, J 8.3, 1.7), 7.42–
7.39 (2H, m), 7.36 (1H, dd, J 8.3, 4.1), 7.21–7.16 (1H, m), 1.09
(10H, s), 0.29 (6H, s). dC (CDCl3, 151 MHz) 153.0, 148.7, 142.3,
135.8, 129.8, 127.0, 121.3, 120.5, 118.0, 26.1, 19.0, ꢀ3.8. m/z
(HRMS APCI) 260.1459; [M þ H]þ requires 260.1471.
tert-Butyldimethylsilyl 2-Acetoxybenzoate
(Table 3, Entry 3)
The general procedure was followed using 2-acetoxybenzoic
acid (90 mg, 0.5 mmol), and the resulting solution was concen-
trated under reduced pressure to afford the corresponding ester
as a colourless oil (147 mg, 0.5 mmol, 100 %). nmax (neat)/cmꢀ1
2957, 2930, 2858, 1759, 1700, 1270, 1078. dH (CDCl3,
600 MHz) 8.00 (1H, d, J 7.8), 7.60–7.49 (1H, m), 7.30 (1H, t,
J 7.6), 7.09 (1H, d, J 8.0), 2.35 (3H, s), 1.00 (9H, s), 0.35 (6H, s).
dC (CDCl3, 151 MHz) 169.9, 164.1, 151.3, 133.9, 132.3, 126.0,
124.6, 123.9, 25.8, 21.3, 18.0, ꢀ4.6. HRMS (APCI) m/z
295.1352; [M þ H]þ requires 295.1366.
tert-Butyldimethyl(naphthalen-1-yloxy)silane
(Table 2, Entry 13)
1-Naphthol (72 mg, 0.5 mmol) was added to tert-butyl-
dimethylsilyl amine (80 mg, 0.6 mmol). The resulting solution
was stirred for 30 min at room temperature. After completion of
the reaction, the crude reaction mixture was purified by prepa-
rative TLC with hexanes/EtOAc 90 : 10 (v/v) to afford the
corresponding silyl ether as a colourless oil (98 mg, 0.38 mmol,
76 %). The spectral data for this compound were in accordance
with those reported in the literature.[45] dH (CDCl3, 500 MHz)
8.18 (1H, m), 7.85–7.76 (1H, m), 7.51–7.42 (3H, m), 7.32 (1H, t,
J 7.8), 6.87 (1H, d, J 7.5), 1.10 (9H, s), 0.29 (6H, s).
tert-Butyldimethylsilyl Hexanoate (Table 3, Entry 4)
The general procedure was followed using hexanoic acid
(63 mL, 0.5 mmol), and the resulting solution was concentrated
under reduced pressure to afford the corresponding ester as a
colourless oil (115 mg, 0.5 mmol, 100 %). nmax (neat)/cmꢀ1
2956, 2931, 2859, 1720 (C=O), 1251, 825, 788. dH (CDCl3,
500 MHz) 2.30 (2H, t, J 7.5), 1.60 (1H, dt, J 14.7, 7.4), 1.39–1.22
(2H, m), 0.93 (9H, s), 0.92–0.81 (2H, m), 0.26 (6H, s).
dC (CDCl3, 151 MHz) 174.5, 36.2, 31.4, 25.7, 24.9, 22.5,
17.7, 14.1, ꢀ4.7. HRMS (EI) m/z 230.1708; [M]þ requires
230.1702.
tert-Butyldimethyl(2-phenoxyphenoxy)silane
(Table 2, Entry 14)
The general procedure was followed using 2-phenoxyphenol
(93 mg, 0.5 mmol) and the addition of THF (0.2 mL) to afford
the corresponding silyl ether determined by GC analysis (85 %
yield). nmax (neat)/cmꢀ1 3040 (C–H), 2930 (C–H), 1582, 1489,
1216, 919, 746. dH (CDCl3, 500 MHz) 7.30–7.23 (1H, m), 7.08–
6.98 (1H, m), 6.97–6.86 (1H, m), 0.86 (2H, s), 0.13 (2H, s). dC

tert-Butyldimethylsilyl Amine (TBDMS-NH2)
G
((2-Bromo-3,4,5-trimethoxybenzyl)oxy)(tert-butyl)
dimethylsilane (Table 3, Entry 6)
phenol as a colourless oil (51 mg, 0.21 mmol, 43 %), and
(3-((tert-butyldimethylsilyl)oxy)phenyl)methanol as a colour-
less oil (13 mg, 0.06 mmol, 11 %). The spectral data for these
compounds were in accordance with those reported in the
literature. (3-((tert-Butyldimethylsilyl)oxy)phenyl)methanol:[39]
dH (CDCl3, 500MHz) 7.21 (1H, t, J 7.8), 6.94 (1H, ddd, J 7.6, 1.6,
1.0), 6.86 (1H, ddd, J 2.2, 1.0, 0.5), 6.79–6.74 (1H, m), 4.64 (2H,
d, J 5.8), 1.58 (2H, s), 0.99 (9H, s), 0.20 (6H, s). 3-(((tert-
Butyldimethylsilyl)oxy)methyl)phenol: nmax (neat)/cmꢀ1 3335
(O–H), 2954, 2929, 2856, 1592, 1459, 833. dH (CDCl3,
500 MHz) 7.18 (2H, t, J 7.8), 6.86 (2H, d, J 7.7), 6.83 (2H, d,
J 2.0), 6.73–6.67 (2H, m), 4.70 (2H, s), 0.95 (9H, s), 0.11 (6H, s).
dC (CDCl3, 151 MHz) 155.8, 143.5, 129.6, 118.4, 113.9, 113.0,
64.8, 26.1, 18.6, ꢀ5.1. HRMS (EI) m/z 238.1395; [M]þ requires
238.1389.
(2-Bromo-3,4,5-trimethoxyphenyl)methanol
(139 mg,
0.5 mmol) was added to magnetically stirred tert-butyldimethyl-
silyl amine (0.75 mmol, 98 mg) to afford the corresponding silyl
ether determined by GC analysis (93 % yield). The spectral data
for this compound were in accordance with those reported in the
literature.[47] dH (CDCl3, 500 MHz) 7.01 (1H, s), 4.68 (2H, s),
3.89 (3H, s), 3.87 (3H, s), 3.87 (1H, s), 0.97 (9H, s), 0.14 (6H, s).
(Benzo[d][1,3]dioxol-5-ylmethoxy)(tert-butyl)
dimethylsilane (Table 3, Entry 7)
1,3-Benzodioxole-5-methanol (61 mg, 0.5 mmol) was added
to tert-butyldimethylsilyl amine (98 mg, 0.75 mmol), and the
mixtures was dissolved in THF (0.2 mL). The resulting solution
was stirred for 20 h at room temperature. After completion of the
reaction, the crude reaction mixture was purified by preparative
TLC with hexanes/EtOAc 90 : 10 (v/v) to afford the correspon-
ding silyl ether as a colourless oil (108 mg, 0.41 mmol, 81 %).
nmax (neat)/cmꢀ1 2856 (C–H), 1490, 1442, 1249, 1040, 830,
774. dH (CDCl3, 500 MHz) 6.85 (1H, s), 6.76 (2H, d, J 1.0), 5.94
(2H, s), 4.64 (2H, s), 0.94 (9H, s), 0.10 (6H, s). dC (CDCl3,
126 MHz) 147.7, 146.6, 135.6, 119.4, 108.1, 107.2, 101.0, 65.0,
26.1, 18.6, ꢀ5.1. m/z (HRMS APCI) 267.1414; [M þ H]
requires 267.1416.
Protection Reaction of Phenol and Benzyl Alcohol
(Scheme 3c)
tert-Butyldimethylsilyl amine (80 mg, 0.6 mmol) was added
to a magnetically stirred mixture of phenol (0.5 mmol) and
benzyl alcohol (0.5 mmol). After 30 min, an aliquot of the
reaction mixture was analyzed by GC-MS to determine the
reaction selectivity (1 : 2, tert-butyldimethyl(phenoxy)silane/
benzyloxy(tert-butyl)dimethylsilane).
Protection Reaction of Phenol and Alkyl Alcohol
(Scheme 3d)
tert-Butyl((2-iodobenzyl)oxy)dimethylsilane
(Table 3, Entry 8)
tert-Butyldimethylsilyl amine (80 mg, 0.6 mmol) was added
to a magnetically stirred mixture of phenol (0.5 mmol) and
heptanol (0.5 mmol). After 30 min, an aliquot of the reaction
mixture was analyzed by GC-MS to determine the reaction
selectivity (1 : 1, tert-butyl(heptyloxy)dimethylsilane/tert-butyl-
dimethyl(phenoxy)silane).
2-Iodobenzyl alcohol (117 mg, 0.5 mmol) was added to mag-
netically stirred tert-butyldimethylsilyl amine (98 mg, 0.75 mmol)
to afford the corresponding silyl ether determined by GC analysis
(76 % yield). The spectral data for this compound were in
accordance with those reported in the literature.[48] dH (CDCl3,
500 MHz) 7.77 (1H, d, J 7.8), 7.51 (1H, d, J 7.6), 7.36 (1H, t, J 6.3),
6.96 (1H, t, J 7.5), 4.62 (2H, s), 0.97 (9H, s), 0.14 (6H, s).
Protection Reaction of Phenol and Benzoic Acid
(Scheme 3e)
Competition Experiments (Scheme 3)
tert-Butyldimethylsilyl amine (80 mg, 0.6 mmol) was added
to a magnetically stirred mixture of phenol (0.5 mmol) and
benzoic acid (0.5 mmol). After 30 min, an aliquot of the reaction
mixture was analyzed by GC-MS to determine the reaction
selectivity (1 : 2, tert-butyldimethyl(phenoxy)silane/tert-butyl-
dimethylsilyl benzoate).
Reaction of 3-Hydroxybenzyl Alcohol (Scheme 3a)
3-Hydroxybenzyl alcohol (62 mg, 0.5 mmol) was added to
magnetically stirred tert-butyldimethylsilyl amine (197 mg,
1.5 mmol). The resulting solution was stirred for 180 min at
room temperature. After completion of the reaction, the crude
reaction mixture was purified by preparative TLC with hexanes/
EtOAc 90 : 10 (v/v) to afford the corresponding silyl ether as a
colourless oil (134 mg, 0.38 mmol, 76 %).The spectral data for
this compound were in accordance with those reported in
the literature for tert-butyl((3-((tert-butyldimethylsilyl)oxy)
benzyl)oxy)dimethylsilane.[49] dH (CDCl3, 500 MHz) 7.17
(1H, t, J 7.8), 6.89 (1H, ddd, J 7.6, 1.5, 0.8), 6.84 (1H, s),
6.75–6.67 (1H, m), 4.69 (2H, s), 0.99 (9H, s), 0.95 (9H, s), 0.20
(6H, s), 0.10 (6H, s).
Supplementary Material
1H and 13C spectra of new and relevant compounds are available
on the Journal’s website.
Acknowledgements
The authors acknowledge the facilities, and the scientific and technical
assistance of the Australian Microscopy and Microanalysis Research Facility
at the Centre for Microscopy, Characterisation and Analysis, The University
of Western Australia – a facility funded by the University, State and
Commonwealth Governments. Further NMR assistance from Associate
Professor Lindsay Byrne and Senior Research Officer Campbell MacKenzie
is gratefully acknowledged. J.A.D. is the recipient of a University Post-
graduate Award scholarship from the University of Western Australia.
Reaction of 3-Hydroxybenzyl Alcohol (Scheme 3b)
3-Hydroxybenzyl alcohol (62 mg, 0.5 mmol) was added to
magnetically stirred tert-butyldimethylsilyl amine (80 mg,
0.6 mmol). The resulting solution was stirred for 30 min at room
temperature. After completion of the reaction, the crude reaction
mixture was purified by preparative TLC with hexanes/EtOAc
90 : 10 (v/v) to afford tert-butyl((3-((tert-butyldimethylsilyl)
oxy)benzyl)oxy)dimethylsilane as a colourless oil (49 mg,
0.14 mmol, 28 %), 3-(((tert-butyldimethylsilyl)oxy)methyl)
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