Aluminium triflate [Al(OTf)3] as a recyclable catalyst for the conversion of α-hydroxyphosphonates, alcohols and phenols to their corresponding O-silylated products with hexamethyldisilazane (HMDS)

Article abstract of DOI:10.1055/s-2005-861789

Al(OTf)₃ as a recyclable catalyst conducts the efficient conversion of various types of α-hydroxyphosphonates to their corresponding α-trimethysilyloxyphosphonates with HMDS in the absence of solvent at room temperature. The general applicabili

Full text of DOI:10.1055/s-2005-861789

PAPER
595
Aluminium Triflate [Al(OTf)3] as a Recyclable Catalyst for the Conversion
of a-Hydroxyphosphonates, Alcohols and Phenols to Their Corresponding
O-Silylated Products with Hexamethyldisilazane (HMDS)
Aluminium
T
riflata3
e
[Al(O
T
f)
b
]
as
a
Recyc
i
lable
C
b
a
talyst Firouzabadi,* Nasser Iranpoor,* Sara Sobhani, Soheila Ghassamipour
Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71454, Iran
Fax +98(711)2280926; E-mail: Firouzabadi@chem.susc.ac.ir; E-mail: Iranpoor@chem.susc.ac.ir
Received 19 September 2004; revised 3 November 2004
other available method, hexamethylsilathiane has been
Abstract: Al(OTf)3 as a recyclable catalyst conducts the efficient
conversion of various types of a-hydroxyphosphonates to their cor-
responding a-trimethysilyloxyphosphonates with HMDS in the ab-
sence of solvent at room temperature. The general applicability of
used as a silylating agent at 50–70 °C.9 We now report
10,11
Al(OTf)3
as a reusable, efficient and easy to handle
catalyst for the high yielding preparation of diethyl a-tri-
the catalyst under solvent-free conditions is demonstrated by apply- methylsilyloxyphosphonates 2a–o by direct reaction of
ing it for the successful silylation of alcohols and phenols with
HMDS in high yields.
diethyl a-hydroxyphosphonates 1a–o with HMDS at
room temperature using neat conditions (Scheme 1,
Keywords: a-hydroxyphosphonates, solvent-free, aluminium tri-
flate, a-acetyloxyphosphonates, alcohols, phenols
Table 1).
O
O
P
Al(OTf)3 (0.05 equiv)
R
P
R
OEt
OEt
OEt
OEt
In conjunction with our interest in the development of
synthetic methods for the preparation of phosphonate de-
rivatives from a-hydroxyphosphonates, we have focused
our attention to the preparation of a-trimethylsilyloxy-
phosphonates by direct silylation of a-hydroxyphospho-
nates with HMDS catalyzed by iodine, Cu(OTf)2 and
Mg(OTf)2.1 a-Trimethylsilyloxyphosphonates are attrac-
tive compounds from different views. They are potential
synthons of masked acyl anions2 which react with various
ketones to produce the corresponding a-hydroxyketones.3
Unsymmetrical ketones can be also produced by the reac-
tion of a-lithiated a-trimethylsilyloxyphosphonates with
alkylating agents.4 a-Lithiated a-trimethylsilyloxyphos-
phonates can undergo acylation with a variety of acylating
agents to produce the corresponding a-acylated products.
These compounds in turn, can be easily transformed to a-
hydroxyketones by the cleavage of Si-O bond and elimi-
nation of dialkyl phosphite in alkaline media.2c,5
HMDS (0.7 equiv)
neat, r.t.
OH
OTMS
1a–o
2a–o
Scheme 1
As shown in Table 1, various types of diethyl a-hy-
droxy(phenylmethyl)phosphonates (1a–k) were cleanly
and efficiently converted into their corresponding diethyl
a-trimethylsilyloxyphosphonates (2a–k) with HMDS in
the presence of a catalytic amount of Al(OTf)3 at room
temperature under solvent-free conditions (yields = 90–
97%). Diethyl a-hydroxy-2-naphthyl-, 3-pyridyl-, alkyl-
and aryl-b,g-unsaturated phosphonates (1l–o) are also si-
lylated efficiently giving the corresponding diethyl a-tri-
methylsilyloxyphosphonates (2l–o) in 90–96% yields
under similar reaction conditions.
C–P and Si–O bonds usually undergo cleavage and they
are sensitive towards reaction conditions. The almost
quantitative yields of the products strongly indicate that
C–P and Si–O bonds tolerate these mild reaction condi-
tions, which is an advantage of the method. Work-up of
the reaction mixture is not a time-consuming process and
the products are isolated in highly pure states and do not
require further purification.
The common methods for the preparation of a-trimethyl-
silyloxyphosphonates include reaction of aldehydes with
either diethyl trimethylsilyloxyphosphite or the mixture
of triethylphosphite and trimethylsilyl chloride.2a,6 These
protocols need harsh reaction conditions and long reaction
times. The other method includes the reaction of trialkyl
phosphate with silyl phenyl ketone, which requires a long
reaction time (12 h) and also proceeds at a rather high tem-
perature (80 °C).7 Procedures for the preparation of a-tri-
methylsilyloxyphosphonates by direct silylation of a-
hydroxyphosphonates8 are limited to only a few reports.1,9
Except in our reported methods in which HMDS has been
used as a silylating agent at room temperature, in the only
The spectral data of the known products (2a, b, g, k, n and
o) are compared with those reported in the literature. The
spectral data of the other known products (2c, e, f, i and j),
which have not been reported before and the spectral data
(1H NMR, 13C NMR, IR and MS) of the unknown prod-
ucts (2d, h, l, m) are presented in the experimental sec-
tion.
In order to show the advantage and limitation of Al(OTf)3,
we have compared the catalytic activity of this catalyst
with LiOTf,15 Ce(OTf)4,16 Hg(OTf)2,17 Cu(OTf)2,18
SYNTHESIS 2005, No. 4, pp 0595–0599
Advanced online publication: 18.01.2005
DOI: 10.1055/s-2005-861789; Art ID: P11304SS
© Georg Thieme Verlag Stuttgart · New York
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596
H. Firouzabadi et al.
PAPER
Table 2 Silylation of Diethyl a-Hydroxy(phenylmethyl)phospho-
nate (1a) with HMDS in the Presence of Various Lewis Acids in Neat
Conditions at Room Temperature
Table 1 Silylation of Diethyl a-Hydroxyphosphonates (1a–o) to
Diethyl a-Trimethylsilyloxyphosphonates (2a–o) with HMDS in the
Presence of Al(OTf)3 Under Solvent-Free Conditions at Room Tem-
perature
Entry
Lewis acid a
Time (h)
% Conversion based
on 1H NMR
Product 2ref
R
Time (min)
Yielda (%)
b
b
a2c,7
b12
c
C6H5
–
97
90
92
90
95
96
95
96
90
91
92
92
96
90
90
1
2
Al(OTf)3
Mg(OTf)2
Cu(OTf)2
Ce(OTf)4
Hg(OTf)2
LiOTf
–
100
100
60
b
b
–
4-CH3C6H4
4-CH3OC6H4
2,4,6-(CH3)3C6H2
2-ClC6H4
–
b
3
4.5
3
–
b
4
80
d
–
5
10
60
e
5
10
5
6
1.5
1
100
100
20
f
3-ClC6H4
g13
h
4-ClC6H4
7
ZnCl2
b
8
Zn(bipy)3Cl2
FeCl3
24
2,6-Cl2C6H3
2-O2NC6H4
3-O2NC6H4
4-O2NC6H4
2-Naphthyl
3-Pyridyl
–
9
1.5
1.5
1.5
4.5
10
80
i
10
20
25
10
10
11
12
14
15
Fe(bipy)Cl3
ZrOCl2.8H2O
AlCl3
30
j
k13
l
30
80
b
CuCl2
20
m
n14
o14
–
MgCl2
6.5
50
PhCH=CH
MeCH=CH
10
25
a The molar ratios of substrate–HMDS–catalyst are 1:0.7:0.1.
b Reaction occurred immediately.
a Yields of isolated products at r.t.
b Reaction occurred immediately.
HMDS
Mg(OTf)2,19 and Lewis acids such as AlCl3, ZnCl2,20a
Zn(bipy)3Cl2,20b FeCl3, Fe(bipy)Cl3,20b CuCl2, MgCl2, and
ZrOCl2·8H2O for the silylation of 1a as a model com-
pound, with HMDS in the absence of solvent at room tem-
perature in our laboratory. We found that Al(OTf)3 was
the most effective catalyst and is comparable with
Mg(OTf)2 among the other catalysts we have studied for
this purpose (Table 2).
Al(OTf)3
+
HN(TMS)2
NH3
–
Al(OTf)3
R
OH
_
In the reactions we have studied, fast evolution of NH3
was observed. We were also able to recover Al(OTf)3 and
reuse it without loss of its catalytic activity. Therefore, we
have proposed a mechanism in which the generation of
NH3 and the catalytic role of Al(OTf)3 in a catalytic cycle
are clarified (Scheme 2).
+
[H3N-Al(OTf)3]
R
OTMS
–
+
(TMS)NH2
Al(OTf)3
R
OH
R
OTMS
In this mechanism, we have suggested that a Lewis acid-
base interaction between metal triflate and nitrogen in
HMDS polarizes N–Si bond of HMDS to produce a reac-
tive silylating agent, 3. Both Mg2+ and Al3+ that are harder
Lewis acids in comparison with Li+, Cu2+, Ce4+, and Hg2+
interact more strongly with the nitrogen atom as a hard
Lewis base in HMDS. Therefore, N–Si bond polarization
effected by Mg(OTf)2 and Al(OTf)3 is more pronounced
(Table 2) than those generated by LiOTf, Cu(OTf)2,
Ce(OTf)4, and Hg(OTf)2. This qualitative explanation jus-
tifies the higher activity of Mg(OTf)2 and Al(OTf)3 than
the other triflates we have studied.
Scheme 2
Silylation of alcohols are among the most frequently used
processes in organic synthesis and provides cheap and ef-
ficient means for the protection of hydroxyl group during
oxidation, peptide coupling and halogenation reactions.21
In order to show general applicability of the presented
method, we have also studied silylation of alcohols and
phenols with HMDS in the presence of catalytic amounts
of Al(OTf)3 under solvent-free conditions at room tem-
perature (Scheme 3).
Synthesis 2005, No. 4, 595–599 © Thieme Stuttgart · New York

PAPER
Scheme 3
Aluminium Triflate [Al(OTf)3] as a Recyclable Catalyst
597
Table 3 Silylation of Alcohols and Phenols with HMDS in the Pres-
ence of Al(OTf)3 at Room Temperature
Entry
1
Substrate
Time (min) Yielda (%)
e
C6H5CH2OH
–
–
–
–
–
–
–
–
–
–
95b
93b
95b
90b
90b
92b
95c
95b
95b
90b
94b
90c
92c
90c
e
e
e
e
e
e
e
e
e
2
4-CH3C6H4CH2OH
4-CH3OC6H4CH2OH
4-ClC6H4CH2OH
2-O2NC6H4CH2OH
PhCH(CH3)OH
Anthracene-9-methanol
(Ph)2CHOH
3
Treatment of several of alcohols with HMDS and the cat-
alyst in the absence of solvent at room temperature pro-
duces the corresponding trimethylsilyl ethers in excellent
yields (Table 3). Substituted benzylic alcohols containing
electron-donating and electron-withdrawing groups, pri-
mary and allylic alcohols are also protected efficiently in
short reaction times in high yields (Table 3, entries 1–14).
Silylation of secondary and tertiary aliphatic alcohols re-
quires longer reaction times under similar reaction condi-
tions (Table 3, entries 16–23). We have also tried
silylation of cholesterol under solvent-free conditions in
the presence of this catalyst with HMDS. Our observation
shows that this compound does not undergo silylation un-
der such conditions and the starting material was isolated
intact after 24 hours. However, we tried this reaction at
room temperature in solution using CH2Cl2. The reaction
proceeded well and the desired compound was isolated in
97% yield after 80 minutes (Table 3, entry 15). Silylation
of phenolic hydroxyl group also proceeded smoothly by
this method. Our studies show that p-cresol is silylated
faster and in a higher yield than phenol and p-chlorophe-
nol (Table 3, entries 24–26). Silylation of thiols and
amines by this protocol failed; the starting materials were
4
5
6
7
8
9
CH2=CHCH2OH
(CH3)2C=CHCH2OH
CH3(CH2)5CH(CH=CH2)OH
PhCH2CH2OH
Ph(CH2)2CH2OH
CH3(CH2)6CH2OH
Cholesterol
10
11
12
13
14
15
16
17
10
15
10
10
24 h
35
24
20
50
60
67
55
90
65
c,f
–
Nopol
90c
92c
96c
92c
93c
95c
95c
90c
90c
70c
70c
Cyclohexanol
2-Octanol
isolated from the mixture after 48 hours (Table 3, entries 18
27–29).
19
Terpineol
In conclusion, Al(OTf)3 is a mild and efficient catalyst for
the preparation of varieties of diethyl a-trimethylsilyloxy-
20
Adamantan-1-ol
t-Amyl alcohol
5-Methyl-5-decanol
t-BuOH
phosphonates by direct silylation of diethyl a-hydroxy-
phosphonates with HMDS. Cleavages of C–P or Si–O
bonds are not observed in the process of the reactions.
High yields, solvent-free, mild reaction conditions, short
reaction times, reusability of the catalyst and easy work-
up are the strong points of the protocol for the preparation
of a-trimethylsilyloxyphosphonate compounds. The pro-
tocol is applicable to the efficient silylation of alcohols
and phenols in high yields.
21
22
23
24
25
26
27
28
29
4-CH3C6H4OH
C6H5OH
140
120
4-ClC6H4OH
f
C6H5SH
48 h
–
Chemicals were purchased from Merck and Fluka. The products
were characterized by comparison of their physical data with those
of known samples or by their spectral data. IR spectra were run on
a Shimadzu model 8300 FT-IR spectrophotometer. NMR spectra
were recorded on a Bruker Avance DPX-250 spectrometer at 250
f
C6H5NH2
48 h
48 h
–
f
Cyclohexyl amine
–
a Yields of isolated products.
MHz for H NMR and at 62.5 MHz for 13C NMR. Mass spectra
1
b The molar ratio of substrate–HMDS–Al(OTf)3 was 1:0.5:0.01.
c The molar ratio of substrate–HMDS–Al(OTf)3 was 1:0.7:0.01.
d CH2Cl2 was used as solvent.
were recorded on a Shimadzu GCMS-QP 1000 EX spectrometer.
The purity of the products and the progress of the reactions were ac-
complished by TLC on silica gel polygram SILG/UV254 plates.
e Immediate reaction occurred.
f Reaction did not occur.
Preparation of Diethyl a-Trimethylsilyloxyphosphonates (2);
General Procedure
Al(OTf)3 (0.05 mmol, 0.024 g) was added to a stirring mixture of 1
(1 mmol, 0.218–0.342 g) and HMDS (0.7 mmol, 0.113 g) at r.t. The
reaction progress was monitored by TLC. After completion of the
reaction, Et2O (10 mL) was added to the reaction mixture, which
Synthesis 2005, No. 4, 595–599 © Thieme Stuttgart · New York

598
H. Firouzabadi et al.
PAPER
was then washed with H2O (3 × 10 mL). The aqueous layer was sep-
arated and evaporated under reduced pressure to afford the catalyst.
The organic layer was dried over anhyd Na2SO4. After evaporation
of the solvent, the pure product (2) was isolated without requiring
further purification in 90–97% yields (Table 1).
1H NMR (CDCl3): d = 0.00 [s, 9 H, Si(CH3)3], 1.10 (t, 2JHH = 7.1 Hz,
6 H, 2-OCH2CH3), 3.79–3.99 (m, 4 H, 2-OCH2CH3), 5.03 (d, 1JPH
=
14.5 Hz, 1 H, CH), 7.33–7.37 (m, 2 H, C10H7), 7.49–7.52 (m, 1 H,
C10H7), 7.69–7.84 (m, 4 H, C10H7).
13C NMR (CDCl3): d = 0.00 [Si(CH3)3], 16.39 (d, 3JCP = 5.6 Hz, 2-
OCH2CH3), 16.48 (d, 3JCP = 5.6 Hz, 2-OCH2CH3), 62.77 (d, 2JCP
=
Trimethylsilylation of Alcohols and Phenols with HMDS Using
Al(OTf)3 in Neat Conditions; General Procedure
7.3 Hz, 2-OCH2CH3), 63.22 (d, 2JCP = 7.3 Hz, 2-OCH2CH3), 72.13
(d, 1JCP = 174.4 Hz, CH), 125.23–126.44, 127.61–128.06, 133.07–
133.21, 134.94–135.48 (C10H7).
Al(OTf)3 (0.01 mmol, 0.005 g) was added to a stirring mixture of
alcohol or phenol (1 mmol) and HMDS (0.5–0.7 mmol, 0.08–0.113
g) at r.t. The reaction progress was monitored by TLC or GC. After
completion of the reaction, Et2O (10 mL) was added to this reaction
mixture, which was then washed with H2O (3 × 10 mL). The aque-
ous layer was separated and evaporated under reduced pressure to
afford the catalyst. The organic layer was dried over anhyd Na2SO4.
After evaporation of the solvent, almost pure trimethylsilyl ether
was obtained. Pure product was obtained by column chromatogra-
phy in 70–97% yields (Table 2).
MS (70 eV): m/z (%) = 439 (16.2) [M + Si(CH3)3], 366 (4.8) [M+],
229 (100) [M – P(O)(OEt)2], 155 (18.8) [229 – Si(CH3)3], 73 (87.5)
[Si(CH3)3].
Anal. Calcd for C18H27O4PSi: C, 59.02; H, 7.38. Found: C, 59.04;
H, 7.35.
Diethyl a-Trimethylsilyloxy-3-pyridylphosphonate (2m)
IR (neat): OH Peak was absent.
1H NMR (CDCl3): d = 0.00 [s, 9 H, Si(CH3)3], 1.13 (t, 2JHH = 7.0 Hz,
Spectral Data and the Elemental Analysis of Unknown Diethyl
a-Trimethylsilyloxyphosphonates
Diethyl a-Trimethylsilyloxy-2,4,6-trimethylbenzylphosphonate
(2d)
6 H, 2-OCH2CH3), 3.91–3.99 (m, 4 H, 2-OCH2CH3), 4.89 (d, 1JPH
=
14.5 Hz, 1 H, CH), 7.15–7.21 (m, 1 H, C5H4N), 7.74 (d, JPH = 7.3
Hz, 1 H, C5H4N), 8.43 (d, JPH = 4.1 Hz, 1 H, C5H4N), 8.54 (s, 1 H,
C5H4N).
IR (neat): OH Peak was absent.
13C NMR (CDCl3): d = 0.00 [Si(CH3)3], 16.51 (d, 3JCP = 5.1 Hz, 2-
1H NMR (CDCl3): d = –0.04 [s, 9 H, Si(CH3)3], 1.02 (t, 2JHH = 7 Hz,
3 H, 2-OCH2CH3), 1.22 (t, 2JHH = 7 Hz, 3 H, 2-OCH2CH3), 2.12 (s,
3 H, CH3), 2.25 (s, 3 H, CH3), 2.51 (s, 3 H, CH3), 3.58–3.68 (m, 1
H, 2-OCH2CH3), 3.81–3.90 (m, 1 H, 2-OCH2CH3), 3.98–4.10 (m, 2
OCH2CH3), 16.58 (d, 3JCP = 5.1 Hz, 2-OCH2CH3), 63.06 (d, 2JCP
=
7.3 Hz, 2-OCH2CH3), 63.43 (d, 2JCP = 7.3 Hz, 2-OCH2CH3), 69.88
(d, 1JCP = 175.8 Hz, CH), 123.31 (d, JCP = 2.6 Hz, C5H4N), 133.53
(C5H4N), 135.14 (d, JCP = 4.9 Hz, C5H4N), 148.69 (d, JCP = 6.7 Hz,
C5H4N), 149.43 (d, JCP = 3.3 Hz, C5H4N).
1
H, 2-OCH2CH3), 5.28 (d, JPH = 18.3 Hz, 1 H, CH), 6.66 (s, 1 H,
C6H2), 6.72 (s, 1 H, C6H2).
MS (70 eV): m/z (%relative intensity) = 390 (62.1) [M + Si(CH3)3],
317 (1.2) [M+], 180 (86.2) [M – P(O)(OEt)2], 108 (48.8) [180 –
Si(CH3)3], 73 (100) [Si(CH3)3].
13C NMR (CDCl3): d = 0.00 [Si(CH3)3], 16.56 (d, 3JCP = 5.9 Hz, 2-
3
OCH2CH3), 16.87 (d, JCP = 5.9 Hz, 2-OCH2CH3), 21.16, 21.67,
21.69 (CH3), 62.70 (d, 2JCP = 7.1 Hz, 2-OCH2CH3), 62.92 (d, 2JCP
=
1
Anal. Calcd for C13H24NO4PSi: C, 49.21; H, 7.57. Found: C, 49.18;
H, 7.51.
7.1 Hz, 2-OCH2CH3), 69.60 (d, JCP = 177.2 Hz, CH), 129.05 (d,
JCP = 2 Hz, C6H2), 130.25 (C6H2), 131.57 (d, JCP = 3.3 Hz, C6H2),
136.08 (d, JCP = 8.1 Hz, C6H2), 137.41 (d, JCP = 3.4 Hz, C6H2),
139.88 (d, JCP = 4.2 Hz, C6H2).
Spectral Data of Known a-Trimethylsilyloxyphosphonates Not
Reported in the Literature
Diethyl a-Trimethylsilyloxy-4-methoxybenzylphosphonate (2c)
IR (neat): OH Peak was absent.
1H NMR (CDCl3): d = 0.00 [s, 9 H, Si(CH3)3], 1.11–1.19 (m, 6 H,
2-OCH2CH3), 3.71 (s, 3 H, 4-OCH3), 3.81–3.99 (m, 4 H, 2-
OCH2CH3), 4.83 (d, 1JPH = 13.4 Hz, 1 H, CH), 7.79 (d, 2JHH = 8.4
Hz, 2 H, C6H4), 7.30 (d, 2JHH = 6.9 Hz, 2 H, C6H4).
13C NMR (CDCl3): d = 0.00 [Si(CH3)3], 16.38–16.59 (2-
OCH2CH3), 55.20 (4-OCH3), 62.65–63.21 (2-CH2CH3), 71.50 (d,
1JCP = 173.7 Hz, CH), 113.58–113.62, 128.49–129.30, 159.47–
159.51 (C6H4).
MS (70 eV): m/z (%) = 431 (19.3) [M + Si(CH3)3], 358 (3.2) [M+],
221 (100) [M – P(O)(OEt)2], 147 (12) [221 – Si(CH3)3], 73 (44.3)
[Si(CH3)3].
Anal. Calcd for C17H31O4PSi: C, 56.98; H, 8.66. Found: C, 56.90;
H, 8.70.
Diethyl a-Trimethylsilyloxy-2,6-dichlorobenzylphosphonate
(2h)
IR (neat): OH Peak was absent.
1H NMR (CDCl3): d = 0.00 [s, 9 H, Si(CH3)3], 1.07–1.24 (m, 6 H,
2-OCH2CH3), 3.89–4.15 (m, 4 H, 2-OCH2CH3), 5.81 (d, 1JPH = 19.3
Hz, 1 H, CH), 7.03–7.10 (m, 1 H, C6H3), 7.20–7.25 (m, 1 H, C6H3).
Diethyl a-Trimethylsilyloxy-2-chlorobenzylphosphonate (2e)
IR (neat): OH Peak was absent.
1H NMR (CDCl3): d = 0.00 [s, 9 H, Si(CH3)3], 1.08–1.24 (m, 6 H,
2-OCH2CH3), 3.79–4.10 (m, 4 H, 2-OCH2CH3), 5.50 (d, 1JPH = 12.3
Hz, 1 H, CH), 7.11–7.27 (m, 3 H, C6H4), 7.65–7.73 (m, 1 H, C6H4).
13C NMR (CDCl3): d = 0.00 [Si(CH3)3], 16.86 (d, 3JCP = 6.8 Hz, 2-
OCH2CH3), 16.96 (d, 3JCP = 6.8 Hz, 2-OCH2CH3), 63.35 (d, 2JCP
=
7.1 Hz, 2-OCH2CH3), 63.60 (d, 2JCP = 7.1 Hz, 2-OCH2CH3), 70.02
(d, 1JCP = 179.8 Hz, CH), 128.60 (d, JCP = 2.0 Hz, C6H3), 129.99 (d,
JCP = 2.9 Hz, C6H3), 131.31 (d, JCP = 2.8 Hz, C6H3), 135.73 (d,
JCP = 8.2 Hz, C6H3), 136.87 (d, JCP = 4.9 Hz, C6H3).
13C NMR (CDCl3): d = 0.47 [Si(CH3)3], 16.47–16.73 (2-
1
OCH2CH3), 63.20–63.69 (2-CH2CH3), 67.89 (d, JCP = 175.8 Hz,
MS (70 eV): m/z (%) = 457 (100) [M + Si(CH3)3], 389 (2.3) [M +
4], 387 (10.8) [M + 2], 385 (14) [M+], 247 (52.2) [M – P(O)(OEt)2],
173 (2.4) [247 – Si(CH3)3], 73 (93.5) [Si(CH3)3].
CH), 127.08–135.80 (C6H4).
Diethyl a-Trimethylsilyloxy-3-chlorobenzylphosphonate (2f)
IR (neat): OH Peak was absent.
1H NMR (CDCl3): d = 0.00 [s, 9 H, Si(CH3)3], 1.09–1.17 (m, 6 H,
2-OCH2CH3), 3.90–4.01 (m, 4 H, 2-OCH2CH3), 4.83 (d, 1JPH = 14.5
Hz, 1 H, CH), 7.14–7.41 (m, 4 H, C6H4).
Anal. Calcd for C14H23Cl2O4PSi: C, 43.64; H, 5.97. Found: C,
43.60; H, 5.91.
Diethyl a-Trimethylsilyloxy-2-naphthylphosphonate (2l)
IR (neat): OH Peak was absent.
Synthesis 2005, No. 4, 595–599 © Thieme Stuttgart · New York

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Aluminium Triflate [Al(OTf)3] as a Recyclable Catalyst
599
13C NMR (CDCl3): d = 0.47 [Si(CH3)3], 16.44–16.59 (2-
(3) Koenigkramer, R. E.; Zimmer, H. Tetrahedron Lett. 1980,
21, 1017.
1
OCH2CH3), 62.94–63.50 (2-CH2CH3), 71.43 (d, JCP = 171.6 Hz,
CH), 125.47–139.73 (C6H4).
(4) (a) Sekine, M.; Nakajima, M.; Hata, T. Tetrahedron Lett.
1979, 4475. (b) Hata, T.; Hashisume, A.; Nakajima, M.;
Sekine, M. Tetrahedron Lett. 1978, 363.
Diethyl a-Trimethylsilyloxy-2-nitrobenzylphosphonate (2i)
IR (neat): OH Peak was absent.
(5) Sekine, M.; Nakajima, M.; Kume, A.; Hashizume, A. Bull.
Chem. Soc. Jpn. 1982, 55, 218.
(6) Evans, D. A.; Hurst, K. M.; Truesdale, L. K.; Takacs, J. M.
Tetrahedron Lett. 1977, 29, 2495.
(7) Sekiguchi, A.; Ikeno, M.; Ando, W. Bull. Chem. Soc. Jpn.
1978, 51, 337.
(8) (a) Texier-Boullet, F.; Foucaud, A. Synthesis 1982, 916.
(b) Baraldi, P. G.; Guarneri, M.; Moroder, F.; Polloni, G. P.;
Simoni, D. Synthesis 1982, 653.
1H NMR (CDCl3): d = 0.00 [s, 9 H, Si(CH3)3], 1.01–1.11 (m, 6 H,
2-OCH2CH3), 3.83–3.97 (m, 4 H, 2-OCH2CH3), 6.02 (d, 1JPH = 15.9
Hz, 1 H, CH), 7.28 (t, 2JHH = 7.3 Hz, 1 H, C6H4), 7.48 (t, 2JHH = 7.3
Hz, 1 H, C6H4), 7.72–7.80 (m, 2 H, C6H4).
13C NMR (CDCl3): d = 0.46 [Si(CH3)3], 16.41–16.60 (2-
1
OCH2CH3), 63.26–63.62 (2-CH2CH3), 66.40 (d, JCP = 172.0 Hz,
CH), 124.70–134.02, 147.94–148.04 (C6H4).
(9) Lebedev, E. P.; Mizhiritskii, M. D.; Baburina, V. A.;
Mironov, V. F.; Ofitserov, E. N. Zh. Obshch. Khim. 1979,
49, 1731.
(10) (a) Iranpoor, N.; Shekarriz, M. Bull. Chem. Soc. Jpn. 1999,
72, 455. (b) Firouzabadi, H.; Karimi, B.; Eslami, S.
Tetrahedron Lett. 1999, 40, 4055. (c) Firouzabadi, H.;
Eslami, S.; Karimi, B. Bull. Chem. Soc. Jpn. 2001, 74, 2401.
(d) Firouzabadi, H.; Iranpoor, N.; Kohmareh, G. Synth.
Commun. 2003, 33, 167.
(11) Olah, G. A.; Farooq, O.; Farnia, S. M. F.; Olah, J. A. J. Am.
Chem. Soc. 1990, 110, 2560.
(12) Ernst, A.; Karola, H.; Hermann, M. Synthesis 1990, 323.
(13) Zhonghua, L.; Chuanfang, Z. Main Group Met. Chem. 1995,
18, 669.
Diethyl a-Trimethylsilyloxy-3-nitrobenzylphosphonate (2j)
IR (neat): OH Peak was absent.
1H NMR (CDCl3): d = 0.00 [s, 9 H, Si(CH3)3], 1.08–1.17 (m, 6 H,
2-OCH2CH3), 3.91–3.99 (m, 4 H, 2-OCH2CH3), 4.96 (d, 1JPH = 14.8
Hz, 1 H, CH), 7.41 (t, 2JHH = 7.8 Hz, 1 H, C6H4), 7.70 (d, 2JHH = 7.4
2
Hz, 1 H, C6H4), 8.01 (d, JHH = 7.9 Hz, 1 H, C6H4), 8.19 (s, 1 H,
C6H4).
13C NMR (CDCl3): d = 0.47 [Si(CH3)3], 16.50–16.63 (2-
1
OCH2CH3), 63.20–63.75 (2-CH2CH3), 71.16 (d, JCP = 171.5 Hz,
CH), 122.11–123.07, 129.12–129.33, 133.32–133.40, 140.23,
148.28–148.33 (C6H4).
(14) Sekine, M.; Nakajima, M.; Kume, A.; Hashizume, A. Bull.
Chem. Soc. Jpn. 1982, 55, 224.
(15) Auge, J.; Leory, F. Tetrahedron Lett. 1996, 37, 7715.
(16) Imamoto, T.; Koide, Y.; Hiyama, S. Chem. Lett. 1990, 1445.
(17) Nishizawa, M.; Takenaka, H.; Nishide, H.; Hayashi, Y.
Tetrahedron Lett. 1983, 24, 2581.
(18) Jenkins, C. L.; Kochi, J. K. J. Am. Chem. Soc. 1972, 94, 843.
(19) Corey, E. J.; Shimoji, K. Tetrahedron Lett. 1983, 24, 169.
(20) (a) Firouzabadi, H.; Karimi, B. Synth. Commun. 1993, 23,
1633. (b) Firouzabadi, H.; Sardarian, A. R.; Khayat, Z.;
Karimi, B.; Tangestaninejad, S. Synth. Commun. 1997, 27,
2709.
(21) Green, T. W.; Wuts, P. G. M. Protective Groups in Organic
Synthesis, 3rd ed.; Wiley: New York, 1999, and references
cited therein.
Acknowledgment
We are thankful to Iran TWAS Chapter Based at ISMO and Shiraz
University Research Council for the support of this work.
References
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Synthesis 2005, No. 4, 595–599 © Thieme Stuttgart · New York