Synthesis of novel calix[4]arenes containing organosilicon groups

Article abstract of DOI:10.1016/j.jorganchem.2009.09.021

Metalation of (RSiMe₂)₃CH (1a R = H, 1b R = Me, 1c R = Ph) with lithium diisopropylamide (LDA) or methyllithium in THF gave organolithium reagents (RSiMe₂)₃CLi, which reacted with the formylated calixarene (2),

Full text of DOI:10.1016/j.jorganchem.2009.09.021

Journal of Organometallic Chemistry 695 (2010) 26–31
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis of novel calix[4]arenes containing organosilicon groups
*
Kazem D. Safa , Yones Mosaei Oskoei
Organosilicon Research Laboratory, Faculty of Chemistry, University of Tabriz, 51664 Tabriz, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 5 August 2009
Received in revised form 6 September 2009
Accepted 10 September 2009
Available online 17 September 2009
Metalation of (RSiMe2)3CH (1a R = H, 1b R = Me, 1c R = Ph) with lithium diisopropylamide (LDA) or meth-
yllithium in THF gave organolithium reagents (RSiMe2)3CLi, which reacted with the formylated calixa-
rene (2), to give the corresponding 5,17-bis[2,2-bis(organosilyl)-1-ethenyl]-25,26,27,28-tetrapropoxy-
calix[4]arenes (3a, 3b and 3c) via the Peterson olefination. The compounds (RSiMe2)3CLi were treated
with 25,26,27,28-tetrakis(4-bromobutoxy)calix[4]arene (4) to give 25,26,27,28-tetrakis[4-(tris(dimethyl-
silyl)methyl)butoxy] calix[4]arene (5a) and 25,26,27,28-tetrakis[4-(tris(trimethylsilyl)methyl)butoxy]
calix[4]arene (5b) via nucleophilic substitution reactions. However the compound 25,26,27,28-tetra-
kis[4-(tris(dimethylphenylsilyl)methyl)butoxy] calix[4]arene (5c) was not obtained, presumably because
(PhSiMe2)3C- is highly sterically hindered and the reactivity of its derivatives is low. The compound 5a
has potential as a core for dendrimers.
Keywords:
Calixarene
Sterically hindered groups
Vinylsilanes
Organosilicon
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
(HSiMe2)3CLi, was obtained by treatment of (HSiMe2)3CH with
LDA at room temperature [24]. The precursor (Me3Si)3CH was pre-
Calixarenes have been widely used as building blocks in the de-
sign and synthesis of new materials for molecular recognition and
supramolecular chemistry [1]. Calixarenes bearing organosilicon
substituents have potential for the recognition of anionic and
nucleophilic substances [2–4], but few such calixarenes have hith-
erto been reported [4–8].
pared from the reaction between CHCl3, Li and Me3SiCl in THF. The
organolithium reagent, (Me3Si)3CLi was obtained by treatment of
(Me3Si)3CH with MeLi under reflux in THF [25]. The precursor
(PhSiMe2)3CH, obtained by the reaction of PhMe2SiCl with CHBr3
in the presence of n-BuLi at À78 °C, was metalated with MeLi un-
der the conditions used for (Me3Si)3CH [26] (Scheme 1).
1,1-Bis(organosilyl)-1-alkenes constitute an important class of
organosilicon reagents which are currently widely used as poten-
tial intermediates in organic and organometallic synthesis. Their
use as precursors for the preparation of ketones, as well as variety
of organosilicon intermediates such as acylsilanes, epoxysilanes,
1-halovinylsilanes, silylenolethers, (E)-alkenylsilanes, and silyleno-
lacetates, stimulates interest in their synthetic availability [9–17].
Therefore, the preparation of calixarenes containing the organosi-
lylvinyl substituents is important.
Organosilicon compounds containing bulky groups, such as
(RSiMe2)3C– (a R = H, b R = Me, c R = Ph) have been widely used
previously [18–24]. In this work, new calixarenes containing
organosilylvinyl substituents at the upper rim and calixarenes
bearing bulky organosilicon groups on the lower rim have been
prepared. The compound 5a has 12 Si–H bonds that might be used
for the preparation of dendrimers.
By using the Peterson olefination reaction, synthetically useful
2,2-bis(organosilyl)ethenyl groups can be prepared by the reaction
of tri(organosilyl)methylmetals with non-enolizable aromatic
aldehydes using a direct addition–elimination process [17,27,28].
The starting point for the synthesis of calixarenes containing
2,2-bis(organosilyl)ethenyl groups was the preparation of 5,
17-diformyl-25,26,27,28-tetrapropoxycalix[4]arene 2, which was
obtained in 75% yield according to Scheme 2 [29].
(RSiMe2)3CLi (1a, 1b and 1c) were treated with the non-enolisa-
ble formylated calixarene 2. The Peterson reaction readily takes
place on the upper rim of the calixarene skeleton and gives the cor-
responding 2,2-bis(organosilyl)-1-ethenyl calixarenes.
It has been postulated that when (RSiMe2)3CLi is treated with a
compound containing a carbonyl group, it initially forms the alkox-
ide intermediate (A), then an intramolecular alkoxide attack takes
place and gives 3. It seems likely that the intermediates A are
unstable and swiftly convert into 3 with the elimination of
RMe2SiOLi [27] (Scheme 3).
2. Results and discussion
The yields for 3a, 3b and 3c are 76%, 62% and 45%, respectively.
A comparison of the reactivities of 1a, 1b and 1c toward the formy-
lated calixarene shows that the Ph group provides much greater
steric hindrance than the Me and H groups, and that the Me group
provides greater hindrance than H. The rate of nucleophilic attack
on the formyl group decreases with increasing size of R.
The precursor (HSiMe2)3CH was made by the reaction of CHBr3
and Mg with HSiMe2Cl in THF [23,24]. The organolithium reagent
* Corresponding author. Tel.: +98 411 3393124; fax: +98 411 3340191.
E-mail address: dsafa@tabrizu.ac.ir (K.D. Safa).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.09.021

K.D. Safa, Y.M. Oskoei / Journal of Organometallic Chemistry 695 (2010) 26–31
27
THF
THF
LDA
12h
(HSiMe2)3CH
(Me3Si)3CH
(HSiMe2)3CLi
(Me3Si)3CLi
HMe2SiCl + CHBr3 + Mg
Me3SiCl + CHCl3 + Li
(1a)
(1b)
MeLi
2h
MeLi
2h
THF
(PhSiMe2)3CH
(PhSiMe2)3CLi (1c)
PhMe2SiCl+ CHBr3 + n-BuLi
Scheme 1. Preparation of organolithium reagents.
AlCl3/PhOH
NaH/DMF/PrBr
Toluene,1h, rt
OH
OH
HO
OH
OPr
PrO
OPr
OPr
OH
OH
HO
O
OH
(D)
NBS
Butanon
Br
O
H
H
Br
Br
Br
Br
Br
1) 2equiv. n-Buli/THF
2)DMF
1) 2equiv. n-Buli/THF
2)MeOH
OPr
OPr
PrO
OPr
OPr
OPr
PrO
OPr
OPr
OPr
PrO
OPr
(2)
Scheme 2. Preparation of the formylated calixarene 2.
SiMe2R
SiMe2R
O
O
SiMe2R
-OLi+
Li+O-
H
H
H
RMe2Si
RMe2Si
SiMe2R
SiMe2R
SiMe2R
SiMe2R
H
THF
Li
+
OPr
OPr
PrO
OPr
OPr
OPr
PrO
OPr
( R=H, Me, Ph)
(A)
(2)
-
2 LiOSiMe2R
RMe2Si
H
SiMe2R
H
RMe2Si
SiMe2R
OPr
OPr
OPr
PrO
(3)
R=H
R=Me
R=Ph
3a
3b
3c
76%
62%
45%
Scheme 3. Synthesis of calixarenes containing bis(organosilyl)ethenyl groups.
The 1H NMR spectra of the calixarene 3a show the complete dis-
appearance of aldehydic proton resonance at 9.41 ppm and the
concomitant appearance of signals assigned to HC@C at
7.81 ppm, SiH at 4.43–4.41 ppm and –SiMe2 protons at 0.3 and

28
K.D. Safa, Y.M. Oskoei / Journal of Organometallic Chemistry 695 (2010) 26–31
Fig. 1. 1H NMR spectra of 3a.
0.4 ppm (Fig. 1). Similar results were observed for 3b and 3c. In
addition the FTIR spectra of the calixarenes 3a, 3b and 3c do not
show a sharp peak at 1696 cmÀ1, indicating the absence of car-
bonyl groups. In the case of 3a, there is a band to show the pres-
ence of Si–H at ca. 2100 cmÀ1. According to the NMR spectrum
and as expected, calixarenes 3 were in the flattened cone (or
pinched cone) conformation [30].
mers, since it has 12 Si–H bonds that could easily be converted to
other functional groups.
4. Experimental
4.1. Solvents and reagents
We also investigated the synthesis of calixarenes bearing bulky
organosilicon groups on the lower rim. Thus 25,26,27,28-tetra-
kis(4-bromobutoxy)calix[4]arene (4) was synthesized by treat-
ment of the dealkylated calixarene (D) with an excess of NaH
and 1,4-dibromobutane in DMF (Scheme 4). This symmetrical
compound allowed for the incorporation of four sterically hindered
groups on the lower rim. Compound 4 was treated with 1a and 1b
and gave 5a and 5b with 82% and 60% yields, respectively. The
reaction of 1c with 4 did not take place under similar conditions
or even under reflux for 36 h. All of the spectroscopic results indi-
cated that the nucleophilic substitution on to 4 with 1a and 1b was
complete.
Reactions involving organolithium reagents were carried out
under dry argon. Solvents were dried by standard methods. Sub-
strates for preparation of (RSiMe2)3CLi, viz., HSiMe2Cl, Mg, CHBr3,
Me3SiCl, CHCl3, Li, n-BuLi, PhBr, Me2SiCl2 and substrates for the
preparation of the formylated calixarene, viz., p-tert-butylphenol,
formaldehyde 35–40%, NaH, DMF, 1-bromopropane, NBS, and
1,4-dibromobutane were purchased from Merck and used without
further purification.
4.2. Spectra
The 1H and 13C NMR spectra were recorded with a Bruker FT-
400 MHz spectrometer at room temperature and with CDCl3 as a
solvent. The mass spectra were obtained with a MALDI-TOF-
PerSeptive Mass Spectrometer. The FTIR spectra were recorded
on a Bruker Tensor 270 spectrometer. Elemental analyses were
made with a Heareus CHN-ORAPID instrument.
3. Conclusion
The formylated calixarene 2 is converted to the corresponding
2,2-bis(organosilyl)-1-ethenylcalixarene derivatives in a one-pot
procedure involving the addition of (RSiMe2)3CLi to the carbonyl
group. The calixarenes containing vinylsilane substituents on the
upper rim are potential intermediates for the functionalization of
calixarenes, which cannot be achieved via other methods. (RSiM-
e2)3C-groups (R = H or Me) were attached to the lower rim of the
calixarene 4 by nucleophilic substitution with (RSiMe2)3CLi. It is
worth noting that the compound 5a is a potential core for dendri-
4.3. Preparation of tris(dimethylsilyl)methyllithium, (HSiMe2)3CLi,
solution in THF [24]
A 50 ml round-bottom flask, equipped with a stirrer, septum,
and gas-inlet needle was charged with diisopropylamine (0.53 g,
5.3 mmol) and 15 ml of THF. The flask was placed in a water-ice

K.D. Safa, Y.M. Oskoei / Journal of Organometallic Chemistry 695 (2010) 26–31
29
NaH /DMF
Br
O
O
O
+
O
Br
OH
OH
HO
OH
Br
Br
Br
Br
(4)
SiMe2R
SiMe2R
SiMe2R
Li
THF
( R=H, Me, Ph)
O
O
O
O
SiMe2R
SiMe2R
SiMe R
RMe2Si
RMe2Si
RMe2Si
RMe2Si
RMe2Si
SiMe2R
SiMe2R
2
SiMe2R
RMe2Si
R=H
R=Me
R=Ph
5a
5b
5c
82%
60%
-----
Scheme 4. Synthesis of 4 and calixarenes 5 bearing bulky organosilicon groups.
bath and then n-BuLi (3.8 ml, 1.5 M solution in hexane) was added
dropwise via a syringe to give a clear yellow solution. The solution
was stirred for an additional 30 min. The lithium diisopropylamide
(LDA) solution was transferred into a dropping funnel and added
dropwise to a 50 ml round-bottom flask containing tris(dimethyl-
silyl)methane, (HSiMe2)3CH, (1 g, 5.3 mmol) in 10 ml THF under
argon atmosphere at room temperature. The orange-red solution
was stirred at ambient temperature for 10 h.
dibromobutane was added. The mixture was stirred at room tem-
perature for 24 h. Then DMF was evaporated in vacuum, and the
residue was taken up in CHCl3 (200 ml) and the extract was
washed with 1 N HCl (2Â50 ml) and brine (50 ml), then dried
(MgSO4). After filtration the solvent was evaporated, and the resi-
due was subjected to column chromatography (n-hexane/ethyl
acetate, 4:1, Rf = 0.80), to yield 4 (4.00 g, 60 %) as a white solid.
m.p. 79–81 °C; 1H NMR (400 MHz, CDCl3, ppm): d 1.96–2.15 (m,
16H, 4ÂCH2CH2CH2CH2), 3.2 (d, 4H, J = 13.4 Hz, 4ÂArCHAr), 3.5 (t,
8H, J = 6.3 Hz, 4ÂCH2CH2CH2CH2O), 3.9 (t, 8H, J = 6.9 Hz,
CH2CH2CH2CH2Br), 4.4 (d, 4H, J = 13.3 Hz, 4ÂArCHAr), 6.55–6.72
(m, 12H, Ar); 13C NMR (100 MHz, CDCl3, ppm): d 27.9, 28.5, 29.8,
32.7, 72.9, 121.2, 127.2, 133.8, 155.0; MALDI-TOF MS m/z:
[M+Na]+ = 987.61; Anal. Calcd for C44H52Br4O4 (964.50): C, 54.79;
H, 5.43. Found: C, 54.32; H, 5.15%.
4.4. Preparation of tris(trimethylsilyl)methyllithium, (Me3Si)3CLi, in
THF
The reagent was prepared as described by Grobel and co-work-
ers [25].
4.5. Preparation of tris(dimethylphenylsilyl)methyllithium,
(PhSiMe2)3CLi, in THF
4.8. General procedure for the synthesis of 5,17-bis[2,2-
bis(triorganosilyl)-1-ethenyl]-25,26,27,28-tetrapropoxy calix[4]arene
The method for the preparation of tris(trimethylsilyl)methyl-
lithium was used.
(3)
To a stirred solution of 1a, 1b or 1c (5.3 mmol) in THF at room
temperature was added formylated calix[4]arene 2 (1 mmol) in
10 ml THF, and the mixture was heated under reflux for 12 h.
The mixture was poured into ammonium chloride solution
(50 ml) and extracted with CH2Cl2 (2 Â 50 ml). The organic phase
was washed with water (100 ml) and dried (Na2SO4), and the sol-
vent was removed in vacuum to yield a cream solid.
4.6. Preparation of the formylated calixarene, 5,17-diformyl-
25,26,27,28-tetrapropoxycalix[4]arene (2)
This was synthesized according to the literature [29].
4.7. Preparation of 25,26,27,28-tetrakis(4-bromobutoxy)calix[4]arene
(4)
4.8.1. Preparation of 5,17-bis[2,2-bis(dimethylsiyl)-1-ethenyl]-
25,26,27,28-tetrapropoxycalix[4]arene (3a)
A mixture of 3 g (7 mmol) dealkylated calixarene (D) and 2.4 g
(60 mmol) NaH (60% in paraffin) in 100 ml of dry DMF was stirred
at room temperature for 0.5 h. Subsequently 20 g (92 mmol) of 1,4-
A white solid 0.66 g (76%) was obtained by preparative TLC (sil-
ica gel, n-hexane, Rf = 0.25), m.p. 142–144 °C; FTIR (KBr, cmÀ1):

30
K.D. Safa, Y.M. Oskoei / Journal of Organometallic Chemistry 695 (2010) 26–31
3
3062 (HC@), 2111 (Si–H), 1598, 1490 (Ph), 1250, 888 (Si–CH3); 1H
NMR (400 MHz, CDCl3, ppm): d 0.3 (d, 12H, 3JHH = 3.8 Hz, 2ÂSiMe2),
NMR (400 MHz, CDCl3, ppm): d 0.1 (d, 72 H, JHH = 3.7 Hz,
12ÂSiMe2), 1.51–1.58 (m, 8H, 4ÂCCH2CH2), 1.66–1.71 (m, 8H,
4ÂCCH2CH2CH2), 1.85–1.93 (m, 8H, 4ÂCCH2CH2CH2CH2), 3.1 (d,
4H, J = 13.4 Hz, 4ÂArCHAr), 3.9 (t, 8H, J = 7.2 Hz, 4ÂCCH2CH2-
CH2CH2O), 3.99–4.05 (m, 12H, 12ÂSiHMe2), 4.4 (d, 4H,
J = 13.3 Hz, 4ÂArCHAr), 6.56–6.62 (m, 12H, Ar); 13C NMR
(100 MHz, CDCl3, ppm): d À4.06 (SiMe2), 0.58 (C(SiMe2H)3), 25.0,
29.5, 30.2, 30.6, 73.7, 120.9, 127.1, 133.8, 155.6; MALDI-TOF MS
m/z: [M+Na]+ = 1424.35; Anal. Calcd for C72H136O4Si12 (1400.77):
C, 61.64; H, 9.77. Found: C, 61.25; H, 9.63%.
3
0.4 (d, 12H, JHH = 3.6 Hz, 2ÂSiMe2), 1.07 (t, 6H, J = 7.4 Hz,
2ÂCH3CH2), 1.21 (t, 6H, J = 7.4 Hz, 2ÂCH3CH2), 2.03–2.11 (m, 8H,
4ÂCH3CH2CH2), 3.3 (d, 4H, J = 13.3 Hz, 4ÂArCHAr), 3.9 (t, 4H,
J = 7.0 Hz, 2ÂCH2CH2O), 4.10 (t, 4H, J = 7.8 Hz, 2ÂCH2CH2O), 4.38–
4.41 (m, 2H, 2ÂSiHMe2), 4.48–4.51 (m, 2H, 2ÂSiHMe2), 4.61 (d,
4H, J = 13.22 Hz, 4ÂArCHAr), 6.49 (s, 6H, Ar), 7.11(s, 4H, Ar), 7.81
(s, 2H, 2ÂHC@); 13C NMR(100 MHz, CDCl3, ppm): d À3.8, À3.2
(SiMe2), 9.0, 9.6, 22.0, 22.3, 30.0, 75.8, 75.9, 121.2, 126.6, 128.1,
132.5, 133.3, 134.6, 136.5, 154.5, 155.4, 156.5; MALDI-TOF MS m/
z: [M+Na]+ = 899.39; Anal. Calcd for C52H76O4Si4 (876.48): C,
71.17; H, 8.73. Found: C, 70.92; H, 8.50%.
4.9.2. Preparation of 25,26,27,28-tetrakis[4-
(tris(trimethylsilyl)methyl)butoxy]calix[4]arene (5b)
A white solid 0.94 g (60 %) was obtained by preparative TLC (sil-
ica gel, n-hexane, ethyl acetate 4:1 Rf = 0.60), m.p. 138–140 °C;
FTIR (KBr, cmÀ1): 3059 (HC@), 1587, 1455 (Ph), 1253, 839 (Si–
CH3); 1H NMR (400 MHz, CDCl3, ppm): d 0.1 (s, 108H, 12ÂSiMe3),
4.8.2. Preparation of 5,17-bis[2,2-bis(trimethylsiyl)-1-ethenyl]-
25,26,27,28-tetra propoxycalix[4]arene (3b)
A white solid 0.57 g (62 %) was obtained by preparative TLC (sil-
icagel, n-hexane, Rf = 0.25), m.p. 176–178 °C; FTIR (KBr, cmÀ1):
3070 (HC@), 1590, 1459 (Ph), 1248, 891(Si–CH3); 1H NMR (400
1.52–1.56
(m,
8H,
4ÂCCH2CH2),
1.66–1.69
(m,
8H,
4ÂCCH2CH2CH2), 1.85–1.89 (m, 8H, 4ÂCCH2CH2CH2CH2), 3.1 (d,
4H, J = 13.4 Hz, 4ÂArCHAr), 3.9 (t, 8H, J = 6.6 Hz, 4ÂCCH2-
CH2CH2CH2O), 4.4 (d, 4H, J = 13.3 Hz, 4ÂArCHAr), 6.51–6.72 (m,
12H, Ar); 13C NMR (100 MHz, CDCl3, ppm): d 1.8 (SiMe3), 5.1
(C(SiMe3)3), 26.1, 29.5, 29.9, 30.9, 73.7, 120.8, 127.1, 133.8,
155.6; MALDI-TOF MS m/z: [M+Na]+ = 1592.4; Anal. Calcd for
C84H160O4Si12 (1568.95): C, 64.21; H, 10.26. Found: C, 64.05; H,
9.95%.
5
MHz, CDCl3, ppm): d 0.0 (d, 18H, JHH = 0.8 Hz, 2ÂSiMe3), 0.19 (d,
5
18H, JHH = 0.7 Hz, 2ÂSiMe3), 0.90 (t, 6H, J = 7.4 Hz, 2ÂCH3CH2),
1.08 (t, 6H, J = 7.5 Hz, 2ÂCH3CH2), 1.86–1.97 (m, 8H,
4
ÂCH3CH2CH2), 3.1 (d, 4H, J = 13.2 Hz, 4ÂArCHAr), 3.71 (t, 4H,
J = 6.9 Hz, 2ÂCH2CH2O), 3.98 (t, 4H, J = 7.9 Hz, 2ÂCH2CH2O), 4.4
(d, 4H, J = 13.2 Hz, 4ÂArCHAr), 6.3 (s, 6H, Ar), 6.9 (s, 4H, Ar), 7.73
(s, 2H, 2ÂHC@); 13C NMR (100 MHz, CDCl3, ppm): d À0.3, 1.2
(SiMe3), 6.0, 9.6, 21.9, 22.4, 30.0, 75.5, 75.8, 121.0, 126.7, 127.4,
132.3, 134.8, 135.3, 143.1, 154.3, 154.6, 156.0; MALDI-TOF MS m/
z: [M+Na]+ = 955.41; Anal. Calcd for C56H84O4Si4(932.54): C,
72.04; H, 9.07. Found: C, 71.85; H, 8.90%.
4.9.3. Tris(dimethylphenylsilyl)methyllithium did not react
with 4 under reflux in THF for 36 h.
Acknowledgment
4.8.3. Preparation of 5,17-bis[2,2-bis(dimethylphenylsiyl)-1-ethenyl]-
25,26,27,28-tetrapropoxycalix[4]arene (3c)
We thank Dr. J.D. Smith for helpful comments.
A yellow viscous oil 0.53 g (45%) was obtained by preparative
TLC (silica gel, n-hexane, Rf = 0.12); FTIR (KBr, cmÀ1): 3066
(HC@), 2111(Si–H), 1589, 1458 (Ph), 1249, 867 (Si–CH3); 1H NMR
(400 MHz, CDCl3, ppm): d 0.49 (s, 12H, 2ÂSiMe2), 0.86 (s, 12H,
2ÂSiMe2), 1.29 (t, 6H, J = 7.4 Hz, 2ÂCH3CH2), 1.48 (t, 6H, J =
7.3 Hz, 2ÂCH3CH2), 2.22–2.37 (m, 8H, 4 ÂCH3CH2CH2), 3.29 (d,
4H, J = 13.3 Hz, 4ÂArCHAr), 4.0 (t, 4H, J = 6.8 Hz, 2ÂCH2CH2O),
4.29 (t, 4H, J = 8.0 Hz, 2ÂCH2CH2O), 4.68 (d, 4H, J = 13.3 Hz,
4ÂArCHAr), 6.39 (d, 4H, J = 7.5, Ar), 6.48–7.07 (m, 6H, Ar), 7.64–
7.82 (m, 20H, Ar), 8.33 (s, 2H, 2ÂHC@); 13C NMR (100 MHz, CDCl3,
ppm): d À1.5, À0.05 (SiMe2), 8.9, 9.7, 21.8, 22.4, 29.8, 75.3, 75.8,
120.9, 126.4, 126.5, 126.6, 127.0, 127.3, 127.6, 128.1, 132.0,
132.8, 133.1, 133.9, 134.1, 134.7, 137.3, 154.0, 156.5, 158.5; MAL-
DI-TOF MS m/z: [M+Na]+ = 1204.61; Anal. Calcd for C76H92O4Si4
(1181.61): C, 77.23; H, 7.85. Found: C, 76.90; H, 7.60%.
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