Efficient hydrosilylation of carbonyl compounds by 1,1,3,3-tetramethyldisiloxane catalyzed by Au/TiO2

Article abstract of DOI:10.1016/j.tet.2014.03.094

1,1,3,3-Tetramethyldisiloxane (TMDS) is a highly reactive reducing reagent in the Au/TiO₂-catalyzed hydrosilylation of carbonyl compounds relative to monohydrosilanes. The reduction of aldehydes or ketones with TMDS can be performed on many occ

Full text of DOI:10.1016/j.tet.2014.03.094

Tetrahedron xxx (2014) 1e8
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Efficient hydrosilylation of carbonyl compounds by 1,1,3,3-
tetramethyldisiloxane catalyzed by Au/TiO2
Eleni Vasilikogiannaki a, Ioannis Titilas a, Charis Gryparis a, Anastasia Louka a,
,
Ioannis N. Lykakis b, Manolis Stratakis a
*
a Department of Chemistry, University of Crete, Voutes, 71003 Iraklion, Greece
b Department of Chemistry, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
a r t i c l e i n f o
a b s t r a c t
Article history:
1,1,3,3-Tetramethyldisiloxane (TMDS) is a highly reactive reducing reagent in the Au/TiO2-catalyzed
hydrosilylation of carbonyl compounds relative to monohydrosilanes. The reduction of aldehydes or
ketones with TMDS can be performed on many occasions at ambient conditions within short reaction
times and at low loading levels of gold, whereas typical monohydrosilanes require excess heating and
prolonged time for completion. The product yields are excellent, while almost stoichiometric amounts of
carbonyl compounds and TMDS can be used. It is postulated that the enhanced reactivity of TMDS is
attributed to the formation of a gold dihydride intermediate. This intermediate is also supported by the
fact that double hydrosilylation of carbonyl compounds by TMDS is a negligible pathway.
Ó 2014 Elsevier Ltd. All rights reserved.
Received 25 January 2014
Received in revised form 25 March 2014
Accepted 27 March 2014
Available online xxx
Keywords:
Hydrosilylation
Carbonyl compounds
Gold nanoparticles
1,1,3,3-Tetramethyldisiloxane
Heterogeneous catalysis
1. Introduction
through activation of the carbonyl group, yet this methodology
works preferably with aromatic substrates, while silyl ethers are
The hydrosilylation of aldehydes or ketones (Scheme 1) is
a straightforward methodology to synthesize silyl ethers of alco-
hols, achieving thus a double functionalization in a single process,
namely, reduction of the carbonyl group and silyl protection of al-
cohol. The deprotection of the silyl moiety is trivial and simple, and
often can take place under the reaction conditions by acid treat-
ment, affording alcohols. This approach has practical advantages
over using the classical, yet pyrophoric and moisture sensitive
boron or aluminum hydrides as reducing agents. In particular, the
hydrosilylation of carbonyl compounds is primarily catalyzed by
a variety of metals,1 but can be also achieved under free radical
conditions.2 Lewis acids (such as BF3) can also catalyze this process3
rapidly deprotected under the reaction conditions.
Among the existing metal-catalyzed hydrosilylation protocols, in
recent years gold was proven as an active catalyst.4 The first example
of the homogeneous gold(I)-catalyzed hydrosilylation of aldehydes
was reported5 in 2000 using Ph3PAuCl (3 mol %) as catalyst. The
reaction requires the co-addition of 20% Bu3P to suppress de-
activation of catalyst, and operates in DMF at 70 ꢀC. One specific
example of a ketone (acetophenone) was examined in this report
and shown to be completely unreactive. Later on, these studies were
expanded to various Au(I)- and Au(III)-based homogeneous cata-
lysts.6e9 In addition, supported gold nanoparticles have also been
recognized as active heterogeneous hydrosilylation catalysts. Corma
and co-workers have shown10 that Au nanoparticles supported on
CeO2 (5% mol) catalyze the hydrosilylation of some aldehydes and
acetophenone in high yields (toluene, 70 ꢀC), using a variety of
hydrosilanes. The molar ratio carbonyl compound/hydrosilane in
those experiments was 1:2. Following this first report, a significantly
lower catalyst-loading protocol was presented by the group of
Raffa11 who studied the hydrosilylation of benzaldehyde and ace-
tophenone in the presence of Au/CeO2 (0.1e0.15 mol %, 100 ꢀC,
18e24 h). The specific gold nanoparticles were prepared either by
the metal vapor synthesis (AuMVS) or by deposition-precipitation
(AuDP). The reaction was not chemoselective, providing apart from
the anticipated silyl-protected alcohols, disilylated pinacols in
Scheme 1. The catalytic hydrosilylation of carbonyl compounds.
* Corresponding author. Fax: þ30 2810545166; e-mail address: stratakis@
chemistry.uoc.gr (M. Stratakis).
0040-4020/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2014.03.094
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E. Vasilikogiannaki et al. / Tetrahedron xxx (2014) 1e8
a relative ratio 40e80%. It was postulated that the hydrosilylation
pathway is catalyzed by Au(I) species, whereas, Au(0) nanoparticles
act as radical initiators forming silyl radicals, which undergo addition
(Et3SiH, PhMe2SiH) using Au/TiO2 (0.5 mol %) as catalyst. The reaction
proceeds at refluxing conditions and forms the hydrosilylation prod-
ucts in good yields, yet excess of hydrosilylating reagent is required
(2e4 M fold depending on the bulkiness of the hydrosilane) to drive
the reaction to completion within a reasonable time scale. These re-
sults are presented in Scheme 2. 1,2-Dichloroethane (DCE) is consid-
ered as the best solvent of choice, as in benzene or toluene the reaction
rate is slower, while in THF although the reaction proceeds faster (w2
times compared to DCE), a gradual destruction of hydrosilane by the
solvent is observed. The conversion of carbonyl compounds was 100%
in all cases, yet the isolated yields of silyl ethers is not that high, ap-
parently due to the intrinsic instability of silylated products
toward deprotection under their chromatographic purification. Sur-
prisingly, even the bulky triphenylsilane works nicely under pro-
longed reaction times (1.0 mol % of catalyst), yet for aldehydes only.
The gold nanoparticles can be recovered at the end of the reaction and
reused with little deterioration of their activity, as occurs for the vast
majority of heterogeneous gold nanoparticle-catalyzed reactions. It is
to the carbonyl group followed by dimerization of the
a-silyloxy
radicals. As the so far reported examples involving Au nanoparticles
as catalysts focus on a limited number of substrates and there is lack
of an efficient protocol in terms of low catalyst-loading, atom
economy, mild conditions, and chemoselectivity, we decided to
12
study Au/TiO2 as a hydrosilylation catalyst for aldehydes and ke-
tones. We were prompted toward this goal, as previous work from
our laboratory has shown that this specific catalyst is a very efficient
one and superior to other gold-based heterogeneous catalysts in the
hydrosilylation of alkynes.13
2. Results and discussion
In our initial experiments, we tested the reaction among a series of
carbonyl compounds (aldehydes and ketones) and hydrosilanes
a)
b)
0.5 mol% of Au/TiO2.
Isolated overall yields after column chromatography.
c)
The consumption of carbonyl compounds was 100% in all cases.
1.0 mol% of Au/TiO2.
Scheme 2. Hydrosilylation of carbonyl compounds by hydrosilanes catalyzed by Au/TiO2.a,b
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E. Vasilikogiannaki et al. / Tetrahedron xxx (2014) 1e8
3
interesting that in the case of cyclohexane carboxaldehyde (2), tri-
phenylsilane forms enol silyl ether 2a as a major product and the
anticipated hydrosilylationproduct as a minor one. Apparently in that
case the bulky hydrosilane preferentially undergoes a Au-catalyzed
dehydrogenative cross coupling14 with the enol form of the alde-
hyde, a rather rare pathway observed under specific catalytic condi-
tions.15 Since any water present into the reaction mixture readily
hydrolyzes the hydrosilanes to the corresponding silanols and even-
tually into 1,3-disiloxanes through a gold-catalyzed process,14 in case
of using non-dried DCE an additional appropriate excess of hydro-
silane is necessary to drive the reactions to completion. Additionally,
the reaction is heterogeneous in nature, as ICP analysis revealed that
the gold content in the supernatant reaction solution is below ppm
level, also shown in previous work from our group dealing with Au/
TiO2 and DCE as solvent under refluxing conditions.16
products in good to excellent yields (Scheme 4). Even sterically
hindered ketones such as 13e15 are very reactive. Peculiar re-
sults were obtained in the hydrosilylation of cyclohexanone (12)
and 2-cyclohexenone (16). Cyclohexanone provides mainly the
enol silane 121a and the anticipated cyclohexanol silyl ether
12b as a minor one. Apparently and rather surprisingly, the enol
form of cyclohexanone reacts significantly faster with TMDS in
a dehydrogenative manner (see also product 2b in Scheme 2).
Its a,b-unsaturated analogue 16 yields the 1,2-addition product
16a (65% relative yield) and the 1,4-addition product 12a (35%).
No dehydrogenative coupling among its enol form and TMDS
was detected. An unselective 1,2- versus 1,4-addition pattern
was reported very recently in the nanoporous Au-catalyzed re-
action of 16 with triethylsilane, which was significantly im-
proved in favor of the 1,4-adduct by using a bimetallic AuPd
nanopore.20
The results presented in Scheme 2 are not exceedingly impres-
sive, despite the fact that Au/TiO2 (0.5 mol %) certainly seems to be
the more efficient hydrosilylation catalytic system so far upon
comparison to previously reported heterogeneous or homogeneous
Au-based catalysts. For instance, Au/CeO2 had been used in 10 fold
The remarkable acceleration of the hydrosilylation reaction
rate by TMDS has some precedents. This specific silane and its
polymeric analogue PMHS are known to reduce carboxamides
into amines under Pt catalysis remarkably faster compared to
simple hydrosilanes,21 as well as in the [CuH(PPh3)]6-catalyzed
11
excess in previous studies,10 while AuMVS/CeO2 although used at
a significantly lower loading level, provides an unselective reaction.
Searching for a more effective hydrosilylation protocol we turned
into 1,1,3,3-tetramethyldisiloxane (TMDS).17 TMDS18 has been al-
ready used in our group19 to achieve the fast dehydrogenative cy-
cloaddition to alkynes, exhibiting a completely different reactivity
1,4-reduction of a,b
-unsaturated carbonyl compounds.22 We at-
tribute the high reactivity of TMDS to the formation of a four-
membered ring dihydrogold intermediate II (Scheme 5), possibly
preceded by gold hydride complex I. The formation of gold
dihydride species23 is well established in recent years. An anal-
ogous rationalization (formation of metal dihydride complex) has
been presented by Nagashima and co-workers24 who showed the
pivotal role of two SieH groups located at a proximal distance,
such as in TMDS, in the Rh(I)-catalyzed hydrosilylation of car-
bonyl compounds. A further support of intermediate II arises
from the observation that the hydrosilylation of carbonyl com-
pounds with TMDS yields mono-hydrosilylation products (e.g.,
product 1d), while double hydrosilylation adducts between
TMDS and carbonyl compounds17 (1,3-dialkoxy-1,1,3,3-
tetramethyldisiloxanes) are formed in yields <5% (GCeMS anal-
ysis) or are even absent in the majority of experiments. The
profound synergistic effect of the proximal SieH groups in TMDS
was also shown (Scheme 6) in the competing Au/TiO2-catalyzed
hydrosilylation of aldehyde 1 by 1,1,3,3-tetramethyldisiloxane
pathway by comparison to typical monohydrosilanes (e.g., PhMe2
-
SiH). We were pleased to see that TMDS readily reacts with a series
of aldehydes in the presence of 0.5 mol % Au/TiO2 (Scheme 3)
leading to the corresponding hydrosilylation products at very mild
conditions within significantly shorter reaction times, and in high
yields. Most importantly, only a small excess of TMDS (typically
20%) is required to drive the reactions to completion. An exception
is the p-F-substituted benzaldehyde (7), which for reasons we do
not clearly understand reacts slowly and the yield of 7a is rather
moderate. Citronellal (10) also provides the hydrosilylation product
10a is high yield without any detectable reaction of the pentant
double bond, in accordance to previous observations from our
group13 that Au/TiO2-catalyzed hydrosilylation of alkenes does not
take place. As the silyl moiety in the hydrosilylation products by
TMDS is very labile, treatment of the crude reaction mixture after
the consumption of the carbonyl compound with a methanolic
solution of acetic acid for a few minutes rapidly deprotects the silyl
ether and delivers the corresponding alcohol in quantitative yield
(GC analysis). After screening several solvents we found that dry
THF is the most appropriate. For example, the hydrosilylation of 1 in
THF occurs almost 2 times as faster as in DCE, and since the Au-
catalyzed hydrosilylation reactions with TMDS in THF are fast, the
destruction of the silane by the solvent under the reaction condi-
tions is negligible. The hydrosilylation reaction may take place even
at room temperature, while at 65 ꢀC quantitative reactions are
observed within 5e10 min. An impressive TOF of 3000 hꢁ1 was
recorded following the kinetics of hydrosilylation of 6 after 3 min at
65 ꢀC. It is roughly estimated based on kinetics that the hydro-
silylation of a carbonyl compound proceeds approximately 25e50
times faster with TMDS by comparison to a simple mono-
hydrosilane (e.g., triethylsilane or dimethylphenylsilane).
(TMDS)
and
the
structurally
similar
1,1,1,3,3-
pentamethyldisiloxane (PMDS). It was found that under identi-
cal reaction conditions, TMDS reacts w20 times faster compared
to PMDS, exemplifying thus the unique reactivity features of
TMDS. The relative reactivity among TMDS and PMDS with
a
limited quantity of 1 was calculated either inter or in-
tramolecularly at the initial stages of the reaction by GC or 1H
NMR. The fact that statistically TMDS possesses two SieH func-
tionalities cannot justify the large difference in their reactivity.
3. Conclusions
In conclusion, we have shown that Au/TiO2 at low loading level
(0.5 mol %) is a highly efficient catalyst for the fast hydrosilylation of
aldehydes or ketones with 1,1,3,3-tetramethyldisiloxane (TMDS)
under mild conditions. This approach is quite attractive for the
synthesis of alkyl silyl ethers from carbonyl compounds, and
complementary to the Au nanoparticle-catalyzed dehydrogenative
coupling25 among alcohols and hydrosilanes. The silyl moiety in
products is very labile and prone to deptotection even on standing,
providing thus the corresponding alcohols. The enhanced reactivity
of TMDS relative to typical monohydrosilanes is attributed to
a synergistic effect of the proximal SieH groups, which probably
form with Au nanoparticle a highly reactive gold dihydride
intermediate.
Ketones also react smoothly with TMDS (typically 1.4 equiv)
under the same conditions, providing the hydrosilylation
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E. Vasilikogiannaki et al. / Tetrahedron xxx (2014) 1e8
a)
b)
0.5 mol% of Au/TiO2.
Isolated overall yields after column chromatography. The consumption of
c)
carbonyl compounds was 100% in all cases. Approximately 10% of the side 1,4-addition product was also
formed (crude reaction mixture) but could not be isolated due to its chromatographic lability.
Scheme 3. Hydrosilylation of aldehydes by TMDS catalyzed by Au/TiO2.a,b
4. Experimental section
4.1. General
experiments were performed with a GCeMS QP 5050 Shimadzu
single-quadrupole mass spectrometer. GC analyses and kinetics
were performed by using a Shimadzu GC-17A model equipped with
a 60 m HP-5 capillary column.
The reactions were monitored by thin-layer chromatography
(TLC) carried out on silica gel plates (60F-254) with UV light as the
visualizing method and an acidic mixture of phosphomolybdic
acid/cerium(IV) sulfate accompanied by heating of the plate as
a developing system. Flash column chromatography was carried
out on SiO2 (silica gel 60, particle size 0.040e0.063 mm) with the
specified eluent. NMR spectra were recorded on a Bruker DPX-300
instrument. Electrospray ionization (ESI) mass spectrometry (MS)
4.2. Typical procedure for the Au/TiO2-catalyzed hydro-
silylation of carbonyl compounds with 1,1,3,3-
tetramethyldisiloxane
To a vial containing cuminaldehyde, 6 (45 mL, 0.3 mmol) and
1,1,3,3-tetramethyldisiloxane (0.063 mL, 0.36 mmol) dissolved in
dry THF (1 mL) was added Au/TiO2 (29 mg, 1 wt % in Au,
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E. Vasilikogiannaki et al. / Tetrahedron xxx (2014) 1e8
5
a)
b)
0.5 mol% of Au/TiO2
Isolated overall yields after column chromatography.
.
The consumption of carbonyl compounds was 100% in all cases.
Scheme 4. Hydrosilylation of ketones by TMDS catalyzed by Au/TiO2.a,b
w0.0015 mmol). The mixture was allowed to react at room tem-
perature and the reaction was complete (40 min) by TLC and
GCeMS. The slurry was filtered with the aid of dichloromethane
(3 mL) through a short pad of silica gel. The filtrate was evaporated
under vacuum and the residue was immediately chromatographed
with hexane as eluent to afford 6a (74 mg, 88% yield). On standing,
6a as well as all hydrosilylation products with TMDS, gradually
deprotect on standing forming the corresponding alcohol.
4.3. Spectroscopic data of hydrosilylation products
4.3.1. Triethyl((4-methylbenzyl)oxy)silane26
(1a). 1H
NMR
Scheme 5. Proposed mechanism for the Au/TiO2-catalyzed hydrosilylation of carbonyl
compounds by TMDS.
(300 MHz, CDCl3): 7.24 (d, J¼8.0 Hz, 2H), 7.15 (d, J¼8.0 Hz, 2H), 4.71
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E. Vasilikogiannaki et al. / Tetrahedron xxx (2014) 1e8
CDCl3): 146.2, 138.1, 133.5, 129.5, 128.1, 127.8, 126.9, 125.4, 71.1, 26.8,
ꢁ0.8, ꢁ1.4.
4.3.9. Triethyl(1-phenylethoxy)silane30 (4b). 1H NMR (300 MHz,
CDCl3): 7.19e7.38 (m, 5H), 4.86 (q, J¼6.5 Hz, 1H), 1.43 (d, J¼6.5 Hz,
3H), 0.91 (t, J¼8.0 Hz, 9H), 0.57 (m, 6H); 13C NMR (75 MHz, CDCl3):
146.9, 128.1, 126.7, 125.2, 70.5, 27.2, 6.8, 4.8.
4.3.10. 1,1,3,3-Tetramethyl-1-((4-methylbenzyl)oxy)disiloxane
(1d). Colorless oil. Rf (hexane/ethyl acetate¼10:1) 0.67; IR (neat,
cmꢁ1): 2960, 2361, 2122, 1516, 1256, 1048, 904, 862, 793, 766; 1H
NMR (300 MHz, CDCl3): 7.24 (d, J¼8.0 Hz, 2H), 7.16 (d, J¼8.0 Hz, 2H),
4.74 (s, 2H), 4.73 (septet, J¼3.0 Hz, 1H), 2.35 (s, 2H), 0.21 (d,
J¼3.0 Hz, 6H), 0.14 (s, 6H); 13C NMR (75 MHz, CDCl3): 137.7, 136.7,
128.9, 126.7, 64.1, 21.1, 0.6, ꢁ1.1; MS (EI): 254 (Mþ, <1%), 237 (3%),
149 (26%), 133 (22%), 119 (13%), 106 (79%), 105 (100%), 91 (53%), 77
(23%); HRMS: MþHþ, found 255.1230. C12H22O2Si2, requires,
255.1237.
Scheme 6. Competing hydrosilylation of 1 by TMDS and PMDS catalyzed by Au/TiO2.
(s, 2H), 2.35 (s, 3H), 0.99 (t, J¼7.5 Hz, 9H), 0.66 (q, J¼7.5 Hz, 6H); 13
C
4.3.11. 1-(Benzyloxy)-1,1,3,3-tetramethyldisiloxane (5a). Colorless
oil. Rf (hexane/ethyl acetate¼10:1) 0.64; IR (neat, cmꢁ1): 2961,
2360, 2123,1454,1378,1256,1047, 903, 860, 821, 792, 767, 726, 694;
1H NMR (300 MHz, CDCl3): 7.35e7.25 (m, 5H), 4.78 (s, 2H), 4.73
(septet, J¼3.0 Hz, 1H), 0.20 (d, J¼3.0 Hz, 6H), 0.15 (s, 6H); 13C NMR
(75 MHz, CDCl3): 140.7, 128.2, 127.1, 126.5, 64.2, 0.6, ꢁ1.1; MS (EI):
240 (Mþ, <1%), 223 (2%), 149 (24%), 133 (21%), 92 (72%), 91 (100%),
65 (21%); HRMS: MþHþ, found 241.0999. C11H20O2Si2þH, requires,
241.1080.
NMR (75 MHz, CDCl3): 138.3, 136.5, 128.9, 126.3, 64.6, 21.1, 6.8, 4.5.
4.3.2. (4-Methylbenzyloxy)dimethylphenylsilane27 (1b). 1H NMR
(300 MHz, CDCl3): 7.62e7.12 (m, 9H), 4.70 (s, 2H), 2.34 (s, 3H), 0.36
(s, 3H), 0.35 (s, 3H); 13C NMR (75 MHz, CDCl3): 138.3, 136.5, 128.9,
126.3, 64.6, 21.1, 6.8, 4.5.
4.3.3. ((4-Methylbenzyl)oxy)triphenylsilane28
(1c). 1H
NMR
(300 MHz, CDCl3): 7.64e7.61 (m, 2H), 7.45e7.39 (m, 3H), 7.21 (d,
J¼7.5 Hz, 2H), 7.15 (d, J¼7.5 Hz, 2H), 4.68 (s, 2H), 2.36 (s, 3H), 0.43 (s,
6H); 13C NMR (75 MHz, CDCl3): 137.7, 136.7, 133.5, 129.6, 128.9,
127.9, 127.4, 126.7, 64.9, 21.1, ꢁ1.7.
4.3.12. 1-((4-Isopropylbenzyl)oxy)-1,1,3,3-tetramethyldisiloxane
(6a). Colorless oil. Rf (hexane/ethyl acetate¼10:1) 0.75; IR (neat,
cmꢁ1): 2959, 2870, 2122, 1514, 1463, 1421, 1376, 1256, 1050, 904,
861, 819, 793, 767; 1H NMR (300 MHz, CDCl3): 7.28 (d, J¼8.0 Hz,
2H), 7.21 (d, J¼8.0 Hz, 2H), 4.74 (s, 2H), 4.73 (septet, J¼3.0 Hz, 1H),
2.91 (septet, J¼7.0 Hz, 1H), 1.25 (d, J¼7.0 Hz, 6H), 0.20 (d, J¼3.0 Hz,
6H), 0.15 (s, 6H); 13C NMR (75 MHz, CDCl3): 147.8, 138.0, 126.7,
126.3, 64.1, 33.8, 24.0, 0.6, ꢁ1.1; MS (EI): 282 (Mþ, <1%), 237 (3%),
149 (18%), 133 (100%), 117 (22%), 105 (27%), 92 (69%), 91 (82%);
HRMS: MþHþ, found 283.1544. C14H26O2Si2þH, requires, 283.1549.
4.3.4. (Cyclohexylmethoxy)dimethyl(phenyl)silane29 (2a). 1H NMR
(300 MHz, CDCl3): 7.63e7.58 (m, 2H), 7.42e7.38 (m, 3H), 3.41 (d,
J¼6.5 Hz, 2H), 1.79e1.67 (m, 5H), 1.58e1.45 (m, 1H), 1.33e1.11 (m,
3H), 0.94e0.81 (m, 2H), 0.40 (s, 6H); 13C NMR (75 MHz, CDCl3):
138.1, 133.5, 129.4, 127.8, 68.7, 40.2, 29.7, 26.7, 25.9, ꢁ1.7.
4.3.5. (Cyclohexylidenemethoxy)triphenylsilane (2b). White solid. Rf
(hexane/ethyl acetate¼10:1) 0.45; 1H NMR (300 MHz, CDCl3):
7.66e7.37 (m, 15H), 6.16 (s, 1H), 2.31 (t, J¼6.0 Hz, 2H), 1.90 (t,
J¼6.0 Hz, 2H), 1.53e1.40 (m, 6H); 13C NMR (75 MHz, CDCl3): 135.4,
133.6, 130.3, 130.2, 127.9, 122.6, 30.4, 28.3, 26.9, 26.8, 25.6; MS (EI):
370 (Mþ, 37%), 292 (11%), 259 (91%), 199 (100%), 181 (35%), 105
(20%); HRMS: MþHþ, found 371.1823. C25H26OSiþH, requires
371.1831.
4.3.13. 1-((4-Fluorobenzyl)oxy)-1,1,3,3-tetramethyldisiloxane
(7a). Colorless oil. Rf (hexane/ethyl acetate¼10:1) 0.59; IR (neat,
cmꢁ1): 2961, 2125, 1728, 1605, 1509, 1465, 1417, 1375, 1257, 1221,
1155, 1048, 904, 858, 821, 794, 767; 1H NMR (300 MHz, CDCl3):
7.33e7.27 (m, 2H), 7.02 (d, J¼7.5 Hz, 2H), 4.72 (s, 2H), 4.71 (septet,
J¼3.0 Hz, 1H), 0.19 (d, J¼3.0 Hz, 6H), 0.13 (s, 6H); 13C NMR (75 MHz,
CDCl3): 162.0 (d, JCeF¼243.0 Hz), 136.4 (d, JCeF¼1.0 Hz), 128.2 (d,
JCeF¼8.0 Hz), 115.1 (d, JCeF¼21.0 Hz), 63.6 (d, JCeF¼0.5 Hz), 0.7, ꢁ1.1;
MS (EI): 258 (Mþ, <1%), 227 (1%), 149 (19%), 133 (10%), 110 (23%),
109 (100%), 83 (12%); HRMS: MþHþ, found 259.0983.
4.3.6. (Cyclohexylmethoxy)triphenylsilane (2c). Colorless oil. Rf
(hexane/ethyl acetate¼10:1) 0.50; IR (neat, cmꢁ1): 3067, 2921, 1891,
1731, 1589, 1427, 1109, 1090, 1026, 709; 1H NMR (300 MHz, CDCl3):
7.64e7.36 (m, 15H), 3.58 (d, J¼6.5 Hz, 2H), 1.79e0.86 (m, 11H); 13C
NMR (75 MHz, CDCl3): 135.4, 134.5, 129.9, 127.8, 69.4, 40.3, 29.7,
26.7, 25.9; MS (EI): 294 (31%), 259 (70%), 216 (18%), 199 (100%), 181
(23%); HRMS: MþHþ, found 373.1983. C25H28OSiþH, requires
373.1988.
C11H19FO2Si2þH, requires, 259.0986.
4.3.14. 1-(Cinnamyloxy)-1,1,3,3-tetramethyldisiloxane
(8a). Colorless oil. Rf (hexane/ethyl acetate¼10:1) 0.55; IR (neat,
cmꢁ1): 3026, 2959, 2857, 2123, 1719, 1600, 1494, 1489, 1258, 1028,
965, 906, 796, 732, 690; 1H NMR (300 MHz, CDCl3): 7.41e7.21 (m,
5H), 6.60 (dd, J1¼16.0 Hz, J2¼1.5 Hz, 1H), 6.31 (dt, J1¼16.0 Hz,
J2¼5.5 Hz, 1H), 4.74 (septet, J¼3.0 Hz, 1H), 4.39 (dd, J1¼5.5 Hz,
J2¼1.5 Hz, 2H), 0.22 (d, J¼3.0 Hz, 6H), 0.16 (s, 6H); 13C NMR (75 MHz,
CDCl3): 137.0, 130.2, 128.5, 128.5, 127.4, 126.4, 63.0, 0.7, ꢁ1.1; MS
(EI): 133 (26%), 118 (70%), 117 (100%), 91 (22%), 73 (19%); HRMS:
MþHþ, found 267.1232. C13H22O2Si2þH, requires, 267.1237.
4.3.7. Dimethyl(octyloxy)(phenyl)silane30 (3a). 1H NMR (300 MHz,
CDCl3): 7.55e7.62 (m, 2H), 7.34e7.43 (m, 3H), 3.59 (t, J¼6.5 Hz, 2H),
1.53 (m, 2H), 1.26 (m, 10H), 0.88 (t, J¼6.5 Hz, 3H), 0.38 (s, 6H); 13C
NMR (75 MHz, CDCl3): 138.1, 133.5, 129.5, 127.8, 63.2, 32.6, 31.8,
29.3, 25.8, 22.6, 14.1, ꢁ1.8.
4.3.8. Dimethyl(phenyl)(1-phenylethoxy)silane15b (4a). 1H NMR
(300 MHz, CDCl3): 7.60e7.22 (m, 10H), 4.89 (q, J¼6.5 Hz, 1H), 1.46
(d, J¼6.5 Hz, 3H), 0.38 (s, 3H), 0.33 (s, 3H); 13C NMR (75 MHz,
4.3.15. 1-(Cyclohexylmethoxy)-1,1,3,3-tetramethyldisiloxane
(2d). Colorless oil. Rf (hexane/ethyl acetate¼10:1) 0.74; IR (neat,
cmꢁ1): 2922, 2854, 2359, 2340, 1450, 1255, 1115, 1050, 904, 821,
Please cite this article in press as: Vasilikogiannaki, E.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2014.03.094

E. Vasilikogiannaki et al. / Tetrahedron xxx (2014) 1e8
7
792, 766; 1H NMR (300 MHz, CDCl3): 4.72 (septet, J¼3.0 Hz, 1H),
3.43 (d, J¼6.5 Hz, 2H), 1.78e0.83 (m, 10H), 0.20 (d, J¼3.0 Hz, 6H),
0.09 (s, 6H); 13C NMR (75 MHz, CDCl3): 68.0, 40.2, 29.7, 26.7, 25.9,
0.7, ꢁ1.3; MS (EI): 246 (Mþ, <1%), 231 (MþꢁMe, 13%), 163 (22%), 149
(12%), 135 (95%), 97 (61%), 73 (27%), 55 (100%); HRMS: MþHþ,
found 247.1543. C11H26O2Si2þH, requires, 247.1549.
1050, 905, 878, 822, 793, 737, 695; 1H NMR (300 MHz, CDCl3):
7.36e7.19 (m, 10H), 5.89 (s, 1H), 4.62 (septet, J¼3.0 Hz, 1H), 0.08 (d,
J¼3.0 Hz, 6H), 0.06 (s, 6H); 13C NMR (75 MHz, CDCl3): 144.6, 128.2,
127.0, 126.5, 76.0, 0.5, ꢁ0.6; MS (EI): 316 (Mþ, 1%), 286 (2%), 267 (2%),
238 (23%), 167 (100%), 152 (26%), 133 (44%), 119 (21%), 91 (64%);
HRMS: MþHþ, found 317.1383. C17H24O2Si2þH, requires, 317.1393.
4.3.16. 1,1,3,3-Tetramethyl-1-(3-phenylbutoxy)disiloxane
(9a). Colorless oil. Rf (hexane/ethyl acetate¼10:1) 0.59; IR (neat,
cmꢁ1): 3028, 2960, 2360, 2341, 1603, 1494, 1452, 1257, 1041, 904,
823, 795, 760, 698; 1H NMR (300 MHz, CDCl3): 7.31e7.15 (m, 5H),
4.69 (septet, J¼3.0 Hz, 1H), 3.60e3.51 (m, 2H), 2.93e2.81 (m, 1H),
1.87e1.80 (m, 2H), 1.26 (d, J¼7.0 Hz, 3H), 0.17 (d, J¼3.0 Hz, 6H), 0.06
(s, 3H), 0.05 (s, 3H); 13C NMR (75 MHz, CDCl3): 147.1, 128.3, 127.0,
125.9, 60.4, 40.8, 36.1, 22.3, 0.6, ꢁ1.2, ꢁ1.3; MS (EI): 282 (Mþ, <1%),
149 (9%), 132 (46%), 117 (100%), 105 (64%), 91 (82%); HRMS: MþHþ,
found 283.1542. C14H26O2Si2þH, requires, 283.1550.
4.3.23. 1-((9H-Fluoren-9-yl)oxy)-1,1,3,3-tetramethyldisiloxane
(14a). Colorless oil. Rf (hexane/ethyl acetate¼10:1) 0.52; IR (neat,
cmꢁ1): 3069, 2959, 2360, 2121, 1610, 1451, 1330, 1256, 1193, 1110,
1048, 904, 873, 793, 735; 1H NMR (300 MHz, CDCl3): 7.65 (d,
J¼7.0 Hz, 2H), 7.58 (d, J¼7.0 Hz, 2H), 7.40e7.28 (m, 4H), 5.80 (s, 1H),
4.80 (septet, J¼3.0 Hz, 1H), 0.24 (d, J¼3.0 Hz, 6H), 0.21 (s, 6H); 13C
NMR (75 MHz, CDCl3): 145.7, 140.0, 128.7, 127.5, 125.2, 119.8, 74.9,
0.7, ꢁ0.0; MS (EI): 314 (Mþ, 9%), 297 (4%), 279 (2%), 165 (100%), 133
(14%); HRMS: MþHþ, found 315.1235. C17H22O2Si2þH, requires,
315.1237.
4 . 3 .17 . 1 - ( ( 3 , 7 - D i m e t hyl o c t - 6 - e n - 1 - yl ) o x y ) - 1,1, 3 , 3 -
tetramethyldisiloxane (10a). Colorless oil. Rf (hexane/ethyl
acetate¼10:1) 0.62; IR (neat, cmꢁ1): 1454, 1377, 1256, 1088, 1052,
903, 821, 793, 767; 1H NMR (300 MHz, CDCl3): 5.10 (t, J¼7.0 Hz, 1H),
4.71 (septet, J¼3.0 Hz, 1H), 3.73e3.62 (m, 2H), 2.04e1.92 (m, 2H),
1.69 (s, 3H), 1.65e1.52 (m, 2H), 1.61 (s, 3H), 1.50e1.41 (m, 2H),
1.30e1.22 (m, 1H), 0.89 (d, J¼7.0 Hz, 3H), 0.20 (d, J¼3.0 Hz, 6H), 0.09
(s, 6H); 13C NMR (75 MHz, CDCl3): 131.1, 124.8, 60.6, 39.6, 37.2, 29.2,
25.7, 25.4, 19.5, 17.6, 0.7, ꢁ1.2; MS (EI): 288 (Mþ, <1%), 201 (7%), 149
(100%), 133 (62%), 95 (48%), 81 (53%).
4. 3 . 24 . 1 - ( ( 1 r, 3 r, 5 r, 7 r ) - A da m a nt an - 2 - ylo x y ) - 1,1, 3 , 3 -
tetramethyldisiloxane (15a). White solid. Rf (hexane/ethyl
acetate¼4:1) 0.85; IR (neat, cmꢁ1): 2959, 2903, 2582, 2360, 2341,
2122, 1450, 1255, 1052, 1035, 956, 903, 872, 823, 789, 766; 1H NMR
(300 MHz, CDCl3): 4.69 (septet, J¼3.0 Hz, 1H), 3.92 (br t, 1H), 2.14
(br d, J¼12.0 Hz, 2H), 1.85e1.52 (m, 10H), 1.44 (br d, J¼12.0 Hz, 2H),
0.19 (d, J¼3.0 Hz, 6H), 0.08 (s, 6H); 13C NMR (75 MHz, CDCl3): 74.8,
37.8, 36.6, 35.1, 31.2, 27.6, 27.2, 0.7, ꢁ0.6; MS (EI): 284 (Mþ, <1%),
369 (Mþ-Me, 3%), 149 (42%), 135 (100%), 119 (17%), 107 (19%), 93
(43%), 79 (48%), 67 (52%); HRMS: MþHþ, found 285.1692.
C14H28O2Si2þH, requires, 285.1706.
4.3.18. 1,1,3,3-Tetramethyl-1-(1-phenylethoxy)disiloxane31
(4c). 1H
NMR (300 MHz, CDCl3): 7.37e7.20 (m, 5H), 4.99 (q, J¼6.5 Hz, 1H),
4.67 (septet, J¼3.0 Hz, 1H), 1.47 (d, J¼6.5 Hz, 3H), 0.15 (d, J¼3.0 Hz,
3H), 0.14 (d, J¼3.0 Hz, 3H), 0.11 (s, 3H), 0.03 (s, 3H); 13C NMR
(75 MHz, CDCl3): 146.2, 128.1, 126.8, 125.3, 70.2, 26.7, 0.6, ꢁ0.5, ꢁ0.8.
4.3.25. 1-(Cyclohex-2-en-1-yloxy)-1,1,3,3-tetramethyldisiloxane
(16a). Colorless oil. Rf (hexane/ethyl acetate¼6:1) 0.70; IR (neat,
cmꢁ1): 3028, 2941, 2360, 2341, 2122, 1255, 1048,1021, 901, 885, 821,
1
791, 767, 722, 696; H NMR (300 MHz, CDCl3): 7.36e7.19 (m, 10H),
5.89 (s, 1H), 4.62 (septet, J¼3.0 Hz, 1H), 0.08 (d, J¼3.0 Hz, 6H), 0.06
(s, 6H); 13C NMR (75 MHz, CDCl3): 144.6, 128.2, 127.0, 126.5, 76.0,
0.5, ꢁ0.6; MS (EI): 230 (Mþ, 1%), 187 (12%), 159 (6%), 149 (93%), 135
(56%), 133 (98%), 119 (23%), 81 (100%); HRMS: MþHþ, found
231.1231. C10H22O2Si2þH, requires, 231.1237.
4 . 3 . 1 9 . 1 - ( 1 - ( 4 - M e t h o x y p h e n y l ) e t h o x y ) - 1, 1, 3 , 3 -
tetramethyldisiloxane31 (11a). 1H NMR (500 MHz, CDCl3): 7.26 (d,
J¼8.5 Hz, 2H), 6.85 (d, J¼8.5 Hz, 2H), 4.94 (q, J¼6.5 Hz, 1H), 4.67
(septet, J¼3.0 Hz, 1H), 1.44 (d, J¼6.5 Hz, 3H), 0.15 (d, J¼3.0 Hz, 3H),
0.14 (d, J¼3.0 Hz, 3H), 0.09 (s, 3H), 0.02 (s, 3H); 13C NMR (125 MHz,
CDCl3): 158.5, 138.4, 126.5, 113.5, 69.9, 55.2, 26.7, 0.6, ꢁ0.5, ꢁ0.7.
4.3.26. 1,1,1,3,3-Pentamethyl-3-((4-methylbenzyl)oxy)disiloxane
(1e). Colorless oil. Rf (hexane/ethyl acetate¼10:1) 0.66; IR (neat,
cmꢁ1): 2958,1516,1376,1254,1044, 838, 792, 752, 684, 632; 1H NMR
(300 MHz, CDCl3): 7.25 (d, J¼7.5 Hz, 2H), 7.14 (d, J¼7.5 Hz, 2H), 4.72 (s,
2H), 2.34 (s, 3H), 0.11 (s, 6H), 0.10 (s, 9H); 13C NMR (75 MHz, CDCl3):
137.8, 136.6, 128.9, 126.6, 64.0, 21.1, 1.8, ꢁ0.8; MS (EI): 268 (Mþ, 36%),
253 (Mþ-Me, 23%), 147 (24%), 132 (13%), 119 (46%), 105 (100%);
HRMS: MþHþ, found 269.1391. C13H24O2Si2, requires, 269.1393.
4.3.20. 1-(Cyclohex-1-en-1-yloxy)-1,1,3,3-tetramethyldisiloxane
(12a). Colorless oil. Rf (hexane/ethyl acetate¼6:1) 0.81; IR (neat,
cmꢁ1): 2961, 2930, 2842, 2360, 2341, 2127, 1672, 1367, 1256, 1188,
1046, 988, 894, 823, 792, 767; 1H NMR (300 MHz, CDCl3): 4.93 (br t,
1H), 4.72 (septet, J¼3.0 Hz, 1H), 2.03e1.98 (m, 4H), 1.70e1.60 (m,
2H), 1.55e1.48 (m, 2H), 0.20 (d, J¼3.0 Hz, 6H), 0.15 (s, 6H); 13C NMR
(75 MHz, CDCl3): 149.5, 104.7, 29.7, 23.8, 23.1, 22.3, 0.6, ꢁ0.6; MS
(EI): 230 (Mþ, 2%), 215 (MþꢁMe, 1%), 187 (8%), 149 (71%), 133
(100%), 67 (48%); HRMS: MþHþ, found 231.1231. C10H22O2Si2þH,
requires, 231.1237.
Acknowledgements
The authors wish to acknowledge co-funding of this research in
part by the European Regional Development Fund of the EU and
national funds e Greek Ministry of Education and Religious Affairs,
Sport and Culture/GGET e EUDE-ETAK, through the Operational
Program Competitiveness and Entrepreneurship (OPC II), NSRF
2007-2013, Action “SYNERGASIA 2011” Project: THERA-CAN e No.
11SUN_1_485. We thank ProFI (ITE, Heraklion Crete) for obtaining
the HRMS spectra.
4.3.21. 1-(Cyclohexyloxy)-1,1,3,3-tetramethyldisiloxane
(12b). Colorless oil. Rf (hexane/ethyl acetate¼10:1) 0.69; IR (neat,
cmꢁ1): 2931, 2858, 2124, 1451, 1255, 1046, 989, 904, 822, 791, 767;
1H NMR (300 MHz, CDCl3): 4.70 (septet, J¼3.0 Hz, 1H), 3.72e3.64
(m, 1H), 1.85e1.11 (m, 10H), 0.20 (d, J¼3.0 Hz, 6H), 0.09 (s, 6H); 13
C
NMR (75 MHz, CDCl3): 70.8, 35.8, 25.5, 24.4, 0.7, ꢁ0.5; MS (EI): 232
(Mþ, <1%), 217 (MþꢁMe, 2%), 149 (47%), 135 (66%), 133 (28%), 55
(33%), 41 (100%); HRMS: MþHþ, found 233.1387. C10H24O2Si2þH,
requires, 233.1393.
Supplementary data
4.3.22. 1-(Benzhydryloxy)-1,1,3,3-tetramethyldisiloxane
(13a). Colorless oil. Rf (hexane/ethyl acetate¼10:1) 0.59; IR (neat,
cmꢁ1): 3064, 3028, 2960, 2361, 2341, 2123, 1599, 1493, 1454, 1257,
Copies of 1H and 13C NMR spectra of products. Supplementary
data associated with this article can be found in the online version,
at http://dx.doi.org/10.1016/j.tet.2014.03.094.
Please cite this article in press as: Vasilikogiannaki, E.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2014.03.094

8
E. Vasilikogiannaki et al. / Tetrahedron xxx (2014) 1e8
T.; Doris, E. Angew. Chem., Int. Ed. 2011, 50, 7533e7536; (d) Li, W.; Wang, A.;
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Please cite this article in press as: Vasilikogiannaki, E.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2014.03.094