Cobalt-Catalyzed Intramolecular Silylperoxidation of Unsaturated Diisopropylsilyl Ethers

Article abstract of DOI:10.1021/acs.joc.9b00642

A cobalt-catalyzed intramolecular silylperoxidation reaction was developed that allows for the conversion of unsaturated diisopropylsilyl ethers to 3-sila-1,2,4-trioxepanes. Reduction of the peroxide unit of the 3-sila-1,2,4-trioxepane yields six-membered

Full text of DOI:10.1021/acs.joc.9b00642

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Featured Article
Cobalt-Catalyzed Intramolecular Silylperoxidation
of Unsaturated Diisopropylsilyl Ethers
Jonathan P Oswald, and Keith A. Woerpel
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b00642 • Publication Date (Web): 02 May 2019
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The Journal of Organic Chemistry
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Cobalt-Catalyzed Intramolecular Silylperoxidation of Unsaturated
Diisopropylsilyl Ethers
Jonathan P. Oswald and K. A. Woerpel*
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Department of Chemistry, New York University, New York, New York 10003, United States
Supporting Information Placeholder
ABSTRACT: A cobalt-catalyzed intramolecular silylperoxidation reaction was developed that allows for the conversion of unsaturated
diisopropylsilyl ethers to 3-sila-1,2,4-trioxepanes. Reduction of the peroxide unit of the 3-sila-1,2,4-trioxepane yields six-membered ring
diisopropylsilylene acetals.
INTRODUCTION
RESULTS AND DISCUSSION
The cobalt-catalyzed oxygenation of alkenes is an effective re-
During our investigation into new applications of the cobalt-cat-
action for the synthesis of silyl peroxides,1 but can also be applied
alyzed oxygenation of alkenes, we found that intramolecular si-
to the synthesis of a variety of endoperoxides,2 including 1,2-diox-
lylperoxidation can be achieved. When unsaturated diisopropylsi-
olanes,3,4,5 1,2-dioxanes,4,6 1,2-dioxepanes,7 and 1,2,4-triox-
lyl ether 1 was subjected to cobalt-catalyzed oxygenation (Scheme
2), after less than an hour, 3-sila-1,2,4-trioxepane 2 was formed as
the major product. In addition, trace amounts of diisopropylsilylene
olanes.8,9 The reaction, which converts alkenes to silyl peroxides
through a peroxyl radical intermediate,1,10,11 uses a cobalt(II) cata-
lyst, molecular oxygen, and a silane reducing agent. Depending on
the choice of substrate, the peroxyl radical intermediate can react
intramolecularly, forming endoperoxides instead. Treatment of ei-
ther a 1,4- or 1,5-diene4,12 with the cobalt-catalyzed oxygenation
conditions resulted in the formation of 1,2-dioxolanes and 1,2-di-
oxanes, respectively (Scheme 1, eq 1). Similar reactivity was ob-
served with vinylcyclopropanes, which formed 1,2-dioxolanes
(Scheme 1, eq 2).3,12 In this Article, we report that unsaturated
diisopropylsilyl ethers can undergo an intramolecular silylperoxi-
dation reaction to form 3-sila-1,2,4-trioxepanes (Scheme 1, eq 3).13
Upon reduction of the peroxide unit using triphenylphosphine, the
corresponding silylene-protected 1,3-diol was formed.
acetal 3 and linear silyl peroxide 4 were detected by 1H NMR spec-
troscopy. Formation of 3-sila-1,2,4-trioxepane 2 as the major prod-
uct was not anticipated because the silylation step of the cobalt-
catalyzed oxygenation of alkenes is generally sensitive to both the
steric and electronic environment of the silane.14,15 In this case,
however, the diisopropylsilyl group was preferentially incorpo-
rated into the peroxide. The above observation was significant be-
cause, for comparison, the synthesis of a triisopropylsilyl peroxide
using the cobalt-catalyzed oxygenation of alkenes is very difficult
considering the poor reactivity of triisopropylsilane.14,16
Scheme 1. Co-Catalyzed Endoperoxide Formation
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using triphenylphosphine.21,22 The above modification to the pro-
Scheme 2. Products of Co-Catalyzed Intramolecular
Silylperoxidation of Unsaturated Diisopropylsilyl Ethers
cedure resulted in a 73% isolated yield of diisopropylsilylene acetal
3 over two steps (Scheme 3). When the cobalt-catalyzed oxygena-
tion was performed using triethylsilane instead of phenylsilane, the
isolated yield of diisopropylsilylene acetal 3 decreased slightly to
60% due to the formation of trace amounts of linear silyl peroxide
4 (Scheme 2).14,23 Linear silyl peroxide 4 can be difficult to separate
from diisopropylsilylene acetal 3.
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Scheme 3. Formation of Diisopropylsilylene Acetal 3 from
3-Sila-1,2,4-Trioxepane 2
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The yield of the 3-sila-1,2,4-trioxepane was found to be sensitive
to the choice of the added silane and cobalt catalyst. When unsatu-
rated diisopropylsilyl ether 5 was subjected to cobalt-catalyzed ox-
ygenation using Co(acac)2, triethylsilane, and catalytic tert-butyl
hydroperoxide (Table 1, entry 1), 3-sila-1,2,4-trioxepane 6 was iso-
lated in 21% yield. Triethylsilane and tert-butyl hydroperoxide
were required to initiate the reaction rapidly.3 The use of a more
sterically bulky silane (Table 1, entries 2 and 3) or one with electron
withdrawing groups (Table 1, entry 4) gave only trace product for-
mation after 20 h. The poor reactivity of these silanes can be ex-
plained by considering that formation of the reactive cobalt-hydride
species is sensitive to the choice of silane.3,14 When Co(thd)2 was
used instead of Co(acac)2, decreased reaction times and increased
yields were observed (Table 1, entries 6–8). The combination of
Co(thd)2 with catalytic phenylsilane (Table 1, entry 7) or stoichio-
metric triethylsilane (Table 1, entry 8) resulted in the greatest yields
of the 3-sila-1,2,4-trioxepane. Optimized reaction conditions were
achieved using 10 mol % Co(thd)2 and one equivalent of tri-
ethylsilane,17 which yielded the 3-sila-1,2,4-trioxepane 2 in 74%
yield, as determined by 1H NMR spectroscopy (Table 1, entry 8).
The isolated yield of 2, however, was only 38% (Table 1, entry 8),
suggesting that the 3-sila-1,2,4-trioxepane was not stable to column
chromatography.18
Several control experiments yielded insight into the reaction
mechanism. The first experiment was aimed at determining
whether the 3-sila-1,2,4-trioxepane could form through a mecha-
nism involving migration of the peroxide between the silicon atoms
(Scheme 4). When linear silyl peroxide 4 was resubjected to the
reaction conditions, none of the 3-sila-1,2,4-trioxepane 2 was ob-
served by 1H NMR spectroscopy after 19 h. Even when a pure sam-
ple of linear silyl peroxide 4 was allowed to stand in deuterated
chloroform, formation of 3-sila-1,2,4-trioxepane 2 was not ob-
served.
Scheme 4. Exchange of Silanes Not Observed
Other control experiments were designed to determine the role
of triethylsilane. One hypothesis was that the triethylsilane cata-
lyzed the initial formation of the cobalt-hydride species. When un-
saturated diisopropylsilyl ether 1 was subjected to the reaction con-
ditions without the addition of triethylsilane, formation of 3-sila-
1,2,4-trioxepane 2 occurred slowly over the course of 19 h, with a
Table 1. Optimization of Co-Catalyzed Intramolecular
Silylperoxidation of Unsaturated Diisopropylsilyl Ethers
1
final yield of 37% by H NMR spectroscopy (Table 2, entry 1).
With the addition of one equivalent of triethylsilane, the reaction
was completed in 0.5 h with a 74% yield of 3-sila-1,2,4-trioxepane
2 by 1H NMR spectroscopy (Table 2, entry 2). These data suggested
that triethylsilane was necessary to catalyze the formation of the
cobalt-hydride species and that the diisopropylsilyl group alone
was not kinetically competent enough to do so. Even with a large
excess of triethylsilane (Table 2, entries 3 and 4), formation of 3-
sila-1,2,4-trioxepane 2 was competitive with the formation of linear
silyl peroxide 4.
aYield determined by 1H NMR spectroscopy with mesitylene as
b
c
the internal standard. Isolated yield. thd = 2,2,6,6-tetramethyl-
3,5-heptanedionato. d1,2, R = 4-(MeO)C6H4; 5,6, R = Ph.
Reducing the 3-sila-1,2,4-trioxepane to the corresponding diiso-
propylsilylene acetal provided a product that was more stable to
purification.19,20 After the cobalt-catalyzed oxygenation was com-
pleted, the peroxide unit of 3-sila-1,2,4-trioxepane 2 was reduced
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Table 2. Equivalents of Triethylsilane and Effect on Product
Distribution
Scheme 6. Proposed Mechanism for the Co-Catalyzed In-
tramolecular Silylperoxidation of Unsaturated
Diisopropylsilyl Ethers
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aYield determined by 1H NMR spectroscopy with mesitylene as
the internal standard.
Further evidence of triethylsilane’s role was observed when al-
cohol 7 and diisopropylsilane 8 were subjected to the cobalt-cata-
lyzed oxygenation (Scheme 5). The purpose of this experiment was
to confirm that the diisopropylsilyl group alone cannot sufficiently
initiate the reaction. With two equivalents of diisopropylsilane 8,
even after 22 h, the conversion of 7 was low and the yield of dia-
stereomers 9 and 10 was 18% (Scheme 5). This observation, com-
bined with the data in Table 2, entry 1, indicates that the addition
of triethylsilane is required to initiate the reaction.
The cobalt-catalyzed intramolecular formation of 3-sila-1,2,4-
trioxepanes was general for several unsaturated diisopropylsilyl
ethers (Table 3).29 Unsaturated silyl ethers 1 and 12–15 (Table 3)30
were synthesized by addition of a Grignard reagent to a carbonyl
compound followed by silylation of the resulting alcohol, as out-
lined for diisopropylsilyl ether 15 in Scheme 7. There was a corre-
lation between the degree of substitution of the alkene substrate and
its reactivity in the intramolecular silylperoxidation.4 When mono-
substituted alkenes 1, 12, and 13 were subjected to the cobalt-cata-
lyzed oxygenation, the reaction was completed in two hours or less
(Table 3, entries 1–3). Di-substituted alkene 14 required heating
and a longer reaction time, ultimately yielding diisopropylsilylene
acetal 18 in 39% (Table 3, entry 4). The added substitution at the
allylic position of unsaturated silyl ether 15 also resulted in the need
for heating and a longer reaction time (Table 3, entry 5). Unsatu-
rated silyl ether 15 (Table 3, entry 5) gave the highest diastereo-
meric ratio out of all of the unsaturated silyl ethers tested. Gener-
ally, when a more sterically hindered alkene undergoes cobalt-cat-
alyzed oxygenation, diastereoselectivity increases.31,32,33
Scheme 5. Co-Catalyzed Silylperoxidation Using
Diisopropylsilane 8
A mechanism can be proposed that is consistent with the above
observations (Scheme 6). The first step in this mechanism is the
formation of a cobalt-hydride species, which is catalyzed by tert-
butyl hydroperoxide24 and triethylsilane.3,25 Addition of the cobalt-
hydride species across the double bond of a molecule of unsatu-
rated diisopropylsilyl ether I, followed by dissociation of the cobalt
catalyst from II, would form alkyl radical III. The addition of co-
balt-hydride occurs in such a way as to generate the more substi-
tuted radical intermediate.3,14 Alkyl radical III can react with mo-
lecular oxygen, forming peroxyl radical IV, which, upon coordina-
tion to cobalt, yields Co(III)–peroxyl intermediate V.4 Co(III)–
peroxyl intermediate V can react by one of two ways. The first
pathway involves an intramolecular transmetalation reaction (VI)
between Co(III)–peroxyl intermediate V and the diisopropylsilyl
group,3 resulting in formation of 3-sila-1,2,4-trioxepane VIII. The
formation of other seven-membered ring products involving a tran-
sition state analogous to VI have been reported.26,27 The alternative
pathway is also a transmetalation reaction, but instead occurs be-
tween Co(III)–peroxyl intermediate V and triethylsilane, yielding
linear silyl peroxide VII. The mechanism of formation of 3-sila-
1,2,4-trioxepane VIII is different from that of other intramolecular
endoperoxide forming reactions (Scheme 1, eqs 1 and 2) in that
product formation occurs from Co(III)–peroxyl intermediate V in-
stead of peroxyl radical IV. It was suspected that because tri-
ethylsilane was only incorporated into less than 5% of the product
(Scheme 2), any remaining triethylsilane either remained unre-
acted28 or was oxidized.3
In some examples (Table 3, entries 3–5), Co(acac)2 was used in-
stead of Co(thd)2 to facilitate the purification process. During the
course of the cobalt-catalyzed oxygenation, Co(thd)2 was con-
verted to Co(thd)3,34,35 which can be difficult to separate from the
diisopropylsilylene acetal product during column chromatography.
Difficulties with the purification process using similar cobalt cata-
lysts has been reported.36 Even though Co(acac)2 improves the pu-
rification process, Co(thd)2 was the better catalyst for these cobalt-
catalyzed intramolecular silylperoxidation reactions. Compared to
Co(acac)2, Co(thd)2 generally resulted in better yields of the 3-sila-
1,2,4-trioxepane, shorter reaction times, and better conversion of
the starting material.
The degree of substitution of the diisopropylsilyl ether affected
the stability of the products from the cobalt-catalyzed intramolecu-
lar silylperoxidation. For example, secondary benzylic silyl ether
12 yielded the least amount of diisopropylsilylene acetal 16 (Table
3, entry 2).37 Diisopropylsilylene acetal 16 was also found to be
sensitive to purification. Prior to chromatography, analysis of the
crude reaction mixture of diisopropylsilylene acetal 16 showed a
diastereomeric ratio of 40:60, however, after purification, only the
1
minor diastereomer of 16 was isolated. By comparing the H and
13C NMR chemical shifts and coupling constants of diisopropylsi-
lylene acetal 16 to structurally similar diisopropylsilylene acetals,38
it was determined that the syn diastereomer of 16 was isolated. De-
composition of diisopropylsilylene 16 had occurred during chro-
matography as evident by the formation of 1,3-diol 20 as a mixture
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of diastereomers (Table 3, entry 2). Decreased stability of benzylic
Scheme 8. Deprotection of Diisopropylsilylene Acetals
diisopropylsilylene acetals has been previously observed.39
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Scheme 7. Synthesis of Unsaturated Diisopropylsilyl Ethers
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Table 3. Unsaturated Silyl Ether Screen
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The cobalt-catalyzed oxygenation of unsaturated diisopropylsi-
lyl ethers could also be applied to the synthesis of five-membered
ring diisopropylsilylene acetals (Scheme 9, eq 6). Unsaturated
diisopropylsilyl ether 25 formed five-membered diisopropylsi-
lylene acetal 26 (Scheme 9, eq 6) upon treatment with the cobalt-
catalyzed oxygenation and subsequent reduction of the peroxide.
This product, however, was not stable to purification by column
chromatography.20 Its formation was suggested by 29Si NMR spec-
troscopy, which showed that not only had the chemical shift of
diisopropylsilylene acetal 26 changed compared to that of the start-
ing material (25), but also that this new chemical shift was within
the range of other five-membered ring silylene acetals (Scheme 9,
eq 6).40,41 These observations were confirmed by demonstrating
that treatment of diisopropylsilylene acetal 26 with tetrabu-
tylammonium fluoride yielded the corresponding 1,2-diol (27) in
19% over three steps (Scheme 9, eq 6).
Synthesis of a seven-membered ring diisopropylsilylene acetal
was not successful (Scheme 9, eq 7). When unsaturated diiso-
propylsilyl ether 28 was subjected to the cobalt-catalyzed oxygen-
ation, no cyclization product was observed. Instead, only linear si-
lyl peroxide 29 (Scheme 9, eq 7) was formed. As the distance be-
tween the alkene and diisopropylsilyl group increases, formation of
the linear silyl peroxide becomes the favored reaction pathway in-
stead of intramolecular cyclization (Scheme 6).
Scheme 9. Ring Size Screen for the Co-Catalyzed Intramo-
lecular Silylperoxidation of Unsaturated Diisopropylsilyl
Ethers
aAr = 4-(MeO)C6H4. bReaction heated to 40 °C for this time. c1,3-
Diol 20 was formed in 21% yield as a 67:33 mixture of diastere-
omers.
Removal of the diisopropylsilylene acetal protecting group using
tetrabutylammonium fluoride yielded the corresponding diol,
which was generally easier to purify. For example, attempts to pu-
rify diisopropylsilylene acetal 17 by chromatography (Table 3, en-
try 3), when the cobalt-catalyzed oxygenation was performed using
Co(thd)2, were unsuccessful because of trace amounts of Co(thd)3
co-eluting with diisopropylsilylene acetal 17. By contrast, when the
crude diisopropylsilylene acetal was treated with tetrabutylammo-
nium fluoride (Scheme 8, eq 4), 1,3-diol 21 was isolated in 79%
yield over three steps (Scheme 8, eq 4). Similarly, diisopropylsi-
lylene acetal 23 was unstable to column chromatography and could
not be purified (Scheme 8, eq 5). Treatment of a crude diiso-
propylsilylene acetal 23 with tetrabutylammonium fluoride yielded
1,3-diol 24 in 73% over three steps.
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The Journal of Organic Chemistry
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CONCLUSION
Synthesis of Alcohols.
In summary, we have demonstrated that an intramolecular si-
lylperoxidation reaction can be applied to the synthesis of 3-sila-
1,2,4-trioxepanes from unsaturated diisopropylsilyl ethers. With
the use of triphenylphosphine, the peroxide unit of the 3-sila-1,2,4-
trioxepane can be reduced to yield diisopropylsilylene acetals. A
mechanism has been suggested in which the addition of tri-
ethylsilane was necessary in order to initiate the reaction. The key
intermediate of this reaction is a Co(III)–peroxyl intermediate,
which can either react intra- or intermolecularly. Intramolecular
formation of the 3-sila-1,2,4-trioxepane is favored over the inter-
molecular reaction, which forms the triethylsilyl peroxide instead.
Formation of the 3-sila-1,2,4-trioxepane does not involve a silane-
exchange pathway, but, an intramolecular transmetalation reaction
cannot be ruled out. More sterically hindered alkenes yielded less
of the diisopropylsilylene acetal. Removal of the diisopropylsi-
lylene acetal group was achieved using tetrabutylammonium fluo-
ride, which yields the corresponding diol.
2-(4-Methoxyphenyl)pent-4-en-2-ol. To a solution of ketone 11
(0.500 g, 3.33 mmol) in THF (5.0 mL) at 0 °C was added a solution
of allylmagnesium chloride in THF (2.0 M, 1.8 mL, 3.7 mmol)
dropwise. The resulting reaction mixture was allowed to warm to
room temperature over 30 min. Saturated aqueous NH4Cl (5.0 mL)
was added and the mixture was extracted with diethyl ether (3 × 5
mL). The combined organic layers were dried over MgSO4 and
concentrated in vacuo. 2-(4-Methoxyphenyl)pent-4-en-2-ol was
isolated as a colorless oil (0.607 g, 95%) and used without further
purification. The spectroscopic data are consistent with the data re-
ported:50 1H NMR (400 MHz, CDCl3) δ 7.36 (d, J = 8.8, 2H), 6.88
(d, J = 8.7, 2H), 5.64 (m, 1H), 5.13 (m, 1H), 5.10 (s, 1H), 3.80 (s,
3H), 2.66 (dd, J = 13.5, 6.7, 1H), 2.49 (dd, J = 13.7, 8.3, 1H), 2.04
(s, 1H), 1.53 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 158.5,
140.1, 134.1, 126.2, 119.5, 113.6, 73.5, 55.4, 48.7, 30.1.
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2-Cyclohexylpent-4-en-2-ol. To a solution of acetylcyclohexane
(0.436 mL, 3.17 mmol) in THF (4.7 mL) at 0 °C was added a solu-
tion of allylmagnesium chloride in THF (2.0 M, 1.7 mL, 3.5 mmol)
dropwise. The resulting reaction mixture was allowed to warm to
room temperature over 30 min. Saturated aqueous NH4Cl (5.0 mL)
was added and the mixture was extracted with diethyl ether (3 × 5
mL). The combined organic layers were dried over MgSO4 and
concentrated in vacuo. Purification by flash chromatography (hex-
anes:EtOAc = 90:10) afforded 2-cyclohexylpent-4-en-2-ol (0.389
g, 73%) as a yellow oil. The spectroscopic data are consistent with
the data reported:50 1H NMR (400 MHz, CDCl3) δ 5.89 (m, 1H),
5.18–5.07 (m, 2H), 2.23 (m, 2H), 1.87–1.64 (m, 5H), 1.39 (s, 1H),
1.36–1.13 (m, 4H), 1.09 (s, 3H), 1.06–0.93 (m, 2H); 13C{1H} NMR
(100 MHz, CDCl3) δ 134.4, 118.8, 74.1, 47.7, 44.5, 27.8, 27.1,
26.97, 26.93, 26.8, 23.9.
EXPERIMENTAL SECTION
1
General Information. All H and 13C NMR spectra were rec-
orded at ambient temperature at 400, 500, and 600 MHz, or 100,
125, and 150 MHz, respectively. The data were reported as follows:
chemical shifts reported in parts per million from residual solvent
peaks (1H NMR CDCl3 δ 7.26, C6D6 δ 7.16; 13C NMR CDCl3 δ
77.23, C6D6 δ 128.4) on the δ scale, multiplicity (s, singlet; br,
broad; d, doublet; t, triplet; q, quartet; quint, quintet; dd, doublet of
doublets; m, multiplet), coupling constants (hertz), and integration.
The multiplicity of carbon peaks was determined using HSQC or
DEPT experiments. Infrared (IR) spectra were recorded using at-
tenuated total reflectance (ATR). High-resolution mass spectra
(HRMS) were recorded using a time-of-flight spectrometer with at-
mospheric-pressure chemical ionization (APCI) or electrospray
ionization (ESI) ionization sources. Liquid chromatography was
performed using forced flow (flash chromatography) of the indi-
cated solvent system on silica gel (SiO2) 60 Å (230−400 mesh) un-
less noted, otherwise, aluminium oxide (Al2O3), neutral, Brock-
mann I, particle size 50-200 μm, 60 Å was used. THF and Et2O
were dried and degassed using a solvent purification system before
being used. All reactions were performed under a nitrogen atmos-
phere in glassware that had been flame-dried under vacuum unless
otherwise stated. All reactions that were performed under an oxy-
gen atmosphere used glassware that was not flame-dried. Unless
otherwise noted, all reagents were commercially available. Prenyl-
magnesium chloride was prepared by known methods.42 Co(acac)2
was prepared by known methods.43 The following alcohols were
prepared by known methods: 2-phenylpent-4-en-2-ol (7),44 1-(4-
methoxyphenyl)but-3-en-1-ol,45 2-(4-methoxyphenyl)hex-5-en-2-
ol,46 trans-2-vinylcyclohexan-1-ol,47 and (E)-3-methyloct-2-en-4-
ol.48 Diisopropylsilyl ether 8 was prepared by known methods.49
2-(4-Methoxyphenyl)-3,3-dimethylpent-4-en-2-ol. To a solution
of ketone 11 (0.300 g, 2.00 mmol) in THF (6.1 mL) at –78 °C was
added a solution of prenylmagnesium chloride in THF (0.4 M, 5.5
mL, 2.2 mmol) dropwise. The resulting reaction mixture was al-
lowed to warm to room temperature over 40 min. Saturated aque-
ous NH4Cl (6.0 mL) was added and the mixture was extracted with
diethyl ether (3 × 6 mL). The combined organic layers were dried
over MgSO4 and concentrated in vacuo. Purification by flash chro-
matography (hexanes:EtOAc = 90:10) afforded 2-(4-methoxy-
phenyl)-3,3-dimethylpent-4-en-2-ol (0.324 g, 74%) as a colorless
oil: 1H NMR (400 MHz, CDCl3) δ 7.33 (d, J = 8.8, 2H), 6.84 (d, J
= 8.8, 2H), 5.96 (dd, J = 17.6, 10.9, 1H), 5.13–5.00 (m, 2H), 3.81
(s, 3H), 1.88 (s, 1H), 1.56 (s, 3H), 1.00 (s, 3H), 0.98 (s, 3H);
13C{1H} NMR (100 MHz, CDCl3) δ 158.3 (C), 145.5 (CH), 137.8
(C), 128.4 (CH), 113.9 (CH2), 112.6 (CH), 77.5 (C), 55.4 (CH3),
44.7 (C), 25.7 (CH3), 22.9 (CH3), 22.6 (CH3); IR (ATR) 3505,
2977, 1509, 1246, 1175, 1033, 830 cm-1; HRMS (ESI) m/z calcd
for C14H20NaO2 (M + Na)+ 243.1356, found 243.1351.
2-(4-Methoxyphenyl)-4-methylpent-4-en-2-ol. To a solution of
ketone 11 (0.300 g, 2.00 mmol) in THF (6.0 mL) at 0 °C was added
a solution of 2-methylallylmagnesium chloride in THF (0.5 M, 4.4
mL, 2.2 mmol) dropwise. The resulting reaction mixture was al-
lowed to warm to room temperature over 1 h. Saturated aqueous
NH4Cl (6.0 mL) was added and the mixture was extracted with di-
ethyl ether (3 × 6 mL). The combined organic layers were dried
over MgSO4 and concentrated in vacuo. Purification by flash chro-
matography (hexanes:EtOAc = 80:20) afforded 2-(4-methoxy-
phenyl)-4-methylpent-4-en-2-ol (0.270 g, 66%) as a colorless oil.
Synthesis of Bis(2,2,6,6-tetramethyl-3,5-heptanedionato)co-
balt(II) (Co(thd)2).
The synthesis of Co(thd)2 was performed using a modified re-
ported procedure.34 Ammonium hydroxide (50% v/v aqueous solu-
tion, 0.63 mL, 8.4 mmol) was added dropwise to a solution of co-
balt(II) chloride hexahydrate (1.00 g, 4.20 mmol) and 2,2,6,6-tetra-
methyl-3,5-heptanedione (1.74 mL, 8.41 mmol) in 50% aqueous
ethanol (12 mL). The resulting reaction mixture was stirred for 1 h.
Distilled H2O was added (23 mL) and, after 1 h, the resulting reac-
tion mixture was poured through Büchner funnel and the filter cake
washed with distilled H2O (3 × 40 mL). The resulting solid was
spread onto a watch glass and allowed to dry at ambient tempera-
ture for 18 h. Co(thd)2 was isolated as a pink solid (1.18 g, 66%)
and used without further purification.
The spectroscopic data are consistent with the data reported:51 1
H
NMR (400 MHz, CDCl3) δ 7.36 (d, J = 8.8, 2H), 6.86 (d, J = 8.8,
2H), 4.89 (m, 1H), 4.74 (m 1H), 3.80 (s, 3H), 2.61 (d, J = 13.3, 1H),
2.49 (d, J = 13.4, 1H), 2.29 (s, 1H), 1.54 (s, 3H), 1.41 (s, 3H);
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13C{1H} NMR (100 MHz, CDCl3) δ 158.4, 142.9, 140.6, 126.1,
(m, 18H); 13C{1H} NMR (100 MHz, CDCl3) δ 135.3 (CH), 117.1
115.7, 113.5, 73.1, 55.4, 52.3, 30.9, 24.5.
(CH2), 77.4 (C), 47.2 (CH2), 44.9 (CH), 27.3 (CH3), 27.2 (CH3),
27.03 (CH3), 27.02 (CH3), 26.9 (CH3), 24.8 (CH2), 18.2 (CH2), 18.1
(CH2), 17.84 (CH2), 17.82 (CH2), 13.72 (CH), 13.67 (CH); IR
(ATR) 2926, 2863, 2091, 1462, 1152, 1000, 814 cm-1; HRMS (ESI)
m/z calcd for C17H34KOSi (M + K)+ 321.2011, found 321.2020.
Anal. Calcd. for C17H34OSi: C, 72.27; H, 12.13. Found: C, 72.55;
H, 12.33.
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Representative Procedure for the Silylation of Alcohols.
Diisopropyl((2-(4-methoxyphenyl)pent-4-en-2-yl)oxy)silane (1).
To solution of 2-(4-methoxyphenyl)pent-4-en-2-ol (0.500 g, 2.60
mmol) and 1H-imidazole (0.354 g, 5.20 mmol) in THF (7.9 mL)
was added diisopropylchlorosilane (0.488 mL, 2.86 mmol) drop-
wise. After 20 min, the reaction mixture was poured through a glass
frit and the filter cake was washed with hexanes (3 × 8 mL). The
filtrate was concentrated in vacuo and purification by flash chro-
matography (hexanes:EtOAc = 95:5) afforded diisopropylsilyl
Diisopropyl((2-(4-methoxyphenyl)-4-methylpent-4-en-2-
yl)oxy)silane (14). Diisopropylsilyl ether 14 was prepared using the
representative procedure for the silylation of alcohols using 2-(4-
methoxyphenyl)-4-methylpent-4-en-2-ol (0.268 g, 1.30 mmol),
1H-imidazole (0.177 g, 2.60 mmol), and diisopropylchlorosilane
(0.244 mL, 1.43 mmol) in THF (3.9 mL). The reaction time was 35
min. Purification by flash chromatography (hexanes:EtOAc = 97:3)
afforded diisopropylsilyl ether 14 (0.334 g, 80%) as a colorless oil:
1H NMR (400 MHz, CDCl3) δ 7.35 (d, J = 8.9, 2H), 6.83 (d, J =
8.9, 2H), 4.74 (m, 1H), 4.56 (m, 1H), 4.27 (s, 1H), 3.80 (s, 3H),
2.56 (d, J = 13.4, 1H), 2.46 (d, J = 13.4, 1H), 1.67 (s, 3H), 1.45 (s,
3H), 1.09–0.86 (m, 14H); 13C{1H} NMR (100 MHz, CDCl3) δ
158.4 (C), 142.8 (C), 140.3 (C), 127.0 (CH), 114.9 (CH2), 113.1
(CH), 76.9 (C), 55.4 (CH3), 54.1 (CH2), 28.0 (CH3), 24.5 (CH3),
18.1 (CH3), 17.93 (CH3), 17.87 (CH3), 17.8 (CH3), 13.5 (CH), 13.4
(CH); IR (ATR) 2941, 2864, 2099, 1611, 1511, 1248, 1097, 829
cm-1. Anal. Calcd. for C19H32O2Si: C, 71.19; H, 10.06. Found: C,
71.48; H, 10.32.
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15
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ether 1 (0.633 g, 79%) as a colorless oil: H NMR (400 MHz,
CDCl3) δ 7.34 (d, J = 8.9, 2H), 6.85 (d, J = 8.9, 2H), 5.62 (m, 1H),
4.97 (s, 1H), 4.94 (m, 1H), 4.34 (s, 1H), 3.81 (s, 3H), 2.56 (m, 2H),
1.62 (s, 3H), 1.08–0.88 (m, 14H); 13C{1H} NMR (100 MHz,
CDCl3) δ 158.3 (C), 140.1 (C), 134.9 (CH), 126.8 (CH), 117.5
(CH2), 113.2 (CH), 76.5 (C), 55.4 (CH3), 50.4 (CH2), 28.2 (CH3),
18.1 (CH3), 17.9 (CH3), 17.83 (CH3), 17.77 (CH3), 13.6 (CH), 13.3
(CH); IR (ATR) 2941, 2864, 2097, 1512, 1248, 1001, 829, 805 cm-
1; Anal. Calcd. for C18H30O2Si: C, 70.53; H, 9.87. Found: C, 70.83;
H, 10.08.
Diisopropyl((2-phenylpent-4-en-2-yl)oxy)silane (5). Diiso-
propylsilyl ether 5 was prepared using the representative procedure
for the silylation of alcohols using alcohol 7 (0.300 g, 1.85 mmol),
1H-imidazole (0.252 g, 3.70 mmol), and diisopropylchlorosilane
(0.379 mL, 2.22 mmol) in THF (5.6 mL). The reaction time was 45
min. Purification by flash chromatography (hexanes:EtOAc = 95:5)
afforded diisopropylsilyl ether 5 (0.273 g, 53%) as a colorless oil:
1H NMR (400 MHz, CDCl3) δ 7.33 (d, J = 7.3, 2H), 7.22 (t, J = 7.3,
2H), 7.12 (t, J = 7.3, 1H), 5.53 (m, 1H), 4.89–4.82 (m, 2H), 4.29 (s,
1H), 2.49 (m, 2H), 1.56 (s, 3H), 1.02–0.83 (m, 14H); 13C{1H} NMR
(100 MHz, CDCl3) δ 147.9 (C), 134.7 (CH), 127.9 (CH), 126.7
(CH), 125.6 (CH), 117.6 (CH2), 76.9 (C), 50.3 (CH2), 28.3 (CH3),
18.2 (CH3), 17.9 (CH3), 17.84 (CH3), 17.76 (CH3), 13.6 (CH), 13.3
(CH); IR (ATR) 2942, 2864, 2098, 1462, 1071, 999, 698 cm-1;
HRMS (ESI) m/z calcd for C17H26NaSi (M + Na – H2O)+ 281.1696,
found 281.1707.
Diisopropyl((2-(4-methoxyphenyl)-3,3-dimethylpent-4-en-2-
yl)oxy)silane (15). Diisopropylsilyl ether 15 was prepared using the
representative procedure for the silylation of alcohols using 2-(4-
methoxyphenyl)-3,3-dimethylpent-4-en-2-ol (0.320 g, 1.45 mmol),
1H-imidazole (0.396 g, 5.81 mmol), and diisopropylchlorosilane
(0.546 mL, 3.20 mmol) in THF (4.4 mL). The reaction time was 18
h. Purification by flash chromatography (hexanes:EtOAc = 98:2)
afforded diisopropylsilyl ether 15 (0.345 g, 71%) as a colorless oil:
1H NMR (400 MHz, CDCl3) δ 7.28 (d, J = 8.8, 2H), 6.79 (d, J =
8.8, 2H), 5.95 (dd, J = 17.8, 10.8, 1H), 4.92 (m, 2H), 4.26 (s, 1H),
3.81 (s, 3H), 1.63 (s, 3H), 1.15 (m, 6H), 1.01–0.84 (m, 14H);
13C{1H} NMR (100 MHz, CDCl3) δ 158.2 (C), 146.0 (CH), 138.0
(C), 129.0 (CH), 112.2 (CH2), 112.1 (CH), 80.8 (C), 55.3 (CH3),
45.9 (C), 24.1 (CH3), 22.9 (CH3), 22.6 (CH3), 18.4 (CH3), 18.1
(CH3), 18.0 (CH3), 17.9 (CH3), 13.8 (CH), 13.6 (CH); IR (ATR)
2942, 2864, 2098, 1510, 1248, 1097, 831, 807 cm-1. Anal. Calcd.
for C20H34O2Si: C, 71.80; H, 10.24. Found: C, 71.54; H, 10.09.
Diisopropyl((1-(4-methoxyphenyl)but-3-en-1-yl)oxy)silane (12).
Diisopropylsilyl ether 12 was prepared using the representative
procedure for the silylation of alcohols using alcohol 1-(4-methox-
yphenyl)but-3-en-1-ol (0.500 g, 2.81 mmol), 1H-imidazole (0.382
g, 5.61 mmol), and diisopropylchlorosilane (0.526 mL, 3.09 mmol)
in THF (8.5 mL). The reaction time was 35 min. Purification by
flash chromatography (hexanes:EtOAc = 95:5) afforded diiso-
propylsilyl ether 12 (0.525 g, 64%) as a colorless oil: 1H NMR (400
MHz, CDCl3) δ 7.22 (d, J = 8.8, 2H), 6.85 (d, J = 8.8, 2H), 5.74 (m,
1H), 5.04–4.97 (m, 2H), 4.67 (t, J = 6.3, 1H), 4.14 (s, 1H), 3.80 (s,
3H), 2.53 (m, 1H), 2.42 (m, 1H), 1.07–0.87 (m, 14H); 13C{1H}
NMR (100 MHz, CDCl3) δ 158.9 (C), 136.6 (C), 135.2 (CH), 127.5
(CH), 117.2 (CH2), 113.6 (CH), 76.9 (CH), 55.4 (CH3), 45.1 (CH2),
17.8 (CH3), 17.7 (CH3), 17.6 (CH3), 17.4 (CH3), 12.8 (CH), 12.7
(CH); IR (ATR) 2941, 2864, 2091, 1512, 1246, 1000, 830, 798 cm-
1; HRMS (ESI) m/z calcd forC17H27O2Si (M + H – H2O)+ 291.1775,
found 291.1771. Anal. Calcd. for C17H28O2Si: C, 69.81; H, 9.65.
Found: C, 69.83; H, 9.71.
Diisopropyl(((1R*,2S*)-2-vinylcyclohexyl)oxy)silane
(22).
Diisopropylsilyl ether 22 was prepared using the representative
procedure for the silylation of alcohols using trans-2-vinylcyclo-
hexan-1-ol (0.134 g, 1.06 mmol), 1H-imidazole (0.145 g, 2.12
mmol), and diisopropylchlorosilane (0.199 mL, 1.17 mmol) in THF
(3.2 mL). The reaction time was 20 min. Purification by flash chro-
matography (hexanes:EtOAc = 99:1 → hexanes:EtOAc = 97:3) af-
forded diisopropylsilyl ether 22 (0.115 g, 45%) as a colorless oil:
1H NMR (500 MHz, CDCl3) δ 5.87 (m, 1H), 5.00 (m, 2H), 4.18 (s,
1H), 3.34 (m, 1H), 1.97 (m, 2H), 1.74 (m, 2H), 1.63 (m, 1H), 1.33–
1.84 (m, 4H), 1.03–0.94 (m, 14H); 13C{1H} NMR (125 MHz,
CDCl3) δ 142.0 (CH), 114.4 (CH2), 77.2 (CH), 49.9 (CH), 35.3
(CH2), 30.9 (CH2), 25.2 (CH2), 24.9 (CH2), 17.81 (CH3), 17.76
(CH3), 17.73 (CH3), 17.66 (CH3), 12.9 (CH); IR (ATR) 2932, 2863,
2090, 1462, 1085, 1001, 907, 733 cm-1; HRMS (ESI) m/z calcd for
C14H27Si (M + H – H2O)+ 223.1877, found 223.1880. Anal. Calcd.
for C14H28OSi: C, 69.93; H, 11.74. Found: C, 69.67; H, 11.92.
((2-Cyclohexylpent-4-en-2-yl)oxy)diisopropylsilane (13). Diiso-
propylsilyl ether 13 was prepared using the representative proce-
dure for the silylation of alcohols using 2-cyclohexylpent-4-en-2-
ol (0.389 g, 2.31 mmol), 1H-imidazole (0.314 g, 4.62 mmol), and
diisopropylchlorosilane (0.434 mL, 2.54 mmol) in THF (7.0 mL).
The reaction time was 1 h. Purification by flash chromatography
(hexanes) afforded diisopropylsilyl ether 13 (0.505 g, 77%) as a
colorless oil: 1H NMR (400 MHz, CDCl3) δ 5.84 (m, 1H), 5.04 (m,
2H), 4.35 (s, 1H), 2.33 (dd, J = 13.9, 7.3, 1H), 2.25 (dd, J = 13.9,
7.4, 1H), 1.83–1.63 (m, 5H), 1.32 (m, 1H), 1.17 (s, 3H), 1.17–0.85
(E)-Diisopropyl((3-methyloct-2-en-4-yl)oxy)silane (25). Diiso-
propylsilyl ether 25 was prepared using the representative proce-
dure for the silylation of alcohols using (E)-3-methyloct-2-en-4-ol
(0.394 g, 2.77 mmol), 1H-imidazole (0.378 g, 5.55 mmol), and
diisopropylchlorosilane (0.521 mL, 3.05 mmol) in THF (8.4 mL).
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The Journal of Organic Chemistry
The reaction time was 50 min. Purification by flash chromatog-
and triethylsilane (0.082 mL, 0.518 mmol) in DCE (2.4 mL). The
reaction time was 1.5 h. Purification by flash chromatography (pen-
tanes:benzene = 80:20) afforded 3-sila-1,2,4-trioxepane 6 (0.017 g,
21%) as a colorless oil. Characterization was performed on an in-
raphy (pentanes) afforded diisopropylsilyl ether 25 (0.487 g, 68%)
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as a colorless oil: H NMR (400 MHz, CDCl3) δ 5.37 (q, J = 6.8,
1H), 4.09 (s, 1H), 3.95 (t, J = 6.8, 1H), 1.59 (d, J = 6.8, 3H), 1.57–
1.43 (m, 5H), 1.34–1.12 (m, 4H), 1.05–0.93 (m, 14H), 0.88 (t, J =
7.2, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 137.7 (C), 120.5
(CH), 81.3 (CH), 35.7 (CH2), 28.2 (CH2), 22.9 (CH2), 17.9 (CH3),
17.70 (CH3), 17.69 (CH3), 17.5 (CH3), 14.3 (CH3), 13.1 (CH3),
12.78 (CH), 12.77 (CH), 10.8 (CH3); 29Si NMR (79.5 MHz, CDCl3)
δ 12.0; IR (ATR) 2938, 2867, 1467, 903, 725 cm-1. Anal. Calcd. for
C15H32OSi: C, 70.24; H, 12.58. Found: C, 69.97; H, 12.40.
1
separable 59:41 mixture of diastereomers: H NMR (400 MHz,
CDCl3) δ 7.54–7.41 (m, 3.5H), 7.34 (m, 3.4H), 7.23 (m, 1.5H), 4.63
(m, 0.7H), 3.94 (m, 1H), 2.53 (m, 1H), 2.15 (m, 1.6H), 1.99 (m,
0.7H), 1.75 (s, 1.8H), 1.57 (s, 3H), 1.28 (m, 6H), 1.22–1.08 (m,
22.9H); 13C{1H} NMR (100 MHz, CDCl3) δ 150.2 (C), 147.3 (C),
128.32 (CH), 128.27 (CH), 126.7 (CH), 126.6 (CH), 125.0 (CH),
124.5 (CH), 79.4 (CH), 79.1 (CH), 78.6 (C), 46.58 (CH2), 34.9
(CH3), 28.2 (CH3), 19.9 (CH3), 18.03 (CH3), 17.98 (CH3), 17.87
(CH3), 17.7 (CH3), 17.6 (CH3), 17.5 (CH3), 13.4 (CH), 13.2 (CH),
12.7 (CH); IR (ATR) 2944, 2867, 1464, 1121, 1035, 884, 699 cm-
1; HRMS (APCI) m/z calcd for C16H25O2Si (M + H – H2O)+
277.1618, found 277.1631.
9
Diisopropyl((2-(4-methoxyphenyl)hex-5-en-2-yl)oxy)silane
(28). Diisopropylsilyl ether 28 was prepared using the representa-
tive procedure for the silylation of alcohols using 2-(4-methoxy-
phenyl)hex-5-en-2-ol (0.230 g, 1.11 mmol), 1H-imidazole (0.152
g, 2.22 mmol), and diisopropylchlorosilane (0.209 mL, 1.22 mmol)
in THF (3.4 mL). The reaction time was 40 min. Purification by
flash chromatography (hexanes → hexanes:EtOAc = 99:1) af-
forded diisopropylsilyl ether 28 (0.225 g, 63%) as a colorless oil:
1H NMR (400 MHz, CDCl3) δ 7.33 (d, J = 8.8, 2H), 6.85 (d, J =
8.8, 2H), 5.73 (m, 1H), 4.90 (m, 2H), 4.63 (s, 1H), 3.81 (s, 3H),
2.01 (m, 1H), 1.86 (m, 2H), 1.77 (m, 1H), 1.63 (s, 3H), 1.12–0.92
(m, 14H); 13C{1H} NMR (100 MHz, CDCl3) δ 158.0 (C), 140.0
(C), 139.1 (CH), 126.3 (CH), 113.9 (CH2), 113.1 (CH), 76.7 (C),
55.2 (CH3), 44.4 (CH2), 29.4 (CH3), 28.6 (CH2), 18.0 (CH3), 17.7
(CH3), 17.6 (CH3), 13.4 (CH), 13.2 (CH); IR (ATR) 2942, 2097,
1611, 1509, 1462, 1247, 999, 907 cm-1; HRMS (ESI) m/z calcd for
C19H33O2Si (M + H)+ 321.2244, found 321.2245.
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3,3-Diethyl-10-isopropyl-8-(4-methoxyphenyl)-6,8,11-trime-
thyl-4,5,9-trioxa-3,10-disiladodecane (4). Linear silyl peroxide 4
was prepared using the representative procedure for the Co-cata-
lyzed silylperoxidation using diisopropylsilyl ether 4 (0.200 g,
0.653 mmol), Co(thd)2 (0.028 g, 0.065 mmol), tert-butyl hydroper-
oxide (0.033 mL, 0.033 mmol), and triethylsilane (1.04 mL, 6.53
mmol) in DCE (3.0 mL). The reaction time was 2 h. Purification by
flash chromatography using Brockmann grade III neutral alumina
(pentanes:benzene = 80:20), then silica gel (hexanes:EtOAc =
97:3) yielded linear silyl peroxide 4 as a colorless oil (0.086 g,
29%). Characterization was performed on an inseparable 67:33
mixture of diastereomers: 1H NMR (600 MHz, CDCl3) δ 7.34 (d, J
= 8.8, 3.5H), 6.84 (m, 3.5H), 4.34 (s, 1H), 4.30 (0.5H), 4.19 (m,
0.5H), 3.80 (s, 4.5H), 3.75 (m, 1H), 2.26 (dd, J = 14.3, 5.1, 1H),
2.17 (dd, J = 14.4, 4.4, 0.5H), 1.86 (dd, J = 14.3, 5.7, 1H), 1.82 (dd,
J = 14.3, 6.2, 0.5H), 1.69 (s, 1.5H), 1.68 (s, 3H), 1.10–1.04 (m,
14.3H), 1.00–0.90 (m, 30.5H), 0.63 (m, 3.6H), 0.57 (m, 6H);
13C{1H} NMR (150 MHz, CDCl3) δ 158.42 (C), 158.40 (C), 140.6
(C), 139.5 (C), 126.9 (CH), 126.7 (CH), 113.3 (CH), 78.9 (CH),
78.6 (CH), 76.5 (C), 75.9 (C), 55.4 (CH3), 50.6 (CH2), 50.1 (CH2),
29.8 (CH3), 28.6 (CH3), 20.19 (CH3), 20.16 (CH3), 18.1 (CH3),
17.94 (CH3), 17.90 (CH3), 17.86 (CH3), 13.54 (CH3), 13.50 (CH3),
13.4 (CH3), 13.3 (CH3), 7.0 (CH3), 6.9 (CH3), 4.0 (CH2), 3.9 (CH2);
IR (ATR) 2954, 2099, 1510, 1248, 906, 729 cm-1; HRMS (ESI) m/z
calcd for C24H45O3Si2 (M + H – H2O)+ 437.2902, found 437.2907.
Representative Procedure for the Co-Catalyzed Silylperoxi-
dation.
3,3-Diisopropyl-5-(4-methoxyphenyl)-5,7-dimethyl-1,2,4,3-tri-
oxasilepane (2). A flask containing DCE (1,2-dichloroethane, 10
mL) was sparged with oxygen for 15 min. To a separate flask was
added Co(thd)2 (0.013 g, 0.032 mmol) followed by diisopropylsilyl
ether 1 (0.097 g, 0.316 mmol). The oxygenated DCE (2.9 mL) was
added to the reaction flask and the reaction vessel was sparged with
oxygen for 2 min. A solution of tert-butyl hydroperoxide in CH2Cl2
(1.0 M, 0.016 mL, 0.016 mmol) was added followed by tri-
ethylsilane (0.051 mL, 0.316 mmol) and the reaction mixture was
stirred at room temperature under a balloon of oxygen for 50 min.
The reaction mixture was filtered through a 6-cm plug of silica,
eluted with CH2Cl2 (45 mL), and concentrated in vacuo. Purifica-
tion by flash chromatography using Brockmann grade III neutral
alumina (pentanes:benzene = 80:20) afforded 3-sila-1,2,4-triox-
epane 2 (0.046 g, 38%) as a colorless oil. Characterization was per-
formed on an inseparable 67:33 mixture of diastereomers: 1H NMR
(600 MHz, CDCl3) δ 7.41 (d, J = 8.9, 1.2H), 7.36 (d, J = 8.9, 2H),
6.88 (m, 3.2H), 4.60 (m, 0.5H), 3.96 (m, 1H), 3.81 (s, 1.8H), 3.80
(s, 3H), 2.50 (dd, J = 15.6, 10.4, 1H), 2.15 (dd, J = 15.4, 10.6, 0.6H),
2.09 (dd, J = 15.6, 3.4, 1H), 1.96 (dd, J = 15.4, 3.1, 0.6H), 1.72 (s,
1.8H), 1.54 (s, 3H), 1.28–1.25 (m, 6H), 1.20–1.17 (m, 3.4H), 1.14–
1.09 (m, 18H); 13C{1H} NMR (150 MHz, CDCl3) δ 158.33 (C),
158.27 (C), 142.6 (C), 139.4 (C), 126.2 (CH), 125.7 (CH), 113.6
(CH), 113.5 (CH), 79.4 (CH), 79.1 (CH), 78.4 (C), 55.49 (CH3),
55.45 (CH3), 46.7 (CH2), 34.9 (CH3), 28.3 (CH3), 19.92 (CH3),
19.88 (CH3), 18.03 (CH3), 17.97 (CH3), 17.87 (CH3), 17.71 (CH3),
17.66 (CH3), 17.59 (CH3), 17.58 (CH3), 17.51 (CH3), 13.4 (CH),
13.2 (CH), 12.73 (CH), 12.68 (CH); IR (ATR) 2945, 2867, 1611,
1248, 1033, 907, 731 cm-1; HRMS (ESI) m/z calcd for C18H29O3Si
(M + H – H2O)+ 321.1880, found 321.1891. Anal. Calcd. for
C18H30O4Si: C, 63.87; H, 8.93. Found: C, 63.95; H, 8.79.
4-((Diisopropyl(1-phenylethoxy)silyl)peroxy)-2-phenylpentan-
2-ol (9 and 10). Linear silyl peroxides 9 and 10 were prepared using
the representative procedure for the Co-catalyzed silylperoxidation
using alcohol 7 (0.050 g, 0.308 mmol), Co(thd)2 (0.013 g, 0.031
mmol), tert-butyl hydroperoxide (0.015 mL, 0.015 mmol), and
diisopropylsilane 8 (0.146 g, 0.616 mmol) in DCE (2.8 mL). The
reaction time was 19 h. Purification by flash chromatography using
Brockmann grade III neutral alumina (hexanes:EtOAc = 97:3)
yielded linear silyl peroxide 9 a colorless oil (0.015 g, 11%) and
linear silyl peroxide 10 as a colorless oil (0.009 g, 7%). Linear Si-
lyl Peroxide 9: Characterization was performed on an inseparable
53:47 mixture of diastereomers: 1H NMR (600 MHz, CDCl3) δ 7.41
(m, 4H), 7.36–7.27 (m, 12H), 7.25–7.20 (m, 4H), 5.05 (q, J = 6.4,
1H), 5.02 (q, J = 6.4, 0.9H), 4.17 (s, 0.9H), 4.13 (s, 1H), 3.93 (m,
1H), 3.86 (m, 0.8H), 2.21–2.08 (m, 4H), 1.48 (m, 6H), 1.44 (m,
6H), 1.14–0.88 (m, 36.4H); 13C{1H} NMR (150 MHz, CDCl3) δ
148.09 (C), 148.07 (C), 146.41 (C), 146.36 (C), 128.4 (CH), 128.29
(CH), 128.28 (CH), 127.04 (CH), 127.01 (CH), 126.5 (CH), 125.4
(CH), 125.3 (CH), 125.22 (CH), 125.21 (CH), 80.2 (CH), 80.1
(CH), 73.89 (C), 73.86 (C), 71.5 (CH), 71.4 (CH), 49.4 (CH2), 49.3
(CH2), 32.6 (CH3), 27.43 (CH3), 27.42 (CH3), 20.11 (CH3), 20.06
(CH3), 17.61 (CH3), 17.56 (CH3), 17.54 (CH3), 17.51 (CH3), 17.50
(CH3), 17.4 (CH3), 11.90 (CH), 11.85 (CH), 11.75 (CH); IR (ATR)
3466, 2868, 1493, 906, 699 cm-1; HRMS (ESI) m/z calcd for
3,3-Diisopropyl-5,7-dimethyl-5-phenyl-1,2,4,3-trioxasilepane
(6). 3-Sila-1,2,4-trioxepane 6 was prepared using the representative
procedure for the Co-catalyzed silylperoxidation using diiso-
propylsilyl ether 5 (0.072 g, 0.259 mmol), Co(acac)2 (0.013 g,
0.052 mmol), tert-butyl hydroperoxide (0.013 mL, 0.013 mmol),
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The Journal of Organic Chemistry
Page 8 of 11
C25H40NO3Si (M + NH4 – H2O)+ 430.2772, found 430.2774. Lin-
27.5H); 13C{1H} NMR (100 MHz, CDCl3) δ 158.3 (C), 158.2 (C),
ear Silyl Peroxide 10: Characterization was performed on a 50:50
mixture of diastereomers: 1H NMR (600 MHz, CDCl3) δ 7.56 (m,
3.8H), 7.39–7.29 (m, 11.6H), 7.22 (m, 3.8H), 5.11 (q, J = 6.3, 2H),
4.29 (m, 2H), 3.28 (s, 0.9H), 3.25 (s, 0.9H), 2.17 (m, 2H), 1.86 (m,
1.9H), 1.58 (s, 5.4H), 1.48 (m, 5.4H), 1.16–0.92 (m, 32.4H);
13C{1H} NMR (150 MHz, CDCl3) δ 148.8 (C), 146.5 (C), 128.3
(CH), 127.1 (CH), 126.7 (CH), 125.4 (CH), 124.9 (CH), 79.7 (CH),
73.4 (C), 71.4 (CH), 49.6 (CH2), 29.8 (CH3), 27.5 (CH3), 20.1
(CH3), 17.6 (CH3), 17.4 (CH3), 11.9 (CH), 11.8 (CH); IR (ATR)
3476, 2867, 1447, 1371, 1095, 907, 731, 699 cm-1; HRMS (ESI)
m/z calcd for C25H38NaO4Si (M + Na)+ 453.2432, found 453.2433.
142.9 (C), 140.0 (C), 126.6 (CH), 125.4 (CH), 113.52 (CH), 113.46
(CH), 76.6 (C), 75.3 (C), 66.3 (CH), 66.2 (CH), 55.5 (CH3), 55.4
(CH3), 50.0 (CH2), 48.9 (CH2), 35.7 (CH3), 29.9 (CH3), 25.0 (CH3),
24.8 (CH3), 17.6 (CH3), 17.4 (CH3), 17.32 (CH3), 17.26 (CH3),
17.23 (CH3), 17.18 (CH3), 17.12 (CH3), 17.11 (CH3), 14.2 (CH2),
13.9 (CH2), 13.41 (CH2), 13.38 (CH2); IR (ATR) 2943, 2865, 1611,
1511, 1248, 983 cm-1; HRMS (ESI) m/z calcd for C18H34NO3Si (M
+ NH4)+ 340.2302, found 340.2308. Anal. Calcd. for C18H30O3Si:
C, 67.03; H, 9.38. Found: C, 67.33; H, 9.46.
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3
4
5
6
7
8
9
Diisopropylsilylene Acetal 3 Prepared Using Catalytic
Phenylsilane. Diisopropylsilylene acetal 3 was prepared using the
representative procedure for the Co-catalyzed synthesis of diiso-
propylsilylene acetals using diisopropylsilyl ether 1 (0.165 g, 0.539
mmol), Co(thd)2 (0.034 g, 0.081 mmol), tert-butyl hydroperoxide
(0.027 mL, 0.027 mmol), and a solution of phenylsilane in PhCF3
(0.20 M, 0.54 mL, 0.11 mmol) in DCE (4.9 mL). The reaction time
was 15 min. Reduction of the peroxide unit was performed using
toluene (1.0 mL) and triphenylphosphine (0.283 g, 1.08 mmol).
The reaction time was 1 h. Oxidation of the remaining tri-
phenylphosphine was performed using hydrogen peroxide (27%
w/w aqueous solution, 0.54 mL, 4.7 mmol). The reaction time was
15 min. Purification by flash chromatography using Brockmann
grade III neutral alumina (hexanes → hexanes:EtOAc = 95:5) af-
forded diisopropylsilylene acetal 3 (0.126 g, 73%) as a colorless
oil. Characterization was performed on an inseparable 50:50 mix-
ture of diastereomers. The spectroscopic data are consistent with
the data reported above for diisopropylsilylene acetal 3.
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12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
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48
49
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3,3-Diethyl-11-isopropyl-9-(4-methoxyphenyl)-6,9,12-trime-
thyl-4,5,10-trioxa-3,11-disilatridecane (29). Linear silyl peroxide
29 was prepared using the representative procedure for the Co-cat-
alyzed silylperoxidation using diisopropylsilyl ether 28 (0.040 g,
0.155 mmol), Co(thd)2 (0.007 g, 0.016 mmol), tert-butyl hydroper-
oxide (0.008 mL, 0.008 mmol), and triethylsilane (0.025 mL, 0.156
mmol) in DCE (1.4 mL). The reaction time was 20 min. Purifica-
tion by flash chromatography using Brockmann grade III neutral
alumina (pentane → hexanes:EtOAc = 98:2) yielded linear silyl
peroxide 29 as a colorless oil (0.028 g, 48%). Characterization was
1
performed on an inseparable 50:50 mixture of diastereomers: H
NMR (500 MHz, CDCl3) δ 7.31 (d, J = 8.9, 4H), 6.84 (d, J = 8.9,
4H), 4.36 (s, 1.9H), 3.89 (m, 2H), 3.80 (s, 6H), 1.90 (m, 2H), 1.78
(m, 2H), 1.61 (s, 6H), 1.35 (m, 2H), 1.13–0.93 (m, 54H), 0.66 (q, J
= 7.9, 12H); 13C{1H} NMR (125 MHz, CDCl3) δ 158.2 (C), 140.2
(C), 140.1 (C), 126.57 (CH), 126.56 (CH), 113.1 (CH), 81.8 (CH),
81.7 (CH), 76.9 (C), 55.4 (CH3), 41.2 (CH2), 41.0 (CH2), 29.9
(CH3), 29.8 (CH3), 29.5 (CH2), 29.3 (CH2), 18.7 (CH3), 18.6 (CH3),
18.17 (CH3), 18.16 (CH3), 18.0 (CH3), 17.9 (CH3), 17.83 (CH3),
17.80 (CH3), 13.7 (CH), 13.6 (CH), 13.37 (CH), 13.35 (CH), 6.9
(CH3), 4.0 (CH2); IR (ATR) 2953, 2097, 1510, 1246, 906, 729 cm-
1; HRMS (ESI) m/z calcd for C24H45O3Si2 (M + H – H2O)+
437.2902, found 437.2907.
2,2-Diisopropyl-4-(4-methoxyphenyl)-6-methyl-1,3,2-dioxasi-
linane (16) and 1-(4-methoxyphenyl)butane-1,3-diol (20). Diiso-
propylsilylene acetal 16 and 1,3-diol 20 were prepared using the
representative procedure for the Co-catalyzed synthesis of diiso-
propylsilylene acetals using diisopropylsilyl ether 12 (0.292 g, 1.00
mmol), Co(thd)2 (0.043 g, 0.100 mmol), tert-butyl hydroperoxide
(0.050 mL, 0.050 mmol), and triethylsilane (0.160 mL, 1.00 mmol)
in DCE (9.1 mL). The reaction mixture was heated to 40 °C for 1
h. Reduction of the peroxide unit was performed using toluene (2.0
mL) and triphenylphosphine (0.524 g, 2.00 mmol). The reaction
time was 2 h. Oxidation of the remaining triphenylphosphine was
performed using hydrogen peroxide (27% w/w aqueous solution,
1.0 mL, 8.7 mmol). Purification by flash chromatography using
Brockmann grade III neutral alumina (pentanes:benzene = 95:5 →
hexanes:EtOAc 50:50 → hexanes:EtOAc 40:60) afforded diiso-
propylsilylene acetal 16 (0.047 g, 15%) as a colorless oil and 1,3-
diol 20 (0.041 g, 21%) as a colorless oil. Diisopropylsilylene Ac-
etal 16: 1H NMR (400 MHz, CDCl3) δ 7.29 (d, J = 8.7, 2H), 6.89
(d, J = 8.7, 2H), 5.07 (dd, J = 11.3, 2.1, 1H), 4.36 (m, 1H), 3.81 (s,
3H), 1.83 (m, 1H), 1.63 (m, 1H), 1.25 (d, J = 6.3, 3H), 1.13–1.03
(m, 14H); 13C{1H} NMR (100 MHz, CDCl3) δ 159.0 (C), 137.4
(C), 126.5 (CH), 113.9 (CH), 75.4 (CH), 70.3 (CH), 55.5 (CH3),
47.6 (CH2), 24.9 (CH3), 17.34 (CH3), 17.31 (CH3), 17.03 (CH3),
17.00 (CH3), 14.0 (CH), 12.4 (CH); IR (ATR) 2864, 1613, 1513,
1245, 1136, 980, 892 cm-1; HRMS (ESI) m/z calcd for C17H27O2Si
(M + H – H2O)+ 291.1775, found 291.1771. 1,3-Diol 20: Charac-
terization was performed on an inseparable 67:33 mixture of dia-
stereomers: 1H NMR (500 MHz, CDCl3) δ 7.27 (m, 2.9H), 6.87 (m,
2.9H), 4.98 (m, 1H), 4.86 (0.5H), 4.07 (m, 1.5H), 3.79 (m, 4.3H),
3.31 (s, 0.5H), 3.28 (s, 0.5H), 3.06 (s, 1H), 2.58 (s, 1H), 1.91–1.69
(m, 3H), 1.21 (m, 4.4H); 13C{1H} NMR (125 MHz, CDCl3) δ 159.3
(C), 159.1 (C), 136.9 (C), 136.8 (C), 127.1 (CH), 127.0 (CH), 114.1
(CH), 114.0 (CH), 75.1 (CH), 71.6 (CH), 68.9 (CH), 65.6 (CH),
55.5 (CH3), 47.2 (CH2), 46.3 (CH2), 24.3 (CH3), 23.4 (CH3); IR
(ATR) 3348, 2966, 1611, 1512, 1244, 904, 726, 648 cm-1; HRMS
(ESI) m/z calcd for C11H16NaO3 (M + Na)+ 219.0992, found
219.1001.
Representative Procedure for the Co-Catalyzed Synthesis of
Diisopropylsilylene Acetals.
2,2-Diisopropyl-4-(4-methoxyphenyl)-4,6-dimethyl-1,3,2-diox-
asilinane (3). A flask containing DCE (1,2-dichloroethane, 10 mL)
was sparged with oxygen for 15 min. To a separate flask was added
Co(thd)2 (0.043 g, 0.100 mmol) followed by diisopropylsilyl ether
1 (0.306 g, 1.00 mmol). The oxygenated DCE (9.1 mL) was added
to the reaction flask and the reaction vessel was sparged with oxy-
gen for 2 min. A solution of tert-butyl hydroperoxide in CH2Cl2
(1.0 M, 0.050 mL, 0.050 mmol) was added followed by tri-
ethylsilane (0.160 mL, 1.00 mmol) and the reaction mixture was
stirred at room temperature under a balloon of oxygen for 30 min.
The reaction mixture was filtered through a 6-cm plug of silica,
eluted with CH2Cl2 (45 mL), and concentrated in vacuo. To the
crude reaction mixture was added toluene (2.0 mL) and tri-
phenylphosphine (0.524 g, 2.00 mmol). The reaction mixture was
stirred at 40 °C for 3 h. Hydrogen peroxide (27% w/w aqueous so-
lution, 1.0 mL, 8.7 mmol) was added and the resulting reaction
mixture was stirred at room temperature for 15 min. The reaction
mixture was diluted with hexanes (9.1 mL) and poured through a
glass frit. The filter cake was washed with hexanes (3 × 9 mL). The
filtrate was dried over Na2SO4 and concentrated in vacuo. Purifica-
tion by flash chromatography using Brockmann grade III neutral
alumina (pentanes:benzene = 80:20) afforded diisopropylsilylene
acetal 3 (0.192 g, 60%) as a colorless oil. Characterization was per-
formed on an inseparable 51:49 mixture of diastereomers: 1H NMR
(400 MHz, CDCl3) δ 7.37 (d, J = 8.8, 3.8H), 6.87 (d, J = 8.8, 3.8H),
4.44 (m, 1H), 3.92 (m, 1H), 3.83 (s, 2.5H), 3.80 (s, 3H), 2.30 (dd,
J =14.7, 1.2, 0.9H), 1.90 (dd, J = 14.4, 2.0, 1H), 1.87 (dd, J = 14.8,
10.9, 0.9H), 1.75 (dd, J = 14.6, 11.3, 1H), 1.59 (s, 3H), 1.46 (s,
2.5H), 1.24 (d, J = 6.1, 3H), 1.18 (d, J = 6.2, 2.7H), 1.11–0.91 (m,
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The Journal of Organic Chemistry
4-Cyclohexyl-2,2-diisopropyl-4,6-dimethyl-1,3,2-dioxasilinane
6.89–6.83 (m, 2.8H), 4.43 (q, J = 6.3, 1H), 4.11 (q, J = 6.7, 0.4H),
3.81 (m, 4.1H), 1.71 (s, 3H), 1.66 (s, 1.3H), 1.29–1.03 (m, 27H),
0.79 (s, 3H), 0.68 (s. 3H), 0.59 (s, 1.3H); 13C{1H} NMR (100 MHz,
CDCl3) δ 158.24 (C), 158.16 (C), 139.7 (C), 138.5 (C), 128.7 (CH),
128.4 (CH), 112.51 (CH), 112.50 (CH), 83.3 (C), 82.5 (C), 73.6
(CH), 72.5 (CH), 55.40 (CH3), 55.39 (CH3), 43.7 (C), 43.6 (C), 27.4
(CH3), 25.9 (CH3), 24.8 (CH3), 22.4 (CH3), 19.5 (CH3), 19.1 (CH3),
18.2 (CH3), 18.1 (CH3), 18.0 (CH3), 17.9 (CH3), 17.8 (CH3), 17.73
(CH3), 17.68 (CH3), 17.66 (CH3), 16.1 (CH3), 15.1 (CH), 15.0
(CH), 14.7 (CH), 13.5 (CH); IR (ATR) 2944, 2865, 1610, 1510,
1245, 1118, 1036, 825, 684 cm-1. Anal. Calcd. for C20H34O3Si: C,
68.52; H, 9.78. Found: C, 68.80; H, 9.86.
(17). Diisopropylsilylene acetal 17 was prepared using the repre-
sentative procedure for the Co-catalyzed synthesis of diisopropylsi-
lylene acetals using diisopropylsilyl ether 13 (0.282 g, 1.00 mmol),
Co(acac)2 (0.103 g, 0.400 mmol), tert-butyl hydroperoxide (0.050
mL, 0.050 mmol), and triethylsilane (0.319 mL, 2.00 mmol) in
DCE (9.1 mL). The reaction mixture was heated to 40 °C for 2 h.
Reduction of the peroxide unit was performed using toluene (2.0
mL) and triphenylphosphine (0.524 g, 2.00 mmol). The reaction
time was 1 h. Oxidation of the remaining triphenylphosphine was
performed using hydrogen peroxide (27% w/w aqueous solution,
1.0 mL, 8.7 mmol). Purification by flash chromatography (pen-
tanes:benzene = 95:5 → pentanes:benzene = 80:20) afforded diiso-
propylsilylene acetal 17 (0.184 g, 62%) as a colorless oil. Charac-
terization was performed on an inseparable 51:49 mixture of dia-
stereomers: 1H NMR (400 MHz, CDCl3) δ 4.26 (m, 1.9H), 2.09 (m,
1H), 1.97–1.40 (m, 14.3H), 1.37–1.08 (m, 16.8H), 1.06 (s, 3H),
1.05–0.84 (m, 30.9H); 13C{1H} NMR (100 MHz, CDCl3) δ 76.5
(C), 76.1 (C), 65.9 (CH), 65.3 (CH), 51.7 (CH), 46.4 (CH), 45.98
(CH), 45.97 (CH2), 29.3 (CH2), 27.8 (CH2), 27.2 (CH2), 27.1 (CH2),
27.02 (CH2), 26.96 (CH2), 26.91 (CH2), 26.89 (CH2), 26.88 (CH2),
25.3 (CH3), 25.23 (CH3), 25.16 (CH3), 23.3 (CH3), 17.5 (CH3), 17.4
(CH3), 17.33 (CH3), 17.28 (CH3), 17.25 (CH3), 17.0 (CH3), 14.0
(CH), 13.9 (CH), 13.5 (CH), 13.3 (CH); IR (ATR) 2927, 2864,
1464, 1148, 980, 882 cm-1; HRMS (ESI) m/z calcd for C17H33OSi
(M + H – H2O)+ 281.2295, found 281.2303.
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5
6
7
8
9
10
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12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
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45
46
47
48
49
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51
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60
2-Cyclohexylpentane-2,4-diol (21). 1,3-Diol 21 was prepared us-
ing a modification of the representative procedure for the Co-cata-
lyzed synthesis of diisopropylsilylene acetals using diisopropylsilyl
ether 13 (0.282 g, 1.00 mmol), Co(thd)2 (0.043 g, 0.100 mmol),
tert-butyl hydroperoxide (0.050 mL, 0.050 mmol), and tri-
ethylsilane (0.160 mL, 1.00 mmol) in DCE (9.1 mL). The reaction
time was 1 h. Reduction of the peroxide unit was performed using
toluene (2.0 mL) and triphenylphosphine (0.524 g, 2.00 mmol).
The reaction time was 1 h. Oxidation of the remaining tri-
phenylphosphine was performed using hydrogen peroxide (27%
w/w aqueous solution, 1.0 mL, 8.7 mmol).
To unpurified diisopropylsilylene acetal 17 was added THF (5.0
mL) followed by a solution of tetrabutylammonium fluoride in
THF (1.0 M, 2.4 mL, 2.4 mmol). The reaction mixture was stirred
for 1 h. Distilled H2O (5.0 mL) was added, then the mixture was
extracted with diethyl ether (3 × 5 mL). The combined organic lay-
ers were dried over MgSO4 and concentrated in vacuo. Purification
2,2-Diisopropyl-4-(4-methoxyphenyl)-4,6,6-trimethyl-1,3,2-di-
oxasilinane (18). Diisopropylsilylene acetal 18 was prepared using
the representative procedure for the Co-catalyzed synthesis of
diisopropylsilylene acetals using diisopropylsilyl ether 14 (0.320 g,
1.00 mmol), Co(acac)2 (0.103 g, 0.400 mmol), tert-butyl hydroper-
oxide (0.050 mL, 0.050 mmol), and triethylsilane (0.319 mL, 2.00
mmol) in DCE (9.1 mL). The reaction mixture was heated to 40 °C
for 3 h. Reduction of the peroxide unit was performed using toluene
(2.0 mL) and triphenylphosphine (0.524 g, 2.00 mmol). The reac-
tion time was 2.5 h. Oxidation of the remaining triphenylphosphine
was performed using hydrogen peroxide (27% w/w aqueous solu-
tion, 1.0 mL, 8.7 mmol). Purification by flash chromatography
(pentanes:benzene = 80:20) afforded diisopropylsilylene acetal 18
by flash chromatography (hexanes:EtOAc 70:30
→ hex-
anes:EtOAc 65:35) afforded 1,3-diol 21 (0.147 g, 79%) as a color-
less oil. Characterization was performed on an inseparable 50:50
mixture of diastereomers: 1H NMR (400 MHz, CDCl3) δ 4.19 (m,
2H), 1.96–1.43 (m, 16H), 1.32–0.92 (m, 24H); 13C{1H} NMR (100
MHz, CDCl3) δ 76.1 (C), 75.9 (C), 65.6 (CH), 65.2 (CH), 50.7
(CH), 47.2 (CH2), 45.5 (CH), 45.2 (CH2), 29.0 (CH2), 27.5 (CH2),
27.14 (CH2), 26.97 (CH2), 26.92 (CH2), 26.91 (CH2), 26.89 (CH2),
26.79 (CH2), 26.76 (CH2), 26.74 (CH2), 25.0 (CH3), 24.7 (CH3),
24.6 (CH3), 23.6 (CH3); IR (ATR) 3329, 2924, 2852, 1450, 1136,
1076 cm-1; HRMS (ESI) m/z calcd for C11H22NaO2 (M + Na)+
209.1512, found 209.1502.
(1R*,2S*)-2-((R*)-1-Hydroxyethyl)cyclohexan-1-ol (24). 1,3-
Diol 24 was prepared using a modification of the representative
procedure for the Co-catalyzed synthesis of diisopropylsilylene ac-
etals using diisopropylsilyl ether 22 (0.145 g, 0.596 mmol),
Co(thd)2 (0.025 g, 0.060 mmol), tert-butyl hydroperoxide (0.030
mL, 0.030 mmol), and triethylsilane (0.091 mL, 0.596 mmol) in
DCE (5.4 mL). The reaction time was 1 h. Reduction of the perox-
ide unit was performed using toluene (1.2 mL) and tri-
phenylphosphine (0.312 g, 1.19 mmol). The reaction time was 2.5
h. Oxidation of the remaining triphenylphosphine was performed
using hydrogen peroxide (27% w/w aqueous solution, 0.60 mL, 5.2
mmol).
1
(0.130 g, 39%) as a colorless oil: H NMR (400 MHz, CDCl3) δ
7.38 (d, J = 8.8, 2H), 6.85 (d, J = 8.8, 2H), 3.80 (s, 3H), 2.30 (d, J
= 14.9, 1H), 2.12 (d, J = 14.9, 1H), 1.49 (s, 3H), 1.30 (s, 3H), 1.12–
0.96 (m, 14H), 0.89 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ
158.1 (C), 142.2 (C), 125.7 (CH), 113.4 (CH), 75.8 (C), 72.6 (C),
55.4 (CH3), 51.6 (CH2), 36.3 (CH3), 33.5 (CH3), 30.8 (CH3), 17.7
(CH3), 17.60 (CH3), 17.57 (CH3), 17.4 (CH3), 14.3 (CH), 14.2
(CH); IR (ATR) 2967, 2865, 1611, 1510, 1243, 1036, 992 cm-1;
HRMS (APCI) m/z calcd for C19H32NaO3Si (M + Na)+ 359.2013,
found 359.2017. Anal. Calcd. for C19H32O3Si: C, 67.81; H, 9.58.
Found: C, 68.07; H, 9.72.
2,2-Diisopropyl-4-(4-methoxyphenyl)-4,5,5,6-tetramethyl-
1,3,2-dioxasilinane (19). Diisopropylsilylene acetal 19 was pre-
pared using the representative procedure for the Co-catalyzed syn-
thesis of diisopropylsilylene acetals using diisopropylsilyl ether 15
(0.290 g, 0.867 mmol), Co(acac)2 (0.089 g, 0.347 mmol), tert-butyl
hydroperoxide (0.043 mL, 0.043 mmol), and triethylsilane (0.277
mL, 1.73 mmol) in DCE (7.9 mL). The reaction mixture was heated
to 40 °C for 5 h. Reduction of the peroxide unit was performed
using toluene (1.7 mL) and triphenylphosphine (0.455 g, 1.73
mmol). The reaction time was 45 min. Oxidation of the remaining
triphenylphosphine was performed using hydrogen peroxide (27%
w/w aqueous solution, 0.87 mL, 7.6 mmol). Purification by flash
chromatography (pentanes:benzene = 80:20) afforded diiso-
propylsilylene acetal 19 (0.098 g, 32%) as a colorless oil. Charac-
terization was performed on an inseparable 70:30 mixture of dia-
To unpurified diisopropylsilylene acetal 23 was added THF (3.0
mL) followed by a solution of tetrabutylammonium fluoride in
THF (1.0 M, 1.4 mL, 1.4 mmol). The reaction time was for 30 min.
Distilled H2O (3.0 mL) was added then, the mixture was extracted
with diethyl ether (3 × 3 mL). The combined organic layers were
dried over MgSO4 and concentrated in vacuo. Purification by flash
chromatography (hexanes:EtOAc = 50:50) afforded 1,3-diol 24
(0.062 g, 73%) as a colorless oil. Characterization was performed
1
on an inseparable 57:43 mixture of diastereomers: H NMR (400
MHz, CDCl3) δ 3.85 (m, 1H), 3.79 (s, 1H), 3.68 (m, 0.8H), 3.58
(m, 1H), 3.44 (m, 0.8H), 3.19 (s, 1H), 3.00 (s, 1H), 1.87 (m, 2H),
1.66–1.44 (m, 6.2H), 1.26–1.03 (m, 11H), 0.94–0.68 (m, 1.8H);
13C{1H} NMR (100 MHz, CDCl3) δ 76.7 (CH), 74.3 (CH), 71.8
1
stereomers: H NMR (400 MHz, CDCl3) δ 7.45–7.36 (m, 2.8H),
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The Journal of Organic Chemistry
Page 10 of 11
(CH), 71.4 (CH), 50.9 (CH), 49.9 (CH), 35.9 (CH2), 35.8 (CH2),
Chin Lin for his assistance with NMR spectroscopy and mass spec-
27.6 (CH2), 27.3 (CH2), 25.8 (CH2), 25.5 (CH2), 24.9 (CH2), 24.7
(CH2), 21.9 (CH3), 18.4 (CH3); IR (ATR) 3329, 2930, 2857, 1449,
1035, 907 cm-1; HRMS (ESI) m/z calcd for C8H18NO (M + NH4 –
H2O)+ 144.1383, found 144.1388.
trometry.
1
2
3
4
5
6
7
8
REFERENCES
3-Methyloctane-3,4-diol (27). 1,2-Diol 27 was prepared using a
modification of the representative procedure for the Co-catalyzed
synthesis of diisopropylsilylene acetals using diisopropylsilyl ether
25 (0.257 g, 1.00 mmol), Co(thd)2 (0.085 g, 0.200 mmol), tert-butyl
hydroperoxide (0.050 mL, 0.050 mmol), and triethylsilane (0.160
mL, 1.00 mmol) in DCE (9.1 mL). The reaction time was 1.5 h.
Reduction of the peroxide unit was performed using toluene (2.0
mL) and triphenylphosphine (0.524 g, 2.00 mmol). The reaction
time was 4 h. Oxidation of the remaining triphenylphosphine was
performed using hydrogen peroxide (27% w/w aqueous solution,
1.0 mL, 8.7 mmol). Characterization was performed on an analyti-
cal sample of diisopropylsilylene acetal 26: 29Si NMR (79.5 MHz,
CDCl3) δ 15.4.
(1) Shigeru, I.; Teruaki, M. Novel Method for the Preparation of
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prop-2-en-1-ols: Application to a New Synthesis of 1,2,4-Trioxanes.
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9
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11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
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48
49
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52
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56
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59
60
To unpurified diisopropylsilylene acetal 26 was added THF (5.0
mL) followed by a solution of tetrabutylammonium fluoride in
THF (1.0 M, 2.4 mL, 2.4 mmol). The reaction mixture was stirred
for 10 min. Distilled H2O (5.0 mL) was added, then the mixture
was extracted with diethyl ether (3 × 5 mL). The combined organic
layers were dried over MgSO4 and concentrated in vacuo. Purifica-
tion by flash chromatography (hexanes = hexanes:EtOAc = 80:20)
afforded 1,2-diol 27 (0.030 g, 19%) as a colorless oil. Characteri-
zation was performed on an inseparable 56:44 mixture of diastere-
omers: 1H NMR (400 MHz, CDCl3) δ 3.39 (m, 1.8H), 2.22 (s, 1H),
2.12 (s, 0.8H), 2.02–1.87 (m, 1.8H), 1.79 (s, 0.8H), 1.67–1.27 (m,
15H), 1.13 (s, 2.3H), 1.07 (s, 3H), 0.95–0.88 (m, 10.7H); 13C{1H}
NMR (100 MHz, CDCl3) δ 78.6 (CH), 77.0 (CH), 75.2 (C), 75.0
(C), 31.7 (CH2), 31.3 (CH2), 31.1 (CH2), 29.2 (CH2), 29.1 (CH2),
28.6 (CH2), 23.1 (CH3), 22.92 (CH2), 22.91 (CH2), 20.6 (CH3), 14.2
(CH3), 7.79 (CH3), 7.75 (CH3); IR (ATR) 3393, 2957, 1461, 1378,
996, 907, 732 cm-1; HRMS (ESI) m/z calcd for C9H23NO (M + NH4
– H2O)+ 161.1774, found 161.1778.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website.
Spectral data (PDF)
AUTHOR INFORMATION
Corresponding Author
(13) Ahmed, A.; Dussault, P. H. Stereoselective Allylation of Chiral
Monoperoxyacetals. Tetrahedron 2005, 61, 4657−4670.
(14) Wu, J.-M.; Kunikawa, S.; Tokuyasu, T.; Masuyama, A.; Nojima, M.;
Kim, H.-S.; Wataya, Y. Co-catalyzed Autoxidation of Alkene in the
Presence of Silane. The Effect of the Structure of Silanes on the Efficiency
of the Reaction and on the Product Distribution. Tetrahedron 2005, 61,
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(16) Shigeru, I.; Teruaki, M. Hydration of Olefins with Molecular
*E-mail: kwoerpel@nyu.edu.
ORCID
K. A. Woerpel: 0000-0002-8515-0301
Jonathan P. Oswald: 0000-0001-8908-8712
Notes
Oxygen
and
Triethylsilane
Catalyzed
by
The authors declare no competing financial interests.
Bis(trifluoroacetylacetonato)cobalt(II). Chem. Lett. 1989, 18, 569−572.
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Lett. 1982, 23, 4871−4874.
ACKNOWLEDGMENT
This research was supported by the National Institute of General
Medical Sciences of the National Institutes of Health
(1R01GM118730). NMR spectra acquired with the TCI cryoprobe
and Bruker Advance 400 spectrometer were supported by the Na-
tional Institutes of Health (OD016343) and the National Science
Foundation (CHE-01162222), respectively. The authors thank Dr.
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