Gold-Nanoparticle-Catalyzed Silaboration of Oxetanes and Unactivated Epoxides

Article abstract of DOI:10.1021/acs.organomet.6b00465

Supported gold nanoparticles catalyze the unprecedented insertion of a silylborane into the C-O bond of oxetanes and unactivated epoxides, forming γ- or β-silyloxy boronates in good to excellent yields. In the silaboration process the boron moiety is acting as a nucleophile and the silyl as an electrophile. No external additives or ligands are required, while the catalytic system is recyclable and reusable.

Full text of DOI:10.1021/acs.organomet.6b00465

Article
pubs.acs.org/Organometallics
Gold-Nanoparticle-Catalyzed Silaboration of Oxetanes and
Unactivated Epoxides
Eleni Vasilikogiannaki, Anastasia Louka, and Manolis Stratakis*
Department of Chemistry, University of Crete, 71003 Voutes, Iraklion, Greece
S
* Supporting Information
ABSTRACT: Supported gold nanoparticles catalyze the unprecedented insertion
of a silylborane into the C−O bond of oxetanes and unactivated epoxides,
forming γ- or β-silyloxy boronates in good to excellent yields. In the silaboration
process the boron moiety is acting as a nucleophile and the silyl as an electrophile.
No external additives or ligands are required, while the catalytic system is
recyclable and reusable.
chloride,6 while some γ- and δ-silyloxy boronates have been
INTRODUCTION
■
employed as starting materials for cross-coupling reactions, but
their synthesis arose via diboration of alkenyl alcohols.7 With
regard to hydroxyl-substituted boronates, the α-hydroxy
derivatives can be easily synthesized primarily via borylation
of carbonyl compounds,8 and there have been a few recent
reports on the synthesis of β-9 and γ-hydroxy boronates,10 but
the concept of these approaches is different from ours. A
similarity might be the fact that in the synthesis of γ-hydroxy
boronates10 epoxides are used as starting materials, which
undergo regioselective Cu-catalyzed coupling with a gem-
diborylmethane.
Boronate esters are valuable building blocks in modern organic
chemistry, widely used in transition-metal-catalyzed cross-
coupling reactions.1 The classical procedures for the synthesis
of boronates include2 reaction of organometallic compounds
with alkoxyboranes, metal-catalyzed hydroboration of alkenes,
borylation of alkanes/arenes via C−H activation, conjugated
alkenes in a Michael fashion, alkyl/aryl halides, π systems, etc.
One of the main protocols for the synthesis of boronates is the
addition of silylboranes and primarily the readily available
PhMe2SiBpin (pin = pinacolato) on unsaturated substrates
under catalytic conditions.3 Typically, noble metals such as
Pd(0) and Pt(0) activate the σ Si−B bond via redox catalysis
followed by addition on π bonds.
We have recently shown that supported Au nanoparticles
(Au NPs) on TiO2 catalyze the cis addition of PhMe2SiBpin to
alkynes under mild conditions, forming in good yields 1,2-vinyl
silyl boronates with abnormal regioselectivity.4 The facile
activation of silylborane by Au NPs spurred us to examine
new potential applications of silaboration to other function-
alities such as oxetanes and epoxides. The inspiration toward
this goal was motivated by the fact that upon studying the Au-
catalyzed silaboration of alkynes4 we had observed that
tetrahydrofuran (THF) is a poor solvent, and analysis of the
reaction mixture revealed that, apart from alkyne silaboration,
the partial addition of PhMe2SiBpin on the cyclic ether formed
the linear silyloxy boronate PhMe2SiOCH2CH2CH2CH2Bpin
(1a) as a minor side product. In a separate experiment we
found that, on mixing PhMe2SiBpin with Au/TiO2 in THF (1)
as solvent (60 °C, 2 h), the adduct 1a was isolated in 52% yield.
Of course, the utility of this addition reaction is low, as one of
the reactants (THF) is the reaction solvent. We anticipated,
however, that more strained cyclic ethers, such as epoxides and
oxetanes,5 might undergo smoother addition by PhMe2SiBpin,
forming silyloxy and indirectly hydroxy boronates.
RESULTS AND DISCUSSION
■
Initially we focused on oxetanes, with commercially available
3,3-dimethyloxetane (2) being examined as a representative
substrate using Au/TiO2 (1 mol %) as catalyst. To our delight,
reaction of oxetane 2 (1 equiv) with PhMe2SiBpin (1.5 equiv)
in dry 1,2-dichloroethane (DCE) as solvent at 60 °C afforded
after 2 h the adduct 2a in 81% isolated yield, with no other
products being formed (Scheme 1). To the best of our
knowledge, this is the first example in the literature of the
silaboration of ethers and essentially constitutes a new method
for the synthesis of functionalized boronates. The studies of
process optimization are discussed below and summarized in
Table S1 in the Supporting Information. When Au/TiO2 was
Scheme 1. Silaboration of 2,2-Dimethyloxetane (2) by
PhMe2Si-Bpin Catalyzed by Au/TiO2
Silyloxy boronates are a class of compounds with scarce
synthetic protocols. The enantioselective synthesis of α-silyloxy
boronates has been reported via borylation of carbonyl
compounds followed by protection of hydroxyl with silyl
Received: June 9, 2016
© XXXX American Chemical Society
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used as catalyst, after 2 h the consumption of oxetane 2 was
100%; in the case of other supported Au catalysts11 such as Au/
Al2O3 and Au/ZnO (also 1 mol %) the conversion yields on
the same time scale were moderate. Thus, we focused on Au/
TiO2. As per solvent suitability, apart from DCE, hexane and
ethyl acetate are also appropriate but require extra time (∼3 h)
to drive the reaction to completion. We also tested several
catalysts which are known to activate PhMe2SiBpin under
homogeneous conditions toward addition reactions to π
systems such as Pd(PPh3)4, Pt(PPh3)4, and (η3-C3H5)Pd-
(PPh3)Cl,12,13 but none were effective14 to catalyze oxetane
silaboration. In addition, soluble ionic gold catalysts such as
AuCl3, AuCl, Ph3PAuNTf2, and (acetonitrile)[(2-biphenyl)-di-
tert-butylphosphine]gold(I) hexafluoroantimonate were
tested,14 but no silaboration product was seen in any case,
other than unidentified mixtures of products (Table S1). The
Au NPs are recyclable and reusable without significant loss of
their activity after five consecutive runs (Table S2 in the
Supporting Information). Recycling was performed by filtration
of the catalyst after each run, washing with solvent, and drying
at 100 °C for 1 h. In blank experiments, the support (TiO2) is
completely inefficient, indicative that Au nanoparticles are the
catalytic sites.
Table 1. Silaboration of Oxetanes by PhMe2Si-Bpin
Catalyzed by Au/TiO2
The highly encouraging reaction outcome among
PhMe2SiBpin and oxetane 2 prompted us to examine the
scope and limitations of this unprecedented transformation. A
series of substituted oxetanes (and parent oxetane as well)
smoothly undergo this addition reaction in good to excellent
yields (Table 1). 3-Substituted oxetanes are excellent substrates
for this purpose, cleanly forming γ-silyloxy boronates. 2,2-
Disubstituted oxetanes seem to be unsuitable substrates, as they
preferentially undergo isomerization under the reaction
conditions (also in the absence of silylborane) primarily into
homoallylic alcohols, a process that is more likely similar to the
isomerization of substituted epoxides into allylic alcohols
catalyzed by gold nanoparticles.15 For instance, in the
attempted silaboration of oxetane 14, the silyl ether of the
corresponding homoallylic alcohol 14a was mainly formed. It is
reasonable that isomerization to homoallylic alcohol is taking
place followed by alcoholysis of PhMe2SiBpin. Notably, 2-aryl
oxetanes 10−12 provide a highly regioselective silaboration,
with the boryl group attached exclusively at the benzylic
position (products 10a−12a). In contrast, the regioselectivity
in the case of 2-cyclohexyloxetane 13 is inferior (13a/13b =
35/65), while the overall yield is much lower due to the partial
competing destructive isomerization of reacting oxetane, just as
in the case of 14.
a
The product ratio was determined by GC and 1H NMR of the crude
b
reaction mixture. Product 14a results from isomerization of oxetane
14 into a homoallylic alcohol catalyzed by Au nanoparticles.
Following the determination of the suitability of oxetanes in
their facile ring-opening silaboration, we focused on epoxides.
In general, under catalysis by Au nanoparticles, epoxides are
known to undergo either deoxygenation in the presence of a
suitable reducing agent16 or fixation with CO2.17 In addition,
suitably substituted epoxides have been previously shown by
our group to undergo Au-nanoparticle-catalyzed isomerization
into allylic alcohols.15
Thus, gem-disubstituted or tri-/tetrasubstituted epoxides
isomerize, while 1,2-disubstituted or monosubstituted epoxides
are unreactive as a consequence of the requirement for
development of a profound partial carbocationic character in
the proposed six-membered-ring concerted transition state of
isomerization. We chose cyclohexene oxide (15) as a suitable
substrate to study, as it does not undergo any isomerization to
allylic alcohol by Au NPs. To our delight, in the reaction of 15
with 1.5 equiv of PhMe2SiBpin in dry DCE (1 mol % of Au/
TiO2), after 2 h at 60 °C the epoxide had been completely
consumed and the adduct 15a (Table 2) was seen as the only
product in the crude 1H NMR spectrum. The relative
stereochemistry of 15a was assigned as trans, given that
deprotection to the corresponding boryl alcohol (15a′) with
KF in methanol and treatment of 15a′ with NaBO3·4H2O
afforded trans-1,2-cyclohexanediol (Scheme 2). Again, as in the
case of oxetanes, Au/TiO2 was proven to be a superior catalyst
relative to Au/Al2O3 or Au/ZnO, while no reaction was seen in
the absence of Au NPs or under homogeneous Pd(0) or Pt(0)
catalysis. As noted earlier, the scope and limitations of this
transformation were somehow limited (Table 2). Epoxides that
have the tendency to isomerize to allylic alcohols in the
presence of Au/TiO2 do not form any silaboration adduct. In
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TiO2. Thus, we examined only the unactivated mono- or 1,2-
disubstituted epoxides. Cyclopentene oxide (16) also works
perfectly, providing a single trans adduct (16a). Notably, cis-2-
butene oxide (17) affords a mixture of threo and erythro
adducts in the relative ratio ∼90/10, while in the case of
isomeric trans-2-butene oxide (18) a relative threo/erythro
ratio of ∼15/85 was seen. The relative stereochemistry of the
above addition products was established after deprotection/
treatment with NaBO3·4H2O and comparison of the resulting
2,3-butanediols with authentic samples (Scheme 2). Mono-
substituted epoxides 19 and 20 afford two regioisomeric
products in a relative ratio of 1/1, a selectivity resembling that
of the 2-monosubstituted cyclohexyloxetane 13.
Table 2. Silaboration of Unactivated Epoxides by PhMe2Si-
Bpin Catalyzed by Au/TiO2
Before discussing the possible reaction mechanism and the
origins of regioselectivity, we present in Scheme 3 the
Scheme 3. Stereochemistry in the Silaboration of Optically
Pure Oxetane 10-R
stereochemical outcome of silaboration of optically active
(R)-2-phenyloxetane (10-R), prepared by treatment of (R)-3-
chloro-1-phenylpropan-1-ol with t-BuOK.18 The silaboration
product of 10-R was deprotected and treated with NaBO3·
4H2O to yield 1-phenylpropane-1,3-diol. Through analysis by
chiral HPLC, it was found that the diol exists as a mixture of
enantiomers in a relative S/R ratio of 55/45 (Figure S19 in the
Supporting Information), which implies that in this specific case
almost complete racemization occurs. Note that oxetane 10-R
does not undergo racemization during the progress of the
reaction, as was proven by chiral HPLC analysis. Partial
epimerization has been also reported in the reaction of 10-R
with triarylborates,19 a reaction proceeding via a profound
carbocationic character at the benzylic position.
The Au-catalyzed silaboration reaction has the following
characteristics that are helpful in the mechanistic discussion. (a)
It could be seen as nucleophilic substitution of the cyclic ether
by the postulated intermediate PhMe2Si-Aun-Bpin,4,20 with the
boron moiety attached to carbon and dimethylphenylsilyl to
oxygen. We emphasize herein that, in the examples of Cu(I)-21
or Rh(I)-catalyzed22 silaboration of oxygen-containing sub-
stances (carbonyl compounds, CO2) known so far, the silyl
group acts as the nucleophile, in contrast to our results where
the boryl group is acting as the nucleophile. (b) Aryl-
substituted oxetanes 10−12 provide a single regioisomer with
the boron moiety attached at the benzylic position. In
cyclohexyl analogue 13, however, the regioselectivity is lower,
with boron primarily attached at the more hindered
(secondary) position. (c) Optically active 2-phenyloxetane
10-R provides an almost nonstereospecific reaction (Scheme 3,
inversion/retention 55/45). (d) Similarly to 2-monosubstituted
oxetane 13, in the case of monosubstituted epoxides 19 and 20,
no substantial regioselectivity is observed, with the boron
moiety attached on both sides (hindered and unhindered) in a
relative ratio of ∼1/1. (e) In addition, cis-epoxide 17 and trans-
epoxide 18 mainly yield threo and erythro adducts, respectively,
but the reaction is not stereospecific. Overall, these stereo-
a
The product ratio was determined by GC and 1H NMR of the crude
b
reaction mixture. Product 21a results from isomerization of epoxide
21 into a allylic alcohol catalyzed by Au nanoparticles.15
Scheme 2. Proof of Relative Stereochemistry of Silaboration
Adducts
the case of 21, for example, the dimethylphenylsilyl ether of the
corresponding allylic alcohol 21a was formed, just as oxetane
14 behaves. Aryl epoxides such as styrene oxide are also
unsuitable, as they quickly isomerize in the presence of Au/
C
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1
3-Phenyloxetane (4). H NMR (500 MHz, CDCl3): δ 7.42−7.27
chemical results (a−e) rule out a typical SN2-type addition
mode, which in monosubstituted epoxides should have formed
one regioisomer, and imply that a partial positive charge is
developing on the carbon atom bonded to the ether oxygen.
Thus, the regioselectivity pattern in oxetane 13 or mono-
substituted epoxides 19 and 20 is a balance among electronic
and steric factors. The partial positive charge becomes more
profound in 2-aryl-substitued oxetanes, where it is stabilized
through resonance, and the stereochemical outcome resembles
that of an SN1 reaction, where complete racemization is rarely
seen. In the case of isomeric epoxides 17 and 18, the partial
positive charge is less apparent relative to oxetanes 10−12;
thus, the selectivity is higher. These conclusions are depicted in
the proposed mechanism applied to a 2-substituted oxetane,
shown in Scheme 4. A completely analogous mechanism could
(m, 5H, Ph), 5.08 (dd, 2JHH = 8.0, 3JHH = 6.0 Hz, 2H, CH2), 4.79 (dd,
2JHH = 8.0 Hz, 3JHH = 8.0 Hz, 2H, CH2), 4.24 (tt, 3JHH = 8.0 Hz, 3JHH
=
6.0 Hz, 1H, benzylic). 13C NMR (125 MHz, CDCl3): δ 141.5 (Ph),
128.7 (2C, Ph), 127.0 (Ph), 126.8 (2C, Ph), 78.9 (2C, C−O), 40.3 (C-
Ph).
3-Benzyloxetane (5). 1H NMR (500 MHz, CDCl3): δ 7.29 (t, 3JHH
= 8.0 Hz, 2H, Ph), 7.21 (t, 3JHH = 8.0 Hz, 1H, Ph), 7.12 (t, 3JHH = 8.0
Hz, 2H, Ph), 4.79 (dd, 2JHH = 8.0, 3JHH = 6.0 Hz, 2H, CH2), 4.48 (dd,
2JHH = 8.0 Hz, JHH = 8.0 Hz, 2H, CH2), 3.30 (m, 1H, CH), 3.22 (d,
3
3JHH = 8.0 Hz, 2H, CH2-Ph). 13C NMR (125 MHz, CDCl3): δ 139.4
(Ph), 128.6 (2C, Ph), 128.3 (2C, Ph), 126.3 (Ph), 77.2 (2C, C−O),
39.6 (tertiary C), 36.1 (C-Ph).
1
2-Oxaspiro[3.5]nonane (6). H NMR (500 MHz, CDCl3): δ 4.35
(s, 4H, CH2-O), 1.74−1.68 (m, 4H, cyclohexyl), 1.42−1.32 (m, 6H,
cyclohexyl). 13C NMR (125 MHz, CDCl3): δ 82.6 (2C, C−O), 40.3
(quaternary C), 35.5 (2C, cyclohexyl), 25.3 (cyclohexyl), 22.9 (2C,
cyclohexyl).
Scheme 4. Proposed Mechanism of Au-Nanoparticle-
Catalyzed Silaboration of a 2-Substituted Oxetane
Oxetanes 7−9 were prepared by derivatization29 of commercially
available (3-methyloxetan-3-yl)methanol.
1
3-((Benzyloxy)methyl)-3-methyloxetane (7). H NMR (500 MHz,
CDCl3): δ 7.40−7.27 (m, 5H, Ph), 4.58 (s, 2H, OCH2Ph), 4.52 (d,
2JHH = 6.0 Hz, 2H, CH2-O), 4.37 (d, 2JHH = 6.0 Hz, 2H, CH2-O), 3.53
(s, 2H, CH2OBn), 1.34 (s, 3H, Me). 13C NMR (125 MHz, CDCl3): δ
138.3 (Ph), 128.4 (2C, Ph), 127.6 (Ph), 127.5 (2C, Ph), 80.1 (2C, C−
O oxetane), 75.3 (C−O), 73.3 (C−O), 39.8 (quaternary C), 21.4 (Me).
tert-Butyldimethyl((3-methyloxetan-3-yl)methoxy)silane (8). 1H
NMR (500 MHz, CDCl3): δ 4.48 (d, 3JHH = 6.0 Hz, 2H, CH2-O), 4.31
3
(d, JHH = 6.0 Hz, 2H, CH2-O), 3.62 (s, 2H, CH2OTBS), 1.26 (s, 3H,
Me), 0.90 (s, 9H, t-Bu), 0.06 (s, 6H, SiMe2). 13C NMR (125 MHz,
CDCl3): δ 79.7 (2C, C−O oxetane), 68.1 (C-OTBS), 40.9
(quaternary), 25.8 (3C, t-Bu), 20.9 (Me), 18.3 (t-Bu), −5.5 (2C,
SiMe2).
1
(3-Methyloxetan-3-yl)methyl Benzoate (9). H NMR (500 MHz,
CDCl3): δ 8.06 (dd, 3JHH = 7.5 Hz, 3JHH = 1.5 Hz, 2H, Ph), 7.58−7.55
(m, 1H, Ph), 7.45−7.43 (m, 2H, Ph), 4.64 (d, 2JHH = 6.0 Hz, 2H, CH2-
2
O), 4.45 (d, JHH = 6.0 Hz, 2H, CH2-O), 4.39 (s, 2H, CH2−OCOPh),
1.42 (s, 3H, Me). 13C NMR (125 MHz, CDCl3): δ 166.5 (CO),
133.1 (Ph), 129.8 (Ph), 129.6 (2C, Ph), 128.4 (2C, Ph), 79.5 (2C, C−
O oxetane), 68.9 (C−O), 39.3 (quaternary C), 21.2 (Me).
Oxetanes 10−15 were prepared using the Corey−Chaykovsky
reaction of an aldehyde or ketone with trimethylsulfoxonium iodide in
the presence of t-BuOK in t-BuOH as solvent.29
be drawn for epoxides. Marginal mechanistic analogies could be
seen in the metal-free borylative ring opening of vinyl epoxides,
which generates hydroxyl-functionalized allylic boronates via an
SN2′ mechanism,23 in the Pd-catalyzed ring-opening borylation
of 2-arylaziridines,24 in the Cu(I)-catalyzed borylation of cyclic
sulfamidates,25 and in the catalytic borylative opening of
propargyl epoxides and oxetanes26 with pinB-Bpin.
2-Phenyloxetane (10). 1H NMR (500 MHz, CDCl3): δ 7.47−7.45
3
3
(d, JHH = 7.5 Hz, 2H, Ph), 7.40 (t, JHH = 7.5 Hz, 2H, Ph), 7.31 (t,
3JHH = 7.5 Hz, 1H, Ph), 5.83 (t, JHH = 7.5 Hz, 1H, benzylic C−H),
3
4.87−4.82 (m, 1H, CH2-O), 4.69−4.65 (m, 1H, CH2-O), 3.07−3.00
(m, 1H, CH2), 2.72−2.65 (m, 1H, CH2). 13C NMR (125 MHz,
CDCl3): δ 143.5 (Ph), 128.4 (2C, Ph), 127.8 (Ph), 125.2 (2C, Ph),
82.9 (O−C−Ph), 68.2 (C−O), 30.7 (aliphatic).
1
2-(4-Fluorophenyl)oxetane (11). H NMR (500 MHz, CDCl3): δ
CONCLUSIONS
■
7.43−7.40 (m, 2H, Ar), 7.09−7.05 (m, 2H, Ar), 5.78 (t, J = 7.5 Hz,
1H, benzylic C−H), 4.84−4.80 (m, 1H, CH2-O), 4.66−4.62 (m, 1H,
CH2-O), 3.04−2.98 (m, 1H, CH2), 2.67−2.60 (m, 1H, CH2). 13C
NMR (125 MHz, CDCl3): δ 162.3 (d, 1JCF = 244.5 Hz, Ar), 139.3 (d,
In summary, we present an unprecedented reaction, the
silaboration of strained ethers (oxetanes and epoxides) to
form γ- and β-silyloxy boronates using as catalysts recyclable
supported Au nanoparticles free of any ligands or external
additives. Our mechanistic analysis suggests that, in the
transition state of addition, a profound partial positive charge
is developing on the carbon atom linked to the ether oxygen.
The current reactivity mode and catalytic application of Au
nanoparticles provide new and unique features of supported Au
nanoparticles in the catalysis of organic transformations.27
3
2
4JCF = 3.0 Hz, Ar), 127.1 (d, JCF = 8.0 Hz, 2C, Ar), 115.3 (d, JCF
=
21.5 Hz, 2C, Ar), 82.3 (O−C−Ar), 68.0 (C−O), 30.8 (aliphatic).
1
2-(p-Tolyl)oxetane (12). H NMR (500 MHz, CDCl3): δ 7.39 (d,
3JHH = 8.0 Hz, 2H, Ar), 7.25 (d, 3JHH = 8.0 Hz, 2H, Ar), 5.82 (t, 3JHH
=
7.5 Hz, 1H, benzylic C−H), 4.87−4.82 (m, 1H, CH2-O), 4.70−4.66
(m, 1H, CH2-O), 3.06−2.99 (m, 1H, CH2), 2.74−2.66 (m, 1H, CH2),
2.41 (s, 3H, Me). 13C NMR (125 MHz, CDCl3): δ 140.4 (Ar), 137.3
(Ar), 129.0 (2C, Ar), 125.2 (2C, Ar), 82.7 (O−C−Ar), 67.9 (C−O),
30.6 (aliphatic), 21.0 (Me).
1
EXPERIMENTAL SECTION
2-Cyclohexyloxetane (13). H NMR (500 MHz, CDCl3): δ 4.64−
■
4.58 (m, 1H, tertiary CH−O), 4.47−4.39 (m, 2H, CH2-O), 2.56−2.50
(m, 1H, oxetane CH2), 2.39−2.32 (m, 1H, oxetane CH2), 1.87−1.83
(m, 1H, cyclohexyl), 1.75−1.55 (m, 5H, cyclohexyl), 1.27−1.08 (m, 3H,
cyclohexyl), 0.90−0.77 (m, 2H, cyclohexyl). 13C NMR (125 MHz,
Synthesis of Substrates. All epoxides used were commercially
available. Oxetanes 2 and 3 are commercially available, while 4−6 were
prepared by successive treatment of the corresponding 1,3-diols with
n-BuLi (1 equiv)/TsCl and then n-BuLi (1 equiv) in THF.28
D
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CDCl3): δ 86.6 (tertiary C−O), 68.0 (secondary C−O), 44.6 (tertiary
C), 27.4, 26.4, 26.0, 25.6, 25.6, 25.4 (all secondary C).
(2C, Ph), 127.7 (2C, Ph), 125.6 (Ph), 82.9 (2C, quaternary Bpin), 66.7
(C−O), 39.5 (C-Ph), 38.9 (C-Bn), 24.9 (2C, Me Bpin), 24.8 (2C, Me
Bpin), −1.7 (SiMe2), −1.8 (SiMe2). HRMS (TOF-ESI): [M + H]+
calcd for C24H35BO3Si + H, 411.2521; found, 411.2520.
Dimethyl(phenyl)((1-((4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)methyl)cyclohexyl)methoxy)silane (6a). 1H NMR (500 MHz,
CDCl3): δ 7.61−7.58 (m, 2H, Ph), 7.40−7.34 (m, 3H, Ph), 3.46 (s,
2H, CH2-O), 1.47−1.27 (m, 10H, cyclohexyl), 1.21 (s, 12H, Me Bpin),
0.90 (s, 2H, CH2-Bpin), 0.35 (s, 6H, SiMe2). 13C NMR (125 MHz,
CDCl3): δ 138.8 (Ph), 133.5 (2C, Ph), 129.2 (Ph), 127.6 (2C, Ph),
82.5 (2C, quaternary Bpin), 70.3 (C−O), 37.1 (quaternary cyclohexyl),
34.2 (2C, cyclohexyl), 26.4 (cyclohexyl), 24.8 (4C, Me Bpin), 21.9 (2C,
(cyclohexyl), −1.7 (2C, SiMe2). HRMS (TOF-ESI): [M + H]+ calcd for
C22H37BO3Si + H, 389.2678; found, 389.2682.
1-Oxaspiro[3.5]nonane (14). 1H NMR (500 MHz, CDCl3): δ 4.47
3
3
(t, JHH = 7.0 Hz, 2H, CH2-O), 2.30 (t, JHH = 7.0 Hz, 2H, oxetane
CH2), 1.83−1.80 (m, 2H, cyclohexyl), 1.69−1.59 (m, 4H, cyclohexyl),
1.39−1.23 (m, 4H, cyclohexyl). 13C NMR (125 MHz, CDCl3): δ 86.5
(quaternary C−O), 64.7 (secondary C−O), 38.6 (2C), 32.3, 25.0, 22.4
(2C).
General Procedure for the Au/TiO2-Catalyzed Silaboration
of Oxetanes or Epoxides. In a vial containing the oxetane or
epoxide (0.2 mmol), PhMe2SiBpin (0.3 mmol), and 1 mL of dry DCE
was placed 40 mg of Au/TiO2 (1.0 mol % in Au). After 2 h at 60 °C
the starting material was typically consumed. The slurry was filtered
with the aid of dichloromethane under a low pressure through a short
pad of silica gel or Celite, and the filtrate was evaporated to afford the
silaboration products, which were purified by flash column
chromatography.
(3-(Benzyloxy)-2-methyl-2-((4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)methyl)propoxy)dimethyl(phenyl)silane (7a). 1H NMR
(500 MHz, CDCl3): δ 7.59−7.57 (m, 2H, Ph), 7.40−7.25 (m, 8H,
2
Ph), 4.50 (s, 2H, O−CH2-Ph), 3.52 (d, JHH = 9.5 Hz, 1H, CH2-OSi),
Characterization of Silaboration Products and Byproducts.
3.47 (d, 2JHH = 9.5 Hz, 1H, CH2-OSi), 3.32 (s, 2H, CH2-OBn), 1.21 (s,
Dimethyl(phenyl)(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
1
2
butoxy)silane (1a). H NMR (500 MHz, CDCl3): δ 7.62−7.56 (m,
12H, Me Bpin), 0.98 (s, 3H, Me), 0.88 (d, JHH = 15.0 Hz, 1H, CH2-
2H, Ph), 7.40−7.33 (m, 3H, Ph), 3.58 (t, 3JHH = 7.0 Hz, 2H, CH2-O),
1.57−1.52 (m, 2H, CH2−C-O), 1.45−1.39 (m, 2H, CH2−C-B), 1.23
(s, 12H, Me Bpin), 0.76 (t, J = 7.5 Hz, 2H, CH2-Bpin), 0.36 (s, 6H,
SiMe2). 13C NMR (125 MHz, CDCl3): δ 138.1 (Ph), 133.5 (2C, Ph),
129.5 (Ph), 127.8 (2C, Ph), 82.9 (2C, quaternary Bpin), 63.0 (C−O),
35.2 (aliphatic), 24.8 (4C, Me Bpin), 20.2 (aliphatic), −1.7 (2C,
SiMe2). HRMS (TOF-ESI): [M + H]+ calcd for C18H31BO3Si + H,
335.2208; found, 335.2208.
2
Bpin), 0.82 (d, JHH = 15.0 Hz, 1H, CH2-Bpin), 0.36 (s, 3H, SiMe2),
0.35 (s, 3H, SiMe2). 13C NMR (125 MHz, CDCl3): δ 139.2 (Ph),
138.6 (Ph), 133.5 (2C, Ph), 129.3 (Ph), 128.1 (2C, Ph), 127.6 (2C,
Ph), 127.3 (2C, Ph), 127.1 (Ph), 82.7 (2C, quaternary Bpin), 75.7 (C−
O), 73.0 (C−O), 68.6 (C−O), 38.6 (quaternary), 24.8 (2C, Me Bpin),
24.8 (2C, Me Bpin), 21.2 (Me), −1.7 (SiMe2), −1.8 (SiMe2). HRMS
(TOF-ESI): [M + H]+ calcd for C26H39BO4Si + H, 455.2783; found,
455.2781.
(2,2-Dimethyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
2,5,8,8,9,9-Hexamethyl-2-phenyl-5-((4,4,5,5-tetramethyl-1,3,2-di-
1
1
propoxy)dimethyl(phenyl)silane (2a). H NMR (500 MHz, CDCl3):
oxaborolan-2-yl)methyl)-3,7-dioxa-2,8-disiladecane (8a). H NMR
δ 7.60−7.57 (m, 2H, Ph), 7.39−7.34 (m, 3H, Ph), 3.29 (s, 2H, CH2-
O), 1.23 (s, 12H, Me Bpin), 0.94 (s, 6H, Me), 0.79 (s, 2H, CH2-Bpin),
0.34 (s, 6H, SiMe2). 13C NMR (125 MHz, CDCl3): δ 138.6 (Ph),
133.5 (2C, Ph), 129.3 (Ph), 127.7 (2C, Ph), 82.7 (2C, quaternary
Bpin), 73.6 (C−O), 34.4 (tertiary), 26.0 (2C, Me), 24.9 (4C, Me Bpin),
−1.7 (2C, SiMe2). HRMS (TOF-ESI): [M + H]+ calcd for
C19H33BO3Si + H, 349.2365; found, 349.2363.
(500 MHz, CDCl3): δ 7.58−7.56 (m, 2H, Ph), 7.40−7.32 (m, 3H,
Ph), 3.43−3.37 (m, 4H, CH2-OTBS + CH2-OSiMe2Ph), 1.21 (s, 12H,
Me Bpin), 0.88 (s, 9H, t-Bu), 0.87 (s, 3H, Me), 0.77 (s, 2H, CH2-Bpin),
0.33 (s, 3H, SiMe2), 0.33 (s, 3H, SiMe2), 0.02 (s, 6H, SiMe2 of TBS).
13C NMR (125 MHz, CDCl3): δ 138.8 (Ph), 133.5 (2C, Ph), 129.2
(Ph), 127.6 (2C, Ph), 82.6 (2C, quaternary Bpin), 67.8 (C−O), 67.8
(C−O), 39.1 (quaternary), 26.0 (3C, t-Bu), 24.8 (2C, Me Bpin), 20.4
(Me), 18.3 (quaternary t-Bu), −1.7 (SiMe2), −1.7 (SiMe2), −5.5 (2C,
(SiMe2 of TBS). HRMS (TOF-ESI): [M + H]+ calcd for C25H47BO4Si2
+ H, 479.3179; found, 479.3175.
Dimethyl(phenyl)(3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
1
yl)propoxy)silane (3a). H NMR (500 MHz, CDCl3): δ 7.58−7.56
(m, 2H, Ph), 7.40−7.34 (m, 3H, Ph), 3.56 (t, 3JHH = 7.0 Hz, 2H, CH2-
O), 1.69−1.63 (m, 2H, CH2−C-O), 1.22 (s, 12H, Me Bpin), 0.77 (t,
3JHH = 8.0 Hz, 2H, CH2-Bpin), 0.37 (s, 6H, SiMe2). 13C NMR (125
MHz, CDCl3): δ 138.1 (Ph), 133.5 (2C, Ph), 129.4 (Ph), 127.7 (2C,
Ph), 82.9 (2C, quaternary Bpin), 64.9 (C−O), 27.0 (aliphatic), 24.8
(4C, Me Bpin), −1.7 (2C, SiMe2). HRMS (TOF-ESI): [M + H]+ calcd
for C17H29BO3Si + H, 321.2052; found, 321.2053.
3-((Dimethyl(phenyl)silyl)oxy)-2-methyl-2-((4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)methyl)propyl Benzoate (9a). 1H NMR
(500 MHz, CDCl3): δ 8.01−7.99 (m, 2H, Ph), 7.56−7.54 (m, 3H,
Ph), 7.42 (t, 3JHH = 7.5 Hz, 2H, Ph), 7.34−7.27 (m, 3H, Ph), 4.24 (d,
2
2JHH = 10.5 Hz, 1H, CH2−OCOPh), 4.21 (d, JHH = 10.5 Hz, 1H,
CH2−OCOPh), 3.55 (d, 2JHH = 10.0 Hz, 1H, CH2-OSi), 3.49 (d, 2JHH
=
Dimethyl(phenyl)(2-phenyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxa-
10.0 Hz, 1H, CH2-OSi), 1.21 (s, 12H, Me Bpin), 1.05 (s, 3H, Me), 0.96
(d, 2JHH = 15.0 Hz, 1H, CH2-Bpin), 0.92 (d, 2JHH = 15.0 Hz, 1H, CH2-
Bpin), 0.34 (s, 3H, SiMe2), 0.33 (s, 3H, SiMe2). 13C NMR (125 MHz,
CDCl3): δ 166.5 (C = O), 138.0 (Ph), 133.4 (2C, Ph), 132.6 (Ph),
130.6 (Ph), 129.5 (2C, Ph), 129.4 (Ph), 128.2 (2C, Ph), 127.7 (2C,
Ph), 83.0 (2C, quaternary Bpin), 69.7 (C−O), 68.2 (C−O), 37.7
(quaternary), 24.8 (2C, Me Bpin), 24.8 (2C, Me Bpin), 20.9 (Me), −1.9
(SiMe2), −1.9 (SiMe2). HRMS (TOF-ESI): [M + H]+ calcd for
C26H37BO5Si + H, 469.2576; found, 469.2576.
1
borolan-2-yl)propoxy)silane (4a). H NMR (500 MHz, CDCl3): δ
7.51−7.48 (m, 2H, Ph), 7.41−7.32 (m, 3H, Ph), 7.27−7.16 (m, 5H,
2
3
Ph), 3.69 (dd, JHH = 10.0 Hz, JHH = 6.5 Hz, 1H, CH2-O), 3.63 (dd,
2JHH = 10.0 Hz, JHH = 7.0 Hz, 1H, CH2-O), 3.11−3.06 (m, 1H, CH-
3
Ph), 1.34 (dd, 2JHH = 15.5 Hz, 3JHH = 6.5 Hz, 1H, CH2-Bpin), 1.10 (dd,
2JHH = 15.5 Hz, 3JHH = 9.0 Hz, 1H, CH2-Bpin), 1.10 (s, 6H, Me Bpin),
1.07 (s, 6H, Me Bpin), 0.29 (s, 3H, SiMe2), 0.28 (s, 3H, SiMe2). 13C
NMR (125 MHz, CDCl3): δ 144.3 (Ph), 138.0 (Ph), 133.4 (2C, Ph),
129.4 (Ph), 128.0 (2C, Ph), 127.9 (2C, Ph), 127.7 (2C, Ph), 126.1
(Ph), 82.9 (2C, quaternary Bpin), 69.5 (C−O), 43.8 (C-Ph), 24.6 (2C,
Me Bpin), 24.5 (2C, Me Bpin), −1.8 (SiMe2), −1.9 (SiMe2). HRMS
(TOF-ESI): [M + H]+ calcd for C23H33BO3Si + H, 397.2365; found,
397.2362.
Dimethyl(phenyl)(3-phenyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxa-
1
borolan-2-yl)propoxy)silane (10a). H NMR (500 MHz, CDCl3): δ
7.56−7.54 (m, 2H, Ph), 7.40−7.34 (m, 3H, Ph), 7.22 (t, 3JHH = 7.5 Hz,
3
3
2H, Ph), 7.16 (d, JHH = 7.5 Hz, 2H, Ph), 7.12 (t, JHH = 7.5 Hz, 1H,
Ph), 3.59−3.50 (m, 2H, CH2-O), 2.45 (t, 3JHH = 8.0 Hz, 1H, benzylic),
2.15−2.08 (m, 1H, CH2-C-OSi), 1.93−1.86 (m, 1H, CH2-C-OSi), 1.17
(s, 6H, Me Bpin), 1.15 (s, 6H, Me Bpin), 0.34 (s, 6H, SiMe2). 13C NMR
(125 MHz, CDCl3): δ 142.6 (Ph), 138.1 (Ph), 133.5 (2C, Ph), 129.4
(Ph), 128.4 (2C, Ph), 128.2 (2C, Ph), 127.8 (2C, Ph), 125.1 (Ph), 83.3
(2C, quaternary Bpin), 62.1 (C−O), 35.0 (secondary), 24.6 (2C, Me
Bpin), 24.5 (2C, Me Bpin), −1.8 (SiMe2), −1.8 (SiMe2). HRMS (TOF-
ESI): [M + H]+ calcd for C23H33BO3Si + H, 397.2365; found,
397.2365.
(2-Benzyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
1
propoxy)dimethyl(phenyl)silane (5a). H NMR (500 MHz, CDCl3):
δ 7.59−7.56 (m, 2H, Ph), 7.41−7.35 (m, 3H, Ph), 7.26−7.14 (m, 5H,
2
3
Ph), 3.50 (dd, JHH = 10.0 Hz, JHH = 5.0 Hz, 1H, CH2-O), 3.42 (dd,
2JHH = 10.0 Hz, 3JHH = 6.5 Hz, 1H, CH2-O), 2.79 (dd, 2JHH = 13.5 Hz,
3JHH = 6.5 Hz, 1H, CH2-Ph), 2.50 (dd, 2JHH = 13.5 Hz, 3JHH = 7.0 Hz,
1H, CH2-Ph), 2.11−2.05 (m, 1H, CH-Bn), 1.20 (s, 6H, Me Bpin), 1.20
(s, 6H, Me Bpin), 0.78 (d, 3JHH = 7.0 Hz, 2H, CH2-Bpin), 0.36 (s, 3H,
SiMe2), 0.36 (s, 3H, SiMe2). 13C NMR (125 MHz, CDCl3): δ 141.0
(Ph), 138.3 (Ph), 133.5 (2C, Ph), 129.5 (2C, Ph), 129.4 (Ph), 128.0
(3-(4-Fluorophenyl)-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)propoxy)dimethyl(phenyl)silane (11a). 1H NMR (500 MHz,
E
DOI: 10.1021/acs.organomet.6b00465
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
CDCl3): δ 7.5−7.53 (m, 2H, Ar), 7.40−7.34 (m, 3H, Ar), 7.11−7.09
CDCl3): δ 83.3 (2C, quaternary Bpin), 71.7 (C−OH), 35.3 (aliphatic),
26.2 (aliphatic), 26.1 (aliphatic), 24.8 (aliphatic), 24.7 (4C, Me Bpin).
HRMS (TOF-ESI): [M + H]+ calcd for C12H23BO3 + H, 227.1813;
found, 227.1814.
3
3
(m, 2H, Ar), 6.91 (dd, JHH = 8.5 Hz, JHF = 8.5 Hz, 2H, Ar), 3.56−
3.48 (m, 2H, CH2-O), 2.44 (t, 3JHH = 8.0 Hz, 1H, benzylic), 2.11−2.04
(m, 1H, CH2-C-OSi), 1.87−1.80 (m, 1H, CH2-C-OSi), 1.17 (s, 6H, Me
Bpin), 1.15 (s, 6H, Me Bpin), 0.34 (s, 6H, SiMe2). 13C NMR (125
trans-Dimethyl(phenyl)((2-(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
1
1
4
lan-2-yl)cyclopentyl)oxy)silane (16a). H NMR (500 MHz, CDCl3):
MHz, CDCl3): δ 160.9 (d, JCF = 241.0 Hz, Ar), 138.2 (d, JCF = 3.0
Hz, Ar), 137.9 (Ar), 133.4 (2C, Ar), 129.6 (d, 3JCF = 8.0 Hz, 2C, Ar),
129.5 (Ar), 127.8 (2C, Ar), 114.9 (d, JCF = 21.0 Hz, 2C, Ar), 83.3
δ 7.61−7.59 (m, 2H, Ph), 7.39−7.33 (m, 3H, Ph), 4.37−4.34 (m, 1H,
CH−OSi), 1.95−1.88 (m, 1H, aliphatic), 1.75−1.33 (m, 6H, aliphatic
+ CH-Bpin), 1.21 (s, 6H, Me Bpin), 1.21 (s, 6H, Me Bpin), 0.38 (s, 3H,
SiMe2), 0.37 (s, 3H, SiMe2). 13C NMR (125 MHz, CDCl3): δ 138.9
(Ph), 133.5 (2C, Ph), 129.2 (Ph), 127.6 (2C, Ph), 82.9 (2C, quaternary
Bpin), 76.9 (C−O), 36.7 (aliphatic), 26.4 (aliphatic), 24.7 (4C, Me
Bpin), 24.2 (aliphatic), −0.9 (2C, SiMe2), −1.1 (2C, SiMe2). HRMS
(TOF-ESI): [M + H]+ calcd for C19H31BO3Si + H, 347.2208; found,
347.2206.
trans-2-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)-
cyclopentanol (16a′). 1H NMR (500 MHz, CDCl3): δ 4.29−4.25 (m,
1H, CH−O), 1.95−1.89 (m, 1H, aliphatic), 1.86−1.81 (m, 1H,
aliphatic), 1.78−1.71 (m, 1H, aliphatic), 1.60−1.52 (m, 3H, aliphatic),
1.26−1.22 (m, 1H, CH-Bpin), 1.24 (s, 12H, Me Bpin). 13C NMR (125
MHz, CDCl3): δ 83.2 (2C, quaternary Bpin), 76.4 (C−O), 35.7
(aliphatic), 25.7 (aliphatic), 24.8 (2C, Me Bpin), 24.7 (2C, Me Bpin),
23.5 (aliphatic). HRMS (TOF-ESI): [M + H]+ calcd for C11H21BO3 +
H, 213.1657; found, 213.1657.
2
(2C, quaternary Bpin), 61.8 (C−O), 35.0 (secondary), 24.6 (2C, Me
Bpin), 24.5 (2C, Me Bpin), −1.8 (2C, SiMe2). HRMS (TOF-ESI): [M
+ H]+ calcd for C23H32BFO3Si + H, 415.2271; found, 415.2271.
Dimethyl(phenyl)(3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
1
yl)-3-(p-tolyl)propoxy)silane (12a). H NMR (500 MHz, CDCl3): δ
7.56−7.54 (m, 2H, Ar), 7.40−7.34 (m, 3H, Ar), 7.05 (d, 3JHH = 7.5 Hz,
2H, Ar), 7.03 (d, 3JHH = 7.5 Hz, 2H, Ar), 3.59−3.48 (m, 2H, CH2-O),
2.40 (t, 3JHH = 8.0 Hz, 1H, benzylic), 2.29 (s, 3H, Me), 2.10−2.05 (m,
1H, CH2-C-OSi), 1.90−1.81 (m, 1H, CH2-C-OSi), 1.17 (s, 6H, Me
Bpin), 1.14 (s, 6H, Me Bpin), 0.34 (s, 6H, SiMe2). 13C NMR (125
MHz, CDCl3): δ 139.5 (Ar), 138.1 (Ar), 134.4 (Ar), 133.5 (2C, Ar),
129.4 (Ar), 129.0 (2C, Ar), 128.3 (2C, Ar), 127.7 (2C, Ar), 83.2 (2C,
quaternary Bpin), 62.2 (C−O), 35.2 (secondary), 24.6 (2C, Me Bpin),
24.5 (2C, Me Bpin), 21.0 (Me), −1.7 (SiMe2), −1.8 (SiMe2). HRMS
(TOF-ESI): [M + H]+ calcd for C24H35BO3Si + H, 411.2521; found,
411.2520.
threo-Dimethyl(phenyl)((3-(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)butan-2-yl)oxy)silane (17a). 1H NMR (500 MHz, CDCl3): δ
7.63−7.61 (m, 2H, Ph), 7.37−7.34 (m, 3H, Ph), 4.03−3.98 (m, 1H,
CH−OSi), 1.24−1.20 (m, 1H, CH-Bpin), 1.23 (s, 6H, Me Bpin), 1.22
(s, 6H, Me Bpin), 1.14 (d, 3JHH = 6.0 Hz, 3H, Me), 0.97 (d, 3JHH = 7.5
Hz, 3H, Me), 0.38 (s, 3H, SiMe2), 0.36 (s, 3H, SiMe2). 13C NMR (125
MHz, CDCl3): δ 139.1 (Ph), 133.5 (2C, Ph), 129.2 (Ph), 127.6 (2C,
Ph), 82.8 (2C, quaternary Bpin), 71.7 (C−O), 24.9 (2C, Me Bpin), 24.6
(2C, Me Bpin), 22.2 (Me), 11.0 (Me), −0.7 (SiMe2), −0.9 (SiMe2).
HRMS (TOF-ESI): [M + H]+ calcd for C18H31BO3Si + H, 335.2208;
found, 335.2208.
(1-Cyclohexyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
propoxy)dimethyl(phenyl)silane (13a). 1H NMR (500 MHz,
CDCl3): δ 7.61−7.59 (m, 2H, Ph), 7.39−7.33 (m, 3H, Ph), 3.43−
3.39 (m, 1H, CH−OSi), 1.73−0.80 (m, 15H, aliphatic), 1.23 (s, 12H,
Me Bpin), 0.37 (s, 6H, SiMe2). 13C NMR (125 MHz, CDCl3): δ 139.0
(Ph), 133.6 (2C, Ph), 129.2 (Ph), 127.6 (2C, Ph), 82.8 (2C, quaternary
Bpin), 78.7 (C−O), 42.6, 29.7, 28.9, 28.2, 27.5, 26.5, 26.5, 24.8 (2C,
Me Bpin), 24.8 (2C, Me Bpin), −0.7 (SiMe2), −0.8 (SiMe2). HRMS
(TOF-ESI): [M + H]+ calcd for C23H39BO3Si + H, 403.2834; found,
403.2835.
(3-Cyclohexyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
propoxy)dimethyl(phenyl)silane (13b). 1H NMR (500 MHz,
CDCl3): δ 7.59−7.56 (m, 2H, Ph), 7.40−7.34 (m, 3H, Ph), 3.61−
3.56 (m, 1H, CH2-O), 3.53−3.47 (m, 1H, CH2-O), 1.73−0.80 (m,
14H, aliphatic), 1.19 (s, 6H, Me Bpin), 1.18 (s, 6H, Me Bpin), 0.37 (s,
6H, SiMe2). 13C NMR (125 MHz, CDCl3): δ 138.1 (Ph), 133.5 (2C,
Ph), 129.4 (Ph), 127.7 (2C, Ph), 82.8 (2C, quaternary Bpin), 63.4 (C−
O), 39.5, 32.7, 32.3, 31.7, 26.8, 26.7, 26.7, 25.0 (2C, Me Bpin), 24.7
(2C, Me Bpin), −1.7 (SiMe2), −1.7 (SiMe2). HRMS (TOF-ESI): [M +
H]+ calcd for C23H39BO3Si + H, 403.2834; found, 403.2835.
(2-(Cyclohex-1-en-1-yl)ethoxy)dimethyl(phenyl)silane (14a). 1H
NMR (500 MHz, CDCl3): δ 7.61−7.59 (m, 2H, Ph), 7.41−7.36 (m,
3H, Ph), 5.41 (br t, 1H, olefinic C−H) 3.66 (t, 3JHH = 7.5 Hz, 2H, CH2-
O), 2.19 (t, 3JHH = 7.0 Hz, 1H, CH2−C-O), 1.99−1.95 (m, 2H, allylic),
1.91−1.87 (m, 2H, allylic), 1.62−1.52 (m, 4H, aliphatic), 0.39 (s, 6H,
SiMe2). 13C NMR (125 MHz, CDCl3): δ 138.0 (Ph), 134.6 (olefinic),
133.5 (2C, Ph), 129.5 (Ph), 127.8 (2C, Ph), 122.8 (olefinic), 62.3 (C−
O), 41.2, 28.7, 25.2, 22.9, 22.3, −1.7 (2C SiMe2).
trans-Dimethyl(phenyl)((2-(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)cyclohexyl)oxy)silane (15a). 1H NMR (500 MHz, CDCl3): δ
7.63−7.61 (m, 2H, Ph), 7.37−7.32 (m, 3H, Ph), 3.84−3.79 (m, 1H,
CH−OSi), 1.77−1.74 (m, 2H, aliphatic), 1.68−1.66 (m, 1H, aliphatic),
1.53−1.49 (m, 1H, aliphatic), 1.31−1.11 (m, 5H, aliphatic + CH-Bpin),
1.23 (s, 6H, Me Bpin), 1.22 (s, 6H, Me Bpin), 0.39 (s, 3H, SiMe2), 0.37
(s, 3H, SiMe2). 13C NMR (125 MHz, CDCl3): δ 139.4 (Ph), 133.5
(2C, Ph), 129.1 (Ph), 127.5 (2C, Ph), 82.8 (2C, quaternary Bpin), 73.0
(C−O), 36.3 (aliphatic), 26.1 (aliphatic), 25.9 (aliphatic), 24.9 (2C,
Me Bpin), 24.6 (2C, Me Bpin), 24.4 (aliphatic), −0.4 (2C, SiMe2), −0.7
(2C, SiMe2). HRMS (TOF-ESI): [M + H]+ calcd for C20H33BO3Si +
H, 361.2365; found, 361.2365.
trans-2-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)-
cyclohexanol (15a′). 1H NMR (500 MHz, CDCl3): δ 3.58−3.53 (m,
1H, CH−O), 2.65 (br s, 1H, −OH), 1.98−1.94 (m, 1H, aliphatic),
1.84−1.79 (m, 1H, aliphatic), 1.78−1.74 (m, 1H, aliphatic), 1.62−1.57
(m, 1H, aliphatic), 1.24 (s, 12H, Me Bpin), 1.26−1.06 (m, 4H,
aliphatic), 0.94−0.90 (m, 1H, CH-Bpin). 13C NMR (125 MHz,
threo-3-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)butan-2-ol
1
(17a′). H NMR (500 MHz, CDCl3): δ 3.78−3.72 (m, 1H, CH−O),
2.35 (br s, 1H, −OH), 1.25 (s, 12H, Me Bpin), 1.20 (d, 3JHH = 6.0 Hz,
3
3H, Me), 1.16−1.11 (m, 1H, CH-Bpin) 1.00 (d, JHH = 7.5 Hz, 3H,
Me). 13C NMR (125 MHz, CDCl3): δ 83.3 (2C, quaternary Bpin), 71.0
(C−O), 24.8 (2C, Me Bpin), 24.6 (2C, Me Bpin), 22.7 (Me), 12.2
(Me). MS (EI): 182 (M+ − H2O, < 1%), 83 (8%), 59 (17%), 45
(100%).
erythro-Dimethyl(phenyl)((3-(4,4,5,5-tetramethyl-1,3,2-dioxabor-
olan-2-yl)butan-2-yl)oxy)silane (18b). 1H NMR (500 MHz, CDCl3):
δ 7.62−7.60 (m, 2H, Ph), 7.37−7.34 (m, 3H, Ph), 3.90−3.85 (m, 1H,
CH−OSi), 1.22 (s, 6H, Me Bpin), 1.21 (s, 6H, Me Bpin), 1.13 (d, 3JHH
3
= 6.0 Hz, 3H, Me), 0.97 (d, JHH = 7.5 Hz, 3H, Me), 0.90−0.85 (m,
1H, CH-Bpin), 0.38 (s, 3H, SiMe2), 0.37 (s, 3H, SiMe2). 13C NMR
(125 MHz, CDCl3): δ 138.9 (Ph), 133.6 (2C, Ph), 129.3 (Ph), 127.6
(2C, Ph), 82.8 (2C, quaternary Bpin), 71.3 (C−O), 24.7 (2C, Me
Bpin), 24.5 (2C, Me Bpin), 23.7 (Me), 12.3 (Me), −0.8 (SiMe2), −1.0
(SiMe2). HRMS (TOF-ESI): [M + H]+ calcd for C18H31BO3Si + H,
335.2208; found, 335.2208.
erythro-3-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)butan-2-
1
ol (18b′). H NMR (500 MHz, CDCl3): δ 3.87−3.82 (m, 1H, CH−
O), 1.80 (bs, 1H, −OH), 1.26−1.22 (m, 1H, CH-Bpin), 1.25 (s, 12H,
Me Bpin), 1.18 (d, 3JHH = 6.5 Hz, 3H, Me), 0.99 (d, 3JHH = 7.5 Hz, 3H,
Me). 13C NMR (125 MHz, CDCl3): δ 83.3 (2C, quaternary Bpin), 70.0
(C−O), 24.7 (2C, Me Bpin), 24.7 (2C, Me Bpin), 21.7 (Me), 10.8
(Me). MS (EI): 182 (M+ − H2O, < 1%), 83 (6%), 59 (20%), 45
(100%).
Dimethyl(phenyl)(2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
1
yl)propoxy)silane (19a). H NMR (500 MHz, CDCl3): δ 7.60−7.58
2
(m, 2H, Ph), 7.40−7.34 (m, 3H, Ph), 3.70 (dd, JHH = 9.5 Hz, 3JHH
=
2
3
6.0 Hz, 1H, CH2-OSi), 3.60 (dd, JHH = 9.5 Hz, JHH = 8.0 Hz, 1H,
CH2-OSi), 1.36−1.30 (m, 1H, CH-Bpin), 1.23 (s, 12H, Me Bpin), 0.98
(d, 3JHH = 7.5 Hz, 3H, Me), 0.35 (s, 6H, SiMe2). 13C NMR (125 MHz,
CDCl3): δ 138.4 (Ph), 133.5 (2C, Ph), 129.3 (Ph), 127.7 (2C, Ph),
83.0 (2C, quaternary Bpin), 66.0 (C−O), 24.7 (2C, Me Bpin), 24.7
F
DOI: 10.1021/acs.organomet.6b00465
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(2C, Me Bpin), 12.1 (Me), −1.7 (SiMe2), −1.7 (SiMe2). HRMS (TOF-
ESI): [M + H]+ calcd for C17H29BO3Si + H, 321.2052; found,
321.2051.
REFERENCES
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Dimethyl(phenyl)((1-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)propan-2-yl)oxy)silane (19b). 1H NMR (500 MHz, CDCl3): δ
7.61−7.59 (m, 2H, Ph), 7.39−7.33 (m, 3H, Ph), 4.18−4.11 (m, 1H,
CH−OSi), 1.22 (s, 6H, Me Bpin), 1.21 (s, 6H, Me Bpin), 1.17 (d, 3JHH
= 6.0 Hz, 3H, Me), 1.15 (dd, 2JHH = 15.0 Hz, 3JHH = 5.5 Hz, 1H, CH2-
Bpin), 1.09 (dd, 2JHH = 15.0 Hz, 3JHH = 8.0 Hz, 1H, CH2-Bpin), 0.38 (s,
3H, SiMe2), 0.37 (s, 3H, SiMe2). 13C NMR (125 MHz, CDCl3): δ
138.9 (Ph), 133.5 (2C, Ph), 129.3 (Ph), 127.6 (2C, Ph), 83.0 (2C,
quaternary Bpin), 66.8 (C−O), 25.8 (Me), 24.9 (2C, Me Bpin), 24.6
(2C, Me Bpin), −0.9 (SiMe2), −1.0 (SiMe2). HRMS (TOF-ESI): [M +
H]+ calcd for C17H29BO3Si + H, 321.2052; found, 321.2051.
Dimethyl(phenyl)((2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)hexyl)oxy)silane (20a). 1H NMR (500 MHz, CDCl3): δ 7.58−7.56
(m, 2H, Ph), 7.37−7.34 (m, 3H, Ph), 3.69−3.64 (m, 2H, CH2-OSi),
1.46−1.20 (m, 7H, aliphatic + CH-Bpin), 1.23 (s, 12H, Me Bpin), 0.86
(t, 3JHH = 7.0 Hz, 3H, Me), 0.34 (s, 6H, SiMe2). 13C NMR (125 MHz,
CDCl3): δ 138.4 (Ph), 133.5 (2C, Ph), 129.3 (Ph), 127.7 (2C, Ph),
82.9 (2C, quaternary Bpin), 64.5 (C−O), 31.2 (aliphatic), 27.1
(aliphatic), 24.8 (2C, Me Bpin), 24.7 (2C, Me Bpin), 23.0 (aliphatic),
14.1 (Me), −1.7 (SiMe2), −1.7 (SiMe2). HRMS (TOF-ESI): [M + H]+
calcd for C20H35BO3Si + H, 363.2521; found, 363.2521.
Dimethyl(phenyl)((1-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)hexan-2-yl)oxy)silane (20b). 1H NMR (500 MHz, CDCl3): δ
7.61−7.59 (m, 2H, Ph), 7.37−7.32 (m, 3H, Ph), 4.01−3.96 (m, 1H,
CH−OSi), 1.50−1.39 (m, 2H, aliphatic), 1.35−1.20 (m, 4H, aliphatic),
1.21 (s, 6H, Me Bpin), 1.20 (s, 6H, Me Bpin), 1.11 (dd, 2JHH = 15.0 Hz,
3JHH = 8.0 Hz, 1H, CH2-Bpin), 1.07 (dd, 2JHH = 15.0 Hz, 3JHH = 6.0 Hz,
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8715.
3
1H, CH2-Bpin), 0.84 (t, JHH = 7.0 Hz, 3H, Me), 0.38 (s, 6H, SiMe2).
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Au) are commercially available and have an average gold crystallite size
of ∼2−3 nm.
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(14) Reaction conditions with Pd and Pt catalysts: silylborane/
oxetane ratio 1/1, catalyst loading 2−5 mol %, toluene or 1,2-
dichloroethane (80 °C, 12 h). Reaction conditions with ionic Au
catalysts: silylborane/oxetane ratio 1/1, catalyst loading 5 mol %, 1,2-
dichloroethane (80 °C, 2 h).
13C NMR (125 MHz, CDCl3): δ 139.0 (Ph), 133.6 (2C, Ph), 129.2
(Ph), 127.6 (2C, Ph), 82.9 (2C, quaternary Bpin), 70.5 (C−O), 39.0
(aliphatic), 27.8 (aliphatic), 24.9 (2C, Me Bpin), 24.6 (2C, Me Bpin),
22.6 (aliphatic), 14.0 (Me), −0.8 (SiMe2), −0.9 (SiMe2). HRMS
(TOF-ESI): [M + H]+ calcd for C20H35BO3Si + H, 363.2521; found,
363.2521.
((2,3-Dimethylbut-3-en-2-yl)oxy)dimethyl(phenyl)silane (21a).
1H NMR (500 MHz, CDCl3): δ 7.65−7.62 (m, 2H, Ph), 7.39−7.35
2
4
(m, 3H, Ph), 4.98 (dq, JHH = 1.5 Hz, JHH = 1.5 Hz, 1H, olefinic C−
2
4
H), 4.75 (dq, JHH = 1.5 Hz, JHH = 1.5 Hz, 1H, olefinic C−H), 1.81
4
4
(dd, JHH = 1.5 Hz, JHH = 1.0 Hz, 3H, allylic Me), 1.37 (s, 6H, Me),
0.40 (s, 6H, SiMe2). 13C NMR (125 MHz, CDCl3): δ 152.0 (olefinic),
140.3 (Ph), 133.3 (2C, Ph), 129.1 (Ph), 127.6 (2C, Ph), 108.6
(olefinic), 76.3 (C−O), 29.6 (2C, Me), 19.0 (allylic Me), 1.2 (2C,
SiMe2). HRMS (TOF-ESI): [M + H]+ calcd for C14H22OSi + H,
235.1513; found, 235.1511.
ASSOCIATED CONTENT
■
S
* Supporting Information
(15) Raptis, C.; Garcia, H.; Stratakis, M. Angew. Chem., Int. Ed. 2009,
48, 3133−3136.
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.6b00465.
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AUTHOR INFORMATION
■
(18) Coppi, D. I.; Salomone, A.; Perna, F. M.; Capriati, V. Chem.
Commun. 2011, 47, 9918−9920.
Corresponding Author
*E-mail for M.S.: stratakis@uoc.gr.
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Notes
The authors declare no competing financial interest.
(20) The insertion of a Au nanoparticle on σ heteroatom bonds (Si−
H, Si−Si, Si−B) has been postulated earlier by our group on several
occasions: (a) Lykakis, I. N.; Psyllaki, A.; Stratakis, M. J. Am. Chem.
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ACKNOWLEDGMENTS
■
We thank ProFI (ITE, Heraklion, Greece) for obtaining the
HRMS spectra and ELKE, University of Crete (program KA
4066), for financial support.
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DOI: 10.1021/acs.organomet.6b00465
Organometallics XXXX, XXX, XXX−XXX

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H
DOI: 10.1021/acs.organomet.6b00465
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