Modular approach to reductive Csp2-H and Csp3-H silylation of carboxylic acid derivatives through single-pot, sequential transition metal catalysis

Article abstract of DOI:10.1021/acs.joc.5b00564

We report a modular approach to catalytic reductive C_sp2-H and C_sp3-H silylation of carboxylic acid derivatives encompassing esters, ketones, and aldehydes. Choice of either an Ir(I)/Rh(I) or Rh(I)/Rh(I) sequence leads to either exhaustive reductive ester or reductive ketone/aldehyde silylation, respectively. Notably, a catalyst-controlled direct formation of doubly reduced silyl ethers is presented, specifically via Ir-catalyzed exhaustive hydrosilylation. The resulting silyl ethers undergo C_sp2-H and benzylic C_sp3-H silylation in a single vessel.

Full text of DOI:10.1021/acs.joc.5b00564

Article
pubs.acs.org/joc
Modular Approach to Reductive Csp2−H and Csp3−H Silylation of
Carboxylic Acid Derivatives through Single-Pot, Sequential
Transition Metal Catalysis
Yuanda Hua, Seongjeong Jung, James Roh, and Junha Jeon*
Department of Chemistry and Biochemistry, University of Texas at Arlington, Arlington, Texas 76019, United States
S
* Supporting Information
ABSTRACT: We report a modular approach to catalytic
reductive Csp2−H and Csp3−H silylation of carboxylic acid
derivatives encompassing esters, ketones, and aldehydes.
Choice of either an Ir(I)/Rh(I) or Rh(I)/Rh(I) sequence
leads to either exhaustive reductive ester or reductive ketone/
aldehyde silylation, respectively. Notably, a catalyst-controlled
direct formation of doubly reduced silyl ethers is presented,
specifically via Ir-catalyzed exhaustive hydrosilylation. The
resulting silyl ethers undergo Csp2−H and benzylic Csp3−H
silylation in a single vessel.
INTRODUCTION
RESULTS AND DISCUSSION
■
■
We envision the development of a modular method for catalytic
dehydrogenative C−H silylation of aromatic carboxylic acid
derivatives through a single-pot, sequential transition metal-
mediated reductive silylation directed by dialkylhydridosilyl
ethers generated in situ (Scheme 1). We recently demonstrated
Strategies for transition metal (TM)-catalyzed C−H activation
and silylation have emerged as important tools for selective
synthesis of functionalized aryl silanes.1 Because organosilanes
are generally environmentally benign, they are widely utilized for
biological applications,2 drug discovery,3 and synthesis of
advanced functional materials.4 Particularly, cyclic silyl ethers,
such as benzoxasiloles and benzoxasilines, have been utilized for
complex molecule synthesis.5 They are also extensively exploited
as cross-coupling partners for silicon-based cross-coupling
tactics, such as Hiyama−Denmark aryl/alkenyl cross-couplin-
g5a,6 or Pd- and Cu-catalyzed alkyl/aryl/alkenyl cross-coupling
using benzoxasilole transfer agents,7 through putative cyclic
penta-coordinate silicate complexes. Thus, several developments
to metal-catalyzed Csp2−H and Csp3−H silylations have been
made.8−16 Hartwig has recently demonstrated methods for in
situ introduction of silyl groups into molecules followed by
annulation of dialkylhydridosilyl intermediates. For instance,
highly efficient Ir-catalyzed reductive Csp2−H and Csp3−H
silylation introducing a dialkylhydridosilyl group through Ir-
catalyzed hydrosilylation of aldehydes and ketones as well as
dehydrogenative silylation of alcohols and challenging amines
have been developed.8f,9a,f However, sequential dehydrogenative
silylation via catalytic exhaustive hydrosilylation of easily
accessible aromatic esters17−19 followed by C−H silylation for
direct synthesis of benzoxasiloles and benzoxasilines has not
been reported to date. In addition, primary alcohol-derived
dialkylhydridosilyl ether-directed, Rh-catalyzed dehydrogenative
Csp3−H silylation has not been described in the literature.
Herein, we report a modular approach for catalytic reductive
Csp2−H and Csp3−H silylation of diverse carboxylic acid
derivatives, including esters, ketones, and aldehydes.
Scheme 1. Modular Approach for Catalytic Reductive Csp2−H
and Csp3−H Silylation of Carboxylic Acid Derivatives
Providing Direct Access to Benzoxasiloles and Benzoxasilines
the synthesis of aryl o-formyl silanols via reductive arene o-
silanolization of aromatic esters.20 During the study, we
recognized that the judicious choice of transition metals and
supporting ligands for hydrosilylation of carboxylic acid
derivatives,17−19 as well as C−H silylation, significantly impacted
the overall efficiency of the single-pot sequence. Because of the
importance of a sequential transition metal-catalyzed reaction in
Received: March 12, 2015
© XXXX American Chemical Society
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DOI: 10.1021/acs.joc.5b00564
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the reductive arene o-C−H silylation of aromatic carboxylic acid
derivatives, we planned to explore an Ir(I)/Rh(I)-mediated
catalytic cascade for esters and a Rh(I)/Rh(I)-mediated catalytic
sequence for ketones and aldehydes, which would directly
provide corresponding cyclic silyl ethers.
(comparatively, silyl ethers derived from diethylsilane were
considerably unstable under the reaction conditions). In
addition, we examined various monodentate phosphine (Table
1, entries 1−7) and phosphite (entries 8−9) ligands to discover
In our previous report examining controlled Ir-catalyzed ester
hydrosilylation of esters (1) to afford silyl acetals (2),18a,20 we
found the formation of doubly reduced cyclic silyl ethers (5) as
minor byproducts, which were only observed when arenes
possessing electron-donating groups, such as an amino group or
unprotected indole, were used (Scheme 2). Under these reaction
Table 1. Evaluation of Ligands for Sequential, Exhaustive,
Reductive Arene o-C−H Silylation
a
Scheme 2. Controlled Access to Either Cyclic Silyl Acetals (3)
or Cyclic Silyl Ethers (5) from Aromatic Esters (6)
b
c
d
entry
ligand (deg)
PPh3
conv. (%)
2a yield (%)
1
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
97
10
91
99
10
45
75
63
64
42
47
80
90
71
72
2
P(o-tol)3
3
P(2-furyl)3
4
P(4-MeOPh)3
P(t-Bu)3
5
6
PCy3
7
RuPhos
8
P(OEt)3
9
P(OPh)3
10
11
12
13
14
15
dppm (72°)
dppe (85°)
dppp (91°)
dppb (98°)
BINAP (92°)
Xantphos (107°)
a
Conditions: (i) 1a (0.2 mmol) in CH2Cl2 (3.3 M), (ii) THF (1 M).
Nbd = norbornadiene; nbe = norbornene; RuPhos = 2-dicyclohexyl-
phosphino-2′,6′-diisopropoxybiphenyl; dppm = bis(diphenyl-
phosphino)methane; dppe = 1,2-bis(diphenylphosphino)ethane;
dppp = 1,3-bis(diphenylphosphino)propane; dppb = 1,4-bis(diphenyl-
phosphino)butane; BINAP = 2,2′-bis(diphenylphosphino)-1,1′-bi-
naphthyl; XantPhos = 4,5-bis(diphenylphosphino)-9,9-dimethylxan-
b
c
conditions, doubly reduced silyl ether intermediates (5) were
first produced, which underwent subsequent C−H silylation to
yield benzoxasiloles (6). We speculated that facile departure of
the alkoxy group likely generates silyl oxocarbenium inter-
mediates while producing silyl ethers ([Si]-OR2), which were
further reduced in the presence of external dialkyl silanes and
metal.21 We also considered an alternative route for the
formation of undesired doubly reduced ethers (4) via a
competing pathway (2 to 4), namely, the elimination of siloxanes
([Si]-O-[Si]) followed by metal hydride reduction of the
resulting oxocarbenium intermediates.21 Our approach requires
suitable catalytic conditions favoring selective access to silyl ether
intermediates (5) over doubly reduced ethers (4) in the catalytic
cascade, which ultimately leads to single-pot, exhaustive,
reductive arene o-silylation.
As mentioned earlier, we observed the formation of
exhaustively reduced silyl ethers (5) from arenes holding
electron-donating groups (e.g., p-dimethylamino group) in our
previous study.20 We first sought a general protocol for a single-
pot, exhaustive, reductive silylation of aromatic esters by
sequencing two transition metals (Ir and Rh) regardless of
electronic differences of arenes or the impedance of silyl ether
(4) formation. To this end, we found that simply warming the
reaction permits exhaustive reductive silylation of the esters (1)
to occur via direct formation of hydridosilyl ether intermediates
(5).19d−g Diisopropylsilane was a particularly effective silylating
agent due to the superior stability of the resulting silyl ethers (6)
thene. The listed bite angles are from ref 22. Determined by GC/MS
analysis and 1H NMR spectroscopy utilizing an internal standard
d
1
(CH2Br2). Determined by H NMR spectroscopy.
conditions for efficient Rh-catalyzed exhaustive reductive arene
o-silylation, as Takai and we reported that monodentate
phosphines effect Rh-catalyzed C−H silylation.10e,20 As seen in
Table 1, electron donating and sterically less hindered
monodentate phosphine P(4-MeOPh)3 serves as the most
effective ligand (99% yield, entry 4) for arene o-C−H silylation of
aromatic esters. Notably, the Rh-catalyzed C−H silylation [0.4
mol % of Rh/(4-MeOPh)3P, 120 °C] was completed within 30
min.8f Other monodentate alkyl phosphines (entries 5−7) and
phosphites (entries 8−9) resulted in lower yields. With the
exception of BINAP and Xantphos (entries 14−15), bis-
phosphine ligands with larger ligand bite angles generally
increased product yields (entries 10−15).22
Upon the reaction conditions being optimized, the scope of
the exhaustive, reductive C−H silylation of aromatic esters was
explored and is shown in Table 2. Both electron-rich and
-deficient aromatic esters underwent exhaustive reductive arene
o-silylation to afford benzoxasiloles (6a−j) in good yields. Furan,
unprotected indole, silyl blocking group (TBS), and trisub-
stituted alkene within 6k−n tolerated the reaction conditions
well. We observed complete regioselectivity within naphthoates
(6o−p), where the C−H silylation of 1-naphthoate only
provided naphthoxasilole 6o via selective activation of kinetically
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a
Table 2. Substrate Scope of Aromatic Esters for Sequential, Exhaustive, Reductive Arene o-C−H Silylation
a
b
1
Conditions: (i) 1 (0.5 mmol) in CH2Cl2 (3.3 M), (ii) THF (1 M). TBS = t-Butyldimethylsilyl; pin = pinacolato. Determined by H NMR
c
d
e
f
spectroscopy utilizing an internal standard (CH2Br2). Yields of 6. Reaction at 80 °C for 4 d. Reaction at 80 °C for 7 d. 0.5 mol % of [Ir(coe)2Cl]2.
g
h
i
1 mol % of [Rh(nbd)Cl]2 and 6 mol % of P(4-MeOPh)3. Reaction at 100 °C for 1 h. 3.5 equiv of H2Sii-Pr2 was used.
acidic hydrogen at C2. In addition, 2-naphthoate yielded 6p as
the sole product, but the reasons behind the observed
regioselectivity are currently unclear.
Previously, Hartwig reported efficient sequential hydro-
silylation of aromatic aldehydes and ketones employing
[Ir(cod)OMe]2 and arene o-C−H silylation using [Ir(cod)-
OMe]2/phen.8f We examined whether the developed catalytic
system of rhodium(I) with monodentate phosphine ligand for
reductive arene o-C−H silylation of esters was also applicable for
reductive arene silylation of aromatic ketones (7, Table 3). In
these cases, we were able to achieve ketone hydrosilylation23 and
arene o-C−H silylation using a single loading of Rh catalyst [i.e.,
Rh/(4-MeOPh)3P] and lower the catalyst loading to 0.2 mol %.
The C−H silylation step required the supporting ligand (4-
MeOPh)3P for efficient annulation. On the basis of the brief
optimization, we probed the scope of arene o-C−H silylation
with aromatic ketones (7). Various para-substituted methyl
ketones provided desired benzoxasiloles 8b−f with good yields.
Substrates 7g−h possessing meta substituents (i.e., trifluoro-
methyl, internal alkyne) afforded benzoxasiloles 8g−h as the sole
C
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Table 3. Substrate Scope of Ketones for Sequential, Reductive
Arene o-C−H Silylation
Scheme 3. Competition of C−H Silylation and Alkene
Hydrosilylation
a
lower yields.8f,9f In addition, these outcomes also imply that
norbornene likely resides on a Rh coordination sphere despite
the fact that norbornene is commonly employed and understood
as an efficient hydrogen scavenger.24,25 When the annulation via
C−H activation is not facile, the alkene hydrosilylation competes
with the C−H silylation. To achieve efficient C−H silylation of
aromatic aldehydes, an additional Rh catalyst (0.4−0.6 mol %
relative to 0.2 mol % for ketones) was required (Table 4). Under
Table 4. Substrate Scope of Aldehydes for Sequential
a
Reductive Silylation
a
Conditions: (i) 7 (1.0 mmol) in THF (1 M), (ii) THF (1 M).
Yields of 8.
b
products with complete site-selectivity favoring functionalization
in less hindered C−H bonds. The more sterically congested
ortho-substituted ketone 7j also gave desired product 8j with
good yield. Sterically hindered isopropyl ketone 7j was examined
and yielded 8j in excellent yield. Finally, cyclic ketone, 1-
tetralone 7k provided tetrahydronaphthoxasilole 8k in 85% yield.
Next, we investigated the scope of arene o-C−H silylation with
aromatic aldehydes (9). Under identical reaction conditions to
the C−H silylation of ketones, we encountered inefficient
cyclization in which a significant amount of alkene hydro-
silylation adducts (11) were produced through the reaction
between hydridosilyl ether and norbornene (i.e., a hydrogen
acceptor) (Scheme 3). Notably, the tendency of the hydro-
silylation correlates well to the electronic nature of the
substituents on arenes. For instance, an electron-donating
group (e.g., Me) in 9a afforded more hydrosilylation adduct
11a (10a:11a = 1.0:1.3). However, electron-withdrawing
substituents, such as Cl and F, reduced the competitive
hydrosilylation process, favoring the formation of benzoxasiloles
(10c:11c = 1.0:1.0 and 10d:11d = 1.0:0.5, respectively). We did
not observe this behavior in the cases of reductive arene C−H
silylation of aromatic ketones and exhaustive reductive arene C−
H silylation of aromatic esters. These results indicate that the
relative rate of cyclization of aldehyde-derived hydridosilyl ethers
is slower than that of the ketone-derived hydridosilyl ethers, as
well as that of the diisopropylhydridosilyl ethers bearing larger
substituents. Thus, the slower the rate of C−H silylation, the
greater the impact of competitive hydrosilylation, resulting in
a
Conditions: (i) 9 (1.0 mmol) in THF (1.0 M), (ii) THF (1. M).
b
c
TIPS = triisopropylsilyl. Yields of 10. 0.6 mol % of [Rh(nbd)Cl]2
and 3.6 mol % of P(4-MeOPh)3.
the reaction conditions, several ortho-, meta-, and para-
substituted aromatic aldehydes (9) provided corresponding
benzoxasiloles 10a−h. Sterically hindered TIPS-protected
salicylic aldehyde 9i also afforded desired product 10i with
good yield.
Lastly, Rh-catalyzed reductive benzylic Csp3−H silylation
reactions of esters, ketones, and aldehydes were studied under
D
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the developed catalytic reaction conditions (Scheme 4). There
have been several reports of catalytic dehydrogenative benzylic
Csp3−H silylation of esters, ketones, and aldehydes to provide
benzoxasilines using either the Ir(I)/Rh(I) or Rh(I)/Rh(I)
catalytic sequence.
Scheme 4. Sequential, Exhaustive, Reductive Benzylic Csp3−H
Silylation of Aromatic Esters, Ketones, and Aldehydes
EXPERIMENTAL SECTION
■
General Experimental Information. Reactions requiring anhy-
drous conditions were performed under an atmosphere of nitrogen or
argon in flame- or oven-dried glassware. Anhydrous toluene and
dichloromethane (DCM) were distilled from CaH2. Anhydrous
tetrahydrofuran (THF) and diethyl ether (Et2O) were distilled from
sodium and benzophenone. Triethylamine and pyridine were distilled
from KOH. DMF and DMSO were stored over 4 Å molecular sieves. All
other solvents and reagents from commercial sources were used as
received. NMR spectra were recorded on a 500 or 300 MHz NMR
1
spectrometer. H NMR chemical shifts are referenced to chloroform
(7.26 ppm) and DMSO-d6 (2.50 ppm). 13C NMR chemical shifts are
referenced to 13CDCl3 (77.23 ppm) and DMSO-d6 (39.52 ppm). The
following abbreviations are used to describe multiplets: s (singlet), d
(doublet), t (triplet), q (quartet), pent (pentet), m (multiplet), nfom
(nonfirst-order multiplet), and br (broad). The following format was
used to report peaks: chemical shift in ppm [multiplicity, coupling
constant(s) in Hz, integral, and assignment]. 1H NMR assignments are
1
indicated by structure environment (e.g., CHaHb). H NMR and 13C
NMR were processed with the iNMR software program. Infrared (IR)
spectra were recorded using neat (for liquid compound) or a thin film
from a concentrated DCM solution. Absorptions are reported in cm−1.
Only the most intense and/or diagnostic peaks are reported. MPLC
refers to medium pressure liquid chromatography (25−200 psi) using
hand-packed columns of silica gel (20−45 μm, spherical, 70 Å pore size),
an HPLC pump, and a differential refractive index detector. High-
resolution mass spectra (HRMS) were recorded in electrospray
ionization time-of-flight (ESI-TOF) mode. Samples were introduced
as solutions in a mixed solution of methanol and methylene chloride
(DCM). GC-MS experiments using electron impact ionization (EI)
were performed at 70 eV using a mass-selective detector. The method
used is noted parenthetically: 5029017 refers to 2 min @ 50 °C − 20 °C/
min − 3 min @ 290 °C. Analytical TLC experiments were performed on
an F254 plate with 250 μm thickness. Detection was performed by UV
light or potassium phosphomolybdic acid, permanganate, and p-
anisaldehyde staining.
Csp3−H silylation.9a,f,c,11 For instance, Hartwig demonstrated
highly efficient Ir-catalyzed Csp3−H silylation directed by
dialkylhydridosilyl ethers derived from tertiary alcohols.
Although dialkylhydridosilyl ethers derived from secondary
alcohols, which specifically hold substituents β to the hydroxyl
groups, were also used for Ir-catalyzed Csp3−H silylation, no
example of primary alcohol-derived dialkylhydridosilyl ether-
directed dehydrogenative Csp3−H silylation has been reported.
When ester 12 was subjected to the catalytic reaction conditions,
sequential Ir- and Rh-catalyzed exhaustive, reductive Csp3−H
silylation indeed afforded benzoxasiline 13 in modest yield
(36%), primarily due to competitive alkene hydrosilylation
between the primary alcohol-derived hydridosilyl ether and
norbornene (C−H silylation:hydrosilylation = 1:1.5). Csp3−H
silylation of aldehyde 15 provided benzoxasiline 17 with modest
yield (43%), similar to those observed in esters, and Rh-catalyzed
reductive Csp3−H silylation of ketone 14 provided benzoxasiline
16 with good yield (84%) through relatively fast cyclization of the
ketone-derived silyl ether.
General Procedure for Ir-Catalyzed Exhaustive Reductive
Ester SilylationPreparation of Hydridodiisopropylsilyl Ethers
(5). [Ir(coe)2Cl]2 (0.5 mg, 0.1 mol %) and ester 1 (0.5 mmol) were
dissolved with CH2Cl2 (0.15 mL, 3.3 M). Diisopropylsilane (0.24 mL,
144 mg, 1.25 mmol) was added to the mixture in one portion. The
septum on the vial was replaced by a screw cap with a Teflon liner. The
reaction mixture was kept at 80 °C and stirred for 2 d unless otherwise
noted in Table 2. The volatiles were removed in vacuo to afford the
hydridodiisopropylsilyl ethers (5), which were directly used for
subsequent reactions without further purification. The yield of 5 was
determined by 1H NMR spectroscopy by the addition of CH2Br2 (0.5
mmol) as an internal standard after the volatiles were removed in vacuo.
General Procedure for Rh-Catalyzed Arene o-C−H Silylation
of Hydridodiisopropylsilyl EthersPreparation of Benzoxasi-
lole (6). [Rh(nbd)Cl]2 (0.9 mg, 0.4 mol %), tris(4-methoxyphenyl)-
phosphine (4.2 mg, 2.4 mol %), norbornene (94 mg, 2 mmol), and THF
(0.25 mL, 2 M) were added to the crude mixture of silyl ethers (5) (0.5
mmol). The septum on the vial was replaced by a screw cap with a
Teflon liner, and the mixture was stirred at 120 °C for 30 min. The
reaction progress was monitored by GC-MS spectrometry. The reaction
was cooled to room temperature. The volatiles were removed in vacuo,
and the crude mixture was purified by MPLC to afford benzoxasilole 6
(hexanes/EtOAc = 40:1, 7 mL/min, 6−10 min).
CONCLUSION
■
In summary, we have developed a modular catalytic reductive
C−H silylation of carboxylic acid derivatives via selective Csp2−H
and Csp3−H activation to provide benzoxasiloles and benzoxasi-
lines. A relay of Ir/Rh or Rh/Rh catalytic systems permits C−H
silylation for esters, ketones, and aldehydes. Exhaustive, reductive
arene o-C−H silylation of esters requires sequential Ir (0.1 mol
%) and Rh/(4-MeOPh)3P (0.4 mol %) catalytic conditions.
Whereas reductive arene o-C−H silylation of ketones afforded
diverse benzoxasiloles with good yields using Rh/(4-MeOPh)3P
(0.2 mol %), the reductive arene silylation of aldehydes was
hindered due to competitive alkene hydrosilylation of
norbornene. This was resolved by employing 0.4−0.6 mol % of
Rh/(4-MeOPh)3P. Finally, we examined reductive benzylic
1,1-Diisopropyl-1,3-dihydrobenzo[c][1,2]oxasilole (6a). Yield
1
(91%, 100.1 mg); clear oil; H NMR (CDCl3, 500 MHz) δ 7.57 (d, J
= 7.2 Hz, 1H), 7.39 (dd, J = 7.7, 7.5 Hz, 1H), 7.28 (dd, J = 7.5, 7.2 Hz,
1H), 7.24 (d, J = 7.7 Hz, 1H), 5.14 (s, 2H), 1.24 (septet, J = 7.4 Hz, 2H),
1.03 (d, J = 7.4 Hz, 6H), 1.01 (d, J = 7.4 Hz, 6H); 13C{1H} NMR
(CDCl3, 125 MHz) δ 151.0, 132.3, 131.9, 129.7, 126.7, 121.7, 72.7, 17.2,
E
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13.3; IR (neat) 3001 (w), 2942 (m), 1463 (s), 1225 (s), 1044 (s), 1030
(s), 879 (s) cm−1; TLC Rf = 0.6 in 20:1 hexanes:EtOAc; GC-MS
(5029017) tR = 10.389 min, m/z 221 [(M + H)+, 5], 220 (M+, 18), 219
[(M − H)+, 100], 177 [(M − iPr)+, 2]; HRMS (ESI/TOF) calcd for [M
+ H]+ [C13H21OSi]+ 221.1356, found 221.1338.
iPr)+, 91]; HRMS (ESI/TOF) calcd for [M + Na]+ [C14H22NaO2Si]+
273.1281, found 273.1264.
1,1-Diisopropyl-5-methoxy-1,3-dihydrobenzo[c][1,2]oxasilole
(6h). Yield (84%, 105.1 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ
7.46 (d, J = 8.0 Hz, 1H), 6.83 (dd, J = 8.0, 2.3 Hz, 1H), 6.75 (d, J = 2.3
Hz, 1H), 5.09 (s, 2H), 3.82 (s, 3H), 1.23 (septet, J = 7.4 Hz, 2H), 1.01
(d, J = 7.4 Hz, 6H), 0.99 (d, J = 7.4 Hz, 6H); 13C{1H} NMR (CDCl3,
125 MHz) δ 161.5, 153.3, 133.4, 122.7, 114.0, 106.4, 72.5, 55.3, 17.2 (2),
13.3; IR (neat) 2941 (w), 1597 (m), 1462 (m), 1238 (s), 1049 (s), 1044
(s), 781 (s) cm−1; TLC Rf = 0.4 in 20:1 hexanes:EtOAc; GC-MS
(5029017) tR i= 10.513 min, m/z 250 (M+, 30), 249 [(M − H)+, 100],
207 [(M − Pr)+, 61]; HRMS (ESI/TOF) calcd for [M + Na]+
[C14H22NaO2Si]+ 273.1281, found 273.1275.
1,1-Diisopropyl-4-methoxy-1,3-dihydrobenzo[c][1,2]oxasilole
(6i). Yield (90%, 112.5 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ
7.30 (dd, J = 7.9, 7.1 Hz, 1H), 7.15 (d, J = 7.1 Hz, 1H), 6.86 (d, J = 7.9
Hz, 1H), 5.13 (s, 2H), 3.83 (s, 3H), 1.24 (septet, J = 7.4 Hz, 2H), 1.04
(d, J = 7.4 Hz, 6H), 1.02 (d, J = 7.4 Hz, 6H); 13C{1H} NMR (CDCl3,
125 MHz) δ 154.4, 139.0, 133.8, 128.5, 123.9, 110.6, 70.5, 54.9, 17.2 (2),
13.2; IR (neat) 2941 (w), 1568 (m), 1464 (m), 1255 (s), 1036 (s), 744
(s) cm−1; TLC Rf = 0.4 in 20:1 hexanes:EtOAc; GC-MS (5029017) tR =
10.377 min, m/z 250 (M+, 37), 249 [(M − H)+, 100], 207 [(M − iPr)+,
32]; HRMS (ESI/TOF) calcd for [M + Na]+ [C14H22NaO2Si]+
273.1281, found 273.1269.
6-Fluoro-1,1-diisopropyl-1,3-dihydrobenzo[c][1,2]oxasilole (6b).
1
Yield (72%, 85.6 mg); clear oil; H NMR (CDCl3, 500 MHz) δ 7.21
[dd, J = 7.8 (J3F−H), 2.5 Hz, 1H], 7.18 [dd, J = 8.4, 4.6 (J4F−H) Hz, 1H],
7.07 [dd, J = 8.4, 8.4 (J3F−H), 2.5 Hz, 1H], 5.10 (s, 2H), 1.23 (septet, J =
7.4 Hz, 2H), 1.02 (d, J = 7.4 Hz, 6H), 1.00 (d, J = 7.4 Hz, 6H); 13C{1H}
NMR (CDCl3, 125 MHz) δ 162.2 (d, J1F−C = 249 Hz), 146.2 (d, J4
=
F−C
1.8 Hz), 134.8 (d, J3F−C = 4.9 Hz), 123.2 (d, J3F−C = 8.2 Hz), 118.0 (d,
J2F−C = 20.4 Hz), 117.14 (d, J2F−C = 22.9 Hz), 72.3, 17.10, 17.08, 13.2; IR
(neat) 2943 (w), 1461 (s), 1255 (s), 1124 (s), 632 (s) cm−1; TLC Rf =
0.6 in 20:1 hexanes:EtOAc; GC-MS (5029017) tR = 8.924 min, m/z 237
[(M − H)+, 100], 195 [(M − iPr)+, 28], 107 (55); HRMS (ESI/TOF)
calcd for [M + H]+ [C13H20FOSi]+ 239.1262, found 239.1247.
6-Chloro-1,1-diisopropyl-1,3-dihydrobenzo[c][1,2]oxasilole (6c).
Yield (82%, 104.1 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ 7.50
(d, J = 2.1 Hz, 1H), 7.35 (dd, J = 8.2, 2.1 Hz, 1H), 7.15 (d, J = 8.2 Hz,
1H), 5.09 (s, 2H), 1.23 (septet, J = 7.4 Hz, 2H), 1.02 (d, J = 7.4 Hz, 6H),
1.00 (d, J = 7.4 Hz, 6H); 13C{1H} NMR (CDCl3, 125 MHz) δ 149.2,
134.8, 133.1, 131.8, 129.9, 123.1, 72.3, 17.1 (2), 13.2; IR (neat) 2943
(w), 1461 (m), 1046 (s), 879 (s), 782 (s) cm−1; TLC Rf = 0.5 in 20:1
hexanes:EtOAc; GC-MS (5029017) tR = 10.097 min, m/z 255 [(M + 2-
H)+, 33], 253 [(M − H)+, 100], 213 [(M + 2-iPr)+, 10], 211 [(M − iPr)+,
30]; HRMS (ESI/TOF) calcd for [M + H]+ [C13H20ClOSi]+ 255.0966,
found 255.0949.
1,1-Diisopropyl-N,N-dimethyl-1,3-dihydrobenzo[c][1,2]oxasilol-6-
1
amine (6j). Yield (96%, 126.2 mg); clear oil; H NMR (CDCl3, 500
MHz) δ 7.11 (d, J = 8.4 Hz, 1H), 6.90 (d, J = 2.5 Hz, 1H), 6.85 (dd, J =
8.4, 2.5 Hz, 1H), 5.08 (s, 2H), 2.97 (s, 6H), 1.23 (septet, J = 7.4 Hz, 2H),
1.05 (d, J = 7.4 Hz, 6H), 1.02 (d, J = 7.4 Hz, 6H); 13C{1H} NMR
(CDCl3, 125 MHz) δ 149.7, 139.3, 132.8, 122.1, 115.48, 115.39, 72.3,
41.3, 17.29, 17.23, 13.3; IR (neat) 2941 (w), 1684 (m), 1487 (m), 1341
(m), 1171 (s), 1040 (s), 783 (s) cm−1; TLC Rf = 0.4 in 20:1
hexanes:EtOAc; GC-MS (5029017) tR = 11.168 min, m/z 264 [(M +
H)+, 42], 263 (M+, 100), 262 [(M − H)+, 39], 220 [(M − iPr)+, 60];
HRMS (ESI/TOF) calcd for [M + Na]+ [C15H25NNaOSi]+ 286.1598,
found 286.1605.
1,1-Diisopropyl-1,3-dihydrofuro[3,2-c][1,2]oxasilole (6k). Yield
(52%, 54.6 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ 7.50 (d, J =
1.7 Hz, 1H), 6.36 (d, J = 1.7 Hz, 1H), 4.83 (s, 2H), 1.13 (septet, J = 7.2
Hz, 2H), 1.00 (d, J = 7.2 Hz, 6H), 0.99 (d, J = 7.2 Hz, 6H); 13C{1H}
NMR (CDCl3, 125 MHz) δ 169.1, 146.3, 111.7, 111.5, 65.1, 17.15,
17.00, 13.4; IR (neat) 2944 (w), 1462 (m), 1133 (s), 1051 (s), 881 (s)
cm−1; TLC Rf = 0.5 in 20:1 hexanes:EtOAc; GC-MS (5029017) tR =
9.135 min, m/z 210 (M+, 7), 209 [(M − H)+, 37], 167 [(M − iPr)+, 4],
141 (100); HRMS (ESI/TOF) calcd for [M + H]+ [C11H19O2Si]+
211.1149, found 211.1137.
8-(Diisopropylsilyl)-1,1-diisopropyl-3,8-dihydro-1H-[1,2]oxasilolo-
[3,4-b]indole (6l). Yield (97%, 180.9 mg); clear oil; 1H NMR (CDCl3,
500 MHz) δ 7.51 (d, J = 7.8 Hz, 1H), 7.47 (d, J = 8.3 Hz, 1H), 7.23 (dd, J
= 8.3, 7.1 Hz, 1H), 7.15 (dd, J = 7.8, 7.1 Hz, 1H), 5.22 (s, 2H), 4.58 (t, J =
4.3 Hz, 1H), 1.13 (septet of d, J = 7.4, 4.3 Hz, 2H), 1.32 (septet, J = 7.5
Hz, 2H), 1.21 (d, J = 7.4 Hz, 6H), 1.13 (d, J = 7.4 Hz, 6H), 1.06 (d, J =
7.5 Hz, 6H), 1.01 (d, J = 7.5 Hz, 6H); 13C{1H} NMR (CDCl3, 125
MHz) δ 147.6, 142.7, 138.3, 126.7, 122.7, 120.0, 119.5, 113.6, 66.4, 18.8,
18.4, 17.6, 17.4, 13.8, 12.8; IR (neat) 2942 (m), 2142 (w), 1501 (m),
1277 (s), 1034 (s), 739 (s) cm−1; TLC Rf = 0.6 in 20:1 hexanes:EtOAc;
GC-MS (5029017) tR = 13.885 min, m/z 374 [(M + H)+, 100], 373 (M+,
50), 330 [(M − iPr)+, 21], 258 [(M − SiiPr2H)+, 7]; HRMS (ESI/TOF)
calcd for [M + H]+ [C21H36NOSi2]+ 374.2330, found 374.2314.
6-[{(tert-Butyldimethylsilyl)oxy}methyl]-1,1-diisopropyl-1,3-
dihydrobenzo[c][1,2]oxasilole (6m). Yield (90%, 163.8 mg); clear oil;
1H NMR (CDCl3, 500 MHz) δ 7.51 (d, J = 1.6 Hz, 1H), 7.35 (dd, J = 7.9,
1.6 Hz, 1H), 7.18 (d, J = 7.9 Hz, 1H), 5.12 (s, 2H), 4.78 (s, 2H), 1.23
(septet, J = 7.4 Hz, 2H), 1.02 (d, J = 7.4 Hz, 6H), 0.99 (d, J = 7.4 Hz,
6H), 0.93 (s, 9H), 0.09 (s, 6H); 13C{1H} NMR (CDCl3, 125 MHz) δ
149.8, 139.8, 131.9, 130.0, 128.1, 121.5, 72.6, 65.3, 26.2, 18.6, 17.2 (2),
13.3, −5.0; IR (neat) 2943 (w), 1462 (m), 1253 (s), 1087 (s), 1046 (s),
835 (s) cm−1; TLC Rf = 0.55 in 20:1 hexanes:EtOAc; GC-MS
(5029017) tR = 12.347 min, m/z 365 [(M + H)+, 29], 364 (M+, 100),
1,1-Diisopropyl-6-(trifluoromethyl)-1,3-dihydrobenzo[c][1,2]-
oxasilole (6d). Yield (71%, 102.2 mg); clear oil; 1H NMR (CDCl3, 500
MHz) δ 7.80 (s, 1H), 7.63 (d, J = 8.0 Hz, 1H), 7.33 (d, J = 8.0 Hz, 1H),
5.17 (s, 2H), 1.26 (septet, J = 7.4 Hz, 2H), 1.02 (d, J = 7.4 Hz, 6H), 1.01
(d, J = 7.4 Hz, 6H); 13C{1H} NMR (CDCl3, 125 MHz) δ 154.8, 133.4,
129.4 (q, J2F−C = 32.3 Hz), 128.9 (q, J3F−C = 3.9 Hz), 126.8 (q, J3
=
F−C
3.5 Hz), 124.7 (q, J1F−C = 272.2 Hz), 122.1, 72.4, 17.06, 17.04, 13.1; IR
(neat) 2945 (w), 1463 (w), 1324 (s), 1123 (s), 1077 (s), 785 (s) cm−1;
TLC Rf = 0.5 in 20:1 hexanes:EtOAc; GC-MS (5029017) tR = 8.610
min, m/z 287 [(M − H)+, 8], 269 [(M − F)+, 100], 245 [(M − iPr)+, 2];
HRMS (ESI/TOF) calcd for [M + H]+ [C14H20F3OSi]+ 289.1230,
found 289.1239.
1,1-Diisopropyl-5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
1,3-dihydrobenzo[c][1,2]oxasilole (6e). Yield (88%, 152.2 mg); clear
oil; 1H NMR (CDCl3, 500 MHz) δ 7.72 (d, J = 7.2 Hz, 1H), 7.69 (s,
1H), 7.59 (d, J = 7.2 Hz, 1H), 5.14 (s, 2H), 1.35 (s, 12H), 1.23 (septet, J
= 7.4 Hz, 2H), 1.01 (d, J = 7.4 Hz, 6H), 0.99 (d, J = 7.4 Hz, 6H); 13C{1H}
NMR (CDCl3, 125 MHz) δ 150.3, 135.8, 132.8 (2), 131.7, 127.8, 84.1,
72.6, 25.1, 17.18, 17.16, 13.3; IR (neat) 2978 (w), 2942 (w), 1381 (s),
1213 (s), 1093 (s), 1047 (s), 672 (s) cm−1; TLC Rf = 0.4 in 20:1
hexanes:EtOAc; GC-MS (5029017) tR = 12.871 min, m/z 346 (M+, 30),
345 [(M − H)+, 100], 303 [(M − iPr)+, 48]; HRMS (ESI/TOF) calcd
for [M + H]+ [C19H32BO3Si]+ 347.2208, found 347.2226.
1,1-Diisopropyl-6-methyl-1,3-dihydrobenzo[c][1,2]oxasilole (6f).
Yield (92%, 107.6 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ 7.37
(s, 1H), 7.21 (d, J = 7.8 Hz, 1H), 7.12 (d, J = 7.8 Hz, 1H), 5.12 (s, 2H),
2.39 (s, 3H), 1.24 (septet, J = 7.4 Hz, 2H), 1.04 (d, J = 7.4 Hz, 6H), 1.02
(d, J = 7.4 Hz, 6H); 13C{1H} NMR (CDCl3, 125 MHz) δ 148.1, 136.0,
132.6, 132.0, 130.8, 121.4, 72.5, 21.4, 17.2 (2), 13.3; IR (neat) 2955 (w),
1685 (s), 1200 (m), 1039 (s), 1003 (s), 707 (s) cm−1; TLC Rf = 0.55 in
20:1 hexanes:EtOAc; GC-MS (5029017) tR = 9.440 min, m/z 234 (M+,
20), 233 [(M − H)+, 100], 191 [(M − iPr)+, 30]; HRMS (ESI/TOF)
calcd for [M + H]+ [C14H23OSi]+ 235.1513, found 235.1502.
1,1-Diisopropyl-6-methoxy-1,3-dihydrobenzo[c][1,2]oxasilole
(6g). Yield (95%, 118.7 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ
7.14 (d, J = 8.3 Hz, 1H), 7.05 (d, J = 2.5 Hz, 1H), 6.95 (dd, J = 8.3, 2.5
Hz, 1H), 5.08 (s, 2H), 3.83 (s, 3H), 1.23 (septet, J = 7.4 Hz, 2H), 1.03
(d, J = 7.4 Hz, 6H), 1.01 (d, J = 7.4 Hz, 6H); 13C{1H} NMR (CDCl3,
125 MHz) δ 158.6, 143.0, 133.6, 122.6, 116.32, 116.23, 72.3, 55.6, 17.18,
17.14, 13.2; IR (neat) 2942 (w), 1463 (s), 1224 (s), 1039 (s), 1044 (s),
879 (s) cm−1; TLC Rf = 0.4 in 20:1 hexanes:EtOAc; GC-MS (5029017)
tR = 10.328 min, m/z 250 (M+, 70), 249 [(M − H)+, 100], 207 [(M −
F
DOI: 10.1021/acs.joc.5b00564
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
321 [(M − iPr)+, 7], 307[(M − tBu)+, 21]; HRMS (ESI/TOF) calcd for
CH2Cl2 (10 mL, 0.3 M), and the solution was kept at 0 °C with an ice
bath. NBS (552 mg, 3.1 mmol) was added in one portion. After being
stirred for 5 min at 0 °C, the reaction mixture was warmed to rt and
stirred for 2 h. Pyridine (0.31 mL, 3.6 mmol) and 1-(3-hydroxyphenyl)-
ethanone (449 mg, 3.3 mmol) in CH2Cl2 (3 mL) were added to the
reaction mixture. The mixture was stirred for 2 h at rt. The volatiles were
removed in vacuo, and the residue was dissolved with pentane and
filtered through a pad of Celite. The volatiles were removed in vacuo,
and the crude mixture was purified by MPLC to afford ketone 7h (0.94
g, 91%) (hexanes/EtOAc = 60:1, 7 mL/min, 7 min).
[M + Na]+ [C20H36NaO2Si2]+ 387.2146, found 387.2129.
1,1-Diisopropyl-6-((3-methylbut-2-en-1-yl)oxy)-1,3-dihydro-
benzo[c][1,2]oxasilole (6n). 6n contains double bond migration
byproduct (1,1-disubstituted alkene 6n′). The ratio of the two
compounds (6n:6n′) is approximately 1:0.08. Combined yield (70%,
106.3 mg); clear oil; 1H NMR (CDCl3, 300 MHz) δ 7.13 (d, J = 8.4 Hz,
1H), 7.07 (d, J = 2.5 Hz, 1H), 6.97 (dd, J = 8.4, 2.5 Hz, 1H), 5.51 (tp, J =
6.8, 1.4 Hz, 1H), 5.08 (s, 2H), 4.86 (app s, 0.08H, 6n′), 4.82 (app s,
0.08H, 6n′), 4.54 (d, J = 6.8 Hz, 2H), 4.10 (t, J = 6.8 Hz, 0.16H, 6n′),
2.52 (t, J = 6.8 Hz, 0.16H, 6n′), 1.82 (s, 0.24H, 6n′), 1.80 (s, 3H), 1.76
(s, 3H), 1.22 (septet, J = 7.3 Hz, 2H), 1.02 (d, J = 7.3 Hz, 6H), 1.00 (d, J
= 7.3 Hz, 6H); 13C{1H} NMR (CDCl3, 75 MHz) only for 6n δ 157.9,
142.9, 138.4, 133.5, 122.5, 120.0, 117.4, 116.9, 72.3, 65.1, 26.1, 18.4, 17.2
(2), 13.3; IR (neat) 2941 (w), 1597 (w), 1563 (w), 1462 (m), 1216 (s),
1045 (s), 880 (s) cm−1; TLC Rf = 0.5 in 20:1 hexanes:EtOAc; GC-MS
(5029017) tR = 12.186 min, m/z 304 (M+, 26), 303 [(M − H)+, 100],
236 [(M − isoprenyl)+, 59]; HRMS (ESI/TOF) calcd for [M + H]+
[C18H29O2Si]+ 305.1931, found 305.1929.
7h: clear oil; 1H NMR (CDCl3, 500 MHz) δ 7.65 (app t, J = 2.0 Hz,
1H), 7.56 (ddd, J = 7.5, 1.5, 1.5 Hz, 1H), 7.32 (dd, J = 8.1, 7.5 Hz, 1H),
7.24 (ddd, J = 8.1, 2.5, 1.5 Hz, 1H), 2.57 (s, 3H), 1.17−1.11 (m, 2H),
1.09 (d, J = 6.2 Hz, 6H), 1.08 (d, J = 6.2 Hz, 6H), 0.18 (s, 9H); 13C{1H}
NMR (CDCl3, 125 MHz) δ 197.9, 155.9, 138.5, 129.4, 124.9, 121.7,
119.7, 118.7, 107.2, 26.8, 17.21, 17.07, 13.1, 0.2; IR (neat) 2947 (w),
2107 (w), 1688 (s), 1464 (w), 1278 (s), 1250 (s), 841 (s), 784 (s), 686
(s) cm−1; TLC Rf = 0.6 in 20:1 hexanes:EtOAc; GC-MS (5029017) tR =
11.710 min, m/z 347 [(M + H)+, 51], 346 (M+, 49), 345 [(M − H)+,
27], 331 [(M − Me)+, 100], 345 [(M − iPr)+, 8]; HRMS (ESI/TOF)
calcd for [M + H]+ [C19H31O2Si2]+ 347.1857, found 347.1839.
General Procedure for Rh-Catalyzed Sequential, Reductive
Arene o-C−H Silylation of Aromatic Ketones (8). [Rh(nbd)Cl]2
(0.9 mg, 0.2 mol %), tris(4-methoxyphenyl)phosphine (4.3 mg, 1.2 mol
%), and ketone 7 (1 mmol) were dissolved in THF (1 mL, 1 M).
Diethylsilane (0.28 mL, 173 mg, 2 mmol) was added to the mixture. The
septum on the vial was replaced by a screw cap with a Teflon liner. The
reaction mixture was kept at rt and stirred for 20 min. The volatiles were
removed in vacuo to afford the crude hydridodiethylsilyl ethers, which
were directly used for subsequent reactions without further purification.
Norbornene (188 mg, 2 mmol) and THF (1 mL, 1 M) were added to
the crude silyl ether reaction mixture. The septum on the vial was
replaced by a screw cap with a Teflon liner, and the mixture was stirred at
120 °C for 0.5−1.5 h. The reaction progress was monitored by GC-MS
spectrometry. The reaction was cooled to room temperature. The
volatiles were removed in vacuo, and the crude mixture was purified by
MPLC to afford benzoxasilole 8 (hexanes/EtOAc = 60:1, 7 mL/min,
10−15 min).
3,3-Diisopropyl-1,3-dihydronaphtho[2,1-c][1,2]oxasilole (6o).
1
Yield (75%, 101.3 mg); clear oil; H NMR (CDCl3, 500 MHz) δ
7.95−7.90 (m, 1H), 7.80 (d, J = 8.0 Hz, 1H), 7.74−7.69 (m, 1H), 7.62
(d, J = 8.0 Hz, 1H), 7.58−7.51 (m, 2H), 5.61 (s, 2H), 1.31 (septet, J = 7.5
Hz, 2H), 1.07 (d, J = 7.5 Hz, 6H), 1.05 (d, J = 7.5 Hz, 6H); 13C{1H}
NMR (CDCl3, 125 MHz) δ 148.5, 134.2, 129.5, 128.8, 128.14, 128.09,
127.3, 126.7, 126.4, 123.2, 72.1, 17.28, 17.23, 13.4; IR (neat) 2941 (w),
1508 (w), 1461 (m), 1070 (s), 1025 (s), 880 (s) cm−1; TLC Rf = 0.5 in
20:1 hexanes:EtOAc; GC-MS (5029017) tR = 12.286 min, m/z 270 (M+,
72), 269 [(M − H)+, 100], 227 [(M − iPr)+, 15]; HRMS (ESI/TOF)
calcd for [M + H]+ [C17H23OSi]+ 271.1513, found 271.1502.
1,1-Diisopropyl-1,3-dihydronaphtho[2,3-c][1,2]oxasilole (6p).
Yield (80%, 108.2 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ 8.11
(s, 1H), 7.90 (d, J = 7.8 Hz, 1H), 7.82 (d, J = 7.8 Hz, 1H), 7.68 (s, 1H),
7.51 (ddd, J = 7.8, 6.8, 1.5 Hz, 1H), 7.47 (ddd, J = 7.8, 6.8, 1.5 Hz, 1H),
5.33 (s, 2H), 1.32 (septet, J = 7.4 Hz, 2H), 1.09 (d, J = 7.4 Hz, 6H), 1.05
(d, J = 7.4 Hz, 6H); 13C{1H} NMR (CDCl3, 125 MHz) δ 147.0, 134.5,
133.0, 132.9, 131.1, 128.5, 128.0, 126.8, 125.6, 119.5, 77.3, 17.2 (2),
13.3; IR (neat) 2941 (w), 1487 (m), 1462 (m), 1051 (s), 1010 (s), 743
(s) cm−1; TLC Rf = 0.5 in 20:1 hexanes:EtOAc; GC-MS (5029017) tR =
12.282 min, m/z 270 (M+, 59), 269 [(M − H)+, 100], 227 [(M − iPr)+,
30]; HRMS (ESI/TOF) calcd for [M + Na]+ [C17H22NaOSi]+
293.1332, found 293.1322.
1,1-Diethyl-3-methyl-1,3-dihydrobenzo[c][1,2]oxasilole (8a).
Yield (88%, 181.2 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ 7.55
(d, J = 7.2 Hz, 1H), 7.40 (dd, J = 7.6, 7.6 Hz, 1H), 7.29 (dd, J = 7.2, 7.2
Hz, 1H), 7.22 (d, J = 7.6 Hz, 1H), 5.34 (q, J = 6.5 Hz, 1H), 1.51 (d, J =
6.5 Hz, 3H), 0.98−0.92 (m, 6H), 0.90−0.74 (m, 4H); 13C{1H} NMR
(CDCl3, 125 MHz) δ 155.2, 133.1, 131.6, 129.8, 126.9, 122.3, 78.3, 25.3,
7.36, 7.25, 6.88, 6.65; IR (neat) 3059 (w), 2956 (w), 1261 (m), 1082 (s),
1019 (s), 922 (s), 711 (s) cm−1; TLC Rf = 0.4 in 20:1 hexanes:EtOAc;
GC-MS (5029017) tR = 8.294 min, m/z 207 [(M + H)+, 42], 206 (M+,
22), 205 [(M − H)+, 77], 191 [(M − Me)+, 100]; HRMS (ESI/TOF)
calcd for [M + H]+ [C12H19OSi]+ 207.1200, found 207.1182.
Synthesis of 1-[3-({Diisopropyl[(trimethylsilyl)ethynyl]silyl}-
oxy)phenyl]ethanone (7h).
1,1-Diethyl-6-methoxy-3-methyl-1,3-dihydrobenzo[c][1,2]-
oxasilole (8b). Yield (76%, 179.4 mg); clear oil; 1H NMR (CDCl3, 500
MHz) δ 7.13 (d, J = 8.4 Hz, 1H), 7.02 (d, J = 2.5 Hz, 1H), 6.96 (dd, J =
8.4, 2.5, Hz, 1H), 5.30 (q, J = 6.4 Hz, 1H), 3.83 (s, 3H), 1.48 (d, J = 6.4
Hz, 3H), 0.98−0.92 (m, 6H), 0.90−0.74 (m, 4H); 13C{1H} NMR
(CDCl3, 125 MHz) δ 158.8, 147.4, 134.8, 123.3, 116.5, 115.3, 78.0, 55.6,
25.5, 7.32, 7.23, 6.89, 6.66; IR (neat) 3058 (w), 2956 (w), 1465 (m),
1266 (m), 1223 (s), 1080 (s), 922 (s), 692 (s) cm−1; TLC Rf = 0.3 in
20:1 hexanes:EtOAc; GC-MS (5029017) tR = 9.817 min, m/z 237 [(M
+ H)+, 17], 236 (M+, 28), 235 [(M − H)+, 59], 220 [(M − H − Me)+,
100]; HRMS (ESI/TOF) calcd for [M + K]+ [C13H20KO2Si]+
275.0864, found 275.0875.
1,1-Diethyl-3-methyl-6-phenyl-1,3-dihydrobenzo[c][1,2]oxasilole
(8c). Yield (59%, 166.4 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ
7.74 (d, J = 1.6 Hz, 1H), 7.64 (dd, J = 8.0, 1.6 Hz, 1H), 7.62−7.60 (m,
2H), 7.46 (app t, J = 7.7 Hz, 2H), 7.36 (dddd, J = 7.4, 7.4, 1.3, 1.3 Hz,
1H), 7.30 (d, J = 8.0 Hz, 1H), 5.39 (q, J = 6.4 Hz, 1H), 1.56 (d, J = 6.4
Hz, 1H), 1.02−0.96 (m, 6H), 0.94−0.79 (m, 4H); 13C{1H} NMR
(CDCl3, 125 MHz) δ 154.3, 141.5, 140.1, 134.0, 130.2, 129.1, 129.0,
127.5, 127.4, 122.7, 78.2, 25.4, 7.39, 7.28, 6.94, 6.72; IR (neat) 3059 (w),
2956 (w), 1675 (m), 1460 (m), 1070 (s), 1004 (s), 922 (s), 764 (s)
Trimethylsilylacetylene (i) (1.4 mL, 10 mmol) was dissolved in THF
(10 mL, 1 M), and the solution was kept at 0 °C with an ice bath.
Ethylmagnesium bromide (4 mL, 3.0 M in Et2O, 12 mmol) was added to
the mixture. The reaction mixture was warmed to rt and stirred for 1h.
Chlorodiisopropylsilane (2.0 mL, 1.77 g, 12 mmol) was added to the
reaction mixture, and the mixture was stirred for 2 h at rt. The reaction
was quenched with aqueous saturated NH4Cl (20 mL), and the mixture
was extracted with diethyl ether (30 mL × 3). The combined organic
phase was washed with water and brine and dried over anhydrous
sodium sulfate. The volatiles were removed in vacuo to afford the crude
disilane (ii), which was directly used for the subsequent reaction without
further purification. Disilane (ii) (636 mg, 3 mmol) was dissolved by
G
DOI: 10.1021/acs.joc.5b00564
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
cm−1; TLC Rf = 0.35 in 20:1 hexanes:EtOAc; GC-MS (5029017) tR =
12.529 min, m/z 283 [(M + H)+, 29], 282 (M+, 58), 281 [(M − H)+,
100], 267 [(M − Me)+, 65]; HRMS (ESI/TOF) calcd for [M + H]+
[C18H23OSi]+ 283.1513, found 283.1501.
1,1-Diethyl-6-fluoro-3-methyl-1,3-dihydrobenzo[c][1,2]oxasilole
(8d). Yield (63%, 141.2 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ
7.17 [dd, J = 7.8 (J3F−H), 2.5 Hz, 1H], 7.16 [dd, J = 8.8, 4.6 (J4F−H) Hz,
1H], 7.07 [ddd, J = 8.8, 8.5 (J3F−H), 2.5 Hz, 1H], 5.30 (q, J = 6.4 Hz, 1H),
1.49 (d, J = 6.4 Hz, 3H), 0.97−0.91 (m, 6H), 0.90−0.74 (m, 4H);
13C{1H} NMR (CDCl3, 125 MHz) δ 162.2 (d, J1F−C = 246 Hz), 150.6
7.5 Hz, 3H), 0.91 (t, J = 7.5 Hz, 3H), 0.89−0.74 (m, 4H); 13C{1H}
NMR (CDCl3, 125 MHz) δ 153.4, 133.2, 131.9, 131.7, 129.3, 127.3,
77.9, 24.4, 19.5, 7.81, 7.19, 7.05, 6.63; IR (neat) 2956 (w), 1458 (w),
1018 (s), 943 (s), 871 (s), 744 (s) cm−1; TLC Rf = 0.55 in 20:1
hexanes:EtOAc; GC-MS (5029017) tR = 9.076 min, m/z 221 [(M +
H)+, 23], 220 (M+, 10), 219 [(M − H)+, 31], 205 [(M − Me)+, 100];
HRMS (ESI/TOF) calcd for [M + H]+ [C13H21OSi]+ 221.1356, found
221.1343.
1,1-Diethyl-3-isopropyl-1,3-dihydrobenzo[c][1,2]oxasilole (8j).
Yield (96%, 224.6 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ 7.56
(d, J = 7.2 Hz, 1H), 7.40 (ddd, J = 7.2, 7.2, 1.3 Hz, 1H), 7.29 (dddd, J =
7.2, 7.2, 1.3, 0.9 Hz, 1H), 7.29 (dq, J = 7.7, 0.9 Hz, 1H), 5.15 (d, J = 2.7
Hz, 1H), 2.13 (qqd, J = 6.8, 6.8, 2.7 Hz, 1H), 1.19 (d, J = 6.8 Hz, 3H),
1.08 (t, J = 8 Hz, 3H), 0.93−0.77 (m, 7H), 0.63 (d, J = 6.8 Hz, 3H);
13C{1H} NMR (CDCl3, 125 MHz) δ 153.1, 134.8, 131.6, 129.7, 126.8,
122.5, 86.69, 34.66, 20.48, 15.21, 7.26, 7.09, 6.98, 6.66; IR (neat) 2957
(w), 1678 (m), 1459 (w), 1231 (m), 1014 (s), 732 (s) cm−1; TLC Rf =
0.6 in 20:1 hexanes:EtOAc; GC-MS (5029017) tR = 9.131 min, m/z 235
[(M + H)+, 4], 234 (M+, 3), 233 [(M − H)+, 15], 191 [(M − iPr)+, 100];
HRMS (ESI/TOF) calcd for [M + H]+ [C14H23OSi]+ 235.1513, found
235.1501.
2,2-Diethyl-6,7,8,8a-tetrahydro-2H-naphtho[1,8-cd][1,2]oxasilole
(8k). Yield (85%, 197.1 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ
7.39 (d, J = 7.4 Hz, 1H), 7.24 (dd, J = 7.2, 7.2 Hz, 1H), 7.14 (app d, J =
7.2 Hz, 1H), 4.96 (dd, J = 11.4, 5.0 Hz, 1H), 2.85 (ddd, J = 17.2, 7.7, 3.0
Hz, 1H), 2.73 (ddd, J = 17.2, 9.7, 7.4 Hz, 1H), 2.35 (dddd, J = 12.0, 5.0,
4.3, 4.3 Hz, 1H), 2.02 (ddddd, J = 14.0, 7.4, 4.6, 4.3, 3.0 Hz, 1H), 1.89
(ddddd, J = 14.0, 12.0, 9.7, 7.7, 4.3 Hz, 1H), 1.47 (dddd, J = 12.0, 12.0,
11.4, 4.6 Hz, 1H), 1.04 (t, J = 7.5 Hz, 3H), 0.96−0.75 (m, 7H); 13C{1H}
NMR (CDCl3, 125 MHz) δ 150.1, 134.0, 133.1, 129.7, 129.1, 127.6 78.8,
31.5, 26.8, 20.7, 6.93, 6.84, 6.79, 6.62; IR (neat) 2951 (w), 1459 (w),
1059 (m), 1006 (s), 724 (s) cm−1; TLC Rf = 0.35 in 20:1
hexanes:EtOAc; GC-MS (5029017) tR = 10.336 min, m/z 233 [(M +
H)+, 19], 232 (M+, 100), 233 [(M − H)+, 15], 206 [(M − H − Me)+, 4];
HRMS (ESI/TOF) calcd for [M + H]+ [C14H21OSi]+ 233.1356, found
233.1343.
(d, J4F−C = 2.1 Hz), 135.9 (d, J3F−C = 4.8 Hz), 123.9 (d, J3F−C = 8.2 Hz),
117.24 (d, J2F−C = 19.3 Hz), 117.19 (d, J2F−C = 22.8 Hz), 78.0, 25.5, 7.25,
7.16, 6.82, 6.58; IR (neat) 2958 (w), 1575 (w), 1464 (m), 1318 (s), 1258
(s), 1149 (s), 925 (s), 725 (s) cm−1; TLC Rf = 0.4 in 20:1
hexanes:EtOAc; GC-MS (5029017) tR = 8.264 min, m/z 225 [(M +
H)+, 34], 224 (M+, 14), 223 [(M − H)+, 51], 209 [(M − Me)+, 100];
HRMS (ESI/TOF) calcd for [M + H]+ [C12H18FOSi]+ 225.1105, found
225.1116.
6-Chloro-1,1-diethyl-3-methyl-1,3-dihydrobenzo[c][1,2]oxasilole
(8e). Yield (65%, 156.1 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ
7.47 (d, J = 2.1 Hz, 1H), 7.35 (dd, J = 8.2, 2.1 Hz, 1H), 7.14 (d, J = 8.2
Hz, 1H), 5.30 (q, J = 6.5 Hz, 1H), 1.48 (d, J = 6.5 Hz, 3H), 0.99−0.91
(m, 6H), 0.90−0.74 (m, 4H); 13C{1H} NMR (CDCl3, 125 MHz) δ
153.5, 135.9, 133.2, 131.1, 130.0, 123.8, 78.0, 25.3, 7.26, 7.17, 6.83, 6.59;
IR (neat) 2957 (w), 1455 (m), 1317 (m), 1136 (s), 1060 (s), 923 (s),
722 (s) cm−1; TLC Rf = 0.4 in 20:1 hexanes:EtOAc; GC-MS (5029017)
tR = 9.505 min, m/z 243 [(M + 2 + H)+, 13], 241 [(M + H)+, 40], 227
[(M + 2 − Me)+, 37], 209 [(M − Me)+, 100]; HRMS (ESI/TOF) calcd
for [M + H]+ [C12H18ClOSi]+ 241.0810, found 241.0819.
1,1-Diethyl-3-methyl-6-(trifluoromethyl)-1,3-dihydrobenzo[c]-
[1,2]oxasilole (8f). Yield (85%, 232.9 mg); clear oil; 1H NMR (CDCl3,
500 MHz) δ 7.78 (s, 1H), 7.35 (d, J = 8.2 Hz, 1H), 7.14 (d, J = 8.2 Hz,
1H), 5.37 (q, J = 6.5 Hz, 1H), 1.52 (d, J = 6.5 Hz, 3H), 0.98−0.91 (m,
6H), 0.93−0.77 (m, 4H); 13C{1H} NMR (CDCl3, 125 MHz) δ 158.9,
134.5, 129.5 (q, J2F−C = 32.1 Hz), 128.4 (q, J3F−C = 3.6 Hz), 126.9 (q,
J3F−C = 3.6 Hz), 124.7 (q, J1F−C = 272.2 Hz), 122.7, 78.2, 25.1, 7.22, 7.14,
6.78, 6.56; IR (neat) 2960 (w), 1324 (m), 1261 (m), 1121 (s), 1077 (s),
925 (s), 729 (s) cm−1; TLC Rf = 0.5 in 20:1 hexanes:EtOAc; GC-MS
(5029017) tR = 8.057 min, m/z 275 [(M + H)+, 100], 274 (M+, 41), 273
[(M − H)+, 70], 259 [(M − Me)+, 42]; HRMS (ESI/TOF) calcd for [M
+ H]+ [C13H18F3OSi]+ 275.1074, found 275.1081.
1,1-Diethyl-3-methyl-5-(trifluoromethyl)-1,3-dihydrobenzo[c]-
[1,2]oxasilole (8g). Yield (79%, 216.5 mg); clear oil; 1H NMR (CDCl3,
500 MHz) δ 7.66 (d, J = 7.5 Hz, 1H), 7.54 (d, J = 7.5 Hz, 1H), 7.45 (s,
1H), 5.37 (q, J = 6.5 Hz, 1H), 1.53 (d, J = 6.5 Hz, 3H), 0.98−0.91 (m,
6H), 0.90−0.77 (m, 4H); 13C{1H} NMR (CDCl3, 125 MHz) δ 155.6,
138.1, 132.13, 132.05 (q, J2F−C = 32 Hz), 124.5 (q, J1F−C = 273.1 Hz),
123.8 (q, J3F−C = 3.6 Hz), 119.0 (q, J3F−C = 3.7 Hz), 78.2, 25.1, 7.19, 7.10,
6.78, 6.55; IR (neat) 2959 (w), 1688 (w), 1370 (m), 1124 (m), 1087 (s),
719 (s) cm−1; TLC Rf = 0.5 in 20:1 hexanes:EtOAc; GC-MS (5029017)
tR = 8.007 min, m/z 275 [(M + H)+, 78], 274 (M+, 27), 273 [(M − H)+,
100], 259 [(M − Me)+, 30], 255 [(M − F)+, 54]; HRMS (ESI/TOF)
calcd for [M + H]+ [C13H18F3OSi]+ 275.1074, found 275.1089.
5-([Diisopropyl{(trimethylsilyl)ethynyl}silyl]oxy)-1,1-diethyl-3-
methyl-1,3-dihydrobenzo[c][1,2]oxasilole (8h). Yield (79%, 340.8
mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ 7.37 (d, J = 7.9 Hz, 1H),
6.97 (dd, J = 7.9, 2.0 Hz, 1H), 6.91 (d, J = 2.0 Hz, 1H), 5.25 (q, J = 6.5
Hz, 1H,), 1.47 (d, J = 6.5 Hz, 3H), 1.15−1.04 (m, 14H), 0.96−0.91 (m,
6H), 0.86−0.71 (m, 4H), 0.18 (s, 9H); 13C{1H} NMR (CDCl3, 125
MHz) δ 157.5, 157.2, 132.4, 124.8, 119.4, 118.3, 113.6, 107.8, 78.0, 25.3,
17.30, 17.26, 17.20 (2), 13.26, 13.24, 7.51, 7.42, 6.91, 6.69, −0.08; IR
(neat) 2956 (w), 1596 (w), 1463 (w), 1276 (s), 1250 (s), 1004 (s), 918
(s), 763 (s) cm−1; TLC Rf = 0.6 in 40:1 hexanes:EtOAc; GC-MS
(5029017) tR = 12.703 min, m/z 433 [(M + H)+, 53], 432 (M+, 100),
418 [(M + H − Me)+, 33]; HRMS (ESI/TOF) calcd for [M + Na]+
[C23H40NaO2Si3]+ 455.2228, found 455.2233.
General Procedure for Rh-Catalyzed Sequential, Reductive
Arene o-C−H Silylation of Aromatic Aldehydes (10). [Rh(nbd)-
Cl]2 (1.8 mg, 0.4 mol %), tris(4-methoxyphenyl)phosphine (8.6 mg, 2.4
mol %), and aldehyde 9 (1 mmol) were dissolved in THF (1 mL, 1 M).
Diethylsilane (0.28 mL, 173 mg, 2 mmol) was added to the mixture. The
septum on the vial was replaced by a screw cap with a Teflon liner. The
reaction mixture was kept at rt and stirred for 20 min. The volatiles were
removed in vacuo to afford the crude hydridodiethylsilyl ethers, which
were directly used for subsequent reactions without further purification.
Norbornene (188 mg, 2 mmol) and THF (1 mL, 1 M) were added to
the crude reaction mixture of silyl ether. The septum on the vial was
replaced by a screw cap with a Teflon liner, and the mixture was stirred at
120 °C for 2 h. The reaction progress was monitored by GC/MS
spectrometry. The reaction was cooled to room temperature. The
volatiles were removed in vacuo, and the crude mixture was purified by
MPLC to afford benzoxasilole 10 (hexanes/EtOAc = 80:1, 7 mL/min,
7−12 min).
1,1-Diethyl-1,3-dihydrobenzo[c][1,2]oxasilole1,1-diethyl-1,3-
dihydrobenzo[c][1,2]oxasilole (10a). Yield (88%, 168.9 mg); clear oil;
1H NMR (CDCl3, 500 MHz) δ 7.58 (d, J = 7.2 Hz, 1H), 7.39 (dd, J = 7.7,
7.7 Hz, 1H), 7.30 (dd, J = 7.2, 7.2 Hz, 1H), 7.24 (d, J = 7.7 Hz, 1H), 5.16
(s, 2H), 0.97−0.94 (m, 6H), 0.91−0.78 (m, 4H); 13C{1H} NMR
(CDCl3, 125 MHz) δ 150.7, 133.3, 131.8, 129.7, 126.9, 121.8, 72.3, 7.15,
6.63; IR (neat) 3003 (w), 2956 (w), 1262 (s), 722 (s) cm−1; TLC Rf =
0.6 in 40:1 hexanes:EtOAc; GC-MS (5029017) tR = 8.197 min, m/z 193
[(M + H)+, 12], 192 (M+, 20), 191 [(M − H)+, 67], 179 (100); HRMS
(ESI/TOF) calcd for [M + H]+ [C11H17OSi]+ 193.1043, found
193.1032.
1,1-Diethyl-6-fluoro-1,3-dihydrobenzo[c][1,2]oxasilole (10b).
Yield (70%, 147.1 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ 7.21
[dd, J = 7.8 (J3F−H), 2.5 Hz, 1H], 7.19 [dd, J = 8.3, 4.5 (J4F−H) Hz, 1H],
7.08 [dd, J = 8.8 (J3F−H), 8.3, 2.5 Hz, 1H], 5.11 (s, 2H), 0.97−0.93 (m,
6H), 0.90−0.77 (m, 4H); 13C{1H} NMR (CDCl3, 125 MHz) δ 162.3
(d, J1F−C = 246 Hz), 145.9 (d, J4F−C = 2.3 Hz), 136.0 (d, J3F−C = 5.3 Hz),
1,1-Diethyl-3,4-dimethyl-1,3-dihydrobenzo[c][1,2]oxasilole (8i).
Yield (86%, 189.2 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ 7.40
(d, J = 7.0 Hz, 1H), 7.23 (app t, J = 7.2 Hz, 1H), 7.18 (d, J = 7.3 Hz, 1H),
5.41 (q, J = 6.3 Hz, 1H), 2.31 (s, 3H), 1.49 (d, J = 6.3 Hz, 3H), 1.03 (t, J =
H
DOI: 10.1021/acs.joc.5b00564
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
123.3 (d, J3F−C = 7.2 Hz), 117.47 (d, J2F−C = 20.3 Hz), 117.17 (d, J2
=
1,1-Diethyl-4-[(triisopropylsilyl)oxy]-1,3-dihydrobenzo[c][1,2]-
oxasilole (10i). Yield (82%, 298.5 mg); clear oil; 1H NMR (CDCl3, 500
MHz) δ 7.18 (dd, J = 7.8, 7.1 Hz, 1H), 7.12 (d, J = 7.1 Hz, 1H), 6.81 (d, J
= 7.8 Hz, 1H), 5.15 (s, 2H), 1.28 (septet, J = 7.3 Hz, 3H), 1.10 (d, J = 7.3
Hz, 18H), 0.97−0.93 (m, 6H), 0.89−0.76 (m, 4H); 13C{1H} NMR
(CDCl3, 125 MHz) δ 150.9, 141.0, 135.4, 128.5, 123.9, 119.0, 70.8, 18.2,
13.1, 7.24, 6.60; IR (neat) 2946 (w), 1566 (w), 1459 (w), 1265 (s), 1047
(s), 759 (s) cm−1; TLC Rf = 0.7 in 40:1 hexanes:EtOAc; GC-MS
(5029017) tR = 13.002 min, m/z 365 [(M + H)+, 3], 364 (M+, 9), 363
[(M − H)+, 13], 322 [(M + H − iPr)+, 13]; HRMS (ESI/TOF) calcd for
[M + H]+ [C20H37O2Si2]+ 365.2327, found 365.2308.
Bicyclo[2.2.1]heptan-2-yldiethyl[(4-methylbenzyl)oxy]silane
(11a). Clear oil; 1H NMR (CDCl3, 500 MHz) δ 7.24 (d, J = 7.8 Hz, 2H),
7.16 (d, J = 7.8 Hz, 2H), 4.73 (s, 2H), 2.36 (s, 3H), 2.31 (br s, 1H), 2.27
(br s, 1H), 1.62−1.53 (m, 3H), 1.38 (dddd, J = 11.6, 9.8, 2.2, 0.8 Hz,
1H), 1.30 (dddd, J = 9.3, 4.0, 2.2, 2.2 Hz, 1H), 1.26−1.21 (nfom, 2H),
1.17 (dddd, J = 9.4, 3.9, 1.7, 1.7 Hz, 1H), 1.01 (t, J = 7.9 Hz, 6H), 0.74
(ddd, J = 9.4, 7.3, 1.3 Hz, 1H), 0.73−0.57(m, 4H); 13C{1H} NMR
(CDCl3, 125 MHz) δ 141.73, 128.4, 127.0, 126.2, 65.0, 38.4, 37.7, 36.9,
34.3, 32.3, 29.1, 27.6, 21.3, 7.3 (2), 4.37, 4.27; IR (neat) 3007 (w), 2947
(w), 1456 (w), 1083 (s), 1007 (s), 749 (s), 721 (s) cm−1; TLC Rf = 0.7 in
40:1 hexanes:EtOAc; GC-MS (5029017) tR = 12.532 min, m/z 301 [(M
− H)+, 4], 273 [(M − Et)+, 20], 207 [(M − norbornyl)+, 3], 105 (100);
HRMS (ESI/TOF) calcd for [M + H]+ [C19H31OSi]+ 303.2139, found
303.2124.
F−C
22.8 Hz), 71.9, 7.07, 6.54; IR (neat) 2957 (w), 1461 (w), 1211 (s), 1050
(s), 785 (s), 706 (s) cm−1; TLC Rf = 0.6 in 40:1 hexanes:EtOAc; GC-MS
(5029017) tR = 8.181 min, m/z 209 [(M − H)+, 85], 181 [(M − Et)+,
10], 109 (100); HRMS (ESI/TOF) calcd for [M + H]+ [C11H16FOSi]+
211.0949, found 211.0957.
6-Chloro-1,1-diethyl-1,3-dihydrobenzo[c][1,2]oxasilole (10c).
Yield (56%, 125.4 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ 7.51
(d, J = 2.1 Hz, 1H), 7.35 (dd, J = 8.2, 2.1 Hz, 1H), 7.16 (d, J = 8.2 Hz,
1H), 5.11 (s, 2H), 0.97−0.92 (m, 6H), 0.90−0.77 (m, 4H); 13C{1H}
NMR (CDCl3, 125 MHz) δ 148.8, 136.0, 133.1, 131.3, 129.9, 123.2,
71.9, 7.06, 6.54; IR (neat) 2956 (w), 1454 (w), 1094 (s), 1049 (s), 765
(s) cm−1; TLC Rf = 0.6 in 40:1 hexanes:EtOAc; GC-MS (5029017) tR =
9.461 min, m/z 227 [(M + 2 + H)+, 21], 225 [(M + H)+, 60], 197 [(M −
Et)+, 2], 89 (100); HRMS (ESI/TOF) calcd for [M + H]+
[C11H16ClOSi]+ 227.0653, found 227.0640.
1,1-Diethyl-6-(trifluoromethyl)-1,3-dihydrobenzo[c][1,2]oxasilole
(10d). Yield (82%, 213.2 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ
7.81 (s, 1H), 7.64 (d, J = 8.2 Hz, 1H), 7.34 (d, J = 8.2 Hz, 1H), 5.18 (s,
2H), 0.98−0.93 (m, 6H), 0.93−0.80 (m, 4H); 13C{1H} NMR (CDCl3,
125 MHz) δ 154.5, 134.6, 129.5 (q, J2F−C = 32.2 Hz), 128.5 (q, J3
=
F−C
3.9 Hz), 126.8 (q, J3F−C = 3.6 Hz), 124.7 (q, J1F−C = 272.5 Hz), 122.2,
72.1, 7.05, 6.52; IR (neat) 2955 (w), 1460 (w), 1325 (m), 1261 (s), 1131
(s), 1078 (s), 725 (s) cm−1; TLC Rf = 0.6 in 40:1 hexanes:EtOAc; GC-
MS (5029017) tR = 7.953 min, m/z 261 [(M + H)+, 2], 260 (M+, 1), 225
[(M − H)+, 7], 241 [(M − F)+, 100]; HRMS (ESI/TOF) calcd for [M +
H]+ [C12H16F3OSi]+ 261.0917, found 261.0928.
(Benzyloxy)(bicyclo[2.2.1]heptan-2-yl)diethylsilane (11b). Clear
1
oil; H NMR (CDCl3, 500 MHz) δ 7.37−7.32 (nfom, 4H), 7.27−
7.22 (m, 1H), 4.76 (s, 2H), 2.29 (br s, 1H), 2.26 (br s, 1H), 1.60−1.51
(m, 3H), 1.39 (dddd, J = 10.8, 9.9, 2.3, 0.7 Hz, 1H), 1.31 (dddd, J = 9.4,
3.9, 1.9, 1.9 Hz, 1H), 1.24−1.20 (m, 2H), 1.15 (dddd, J = 9.4, 3.8, 1.7, 1.7
Hz, 1H), 0.99 (t, J = 7.9 Hz, 6H), 0.76 (ddd, J = 9.4, 7.2, 1.7 Hz, 1H),
0.72−0.60 (m, 4H); 13C{1H} NMR (CDCl3, 125 MHz) δ 138.7, 136.6,
129.1, 126.3, 65.0, 38.4, 37.7, 36.9, 34.4, 32.3, 29.1, 27.6, 7.31 (2), 4.38,
4.28; IR (neat) 3029 (w), 2947 (w), 1454 (w), 1093 (s), 1067 (s), 1006
(s), 724 (s), 694 (s) cm−1; TLC Rf = 0.7 in 40:1 hexanes:EtOAc; GC-MS
(5029017) tR = 12.059 min, m/z 287 [(M − H)+, 1], 259 [(M − Et)+, 1],
193 [(M − norbornyl)+, 20], 91 (100); HRMS (ESI/TOF) calcd for [M
+ H]+ [C18H29OSi]+ 289.1982, found 289.1967.
Bicyclo[2.2.1]heptan-2-yldiethyl[(4-chlorobenzyl)oxy]silane (11c).
Clear oil; 1H NMR (CDCl3, 500 MHz) δ 7.30 (d, J = 8.5 Hz, 2H), 7.26
(d, J = 8.5 Hz, 2H), 4.71 (s, 2H), 2.28−2.24 (m, 2H), 1.58−1.51 (m,
3H), 1.38 (ddd, J = 11.9, 10.0, 2.2 Hz, 1H), 1.28 (dddd, J = 9.4, 3.9, 2.0,
2.0 Hz, 1H), 1.23 (dd, J = 6.0, 2.2 Hz, 1H), 1.20 (dd, J = 6.2, 2.2 Hz, 1H),
1.15 (dddd, J = 9.4, 3.6, 1.7, 1.7 Hz, 1H), 0.98 (t, J = 7.9 Hz, 6H), 0.75
(ddd, J = 9.4, 7.6, 1.6 Hz, 1H), 0.71−0.58 (m, 4H); 13C{1H} NMR
(CDCl3, 125 MHz) δ 140.24, 132.7, 128.5, 127.6, 64.4, 38.4, 37.7, 36.9,
34.3, 32.2, 29.1, 27.6, 7.28 (2), 4.34, 4.24; IR (neat) 2948 (w), 1490 (m),
1275 (m), 1084 (s), 1027 (s), 808 (s), 722 (s) cm−1; TLC Rf = 0.7 in
40:1 hexanes:EtOAc; GC-MS (5029017) tR = 13.079 min, m/z 323[(M
+ 2 − H)+, 37], 321 [(M − H)+, 100], 293 [(M − Et)+, 14], 227 [(M −
norbornyl)+, 16]; HRMS (ESI/TOF) calcd for [M + H]+
[C18H28ClOSi]+ 323.1592, found 323.1578.
1,1-Diethyl-6-methyl-1,3-dihydrobenzo[c][1,2]oxasilole (10e).
Yield (94%, 193.6 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ 7.38
(s, 1H), 7.21 (d, J = 8.0 Hz, 1H), 7.13 (d, J = 8.0 Hz, 1H), 5.12 (s, 2H),
2.38 (s, 3H), 0.98−0.94 (m, 6H), 0.90−0.77 (m, 4H); 13C{1H} NMR
(CDCl3, 125 MHz) δ 147.8, 136.3, 133.4, 132.1, 130.8, 121.5, 72.2, 21.4,
7.16, 6.65; IR (neat) 2955 (w), 1461 (w), 1267 (s), 1046 (s), 794 (s),
729 (s) cm−1; TLC Rf = 0.6 in 40:1 hexanes:EtOAc; GC-MS (5029017)
tR = 8.813 min, m/z 207 [(M + H)+, 100], 205 [(M − H)+, 90], 179 [(M
− Et)+, 20]; HRMS (ESI/TOF) calcd for [M + H]+ [C12H19OSi]+
207.1200, found 207.1213.
1,1-Diethyl-6-methoxy-1,3-dihydrobenzo[c][1,2]oxasilole (10f).
Yield (90%, 199.8 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ 7.15
(d, J = 8.4 Hz, 1H), 7.06 (d, J = 2.5 Hz, 1H), 6.96 (dd, J = 8.4, 2.5 Hz,
1H), 5.10 (s, 2H), 3.84 (s, 3H), 0.97−0.93 (m, 6H), 0.90−0.77 (m, 4H);
13C{1H} NMR (CDCl3, 125 MHz) δ 158.8, 142.7, 134.9, 122.7, 116.6,
115.5, 72.0, 55.6, 7.13, 6.64; IR (neat) 3002 (w), 2954 (w), 1464 (w),
1224 (s), 1047 (s), 1030 (s), 790 (s), 705 (s) cm−1; TLC Rf = 0.55 in
40:1 hexanes:EtOAc; GC-MS (5029017) tR = 9.761 min, m/z 223 [(M
+ H)+, 26], 222 (M+, 84), 221 [(M − H)+, 100], 193[(M − Et)+, 43];
HRMS (ESI/TOF) calcd for [M + Na]+ [C12H18NaO2Si]+ 245.0968,
found 245.0981.
5-Chloro-1,1-diethyl-1,3-dihydrobenzo[c][1,2]oxasilole (10g).
Yield (87%, 194.8 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ 7.49
(d, J = 7.7 Hz, 1H), 7.27 (ddq, J = 7.7, 1.8, 0.8 Hz, 1H), 7.23 (dq, J = 1.8,
0.8 Hz, 1H), 5.11 (s, 2H), 0.94 (t, J = 7.6 Hz, 6H), 0.90−0.78 (m, 4H);
13C{1H} NMR (CDCl3, 125 MHz) δ 152.8, 136.3, 132.9, 131.6, 127.4,
122.1, 71.8, 7.11, 6.57; IR (neat) 2956 (w), 1586 (w), 1457 (w), 1189
(s), 1054 (s), 790 (s), 729 (s) cm−1; TLC Rf = 0.6 in 40:1
hexanes:EtOAc; GC-MS (5029017) tR = 9.462 min, m/z 227 [(M + 2
+ H)+, 21], 225 [(M + H)+, 60], 197 [(M − Et)+, 2], 89 (100); HRMS
(ESI/TOF) calcd for [M + H]+ [C11H16ClOSi]+ 227.0653, found
227.0641.
1,1-Diethyl-4-methyl-1,3-dihydrobenzo[c][1,2]oxasilole (10h).
Yield (98%, 201.9 mg); clear oil; 1H NMR (CDCl3, 500 MHz) δ 7.41
(d, J = 7.2 Hz, 1H), 7.24 (dd, J = 7.2, 7.2 Hz, 1H), 7.18 (d, J = 7.2 Hz,
1H), 5.10 (s, 2H), 2.22 (s, 3H), 0.98−0.94 (m, 6H), 0.90−0.77 (m, 4H);
13C{1H} NMR (CDCl3, 125 MHz) δ 149.1, 132.9, 131.7, 130.9, 129.1,
127.5, 71.7, 18.3, 7.23, 6.64; IR (neat) 2955 (w), 1457 (m), 1047 (s),
720 (s) cm−1; TLC Rf = 0.65 in 40:1 hexanes:EtOAc; GC-MS
(5029017) tR = 8.943 min, m/z 207 [(M + H)+, 100], 206 (M+, 17), 205
[(M − H)+, 42]; HRMS (ESI/TOF) calcd for [M + H]+ [C12H19OSi]+
207.1200, found 207.1208.
Bicyclo[2.2.1]heptan-2-yldiethyl[(4-fluorobenzyl)oxy]silane (11d).
Clear oil; 1H NMR (CDCl3, 500 MHz) δ 7.29 [dd, J = 8.7, 5.6 (J4
)
Hz, 1H], 7.01 [dd, J = 8.7, 8.7 (J3F−H) Hz, 1H], 4.71 (s, 2H), 2.28−F2−.2H4
(m, 2H), 1.58−1.51 (m, 3H), 1.38 (ddd, J = 11.9, 10.0, 2.3 Hz, 1H), 1.29
(dddd, J = 9.4, 3.8, 2.0, 2.0 Hz, 1H), 1.23 (dd, J = 6.0, 2.5 Hz, 1H), 1.20
(dd, J = 6.3, 3.0 Hz, 1H), 1.15 (dddd, J = 9.4, 3.7, 1.7, 1.7 Hz, 1H), 0.98
(t, J = 7.9 Hz, 6H), 0.75 (ddd, J = 9.4, 7.6, 1.6 Hz, 1H), 0.71−0.58 (m,
4H); 13C{1H} NMR (CDCl3, 125 MHz) δ 162.1 (d, J1F−C = 243.7 Hz),
137.4 (d, J4F−C = 3.5 Hz), 127.9 (d, J3F−C = 7.2 Hz), 115.2 (d, J2
=
F−C
20.7 Hz), 64.4, 38.4, 37.7, 36.9, 34.3, 32.3, 29.1, 27.6, 7.28 (2), 4.35, 4.25;
IR (neat) 2948 (w), 1604 (m), 1509 (s), 1221 (m), 1101 (s), 1082 (s),
751 (s), 721 (s) cm−1; TLC Rf = 0.7 in 40:1 hexanes:EtOAc; GC-MS
(5029017) tR = 12.007 min, m/z 305 [(M − H)+, 8], 277 [(M − Et)+, 2],
207 [(M − norbornyl)+, 6], 109 (100); HRMS (ESI/TOF) calcd for [M
+ H]+ [C19H31O2Si]+ 319.2088, found 319.2085.
Procedure for Benzylic Csp3−H Silylation of Ester via
Exhaustive, Reductive Silylation (13). [Ir(coe)2Cl]2 (3.6 mg, 2
mol %) and ester 12 (0.2 mmol) were dissolved with toluene (0.2 mL, 1
I
DOI: 10.1021/acs.joc.5b00564
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
M). Diisopropylsilane (0.16 mL, 96 mg, 0.8 mmol) was added to the
mixture in one portion. The septum on the vial was replaced by a screw
cap with a Teflon liner. The reaction mixture was kept at 150 °C and
stirred for 2 d. The volatiles were removed in vacuo to afford the
corresponding crude hydridodiisopropylsilyl ether, which was directly
used for subsequent reactions without further purification. [Rh(nbd)-
Cl]2 (4.6 mg, 5 mol %), tris(4-methoxyphenyl)phosphine (21.1 mg, 30
mol %), norbornene (37.6 mg, 0.4 mmol), and THF (0.5 mL, 0.4 M)
were added to the hydridodiisopropylsilyl ether. The septum on the vial
was replaced by a screw cap with a Teflon liner, and the mixture was
stirred at 150 °C for 10 h. The reaction progress was monitored by GC-
MS spectrometry. The reaction was cooled to rt. The volatiles were
removed in vacuo, and the crude mixture was purified by HPLC
(hexanes/EtOAc = 80:1, 4 mL/min, 19 min) to afford oxasiline 13 (18.1
mg, 36% yield) as a colorless liquid.
8-Fluoro-3,3-dipropyl-3,4-dihydro-1H-benzo[d][1,2]oxasiline
(13). Clear oil; 1H NMR (CDCl3, 500 MHz) δ 7.13 [ddd, J = 7.9, 7.9, 5.8
(J4F−H) Hz, 1H], 6.95 [d, J = 7.9 Hz, 1H], 6.83 [dd, J = 9.0 (J3F−H), 7.9
Hz, 1H], 4.95 [d, J = 1.2 (J4F−H) Hz, 2H], 2.09 (s, 2H), 1.03−0.97 (m,
2H), 0.94 (d, J = 6.7 Hz, 6H), 0.93 (d, J = 6.7 Hz, 6H); 13C{1H} NMR
(CDCl3, 125 MHz) δ 159.1 (d, J1F−C = 247 Hz), 139.8 (d, J3F−C = 4.5
Hz), 128.7 (d, J3F−C = 9.1 Hz), 126.06 (d, J2F−C = 22.4 Hz), 126.04 (d,
J4F−C = 2.4 Hz), 111.9 (d, J2F−C = 22.7 Hz), 59.2 (d, J3F−C = 7.0 Hz), 17.4,
17.2, 13.54, 13.09; IR (neat) 2942 (w), 1616 (m), 1462 (s), 1239 (s),
1054 (s), 1022 (s), 785 (s) cm−1; TLC Rf = 0.4 in 40:1 hexanes:EtOAc;
GC-MS (5029017) tR = 9.915 min, m/z 253 [(M + H)+, 18], 252 (M+,
14), 251 [(M − H)+, 44], 233 [(M − F)+, 4], 209 [(M − iPr)+, 40], 122
(100); HRMS (ESI/TOF) calcd for [M + H]+ [C14H22FOSi]+
253.1418, found 253.1406.
Procedure for Benzylic Csp3−H Silylation of Ketone and
Aldehyde via Rh-Catalyzed Reductive Silylation (16 and 17).
Ketone 14 or aldehyde 15 (0.5 mmol), [Rh(nbd)Cl]2 (6.9 mg, 3 mol
%), and tris(4-methoxyphenyl)phosphine (19.0 mg, 18 mol %) were
dissolved with THF (1 mL, 0.5 M). Diethylsilane (0.14 mL, 86 mg, 1
mmol) was added to the crude mixture slowly. The septum on the vial
was replaced by a screw cap with a Teflon liner, and the mixture was
stirred for 2 h at rt. The reaction progress was monitored by GC-MS
spectrometry. The volatiles were removed in vacuo to afford the
corresponding crude silyl ethers, which were directly used for
subsequent reactions without further purification. Norbornene (94
mg, 1 mmol) and THF (1 mL, 0.5 M) were added to the crude silyl
ethers. The septum on the vial was replaced by a screw cap with a Teflon
liner, and the mixture was stirred at 120 °C for 4 h. The reaction was
cooled to rt. The volatiles were removed in vacuo, and the crude mixture
was purified by MPLC to afford 16 (104.1 mg, 84% yield, hexanes/
EtOAc = 80:1, 7 mL/min, 13 min) and 17 (50.3 mg, 43% yield, hexanes/
EtOAc = 80:1, 6 mL/min, 11 min).
ASSOCIATED CONTENT
* Supporting Information
Spectroscopic characterization data for the preparation of all new
compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Author
*E-mail: jjeon@uta.edu.
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This paper is dedicated to Prof. Xuelong Hou at the Shanghai
Institute of Organic Chemistry (SIOC) on the occasion of his
60th birthday. We thank the University of Texas at Arlington
start-up funds, UTA Research Enhancement Program, and the
American Chemical Society Petroleum Research Fund (PRF#
54831-DNI1) for support of our program. The NSF (CHE-
0234811 and CHE-0840509) is acknowledged for partial funding
of the purchases of the NMR spectrometers used in this work.
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1
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DOI: 10.1021/acs.joc.5b00564
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