Photochemical intermolecular silylacylations of electron-deficient internal alkynes

Article abstract of DOI:10.1021/jo402457x

Light-induced Brook rearrangements of acylsilanes facilitate silylacylation reactions of electron-deficient internal alkynes. A wide range of aromatic substituents on the acylsilane aryl group are tolerated, affording a series of functionalized enonyl silanes. The presence of electron-withdrawing substituents on the alkyne is crucial for the success of the addition process.

Full text of DOI:10.1021/jo402457x

Note
pubs.acs.org/joc
Photochemical Intermolecular Silylacylations of Electron-Deficient
Internal Alkynes
Peter Becker, Daniel L. Priebbenow, Hui-Jun Zhang,† Ramona Pirwerdjan, and Carsten Bolm*
Institute of Organic Chemistry, RWTH Aachen University, Landoltweg 1, D-52074 Aachen, Germany
S
* Supporting Information
ABSTRACT: Light-induced Brook rearrangements of acylsilanes
facilitate silylacylation reactions of electron-deficient internal alkynes.
A wide range of aromatic substituents on the acylsilane aryl group are
tolerated, affording a series of functionalized enonyl silanes. The
presence of electron-withdrawing substituents on the alkyne is crucial
for the success of the addition process.
ver the past 40 years, the hydroacylation reactions of
alkenes and alkynes with aldehydes have been developed
Scheme 1. Photochemically Induced Intermolecular
Silylacylation of Alkynes
O
as efficient tools for C−C bond formation in organic
chemistry.1 Various transition metals have been applied as
catalysts in the aforementioned process to form the
corresponding adducts in a highly atom-economic manner.
Interestingly, the analogous silylacylation reactions utilizing
acylsilanes instead of aldehydes to afford useful silylated
products have attracted very little interest.2 In this context,
Narasaka and co-workers reported the rhodium-catalyzed
cyclization of alkynyl-substituted acylsilanes to form cyclic
ketones. However, the silyl group was not incorporated into the
final product during this transformation.3
In his early reports, Brook described his thorough
investigations into the thermally or photochemically induced
silicon-to-oxygen shift of acylsilanes (now known as the Brook
rearrangement).4 Despite this work, only a few reports
describing synthetically useful transformations based on this
unique process exist.4g−i,j Encouraged by Brook’s seminal
reports, our group recently investigated silylacylation reactions
of acylsilanes with ortho-tethered alkynes. During this process, a
siloxycarbene generated in situ by light irradiation reacted with
the proximal alkyne, and this was followed by a retro-Brook
rearrangement step to afford highly fuctionalized chromone
derivatives containing a vinylic silane moiety.5 To further
explore this chemistry, we next focused our attention on the
previously unknown intermolecular silylacylation of alkynes
(Scheme 1).6
Scheme 2. Scope of Aroylsilanes in the Intramolecular
Silylacylation Reaction
Assuming an analogous reaction pathway7 as in the
previously reported intramolecular process,5 we started our
investigation by applying a range of aroylsilanes with various
silyl moieties under conditions that involved light irradiation of
the acylsilane in the presence of 2.0 equiv of dimethyl
acetylenedicarboxylate (DMAD, 3a) in CH2Cl2 (Scheme 2).
Compared with the trimethylsilyl-containing aroylsilane 1a,
which gave an 81% yield of the corresponding product 4a, the
reactions of triethylsilyl (1b), tert-butyldimethylsilyl (1c), and
dimethylphenylsilyl (1d) aroylsilanes with DMAD resulted in
lower yields of the respective enonyl silanes (4b, 31%; 4c, 44%;
4d, 27%), presumably as a result of steric factors associated
with the bulkier groups attached to silicon. Whether or not that
effect was related to the formation of the suggested
intermediates 5 or their rearrangements to the corresponding
products 4 (Scheme 1) remained unanswered.
Received: November 5, 2013
Published: December 18, 2013
© 2013 American Chemical Society
814
dx.doi.org/10.1021/jo402457x | J. Org. Chem. 2014, 79, 814−817

The Journal of Organic Chemistry
Note
Subsequently, other aroylsilanes (1e−l) with different aryl
groups were investigated. The presence of an electron-neutral
methyl group at the para position of the aryl ring (as in 1e) did
not significantly affect the product yield (85%) compared with
the unsubstituted aroylsilane. A substitution with an electron-
withdrawing group at the para position of the aromatic ring,
such as Cl (as in 1g) or CF3 (as in 1h), led to a decrease in the
yield (4g, 76%; 4h, 53%). An electron-donating methoxy group
attached to the para or meta position of the aroylsilane (as in 4f
and 4i, respectively) afforded the corresponding enonyl silanes
in excellent yields (4f, 94%; 4i, 95%). Dramatically, substitution
at the ortho position of the arene (as in 1j) led to a very poor
yield in this reaction process (4j, 12%). The replacement of the
aryl group with a furanyl moiety (as in 1k) or a thiophenyl
moiety (as in 1l) afforded the desired adducts in moderate
yields (4k, 62%; 4l, 61%).
Next, the application of alkynes other than DMAD (3a) in
this reaction process was explored. With diethyl acetylenedi-
carboxylate (3b), the yield of the corresponding product (4m,
67%) decreased only slightly, whereas more bulky ester groups
such as isopropyl (as in 3c) or tert-butyl (as in 3d) significantly
lowered the yields of the resulting products (4n, 40%; 4o,
53%), proposedly as a result of steric effects (Table 1, entries
2−4).
entries 7 and 8). When the terminal alkyne methyl propiolate
(3i) was applied, none of the expected addition product was
obtained (Table 1, entry 9).
In summary, we investigated light-induced additions of
aroylsilanes to alkynes and obtained enonyl silanes in good to
excellent yields. The process is highly regio- and chemoselective
and proceeds with complete atom economy. Presumably, the
aroylsilanes undergo Brook rearrangements to provide
siloxycarbenes as intermediates, which add to electron-deficient
alkynes leading to cyclopropene derivatives that rearrange to
form the observed products.
EXPERIMENTAL SECTION
■
General Experimental. Unless otherwise stated, the reactions
were carried out in oven-dried reaction vessels under an argon
atmosphere. The CH2Cl2 used for the experiments was dried by
distillation over CaH2. All of the product mixtures were analyzed by
thin-layer chromatography using TLC silica gel plates with fluorescent
indicator (λ = 254 nm). NMR spectra were recorded in deuterated
chloroform at 25 °C. Chemical shifts (δ) are reported in parts per
million, and spin−spin coupling constants (J) are quoted in hertz. The
multiplicities in NMR are given by the standard abbreviations: br s
(broad singlet), s (singlet), d (doublet), t (triplet), q (quartet), and m
(multiplet). Mass spectrometry was performed on a hybrid ion trap−
Orbitrap mass spectrometer. IR spectra were recorded on an FT-IR
spectrometer, and the wavenumbers of the absorption peaks are
reported in cm−1. All of the acylsilanes used in the following
experiments were prepared in accordance with previously published
synthetic strategies.8
Table 1. Investigations into the Different Types of Alkynes
a
Applicable to This Reaction Process
General Procedure for the Intermolecular Silylacylation. The
acylsilane (0.3 mmol, 1 equiv) was added to a solution of the electron-
deficient alkyne (0.6 mmol, 2 equiv) in dry DCM (1 mL) in a
common 4 mL screw-capped vial under an argon atmosphere. The
resulting solution was stirred for 2−4 days under light irradiation9 with
a Philips Genie Long Life 23 W fluorescent lamp. Then the solvent
was removed under reduced pressure, and the product was purified by
column chromatography (EtOAc/pentane, 1:9).
Dimethyl 2-Benzoyl-3-(trimethylsilyl)maleate (4a). Following the
general procedure, the product was obtained as colorless crystals in
81% yield (78 mg). 1H NMR (400 MHz, CDCl3): δ = 7.93−7.86 (m,
2H), 7.62−7.55 (m, 1H), 7.50−7.43 (m, 2H), 3.84 (s, 3H), 3.61 (s,
3H), 0.04 (s, 9H) ppm. 13C NMR (101 MHz, CDCl3): δ = 193.4,
170.8, 163.1, 154.5, 141.0, 136.6, 134.1, 129.4, 128.9, 52.8, 52.2, −1.3
ppm. HRMS (ESI-MS): calcd for [C16H20O5Si + Na]+, 343.0978;
found, 343.0972. IR ν (cm−1): 2956, 1727, 1678, 1595, 1440, 1238,
1238, 1117, 938, 850. Mp: 72 °C.
Dimethyl 2-Benzoyl-3-(triethylsilyl)maleate (4b). Following the
general procedure, the product was obtained as colorless crystals in
31% yield (34 mg). 1H NMR (400 MHz, CDCl3): δ = 7.94−7.88 (m,
2H), 7.63−7.57 (m, 1H), 7.51−7.45 (m, 2H), 3.86 (s, 3H), 3.63 (s,
3H), 0.85 (t, J = 7.9 Hz, 9H), 0.55 (q, J = 7.6 Hz, 6H) ppm. 13C NMR
(101 MHz, CDCl3): δ = 193.3, 171.0, 163.3, 153.5, 142.0, 136.6,
134.0, 129.4, 128.9, 52.8, 52.2, 7.1, 3.2 ppm. HRMS (ESI-MS): calcd
for [C19H26O5Si + Na]+, 385.1447; found, 385.1442. IR ν (cm−1):
2955, 1727, 1593, 1447, 1233, 1114, 1020, 724. Mp: 54 °C.
entry alkyne
R1
R2
CO2Me
product yield (%)
1
2
3
4
5
6
7
8
9
3a
3b
3c
3d
3e
3f
CO2Me
CO2Et
CO2i-Pr
CO2t-Bu
CO2Me
CO2Me
Et
4a
4m
4n
4o
4p
4q
4r
81
67
40
53
50
28
−
CO2Et
CO2i-Pr
CO2t-Bu
c
CO2Ph
b
CO-morpholinyl
3g
3h
3i
Et
Ph
H
Ph
4s
−
CO2Me
4t
−
a
Reaction conditions: acylsilane 1a (1.0 equiv), alkyne 3 (2.0 equiv),
b
c
CH2Cl2, light irradiation, 3 days. Reaction time of 6 days. E/Z ratio
= 11/1.
In order to investigate the regioselectivity of the
siloxycarbene addition, the mixed diester methyl phenyl
acetylenedicarboxylate (3e) was applied (Table 1, entry 5).
The reaction resulted in the formation of a single isomer (4p,
50%), with the silyl group next to the phenyl ester moiety.
Interestingly, an E/Z isomer mixture in a ratio of 11:1 was
observed in this case. Finally, the use of alkyne 3f containing
both an ester and an amide functionality was explored. Suitable
amounts of the corresponding product 4q could be obtained
only after 6 days of reaction time, and even under those
optimized conditions, 4q was formed in only 28% yield (Table
1, entry 6). We hypothesize that the decrease in reactivity of 3f
is due to the reduced electron-withdrawing capability of the
amide group.
Dimethyl 2-Benzoyl-3-(tert-butyldimethylsilyl)maleate (4c). Fol-
lowing the general procedure, the product was obtained as colorless
1
crystals in 44% yield (48 mg). H NMR (400 MHz, CDCl3): δ =
7.94−7.89 (m, 2H), 7.62−7.55 (m, 1H), 7.51−7.44 (m, 2H), 3.83 (s,
3H), 3.61 (s, 3H), 0.91 (s, 9H), −0.05 (s, J = 0.8 Hz, 6H) ppm. 13C
NMR (101 MHz, CDCl3): δ = 193.2, 171.1, 163.4, 152.2, 142.8, 136.8,
134.0, 129.3, 128.9, 52.9, 52.2, 27.2, −4.54 ppm. HRMS (ESI-MS):
calcd for [C19H26O5Si + Na]+, 385.1447; found, 385.1442. IR ν
(cm−1): 2948, 1726, 1592, 1447, 1234, 1113, 1019, 816. Mp: 45 °C.
Dimethyl 2-Benzoyl-3-(dimethyl(phenyl)silyl)maleate (4d). Fol-
lowing the general procedure, the product was obtained as colorless
crystals in 27% yield (31 mg). 1H NMR (400 MHz, CDCl3): δ = 7.65
(dd, J = 8.3, 1.3 Hz, 2H), 7.51−7.45 (m, 1H), 7.36−7.27 (m, 4H),
Electron-neutral internal alkynes such as 3-hexyne (3g) and
1,2-diphenylethyne (3h) did not afford the corresponding
products, and the starting materials were recovered (Table 1,
815
dx.doi.org/10.1021/jo402457x | J. Org. Chem. 2014, 79, 814−817

The Journal of Organic Chemistry
Note
7.18−7.08 (m, 3H), 3.74 (s, 3H), 3.60 (s, 3H), 0.40 (s, 6H) ppm. 13
C
Dimethyl 2-(Thiophene-2-carbonyl)-3-(trimethylsilyl)maleate
(4l). Following the general procedure, the product was obtained as
colorless crystals in 61% yield (60 mg). 1H NMR (600 MHz, CDCl3):
δ = 7.75 (dd, J = 4.9, 0.8 Hz, 1H), 7.62 (dd, J = 3.7, 0.9 Hz, 1H), 7.14
(dd, J = 4.8, 3.9 Hz, 1H), 3.84 (s, 3H), 3.68 (s, 3H), 0.09 (s, 9H) ppm.
13C NMR (151 MHz, CDCl3): δ = 185.5, 170.7, 163.1, 154.4, 144.2,
NMR (101 MHz, CDCl3): δ = 192.9, 170.7, 163.2, 153.3, 142.0, 136.2,
134.6, 133.7, 133.5, 129.9, 129.3, 128.5, 127.6, 52.8, 52.2, −2.6 ppm.
HRMS (ESI-MS): calcd for [C21H22O5Si + Na]+, 405.1129; found,
405.1139. IR ν (cm−1): 2954, 1728, 1676, 1595, 1433, 1236, 1116,
938, 843, 817, 787, 735, 697. Mp: 72 °C.
Dimethyl 2-(4-Methylbenzoyl)-3-(trimethylsilyl)maleate (4e). Fol-
lowing the general procedure, the product was obtained as white
crystals in 85% yield (85 mg). H NMR (300 MHz, CDCl3): δ =
7.83−7.76 (m, 2H), 7.30−7.24 (m, 2H), 3.85 (s, 3H), 3.63 (s, 3H),
2.42 (s, 3H), 0.05 (s, 9H) ppm. 13C NMR (101 MHz, CDCl3): δ =
193.0, 171.0, 163.3, 154.1, 145.3, 141.2, 134.3, 129.7, 129.6, 52.8, 52.2,
22.0, −1.2 ppm. HRMS (ESI-MS): calcd for [C17H22O5Si + Na]+,
357.1129; found, 357.1128. IR ν (cm−1): 2955, 1726, 1674, 1605,
1435, 1238, 1116, 848. Mp: 79 °C.
140.4, 135.8, 135.2, 128.5, 52.9, 52.2, −1.3 ppm. HRMS (ESI-MS):
calcd for [C14H18O5SSi + Na]+, 349.0536; found, 349.0544. IR ν
(cm−1): 2954, 1723, 1647, 1409, 1218, 1110, 1018, 845. Mp: 54 °C.
Diethyl 2-Benzoyl-3-(trimethylsilyl)maleate (4m). Following the
general procedure, the product was obtained as a colorless oil in 67%
yield (70 mg). 1H NMR (600 MHz, CDCl3): δ = 7.91−7.87 (m, 2H),
7.60−7.56 (m, 1H), 7.48−7.45 (m, 2H), 4.32 (q, J = 7.2 Hz, 2H), 4.08
(q, J = 7.1 Hz, 2H), 1.35 (t, J = 7.2 Hz, 3H), 1.02 (t, J = 7.1 Hz, 3H),
0.07 (s, 9H) ppm. 13C NMR (151 MHz, CDCl3): δ = 193.7, 170.4,
162.7, 154.2, 141.3, 136.9, 133.9, 129.3, 128.8, 61.8, 61.2, 14.3, 13.8,
−1.1 ppm. HRMS (ESI-MS): calcd for [C18H24O5Si + Na]+, 371.1285;
found, 371.1281. IR ν (cm−1): 2981, 1724, 1678, 1450, 1367, 1230,
1111, 1033, 850.
1
Dimethyl 2-(4-Methoxybenzoyl)-3-(trimethylsilyl)maleate (4f).
Following the general procedure, the product was obtained as yellow
1
crystals in 94% yield (99 mg). H NMR (300 MHz, CDCl3): δ =
7.90−7.83 (m, 2H), 6.97−6.89 (m, 2H), 3.86 (s, 3H), 3.83 (s, 3H),
3.62 (s, 3H), 0.03 (s, 9H) ppm. 13C NMR (75 MHz, CDCl3): δ =
191.8, 171.0, 164.4, 163.3, 153.6, 141.3, 131.9, 129.8, 114.1, 55.6, 52.8,
52.1, −1.3 ppm. HRMS (ESI-MS): calcd for [C17H22O6Si + Na]+,
373.1078; found, 373.1076. IR ν (cm−1): 2438, 2953, 1725, 1667,
1596, 1436, 1245, 1174, 1115, 849. Mp: 62 °C.
Diisopropyl 2-Benzoyl-3-(trimethylsilyl)maleate (4n). Following
the general procedure, the product was obtained as colorless crystals in
40% yield (45 mg). 1H NMR (600 MHz, CDCl3): δ = 7.90−7.86 (m,
2H), 7.59−7.55 (m, 1H), 7.47−7.43 (m, 2H), 5.21 (dt, J = 12.6, 6.3
Hz, 1H), 4.93 (dt, J = 12.5, 6.2 Hz, 1H), 1.33 (d, J = 6.3 Hz, 6H), 0.98
(d, J = 6.3 Hz, 6H), 0.08 (s, 9H) ppm. 13C NMR (151 MHz, CDCl3):
δ = 194.0, 169.8, 162.1, 154.3, 141.6, 137.1, 133.7, 129.2, 128.7, 69.6,
68.9, 22.0, 21.4, −1.0 ppm. HRMS (ESI-MS): calcd for [C20H28O5Si +
Na]+, 399.1598; found, 399.1604. IR ν (cm−1): 2980, 1719, 1668,
1550, 1460, 1374, 1231, 1098, 1007, 915, 841, 767. Mp: 52 °C.
Di-tert-butyl 2-Benzoyl-3-(trimethylsilyl)maleate (4o). Following
the general procedure, the product was obtained as colorless crystals in
53% yield (64 mg). 1H NMR (600 MHz, CDCl3): δ = 7.89−7.86 (m,
2H), 7.58−7.54 (m, 1H), 7.47−7.42 (m, 2H), 1.54 (s, 9H), 1.19 (s,
9H), 0.10 (s, 9H) ppm. 13C NMR (151 MHz, CDCl3): δ = 194.3,
169.2, 161.7, 153.5, 142.6, 137.4, 133.5, 129.0, 128.7, 82.6, 82.2, 28.3,
27.7, −0.8 ppm. HRMS (ESI-MS): calcd for [C22H32O5Si + Na]+,
427.1911; found, 427.1912. IR ν (cm−1): 2978, 1719, 1667, 1595,
1452, 1368, 1244, 1154, 1116, 1001, 891, 842, 765. Mp: 115 °C.
1-Methyl 4-Phenyl 2-Benzoyl-3-(trimethylsilyl)maleate (4p).
Following the general procedure, the product was obtained as white
Dimethyl 2-(4-Chlorobenzoyl)-3-(trimethylsilyl)maleate (4g). Fol-
lowing the general procedure, the product was obtained as white
1
crystals in 76% yield (81 mg). H NMR (300 MHz, CDCl3): δ =
7.86−7.80 (m, 2H), 7.48−7.42 (m, 2H), 3.85 (s, 3H), 3.62 (s, 3H),
0.05 (s, 9H) ppm. 13C NMR (75 MHz, CDCl3): δ = 192.3, 170.7,
162.9, 155.2, 140.7, 140.5, 135.1, 130.7, 129.3, 52.9, 52.3, −1.3 ppm.
HRMS (ESI-MS): calcd for [C16H19ClO5Si + Na]+, 377.0583; found,
377.0579. IR ν (cm−1): 2956, 1715, 1676, 1585, 1430, 1230, 1116,
1093, 841. Mp: 74 °C.
Dimethyl 2-[4-(Trifluoromethyl)benzoyl]-3-(trimethylsilyl)-
maleate (4h). Following the general procedure, the product was
obtained as a colorless oil in 53% yield (62 mg). 1H NMR (300 MHz,
CDCl3): δ = 8.01 (d, J = 8.1 Hz, 2H), 7.75 (d, J = 8.5 Hz, 2H), 3.87 (s,
3H), 3.63 (s, 3H), 0.07 (s, 9H) ppm. 13C NMR (75 MHz, CDCl3): δ
= 192.6, 170.6, 162.8, 156.2, 140.2, 139.3, 135.9, 135.4, 135.0, 134.6,
129.6, 126.1, 121.8, 53.0, 52.3, −1.3 ppm. HRMS (ESI-MS): calcd for
[C17H19O5F3Si + Na]+, 411.0852; found, 411.0846. IR ν (cm−1): 2958,
1729, 1688, 1435, 1323, 1240, 1173, 1129, 851.
Dimethyl 2-(3-Methoxybenzoyl)-3-(trimethylsilyl)maleate (4i).
Following the general procedure, the product was obtained as a
colorless oil in 95% yield (100 mg). 1H NMR (300 MHz, CDCl3): δ =
7.47−7.40 (m, 2H), 7.38−7.32 (m, 1H), 7.15−7.10 (m, 1H), 3.84 (s,
6H), 3.61 (s, 3H), 0.05 (s, 9H) ppm. 13C NMR (75 MHz, CDCl3): δ
= 193.2, 170.8, 163.1, 160.1, 154.4, 140.9, 137.9, 129.9, 122.7, 120.9,
112.5, 55.5, 52.8, 52.2, −1.3 ppm. HRMS (ESI-MS): calcd for
[C17H22O6Si + Na]+, 373.1078; found, 373.1074. IR ν (cm−1): 2955,
1726, 1678, 1593, 1437, 1240, 1110, 1040, 853.
1
crystals in 50% yield (57 mg). H NMR (600 MHz, CDCl3): δ =
7.98−7.96 (m, 2H), 7.65−7.61 (m, 1H), 7.53−7.50 (m, 2H), 7.46−
7.42 (m, 2H), 7.34−7.31 (m, 2H), 7.29−7.25 (m, 1H), 3.70 (s, 3H),
0.18 (s, 9H) ppm. 13C NMR (151 MHz, CDCl3): δ = 193.4, 168.8,
163.1, 153.7, 150.6, 141.5, 136.6, 134.3, 129.7, 129.5, 129.0, 126.2,
121.8, 53.0, −1.0 ppm. HRMS (ESI-MS): calcd for [C21H22O5Si +
Na]+, 405.1129; found, 405.1133. IR ν (cm−1): 3062, 2960, 1725,
1671, 1590, 1487, 1448, 1314, 1235, 1181, 1115, 1023, 978, 841, 755,
730, 690, 662. Mp: 94 °C. Two isomers were observed in the NMR
spectra in a ratio of 11:1.
Methyl (E)-2-Benzoyl-4-morpholino-4-oxo-3-(trimethylsilyl)but-
2-enoate (4q). Following the general procedure, the product was
obtained as yellow crystals in 28% yield (32 mg). 1H NMR (600 MHz,
CDCl3): δ = 7.91−7.88 (m, 1H), 7.61−7.58 (m, 1H), 7.49−7.46 (m,
2H), 3.89−3.85 (m, 1H), 3.81−3.74 (m, 2H), 3.64 (ddd, J = 15.4, 8.7,
4.9 Hz, 3H), 3.61 (s, 3H), 3.43 (ddd, J = 13.1, 7.4, 3.3 Hz, 1H), 3.37
(ddd, J = 13.1, 5.5, 3.3 Hz, 1H), 0.06 (s, 9H) ppm. 13C NMR (151
MHz, CDCl3): δ = 194.0, 169.9, 163.4, 157.6, 140.1, 136.8, 134.2,
129.5, 129.0, 66.6, 66.3, 52.7, 46.5, 41.5, −0.8 ppm. HRMS (ESI-MS):
calcd for [C19H25NO5Si + Na]+, 398.1394; found, 398.1390. IR ν
(cm−1): 2920, 2857, 1724, 1634, 1428, 1222, 1113, 1061, 991, 903,
847, 746, 699. Mp: 82 °C.
Dimethyl 2-(2-Methylbenzoyl)-3-(trimethylsilyl)maleate (4j). Fol-
lowing the general procedure, the product was obtained as a colorless
oil in 12% yield (12 mg). 1H NMR (400 MHz, CDCl3): δ = 7.66 (dd,
J = 7.8, 1.3 Hz, 1H), 7.43 (td, J = 7.5, 1.4 Hz, 1H), 7.31−7.23 (m, 2H),
3.85 (s, 3H), 3.59 (s, 3H), 2.63 (s, 3H), 0.11 (s, 9H) ppm. 13C NMR
(101 MHz, CDCl3): δ = 195.1, 171.1, 163.5, 154.0, 142.4, 140.4,
135.6, 132.9, 132.5, 131.9, 125.9, 52.8, 52.2, 21.9, −1.2 ppm. HRMS
(ESI-MS): calcd for [C17H22O5Si + Na]+, 357.1129; found, 357.1136.
IR ν (cm−1): 2955, 1727, 1677, 1600, 1438, 1236, 1102, 849.
Dimethyl 2-(Furan-2-carbonyl)-3-(trimethylsilyl)maleate (4k).
Following the general procedure, the product was obtained as a
colorless oil in 62% yield (58 mg). 1H NMR (600 MHz, CDCl3): δ =
7.65−7.63 (m, 1H), 7.24−7.20 (m, 1H), 6.59−6.56 (m, 1H), 3.84 (s,
3H), 3.69 (s, 3H), 0.10 (s, 9H) ppm. 13C NMR (151 MHz, CDCl3): δ
= 180.8, 170.7, 163.0, 155.4, 152.6, 147.8, 139.8, 129.9, 120.0, 112.8,
52.9, 52.2, −1.3 ppm. HRMS (ESI-MS): calcd for [C14H18O6Si +
Na]+, 333.0770; found, 333.0763. IR ν (cm−1): 2955, 1726, 1678,
1593, 1437, 1240, 1110, 1040, 853.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 13C NMR spectra. This material is available free of
charge via the Internet at http://pubs.acs.org.
816
dx.doi.org/10.1021/jo402457x | J. Org. Chem. 2014, 79, 814−817

The Journal of Organic Chemistry
Note
pressure mercury lamp was applied. Utilizing a 420 nm LED as the
light source for the reaction with aroylsilane 1a shortened the reaction
time.
AUTHOR INFORMATION
Corresponding Author
*E-mail: Carsten.bolm@oc.rwth-aachen.de.
■
Present Address
†H.-J.Z.: Department of Chemistry, College of Chemistry and
Chemical Engineering, Xiamen University, Xiamen 361005,
Fujian, P. R. China.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
D.L.P. and H.-J.Z. are grateful to the Alexander von Humboldt
Foundation for postdoctoral fellowships.
■
REFERENCES
■
(1) (a) Fu, G. C. In Modern Rhodium-Catalyzed Organic Reactions;
Evans, P. A., Ed.; Wiley-VCH: New York, 2005; pp 79−91. (b) Willis,
M. C. Chem. Rev. 2010, 110, 725. (c) Biju, A. T.; Kuhl, N.; Glorius, F.
Acc. Chem. Res. 2011, 44, 1182.
(2) For reviews of acylsilanes, see: (a) Zhang, H. J.; Priebbenow, D.
L.; Bolm, C. Chem. Soc. Rev. 2013, 42, 8540. (b) Patrocínio, A. F.;
Moran, P. J. S. J. Braz. Chem. Soc. 2001, 12, 7.
(3) Yamane, M.; Amemiya, T.; Narasaka, K. Chem. Lett. 2001, 1210.
(4) For the formation of siloxycarbenes from acylsilanes, see:
(a) Duff, J. M.; Brook, A. G. Can. J. Chem. 1973, 51, 2869. (b) Brook,
A. G. Adv. Organomet. Chem. 1969, 7, 95. (c) Brown, R. S. Can. J.
Chem. 1975, 53, 2446. (d) Bernardi, F.; Lunazzi, L.; Ricci, A.; Seconi,
G.; Tonachini, G. Tetrahedron 1986, 42, 3607. (e) Perrin, H. M.;
White, W. R.; Platz, M. S. Tetrahedron Lett. 1991, 32, 4443.
(f) Trommer, M.; Sander, W. Organometallics 1996, 15, 189.
(g) Bassindale, A. R.; Brook, A. G.; Harris, J. J. Organomet. Chem.
1975, 90, C6. (h) Brook, A. G. Acc. Chem. Res. 1974, 7, 77. (i) Shen,
Z.; Dong, V. M. Angew. Chem. 2009, 121, 798; Angew. Chem., Int. Ed.
2009, 48, 784. (j) Becker, P.; Priebbenow, D. L.; Pirwerdjan, R.; Bolm,
C. Angew. Chem., Int. Ed. 2013, DOI: 10.1002/anie.201307446.
(5) Zhang, H.-J.; Becker, P.; Huang, H.; Pirwerdjan, R.; Pan, F.-F.;
Bolm, C. Adv. Synth. Catal. 2012, 354, 2157.
(6) For a single example of an intermolecular addition of a
photochemically generated silyoxycarbene to an internal alkyne that
leads, however, to a different product type, see: Brook, A. G.; Kucera,
H. W.; Pearce, R. Can. J. Chem. 1971, 49, 1618.
(7) Additions of acylsilanes to alkenes have been suggested to
proceed via short-lived 1,4-diradicals that rearrange and undergo ring
closure to yield cyclopropane derivatives. See: Dalton, J. C.; Bourque,
R. A. J. Am. Chem. Soc. 1981, 103, 699. Although we cannot exclude
such a pathway here, we do not regard it as being relevant because (1)
the presence of radical traps (TEMPO or 2,4,6-trimethylphenol) did
not affect the product formation and (2) the addition of 2-propanol
led to an acetal-like product, which is indicative of the involvement of a
carbene-type intermediate.
(8) (a) Brook, A. G.; Duff, J. M.; Jones, P. F.; Davis, N. R. J. Am.
Chem. Soc. 1967, 89, 431. (b) Corey, E. J.; Seebach, D.; Freedman, R.
J. Am. Chem. Soc. 1967, 89, 434. (c) Patrocínio, A. F.; Correa, I. R., Jr.;
̂
Moran, P. J. S. J. Chem. Soc., Perkin Trans. 1 1999, 3133. (d) Patrocínio,
A. F.; Moran, P. J. S. J. Organomet. Chem. 2000, 603, 220. (e) Wu, X.-
F.; Neumann, H.; Beller, M. Tetrahedron Lett. 2012, 53, 582.
(f) Yamamoto, K.; Suzuki, S.; Tsuji, J. Tetrahedron Lett. 1980, 21,
1653. (g) Ricci, A.; Degl’Innocenti, A.; Chimichi, S.; Fiorenza, M.;
Rossini, G. J. Org. Chem. 1985, 50, 130. (h) Yamamoto, K.; Hayashi,
A.; Suzuki, S.; Tsuji, J. Organometallics 1987, 6, 974. (i) Ito, K.;
Tamashima, H.; Iwasawa, N.; Kusama, H. J. Am. Chem. Soc. 2011, 133,
3716.
(9) Under the assumption that visible light (410−440 nm, correlating
to the maximal n−π* absorption of the acylsilanes) promoted the
reaction process, a low-cost household compact fluorescent lamp with
a broad emission spectrum was used in this study. The yield was
significantly lower when Pyrex glassware in combination with a high-
817
dx.doi.org/10.1021/jo402457x | J. Org. Chem. 2014, 79, 814−817