Aryl trialkylsilyl ketenes: Acid-catalyzed synthesis from 1-aryl-2-diazo-2-trialkylsilylethanones and their conversion into 3-silyl-1-silyloxyallenes

Article abstract of DOI:10.1002/ejoc.200800524

Aryl-substituted α-silyl α-diazo ketones are readily transformed into aryl silyl ketenes in the presence of a catalytic amount of triflic acid. Thus, a convenient method to prepare these silyl ketenes becomes available, which combines two steps, silylation of an aryl diazomethyl ketone and acid-induced Wolff rearrangement of the formed α-silyl α-diazo ketone, in a one-pot procedure. It appears that the trialkyl-ammonium salt, which is formed in the silylation step, can also catalyze the Wolff rearrangement, but distinctly more slowly than the proton acid. The silyl ketenes react smoothly with α-silyl α-diazo ketones to form 3-silyl-1-silyloxyallenes in fairly good yields. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejoc.200800524

FULL PAPER
DOI: 10.1002/ejoc.200800524
Aryl Trialkylsilyl Ketenes: Acid-Catalyzed Synthesis from 1-Aryl-2-diazo-2-
trialkylsilylethanones and Their Conversion into 3-Silyl-1-silyloxyallenes
Stefan M. Bucher,[a] Ralf Brückmann,[a][‡] and Gerhard Maas*[a]
Keywords: Allenes / Diazo compounds / Ketenes / Rearrangement / Silylation
Aryl-substituted α-silyl α-diazo ketones are readily trans-
formed into aryl silyl ketenes in the presence of a catalytic
amount of triflic acid. Thus, a convenient method to prepare
these silyl ketenes becomes available, which combines two
steps, silylation of an aryl diazomethyl ketone and acid-in-
duced Wolff rearrangement of the formed α-silyl α-diazo
ketone, in a one-pot procedure. It appears that the trialkyl-
ammonium salt, which is formed in the silylation step, can
also catalyze the Wolff rearrangement, but distinctly more
slowly than the proton acid. The silyl ketenes react smoothly
with α-silyl α-diazo ketones to form 3-silyl-1-silyloxyallenes
in fairly good yields.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
practical method to prepare α-silyl α-diazo ketones.[4,8,9]
Typically, diethyl ethyl ether is used as the reaction medium,
from which most (but not all) of the formed trialkylammon-
ium triflate precipitates as the reaction proceeds. In order to
avoid protonation/desilylation of the product by the acidic
ammonium salt, Danheiser et al. have used the less polar
reaction medium diethyl ether/hexane (1:1), in which the
ammonium salt is less soluble, and in fact obtained the silyl-
diazo ketones in higher yields.[10]
The silylation of diazomethyl ketones 1a–c with trimeth-
ylsilyl triflate or triethylsilyl triflate and diisopropylethyl-
amine in ether or diethyl ether/pentane mixtures provided
the corresponding α-silyl α-diazo ketones 2a–e (Scheme 1).
The synthesis of 2b and 2d by this method has been de-
scribed before,[4,8] but in the present study we prepared only
concentrated solutions of 2a–e that were suitable for further
transformations (see below). It should be recalled that no α-
Introduction
Due to their remarkable chemical stability, silyl ketenes
have received much attention as versatile building blocks in
organic synthesis.[1,2] For example, trialkylsilyl ketenes can
be transformed into allenylsilanes with phosphonium ylides
by Wittig olefination[3,4] and also with organometallic
methylenation reagents.[4] The long-known[5] reactivity of
ketenes towards diazoalkanes has also been extended to
silyl ketenes.[1,2] Of particular interest to the present study
are reactions between (diazomethyl)trialkylsilanes and tri-
methylsilyl ketene, which afford 1-trimethylsilyl-2-trialkyl-
silylcyclopropanones.[6] In contrast, when TMS-diazometh-
ane is combined with phenyl (phosphoryl, sulfonyl, or vi-
nyl) ketenes, the cyclopropanone adduct appears to be a
reactive intermediate that readily decarbonylates to form β-
(trimethylsilyl)styrenes [or 1-(trimethylsilyl)-1,3-dienes, in
the case of a vinyl substituent] in good yields.[7] We intro-
duce here a formally similar transformation, by which 3-
silyl-1-silyloxyallenes are obtained from the reaction of tri-
alkylsilyl ketenes with 1-aryl-2-diazo-2-trialkylsilyl-1-etha-
nones. In the course of this investigation, we detected a sur-
prisingly simple one-pot preparation of the required α-silyl
α-diazo ketones from aryl diazomethyl ketones.
Results and Discussion
Electrophilic silylation of α-diazo ketones with silyl tri-
flates in the presence of a tert-amine presents a versatile and
[a] Institute for Organic Chemistry I, University of Ulm,
Albert-Einstein-Allee 11, 89081 Ulm, Germany
Fax: +49-(0)731-5022803
E-mail: gerhard.maas@uni-ulm.de
[‡] Current address: CHT R. Beitlich GmbH,
Bismarckstraße 102, 72072 Tübingen
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
Scheme 1. Synthesis of silyldiazo ketones 2 and silyl ketenes 3.
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Eur. J. Org. Chem. 2008, 4426–4433
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From Aryl Trialkylsilyl Ketenes to 3-Silyl-1-silyloxyallenes
trimethylsilyl-substituted α-diazo ketones have so far been
isolated in pure form and that decomposition of 2a during
workup has been reported.[8]
To our surprise, the aryl trialkylsilyl ketenes 3a–d rather
than silyldiazo ketones 2 were obtained when the reactions
were carried out in dichloromethane or chloroform solution
(Ͼ95% conversion according to 1H NMR spectroscopy, see
for example the spectrum of crude 3c in the Supporting
Information; 60–70% yield after kugelrohr distillation). In
these solvents, ammonium triflate 4 is completely soluble,
suggesting that it catalyzes the conversion of first-formed
diazo ketones 2 into silyl ketenes 3. In fact, we found that
2c, prepared in ether solution as described above, is stable
in the presence of chloroform for at least 90 min, but gas
evolution sets in immediately after addition of ammonium
salt 4 and, depending on the amount of 4, the diazo ketone
is either completely converted into silyl ketene 3c or a mix-
ture of 3c and allene 5g (see next paragraph) or, with only
0.1 equiv. of salt 4, allene 5g accompanied by small
amounts of the original diazomethyl ketone 1b. A more de-
Scheme 2. Acid-induced transformation of 2b.
tailed study was then carried out with purified silyldiazo 1.1 equiv. of NEtiPr2); complete conversion of the first-
ketone 2b (Scheme 2). Again, it was found that ammonium formed silyldiazo ketone 2b into silyl ketene 3b was noted
salt 4 was able to convert 2b into silyl ketene 3b. However, only after 14 h (as opposed to 2 h with less pure Et3SiOTf).
the reaction time for complete consumption of 2b was 20 h (b) Two equivalents of NEtiPr2 were used for the silylation
at 20 °C, even when 1.5 molar equivalents of salt 4 were of 1a with Et3SiOTf, that is, a 1:1 mixture of Et3SiOTf and
applied, and the product mixture consisted of ketene 3b, amine was added to a 1:1 mixture of 1a and amine in
diazo ketone 1a, and allene 5l in a 57:14:29 ratio [1H NMR dichloromethane. Silyldiazo ketone 2b was formed as usual,
integration; separation of allene 5l from ketene 3b by but it remained unchanged in the reaction solution for at
chromatography or distillation was not possible; NMR least 24 h and no ketene 3b was formed. Presumably, the
spectroscopic data of 5l: δ(1H) = 0.49–0.55 (m, 12 H), 0.91– presence of a second equivalent of the amine base not only
0.98 (m, 18 H), 7.18–7.21 (m, 2 H), 7.30–7.37 (m, 6 H), quenches triflic acid effectively, but also deactivates the tri-
7.43–7.48 (m, 2 H) ppm]. These results differ partially from alkylammonium ion by formation of a [R3N···H+···NR3]
those obtained under the conditions for the synthesis of 3b complex. The latter experiment shows that the silyldiazo
from 1a as shown in Scheme 1, where the reaction was over ketone synthesis can also be carried out successfully in
after 2 h at 20 °C and no significant amounts of products CH2Cl2 solution provided that a sufficient excess of the amine
other than 3b could be detected. Thus, there is some evi- base is present.
dence that general acid catalysis by the diisopropylethylam-
The formation of silyl ketenes 3 can thus be explained
monium ion is sufficient to achieve the transformation of as an acid-induced Wolff-type rearrangement of silyldiazo
silyldiazo ketones 2 into silyl ketenes 3. However, another ketones 2, which presumably includes O or C protonation
catalytic process is also operating and is obviously more of the diazo ketone (vide infra),[11] dediazoniation, and 1,2-
relevant.
aryl migration. Acceleration of the Wolff rearrangement in
Taking into account that trialkylsilyl triflates can contain the presence of protic nucleophiles, such as alcohols and
trace amounts of triflic acid (either because of partial hy- water at neutral pH, has been observed before for other
drolysis or from the production process) that are not elimin- diazo ketones, for example, 1-aryl-2-diazo-2-phenyl-1-etha-
ated by simple distillation before use, we exposed pure silyl- nones (substituted azibenzils); in contrast, solvolysis of azi-
diazo ketone 2b to a catalytic quantity (1 mol-%) of triflic benzils by aqueous acids affords only low yields of the ke-
acid (HOTf) and found that in fact gas evolution started tene-derived diarylacetic acids.[12,13] However, the influence
immediately and complete conversion took place within 2 h of protons or protic nucleophiles on the decomposition
to yield silyl ketene 3b and diazo ketone 1b in a 95:5 ratio. pathways of α-diazo ketones has been a subject of some
The suspected catalysis by trace amounts of HOTf is also discussion. On the basis of these investigations and other
in line with the following observations: (a) Commercial tri- knowledge of the behavior of α-diazo ketones toward ac-
ethylsilyl triflate was typically distilled prior to its use for ids,[12] one may assume that silyldiazo ketone 3 is initially
silylation of the diazo ketones. For a representative sample O protonated by HOTf to form a β-enoldiazonium ion,
of Et3SiOTf, we determined the content of triflic acid by which is then transformed into a vinyl cation by loss of N2;
salt formation with diisopropylethylamine (see Supporting 1,2-aryl shift and proton loss would finally yield silyl ketene
Information) as 0.38 wt.%. Then, triethylsilyl triflate was 3. In contrast, C protonation of 3 and counterion-assisted
distilled from calcium hydride and directly used for the si- desilylation would explain the formation of small amounts
lylation of ω-diazoacetophenone (1a) (CH2Cl2, 20 °C, of diazo ketones 1.
Eur. J. Org. Chem. 2008, 4426–4433
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S. M. Bucher, R. Brückmann, G. Maas
FULL PAPER
It is obvious from the experiments described above that
the direct one-pot synthesis of aryl silyl ketenes 3 from di-
azo ketones 1 and silyl triflates is somewhat capricious, be-
cause the intervening transformation of first-formed silyldi-
azo ketones 2 into 3 requires acid catalysis. In order to
achieve the formation of the silyl ketene in good yield and
with short reaction times, we therefore recommend the ad-
dition of a catalytic amount (1–4 mol-%) of triflic acid to
the reaction mixture when the silylation step is complete.
The synthesis of silyl ketene 3f by this procedure is shown
exemplarily in Scheme 3.
Scheme 4. Transformation of silyldiazo ketone 2c during workup.
chromatography over silica gel with a 20:1 mixture of pen-
tane/diethyl ether. Due to the low water content of this elu-
ent system, hydrolysis of the allene during chromatography
could be largely suppressed, and the contamination of the
allenes by the corresponding β-acylvinylsilane, if any, was
less than 4%. The constitution of allenes 5a and 5h was
confirmed by XRD analysis (Figures 1 and 2). Spectroscop-
ically, the allenes are characterized by a weak IR absorption
at 1901Ϯ7 cm–1 and the 13C NMR resonance of the central
allenic carbon at δ = 204.5–208.0 ppm.
Scheme 3. One-pot synthesis of silyl ketene 3f by diazo ketone
silylation/acid-induced Wolff rearrangement.
The full scope of this transformation for the synthesis of
silyl ketenes remains to be explored (e.g., the extension to
alkyl silyl ketenes), but it can be stated that the one-pot
formation of silyl ketenes 3a–d from diazomethyl ketones 1
and silyl triflates represents a considerable improvement
over existing methods. Usually, silyl ketenes are prepared
from silyldiazo ketones such as 2 in an additional step by a
photochemical[10,14,15] or transition-metal (copper[14] or
rhodium[4]) catalyzed Wolff rearrangement.
Attempts to isolate silyldiazo ketone 2c met with another
surprise (Scheme 4): diazo ketone 1b was trimethylsilylated
in ether in the presence of NEtiPr2 as usual, the precipitated
ammonium salt was filtered off, and the solvent was re-
moved completely. A slightly exothermic reaction ac-
companied by gas evolution started almost immediately to
give an oil, from which only β-acylvinylsilane 6 could be
isolated in low yield after column chromatography. The as-
sumption that 6 was formed by hydrolysis of allene 5g dur-
ing chromatography was later confirmed by treatment of an
independently synthesized sample of 5g with silica gel in
Scheme 5. Synthesis of 3-silyl-1-silyloxyallenes 5.
Table 1. Synthesis of 3-silyl-1-silyloxyallenes 5 (see Scheme 5).[a]
Allene Reactants Ar1
R1
Ar2
R2
Yield [%]
chloroform. As the concentrated solution before complete 5a
2a + 3a
2c + 3a
2e + 3a
2b + 3a
2d + 3a
2a + 3c
2c + 3c
2e + 3c
2b + 3c
2d + 3c
2b + 3d
Ph
An
Me
Me
Ph
Ph
Ph
Ph
Ph
An
An
An
An
An
An
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Et
51
65
84
63
59
70
71
69
59
83
69
5b
removal of the solvent contained only silyldiazo ketone 2c,
but no silyl ketene or allene, we speculated that in the ab-
sence of solvent, 2c was partly converted into silyl ketene
5c
2-furyl Me
5d
Ph
An
Ph
An
Et
Et
Me
Me
5e
3c by the residual (i.e., diethyl ether soluble amounts of)
trialkylammonium salt. Allene 5g would in turn result from
a reaction of 2c with 3c.
When silyldiazo ketones 2 and silyl ketenes 3 were com-
bined at 0–20 °C, gas evolution began immediately and af-
ter reaction times ranging from 3 (2c + 3c) to about 12 h,
1,3-diaryl-3-silyl-1-silyloxyallenes 5 were formed in fairly
good yields (Scheme 5 and Table 1). In order to avoid mate-
5f
5g
5h
5i
2-furyl Me
Ph
An
Ph
Et
Et
Et
5j
5k
[a] An = C6H4-4-OCH3.
A mechanistic proposal for the formation of allenes 5 is
rial losses in purification steps, both reactants were used given in Scheme 6. Previously, we have presented evidence
in crude form. The purification of allenes 5 required some that α-silyl α-diazo ketones 2 are in equilibrium with minute
experimentation, as they were rather labile towards column amounts of 1-diazo-2-silyloxyethenes 2Ј through
a
chromatography (silica gel or reverse-phase columns) with 1,3(CǞO) silyl shift.[16] Although the diazo cumulene
various eluents. The method of choice turned out to be isomer has not been observed directly so far, it can be
4428
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 4426–4433

From Aryl Trialkylsilyl Ketenes to 3-Silyl-1-silyloxyallenes
Scheme 6. Proposed mechanism for the formation of allenes 5.
Allenes 5 combine the structural and functional moieties
of allenylsilanes[19,20] and silyloxyallenes,[21,22] both of
which are versatile intermediates in organic synthesis. A few
3-silyl-1-silyloxyallenes have been mentioned in the litera-
ture.[20,23] They are easily converted into β-acylvinylsilanes
by acidic hydrolysis and by electrophilic C2-alkylation.
Figure 1. Molecular structure of allene 5a in the solid state. Ther-
mal displacement ellipsoids are drawn at 30% probability. Selected
bond lengths and angles (only one of the two molecules in the
asymmetric unit is shown above; data for the second molecule are
enclosed in brackets): C1–O1 1.375(3) [1.383(3)], O1–Si1 1.655(2)
[1.662(2)], C1–C2 1.320(3) [1.320(3)], C2–C3 1.318(3) [1.318(3)],
C3–Si2 1.893(2) [1.899(2)]Å; C1–O1–Si1 129.9(2) [129.0(1)], C1–
C2–C3 170.1(2) [172.2(2)], C2–C3–Si2 114.1(2) [114.8(2)]°; torsion
angles: C2–C1–C4–C5 9.3(3) [4.9(3)], C2–C3–C13–C18 –5.2(3)
[173.9(3)], C2–C1–O1–Si1 10.3(3) [19.1(3)]°.
Conclusions
We have made the surprising observation that aryl-sub-
stituted α-silyl α-diazo ketones are readily transformed into
aryl silyl ketenes in the presence of catalytic amounts of
triflic acid. This acid-induced Wolff rearrangement can be
combined in a one-pot procedure with the preparation of
the silyldiazo ketones from diazomethyl ketones and silyl
triflates in the presence of diisopropylethylamine. The trial-
kylammonium salt, which is formed during the silylation
reaction, also seems to catalyze the Wolff rearrangement,
but distinctly more slowly than triflic acid. A simple solvent
shift from ether (or diethyl ether/pentane), where this salt
has low solubility, to dichloromethane, where it is highly
soluble, changes the reaction product from the α-silyl α-
diazo ketone to the aryl silyl ketene, unless an excess
amount of the tert-amine base is present.
The prepared ketenes react smoothly with α-silyl α-diazo
ketones (or, more likely, with isomeric 2-silyloxy-1-diazo-
ethenes, which coexist in a silatropic equilibrium with the
former) to yield 1,3-diaryl-1-silyloxy-3-silylallenes. Further
investigations will show whether this reaction type can be
extended to silyl ketenes and silyldiazo ketones that bear
aliphatic rather than aromatic substituents.
Figure 2. Molecular structure of allene 5h in the solid state. Ther-
mal displacement ellipsoids are drawn at 50% probability. Selected
bond lengths and angles: C1–O1 1.380(3), O1–Si1 1.665(2), C1–C2
1.316(4), C2–C3 1.322(4), C3–Si2 1.898(3) Å; C1–O1–Si1 128.6(2),
C1–C2–C3 172.6(3), C2–C3–Si2 115.0(2)°.
Experimental Section
trapped selectively by [3+2] cycloaddition with various
General Information: All reactions were carried out under an atmo-
dipolarophiles, including N-phenylmaleimide, norbornene, sphere of argon by using standard Schlenk techniques. Rigorously
dried solvents were used. Kugelrohr distillations were performed
with a Büchi GKR 50 apparatus; oven temperatures are reported.
Chromatographic purifications were performed on Merck Lobar
columns (silica gel Si60, column size B or C). Melting points were
determined with a Büchi B-540 apparatus. Infrared spectra (IR)
were recorded with a Bruker Vector 22 FTIR spectrometer by using
KBr disks for solids and thin films between NaCl plates for liquids.
1H NMR (400.13 MHz) and 13C NMR (100.62 MHz) spectra were
measured with a Bruker DRX 400 spectrometer. All NMR spectra
were recorded in CDCl3 at 298 K and are reported in ppm relative
to TMS. Mass spectra were obtained with a Bruker micrOTOF-Q
cyclopropenes,
phosphaalkenes,
and
heterophos-
pholes.[16–18] We assume that diazo cumulenes 2Ј add also
across the C=C bond of silyl ketenes 3 to form pyrazoline
derivatives, which immediately undergo ring contraction to
form 2-methylenecyclopropanones 6, which in turn are de-
carbonylated to form allenes 5. The alternative pathway, N2
extrusion from 2Ј and [2+1] cycloaddition of the resulting
vinylidene, is disfavored, because these β-arylalkylidene
carbenes would undergo rapid 1,2-aryl shift to form silyl-
oxyalkynes.[8]
Eur. J. Org. Chem. 2008, 4426–4433
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4429

S. M. Bucher, R. Brückmann, G. Maas
FULL PAPER
46 instrument by using electron spray ionization (ESI) unless stated
otherwise. EI refers to electron ionization.
anone (1b) (0.88 g, 5.0 mmol) and triethylsilyl triflate (1.13 mL,
5.0 mmol). The crude product was purified by kugelrohr distillation
(0.05 mbar/140 °C), and 3d was obtained as a slightly yellow oil
Starting Materials: Diazo ketones 1a–c [ArCOCHN2, Ar = Ph (1a),
4-methoxyphenyl (1b), 2-furyl (1c)] were prepared by a published
procedure.[24] Trimethylsilyl and triethylsilyl triflate were donated
by Chemische Fabrik Karl Bucher GmbH (-89367 Waldstetten),
triisopropylsilyl triflate from Wacker Chemie AG (Munich). All
silyl triflates were distilled prior to use and kept under an atmo-
sphere of argon.
(0.92 g, 70%). IR (NaCl, film): ν = 2956 (s), 2911 (m), 2878 (m),
˜
2836 (m), 2085 (s, C=C=O), 1609 (m), 1578 (w), 1510 (s), 1464 (m),
1416 (w), 1281 (m), 1247 (s), 1180 (s), 1109 (w), 1036 (s), 959 (w),
914 (w), 827 (s) cm–1. 1H NMR: δ = 0.78 (q, 4J = 7.9 Hz, 6 H),
3
2
1.01 (t, J = 7.9 Hz, 9 H), 3.79 (s, 3 H), 6.87 (d, J = 8.7 Hz, 2 H),
2
7.07 (d, J = 8.8 Hz, 2 H) ppm. 13C NMR: δ = 3.9, 7.1, 18.4, 55.1,
114.5, 122.7, 129.5, 157.2, 182.1 ppm.
General Procedure for the Preparation of Aryl Trialkylsilyl Ketenes
3: A trialkylsilyl triflate (5 mmol) diluted in dichloromethane
(5 mL) was added dropwise to a stirred solution of aryl di-
azomethyl ketone 1 (5 mmol) and diisopropylethylamine (0.88 mL,
5 mmol) in dichloromethane (20 mL) at 0 °C. After completion of
the addition, a solution of trifluoromethanesulfonic acid (0.5  in
dichloromethane, 0.1 mL, 0.05 mmol) was added. The solution was
stirred at room temperature, and after 2 h, a solution of diisopropy-
lethylamine (0.5  in dichloromethane, 0.1 mL, 0.05 mmol) was
added. The solvent was evaporated at 0.05 mbar/20 °C. Pentane
(20 mL) was added, and the precipitated trialkylammonium triflate
was filtered off and washed with pentane (10 mL). The volatiles
were evaporated at 0.05 mbar/20 °C, and the resulting oil was sub-
mitted to kugelrohr distillation.
2-Phenyl-2-(triisopropylsilyl)ethenone (3f). Carried out by the gene-
ral procedure above with 2-diazo-1-phenylethanone (1a) (0.73 g,
5.0 mmol) and triisopropylsilyl triflate (1.34 mL, 5.0 mmol). The
crude product was purified by kugelrohr distillation (0.05 mbar/
145 °C), and 3f was obtained as a slightly yellow oil (0.89 g, 65%).
IR (NaCl, film): ν = 2946 (s), 2891 (m), 2868 (s), 2082 (s, C=C=O),
˜
1596 (m), 1495 (m), 1464 (m), 1385 (w) 1314 (w), 1255 (m), 1169
1
(m), 1073 (m), 1018 (m), 919 (s), 883 (s) cm–1. H NMR: δ = 1.14
3
3
(d, J = 7.3 Hz, 18 H), 1.31 (m, 3 H), 7.13 (t, J = 7.3 Hz, 1 H),
7.19 (d, J = 7.3 Hz, 2 H), 7.26–7.30 (m, 2 H) ppm. 13C NMR: δ
2
= 12.5, 18.5, 19.1, 125.0, 128.9, 129.2, 131.8, 181.9 ppm.
General Procedure for the Preparation of 3-Silyl-1-silyloxyallenes
(5): A trialkylsilyl triflate (5.0 mmol) dissolved in dichloromethane
(5 mL) was added drop by drop to a stirred solution of aryl di-
azomethyl ketone 1a–c (5.0 mmol) and diisopropylethylamine
(0.88 mL, 5.0 mmol) in dichloromethane (20 mL) at 0 °C. The re-
sulting solution was stirred at 20 °C for 2 h, and the solvent was
evaporated at 0.05 mbar/20 °C. Pentane (20 mL) was added, and
the precipitated trialkylammonium triflate was filtered off and
washed with pentane (10 mL). After evaporation of the solvent
from the combined filtrates at 0.05 mbar/20 °C, silyl ketene 3 was
left as a brown oil, which was used without purification.
Ketenes 3b[4b,8,14] and 3d[4b] have been synthesized before by photo-
chemical or rhodium-catalyzed decomposition of the correspond-
ing silyldiazo ketone.
2-Phenyl-2-(trimethylsilyl)ethenone (3a): Synthesis by the general
procedure from 2-diazo-1-phenylethanone (1a) (0.73 g, 5.0 mmol)
and trimethylsilyl triflate (0.91 mL, 5.0 mmol). The crude product
was purified by kugelrohr distillation (0.06 mbar/80 °C), and 3a
was obtained as a slightly yellow oil (0.57 g, 60%). IR (NaCl, film):
ν = 2959 (m), 2900 (w), 2084 (s, C=C=O), 1598 (m), 1497 (s), 1464
˜
In a parallel experimental setup, silyldiazo ketone 2 was generated
by dropwise addition of a solution of a trialkylsilyl triflate
(5.0 mmol) in pentane/diethyl ether (10:1, 22 mL) to a solution of
diisopropylethylamine (0.88 mL, 5.0 mmol) and aryl diazomethyl
ketone 1 (5.0 mmol) in ethyl ether (18 mL) at 0 °C. The solution
was stirred for 2 h at room temperature, the precipitated trialkylam-
monium triflate was filtered off, and the filtered solution [the pres-
ence of 2 was verified by 13C NMR spectroscopy of the reaction
solution, e.g., 2c: δ = 52.9 (CN2), 191.5 ppm (CO)] was added to
crude silyl ketene 3. The mixture was stirred for 12 h at room tem-
perature, the solvent was evaporated at 0.05 mbar/20 °C, pentane
(40 mL) was added to the residue, and the undissolved solid was
filtered off and discarded. Pentane was evaporated at 0.05 mbar/
20 °C, and the crude product was purified by column chromatog-
raphy (pentane/diethyl ether, 20:1) to yield 3-silyl-1-silyloxyallenes 5.
(m), 1411 (s), 1348 (w), 1304 (w), 1253 (s), 1166 (m), 1028 (s), 1001
1
(m), 948 (m), 925 (m), 843 (s) cm–1. H NMR: δ = 0.34 (s, 9 H),
7.10–7.14 (m, 3 H), 7.28–7.31 (m, 2 H) ppm.13C NMR: δ = –0.3,
24.0, 124.5, 127.8, 129.0, 131.9, 182.6 ppm.
2-Phenyl-2-(triethylsilyl)ethenone (3b). Synthesis by the general pro-
cedure from 2-diazo-1-phenylethanone (1a) (0.73 g, 5.0 mmol) and
triethylsilyl triflate (1.13 mL, 5.0 mmol). The crude product was
purified by kugelrohr distillation (0.08 mbar/100 °C), and 3b was
obtained as a slightly yellow oil (0.76 g, 69%). IR (NaCl, film): ν
˜
= 2957 (m), 2912 (m), 2878 (m), 2084 (s, C=C=O), 1597 (m), 1496
(m), 1458 (m), 1415 (w), 1380 (w), 1318 (w), 1262 (m), 1240 (m),
1166 (m), 1072 (m), 1005 (s), 920 (m) cm–1. 1H NMR: δ = 0.78 (q,
3
4J = 7.8 Hz, 6 H), 0.99 (t, J = 7.8 Hz, 9 H), 7.10–7.12 (m, 3 H),
7.24–7.28 (m, 2 H) ppm. 13C NMR: δ = 4.0, 7.1, 20.2, 124.6, 128.0,
128.9, 131.8, 181.8 ppm.
1,3-Diphenyl-3-trimethylsilyl-1-trimethylsilyloxy-1,2-propadiene
(5a): Preparation by the general procedure from 2-diazo-1-phenyl-
ethanone (1a) (0.73 g, 5.0 mmol) and trimethylsilyl triflate
(0.91 mL, 5.0 mmol) for silyl ketene 3a, and 2-diazo-1-phenyl-
ethanone (1a) (0.73 g, 5.0 mmol) and trimethylsilyl triflate
(0.91 mL, 5.0 mmol) for silyldiazo ketone 2a. The crude product
was purified by column chromatography (pentane/diethyl ether,
20:1), and 5a was obtained as a slightly yellow oil, which solidified
immediately to give colorless crystals (0.89 g, 51%). M.p. 71–72 °C.
2-(4-Methoxyphenyl)-2-(trimethylsilyl)ethenone (3c). Synthesis by
the general procedure from 2-diazo-1-(4-methoxyphenyl)ethanone
(1b) (0.88 g, 5.0 mmol) and trimethylsilyl triflate (0.91 mL,
5.0 mmol). The crude product was purified by kugelrohr distillation
(0.06 mbar/100 °C), and 3c was obtained as a slightly yellow oil
(0.76 g, 69%). IR (NaCl, film): ν = 2958 (s), 2903 (m), 2836 (m),
˜
2082 (s, C=C=O), 1608 (m), 1578 (w), 1510 (s), 1466 (m), 1442 (m),
1282 (s), 1249 (s), 1180 (s), 1110 (w), 1036 (s), 919 (m), 843 (s)
cm–1. 1H NMR: δ = 0.29 (s, 9 H), 3.79 (s, 3 H), 6.85 (d, 2J = 8.8 Hz,
2 H), 7.04 (d, 2J = 8.8 Hz, 2 H) ppm. 13C NMR: δ = –0.4, 22.3,
55.3, 114.6, 122.8, 129.3, 157.2, 182.9 ppm. C12H16O2Si (220.3):
calcd. C 65.4, H 7.3; found C 65.2, H 7.2.
IR (NaCl, film): ν = 2956 (m), 2897 (w), 1898 (m, C=C=C), 1593
˜
(m), 1577 (w), 1490 (m), 1448 (m), 1407 (w), 1346 (s), 1263 (s),
1248 (s), 1192 (m), 1176 (m), 1072 (m), 1061 (m), 1024 (m), 999
(w), 870 (s), 839 (s) cm–1. 1H NMR: δ = 0.19 (s, 9 H), 0.31 (s, 9
H), 7.19–7.25 (m, 2 H), 7.29–7.40 (m, 6 H), 7.47–7.49 (m, 2 H)
ppm. 13C NMR: δ = –0.1, 0.2, 117.7, 124.0, 126.0, 126.7, 127.0,
2-(4-Methoxyphenyl)-2-(triethylsilyl)ethenone (3d). Carried out by
the general procedure above with 2-diazo-1-(4-methoxyphenyl)eth-
4430
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 4426–4433

From Aryl Trialkylsilyl Ketenes to 3-Silyl-1-silyloxyallenes
127.9, 128.2, 128.5, 135.6, 137.3, 204.5 ppm. C21H28OSi2 (352.6): 1H NMR: δ = 0.29 (s, 9 H), 0.64 (q, J = 7.8 Hz, 6 H), 0.93 (t, J
4
3
calcd. C 71.53, H 8.00; found C 71.34, H 8.02.
= 7.9 Hz, 9 H), 3.81 (s, 3 H), 6.87–6.89 (m, 2 H), 7.20–7.24 (m, 1
H), 7.29–7.32 (m, 2 H), 7.35–7.37 (m, 2 H), 7.40–7.43 (m, 2 H)
ppm. 13C NMR: δ = –0.16, 4.7, 6.7, 55.3, 113.8, 117.7, 125.3, 126.0,
126.8, 127.8, 128.0, 128.4, 137.7, 158.7, 208.0 ppm. MS (ESI): m/z
= 425.2 [M – H]+.
1-(4-Methoxyphenyl)-3-phenyl-3-trimethylsilyl-1-trimethylsilyloxy-
1,2-propadiene (5b): Preparation by the general procedure from 2-
diazo-1-phenylethanone (1a) (0.73 g, 5.0 mmol) and trimethylsilyl
triflate (0.91 mL, 5.0 mmol) for silyl ketene 3a, and 2-diazo-1-(4-
methoxyphenyl)ethanone (1b) (0.88 g, 5.0 mmol) and trimethylsilyl
triflate (0.91 mL, 5.0 mmol) for silyldiazo ketone 2c. The crude
product was purified by column chromatography (pentane/diethyl
ether, 20:1), and 5b was obtained as a yellow oil (1.25 g, 65%). IR
3-(4-Methoxyphenyl)-1-phenyl-3-trimethylsilyl-1-trimethylsilyloxy-
1,2-propadiene (5f): Preparation by the general procedure from 2-
diazo-1-(4-methoxyphenyl)ethanone (1b) (0.88 g, 5.0 mmol) and
trimethylsilyl triflate (0.91 mL, 5.0 mmol) for silyl ketene 3c, and
(NaCl, film): ν = 2957 (s), 2900 (m), 2836 (w), 1903 (w, C=C=C), 2-diazo-1-phenylethanone (1a) (0.73 g, 5.0 mmol) and trimethylsilyl
˜
1723 (w), 1607 (s), 1579 (w), 1509 (s), 1489 (m), 1443 (m), 1417
(w), 1350 (s), 1250 (s), 1170 (s), 1109 (m), 1077 (w), 1060 (m), 1033
(s), 1008 (w), 876 (s), 839 (s) cm–1. 1H NMR: δ = 0.17 (s, 9 H),
triflate (0.91 mL, 5.0 mmol) for silyldiazo ketone 2a. The crude
product was purified by column chromatography (pentane/diethyl
ether, 20:1), and 5f was obtained as white crystals (1.35 g, 70%).
0.30 (s, 9 H), 3.81 (s, 3 H), 6.87–6.89 (m, 2 H), 7.20–7.24 (m, 1 H), M.p. 78–79 °C. IR (NaCl, film): ν = 2958 (s), 2900 (m), 2836 (w),
˜
7.29–7.40 (m, 6 H) ppm. 13C NMR: δ = –0.1, 0.2, 55.3, 113.8,
1899 (w, C=C=C), 1604 (s), 1577 (w), 1507 (s), 1492 (m), 1449 (m),
117.7, 125.3, 126.0, 126.9, 127.8, 128.1, 128.5, 137.5, 158.7, 1414 (w), 1345 (m), 1250 (s), 1193 (m), 1172 (s), 1110 (w), 1062
1
207.7 ppm. MS (ESI): m/z = 383.2 [M – H]+.
(m), 1037 (m), 1024 (m), 910 (m), 874 (s), 841 (s) cm–1. H NMR:
δ = 0.19 (s, 9 H), 0.30 (s, 1 H), 3.81 (s, 3 H), 6.85–6.87 (m, 2 H),
7.12–7.22 (m, 1 H), 7.30–7.34 (m, 4 H), 7.45–7.47 (m, 2 H) ppm.
13C NMR: δ = –0.1, 0.2, 55.2, 113.9, 116.9, 124.1, 125.9, 126.6,
128.2, 129.0, 129.4, 135.8, 158.7, 205.8 ppm. C22H30O2Si2 (382.6):
calcd. C 69.06, H 7.90; found C 68.93, H 7.72.
1-(2-Furyl)-3-phenyl-3-trimethylsilyl-1-trimethylsilyloxy-1,2-propa-
diene (5c): Preparation by the general procedure from 2-diazo-1-
phenylethanone (1a) (0.73 g, 5.0 mmol) and trimethylsilyl triflate
(0.91 mL, 5.0 mmol) for silyl ketene 3a, and 2-diazo-1-(2-furyl)eth-
anone (1c) (0.68 g, 5.0 mmol) and trimethylsilyl triflate (0.91 mL,
5.0 mmol) for silyldiazo ketone 2e. The crude product was purified
by column chromatography (pentane/diethyl ether, 20:1), and 5c
1,3-Bis(4-methoxyphenyl)-3-trimethylsilyl-1-trimethylsilyloxy-1,2-
propadiene (5g): Preparation by the general procedure from 2-di-
azo-1-(4-methoxyphenyl)ethanone (1b) (0.88 g, 5.0 mmol) and tri-
was obtained as a yellow oil (1.43 g, 84%). IR (NaCl, film): ν =
˜
2960 (m), 2899 (w), 1908 (w, C=C=C), 1596 (w), 1520 (w), 1489 methylsilyl triflate (0.91 mL, 5.0 mmol) for silyl ketene 3c, and 2-
(m), 1447 (m), 1408 (w), 1382 (w), 1334 (s), 1252 (s), 1220 (m),
1193 (s), 1158 (m), 1125 (w), 1089 (m), 1062 (m), 1006 (s), 928 (m),
diazo-1-(4-methoxyphenyl)ethanone (1b) (0.88 g, 5.0 mmol) and
trimethylsilyl triflate (0.91 mL, 5.0 mmol) for silyldiazo ketone 2c.
The crude product was purified by column chromatography (pen-
tane/diethyl ether, 20:1), and 5g was obtained as a colorless oil
1
902 (w), 842 (s) cm–1. H NMR: δ = 0.17 (s, 9 H), 0.29 (s, 9 H),
6.35–6.37 (m, 1 H), 6.42–6.43 (m, 1 H), 6.85–6.87 (m, 2 H), 7.21–
7.25 (m, 1 H), 7.30–7.39 (m, 5 H) ppm. 13C NMR: δ = –0.3, 0.1,
106.4, 111.3, 118.9, 120.0, 127.0, 128.0, 128.4, 137.5, 141.7, 149.5,
205.9 ppm.
(1.48 g, 71%). IR (NaCl, film): ν = 2957 (s), 2901 (w), 2836 (w),
˜
1901 (w, C=C=C), 1651 (w), 1605 (s), 1578 (m), 1507 (s), 1464 (m),
1442 (m), 1418 (w), 1349 (m), 1287 (m), 1249 (s), 1192 (m), 1170
(s), 1109 (m), 1062 (m), 1035 (s), 1008 (w), 911 (m), 876 (s), 840 (s)
1,3-Diphenyl-1-triethylsilyloxy-3-trimethylsilyl-1,2-propadiene (5d):
Preparation by the general procedure from 2-diazo-1-phenyl-
ethanone (1a) (0.73 g, 5.0 mmol) and trimethylsilyl triflate
(0.91 mL, 5.0 mmol) for silyl ketene 3a, and 2-diazo-1-phenyle-
thanone (1a) (0.73 g, 5 mmol) and triethylsilyl triflate (1.13 mL,
5 mmol) for silyldiazo ketone 2b. The crude product was purified
by column chromatography (pentane/diethyl ether, 20:1), and 5d
was obtained as a slightly yellow oil (1.25 g, 63%). IR (NaCl, film):
1
cm–1. H NMR: δ = 0.17 (s, 9 H), 0.29 (s, 9 H), 3.80 (s, 3 H), 3.81
(s, 3 H), 6.84–6.88 (m, 4 H), 7.31–7.39 (m, 4 H) ppm. 13C NMR:
δ = 0.0, 0.2, 55.3 (2 C), 113.8, 113.9, 116.9, 125.3, 128.1, 129.0,
129.8, 158.7, 158.7, 206.3 ppm. MS (ESI, addition of AgNO3): m/z
= 519.1 [M + Ag]+.
1-(2-Furyl)-3-(4-methoxyphenyl)-3-trimethylsilyl-1-trimethyl-
silyloxy-1,2-propadiene (5h): Preparation by the general procedure
from 2-diazo-1-(4-methoxyphenyl)ethanone (1b) (0.88 g, 5.0 mmol)
ν = 2957 (s), 2912 (m), 2877 (m), 1900 (w, C=C=C), 1596 (m), 1518
˜
(w), 1491 (m), 1449 (m), 1413 (w), 1379 (w), 1345 (m), 1260 (s), and trimethylsilyl triflate (0.91 mL, 5.0 mmol) for silyl ketene 3c,
1191 (m), 1119 (w), 1074 (m), 1061 (m), 1005 (m), 975 (w), 944 (w), and 2-diazo-1-(2-furyl)ethanone (1c) (0.68 g, 5.0 mmol) and tri-
916 (w) 873 (w), 837 (s) cm–1. 1H NMR: δ = 0.30 (s, 9 H), 0.67 (q,
methylsilyl triflate (0.91 mL, 5.0 mmol) for silyldiazo ketone 2e.
6 H), 0.94 (t, 9 H) 7.19–7.25 (m, 2 H), 7.30–7.38 (m, 6 H), 7.47– The crude product was purified by column chromatography (pen-
7.51 (m, 2 H) ppm. 13C NMR: δ = –0.2, 4.7, 6.7, 117.6, 124.0, tane/diethyl ether, 20:1), and 5h was obtained as a colorless oil
125.9, 126.7, 126.9, 127.8, 128.2, 128.4, 135.7, 137.4, 207.5 ppm.
(1.28 g, 69%). IR (NaCl, film): ν = 2959 (m), 2900 (w), 2837 (w),
˜
MS (ESI): m/z = 395.2 [M – H]+.
1905 (w, C=C=C), 1605 (m), 1577 (w), 1508 (s), 1463 (w), 1442
(w), 1413 (w), 1382 (w), 1332 (m), 1250 (s), 1220 (m), 1195 (s), 1173
(s), 1158 (m), 1110 (w), 1086 (m), 1063 (m), 1037 (m), 1006 (m),
1-(4-Methoxyphenyl)-3-phenyl-1-triethylsilyloxy-3-trimethylsilyl-
1,2-propadiene (5e): Preparation by the general procedure from 2-
diazo-1-phenylethanone (1a) (0.73 g, 5.0 mmol) and trimethylsilyl
triflate (0.91 mL, 5.0 mmol) for silyl ketene 3a, and 2-diazo-1-(4-
methoxyphenyl)ethanone (1b) (0.88 g, 5.0 mmol) and triethylsilyl
triflate (1.13 mL, 5.0 mmol) for silyldiazo ketone 2d. The crude
product was purified by column chromatography (pentane/diethyl
ether, 20:1), and 5e was obtained as a yellow oil (1.24 g, 59%). IR
1
924 (m), 907 (m), 842 (s) cm–1. H NMR: δ = 0.17 (s, 9 H), 0.29
(s, 9 H), 3.81 (s, 3 H), 6.34–6.35 (m, 1 H), 6.41–6.43 (m, 1 H), 6.85–
6.87 (m, 2 H), 7.32–7.34 (m, 3 H) ppm. 13C NMR: δ = –0.2, 0.1,
55.2, 106.2, 111.3, 113.8, 118.1, 119.9, 129.2, 129.6, 141.7, 149.7,
158.8, 204.5 ppm.
3-(4-Methoxyphenyl)-1-phenyl-1-triethylsilyloxy-3-trimethylsilyl-
(NaCl, film): ν = 2956 (s), 2911 (m), 2877 (m), 2836 (w), 1903 (w, 1,2-propadiene (5i): Preparation by the general procedure with 2-
˜
C=C=C), 1654 (w), 1605 (s), 1578 (m), 1509 (s), 1489 (m), 1461
diazo-1-(4-methoxyphenyl)ethanone (1b) (0.88 g, 5.0 mmol) and
(m), 1416 (m), 1349 (s), 1250 (s), 1170 (s), 1108 (m), 1107 (m), 1077 trimethylsilyl triflate (0.91 mL, 5.0 mmol) for silyl ketene 3c, and
(m), 1060 (m), 1034 (s), 1005 (m), 974 (w), 916 (w), 836 (s) cm–1. 2-diazo-1-phenylethanone (1a) (0.73 g, 5.0 mmol) and triethylsilyl
Eur. J. Org. Chem. 2008, 4426–4433
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4431

S. M. Bucher, R. Brückmann, G. Maas
FULL PAPER
triflate (1.13 mL, 5.0 mmol) for silyldiazo ketone 2b. The crude
product was purified by column chromatography (pentane/diethyl
ether, 20:1), and 5i was obtained as a yellow oil (1.26 g, 59%). IR
158.57, 163.34, 164.03, 190.19 ppm. MS (EI, 70 eV): m/z (%) = 340
(21) [M]+, 325 (100), 310 (18), 309 (11), 290 (17), 267 (10), 260 (12),
248 (15), 195 (9), 192 (9), 135 (16), 107 (10). C20H24O3Si (340.5):
(NaCl, film): ν = 2956 (s), 2911 (m), 2877 (m), 2836 (w), 1898 (w, calcd. C 70.5, H 7.10; found C 70.5, H 7.09.
˜
C=C=C), 1604 (s), 1577 (w), 1508 (s), 1492 (m) 1462 (m), 1449 (m),
Crystal-Structure Determination for 5a and 5h: Crystals were ob-
1414 (s), 1379 (s), 1344 (m), 1250 (s), 1193 (m), 1172 (s), 1110 (w),
1062 (m), 1037 (s), 1024 (m), 975 (w), 910 (m), 838 (s) cm–1. 1H
NMR: δ = 0.29 (s, 9 H), 0.65 (q, 6 H), 0.94 (t, 9 H), 3.84 (s, 3 H),
6.84–6.86 (m, 2 H), 7.18–7.21 (m, 1 H), 7.30–7.34 (m, 4 H), 7.47–
7.49 (m, 2 H) ppm. 13C NMR: δ = –0.1, 4.7, 6.7, 55.2, 113.9, 116.8,
124.1, 125.8, 126.6, 128.2, 129.0, 129.6, 135.9, 158.7, 206.0 ppm.
tained from pentane solution. The data collection was performed
with an image-plate diffractometer (Stoe IPDS) by using mono-
chromated Mo-Kα radiation (λ = 0.71073 Å). Both structures were
solved by direct methods and refined with a full-matrix least-
squares method by using F2 values. Hydrogen atom positions were
calculated geometrically and treated as riding on their bond neigh-
bors in the refinement procedure. Software for structure solution
and refinement: SHELX-97;[25] molecule plots: ORTEP-3.[26] Fur-
ther details are provided in Table 2.
1,3-Bis(4-methoxyphenyl)-1-triethylsilyloxy-3-trimethylsilyl-1,2-pro-
padiene (5j): Preparation by the general procedure from 2-diazo-1-
(4-methoxyphenyl)ethanone (1b) (0.88 g, 5.0 mmol) and trimethyl-
silyl triflate (0.91 mL, 5.0 mmol) for silyl ketene 3c, and 2-diazo-1-
(4-methoxyphenyl)ethanone (1b) (0.88 g, 5.0 mmol) and triethyl-
silyl triflate (1.13 mL, 5.0 mmol) for silyldiazo ketone 2d. The crude
product was purified by column chromatography (pentane/diethyl
ether, 20:1), and 5j was obtained as an orange oil (1.90 g, 83%).
1H NMR: δ = 0.29 (s, 9 H), 0.65 (q, 6 H), 0.95 (t, 9 H), 3.810 (s,
3 H), 3.813 (s, 3 H), 6.84–6.89 (m, 4 H), 7.30–7.42 (m, 4 H) ppm.
13C NMR: δ = –0.1, 4.7, 6.7, 55.2, 55.3, 113.7, 113.8, 116.8, 125.3,
125.8, 128.2, 128.9, 129.8, 158.6, 206.4 ppm.
Table 2. Crystallographic data and details of data collection and
structure refinement for 5a and 5h.
5a
5h
Empirical formula
Formula weight
Temperature [K]
Crystal size [mm]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
C21H28OSi2
352.6
193(2)
0.23ϫ0.15ϫ0.04 0.38ϫ0.23ϫ0.12
monoclinic
P 21/n
16.825(2)
14.488(1)
18.702(2)
90
C20H28O3Si2
372.6
193(2)
monoclinic
P 21/n
8.901(1)
20.008(2)
12.292(2)
90
3-(4-Methoxyphenyl)-1-phenyl-1-triethylsilyloxy-3-triethylsilyl-1,2-
propadiene (5k): Preparation by the general procedure from 2-di-
azo-1-(4-methoxyphenyl)ethanone (1b) (0.88 g, 5.0 mmol) and tri-
ethylsilyl triflate (1.13 mL, 5.0 mmol) for silyl ketene 3d, and 2-
diazo-1-phenylethanone (1a) (0.73 g, 5.0 mmol) and triethylsilyl
triflate (1.13 mL, 5.0 mmol) for silyldiazo ketone 2b. The crude
product was purified by column chromatography (pentane/diethyl
ether, 20:1), and 5k was obtained as a colorless oil (1.61 g, 69%).
β [°]
110.27(1)
90
4276.5(9)
8
1.095
0.931
97.31(2)
90
2171.4(5)
4
1.140
0.178
γ [°]
V [Å3]
Z
Density [gcm–3
]
µ(Mo-Kα) [mm–1
F (000)
]
IR (NaCl, film): ν = 2955 (s), 2911 (s), 2876 (s), 2835 (m), 1895 (w,
˜
C=C=C), 1604 (s), 1577 (w), 1507 (s) 1492 (m), 1460 (m), 1414 (m),
1379 (w), 1343 (m), 1286 (m), 1248 (s), 1192 (m), 1171 (s), 1109
(w), 1057 (m), 1037 (m), 1006 (s), 974 (m), 897 (w), 830 (s) cm–1.
1H NMR: δ = 0.63–0.67 (m, 6 H), 0.78–0.82 (m, 6 H), 0.91–0.99
(m, 18 H), 3.81 (s, 3 H), 6.83–6.85 (m, 2 H), 7.12–7.21 (m, 1 H),
7.29–7.33 (m, 4 H), 7.49–7.51 (m, 4 H) ppm. 13C NMR: δ = 4.3,
4.8, 6.7, 7.6, 55.2, 113.8, 114.6, 124.1, 125.3, 126.5, 128.1, 128.8,
130.1, 136.1, 158.7, 207.4 ppm.
1088
800
θ range [°]
Reflections collected
2.32–25.03
30440
2.52–25.03
15580
Independent reflections (Rint
Completeness to θmax [%]
Data/restraints/parameters[a]
Goodness-of-fit on F2
)
7256 (0.0750)
96.1
7256/0/445
0.825
3663 (0.1205)
95.6
3663/0/233
0.869
Final R indices [IϾ2σ(I)]: R1,
0.0389, 0.0824
0.0524, 0.1075
[b]
wR2
[b]
R indices (all data): R1, wR2
0.0825, 0.0947
0.0975, 0.1178
1,3-Bis(4-methoxyphenyl)-3-trimethylsilylprop-2-en-1-one (6): A
solution of ω-diazoacetophenone (1.76 g, 10.0 mmol) and diisopro-
pylethylamine (1.74 mL, 10.0 mmol) in diethyl ether (60 mL) was
cooled to 0 °C, and a solution of trimethylsilyl triflate (1.81 mL,
10.0 mmol) in diethyl ether (50 mL) was added drop by drop. After
the addition was complete, the mixture was brought to room tem-
perature and stirred for 2 h. The precipitated diisopropylethyl-
ammonium triflate was filtered off, and the solvent was completely
removed at 15 mbar. A yellow oil was left, which started to undergo
a slightly exothermic reaction with vigorous gas evolution within a
minute (CAUTION!). After 30 min, the viscous oil was extracted
with pentane (3ϫ50 mL). The extracts were combined and concen-
trated, and the residue was subjected to column chromatography
over silica gel (90 g; CHCl3/pentane, 4:1). The first fraction (the
following ones were discarded because of the low amount of prod-
uct) furnished a yellow oil (0.48 g) that was dissolved in a small
volume of pentane. After several days at –18 °C, yellow crystals of
Largest diff. peak and hole
0.24, –0.23
0.31, –0.30
[eÅ–3
]
[a] Refinement based on F2 values. [b] R1 = Σ||Fo| – |Fc|/Σ |Fo||; wR2
2
2 2
= [Σ(w(Fo – Fc ) )/Σw(Fo2)2]1/2
.
CCDC-661871 (for 5a) and -687385 (for 5h) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from the Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supporting Information (see also the footnote on the first page of this
article): 1H and 13C NMR spectra for compounds 2c, 3a–d,f, and
5a–k; procedure to determine the acid content in triethylsilyl triflate.
Acknowledgments
We thank Dr. Ulrich Jäger (Hochschule Aalen) for the EI and CI
mass spectra.
1
6 were obtained (0.23 g, 14%). M.p. 88–89 °C. H NMR: δ = 0.21
(s, 9 H), 3.82 (s, 3 H), 3.88 (s, 3 H), 6.92–6.95 (m, 2 H), 6.98 (s, 1
H), 7.07–7.10 (m, 1 H), 7.15–7.19 (m, 2 H), 7.32–7.37 (m, 2 H),
7.43–7.45 (m, 1 H), 7.86–7.81 (m, 2 H) ppm. 13C NMR: δ = 0.3,
55.2, 55.5, 113.4, 113.8, 127.8, 130.9, 131.04, 137.46, 138.36,
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Received: May 29, 2008
Published Online: July 24, 2008
Eur. J. Org. Chem. 2008, 4426–4433
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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