Regioselective transition-metal-free synthesis of 2-(trimethylsilylmethylene)pyrrol-3-ones by thermal cyclization of acetylenic enamines

Article abstract of DOI:10.1021/acs.joc.5b00398

Acetylenic enamines generated in situ from readily available enynones and primary amines undergo thermal cyclization in diphenyl ether providing easy access to 4-aryl-2-(trimethylsilylmethylene)-1,2-dihydro-3H-pyrrol-3-ones. This reaction is inherently ve

Full text of DOI:10.1021/acs.joc.5b00398

Article
pubs.acs.org/joc
Regioselective Transition-Metal-Free Synthesis of
2‑(Trimethylsilylmethylene)pyrrol-3-ones by Thermal Cyclization of
Acetylenic Enamines
Pavel R. Golubev, Alena S. Pankova, and Mikhail A. Kuznetsov*
Institute of Chemistry, Saint Petersburg State University, Universitetsky pr. 26, 198504 Saint Petersburg, Russia
S
* Supporting Information
ABSTRACT: Acetylenic enamines generated in situ from
readily available enynones and primary amines undergo
thermal cyclization in diphenyl ether providing easy access
to 4-aryl-2-(trimethylsilylmethylene)-1,2-dihydro-3H-pyrrol-3-
ones. This reaction is inherently versatile, allowing for
variations of substituents in both enynone and amine. Full regioselectivity along with short reaction time (1−2 h) and
simple workup afford single products in good to excellent isolated yields. Fluorescent properties of the obtained compounds were
studied.
key starting compounds are cross-conjugated TMS-protected
enynones 1, readily available from bis(trimethylsilyl)acetylene
and arylacetyl chlorides.15 Previously we thoroughly inves-
tigated the reactions of compounds 1 with binucleophiles,15
and herein we report the results obtained by employment of
amines in reactions with enynones 1.
INTRODUCTION
■
The 3-pyrrolone core represents a valuable subclass of
azaheterocycles which can be found in some pharmaceuticals
and biologically active compounds. For example, β-pyrrolone
derivatives were reported to possess antimalarial activity1 as
well as HIV-1 protease inhibitory2 activity. In addition, 3,5-
linked polypyrroline-4-ones were studied as nonpeptide
peptidomimetics with promising pharmacological properties.3
Several synthetic strategies toward a pyrrolone core have
been developed, mostly via cyclization of corresponding open-
chain precursors. Among these, substituted 1-aminobut-3-yn-2-
ones are the most commonly used starting material. It was
shown that such compounds undergo gold-4 or platinum-
catalyzed5 cyclization or can be transformed into pyrrolones by
treatment with I2 in PEG under microwave irradiation.6 On the
other hand, several enaminones were reported to undergo
cyclization upon treatment with phenyliodine(III) bis-
(trifluoroacetate) and TFA to form polysubstituted pyrro-
lones.7 Similar substrates can be converted into diacetylpyrro-
lones by Cu(TFA)2-catalyzed oxidative cyclization.8 Other
known methods include gold-catalyzed oxidative rearrangement
of homopropargyl azides,9 flash-vacuum pyrolysis of Meldrum’s
acid aminomethylene derivatives,10 cyclization of amino-
acetylmalononitriles under acidic conditions,11 and a three-
component reaction of primary amines with 1,3-diketones in
aqueous H2O2.12 N-Aminopyrrolones can be obtained by a
PtCl2-catalyzed cyclization of tosylhydrazones of unsaturated
hydroxyketones,13 and a NIS-promoted coupling/cyclization of
symmetrical diynones with primary amines was explored for the
synthesis of iodinated products.14 Nevertheless, development of
rapid and efficient methodologies for direct construction of a
pyrrolone core compatible with various functional groups is still
of interest.
RESULTS AND DISCUSSION
■
We first used enynone 1a bearing a p-nitrophenyl group and p-
anisidine (2a) to optimize reaction conditions, and an excellent
result was obtained immediately: corresponding enamine 3aa
was isolated in nearly quantitative yield after an equimolar
mixture of initial compounds was stirred in ethanol for 1 h at
room temperature (Table 1). Nevertheless, we performed a few
more experiments in other solvents, which revealed that
ethanol was in fact the least effective one, and the reaction
time could be reduced to 30 min by using THF. In general, the
reaction could be successfully performed in any conventional
solvent (benzene, CH2Cl2, THF, CH3CN, etc.). Even in the
presence of excess amine the only isolated product was the
corresponding enamine 3aa, and no products of addition to the
carbonyl group or triple bond were observed. Enamine 3aa
exists in solution as a mixture of (E)- and (Z)-isomers, and
distinction between two forms can be easily made on the basis
of the difference in NH proton signal positions: 12.5 ppm due
to intramolecular hydrogen bonding in (Z)-form and ∼8.5 ppm
in (E)-form (1H NMR spectrum in CDCl3). The structure of
the (Z)-isomer was also obtained from the X-ray analysis.16 We
have found that ratio of (E)- to (Z)-isomers depends on the
solvent polarity but not on the temperature. Thus, in nonpolar
CDCl3 the (Z)-isomer is preferable due to its stabilization by an
intramolecular hydrogen bond, and the (E)/(Z) ratio is ∼1:10
We have designed a straightforward method for the synthesis
of 2-(trimethylsilylmethylene)pyrrol-3-ones bearing various
substituents at 1- and 4-positions of the pyrrole core. The
Received: February 19, 2015
© XXXX American Chemical Society
A
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a
Table 1. Reaction of Ketones 1a−c with Anilines 2a−c
entry
ketone
R1
aniline
R2
pyrrolone
isolated yield, %
b
c
1
2
3
4
5
6
7
1a
1a
1a
1b
1b
1c
1c
NO2
NO2
NO2
H
2a
2b
2c
2a
2b
2a
2b
OCH3
H
4aa
90 (70)
88
4ab
4ac
4ba
4bb
4ca
4cb
NO2
OCH3
H
trace
66
H
65
OCH3
OCH3
OCH3
H
74
70
a
b
c
Reactions were performed on a 0.35 mmol scale. Enamine 3aa was isolated in 95% yield. Reaction was performed on a 5 mmol scale.
at 20−60 °C. On the other hand, when the 1H NMR spectrum
was registered in DMSO-d6, the (E)-isomer was determined as
the major one (ratio (E)/(Z) ∼3:1), since intramolecular
hydrogen bonding was suppressed by interaction with polar
solvent. No imine form of compound 3aa was detected in the
NMR spectra, since it would possess an upfield signal from the
Ar−CH proton.
used, the reaction proceeded smoothly, and targeted products
were formed in good to excellent yields. Not surprisingly, p-
nitroaniline (2c) did not react even with ketone 1a, and neither
full conversion to enamine nor formation of cyclized product
was achieved even after several hours of heating at 200 °C. For
this reason reactions of enynones 1b,c with nitroaniline 2c were
not performed.
The combination of an activated triple bond and a
disubstituted amine nitrogen atom in the structure of enamine
3aa creates an opportunity for a ring closure, and therefore we
have examined its thermal transformations and started with
heating at 110 °C in toluene. No reaction was observed under
these conditions, and further experiments in xylene, DMF, and
DMSO were performed at 140, 150, and 180 °C, respectively.
Very slow formation of a new product occurred in the first two
cases, while heating in DMSO led to decomposition of starting
material. From these experiments it was clear that the desired
transformation could be executed effectively only at temper-
ature higher than 180 °C in inert medium. For this reason we
decided to try diphenyl ether as reaction solvent. Upon being
heated in Ph2O for 0.5 h at 200 °C, enamine 3aa smoothly
underwent cyclization, and a single product was obtained in
95% yield (estimated by 1H NMR spectrum of a crude reaction
mixture after removal of Ph2O). Finally, we attempted to
perform both reactions without isolation of enamine 3aa, but
poor yield of cyclization product was obtained when an
equimolar mixture of enynone 1a and anisidine 2a in Ph2O was
heated at 200 °C. Nevertheless, we managed to obtain the final
product in 90% yield, when the reaction mixture was stirred at
80 °C for 0.5 h (at this point the full conversion of starting
compounds was observed) and then at 200 °C for an additional
0.5 h. This stepwise approach was taken as the optimal one for
further experiments.
For compound 4ab we managed to obtain X-ray analysis data
to unambiguously determine its structure as substituted 2-
(trimethylsilylmethylene)pyrrol-3-one.17 The same structure
was ascribed to other obtained products due to the similarity of
their NMR spectra, since a very consistent set of signals
referring to the core of the molecule was observed in all cases.
1
Thus, H NMR spectra contain two characteristic singlets at
∼5.8 and ∼8.1 ppm assigned to the CHSi fragment and
H5 proton of the pyrrole core, respectively, and carbon atoms
of 2-methylenepyrrol-3-one also feature signals at constant
positions [δ ≈ 112 (C4), 121 (CHSi), 146 (C2), 152 (C5),
and 184 (C3) ppm] in 13C NMR spectra.
The substrate scope of the presented two-step trans-
formation was successfully extended to other anilines, including
those with electron-withdrawing substituents, as well as to
alkylamines and some aminoheterocycles (Scheme 1).
In the first reaction series we used ketone 1a to test various
anilines. p-Fluoroaniline (2d) provided high yield of
pyrrolinone 4ad, and even anilines with stronger electron-
withdrawing groups [e.g., methyl 4-aminobenzoate (2e) and p-
trifluoromethylaniline (2f)] furnished the corresponding
pyrrolinones 4ae and 4af in 68% yield. In addition, ortho-
substituted anilines 2g−i were tested, and despite longer
reaction times as compared to those of 4-substituted analogues
(2c vs 2i; 2f vs 2g), targeted products were obtained in all
cases. Mesitylamine 2j reacted smoothly as well, and even
sterically crowded 2,6-diisopropylaniline (2k) provided a
surprisingly high 80% yield of corresponding product 4ak
demonstrating reaction tolerance to steric hindrances in the
aniline core. Next, several aminoheterocycles were explored to
obtain N-heteroarylpyrrolinones. In this series we failed to
obtain desired products when 2-, 3-, and 4-aminopyridines were
used; in addition, 2-amino-1,3,4-oxa- and thiadiazoles were
Having found the optimal conditions, we carried out a series
of experiments with various combinations of substituents in
aromatic cores of both starting compounds to study the
influence of electronic factors on the reaction course (Table 1).
In line with our previous studies,15 enynone 1a was slightly
more active than two other ketones and provided better yields
of products. When p-anisidine (2a) or parent aniline (2b) was
B
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a
Scheme 1. Study of Amine Scope for the Synthesis of Pyrrolinones
a
Reactions were performed on 0.35 mmol scale. Isolated yields of pyrrolinones 4ad−ar are given.
Scheme 2. Reaction of Ketone 1a with Benzidine 2s
found to be inert under reaction conditions, too. However,
reactions with 2-aminothiazole 2l and 5-aminopyrazole 2m
were successful, indicating that aminoheterocycles with π-
donating core seem to be the only ones suitable for this
transformation. Finally, reactions with alkylamines were
studied. n-Propylamine (2n) allowed lower temperature for
the second step, and the corresponding enamine already
underwent cyclization at 175 °C. Good yields were obtained in
reactions with cyclopentyl- and tert-butylamines (2o,p), as well
as with benzylamine (2q) and its heteroaromatic analogue, 2-
furylmethylamine (2r), which provided 90% and 80% yields of
products, respectively.
synthesis of linked bis-pyrrolones (Scheme 2). We were unable
to obtain enamine 3as in Ph2O (most likely due to poor
solubility of benzidine), but it was isolated in excellent yield
after the reaction mixture was heated in THF. Compound 3as,
in theory, can exist in 3 forms, (E,E), (Z,Z), and (E,Z), and it is
interesting to notice that only symmetrical (E,E)- and (Z,Z)-
forms were seen in the 1H NMR spectrum. As expected,
enamine 3as smoothly underwent cyclization upon heating in
standard conditions leading to the bis-pyrrolone derivative 4as
in 72% yield.
It is worth mentioning the full regioselectivity in all reactions,
where no isomeric 4-pyridones 5 were detected (Scheme 3).
Well-known aza-Michael-type addition of nitrogen nucleophiles
to activated multiple bonds usually occurs on the β-carbon
The reaction between ketone 1a and benzidine 2s was
attempted to demonstrate the applicability of diamines for the
C
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Scheme 3. Plausible Mechanism for the Thermal Cyclization of Enamines 3
Scheme 4. Reactions of Ketone 1a with Hydrazines
atom to an electron-withdrawing group, and according to
literature data,18 intramolecular addition to a triple bond
attached to a carbonyl group mainly proceeds in the same
manner. Intramolecular addition to silylated acetylenes has not
been previously investigated, but inverse regioselectivity in the
case of enamines 3 is obviously powered by the TMS group at
the terminal position of a triple bond. It is well-known that the
Me3Si group creates no real steric hindrance, but on the other
hand, a silicon atom in α-position effectively stabilizes the anion
center of intermediate A.19 For this reason, instead of 6-endo-
dig-type cyclization leading to 4-pyridones 5, reaction occurs
exclusively as a 5-exo-dig-process providing 2-methylenepyrrol-
3-ones 4 as single products.
Finally, we expected to obtain N-amino-substituted pyrro-
lones using the reaction of ketone 1a with N,N-dimethylhy-
drazine and benzhydrazide (Scheme 4). Initially, both reactions
were executed in a standard one-pot fashion, and formation of
new compounds, which were presumably identified as
enhydrazines 3at and 3au by analogy with previous results,
was observed by TLC when the reaction mixtures were heated
at 40 or 80 °C, respectively. However, further increase of
temperature led to full destruction of these compounds even
under inert atmosphere, most likely due to the breach of a weak
N−N bond under conditions of thermolysis. After this, the
adduct with dimethylhydrazine 3at was prepared individually,
and its structure was confirmed by HRMS and NMR
spectroscopic data.
pyrrolone core is crucial for the molecule to exhibit
fluorescence under UV irradiation, since very weak emission
was observed for compounds 4bb and 4cb, while none was
registered for compounds 4ba and 4ca. On the other hand, the
substituent at the nitrogen atom also has a profound effect, and
fluorescence increases in the following sequence: alkyl < C6H4-
EDG < C6H4-EWG < heteroaryl. Thus, the best one was the 2-
thiazolyl-substituted pyrrolone 4al. For this compound we have
estimated the quantum yield of fluorescence following a
reported procedure,20 and a calculated Φ value of 6
1%
was obtained. To the best of our knowledge it is the first
mention of fluorescence properties for a 2-methylenepyrrolin-3-
one scaffold, and we believe that these data may serve as a good
start for development of novel fluorescent materials.
CONCLUSIONS
■
We have developed a rapid, general, and efficient method for
the synthesis of previously unknown 2-(trimethylsilylmethy-
lene)-1,2-dihydro-3H-pyrrol-3-one derivatives from easily
accessible starting material. The described procedure is atom-
efficient, since only 1 molecule of TMSCl and 3 molecules of
EtOH are liberated during the whole sequence starting from
bis(trimethylsilyl)acetylene. The key thermal cyclization of
acetylenic enamines occurs in a regioselective manner via a 5-
exo-dig-process providing single products in high yields.
Moreover, most of the obtained compounds display fluo-
rescence under UV irradiation.
Pyrrolones 4 appear as brightly colored solids (bright orange
to deep red) and demonstrate distinctive fluorescence under a
conventional UV lamp; therefore, their UV−vis spectra were
studied. In Figure 1 the absorption and emission spectra of
compound 4ab are shown as a representative example. In all
cases two or three bands were observed in the absorption
spectra of pyrrolones: the one at 432−479 nm is characteristic;
the emission wavelengths are ∼550 nm. We have found that the
presence of a p-nitrophenyl ring at the C4 position of the
EXPERIMENTAL SECTION
■
1
General Methods. H and 13C NMR spectra were recorded in
CDCl3, DMSO-d6, or acetone-d6 and were referenced to the solvent
residual proton (δH = 7.26, 2.50, and 2.05 ppm, respectively) and
carbon signals (δC = 77.0, 39.5, and 29.8 ppm, respectively). DEPT
spectra were used for the assignment of carbon signals. 19F NMR
spectra were recorded in CDCl3 and referenced to an internal standard
(fluorobenzene, δF = −113.2 ppm). UV−vis spectra were recorded for
D
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Figure 1. Overlay of UV−vis spectra for 10−5 M solution of pyrrolone 4ab in CHCl3: blue, absorption spectrum; red, excitation spectrum; green,
emission spectrum. Left y-axis refers to the absorption spectrum, and the right one refers to emission and excitation spectra.
10−5 M solutions in CHCl3; extinction coefficients are given in
parentheses. Preparation of enynones 1a−c was described earlier.15a
General Procedure for the Preparation of Enamines 3. A
mixture of enynone 1a (100 mg, 0.32 mmol) and corresponding amine
(0.32 mmol, 1 equiv for 3aa, 3at or 0.16 mmol, 1 equiv for 3as) in
THF (2 mL) was heated at 60 °C (enamines 3aa, 3as) or 40 °C (3at)
until TLC indicated the full conversion of starting material (0.5−2 h).
Upon completion, solvent was removed by evaporation, and the
residue was subjected to flash chromatography on silica (n-hexane/
ethyl acetate 1:0 to 8:1) to afford enamine 3. For TLC analysis, 1 drop
of solution was taken from the reaction mixture, diluted by CH2Cl2
(0.1 mL), and used without additional workup.
of the minor (E)-form are clearly seen. HRMS (ESI-TOF) m/z: [M −
H]− calcd for C21H22N2O4Si 393.1276; found 393.1268.
1,1′-[1,1′-Biphenyl]-4,4′-diyldi(imino)]bis[2-(4-nitrophenyl)-5-
(trimethylsilyl)pent-1-en-4-yn-3-one] (3as). Orange solid; yield 93
mg (80%); mp 227−228 °C (dec). Mixture of (E,E)- and (Z,Z)-
isomers in ratio 4:1 (DMSO-d6). 1H NMR (400 MHz, DMSO-d6): δ =
0.09 (s, 3.6 H(Z)), 0.29 (s, 14.4 H(E)), 7.32 (d, J = 8.7 Hz, 3.2 H(E)),
7.55 (d, J = 8.7 Hz, 4 H(E),(Z)), 7.70−7.74 (m, 4 H(E),(Z)), 7.80 (d, J =
8.7 Hz, 0.8 H(Z)), 8.16 (d, J = 12.7 Hz, 0.4 H(Z)), 8.21 (d, J = 8.7 Hz,
0.8 H(Z)), 8.28 (d, J = 8.7 Hz, 3.2 H(E)), 8.53 (d, J = 13.6 Hz, 1.6 H(E)),
9.80 (d, J = 13.6 Hz, 1.6 H(E)), 12.38 (d, J = 12.7 Hz, 0.4 H(Z)) ppm.
13C NMR (100 MHz, DMSO-d6): δ = −1.4 (CH(Z)), −1.0 (CH(E)),
1-[(4-Methoxyphenyl)amino]-2-(4-nitrophenyl)-5-(trimethylsilyl)-
pent-1-en-4-yn-3-one (3aa). Bright orange crystals; yield 120 mg
(95%); mp 63−65 °C. Mixture of (E)- and (Z)-isomers in ratio 3:1
(DMSO-d6) or 1:10 (CDCl3), respectively. 1H NMR (400 MHz,
DMSO-d6): δ = 0.09 (s, 2.25 H(Z)), 0.26 (s, 6.75 H(E)), 3.74 (s, 2.25
H
(E)), 3.75 (s, 0.75 H(Z)), 6.94−6.97 (m, 2 H(Z),(E)), 7.19 (d, J = 9.0
Hz, 1.5 H(E)), 7.43 (d, J = 9.0 Hz, 0.5 H(Z)), 7.53 (d, J = 8.7 Hz, 1.5
95.7 (C(E)), 101.3 (C(E)), 116.2 (C(E)), 117.3 (CH(E)), 118.0 (CH(Z)),
122.4 (CH(Z)), 123.1 (CH(E)), 127.0 (CH(E)), 127.1 (CH(Z)), 130.6
(CH(Z)), 131.7 (CH(E)), 134.5 (C(E)), 139.8 (C(E)), 140.2 (C(E)),
146.3 (C(E)), 147.1 (CH(E)), 147.4 (CH(Z)), 172.5 (C(E)) ppm. Not all
carbon signals of the minor (Z, Z)-form are clearly seen. HRMS (ESI-
TOF) m/z: [M + H]+ calcd for C40H38N4O6Si2 727.2403; found
727.2412.
H
(E)), 7.78 (d, J = 8.8 Hz, 0.5 H(Z)), 8.04 (d, J = 12.9 Hz, 0.25 H(Z)),
8.19 (d, J = 8.8 Hz, 0.5 H(Z)), 8.25 (d, J = 8.7 Hz, 1.5 H(E)), 8.39 (br. d,
J = 9.3 Hz, 0.75 H(E)), 9.70 (br. d, J = 9.3 Hz, 0.75 H(E)), 12.45 (d, J =
12.9 Hz, 0.25 H(Z)) ppm. H NMR (400 MHz, CDCl3): δ = 0.11 (s,
1
8.2 H(Z)), 0.29 (s, 0.8 H(E)), 3.81 (s, 3 H(Z),(E)), 6.90−6.93 (m, 2
H
(Z),(E)), 6.99 (d, J = 9.0 Hz, 0.18 H(E)), 7.07−7.10 (m, 1.82 H(Z)),
7.50 (d, J = 8.8 Hz, 0.18 H(E)), 7.54 (d, J = 12.7 Hz, 0.91 H(Z)), 7.59−
7.62 (m, 1.82 H(Z)), 7.96 (br. s, 0.09 H(E)), 8.17−8.21 (m, 1.82 H(Z)),
8.27 (d, J = 8.8 Hz, 0.18 H(E)), 8.47 (d, J = 14.3 Hz, 0.09 H(E)), 12.52
(br. d, J = 12.7 Hz, 0.91 H(Z)) ppm. 13C NMR (100 MHz, DMSO-d6):
δ = −1.1 (CH(Z)), −0.7 (CH(E)), 55.37 (CH(E)), 55.41 (CH(Z)), 95.4
(C), 98.1 (C), 101.5 (C), 103.3 (C), 111.9 (C), 114.8 (CH(E)), 114.9
(CH(Z)), 115.3 (C), 118.8 (CH(E)), 119.4 (CH(Z)), 122.8 (CH(Z)),
123.4 (CH(E)), 130.6 (CH(Z)), 132.0 (CH(E)), 132.4 (C(Z)), 134.3
(C(E)), 140.7 (C(E)), 145.2 (C(Z)), 145.4 (C(Z)), 146.2 (C(E)), 149.0
(br, CH(E)), 149.2 (br, CH(Z)), 156.2 (C(E)), 157.0 (C(Z)), 172.2
(C(E)), 172.4 (C(Z)) ppm. 13C NMR (100 MHz, CDCl3): δ = −0.9
(CH(Z)), −0.6 (CH(E)), 55.57 (CH(Z)), 55.60 (CH(E)), 100.0 (C(Z)),
102.7 (C(Z)), 104.2 (C(E)), 106.7 (C(E)), 112.7 (C(Z)), 115.1 (CH(Z)),
118.1 (CH(E)), 118.9 (CH(Z)), 123.1 (CH(Z)), 124.1 (CH(E)), 130.2
(CH(Z)), 131.3 (CH(E)), 132.5 (CH(Z)), 145.2 (C(Z)), 146.2 (C(Z)),
147.7 (CH(Z)), 157.5 (C(Z)), 173.9 (C(Z)) ppm. Not all carbon signals
1-(2,2-Dimethylhydrazino)-2-(4-nitrophenyl)-5-(trimethylsilyl)-
pent-1-en-4-yn-3-one (3at). Pale yellow solid; yield 100 mg (96%);
mp 114−116 °C (dec). Mixture of (Z)- and (E)-isomers in ratio
∼1:0.07 (CDCl3). Not all signals of minor (E)-isomer are visible in the
1
NMR spectra. H NMR (400 MHz, CDCl3): δ = 0.1 (s, 9 H(Z)), 0.27
(s, 0.63 H(E)), 2.60 (s, 0.42 H(E)), 2.73 (s, 6 H(Z)), 7.32 (d, J = 8.0 Hz,
1 H(Z)), 7.39 (d, J = 8.7 Hz, 0.14 H(E)), 7.55 (d, J = 8.8 Hz, 2 H(Z)),
8.15 (d, J = 8.8 Hz, 2 H(Z)), 8.21 (d, J = 8.7 Hz, 0.14 H(E)), 11.48 (d, J
= 8.0 Hz, 1 H(Z)) ppm. 13C NMR (100 MHz, CDCl3): δ = −0.9
(CH(Z)), −0.6 (CH(E)), 47.4 (CH(Z)), 99.8 (C(Z)), 101.9 (C(Z)), 110.8
(C(Z)), 123.1 (CH(Z)), 129.8 (CH(Z)), 131.0 (CH(E)), 145.2 (C(Z)),
146.0 (C(Z)), 149.8 (CH(Z)), 165.1 (C(Z)) ppm. HRMS (ESI-TOF) m/
z: [M + H]+ calcd for C16H21N3O3Si 332.1425; found 332.1424.
General Procedure for the Preparation of Pyrrolones 4. A 3
mL screw-cap vial was charged with a solution of enynone 1a−c (0.35
mmol) in diphenyl ether (1 mL). Then, the corresponding amine
E
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(0.35 mmol, 1 equiv) was added in one portion to the stirred solution,
and the vial was sealed and heated at 80 °C (40 °C for 4an) until TLC
indicated the full conversion of starting material (15−60 min). The
reaction mixture was then heated at 200 °C (175 °C for 4an) in an oil
bath for an additional 30−60 min. After cooling to room temperature
the reaction mixture was subjected to flash chromatography on silica
(n-hexane/ethyl acetate 1:0 to 10:1) to afford pyrrolones 4.
(2E)-4-(4-Nitrophenyl)-1-[2-(trifluoromethyl)phenyl]-2-
[(trimethylsilyl)methylene]-1,2-dihydro-3H-pyrrol-3-one (4ag). Or-
ange crystals; yield 94 mg (62%); mp 132−133 °C. H NMR (400
1
MHz, (CD3)2CO): δ = 0.25 (s, 9 H), 5.45 (s, 1 H), 7.74 (d, J = 7.9
Hz, 1 H), 7.82−7.86 (m, 1 H), 7.93−7.97 (m, 1 H), 8.01 (d, J = 7.9
Hz, 1 H), 8.20−8.26 (m, 4 H), 8.91 (s, 1 H) ppm. 13C NMR (100
MHz, (CD3)2CO): δ = −1.0 (CH), 111.9 (C), 122.7 (CH), 124.2 (q,
JC−F = 272.9 Hz, CF3), 124.7 (CH), 125.3 (CH), 128.6 (q, JC−F = 5.1
Hz, CH), 129.6 (q, JC−F = 30.7 Hz, C), 131.1 (CH), 132.9 (CH),
135.1 (CH), 136.3 (C), 140.0 (C), 146.1 (C), 149.0 (C), 157.4 (CH),
184.8 (C) ppm. 19F NMR (376.5 MHz, CDCl3): δ = −60.4 ppm.
HRMS (ESI-TOF) m/z: [M + H]+ calcd for C21H19F3N2O3Si
433.1190; found 433.1180. UV−vis λmax (ε × 10−4): 366 (1.52), 432
(0.99) nm. Emission λmax 538 nm.
(2E)-1-(4-Methoxyphenyl)-4-(4-nitrophenyl)-2-[(trimethylsilyl)-
methylene]-1,2-dihydro-3H-pyrrol-3-one (4aa). Orange crystals;
1
yield 124 mg (90%); mp 57−59 °C. H NMR (400 MHz, CDCl3):
δ = 0.27 (s, 9 H), 3.87 (s, 3 H), 5.81 (s, 1 H), 7.02 (d, J = 8.9 Hz, 2
H), 7.21 (d, J = 8.9 Hz, 2 H), 7.95 (d, J = 9.0 Hz, 2 H), 8.18 (d, J = 9.0
Hz, 2 H), 8.21 (s, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ = −1.1
(CH), 55.6 (CH), 111.0 (C), 115.1 (CH), 123.2 (CH), 124.1 (CH),
124.2 (CH), 127.2 (CH), 130.3 (C), 138.8 (C), 145.1 (C), 146.8 (C),
153.9 (CH), 159.3 (C), 184.0 (C) ppm. HRMS (ESI-TOF) m/z: [M
+ H]+ calcd for C21H22N2O4Si 395.1422; found 395.1422. UV−vis
λmax (ε × 10−4): 262 (1.74), 382 (1.64), 456 (0.98) nm. Emission λmax
567 nm.
2-{(2E)-4-(4-Nitrophenyl)-3-oxo-2-[(trimethylsilyl)methylene]-2,3-
dihydro-1H-pyrrol-1-yl}benzonitrile (4ah). Dark orange crystals; yield
1
89 mg (65%); mp 194−195 °C. H NMR (400 MHz, (CD3)2CO): δ
= 0.27 (s, 9 H), 5.80 (s, 1 H), 7.71−7.74 (m, 1 H), 7.78 (d, J = 8.1 Hz,
1 H), 7.93−7.97 (m, 1 H), 8.03 (d, J = 7.7 Hz, 1 H), 8.20−8.26 (m, 4
H), 9.10 (s, 1 H) ppm. 13C NMR (100 MHz, (CD3)2CO): δ = −1.0
(CH), 112.2 (C), 112.9 (C), 116.7 (C), 122.9 (CH), 124.7 (CH),
125.6 (CH), 129.8 (CH), 130.1 (CH), 135.3 (CH), 135.6 (CH),
139.6 (C), 140.8 (C), 146.3 (C), 146.4 (C), 156.4 (CH), 184.8 (C)
ppm. HRMS (ESI-TOF) m/z: [M + H]+ calcd for C21H19N3O3Si
390.1268; found 390.1271. UV−vis λmax (ε × 10−4): 362 (1.85), 432
(1.07) nm. Emission λmax 537 nm.
(2E)-4-(4-Nitrophenyl)-1-phenyl-2-[(trimethylsilyl)methylene]-1,2-
dihydro-3H-pyrrol-3-one (4ab). Orange crystals; yield 108 mg (85%);
1
mp 167−169 °C. H NMR (400 MHz, CDCl3): δ = 0.27 (s, 9 H),
5.96 (s, 1 H), 7.30−7.32 (m, 2 H), 7.41−7.45 (m, 1 H), 7.52−7.56
(m, 2 H), 7.96 (d, J = 9.0 Hz, 2 H), 8.18 (d, J = 9.0 Hz, 2 H), 8.29 (s, 1
H) ppm. 13C NMR (100 MHz, CDCl3): δ = −1.1 (CH), 111.6 (C),
123.2 (CH), 124.1 (CH), 124.3 (CH), 125.4 (CH), 128.0 (CH),
130.0 (CH), 137.7 (C), 138.6 (C), 145.2 (C), 145.9 (C), 153.5 (CH),
184.1 (C) ppm. HRMS (ESI-TOF) m/z: [M + Na]+ calcd for
C20H20N2O3Si 387.1135; found 387.1125. UV−vis λmax (ε × 10−4):
265 (1.58), 377 (1.73), 451 (1.1) nm. Emission λmax 554 nm.
(2E)-1-(2-Methoxyphenyl)-4-(4-nitrophenyl)-2-[(trimethylsilyl)-
methylene]-1,2-dihydro-3H-pyrrol-3-one (4ai). Orange crystals; yield
116 mg (84%); mp 71−73 °C. 1H NMR (400 MHz, (CD3)2CO): δ =
0.25 (s, 9 H), 3.88 (s, 3 H), 5.58 (s, 1 H), 7.11−7.15 (m, 1 H), 7.27
(d, J = 8.3 Hz, 1 H), 7.40−7.43 (m, 1 H), 7.46−7.51 (m, 1 H), 8.18−
8.22 (m, 4 H), 8.85 (s, 1 H) ppm. 13C NMR (100 MHz, (CD3)2CO):
δ = −0.9 (CH), 56.3 (CH), 110.9 (C), 113.7 (CH), 121.4 (CH),
121.9 (CH), 124.6 (CH), 124.9 (CH), 126.6 (C), 129.6 (CH), 130.9
(CH), 140.5 (C), 145.7 (C), 147.4 (C), 156.0 (C), 158.2 (CH), 184.8
(C) ppm. HRMS (ESI-TOF) m/z: [M + H]+ calcd for C21H22N2O4Si
395.1422; found 395.1431. UV−vis λmax (ε × 10−4): 380 (1.55), 448
(1.05) nm. Emission λmax 551 nm.
(2E)-1-Mesityl-4-(4-nitrophenyl)-2-[(trimethylsilyl)methylene]-1,2-
dihydro-3H-pyrrol-3-one (4aj). Orange crystals; yield 119 mg (84%);
mp 178−180 °C. 1H NMR (400 MHz, (CD3)2CO): δ = 0.24 (s, 9 H),
2.13 (s, 6 H), 2.34 (s, 3 H), 5.32 (s, 1 H), 7.07 (s, 2 H), 8.20 (s, 4 H),
8.82 (s, 1 H) ppm. 13C NMR (100 MHz, (CD3)2CO): δ = −0.9 (CH),
17.6 (CH), 21.1 (CH), 110.9 (C), 121.4 (CH), 124.6 (CH), 124.9
(CH), 130.3 (CH), 133.2 (C), 137.8 (C), 140.1 (C), 140.6 (C), 145.7
(C), 146.9 (C), 158.0 (CH), 184.5 (C) ppm. HRMS (ESI-TOF) m/z:
[M + H]+ calcd for C23H26N2O3Si 407.1785; found 407.1778. UV−vis
λmax (ε × 10−4): 258 (1.33), 378 (1.72), 451 (1.12) nm. Emission λmax
551 nm.
(2E)-1-(4-Fluorophenyl)-4-(4-nitrophenyl)-2-[(trimethylsilyl)meth-
ylene]-1,2-dihydro-3H-pyrrol-3-one (4ad). Orange crystals; yield 121
1
mg (90%); mp 187−188 °C. H NMR (400 MHz, CDCl3): δ = 0.28
(s, 9 H), 5.83 (s, 1 H), 7.21−7.25 (m, 2 H), 7.27−7.31 (m, 2 H),
7.93−7.97 (m, 2 H), 8.17−8.20 (m, 2 H), 8.23 (s, 1 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = −1.1 (CH), 111.7 (C), 117.1 (d, JC−F
23.1 Hz, CH), 123.2 (CH), 124.1 (CH), 124.4 (CH), 127.6 (d, JC−F
=
=
8.6 Hz, CH), 133.7 (d, JC−F = 3.3 Hz, C), 138.4 (C), 145.3 (C), 146.2
(C), 153.4 (CH), 161.9 (d, JC−F = 249.2 Hz, C), 184.0 (C) ppm. 19F
NMR (376.5 MHz, CDCl3): δ = −112.2 ppm. HRMS (ESI-TOF) m/
z: [M + H]+ calcd for C20H19FN2O3Si 383.1222; found 383.1225.
UV−vis λmax (ε × 10−4): 263 (1.43), 374 (1.59), 450 (0.91) nm.
Emission λmax 553 nm.
Methyl 4-{(2E)-4-(4-Nitrophenyl)-3-oxo-2-[(trimethylsilyl)methyl-
ene]-2,3-dihydro-1H-pyrrol-1-yl}benzoate (4ae). Orange crystals;
yield 100 mg (68%); mp 202−203 °C. 1H NMR (400 MHz,
DMSO-d6): δ = 0.25 (s, 9 H), 3.89 (s, 3 H), 6.10 (s, 1 H), 7.65 (d, J =
8.6 Hz, 2 H), 8.12 (d, J = 8.6 Hz, 2 H), 8.17−8.23 (m, 4 H), 9.35 (s, 1
H) ppm. 13C NMR (100 MHz, DMSO-d6): δ = −0.9 (CH), 52.3
(CH), 111.0 (C), 122.0 (CH), 123.9 (CH), 124.6 (CH), 124.7 (CH),
127.9 (C), 130.8 (CH), 138.8 (C), 141.1 (C), 144.5 (C), 144.6 (C),
156.6 (CH), 165.5 (C), 183.9 (C) ppm. HRMS (ESI-TOF) m/z: [M
+ H]+ calcd for C22H22N2O5Si 423.1371; found 423.1381. UV−vis
λmax (ε × 10−4): 316 (0.90), 370 (1.83), 445 (0.99) nm. Emission λmax
547 nm.
(2E)-1-(2,6-Diisopropylphenyl)-4-(4-nitrophenyl)-2-[(trimethyl-
silyl)methylene]-1,2-dihydro-3H-pyrrol-3-one (4ak). Bright orange
1
crystals; yield 125 mg (80%); mp 73−75 °C. H NMR (400 MHz,
(CD3)2CO): δ = 0.24 (s, 9 H), 1.17 (d, J = 6.9 Hz, 6 H), 1.21 (d, J =
6.9 Hz, 6 H), 2.82 (sept, J = 6.9 Hz, 2 H), 5.32 (s, 1 H), 7.40 (d, J =
7.8 Hz, 2 H), 7.53 (t, J = 7.8 Hz, 1 H), 8.20−8.25 (m, 4 H), 8.94 (s, 1
H) ppm. 13C NMR (100 MHz, (CD3)2CO): δ = −1.0 (CH), 24.3
(CH), 24.7 (CH), 29.5 (CH), 111.0 (C), 122.8 (CH), 124.7 (CH),
125.0 (CH), 125.4 (CH), 131.3 (CH), 133.0 (C), 140.5 (C), 145.8
(C), 148.9 (C), 149.2 (C), 158.2 (CH), 184.5 (C) ppm. HRMS (ESI-
TOF) m/z: [M + H]+ calcd for C26H32N2O3Si 449.2255; found
449.2245. UV−vis λmax (ε × 10−4): 376 (1.67), 451 (1.03) nm.
Emission λmax 551 nm.
(2E)-4-(4-Nitrophenyl)-1-(4-(trifluoromethyl)phenyl)-2-[(trimeth-
ylsilyl)methylene]-1,2-dihydro-3H-pyrrol-3-one (4af). Dark orange
1
crystals; yield 103 mg (68%); mp 192−193 °C. H NMR (400 MHz,
(CD3)2CO): δ = 0.29 (s, 9 H), 6.19 (s, 1 H), 7.79 (d, J = 8.4 Hz, 2 H),
7.93 (d, J = 8.4 Hz, 2 H), 8.23 (s, 4 H), 9.14 (s, 1 H) ppm. 1H NMR
(400 MHz, CDCl3): δ = 0.30 (s, 9 H), 6.03 (s, 1 H), 7.45 (d, J = 8.4
Hz, 2 H), 7.81 (d, J = 8.4 Hz, 2 H), 7.96 (d, J = 8.9 Hz, 2 H), 8.18 (d, J
= 8.9 Hz, 2 H), 8.32 (s, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
−1.1 (CH), 112.9 (C), 123.3 (CH), 123.6 (q, JC−F = 272.1 Hz, CF3),
124.1 (CH), 124.7 (CH), 125.2 (CH), 127.3 (q, JC−F = 3.7 Hz, CH),
129.7 (q, JC−F = 33.1 Hz, C), 138.0 (C), 140.8 (C), 145.0 (C), 145.6
(C), 152.5 (CH), 184.1 (C) ppm. 19F NMR (376.5 MHz, CDCl3): δ =
−62.6 ppm. HRMS (ESI-TOF) m/z: [M + H]+ calcd for
C21H19F3N2O3Si 433.1190; found 433.1200. UV−vis λmax (ε ×
10−4): 368 (1.49), 443 (0.84) nm. Emission λmax 547 nm.
(2E)-4-(4-Nitrophenyl)-1-(1,3-thiazol-2-yl)-2-[(trimethylsilyl)-
methylene]-1,2-dihydro-3H-pyrrol-3-one (4al). Red crystals; yield 59
1
mg (45%); mp 176−177 °C (dec). H NMR (400 MHz, DMSO-d6):
δ = 0.27 (s, 9 H), 7.16 (s, 1 H), 7.56 (s, 1 H), 7.68 (s, 1 H), 8.22 (s, 4
H), 9.38 (s, 1 H) ppm. 13C NMR (100 MHz, DMSO-d6): δ = −0.9
(CH), 113.4 (C), 115.8 (CH), 123.8 (CH), 125.6 (CH), 125.7 (CH),
137.4 (C), 139.4 (CH), 142.3 (C), 145.3 (C), 153.5 (CH), 158.5 (C),
183.9 (C) ppm. HRMS (ESI-TOF) m/z: [M + Na]+ calcd for
F
DOI: 10.1021/acs.joc.5b00398
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
C17H17N3O3SSi 394.0652; found 394.0654. UV−vis λmax (ε × 10−4):
272 (1.10), 360 (1.39), 438 (0.85) nm. Emission λmax 540 nm.
(2E)-1-[3-(4-Chlorophenyl)-1-phenyl-1H-pyrazol-5-yl]-4-(4-nitro-
phenyl)-2-[(trimethylsilyl)methylene]-1,2-dihydro-3H-pyrrol-3-one
(4am). Orange crystals; yield 155 mg (82%); mp 205−207 °C (dec).
1H NMR (400 MHz, CDCl3): δ = 0.19 (s, 9 H), 5.70 (s, 1 H), 6.77 (s,
1 H), 7.37−7.48 (m, 7 H), 7.84−7.86 (m, 4 H), 8.02 (s, 1 H), 8.17 (d,
J = 8.8 Hz, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = −1.4 (CH),
102.2 (CH), 114.0 (C), 123.1 (CH), 124.0 (CH), 125.0 (CH), 125.1
(CH), 126.9 (CH), 128.5 (CH), 129.0 (CH), 129.7 (CH), 130.7 (C),
134.6 (C), 136.1 (C), 137.4 (C), 138.1 (C), 144.5 (C), 145.9 (C),
150.9 (C), 151.9 (CH), 183.4 (C) ppm. HRMS (ESI-TOF) m/z: [M
+ H]+ calcd for C29H25ClN4O3Si 541.1457; found 541.1450.
(2E)-4-(4-Nitrophenyl)-1-propyl-2-[(trimethylsilyl)methylene]-1,2-
dihydro-3H-pyrrol-3-one (4an). Ruby crystals; yield 104 mg (90%);
mp 129−131 °C. 1H NMR (400 MHz, (CD3)2CO): δ = 0.28 (s, 9 H),
0.96 (t, J = 7.3 Hz, 3 H), 1.78 (sext, J = 7.3 Hz, 2 H), 3.76 (t, J = 7.3
Hz, 2 H), 5.98 (s, 1 H), 8.08−8.11 (m, 2 H), 8.14−8.17 (m, 2 H), 8.85
(s, 1 H) ppm. 13C NMR (100 MHz, (CD3)2CO): δ = −0.8 (CH), 11.5
(CH), 22.7 (CH2), 48.7 (CH2), 109.0 (C), 120.7 (CH), 124.3 (CH),
124.6 (CH), 141.0 (C), 145.2 (C), 147.1 (C), 158.1 (CH), 184.9 (C)
ppm. HRMS (ESI-TOF) m/z: [M + H]+ calcd for C17H22N2O3Si
331.1472; found 331.1470. UV−vis λmax (ε × 10−4): 382 (1.59), 459
(0.86) nm. Emission λmax 558 nm.
(2E,2′E)-1,1′-Biphenyl-4,4′-diylbis{4-(4-nitrophenyl)-2-[(trimethyl-
silyl)methylene]-1,2-dihydro-3H-pyrrol-3-one} (4as). This material
was obtained from enamine 3as (0.16 mmol) after heating at 200 °C
in Ph2O for 1 h and was purified by flash chromatography under
conditions that were the same as those for other compounds 4. Red
1
powder; yield 84 mg (72%); mp 260−261 °C (dec). H NMR (400
MHz, DMSO-d6): δ = 0.26 (s, 18 H), 6.05 (s, 2 H), 7.63 (d, J = 8.3
Hz, 4 H), 7.95 (d, J = 8.3 Hz, 4 H), 8.19−8.24 (m, 8 H), 9.34 (s, 2 H)
ppm. 13C NMR (100 MHz, DMSO-d6): δ = −0.9 (CH), 110.2 (C),
121.7 (CH), 123.9 (CH), 124.3 (CH), 125.7 (CH), 128.0 (CH),
136.7 (C), 138.0 (C), 139.2 (C), 144.3 (C), 145.4 (C), 157.1 (CH),
183.8 (C) ppm. HRMS (ESI-TOF) m/z: [M + H]+ calcd for
C40H38N4O6Si2 727.2403; found 727.2397. UV−vis λmax (ε × 10−4):
312 (2.06), 376 (3.96), 454 (2.36) nm. Emission λmax 556 nm.
(2E)-1-(4-Methoxyphenyl)-4-phenyl-2-[(trimethylsilyl)methylene]-
1,2-dihydro-3H-pyrrol-3-one (4ba). Dark red crystals; yield 80 mg
(66%); mp 119−120 °C. 1H NMR (400 MHz, CDCl3): δ = 0.27 (s, 9
H), 3.87 (s, 3 H), 5.71 (s, 1 H), 7.00−7.02 (m, 2 H), 7.17−7.21 (m, 3
H), 7.33−7.37 (m, 2 H), 7.75−7.76 (m, 2 H), 8.05 (s, 1 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = −0.96 (CH), 55.6 (CH), 113.4 (C),
114.9 (CH), 120.2 (CH), 124.8 (CH), 125.9 (CH), 127.0 (CH),
128.5 (CH), 131.2 (C), 131.6 (C), 146.9 (C), 152.7 (CH), 158.7 (C),
185.0 (C) ppm. HRMS (ESI-TOF) m/z: [M + H]+ calcd for
C21H23NO2Si 350.1571; found 350.1575. UV−vis λmax (ε × 10−4): 291
(2.64), 467 (0.37) nm.
(2E)-1-Cyclopentyl-4-(4-nitrophenyl)-2-[(trimethylsilyl)methyl-
ene]-1,2-dihydro-3H-pyrrol-3-one (4ao). Dark red crystals; yield 96
1
mg (77%); mp 162−164 °C. H NMR (400 MHz, (CD3)2CO): δ =
0.28 (s, 9 H), 1.67−1.78 (m, 2 H), 1.83−1.94 (m, 4 H), 2.08−2.17
(m, 2 H), 4.42−4.49 (m, 1 H), 6.03 (s, 1 H), 8.14 (s, 4 H), 8.88 (s, 1
H) ppm. 13C NMR (100 MHz, (CD3)2CO): δ = −0.8 (CH), 24.4
(CH2), 31.8 (CH2), 57.1 (CH), 109.5 (C), 121.1 (CH), 124.4 (CH),
124.5 (CH), 141.0 (C), 145.2 (C), 147.7 (C), 154.8 (CH), 185.1 (C)
ppm. HRMS (ESI-TOF) m/z: [M + H]+ calcd for C19H24N2O3Si
357.1629; found 357.1634. UV−vis λmax (ε × 10−4): 387 (1.54), 462
(0.88) nm. Emission λmax 562 nm.
(2E)-1,4-Diphenyl-2-[(trimethylsilyl)methylene]-1,2-dihydro-3H-
pyrrol-3-one (4bb). Dark red crystals; yield 73 mg (65%); mp 133−
134 °C. 1H NMR (400 MHz, CDCl3): δ = 0.29 (s, 9 H), 5.87 (s, 1 H),
7.19−7.22 (m, 1 H), 7.28−7.30 (m, 2 H), 7.34−7.39 (m, 3 H), 7.49−
7.53 (m, 2 H), 7.76−7.78 (m, 2 H), 8.13 (s, 1 H) ppm. 13C NMR (100
MHz, CDCl3): δ = −0.78 (CH), 114.3 (C), 120.4 (CH), 125.1 (CH),
125.3 (CH), 126.3 (CH), 127.3 (CH), 128.7 (CH), 130.0 (CH),
131.5 (C), 138.6 (C), 146.2 (C), 152.4 (CH), 185.3 (C) ppm. HRMS
(ESI-TOF) m/z: [M + H]+ calcd for C20H21NOSi 320.1465; found
320.1467. UV−vis λmax (ε × 10−4): 296 (3.89), 462 (0.64) nm.
Emission λmax 468 nm.
(2E)-1-(tert-Butyl)-4-(4-nitrophenyl)-2-[(trimethylsilyl)methylene]-
1,2-dihydro-3H-pyrrol-3-one (4ap). Orange crystals; yield 88 mg
1
(73%); mp 180−182 °C. H NMR (400 MHz, (CD3)2CO): δ = 0.29
(s, 9 H), 1.65 (s, 9 H), 6.20 (s, 1 H), 8.11−8.16 (m, 4 H), 8.88 (s, 1
H) ppm. 13C NMR (100 MHz, (CD3)2CO): δ = −0.4 (CH), 29.3
(CH), 58.2 (C), 108.5 (C), 119.6 (CH), 124.50 (CH), 124.52 (CH),
141.1 (C), 145.2 (C), 146.0 (C), 156.8 (CH), 185.0 (C) ppm. HRMS
(ESI-TOF) m/z: [M + H]+ calcd for C18H24N2O3Si 345.1629; found
345.1625. UV−vis λmax (ε × 10−4): 381 (1.41), 454 (0.71) nm.
Emission λmax 552 nm.
(2E)-1,4-Bis(4-methoxyphenyl)-2-[(trimethylsilyl)methylene]-1,2-
dihydro-3H-pyrrol-3-one (4ca). Red crystals; yield 98 mg (74%); mp
88−89 °C. 1H NMR (400 MHz, CDCl3): δ = 0.26 (s, 9 H), 3.81 (s, 3
H), 3.86 (s, 3 H), 5.68 (s, 1 H), 6.90 (d, J = 8.8 Hz, 2 H), 7.00 (d, J =
8.8 Hz, 2 H), 7.19 (d, J = 8.8 Hz, 2 H), 7.68 (d, J = 8.8 Hz, 2 H), 7.96
(s, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ = −0.9 (CH), 55.3
(CH), 55.6 (CH), 113.4 (C), 114.0 (CH), 114.9 (CH), 119.6 (CH),
124.2 (C), 126.1 (CH), 126.9 (CH), 131.4 (C), 146.9 (C), 151.9
(CH), 158.0 (C), 158.6 (C), 185.2 (C) ppm. HRMS (ESI-TOF) m/z:
[M + H]+ calcd for C22H25NO3Si 380.1677; found 380.1682. UV−vis
λmax (ε × 10−4): 290 (2.25), 479 (0.26) nm.
(2E)-1-Benzyl-4-(4-nitrophenyl)-2-[(trimethylsilyl)methylene]-1,2-
dihydro-3H-pyrrol-3-one (4aq). Orange crystals; yield 119 mg (90%);
mp 145−146 °C. 1H NMR (400 MHz, (CD3)2CO): δ = 0.23 (s, 9 H),
5.04 (s, 2 H), 5.96 (s, 1 H), 7.30−7.36 (m, 1 H), 7.38−7.41 (m, 4 H),
8.10−8.12 (m, 2 H), 8.16−8.18 (m, 2 H), 8.94 (s, 1 H) ppm. 13C
NMR (100 MHz, (CD3)2CO): δ = −0.9 (CH), 50.8 (CH2), 109.9
(C), 121.7 (CH), 124.60 (CH), 124.64 (CH), 128.0 (CH), 128.7
(CH), 129.7 (CH), 137.3 (C), 140.7 (C), 145.5 (C), 147.1 (C), 158.2
(CH), 185.0 (C) ppm. HRMS (ESI-TOF) m/z: [M + H]+ calcd for
C21H22N2O3Si 379.1472; found 379.1483. UV−vis λmax (ε × 10−4):
379 (1.55), 454 (0.91) nm. Emission λmax 558 nm.
(2E)-1-(2-Furylmethyl)-4-(4-nitrophenyl)-2-[(trimethylsilyl)meth-
ylene]-1,2-dihydro-3H-pyrrol-3-one (4ar). Deep red crystals; yield
103 mg (80%); mp 117−118 °C. 1H NMR (400 MHz, (CD3)2CO): δ
= 0.26 (s, 9 H), 5.02 (s, 2 H), 6.10 (s, 1 H), 6.42 (dd, J = 3.2, 1.9 Hz, 1
H), 6.51 (d, J = 3.2 Hz, 1 H), 7.55 (d, J = 1.9 Hz, 1 H), 8.08−8.11 (m,
2 H), 8.16−8.18 (m, 2 H), 8.86 (s, 1 H) ppm. 13C NMR (100 MHz,
(CD3)2CO): δ = −0.9 (CH), 43.7 (CH2), 109.9 (CH), 110.2 (C),
111.5 (CH), 121.4 (CH), 124.64 (CH), 124.65 (CH), 140.6 (C),
144.0 (CH), 145.6 (C), 146.7 (C), 150.2 (C), 157.6 (CH), 184.9 (C)
ppm. HRMS (ESI-TOF) m/z: [M + H]+ calcd for C19H20N2O4Si
369.1265; found 369.1260. UV−vis λmax (ε × 10−4): 377 (1.45), 450
(0.89) nm. Emission λmax 557 nm.
(2E)-4-(4-Methoxyphenyl)-1-phenyl-2-[(trimethylsilyl)methylene]-
1,2-dihydro-3H-pyrrol-3-one (4cb). Red crystals; yield 86 mg (70%);
1
mp 146−148 °C. H NMR (400 MHz, CDCl3): δ = 0.27 (s, 9 H),
3.81 (s, 3 H), 5.85 (s, 1 H), 6.89−6.91 (m, 2 H), 7.26−7.28 (m, 2 H),
7.33−7.36 (m, 1 H), 7.47−7.51 (m, 2 H), 7.68−7.70 (m, 2 H), 8.04
(s, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ = −0.9 (CH), 55.3
(CH), 114.0 (CH), 114.1 (C), 119.7 (CH), 124.0 (C), 125.0 (CH),
126.2 (CH), 126.9 (CH), 129.8 (CH), 138.6 (C), 146.0 (C), 151.3
(CH), 158.1 (C), 185.3 (C) ppm. HRMS (ESI-TOF) m/z: [M + H]+
calcd for C21H23NO2Si 350.1571; found 350.1579. UV−vis λmax (ε ×
10−4): 298 (2.57), 473 (0.35) nm. Emission λmax 502 nm.
ASSOCIATED CONTENT
■
S
* Supporting Information
General protocol for the synthesis of enynones 1; copies of 1H,
13C, and 19F NMR spectra for compounds 3aa,as,at, 4aa−as,
and 4ba−cb; UV−vis spectra of pyrrolones 4aa−as and 4ba−
G
DOI: 10.1021/acs.joc.5b00398
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
(17) CCDC 1046271 (for compound 4ab) and 1050103 (for
compound 4ar) contain the supplementary 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.
(18) (a) Chauvelier, J. Bull. Soc. Chim. Fr. 1954, 734−738. (b) Metler,
T.; Uchida, A.; Miller, S. I. Tetrahedron 1968, 24, 4285−4297.
(19) Elschenbroich, C. Organometallchemie, 6th ed.; Springer:
Wiesbaden, 2008; Chapter 8.
cb; and X-ray diffraction data for compounds 3aa, 4ab, 4ar. X-
ray crystallographic data files (CIF). This material is available
free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: m.kuznetsov@spbu.ru.
Notes
(20) A Guide to Recording Fluorescence Quantum Yields; manual by
HORIBA Jobin Yvon SAS.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors thank the Russian Scientific Fund for financial
support (Grant 14-13-00126). NMR, HRMS, UV, and XRD
analyses were performed at the Saint Petersburg State
University Center for Magnetic Resonance, Center for
Chemical Analysis and Materials Research, Educational
Resource Center of Chemistry, and X-ray Diffraction Center,
respectively.
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H
DOI: 10.1021/acs.joc.5b00398
J. Org. Chem. XXXX, XXX, XXX−XXX