Superelectrophilic nazarov cyclizations with N-heterocycles

Article abstract of DOI:10.1016/j.tet.2020.131644

A series of Nazarov cyclizations has been studied involving N-heterocyclic-substituted 1-arylprop-2-en-1-one derivatives (aza-chalcones). Superacid catalyzed reactions of these derivatives provide good yields of heterocyclic-substituted 1-indanones. A mec

Full text of DOI:10.1016/j.tet.2020.131644

Tetrahedron xxx (xxxx) xxx
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Superelectrophilic nazarov cyclizations with N-heterocycles
Hien Vuong, Harouna Amadou, Michael R. Stentzel, Douglas A. Klumpp*
Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL, 60115, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of Nazarov cyclizations has been studied involving N-heterocyclic-substituted 1-arylprop-2-en-
1-one derivatives (aza-chalcones). Superacid catalyzed reactions of these derivatives provide good yields
of heterocyclic-substituted 1-indanones. A mechanism is proposed involving diprotonated, super-
electrophilic intermediates.
Received 1 August 2020
Received in revised form
15 September 2020
Accepted 21 September 2020
Available online xxx
© 2020 Elsevier Ltd. All rights reserved.
Keywords:
Heterocycles
Nazarov
Indanone
Superacid
Superelectrophile
1. Introduction
AlCl3 [7]. Several other reports describe chalcone cyclizations
involving primarily electron rich aryl rings [8], such as Lawrence’s
Olah and coworkers first recognized the concept of super-
electrophilic activation [1]. It was proposed that monocationic
electrophiles, such as nitronium (NOþ2 ) and acetyl (CH3COþ) cat-
ions, could undergo further protonation in sufficiently acidic media
and the resulting species should exhibit enhanced electrophilic
reactivities [2]. This concept has been confirmed by numerous
experimental studies with these multiply charged intermediates, or
superelectrophiles [2]. As a result of the high reactivities of super-
electrophiles, they have been used in many novel synthetic
methods [2,3]. In previous studies, we and others have demon-
strated that stable cationic charges - from protonated N-heterocy-
clic rings e have a profound activating effect in electrophilic
reactions [4]. These N-heterocycle-based systems often have re-
activities similar to Olah’s superelectrophiles.
microwave-assisted synthesis of potential tubulin-binding agents.
[8a] In the following manuscript, we describe the use of protonated
N-heterocyclic rings to facilitate the Nazarov reaction and provide
functionalized 1-indanone products in good yields.
2. Results and discussion
In previous studies from our group, protonated N-heterocyclic
rings have been shown to enhance the reactivities of carboxonium
ion and carbenium ion electrophiles.[4b,c,d] Likewise, the presence
of monocationic or dicationic protonated N-heterocyclic rings
activated Diels-Alder dienes for cycloaddition reactions with
ethylene [9]. In order to probe the effects of N-heterocyclic rings on
the Nazarov reaction, a series of 1-arylprop-2-en-1-one derivatives
(1) were prepared [10]. Derivatives of compound 1 were typically
prepared using condensation chemistry, for example acetophenone
reacts with 2-pyridinecarboxaldehyde to give 1-phenyl-3-(pyridin-
2-yl)prop-2-en-1-one (1a, see Experimental Section). Upon treat-
ment with excess superacid, CF3SO3H, substrate 1a provides the
functionalized indanone (2) in quantitative yield (Table 1). The
same substrate does not cyclize in excess H2SO4 or weaker acids at
80 ꢀC. Likewise, the pyridyl isomers 1 b,c give the respective
products 3 and 4 in good yields. Halogenated derivatives 5e6 and
alkylated derivatives 7e8 are prepared in fair to good yields.
Cyclization involving a 1-napthyl ring provides product 9 in 92%
yield, with cyclization occurring preferentially at the 2-position.
A number of recent studies have shown that strongly acidic
media may be used to promote the Nazarov cyclization of chalcone
derivatives to provide functionalized indanones [5]. For example,
Koltunov and coworkers utilized zeolite and solid acid catalysts to
convert chalcone to 3-phenyl-1-indanone (Scheme 1) [6].
A
diprotonated superelectrophile was proposed as the possible in-
termediate leading to cyclization. Others have accomplished this
transformation using forcing conditions and excess acids such as
* Corresponding author.
E-mail address: dklumpp@niu.edu (D.A. Klumpp).
https://doi.org/10.1016/j.tet.2020.131644
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Please cite this article as: H. Vuong, H. Amadou, M.R. Stentzel et al., Superelectrophilic nazarov cyclizations with N-heterocycles, Tetrahedron,
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H. Vuong, H. Amadou, M.R. Stentzel et al.
Tetrahedron xxx (xxxx) xxx
Table 1
Products and isolated yields for the reactions of 1 and CF3SO3H at 80 ꢀC.
Scheme 1.
Other N-heterocyclic groups promote the cyclization, including the
pyrazine and benzothiazole derivatives to give 10e11, respectively.
Heterocycle-substituted 1-indanones have been useful as phar-
maceutical intermediates and the above chemistry provides
improved access to these structures. For example, the synthesis of
compound 4 was described recently in a patent and an optimized
procedure required no less than five synthetic steps (yields not
given) [11]. Our methodology provides this compound in just two
synthetic steps.
arylprop-2-en-1-one (1) derivatives likely involve diprotonated
species or electron-deficient carboxonium ions. For example,
compound 1a is first protonated at the N-heterocycle and then at
the carbonyl group to provide the dication 19 (Scheme 2). It is
Some time ago, we reported the condensation reactions of
acrylic acid derivatives with benzene in superacid [12]. It was
observed that electron-deficient substrates, including those with N-
heterocyclic derivatives, provide 1-phenylprop-2-en-1-ones.
suggested that this superelectrophilic species triggers the 4
p
electrocyclization - which leads to intermediate 20. Deprotonation
steps then provide the final product, indanone 2. Previous work by
Ohwada and coworkers has suggested that charge delocalization is
an important driving force in the Nazarov cyclization with dica-
tionic or superelectrophilic species [13]. The cyclization of dication
19 effective separates the two cationic charges, wherein dication 20
For example, 3-(pyridin-3-yl)acrylic acid (12) provides the aza-
chalcone (1b) in 85% yield from a reaction with CF3SO3H and
C6H6 at 25 ꢀC (eq 1).12 We reasoned that the cyclization reaction
conditions (80 ꢀC) should provide substituted-indanones directly
from the electron deficient acrylic acid derivatives. Thus, reaction of
the imidazole derivative 13 provides the cyclization product 14 in a
single synthetic step in 64% yield (Table 2). Likewise, the pyridine
derivatives (12, 15e16) give good yields of the respective indanones
(2, 3, and 4). The previous study from our group also showed that
pentafluorocinnamic acid (17) reacts with benzene in triflic acid to
provide the fluorinated chalcone.12 Similar to the heterocyclic de-
rivatives, pentafluorocinnamic acid (17) provides the cyclization
product (18) in high yield.
has two monocation p-systems that are no longer in conjugation. In
the case of the pyrazine substrate, protonation will likely give an
equilibrium containing both the di- and triprotonated species (21).
In the conversions involving pentafluorocinnamic acid (17), Friedel-
Crafts chemistry gives the corresponding chalcone and the pro-
tonated derivative 22 is assumed to be the reactive intermediate
leading to the Nazarov cyclization product. No other reasonably
good base-site exists, so diprotonation is not likely with the pen-
tafluorochalcone. With intermediate 22, charge-charge repulsive
effects are not a likely a driving force for the cyclization. Rather,
cyclization is driven by the strongly electrophilic
b-carbon of this
species. A similar inductive effect may also be an important
In the conversions to indanones, the cyclizations of the 1-
2

H. Vuong, H. Amadou, M.R. Stentzel et al.
Tetrahedron xxx (xxxx) xxx
Table 2
Products and yields from the reactions of acrylic acid derivatives with CF3SO3H and C6H6 at 80 ꢀC.
Scheme 3.
cyclization, even with elevated temperatures and prolonged reac-
tion times. Substrate 1m could be isolated quantitatively following
the unsuccessful efforts. These results suggest a modest or slight
increase in reactivity for the aza-chalcones over the chalcones. For
example, Yin and coworkers studied the AlCl3-promoted reactions
of substituted benzenes with cinnamoyl chloride using microwave
irradiation. [7a] In the case of chlorobenzene, the chloro-
substituted chalcone (26) is formed as a mixture of regioisomers
and the corresponding isomeric 1-indanones (27) are obtained in a
crude yield of 88%. Purification of 5-chloro-3-phenyl-1-indanone
(the phenyl analog of 23) provides a 45% isolated yield of this
indanone product. Considering the microwave induced trans-
formation of 26 is done at 185 ꢀC, while the aza-chalcone chemistry
is done at a lower temperature (80 ꢀC), this is consistent with a
Scheme 2.
contributing factor in the cyclizations of the aza-chalcones.
One of the hallmarks of superelectrophiles is their ability to
react with weak nucleophiles and deactivated aromatic rings [2]. In
order to examine this aspect of the chemistry, aza-chalcones (1k-
m) were prepared with increasingly deactivated aryl groups
(Scheme 3). Upon reaction in superacid, reasonable yields were
obtained from both the chlorophenyl and 3,4-dichlorophenyl de-
rivatives. Thus, substrate 1k gives a 55% yield of the 5-chloro-1-
indanone (23). While the dichlorophenyl derivative (1l) does un-
dergo cyclization in fair yield, the two regioisomers (24) are
formed. The 4-nitrophenyl derivative (1m) did not undergo
3

H. Vuong, H. Amadou, M.R. Stentzel et al.
Tetrahedron xxx (xxxx) xxx
somewhat higher level of reactivity for the aza-chalcone (1k). A
reasonably good yield of the dichloroindanone product (24) is also
obtained, despite the deactivating effects of the 3,4-dichlorophenyl
group in the aza-chalcone 1l. Nevertheless, attempts to obtain the
cyclization product were unsuccessful with the 4-nitrophenyl de-
rivative 1m. In excess superacid, this system is likely protonated at
the three good base sites e the pyridyl, carbonyl, and nitro groups.
As such, the protonated 4-nitrophenyl group is expected to be
highly deactivated, consequently even forcing conditions do not
trigger the Nazarov cyclization. It has also been previously reported
that chalcone does not undergo the Nazarov cyclization in excess
CF3SO3H at 80 ꢀC,13 the same conditions used to provide good yields
from the aza-chalcones (Table 1). This observation suggests an in-
crease in reactivities for the aza-chalcone and a strong activating
effect from the protonated N-heterocyclic groups.
(hexanes:ethyl acetate).
Procedure C: Synthesis of 1-indanones. NOTE: this procedure
is done near the boiling point of benzene, so adequate precautions
should be made to handle the potential buildup of pressure in a
closed reaction vessel. In a vessel flushed with inert gas, benzene
(0.5 mL) and CF3SO3H (2 mL, 22 mmol) are combined, into which is
added the acrylic acid derivative (1 mmol). The vessel is sealed,
heated to 80 ꢀC, and the solution stirred for 18 h. Following the
reaction period, the solution is cooled and then poured over ice.
Chloroform (15 mL) is added to the mixture and the aqueous so-
lution is made basic by the addition of saturated sodium bicar-
bonate. The organic extract is washed with water, then brine, and
dried with anhydrous sodium sulfate. Filtration and removal of the
solvent gives the crude indanone product - which is further puri-
fied by column chromatography (hexanes:ethyl acetate).
3. Conclusion
4.1. (E)-3-(6-Bromopyridin-2-yl)-1-phenylprop-2-en-1-one (1d)
In summary, we have found that aza-chalcones undergo effi-
cient Nazarov cyclizations in the presence of superacidic CF3SO3H.
The chemistry represents a simple method of preparing 1-
indanones having N-heterocyclic substituents. A mechanism is
proposed involving dicationic intermediates. Empirical evidence
suggests that the protonated N-heterocyclic substituents activate
the system towards cyclization - leading to good yields of products
at modest temperatures.
Using General Procedure A, acetophenone (120 mg,1 mmol) and
6-bromopicolinaldehyde (186 mg, 1 mmol) provides aza-chalcone
1d (259 mg, 0.90 mmol, 90%) as yellow solid, Rf ¼ 0.6 (hexane:
ethyl acetate, 1:1). 1H NMR (500 MHz CDCl3)
d
¼ 8.09 (1H, s), 8.05
(2H, t, J ¼ 7 Hz), 7.65 (1H, s), 7.62e7.55 (2H, m), 7.49 (2H, t,
J ¼ 7.5 Hz), 7.44 (1H, d, J ¼ 7.5 Hz), 7.39 (1H, d, J ¼ 7.5 Hz). 13C NMR
(125 MHz, CDCl3)
128.8, 128.75, 128.72, 126.9, 124.0. Mass spectrum (low resolution,
d
¼ 190.0, 154.4, 142.6, 140.8, 139.1, 137.6, 133.2,
EI): 287 [Mþ], 260, 210, 180, 105, 77, 51. HRMS calculated for
4. Experimental
C
14H11BrNO, 288.0024 (MHþ). Found 288.0012.
All reactions were performed using oven e dried glassware
under an argon atmosphere. Trifluoromethanesulfonic acid (triflic
acid) was freshly distilled prior to use. A previous report describes a
4.2. (E)-1-(4-Bromophenyl)-3-(pyridin-2-yl)prop-2-en-1-one (1e)
procedure
for
the
quantitative
recycling
of
tri-
Using General Procedure A, 4-bromoacetophenone (199 mg,
1 mmol) and 2-pyridinecarboxyaldehyde (107 mg, 1 mmol) pro-
vides aza-chacone (1e) (259 mg, 0.90 mmol, 90%) as yellow solid,
Rf ¼ 0.7 (hexane: ethyl acetate, 1:1). 1H NMR (500 MHz CDCl3)
fluoromethanesulfonic acid [14]. All commercially available com-
pounds and solvents were used as received. 1H and 13C NMR were
done using either 300 MHz or 500 MHz spectrometer. Reaction
done with benzene at 80 ꢀC were done in a high-pressure, glass
reaction tube having a Teflon screw cap (obtained from a com-
mercial glassware supplier). Low resolution mass spectra were
obtained from a gas chromatography instrument equipped with a
mass-selective detector. Ionization was accomplished with electron
impact ionization. High resolution mass spectroscopy was done by
a commercial laboratory (electron impact ionization or electro-
spray; sector instrument analyzer type). Aza-chalcones 1a [15], 1b
[16], 1c [16], 1f [17], 1h [18], 1k [19], 1l [20], and 1m [19], are known
compounds. Indanone 23 is a known compound. [7a] Compounds
12, 13, 15e17, were purchased from a commercial supplier.
Procedure A: Synthesis of aza-chalcones, 1. A solution is pre-
pared from 10 mL H2O, 5 mL ethanol, pyridine (0.16 mL, 0.154 g,
2 mmol), and NaOH (0.2 g, 5 mmol). To this solution is added the
aryl ketone (1 mmol) and heterocyclic aldehyde (1 mmol) and the
solution is stirred at 25 ꢀC for 12 h. A precipitate generally forms
and this is filtered off, rinsed with water, and dried. The crude aza-
chalcone is then further purified by silica gel column chromatog-
raphy [14].
Procedure B: Synthesis of 1-indanones. In a vessel flushed
with inert gas, the aza-chalcone (1 mmol) is added to 2 mL of
CF3SO3H (22 mmol). The vessel is sealed, heated to 80 ꢀC, and the
solution stirred for 18 h. Following the reaction period, the solution
is cooled and then poured over ice. Chloroform (15 mL) is added to
the mixture and the aqueous solution is made basic by the addition
of saturated sodium bicarbonate. The organic extract is washed
with water, then brine, and dried with anhydrous sodium sulfate.
Filtration and removal of the solvent gives the crude indanone
product - which is further purified by column chromatography
d
¼ 8.62 (1H, d, J ¼ 3 Hz), 8.01 (1H, d, J ¼ 15 Hz), 7.89 (2H, d,
J ¼ 8 Hz), 7.73e7.65 (2H, m), 7.56 (2H, d, 8 Hz), 7.40 (1H, d,
J ¼ 7.5 Hz), 7.23 (1H, t, J ¼ 5 Hz). 13C NMR (125 MHz, CDCl3)
d
¼ 189.1, 152.9, 150.2, 143.2, 136.9, 136.5, 131.9, 130.2, 128.2, 125.5,
124.8, 124.5. HRMS calculated for C14H11BrNO, 288.0024 (MHþ).
Found 288.0014.
4.3. (E)-2-Methyl-1-phenyl-3-(pyridin-2-yl) prop-2-en-1-one (1g)
Propiophenone (134.2 mg,1 mmol) is dissolved in 10 mL of ethyl
ether and sodium hydride (36 mg, 1.5 mmol) is added to the
mixture at
0
ꢀC. After stirring for 30 min, 2-
pyridinecarboxyaldehyde (109 mg, 1 mmol) is added to the
mixture. The solution is allowed to warm to room temperature,
stirred for another 12 h and then 5 mL of 1 M HCl is added to the
mixture. The solution is stirred for 5 h and then poured over 10 g of
ice, neutralized by saturated NaHCO3, and the organic product is
extracted into diethyl ether. The organic extract is washed with
water and then (2x) with brine solution, followed by drying with
sodium sulfate, filtration, and concentrating under vacuum. The
crude product mixture is purified by flask chromatography (hex-
ane: ethyl acetate) to provide aza-chalcone (1g). 1H NMR (500 MHz
CDCl3)
d
¼ 8.70 (1H, s), 7.79 (2H, t, J ¼ 5 Hz), 7.70 (1H, dd, J ¼ 1.5,
J ¼ 7.5 Hz), 7.53 (1H, dd, J ¼ 2, J ¼ 6 Hz), 7.46 (2H, d, J ¼ 4.5 Hz), 7.36
(1H, d, J ¼ 5.5 Hz), 7.21 (1H, t, J ¼ 1 Hz), 7.12 (1H, d, J ¼ 0.5 Hz), 2.45
(3H, d, J ¼ 1.5 Hz). 13C NMR (125 MHz, CDCl3)
¼ 199.6,155.1, 149.7,
d
140.3, 139.4, 137.9, 136.3, 131.9, 129.5, 128.3, 125.5, 122.6.14.7. HRMS
calculated for C15H14NO, 224.1075 (MHþ). Found 224.1069.
4

H. Vuong, H. Amadou, M.R. Stentzel et al.
Tetrahedron xxx (xxxx) xxx
4.4. (E)-1-(Naphthalen-1-yl)-3-(pyridin-2-yl)prop-2-en-1-one
calculated for C14H12NO, 210.0919 (MHþ). Found 210.0910.
(1h)
4.8. 3-(3-Pyridinyl)-1-indanone (3)
Known compound, but unreported characterization data. [21]
Using General Procedure A, compound 1h was isolated. 1H NMR
Using General Method B, aza-chalcone 1b (209.1 mg, 1 mmol)
provides indanone 3 (194.3 mg, 0.93 mmol, 93%). Alternatively,
General Method C also provides indanone 3, Thus, aryclic acid 12
(149.1 mg, 1 mmol) provides indanone 3 (192.3 mg, 0.92 mmol,
92%) as a yellow oil. Rf ¼ 0.3 (hexane: ethyl acetate, 1: 1). 1H NMR
(500 MHz CDCl3)
d
¼ 8.68 (1H, d, J ¼ 4 Hz), 8.47 (1H, d, J ¼ 8.5 Hz),
8.01 (1H, d, J ¼ 8 Hz), 7.93e7.85 (3H, m), 7.73e7.70 (1H, m),
7.66e7.53 (4H, m), 7.47 (1H, d, J ¼ 8 Hz), 7.29e7.27 (1H, m). 13C NMR
(125 MHz, CDCl3)
d
¼ 195.2, 153.2, 150.2, 143.9, 136.8, 136.5, 133.9,
132.1, 130.6, 130.3, 128.5, 127.9, 127.6, 126.5, 125.7, 124.9, 124.5,
124.4. Mass spectrum (low resolution, EI): 258 [Mþ], 230, 181, 127,
104, 78, 51. HRMS calculated for C18H14NO, 260.1075 (MHþ). Found
260.1062.
(300 MHz CDCl3)
d
¼ 8.51 (2H, s), 7.79 (1H, d, J ¼ 7.5 Hz), 7.57 (1H,
td, J ¼ 0.9, J ¼ 7.5 Hz), 7.43 (1H, t, J ¼ 7.5 Hz), 7.32 (1H, t, J ¼ 5.7 Hz),
7.27e7.19 (3H, m), 4.62e4.59 (1H, m), 3.29e3.22 (1H, m), 2.67e2.59
(1H, m). 13C NMR (75 MHz, CDCl3)
d
¼ 204.8, 156.6, 149.3, 148.6,
139.2, 136.8, 135.3, 134.7, 128.3, 126.7, 129.6, 46.4, 41.8. Mass spec-
trum (low resolution, EI): 209 [Mþ], 180, 152, 131, 103, 77, 51. HRMS
calculated for C14H12NO, 210.0919 (MHþ). Found 210.0908.
4.5. (E)-1-Phenyl-3-(pyrazin-2-yl)prop-2-en-1-one (1i)
1-Phenylprop-2-yn-1-ol (159 mg, 1.2 mmol), 2-iodopyrazine
(205 mg, 1 mmol), triethyl amine (0.2 mL), 1.5 mL THF are added
in a 5 mL microwave vial. The mixture is then degassed by an argon
gas stream. To this solution, CuI (19 mg, 0.1 mmol) and palladium
bis triphenylphosphine dichloride (70 mg, 0.1 mmol) is added, the
vial is sealed, and placed in microwave reactor. The reaction is run
for 15 min at 150 ꢀC, after which the product mixture iss diluted
with 10 mL of diethyl ether and washed with brine (10 mL). The
aqueous phase is back extracted with diethyl ether (2 ꢁ 5 mL), the
organic lextracts are combined, and dried over anhydrous MgSO4.
Removal of the solvent is followed by purification of the product
with flash column chromatography (ethyl acetate:hexanes, 1:1) to
provide aza-chalcone 1i (99 mg, 0.47 mmol, 47%). 1H NMR
4.9. 3-(4-Pyridyl)-1-indanone (4)
Using General Method B, aza-chalcone 1a (209.1 mg, 1 mmol)
provides indanone 4 (194.3 mg, 0.93 mmol, 93%). Alternatively,
General Method C also provides indanone 4. Thus, aryclic acid 16
(149.1 mg, 1 mmol) provides indanone 4 (192.3 mg, 0.92 mmol,
92%) as yellow oil. Rf ¼ 0.6 (hexane: ethyl acetate, 1: 1). 1H NMR
(300 MHz CDCl3)
d
¼ 8.53 (2H, d, J ¼ 5.7 Hz), 7.82 (1H, d, J ¼ 7.5 Hz),
7.59 (1H, td, J ¼ 0.9, J ¼ 7.5 Hz), 7.45 (1H, t, J ¼ 6 Hz), 7.26 (2H, d,
J ¼ 8.1 Hz), 7.05 (2H, d, J ¼ 6 Hz), 4.58e4.53 (1H, m), 3.27e3.18 (1H,
m), 2.68e2.60 (1H, m). 13C NMR (75 MHz, CDCl3)
d
¼ 204.5, 155.9,
152.4, 150.3, 136.8, 135.3, 128.4, 126.7, 123.7, 122.8, 45.9, 43.7. Mass
spectrum (low resolution, EI): 209 [Mþ], 180, 131, 103, 77, 51. HRMS
calculated for C14H12NO, 210.0919 (MHþ). Found 210.0918.
(300 MHz CDCl3)
d
¼ 8.68 (1H, d, J ¼ 1.2 Hz), 8.59 (1H, t, J ¼ 2.1 Hz),
8.52 (1H, d, J ¼ 2.4 Hz), 8.15 (1H, d, J ¼ 15.3 Hz), 8.03 (2H, t,
J ¼ 6.9 Hz), 7.75 (1H, d, J ¼ 15.3 Hz), 7.59e7.53 (1H, m), 7.49e7.44
(2H, m). 13C NMR (75 MHz, CDCl3)
d
¼ 189.6, 148.8, 145.8, 145.2,
4.10. 3-(6-Bromo-2-pyridyl)-1-indanone (5)
144.8, 138.7, 137.4, 133.3, 128.72, 128.70, 127.5. HRMS calculated for
13H11N2O, 211.0871 (MHþ). Found 211.0870.
C
Using General Method B, aza-chalcone 1d (289.0 mg, 1 mmol)
provides indanone 5 (257.2 mg, 0.89 mmol, 89%) as white solid. 1H
NMR (500 MHz CDCl3)
d
¼ 7.79 (1H, d, J ¼ 7.5 Hz), 7.57 (1H, t,
4.6. (E)-3-(Benzo[d]thiazol-2-yl)-1-phenylprop-2-en-1-one (1j)
J ¼ 7.2 Hz), 7.51e7.39 (2H, m), 7.34 (2H, t, J ¼ 8.4 Hz), 7.03 (1H,
J ¼ 7.5 Hz), 4.77e4.73 (1H, m), 3.23e3.14 (1H, m), 2.98e2.90 (1H,
Using General Procedure A, acetophenone (120 mg,1 mmol) and
2-pyridinecarboxyaldehyde (163 mg, 1 mmol) in 25 mL of water
provide aza-chalcone 1j (164.5 mg, 0.62 mmol, 62%) as yellow
solid; Rf ¼ 0.56 (hexane: ethyl acetate, 3:1). 1H NMR (500 MHz
m). 13C NMR (125 MHz, CDCl3)
d
¼ 205.0, 163.8, 155.6, 142.0, 139.2,
136.7, 135.0, 128.3, 126.5, 123.8, 120.6, 46.1, 44.3. Mass spectrum
(low resolution, EI): 287 [Mþ], 260, 210, 180, 105, 77, 51. HRMS
calculated for C14H11BrNO, 288.0024 (MHþ). Found 288.0021.
CDCl3)
d
¼ 8.07 (1H, d, J ¼ 8 Hz), 8.03 (2H, d, J ¼ 8 Hz), 7.89 (2H, d,
J ¼ 7.5 Hz), 7.86 (1H, d, J ¼ 8.5 Hz), 7.58 (1H, t, J ¼ 7.5 Hz), 7.48 (3H, t,
J ¼ 7.5 Hz), 7.40 (1H, t, J ¼ 7.5 Hz). 13C NMR (125 MHz, CDCl3)
4.11. 5-Bromo-3-(2-pyridyl)-1-indanone (6)
d
¼ 189.1, 163.8, 154.0, 137.2, 135.9, 135.4, 133.4, 128.8, 128.7, 128.6,
126.9, 126.5, 124.0, 121.8. Mass spectrum (low resolution, EI): 265
[Mþ], 236, 160, 116, 105, 77, 51. HRMS calculated for C16H11NOS,
266.0640 (MHþ). Found 266.0636.
Using General Method B, aza-chalcone 1e (289.1 mg, 1 mmol)
provides indanone (6) (130 mg, 0.45 mmol, 45%) as a light yellow
solid, MP ¼ 119e121 ꢀC, Rf ¼ 0.45 (hexane: ethyl acetate, 1:1). 1H
NMR (500 MHz CDCl3)
d
¼ 8.58 (1H, s), 7.72 (1H, s), 7.69 (1H, d,
J ¼ 8.5 Hz), 7.57 (1H, d, J ¼ 8.5 Hz), 7.47 (1H, s), 7.28e7.21 (2H, m),
4.7. 3-(2-Pyridyl)-1-indanone (2)
4.75 (1H, t, J ¼ 3.5 Hz), 3.21e3.17 (1H, m), 3.07e3.03 (1H, m). 13
C
NMR (125 MHz, CDCl3)
d
¼ 204.2, 161.2, 158.1, 150.1, 137.1, 135.6,
Using General Method B, aza-chalcone 1a (209.1 mg, 1 mmol)
provides indanone 2 (198.6 mg, 0.95 mmol, 95%). Alternatively,
General Method C also provides indanone 2. Thus, aryclic acid 15
(149.1 mg, 1 mmol) provides indanone 2 (186.1 mg, 0.89 mmol,
89%) as yellow solid, Rf ¼ 0.5 (hexane: ethyl acetate, 1: 1). 1H NMR
131.7, 130.2, 129.8, 124.9, 122.3, 122.3, 46.2, 44.4. Mass spectrum
(low resolution, EI): 289 [Mþ], 258, 155, 132, 104, 78, 51. HRMS
calculated for C14H11BrNO, 288.0024 (MHþ). Found 288.0011.
(300 MHz CDCl3)
d
¼ 8.53 (1H, dd, J ¼ 1.8, J ¼ 5.7 Hz), 7.80 (1H, d,
4.12. 5-Methyl-3-(2-pyridyl)-1-indanone (7)
J ¼ 7.5 Hz), 7.64 (1H, td, J ¼ 1.8, J ¼ 9.3 Hz), 7.55 (1H, td, J ¼ 1.2,
J ¼ 7.5 Hz), 7.40 (1H, t, J ¼ 7.5 Hz), 7.28 (1H, dd, J ¼ 0.9, J ¼ 7.8 Hz),
7.18e7.14 (2H, m), 4.77e4.73 (1H, m), 3.23e3.14 (1H, m), 3.03e2.95
Using General Method B, aza-chalcone 1f (223 mg, 1 mmol)
provides indanone 7 as dark orange solid (180 mg, 0.81 mmol, 81%),
MP: 102e104 ꢀC, Rf ¼ 0.38 (hexane: ethyl acetate, 1:2). 1H NMR
(1H, m). 13C NMR (75 MHz, CDCl3)
d
¼ 205.7, 162.1, 156.6, 149.9,
136.9, 136.7, 134.9, 128.0, 126.5, 123.7, 122.1, 122.0, 46.5, 44.5. Mass
(500 MHz CDCl3)
7.67e7.63 (1H, m), 7.21 (1H, d, J ¼ 7.5 Hz), 7.18e7.14 (2H, m), 7.08
d
¼ 8.55 (1H, d, J ¼ 4.5 Hz), 7.70 (1H, d, J ¼ 8 Hz),
spectrum (low resolution, EI): 209 [Mþ], 180, 152, 131, 77, 51. HRMS
5

H. Vuong, H. Amadou, M.R. Stentzel et al.
Tetrahedron xxx (xxxx) xxx
(1H, s), 4.72e4.69 (1H, m), 3.19e3.13 (1H, m), 3.00e2.95 (1H, m),
1 mmol) provides indanone 14 (126.7 mg, 0.64 mmol, 64%) as
yellow oil, Rf ¼ 0.4 (ethyl acetate: methanol, 9:1). 1H NMR
2.37 (3H, s). 13C NMR (125 MHz, CDCl3)
d
¼ 205.2,162.3,157.1,149.9,
146.1, 136.9, 134.5, 129.3, 126.7, 123.5, 122.1, 122.0, 46.4, 44.7, 22.1.
Mass spectrum (low resolution, EI): 223 [Mþ], 194, 115, 89, 78, 51.
HRMS calculated for C15H14NO, 224.1075 (MHþ). Found 224.1065.
(500 MHz CDCl3)
d
¼ 7.75 (1H, d, J ¼ 7.5 Hz), 7.62 (1H, t, J ¼ 8 Hz),
7.53 (1H, s), 7.49 (1H, d, J ¼ 8 Hz), 7.40 (1H, t, J ¼ 7.5 Hz), 6.79 (1H, s),
4.69e4.66 (1H, m), 3.19e3.14 (1H, m), 2.88e2.83 (1H, m). 13C NMR
(125 MHz, CDCl3)
127.9, 126.6, 123.5, 44.7, 37.3. HRMS calculated for C12H11N2O,
199.0871 (MHþ). Found 199.0864.
d
¼ 205.9, 156.6, 136.6, 135.4, 134.9, 128.5, 128.4,
4.13. Trans-2-Methyl-3-(2-pyridyl)-1-indanone (8)
Using General Method B, aza-chalcone 1g (224 mg, 1 mmol)
provided indanone 8 (170.2 mg, 0.76 mmol, 76%) as an oil. Rf ¼ 0.36
4.18. 3-(Pentafluorophenyl)-1-indanone (18)
(hexane: ethyl acetate/1:1). 1H NMR (500 MHz CDCl3)
d
¼ 8.59 (1H,
dd, J ¼ 2, J ¼ 5.5 Hz), 7.82 (1H, d, J ¼ 8 Hz), 7.72e7.68 (1H, m), 7.57
(1H, td, J ¼ 1, J ¼ 8.5 Hz), 7.42 (1H, t, J ¼ 7.5 Hz), 7.23e7.21 (3H, m),
Using General Method C, pentafluorocinnamic acid 17
(238.2 mg, 1 mmol) provides indanone 18 (271.3 mg, 0.91 mmol,
91%) as white solid, MP ¼ 101e103, Rf ¼ 075 (hexane: ethyl acetate,
4.26 (1H, d, J ¼ 5 Hz), 3.03e2.97 (1H, m), 1.41 (3H, d, J ¼ 7.5 Hz). 13
C
4:1). 1H NMR (500 MHz CDCl3)
d
¼ 7.84 (1H, d, J ¼ 7.5 Hz), 7.64e7.60
NMR (125 MHz, CDCl3)
d
¼ 207.7, 161.5, 154.9, 149.7, 136.9, 136.2,
134.9, 128.1, 126.2, 123.8, 122.8, 122.2, 55.6, 51.3, 14.3. Mass spec-
trum (low resolution, EI): 223 [Mþ], 208, 194, 180, 167, 115, 78, 51.
HRMS calculated for C15H14NO, 224.1075 (MHþ). Found 224.1067.
(1H, m), 7.47 (1H, t, J ¼ 7.5 Hz), 7.27 (1H, d, J ¼ 7.5 Hz), 5.01e4.99
(1H, m), 3.24e3.19 (1H, m), 2.86e2.82 (1H, m). 13C NMR (125 MHz,
CDCl3)
d
¼ 203.4, 154.1, 136.3, 135.3, 128.5, 125.5, 123.9, 43.0, 33.0,
and 146e116 (pentafluorophenyl multiplets). Mass spectrum (low
resolution, EI): 298 [Mþ], 250, 219, 201, 131, 76, 50. HRMS calcu-
lated for C15H18F5O, 299.0495 (MHþ). Found 299.0501.
4.14. 3-(Pyridin-2-yl)-2,3-dihydro-1H-cyclopenta[a]naphtha-len-
1-one (9)
Using General Method B, aza-chalcone 1h (259 mg, 1 mmol)
provides ketone 9 (238 mg, 0.92 mmol, 92%) as yellow solid, MP:
115e117 ꢀC, Rf ¼ 0.48 (hexane: ethyl acetate/1:2). 1H NMR
4.19. Dichloro-3-(pyridin-2-yl)-2,3-dihydro-1H-inden-1-one
(24a,b)
(500 MHz CDCl3)
d
¼ 9.21 (1H, d, J ¼ 8.5 Hz), 8.52 (1H, d, J ¼ 4.5 Hz),
Using General Procedure B, aza-chalcone 1l (0.28 g, 1 mmol)
provides indanone 24 as an inseparable mixture of regioisomers
(24a,b, 128 mg, 0.46 mmol, 46%). 1H NMR (300 MHz, CDCl3, 25 ꢀC):
7.94 (1H, d, J ¼ 8.5 Hz), 7.82 (1H, d, J ¼ 8 Hz), 7.65 (1H, t, J ¼ 7 Hz),
7.61e7.59 (1H, m), 7.53 (1H, t, J ¼ 8 Hz), 7.27 (1H, d, J ¼ 8.5 Hz), 7.13
(2H, t, J ¼ 5 Hz), 4.77e4.75 (1H, m), 3.28e3.23 (1H, m), 3.08e3.03
d
8.48 (dd, J ¼ 5.38 Hz, J ¼ 1.52 Hz, 1H), 8.43 (dq, J ¼ 3.98 hz,
(1H, m). 13C NMR (125 MHz, CDCl3)
d
¼ 206.2, 161.9, 159.3, 149.9,
J ¼ 0.78 Hz, 1H), 7.79 (s, 1H), 7.65e7.54 (m, 3H), 7.49 (d, J ¼ 8.07 Hz,
1H), 7.32 (d, J ¼ 0.85 Hz,1H), 7.19 (s, 1H), 7.16e7.12 (m, 2H), 7.08 (qd,
J ¼ 2.72 Hz, J ¼ 1.06 Hz, 2H), 4.76 (dd, J ¼ 8.25 Hz, J ¼ 2.63 Hz, 1H),
4.63 (dd, J ¼ 7.89 hz, J ¼ 4.06 Hz, 1H), 3.20e3.08 (m, 2H), 2.98 (dd,
J ¼ 18.90 Hz, J ¼ 4.20 Hz,1H), 2.77 (dd, J ¼ 18.90 hz, J ¼ 2.80 Hz,1H).;
136.9, 136.0, 132.8, 130.8, 129.2, 129.0, 128.1, 126.9, 124.3, 123.5,
122.3, 122.1, 46.5, 45.2. Mass spectrum (low resolution, EI): 259
[Mþ], 230,152, 126, 78, 51. HRMS calculated for C18H14NO, 260.1075
(MHþ). Found 260.1072.
13C NMR (300 MHz, CDCl3, 25 ꢀC):
d 203.43, 202.99, 160.71, 155.34,
4.15. 3-(2-Pyrazinyl)-1-indanone (10)
154.76, 150.17, 149.93, 139.74, 139.36, 137.61, 137.18, 136.73, 136.29,
133.29, 131.56, 130.96, 128.47, 125.17, 122.98, 122.48, 122.36, 122.26,
122.05, 46.11, 45.77, 45.72, 44.61. High-Resolution MS (EI) (M þ H),
calcd for C14H10NOCl2, 278.0139, found, 278.0137.
Using General Method B, aza-chalcone 1i (210 mg, 1 mmol)
provides indanone 10 (182.8 mg, 0.87 mmol, 87%) as brown oil.
Rf ¼ 0.16 (hexane: ethyl acetate/1:1). 1H NMR (500 MHz CDCl3)
d
¼ 8.63 (1H, s), 8.54 (2H, s), 7.86 (1H, d, J ¼ 8 Hz), 7.61 (1H, td,
5. Experimental
J ¼ 1.5, J ¼ 7.5 Hz), 7.47 (1H, t, J ¼ 7.5 Hz), 7.30 (1H, dd, J ¼ 1, J ¼ 8 Hz),
4.83 (1H, dd, J ¼ 4, J ¼ 8 Hz), 3.22 (1H, dd, J ¼ 8, J ¼ 10.5 Hz), 3.05
The paper must include the following: (1) Introduction, (2)
Results/Discussion, (3) Conclusion, (4) Experimental Section and
(5) References. Supplementary data and other sections are optional.
You will usually want to divide your article into (numbered) sec-
tions and subsections (perhaps even subsubsections). Code section
headings using the options in the ‘Styles’ menu. Headings should
reflect the relative importance of the sections. Note that text runs
on after a 4th order heading. Use the heading style for the whole
paragraph, but remove the italic coding except for the actual
heading.
Ensure that all tables, figures and schemes are cited in the text in
numerical order. Trade names should have an initial capital letter,
and trademark protection should be acknowledged in the standard
fashion, using the superscripted characters for trademarks and
registered trademarks respectively. All measurements and data
should be given in SI units where possible, or other internationally
accepted units. Abbreviations should be used consistently
throughout the text, and all nonstandard abbreviations should be
defined on first usage. Authors are requested to draw attention to
hazardous materials or procedures by adding the word CAUTION
followed by a brief descriptive phrase and literature references if
appropriate. The experimental information should be as concise as
(1H, dd, J ¼ 4, J ¼ 15 Hz). 13C NMR (125 MHz, CDCl3)
d
¼ 204.8,
155.3, 144.8, 143.8, 143.4, 136.7, 135.1, 128.4, 126.3, 123.9, 43.9, 43.8.
Mass spectrum (low resolution, EI): 210 [Mþ], 181, 127, 102, 77, 51.
HRMS calculated for C13H11N2O, 211.0871 (MHþ). Found 211.0869.
4.16. 3-(2-Benzthiazolyl)-1-indanone (11)
Using General Method B, aza-chalcone 1j (264 mg, 1 mmol)
provided indanone 11 as yellow solid (250 mg, 0.95 mmol, 95%),
MP: 139e143 ꢀC Rf ¼ 0.47 (hexane: ethyl acetate, 3:1). 1H NMR
(300 MHz CDCl3)
d
¼ 8.01 (1H, d, J ¼ 8.4 Hz), 7.85 (2H, t, J ¼ 6.6 Hz),
7.65e7.61 (2H, m), 7.53e7.47 (2H, m), 7.41e7.36 (1H, m), 5.18e5.16
(1H, m), 3.41e3.32 (1H, m), 3.22e3.14 (1H, m). 13C NMR (75 MHz,
CDCl3)
d
¼ 203.6, 172.4, 153.9, 153.1, 136.4, 135.2, 135.0, 128.9, 126.9,
126.3, 125.3, 123.9, 123.0, 121.7, 44.3, 43.2. Mass spectrum (low
resolution, EI): 265 [Mþ], 236, 103, 77, 63, 51. HRMS calculated for
C
16H11NOS, 266.0640 (MHþ). Found 266.0633.
4.17. 3-(1H-imidazole-4-yl)-1-indanone (14)
Using General Method C, acrylic acid derivative 13 (138 mg,
6

H. Vuong, H. Amadou, M.R. Stentzel et al.
Tetrahedron xxx (xxxx) xxx
A.V. Vasilyev, Beilstein J. Org. Chem. 12 (2016) 2125e2135;
p D.A. Klumpp, S. Kennedy, ARKIVOC (2018) 215e232, part ii;
q S. Thibaudeau, H. Carreyre, A. Mingot, in: H. Groult, F.R. Leroux, A. Tressaud
(Eds.), Modern Synthesis Processes and Reactivity of Fluorinated Compounds,
Elsevier, London, UK, 2017, pp. 349e388;
possible, while containing all the information necessary to guar-
antee reproducibility.
Declaration of competing interest
r D.A. Klumpp, Beilstein J. Org. Chem. 7 (2011) 346e363.
[4] a M. Gasonoo, A. Sumita, K. Giuffre, K. Boblak, T. Ohwada, D.A. Klumpp, J. Org.
Chem. 82 (2017) 6044e6053;
The authors declare that they have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
b K.N. Boblak, D.A. Klumpp, J. Org. Chem. 79 (2014) 5852e5857;
c D.A. Klumpp, G. Garza, G.V. Sanchez, S. Lau, S. DeLeon, J. Org. Chem. 65
(2000) 8997e9000;
d Y. Zhang, A. McElrea, G.V. Sanchez Jr., D.A. Klumpp, D. Do, A. Gomez,
S.L. Aguirre, R.J. Rendy, Org. Chem. 68 (2003) 5119e5124;
e S.E. Denmark, Z.J. Wu, Org. Chem. 63 (1998) 2810e2811;
f E.J. Corey, T. Shibata, T.W. Lee, J. Am. Chem. Soc. 124 (2002) 3808e3809;
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[5] a J. Zhu, C. Zhong, H.-F. Lu, G.-Y. Li, X. Sun, Synlett (2008) 458e462;
Acknowledgments
The support of the NIGMS -NIH(1R15GM126498-01) is grate-
fully acknowledged. We also acknowledge the generous support
from the NSF MRI program (award no. CHE:1726931) for the pur-
chase of the high-resolution mass spectrometer and Northern Illi-
nois University for the support of the Molecular Analysis Core
Facility.
b
A. Saito, M. Umakoshi, N. Yagyu, Y. Hanzawa, Org. Lett. 10 (2008)
1783e1785;
c Y. Liu, P. Zhao, B. Zhang, C. Xi, Org. Chem. Front. 3 (2016) 1116e1119;
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g H.J. Williams, R.L. Harlow, J. Chem. Soc., Perkin Trans. 1 (1975) 1537e1539.
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a K.Y. Koltunov, S. Walspurger, J. Sommer, Tetrahedron Lett. 46 (2005)
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Supplementary data to this article can be found online at
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b A.S. Souna Sido, S. Chassaing, M. Kumarraja, P. Pale, J. Sommer, Tetrahedron
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7