NHC Bronsted base-catalyzed transformations of isochromene derivatives: Regulation of products by the structures of carbene catalysts

Article abstract of DOI:10.1039/c2ob26622a

Two different transformations of α-(isochromen-1-yl)ketones catalyzed by NHC Bronsted bases are reported. In the presence of a triazole carbene, α-(isochromen-1-yl)ketones isomerized into β-(2-(aroylmethylene) phenyl)-α,β-unsaturated ketones in 38-88% yields, while the same reaction catalyzed by an imidazole carbene produced 1-aroylnaphthalene derivatives in 90-99% yields. This work not only provides a new method for the synthesis of a novel type of α,β-unsaturated ketone and multi-substituted naphthalene derivatives, but also advances the application of NHC catalysts in the field of Bronsted base-catalysis.

Full text of DOI:10.1039/c2ob26622a

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PAPER
NHC Brønsted base-catalyzed transformations of isochromene derivatives:
regulation of products by the structures of carbene catalysts†
Xing-Wen Fan and Ying Cheng*
Received 15th August 2012, Accepted 8th October 2012
DOI: 10.1039/c2ob26622a
Two different transformations of α-(isochromen-1-yl)ketones catalyzed by NHC Brønsted bases are
reported. In the presence of a triazole carbene, α-(isochromen-1-yl)ketones isomerized into
β-(2-(aroylmethylene)phenyl)-α,β-unsaturated ketones in 38–88% yields, while the same reaction
catalyzed by an imidazole carbene produced 1-aroylnaphthalene derivatives in 90–99% yields. This work
not only provides a new method for the synthesis of a novel type of α,β-unsaturated ketone and multi-
substituted naphthalene derivatives, but also advances the application of NHC catalysts in the field of
Brønsted base-catalysis.
the numerous studies on NHC-mediated catalysis based on the
nucleophilicity or Lewis basicity of NHCs, the Brønsted base
Introduction
N-Heterocyclic carbenes (NHCs) have remarkable scope as orga-
nocatalysts.1 The majority of NHC-catalyzed reactions were
initiated from nucleophilic additions of carbene catalysts to car-
bonyl compounds, which led to the umpolung reactivity of car-
bonyl groups. These umpolung reactions were exemplified by
benzoin reactions,1,2 Stetter reactions,1,3 the reactions of homo-
enolates derived from enals,1,4 and the cycloadditions of
ketenes,5 etc. The umpolung of electron-deficient alkenes has
also been achieved by the nucleophilic addition of NHCs to
Michael acceptors,6 while acid esters and acid fluorides could be
activated, but without umpolung of the carbonyls, by nucleophi-
lic addition of NHCs to these carboxylic derivatives.7 Although
N-heterocyclic carbene catalysts have been demonstrated to have
moderate nucleophilicity but high Lewis and Brønsted basicity,8
their catalysis as Brønsted bases remains very limited. The main
application of NHC Brønsted base-catalysis is the promotion of
transesterification reactions,9 in which NHCs activate the reac-
tion by deprotonation of alcohols. NHCs have also been utilized
as Brønsted base catalysts in the Michael addition of alcohols or
amines to α,β-unsaturated ketones.10 Very few examples of the
NHC-catalyzed deprotonation of ortho-protons of carbonyl com-
pounds have been reported, which lead to the formation of enol
ethers11 or the intramolecular Michael addition.12 Compared to
activations of NHCs have been largely unexplored. We con-
sidered that the mild NHCs-catalysis might attenuate unwanted
side reactions that could take place under anionic base catalysis
conditions. Therefore, the development of NHCs as efficient
Brønsted base catalysts is of great importance.
We have been interested in the reactivity and synthetic appli-
cations of N-heterocyclic carbenes for many years.13 Recently,
our attention was drawn to NHC-catalyzed reactions.14 During
our study on the NHC-catalyzed condensation of carbonyl com-
pounds, we discovered two different transformations of α-(iso-
chromen-1-yl)ketones. Herein, we reported the NHC Brønsted
base-catalyzed transformations of isochromene derivatives,
which leads to the formation of β-(2-(aroylmethylene)phenyl)-
α,β-unsaturated ketones or 1-aroylnaphthalenes and is regulated
by the structures of the NHC catalysts.
Results and discussion
In this work, the reactants α-(3-arylisochromen-1-yl) substituted
ketones 3 were prepared from the reaction of 2-(arylethynyl)-
benzaldehydes 1 with ketones 2 catalyzed by PdCl2 (See ESI†).
Initially, the 1-(3-phenylisochromen-1-yl)propan-2-one 3a was
stirred with 10 mol% of different NHC precursors 4 and DBU in
acetonitrile for 6–12 h at room temperature. It was found that
1-(3-phenylisochromen-1-yl)propan-2-one 3a was transformed
into (E)-4-(2-(benzoylmethylene)phenyl)-3-buten-2-one 5a in
20–28% yields in the presence of triazole carbenes 4a′–4c′,
while 3a catalyzed by imidazole carbenes 4d′ and 4e′ was con-
verted to 1-benzoyl-2-methylnaphthalene 6a in 33–37% yields
(Table 1, entries 1–5). Under the same conditions, thiazole
carbene 4f′ was totally inefficient for these transformations.
When the reaction was operated in refluxing acetonitrile, 49% of
College of Chemistry, Beijing Normal University, Beijing 100875,
China. E-mail: ycheng2@bnu.edu.cn; Fax: +861058805558;
Tel: +861058805558
†Electronic supplementary information (ESI) available: The preparation
and characterization of α-(3-arylisochromen-1-yl)ketones 3, copies of
1H NMR and 13C NMR spectra of compounds 3, 5 and 6 are available.
CCDC 895476, 895477 and 895478 [3a, 3f-II and 5f]. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c2ob26622a
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Table 1 NHC-catalyzed transformations of 1-(3-phenylisochromen-1-
yl)propan-2-one 3a under different conditions
Table 2 Triazole carbene-catalyzed transformation of α-(3-aryl-
isochromen-1-yl)ketones 3 under optimized conditions
Entry
1
Reactant 3
T (h)
Product 5
Yield (%)a
6
5a: 55
Reaction conditions
Yield
(%)
Cat.
Entry (mol %) Basea
Sol.
T (°C) T (h) 5a 6a
2
3
4
6
6
6
5b: 88
5c: 66
5d: 38
1
2
3
4
5
6
7
8
4a (10)
4b (10) DBU
4c (10) DBU
4d (10) DBU
DBU
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
Dioxane
Benzene
rt
rt
rt
rt
rt
rt
6
6
6
6
6
12
20
17
28
7
—
—
—
33
37
—
—
89
—
98
—
—
—
4e (10)
4f (10)
4c (10)
4e (10)
4c (20)
4e (20)
4c (20)
4c (20)
4c (20)
4c (20)
4c (20)
—
DBU
DBU
DBU
DBU
DBU
DBU
DBU
DBU
DBU
8
—
49
—
55
—
33
22
23
Reflux 10
Reflux 10
Reflux
Reflux
80
9
6
2
6
6
6
6
6
6
10
11
12
13
14
15
16
80
ClCH2CH2Cl 80
t-BuOK CH3CN
NaH
DBU
Reflux
Reflux
Reflux
35 23
28 67
6
CH3CN
CH3CN
—
a The mol% of bases are equal to the mol% of carbene catalysts.
5
6
6
1
5e: 41
5f: 81
5a or 89% of 6a was obtained from 1-isochromenylpropanone
3a by using 10 mol% of N,N-dibenzyltriazole carbene 4c′ or N,
N-dibenzylimidazole carbene 4e′ as the catalyst, respectively. In
refluxing acetonitrile, the catalyst loading of triazole carbene 4c′
or imidazole carbene 4e′ was then increased to 20 mol% and the
yield of 5a or 6a was improved to 55% or 98%, respectively
(Table 1, entries 9 and 10). To improve the yield of α,β-unsatu-
rated ketone 5a, the reaction conditions were further optimized
by varying the solvent and base utilized to generate the carbene
catalyst. However, under the catalysis of triazole carbene 4c′ and
at a similar temperature as the refluxing acetonitrile, the reactions
in 1,4-dioxane, benzene and 1,2-dichloroethane all led to a
diminishing of the yield of product 5a (Table 1, entries 11–13).
The use of strong bases t-BuOK or NaH to generate the carbene
catalyst decreased the selectivity in the formation of products 5a
and 6a (Table 1, entries 14–15).
7
8
1
6
5f: 83
5g: 53
Under the same conditions as that of the reaction catalyzed by
20 mol% of 4c, the reaction of 3a catalyzed by DBU alone only
yielded 6% of product 5a and 88% of reactant 3a was recovered
(Table 1, entry 16), which confirmed that the catalysis is due to
the N-heterocyclic carbenes.
a 4%–14% of 6 were also isolated.
phenyl)-α,β-unsaturated ketones 5 from isochromenyl substituted
ketones, a variety of α-(3-arylisochromen-1-yl)ketones 3 was
surveyed under the catalysis of triazole carbene 4c′ in refluxing
acetonitrile. As shown in Table 2, the aryls and alkyls attached to
The
4-(2-(benzoylmethylene)phenyl)-3-buten-2-one
5a
represents a novel skeleton of β-(2-(aroylmethylene)phenyl)-α,β-
unsaturated ketones that has never been reported before. To assess
the generality for the preparation of β-(2-(aroylmethylene)-
9080 | Org. Biomol. Chem., 2012, 10, 9079–9084
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Table 3 Imidazole carbene-catalyzed reaction of α-(3-arylisochromen-
1-yl)ketones 3 under optimized conditions
both the isochromene rings and the α-positions of the
carbonyls of 3 have influence on the outcomes of the reactions.
For example, the electron-donating p-anisyl or p-tolyl substituted
isochromenylpropanones 3b or 3c afforded a yield of product 5b
or 5c higher than isochromenylpropanones 3a and 3d attached
by phenyl and p-chlorophenyl, respectively (Table 2, entries
1–4). On the other hand, among α-(3-phenylisochromen-1-yl)-
cyclopentanone 3f, -propanone 3a, -pentanone 3e and -cyclohexa-
none 3g, cyclopentanone 3f was the most reactive one and pro-
duced the highest yield of product 5f (Table 2, entries 1, 5–8).
Except for α-(3-arylisochromen-1-yl)propanones 3a–3d, other
reactants including α-(isochromen-1-yl)pentanone 3e, α-(isochro-
men-1-yl)cyclopentanone 3f and α-(isochromen-1-yl)cyclohexa-
none 3g have a pair of diastereoisomers 3-I and 3-II. Both cis-
isomers 3-I and trans-isomers 3-II were obtained from the PdCl2-
catalyzed reaction of 2-(arylethynyl)benzaldehydes with ketones
(See ESI†). It was found that the cis and trans isomers produced
the same products in very similar yields under the same conditions
(Table 2, entries 6 and 7). Thus, all cis-isomers 3-I, trans-isomers
3-II, or a mixture of two diastereoisomers 3-I and 3-II could be
used as the starting materials.
To develop a new method for the synthesis of multi-substi-
tuted naphthalene derivatives, the reaction of α-(3-arylisochro-
men-1-yl)ketones 3 catalyzed by an imidazole carbene was then
examined in refluxing acetonitrile. In the presence of N,N-di-
benzylimidazole carbene 4e′, all α-(3-arylisochromen-1-yl)-
ketones 3a–3g with different aryls and alkyls attached to the
isochromene rings and the α-positions of the carbonyls reacted
efficiently to afford 1-aroylnaphthalenes 6 in almost quantitative
yields (Table 3).
The structures of all products 5 and 6 were ascertained by
spectroscopic methods. Theoretically, the transformation of
α-(isochromen-1-yl)ketones 3 to α,β-unsaturated ketones 5 could
form a pair of Z- and E-isomers. However, no Z-configured
isomers of 5 were detected in any reactions. The coupling con-
stants (3J) of the two vinyl protons of 4-(2-(aroylmethylene)-
phenyl)-3-buten-2-ones 5a–5d were around 16 Hz, which are in
agreement with the E-configuration of carbon–carbon double
bonds. The configuration of the trisubstituted CvC bonds of
5e–5g cannot be assigned using coupling constants of the vinyl
protons. To determine the configurations of 5e–5g beyond doubt,
single crystal X-ray diffraction analysis of 5f was performed,15
which confirmed unambiguously that 5f is (E)-2-(2-(benzoyl-
methylene)benzylidene)cyclopentanone.†
Entry
1
Reactant 3
T (h)
Product 5
Yield (%)
2
6a: 98
2
3
2
4
6b: 99
6c: 97
4
5
6
2
2
2
6d: 97
6e: 91
6f: 96
7
2
6g: 90
The transformations of α-(3-arylisochromen-1-yl)ketones 3 to
α,β-unsaturated ketones 5 and naphthalene derivatives 6 can be
explained by the deprotonation of ketones 3 under the catalysis
of NHCs. As shown in Scheme 1, the triazole or imidazole
carbene acts as Brønsted base to deprotonate the α-protons of
ketones 3, which leads to the formation of carbon anion inter-
mediates 7. Isomerization of 7 to anions 8 followed by protona-
tion of 8 affords products 5. In the presence of an imidazole
carbene, the intramolecular aldol condensation of bisketones 5
forms the dihydronaphthalen-2-ols 11, which produce products 6
after dehydration. During the formation of naphthalene rings, the
isomerization of the E-configuration of α,β-unsaturated ketones 5
to the Z-configuration probably proceeds via the resonance of
anions 8 with 9 and 10. According to the study of Herbert Mayr
and co-workers,8 imidazole carbenes have stronger basicity than
the corresponding triazole carbenes due to the electron-with-
drawing effect of the additional nitrogen atom of the triazole
ring. Therefore, the different transformations of α-isochrome-
nylketones 3 under the catalysis of imidazole carbene and tri-
azole carbene can be explained by the stronger basicity of the
imidazole carbene which promotes the intramolecular aldol con-
densation of product 5. In refluxing acetonitrile, product 5a cata-
lyzed by imidazole carbene 4e′ was almost totally converted into
6a in 1 h, which supported our mechanism.
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were dissolved in acetonitrile (20 mL), and then DBU
(0.2 mmol) was added using a microliter syringe. The reaction
mixture was refluxed for 1–6 h. The solvent was removed under
vacuum and the residue was chromatographed on a silica gel
column eluting with a mixture of petroleum ether and ethyl
acetate (20 : 1 to 10 : 1) to afford β-(2-(aroylmethylene)phenyl)-
α,β-unsaturated ketones 5 in 38–88% yields.
(E)-4-(2-(Benzoylmethylene)phenyl)-3-buten-2-one 5a
55%, mp 87–88 °C; IR v (cm−1) 1680, 1655, 1619, 1597, 1581;
1H NMR (400 MHz, CD3COCD3) δ (ppm) 7.98 (d, J = 7.1 Hz,
2H), 7.64 (d, J = 16.3 Hz, 1H), 7.63 (d, J = 5.9 Hz, 1H), 7.52 (t,
J = 7.4 Hz, 1H), 7.43 (t, J = 7.3 Hz, 2H), 7.21–7.26 (m, 3H),
6.54 (d, J = 16.1 Hz, 1H), 4.56 (s, 2H), 2.10 (s, 3H); 13C NMR
(100 MHz, CD3COCD3) δ (ppm) 198.2, 197.8, 141.4, 137.8,
136.5, 135.5, 134.1, 132.8, 130.9, 129.6, 129.5, 129.2, 128.3,
127.4, 43.7, 27.5; HRMS (TOF-ESI): [M + Na]+ calcd for
C18H16O2Na: 287.1048; found: 287.1053.
(E)-4-(2-(p-Methoxybenzoylmethylene)phenyl)-3-buten-2-one 5b
88%, mp 68–69 °C; IR v (cm−1) 1672, 1646, 1624, 1602, 1577;
1H NMR (400 MHz, CD3COCD3) δ (ppm) 8.00 (d, J = 8.7 Hz,
2H), 7.71 (d, J = 16.1 Hz, 1H), 7.63 (d, J = 7.4 Hz, 1H), 7.35 (t,
J = 7.2 Hz, 1H), 7.30 (t, J = 7.4 Hz, 1H), 7.24 (d, J = 7.6 Hz,
1H), 6.95 (d, J = 8.8 Hz, 2H), 6.62 (d, J = 16.0 Hz, 1H), 4.40 (s,
2H), 3.87 (s, 3H), 2.29 (s, 3H); 13C NMR (100 MHz, CDCl3)
δ (ppm) 198.4, 195.5, 163.9, 140.8, 135.1, 134.3, 131.5, 130.8,
130.4, 129.5, 129.0, 127.8, 127.0, 114.0, 55.6, 43.0, 27.7;
HRMS (TOF-ESI): [M + H]+ calcd for C19H19O3: 295.1334;
found: 295.1335. Anal. Calcd for C19H18O3: C 77.53, H 6.16;
found: C 77.38, H 6.00.
Scheme 1 Proposed mechanism.
(E)-4-(2-(p-Methylbenzoylmethylene)phenyl)-3-buten-2-one 5c
1
66%, mp 79–80 °C; IR v (cm−1) 1676, 1647, 1608; H NMR
Conclusions
(400 MHz, CDCl3) δ (ppm) 7.85 (d, J = 8.2 Hz, 2H), 7.63 (d,
J = 16.0 Hz, 1H), 7.56 (dd, J = 7.3, 1.2 Hz, 1H), 7.24–7.31 (m,
2H), 7.21 (d, J = 8.0 Hz, 2H), 7.17 (dd, J = 7.6, 1.3 Hz, 1H),
6.55 (d, J = 16.0 Hz, 1H), 4.36 (s, 2H), 3.35 (s, 3H), 2.21 (s,
3H); 13C NMR (100 MHz, CDCl3) δ (ppm) 198.2, 196.5, 144.4,
140.7, 134.8, 134.3, 134.0, 131.4, 130.3, 129.4, 129.0, 128.5,
127.7, 126.9, 43.1, 27.6, 21.7; HRMS (TOF-ESI): [M + H]+
calcd for C19H19O2: 279.1385; found: 279.1387. Anal. Calcd for
C19H18O2: C 81.99, H 6.52; found: C, 81.70, H 6.35.
In summary, the NHC-catalyzed transformations of α-(isochro-
men-1-yl)ketones were studied. In the presence of a triazole
carbene, α-(isochromen-1-yl)ketones isomerized into β-(2-
(aroylmethylene)phenyl)-α,β-unsaturated ketones in moderate to
good yields, while the same reaction catalyzed by an imidazole
carbene produced 1-aroylnaphthalene derivatives in excellent
yields. Both reactions were initiated by the deprotonation of the
α-protons of the ketones with a NHC catalyst. This work not
only provides a new method for the synthesis of novel α,β-un-
saturated ketones and multi-substituted naphthalene derivatives,
but also advances the application of NHC catalysts in the field of
Brønsted base-catalysis.
(E)-4-(2-(p-Chlorobenzoylmethylene)phenyl)-3-buten-2-one 5d
1
38%, mp 113–114 °C; IR v (cm−1) 1680, 1643, 1619; H NMR
Experimental section
(400 MHz, CDCl3) δ (ppm) 7.95 (d, J = 8.4 Hz, 2H), 7.68 (d,
J = 16.2 Hz, 1H), 7.65 (d, J = 8.7 Hz, 1H), 7.46 (d, J = 8.5 Hz,
2H), 7.37 (t, J = 7.2 Hz, 1H), 7.33 (t, J = 7.1 Hz, 1H), 7.22 (d,
J = 7.0 Hz, 1H), 6.64 (d, J = 15.9 Hz, 1H), 4.42 (s, 2H), 2.30 (s,
3H); 13C NMR (100 MHz, CDCl3) δ (ppm) 198.0, 195.7, 140.3,
140.0, 134.7, 134.2, 131.3, 130.4, 129.8, 129.1, 128.9, 127.9,
127.0, 43.2, 27.7; HRMS (TOF-ESI): [M + Na]+ calcd for
1. General procedure for the preparation of β-(2-
(aroylmethylene)phenyl)-α,β-unsaturated ketones 5 from
α-(3-arylisochromen-1-yl)ketones 3
Under a nitrogen atmosphere, α-(isochromen-1-yl)ketones 3
(1 mmol) and N,N-benzyl-1,2,4-triazolium salt 4c (0.2 mmol)
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(2-Methylnaphthalen-1-yl)(phenyl)methanone 6a
C18H15ClO2Na: 321.0658; found: 321.0663. Anal. Calcd for
C18H15ClO2: C 72.36, H 5.06; found: C, 72.12, H 4.67.
98%, mp 71–72 °C (lit.16 mp 74–75 °C); IR v (cm−1) 1667,
1
1594, 1578; H NMR (400 MHz, CDCl3) δ (ppm) 7.85 (d, J =
8.4 Hz, 2H), 7.82 (d, J = 7.4 Hz, 2H), 7.60 (t, J = 7.4 Hz, 1H),
7.48 (d, J = 8.4 Hz, 1H), 7.43 (t, J = 7.6Hz, 3H), 7.37 (d, J =
8.5 Hz, 1H), 7.36 (t, J = 8.0 Hz, 1H), 2.31 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ (ppm) 200.3, 137.5, 135.9, 133.8, 132.2,
131.6, 130.6, 129.7, 128.9, 128.8, 128.5, 128.1, 126.7, 125.4,
124.9, 19.7; MS (ESI): 247 [M + H]+.
(E)-2-Methyl-1-(2-(benzoylmethylene)phenyl)pent-1-en-3-one 5e
1
41%, mp 52–53 °C; IR v (cm−1) 1677, 1668, 1636; H NMR
(400 MHz, CDCl3) δ (ppm) 7.94 (d, J = 7.2 Hz, 2H), 7.57 (t,
J = 7.4 Hz, 1H), 7.51 (s, 1H), 7.45 (t, J = 7.4 Hz, 2H),
7.27–7.33 (m, 3H), 7.22 (dd, J = 5.2, 4.2 Hz, 1H), 4.28 (s, 2H),
2.66 (q, J = 7.3 Hz, 2H), 1.81 (d, J = 1.2 Hz, 3H), 1.06 (t,
J = 7.3 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ (ppm) 202.9,
197.2, 139.0, 137.2, 136.0, 133.5, 133.3, 130.7, 129.2, 128.7,
128.4, 128.3, 127.1, 43.7, 30.8, 13.0, 8.6; HRMS (TOF-ESI):
(4-Methoxyphenyl)(2-methylnaphthalen-1-yl)methanone 6b17
[M
+
Na]+ calcd for C20H20O2Na: 315.1361; found:
1
99%, mp 101–102 °C; IR v (cm−1) 1657, 1600, 1574; H NMR
315.1358. Anal. Calcd for C20H20O2: C 82.16, H 6.89; found:
C, 82.20, H 6.88.
(400 MHz, CDCl3) δ (ppm) 7.84 (d, J = 8.0 Hz, 1H), 7.83 (d,
J = 8.4 Hz, 1H), 7.78 (d, J = 7.6 Hz, 2H), 7.49 (d, J = 8.3 Hz,
1H), 7.42 (d, J = 7.7 Hz, 1H), 7.36 (d, J = 8.4 Hz, 1H), 7.83 (t,
J = 8.7 Hz, 1H), 6.89 (d, J = 8.7 Hz, 2H), 3.85 (s, 3H), 2.31 (s,
3H); 13C NMR (100 MHz, CDCl3) δ (ppm) 198.9, 164.2, 136.4,
132.3, 132.1, 131.8, 130.9, 128.8, 128.6, 128.1, 126.7, 125.5,
125.1, 114.2, 55.6, 19.8; MS (ESI) 277 [M + H]+.
(E)-2-(2-(Benzoylmethylene)benzylidene)cyclopentanone 5f
1
83%, mp 126–127 °C; IR v (cm−1) 1707, 1680, 1614, 1595; H
NMR (400 MHz, CDCl3) δ (ppm) 7.97 (dd, J = 7.6, 1.3 Hz,
2H), 7.57 (t, J = 7.4 Hz, 1H), 7.44–7.48 (m, 4H), 7.33 (t, J =
4.0 Hz, 1H), 7.31 (t, J = 4.3 Hz, 1H), 7.23 (dd, J = 5.7, 4.1 Hz,
1H), 4.42 (s, 2H), 2.66 (td, J = 7.2, 2.6 Hz, 2H), 2.37 (t, J =
7.8 Hz, 2H), 1.96 (quintet, J = 7.4 Hz, 2H); 13C NMR
(100 MHz, CDCl3) δ (ppm) 207.7, 197.0, 138.2, 136.7, 135.5,
135.2, 133.4, 131.1, 129.4, 129.3, 129.2, 128.8, 128.5, 127.2,
43.1, 38.1, 29.3, 20.5; HRMS (TOF-ESI): [M + Na]+ calcd for
C20H18O2Na: 313.1204; found: 313.1201. Anal. Calcd for
C20H18O2: C 82.73, H 6.25; found: C, 82.47, H 5.97.
(2-Methylnaphthalen-1-yl)(4-methylphenyl)methanone 6c18
97%, mp 104–105 °C (lit.18 mp 106 °C); IR v (cm−1) 1658,
1601; 1H NMR (400 MHz, CDCl3) δ (ppm) 7.77 (d, J = 8.6 Hz,
2H), 7.64 (d, J = 7.9 Hz, 2H), 7.41 (d, J = 8.3 Hz, 1H), 7.34 (t,
J = 7.1 Hz, 1H), 7.29 (d, J = 8.4 Hz, 1H), 7.27 (td, J = 7.0,
1.0 Hz, 1H), 7.15 (d, J = 8.1 Hz, 2H), 2.33 (s, 3H), 2.24 (s, 3H);
13C NMR (100 MHz, CDCl3) δ (ppm) 199.9, 144.8, 136.2,
135.2, 132.1, 131.7, 130.7, 129.9, 129.5, 128.8, 128.0, 126.6,
125.4, 125.0, 21.8, 19.7; MS (ESI) 261 [M + H]+.
(E)-2-(2-(Benzoylmethylene)benzylidene)cyclohexanone 5g
1
53%, mp 169–170 °C; IR v (cm−1) 1676, 1593, 1580, 1566; H
NMR (400 MHz, CDCl3) δ (ppm) 7.88 (d, J = 7.2 Hz, 2H),
7.49 (t, J = 7.4 Hz, 1H), 7.40 (s, 1H), 7.37 (dd, J = 7.3, 1.5 Hz,
2H), 7.16–7.23 (m, 3H), 7.12 (dd, J = 6.3, 2.4 Hz, 1H), 4.42 (s,
2H), 2.50 (td, J = 7.0, 1.8 Hz, 2H), 2.34 (t, J = 6.7 Hz, 2H),
1.79 (quintet, J = 5.4 Hz, 2H), 1.59 (quintet, J = 5.8 Hz, 2H);
13C NMR (100 MHz, CDCl3) δ (ppm) 202.0, 197.2, 139.4,
136.8, 135.6, 134.5, 133.5, 133.3, 130.7, 129.4, 128.8, 128.6,
128.4, 126.9, 43.2, 40.7, 28.8, 24.1, 23.8; HRMS (TOF-ESI):
[M + Na]+ calcd for C21H20O2Na: 327.1361; found: 327.1363.
Anal. Calcd for C21H20O2: C 82.86, H 6.62; found: C, 82.81, H
6.23.
(4-Chlorophenyl)(2-methylnaphthalen-1-yl)methanone 6d
97%, mp 106–107 °C; IR v (cm−1) 1669, 1585; 1H NMR
(400 MHz, CDCl3) δ (ppm) 7.79 (d, J = 8.2 Hz, 2H), 7.68 (d,
J = 8.4 Hz, 2H), 7.27–7.38 (m, 6H), 2.23 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ (ppm) 199.0, 140.4, 135.9, 135.4, 132.3,
131.7, 131.1, 129.2, 128.53, 128.47, 128.2, 126.9, 125.6, 124.7,
19.7; HRMS (TOF-ESI): [M + H]+ calcd for C18H14ClO:
281.0733; found: 281.0739. Anal. Calcd for C18H13ClO:
C 77.01, H 4.67; found: C, 76.94, H 4.88.
2. General procedure for the preparation of 1-
(2-Ethyl-3-methylnaphthalen-1-yl)(phenyl)methanone 6e
aroylnaphthalenes 6 from α-(3-arylisochromen-1-yl)ketones 3
1
91%, mp 108–109 °C; IR v (cm−1) 1660, 1592, 1578; H NMR
Under a nitrogen atmosphere, α-(isochromen-1-yl)ketones 3
(1 mmol) and N,N-benzylimidazole salt 4e (0.2 mmol) were dis-
solved in acetonitrile (20 mL), and then DBU (0.2 mmol) was
added. The reaction mixture was refluxed for 2–4 h. After
removal of solvent under vacuum, the residue was chromato-
graphed on a silica gel column eluting with a mixture of
petroleum ether and ethyl acetate (20 : 1) to give 1-aroylnaphtha-
lenes 6 in 90–99% yields.
(400 MHz, CDCl3) δ (ppm) 7.82 (d, J = 7.5 Hz, 2H), 7.77 (d,
J = 8.0 Hz, 1H), 7.72 (s, 1H), 7.56 (t, J = 7.4 Hz, 1H),
7.36–7.43 (m, 4H), 7.27 (t, J = 8.2 Hz, 1H), 2.70 (br, 1H), 2.54
(br, 1H), 2.54 (s, 3H), 1.09 (t, J = 7.8 Hz, 3H); 13C NMR
(100 MHz, CDCl3) δ (ppm) 201.0, 137.5, 135.91, 135.89,
133.9, 132.8, 131.8, 129.8, 129.3, 128.9, 128.1, 127.5, 125.8,
125.5, 124.7, 30.2, 27.4, 22.9; HRMS (TOF-ESI): [M + H]+
calcd for C20H19O: 275.1436; found: 275.1431.
This journal is © The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 9079–9084 | 9083

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(Cyclopenta[b]naphthalen-4-yl)(phenyl)methanone 6f19
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96%, mp 108–109 °C; IR v (cm−1) 1666, 1653, 1594, 1578; H
NMR (400 MHz, CDCl3) δ (ppm) 7.83 (d, J = 7.1 Hz, 2H),
7.81 (d, J = 7.8 Hz, 1H), 7.77 (s, 1H), 7.58 (t, J = 7.4 Hz, 1H),
7.57 (d, J = 8.6 Hz, 1H), 7.43 (t, J = 7.8 Hz, 2H), 7.39 (d, J =
7.2 Hz, 1H), 7.31 (t, J = 7.0 Hz, 1H), 3.08 (t, J = 7.2 Hz, 2H),
2.80 (t, J = 7.4 Hz, 2H), 2.09 (quintet, J = 7.4 Hz, 3H); 13C
NMR (100 MHz, CDCl3) δ (ppm) 199.4, 143.2, 141.4, 137.8,
133.8, 133.1, 132.4, 130.1, 130.0, 128.9, 128.0, 125.9, 125.5,
125.2, 124.1, 32.5, 31.9, 26.1; MS (ESI): 273 [M + H]+.
1
(Phenyl)(tetrahydroanthracen-9-yl)methanone 6g
90%, mp 147–148 °C (lit.20 mp 158 °C); IR v (cm−1) 1657,
1
1593, 1578; H NMR (400 MHz, CDCl3) δ (ppm) 7.81 (d, J =
7.1 Hz, 2H), 7.76 (d, J = 8.2 Hz, 1H), 7.65 (s, 1H), 7.57 (t, J =
7.4 Hz, 1H), 7.42 (t, J = 7.6 Hz, 2H), 7.39 (d, J = 6.4 Hz, 1H),
7.37 (t, J = 8.1 Hz, 1H), 7.26 (t, J = 8.2 Hz, 1H), 3.02 (t, J =
6.4 Hz, 2H), 2.80 (br, 1H), 2.57 (br, 1H), 1.81–1.87 (m, 2H),
1.77 (br, 2H); 13C NMR (100 MHz, CDCl3) δ (ppm) 201.0,
137.5, 135.91, 135.89, 133.9, 132.8, 131.8, 129.8, 129.3, 128.9,
128.1, 127.5, 125.8, 125.5, 124.7, 30.2, 27.4, 23.0, 22.9; MS
(ESI): 287 [M + H]+.
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Acknowledgements
This work was supported by the National Natural Science Foun-
dation of China (No. 21172021 and 20832006), Beijing Munici-
pal Commission of Education and the Fundamental Research
Funds for the Central Universities (2009SC-1).
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9084 | Org. Biomol. Chem., 2012, 10, 9079–9084
This journal is © The Royal Society of Chemistry 2012