Palladium-catalyzed selective synthesis of naphthalenes and indenones and their luminescent properties

Article abstract of DOI:10.1002/ejoc.201101506

Selective synthesis of functionalized naphthalenes and indenones by palladium-catalyzed cyclization of o-haloacetophenones and terminal alkynes in the presence of a secondary amine is reported. Under a nitrogen atmosphere, the palladium-catalyzed reaction

Full text of DOI:10.1002/ejoc.201101506

FULL PAPER
DOI: 10.1002/ejoc.201101506
Palladium-Catalyzed Selective Synthesis of Naphthalenes and Indenones and
Their Luminescent Properties
Xiaopeng Chen,[a] Jisong Jin,[a] Ningning Wang,[a] Ping Lu,*[a] and Yanguang Wang*[a]
Keywords: Cyclization / Naphthalenes / Indenones / Cascade reactions / Luminescence / Sensors
Selective synthesis of functionalized naphthalenes and ind-
the reaction was conducted in air, 1-indenone-3-carb-
enones by palladium-catalyzed cyclization of o-haloaceto- aldehydes were obtained. The synthesized β-arylnaphthal-
phenones and terminal alkynes in the presence of a second-
ary amine is reported. Under a nitrogen atmosphere, the pal-
enes 4a–f emit light in a range from 386 to 452 nm with quan-
tum yields from 0.10 to 0.48 in cyclohexane. The absorption
ladium-catalyzed reaction of o-haloacetophenones with ter- and emission efficiency of 4d were finely tuned by the acidity
minal alkynes in the presence of wet secondary amines
generated 1-(dialkylamino)-3-aryl/alkylnaphthalenes. When
of the environment, and this might be useful in the use of 4d
as a fluorescent pH sensor.
when we carried out the palladium-catalyzed Sonogashira
reaction between o-bromoacetophenone and phenylacetyl-
ene in the presence of piperidine, an unexpected three-com-
ponent product, 1-(1-piperidinyl)-3-phenylnaphthalene, was
obtained along with the normal Sonogashira coupling
product. With regard to the potential applications of β-aryl-
naphthalenes in the field of luminescent materials and fluo-
rescent sensors, we investigated the selectivity of this three-
component reaction and developed a selective synthesis of
β-aryl/alkyl naphthalenes and 1-indenone-3-carbaldehydes
by controlling the reaction conditions. Herein, we would
like to report the details of this effort.
Introduction
β-Arylnaphthalene derivatives,[1] usually modeled as sim-
plified genisteins to enhance estrogen receptor selectivity,[2]
have been widely explored, and it has been demonstrated
that they have unique advantages over other classes, such
as biphenyls,[3] tetrahydrochrysenes,[4] arylbenzthioph-
enes,[5] triazines,[6] and diarylpropionitriles.[7] β-Arylnaphth-
alene derivatives are also useful luminescent materials[8]
and smectic liquid crystalline photoconductors[9] in the
study of intrinsic photocarrier generation.[10] In view of
these important applications, the development of facile and
efficient methodologies for the construction of β-aryl-
naphthalenes has attracted much attention.[11] Meanwhile,
indenone derivatives are important in pharmaceuticals and
organic synthesis. They exhibit antihypertensive activity[12]
and function as a kind of template for peroxisome prolifer-
ator-activated receptor agonists,[13] which are of interest in
the treatment of diabetes. Furthermore, indenone deriva-
tives are useful synthetic precursors to steroids.[14] Lots of
synthetic routes leading to indenones have been devel-
oped.[15] Recent examples include the rhodium-catalyzed re-
action of alkynes, o-bromophenylboronic acids, and para-
formaldehyde.[16]
Results and Discussion
The Palladium-Catalyzed Three-Component Reaction of o-
Haloacetophenones, Terminal Alkynes, and Secondary
Amines
In our primary experiment, the Pd(PPh3)4/CuI-catalyzed
coupling between o-bromoacetophenone (1a) and phenyl-
acetylene (2a) in dry diisopropylamine produced the Sono-
gashira coupling product 1-[2-(phenylethynyl)phenyl]eth-
anone (5a) in a yield of 95% under a nitrogen atmosphere.
However, when the reaction was conducted in wet piperid-
ine, which was not dried and distilled before use, we ob-
tained an unexpected product, 1-(1-piperidinyl)-3-phenyl-
naphthalene (4a), in 66% yield (Table 1, entry 1),[24] whose
structure possessed a naphthalene skeleton. Piperidine did
participate in the reaction. Delighted by this result, we opti-
mized the reaction conditions for this transformation. We
examined the palladium sources at first, and found that
Pd(PPh3)2Cl2 (Table 1, entry 2) and Pd(OAc)2 (Table 1, en-
try 3) could also work for this reaction, but the yields were
relatively low. In contrast to entry 1, the yield of 4a de-
The Sonogashira reaction[17] has been evidenced to be an
efficient approach to conjugated oligomers,[18] dendri-
mers,[19] and polymers[20] for optoelectronic studies in the
fields of organic light-emitting diodes (OLED),[21] organic
solar cells,[22] and two-photon absorption.[23] Recently,
[a] Department of Chemistry, Zhejiang University,
Hangzhou 310027, P. R. China
Fax: +86-571-87952543
E-mail: pinglu@zju.edu.cn
orgwyg@zju.edu.cn
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201101506.
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Palladium-Catalyzed Selective Synthesis of Naphthalenes and Indenones
creased when the reaction was terminated after 7 h (Table 1, para position of phenylacetylene benefited the reaction,
entry 4). By decreasing the reaction temperature to 50 °C, while an electron-withdrawing group at the para position of
the normal Sonogashira coupling product 5a was isolated phenylacetylene decreased the yield considerably (Table 2,
in 66% yield, while the yield of 4a was only 12% (Table 1, entries 4–8). 4-Cyanophenylacetylene did not afford the de-
entry 5). At room temperature, the reaction did not occur, sired product, with many spots on the TLC plate after reac-
and 1a was recovered quantitatively (Table 1, entry 6). tion (Table 2, entry 9). Terminal alkynes with a primary
When 1,4-dioxane or tetrahydrofuran functioned as the sol- alkyl group (2h–2j) or a secondary alkyl group (2k) gave
vent and 10 equiv. of piperidine was added, 5a was isolated the corresponding 1-dialkylamino-3-alkylnaphthalenes (4g–
in yields of 48 and 50%, respectively (Table 1, entries 7 and 4j) in high yields (81–95%) (Table 2, entries 10–13). How-
8). Compound 4a could also be obtained as the major prod- ever, a terminal alkyne with a tertiary alkyl group (2l)
uct when the solvent was altered to N,N-dimethylform- formed the normal Sonogashira product 5b in 85% yield
amide (DMF) or N,N-dimethylacetamide (DMA) (Table 1, when the reaction was run at 80 °C for 48 h (Table 2, entry
entries 9 and 10). When piperidine was dried and distilled 14). When 2m was used, compound 7 (Scheme 1) was ob-
before use, the normal Sonogashira coupling product 5a tained in 59% yield (Table 2, entry 15). In this case, the SN2
was obtained as the major product, and 4a was isolated as replacement of –OTs with piperidine must have occurred.
the minor product, regardless of whether the reaction was Finally, we examined other secondary amines. Similar to
catalyzed by Pd(PPh3)2Cl2 or Pd(PPh3)4 (Table 1, entries 11 piperidine, pyrrolidine (3b) or morpholine (3c) worked well
and 12).
for this reaction and afforded 4k and 4l in yields of 52 and
43%, respectively (Table 2, entries 16 and 17). When dieth-
Table 1. Optimization of reaction conditions for the formation of ylamine (3d) or diisopropylamine (3e) was used, the normal
4a.[a]
Sonogashira coupling product 5a was obtained in yields of
90 and 95%, respectively (Table 2, entries 18 and 19). When
diethylamine was used in 10 equiv. molar ratio to 1, and
triethylamine was added as the solvent, 4m could be ob-
tained, but in 15% yield only. In this case, 5a was isolated
in a yield of 80% (Table 2, entry 20).
Table 2. Formation of various 3-aryl/alkylnaphthalenes 4.[a]
Entry
Pd catalyst
Pd(PPh3)4
Solvent[b]
piperidine
Temp.
(°C)
% Yield[c]
4a
5a
1
2
80
80
80
80
50
r.t.
80
reflux
80
80
66
55
35
60
12
Ͻ5%
Ͻ5%
26
Pd(PPh3)2Cl2 piperidine
3
Pd(OAc)2
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
piperidine
piperidine
piperidine
piperidine
1,4-dioxane
THF
4[d]
5
Ͻ5%
66
6
N.R.[e] N.R.
2 (R1)
3
Product (% yield)[b]
7[f]
8[f]
9[f]
10[f]
11
12
Ͻ5
Ͻ5
58
59
17
48
50
16
12
62
50
Entry
1 (X)
1
2
3
4
5
6
7
8
1a (Br)
1b (OTf) 2a
2a (Ph)
3a
3a
3a
3a
3a
4a (66)
4a (76)
4a (36) + 6a (17)
4b (77)
4c (82)
4d (89)
4e (55)
4f (60)
–
4g (95)
4h (98)
4i (87)
4j (81)
5b (85)
7 (59)
4k (52)
4l (43)
5a (90)
5a (95)
4m (15) + 5a (80)
DMF
DMA
1c (I)
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
2a
Pd(PPh3)2Cl2 piperidine[g]
Pd(PPh3)4
80
80
2b (p-MeC6H4)
2c (p-MeOC6H4)
2d (p-Me2NC6H4) 3a
piperidine[g]
20
[a] The reaction was conducted under N2 with 1a (0.5 mmol), 2a
(0.75 mmol), Pd catalyst (5 mol-%, 0.025 mmol), and CuI (10 mol-
%, 0.05 mmol) in solvent (2 mL) for 12 h unless specially indicated
otherwise. [b] Solvent used without pretreatment. [c] Isolated by
column chromatography. [d] The reaction was terminated after 7 h,
and about 10% 1a was recycled. [e] N.R.: no reaction. [f] 10 equiv.
of piperidine was added. [g] Piperidine was distilled from desiccant
and degassed.
2e (p-FC6H4)
2f (p-BrC6H4)
2g (p-CNC6H4)
2h (n-C4H9)
2i (n-C5H11)
2j (c-C6H11CH2)
2k (iso-C3H7)
2l (tert-C4H9)
2m (TsOCH2)
2a
2a
2a
2a
2a
3a
3a
3a
3a
3a
3a
3a
3a
3a
3b
3c
3d
3e
3d
9
10
11
12
13
14[c]
15
16
17
18
19
20[d]
As the next step, we investigated the substrate scope
(Table 2). Initially, we tested different leaving groups (X) in
1 (Table 2. entries 1–3). By changing o-bromoacetophenone
(1a) to 2-acetylphenyl trifluoromethanesulfonate (1b), a bet-
ter yield (76%) was achieved. When the leaving group was
iodide, the yield of 4a decreased to 36%. In this case, 1-
formyl-2-phenyl-3-oxo-3H-indene (6a) was isolated in 17%
yield, the structure of which was established by X-ray crys-
[a] The reaction was conducted under N2 with 1 (0.5 mmol), 2
(1.5 equiv., 0.75 mmol), Pd(PPh3)4 (5 mol-%, 0.025 mmol), and CuI
(10 mol-%, 0.05 mmol) in 3 (2 mL) for 12 h. [b] Isolated by column
chromatography. [c] The reaction was run for 48 h. [d] The reaction
tallographic analysis.[25] An electron-donating group at the was conducted with 3d (10 equiv., 5 mmol) in triethylamine (2 mL).
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X. Chen, J. Jin, N. Wang, P. Lu, Y. Wang
FULL PAPER
or lowering the reaction temperature decreased the yields
(Table 3, entries 2, 7 and 8). At room temperature, 1c was
recovered (Table 3, entry 9). By replacing morpholine with
piperidine or pyrrolidine, 6a was isolated in yields of 42%
and 31%, respectively (Table 3, entries 10 and 11). When
triethylamine or diisopropylamine was used, 5a was ob-
tained as the major product, and 6a was not detected by
TLC (Table 3, entries 12 and 13). In addition to 5a, dieth-
ylamine afforded 6a in 13% yield (Table 3, entry 14).
Scheme 1. Structure of compound 7.
With the optimized reaction conditions for the formation
of 6a in hand, we tested various substrates (Table 4). Alter-
ing the leaving group in 1 from iodide (1c) to bromide (1a),
and to triflate (1b) caused the yields of 6a to decrease
(Table 4, entries 1–3). Changing the substituent group at the
para-position of phenylacetylene, revealed an electron effect
(Table 4, entries 4–9). If the substituent was an electron-
donating group, such as methyl or methoxy, the yields de-
creased to 47 or 42%, respectively (Table 4, entries 4–5).
For 4-(dimethylamino)phenylacetylene (2d), no desired
product was isolated, although the reactants disappeared
completely (Table 4, entry 6). Increased yields were ob-
tained when the substituent group was electron-with-
drawing (2e–g) (Table 4, entries 7–9). Alkylacetylenes did
not favor this transformation. For example, 1-hexyne (2h)
did not afford the desired indenone (Table 4, entry 10).
The Palladium-Catalyzed Tandem Reaction of
o-Haloacetophenones with Terminal Alkynes in Air
With regard to the unexpected formation of 6a (Table 2,
entry 3) and its importance as indicated above,[12–14] we
tried to optimize the reaction conditions for higher yield of
6a by using 1c and 2a as substrates (Table 3). First, we
changed the palladium source. With the combination of
Pd(PPh3)2Cl2, CuI, and PPh3, 6a was obtained in a yield of
48% (Table 3, entry 1). When the reaction was conducted
in air, the yield could be increased up to 54% (Table 3, entry
2). Opening to air also benefited the reaction when
Pd(PPh3)4 was used as catalyst (Table 3, entries 3 and 4).
Pd(OAc)2 was not effective for the formation of 6a, and no
main product was detected in the TLC plate regardless of
whether the reaction was conducted under nitrogen or in
air (Table 3, entries 5 and 6). Decreasing the reaction time
Table 4. Formation of various indenones (6).[a]
Table 3. Optimization of reaction condition for the formation of 1-
formyl-2-phenyl-3-oxo-3H-indene (6a).
Entry 1 (X)
2 (R1)
Product (% yield[b]
)
1
2
3
4
5
6
7
8
9
1c (I)
1a (Br)
1b (OTf)
1c
2a (Ph)
6a (54)
6a (29)
6a (38)
6b (47)
6c (42)
–
6d (58)
6e (53)
6f (62)
–
2a
Entry
Pd catalyst
Solvent[a]
Temp.
(°C)
% Yield[b]
2a
2b (p-MeC6H4)
2c (p-MeOC6H4)
2d (p-Me2NC6H4)
2e (p-FC6H4)
2f (p-BrC6H4)
2g (p-CNC6H4)
2h (n-C4H9)
1[c]
Pd(PPh3)2Cl2 morpholine 80
Pd(PPh3)2Cl2 morpholine 80
Pd(PPh3)4
Pd(PPh3)4
Pd(OAc)2
Pd(OAc)2
Pd(PPh3)2Cl2 morpholine 80
Pd(PPh3)2Cl2 morpholine 50
Pd(PPh3)2Cl2 morpholine r.t.
Pd(PPh3)2Cl2 piperidine
Pd(PPh3)2Cl2 pyrrolidine 80
Pd(PPh3)2Cl2 Et3N
Pd(PPh3)2Cl2 iPr2NH
Pd(PPh3)2Cl2 Et2NH
48
54
29
1c
2[d]
1c
3[c]
morpholine 80
morpholine 80
morpholine 80
morpholine 80
1c
4[d]
32
1c
5[c]
N.D.[e]
1c
6[d]
N.D.
46
33
N.R.
42
31
5a (84)
5a (76)
10
1c
7[d,f]
8[d]
[a] The reaction was carried out in air with 1a (0.5 mmol), 2a
(1.5 equiv., 0.75 mmol), Pd(PPh3)2Cl2 (5 mol-%, 0.025 mmol), CuI
(10 mol-%, 0.05 mmol), and PPh3 (10 mol-%, 0.05 mmol) in
morpholine (2 mL) for 12 h. [b] Isolated yield.
9[d]
10[d]
11[d]
12[d,g]
13[d,g]
14[d,g]
80
80
80
reflux
6a (13) + 5a (63)
Proposed Mechanism for the Formation of 4 and 6
[a] The solvent was used without distillation. [b] Isolated yield. [c]
The reaction was carried out under N2 with 1a (0.5 mmol), 2a
(1.5 equiv., 0.75 mmol), Pd catalyst (5 mol-%, 0.025 mmol), CuI
(10 mol-%, 0.05 mmol), PPh3 (10 mol-%, 0.05 mmol), air (5 mL),
H2O (10 μL), and solvent (2 mL) for 12 h. [d] The reaction was
carried out in air with 1a (0.5 mmol), 2a (1.5 equiv., 0.75 mmol),
Pd(PPh3)2Cl2 (5 mol-%, 0.025 mmol), CuI (10 mol-%, 0.05 mmol),
PPh3 (10 mol-%, 0.05 mmol), and solvent (2 mL) for 12 h. [e] N.D.:
not detected. [f] The reaction was terminated after 7 h, and 16%
1c was recycled. [g] The normal Sonogashira coupling product 5a
was isolated as the major product.
On the basis of the investigated reaction conditions and
the substrate diversity, we postulated a possible mechanism
for the formation of 4 and 6 as shown in Scheme 2. The
first step in the formation of 4 is the condensation of o-
haloacetophenone 1 with amine 3 to form enamine A. This
process can be sped up by water.[26] The resulting A sub-
sequently couples with the terminal alkyne by a Sonoga-
shira reaction, then B is nucleophilically attacked by the
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Palladium-Catalyzed Selective Synthesis of Naphthalenes and Indenones
Scheme 2. Possible mechanism for the formation of 4 and 6.
adjacent enamine to form a cyclized intermediate C. Fi- naphthalenes 4. Although morpholine is not good for the
nally, 4 is constructed by metal hydrogen exchange. As evi- formation of enamine A, it can chemoselectively catalyze
dence, an enamine,[27] prepared from o-bromoacetophenone the intramolecular aldol condensation of D to E via the
(1a) and piperidine (3a), could readily undergo Sonogashira favored enamine intermediate (Scheme 3), which leads to
coupling with phenylacetylene (2a) and subsequent cycliza- the formation of final product 6.
tion to afford 4a in a yield of 54% under the reaction condi-
tions. The first step in the formation of 6 is the Sonogashira
coupling, generating 2-alkynylacetophenone 5. Then, hy-
dration of 5 could lead to the formation of diketone D,
which can be promoted by palladium in wet media. Inter-
mediate D undergoes a secondary amine-catalyzed intramo-
lecular aldol condensation to give indenone E.[28] When 2g
was used as substrate, we obtained 2-(4-cyanophenyl)-3-
methylindenone (8) (26% yield) by terminating the reaction
after 4 h. Finally, the resulting E is oxidized to aldehyde 6
by a palladium-catalyzed allylic oxidation.[29,30]
The direction of the reaction depends on the preferential
formation of enamine A or 2-alkynylacetophenone 5. Be-
cause the order of reactivity of the leaving groups in 1 is I Ͼ Scheme 3. Chemoselective formation of E.
OTfϾ Br, o-iodoacetophenone (1c) favors the Sonogashira
coupling, while o-bromoacetophenone (1a) and 2-acet-
ylphenyl trifluoromethanesulfonate (1b) lead to enamine A.
Chemoselective Sonogashira coupling of the terminal
Photophysical Properties of β-Arylnaphthalenes
alkyne with C–I rather than C–Br could be successfully
As we know that β-arylnaphthalenes can be used as lumi-
achieved by Pd(PPh3)2Cl2 catalyst in triethylamine under nescent materials for optoelectronic devices,[8] we selected
nitrogen.[19b] Thus, Pd(PPh3)2Cl2 was used for the preferen- the synthesized β-arylnaphthalenes to examine their emis-
tial formation of 5. Furthermore, secondary amines in this sion properties. Compounds 4a–f were found to emit light
report could be categorized into three kinds on the basis of in the range 386–452 nm, with quantum yields of 0.10–0.48
their basicity and degree of steric hindrance. The pKa val- in cyclohexane, based on the 9,10-diphenylanthracene stan-
ues[31] for the conjugated acids of morpholine, piperidine, dard (Φ = 0.90 in cyclohexane).[32] Compared with β-aryl-
pyrrolidine, diethylamine, and diisopropylamine are 8.36, naphthalenes, alkyl-substituted compounds 4g–j did not
11.22, 11.27, 10.98, and 11.05, respectively. Morpholine is emit light at all. Moreover, emission spectra were largely
a relatively weak base, so it is not suitable for the formation dependent on the solvent polarity. For example, the maxi-
of enamine A (Table 2, entry 17). Although diethylamine mum emission wavelengths for 4d varied from 389 nm in
and diisopropylamine are basic enough to form enamine cyclohexane to 454 nm in DMSO (Figure S47). This implies
A, they have increased steric hindrance, which inhibits the that compound 4d might be used as a fluorescent sensor for
formation of enamine A (Table 2, entries 18 and 19). Thus, solvent polarity.
piperidine and pyrrolidine are good candidates for the for-
In addition to this, absorption and emission spectra of
mation of enamine A and finally favor the construction of 4d were tightly related to the acidity of the environment
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X. Chen, J. Jin, N. Wang, P. Lu, Y. Wang
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Figure 1. Absorption (a) and emission (b) spectra of 4d at variable acidity (λex = 325 nm).
Scheme 4. Three states of 4d (4d, 4d + H+, and 4d + 2H+) in acidic environment.
(Figure 1). Compound 4d bears two amino groups and absorption at 252 nm was accompanied by a decreasing ab-
might present three stable forms if it abstracted a proton sorption at 325 nm. This pointed out that a second proton-
from the environment (Scheme 4). The PCM model was ation occurred. The maximum absorption wavelengths ob-
used to simulate the ground state of 4d in methanol with served at 300, 325, and 252 nm were well matched to the
the Gaussian 03 program at the B3LYP level with the stan- above calculation results (321, 360, and 280 nm for 4d, 4d
dard 6-31G(d) basis set.[33] According to the calculated re- + H+, and 4d + 2H+, respectively).
sult, the electronegativity of the nitrogen atom in the di-
methylamino group was –0.47e, and that in piperidine was
–0.50e. Therefore, the nitrogen atom in piperidine abstrac-
ted the proton first. Ground states of 4d + H+ and 4d +
2H+ were simulated by using the same basis set. On the
basis of these results, the energy gaps of 4d, 4d + H+, and 4d
+ 2H+ were calculated to be 3.88 eV, 3.45 eV, and 4.44 eV,
respectively, and their simulated maximum absorption
wavelengths were calculated to be 321, 360, and 280 nm,
respectively.
When the acidity of the solution was increased from pH
6.48 to pH 3.00 by gradual addition of hydrochloric acid,
the decreased absorption of 4d at 300 and 325 nm was
matched to an increased absorption at 252 nm. The isosbes-
tic point at 280 nm indicated two states of 4d and 4d + H+.
However, the relative intensity of the peak at 325 nm to that
of the peak at 300 nm gradually increased. This meant that
the quantity of 4d + H+ increased as the acidity increased
(Figure 2). When the acidity was increased further, from pH
3.00 to pH 2.20, absorption spectra were almost the same
as that of a stable I325/I300, which indicated the co-existence
Figure 2. The relation of the relative intensity (I325/I300) and the pH
value.
Emission spectra of 4d were recorded accordingly, with
of three states. As the acidity was increased from pH 2.20 excitation at 325 nm. Fluorescence efficiency was gradually
to pH 0.81, a sudden change was observed. The increasing quenched as the acidity of the solution increased. Mean-
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Palladium-Catalyzed Selective Synthesis of Naphthalenes and Indenones
7.46 (t, J = 7.1 Hz, 1 H), 7.42 (s, 1 H), 3.22 (br., 4 H), 2.08–1.58
(m, 6 H) ppm. 13C NMR (125 MHz, CDCl3, Figure S2): δ =
151.66, 141.91, 138.88, 135.22, 129.03, 128.92, 128.45, 127.68,
127.50, 126.40, 125.50, 123.99, 121.26, 114.69, 54.97, 26.87, 24.86
ppm. HRMS (EI): calcd. for C21H21N [M+] 287.1674; found
287.1683.
while, the maximum emission wavelength was shifted from
435 nm to 457 nm as the pH changed from 6.48 to 2.20,
and it shifted to 485 nm finally when the pH value ap-
proached 0.81. In addition, the emission peak broadened,
which indicated a new emission derived from an ICT pro-
cess in 4d + H+.[34] No emission from 4d + 2H+ was de-
tected when the solution was excited at 325 nm, as 4d +
2H+ absorbed at 252 nm. The dependence of the absorption
and emission of 4d on pH might enable its use as a fluores-
cent pH sensor in the future.
Typical Procedure for the Synthesis of 1-Formyl-2-phenyl-3-oxo-3H-
indene (6a) and Characterization Data: To a solution of 1c (127 mg,
0.5 mmol), 2a (80 mg, 0.75 mmol) in morpholine (3c, 2 mL),
Pd(PPh3)2Cl2 (17.5 mg, 0.025 mmol), were added CuI(9.5 mg,
0.05 mmol) and PPh3 (13.0 mg, 0.05 mmol). In air, the reaction
mixture was stirred at 80 °C for 12 h. Then, morpholine was dis-
tilled under reduced pressure. The residue was dissolved in dichlo-
romethane (25 mL), washed with water (3ϫ25 mL), and dried with
anhydrous Na2SO4. After removal of the solvent under reduced
pressure, the crude product was purified by flash chromatography
on silica gel (eluent solvent: CH2Cl2/hexane). Compound 6a was
Conclusions
Palladium-catalyzed cyclizations of o-haloacetophenones
and terminal alkynes in the presence of secondary amines
were developed. The chemical outcome of the reaction was
largely dependent on the reaction conditions. When dried
and distilled secondary amines were used under a nitrogen
atmosphere, the normal Sonogashira coupling products
were generated. When the secondary amine was wet, 1-(di-
alkylamino)-3-aryl/alkylnaphthalenes were obtained. Con-
ducting the reaction in air gave rise to 2-aryl-3-formylinde-
nones. A possible mechanism for the selective formation of
naphthalenes and indenones was proposed. Furthermore,
the synthesized β-arylnaphthalenes emit light in the range
386–452 nm with quantum yields varying from 0.10 to 0.48
in cyclohexane, which suggests that these compounds can
be applied as fluorescent materials in optoelectronic de-
vices. As a typical example, absorption and emission of 4d
relies on the acidity of the environment, which makes it a
potential fluorescent pH sensor.
1
obtained as an orange solid (yield 54%). M.p. 155.6–156.9 °C. H
NMR (400 MHz, CDCl3, Figure S31): δ = 10.29 (s, 1 H), 7.96 (d,
J = 7.4 Hz, 1 H), 7.60 (d, J = 7.2 Hz, 1 H), 7.52 (m, 5 H), 7.46
(dd, J = 7.6 Hz, 1 H), 7.34–7.28 (dd, J = 7.6 Hz, 1 H) ppm. 13C
NMR (100 MHz, CDCl3, Figure S32): δ = 196.78, 190.93, 144.90,
143.58, 142.26, 134.61, 130.64, 130.45, 129.49, 129.26, 128.68,
128.10, 124.17, 124.12 ppm. HRMS (EI): calcd. for C16H10O2 [M+]
234.0681; found 234.0684.
Supporting Information (see footnote on the first page of this arti-
cle): General synthesis procedures, NMR and absorption/emission
spectra.
Acknowledgments
Ping Lu and Yanguang Wang thank the National Nature Science
Foundation of China (No. 20972137, 21032005, and J0830413) for
financial support.
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Experimental Section
General Methods: Unless otherwise noted, all materials were ob-
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washed with water (3ϫ25 mL), and dried with anhydrous Na2SO4.
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Eur. J. Org. Chem. 2012, 824–830
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
829

X. Chen, J. Jin, N. Wang, P. Lu, Y. Wang
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Received: October 16, 2011
Published Online: December 7, 2011
830
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