Palladium catalyzed bicyclization of 1,8-diiodonaphthalene and tertiary propargylic alcohols to phenalenones and their applications as fluorescent chemosensor for fluoride ions

Article abstract of DOI:10.1039/c0cc04875e

Phenalenone derivatives were efficiently constructed from 1,8-diiodonaphthalene and tertiary propynols via a one-pot domino reaction which eventually included Pd-catalyzed Sonogoshira coupling, Pd-catalyzed allylic oxidation and Pd-catalyzed Csp²

Full text of DOI:10.1039/c0cc04875e

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Palladium catalyzed bicyclization of 1,8-diiodonaphthalene and tertiary
propargylic alcohols to phenalenones and their applications as fluorescent
chemosensor for fluoride ionsw
Xiaopeng Chen, Hongbo Wang, Xiaohan Jin, Jinwu Feng, Yanguang Wang* and Ping Lu*
Received 9th November 2010, Accepted 14th December 2010
DOI: 10.1039/c0cc04875e
Phenalenone derivatives were efficiently constructed from 1,8-
diiodonaphthalene and tertiary propynols via a one-pot domino
reaction which eventually included Pd-catalyzed Sonogoshira
coupling, Pd-catalyzed allylic oxidation and Pd-catalyzed
Table 1 Optimization of reaction conditions for the preparation of 3aa
Csp2–H activation. Moreover, the synthesized phenalenone
derivative presented a practical application as a fluorescent
chemosensor for fluoride anion with high sensitivity and selectivity.
The palladium-catalyzed Sonogashira coupling reaction has
become a booming methodology to prepare arylalkynes and
conjugated enynes, which are precursors for natural products,
pharmaceuticals and optoelectronics materials.1–3 Our previous
works on the synthesis of acetylene-linked light emitting
materials confirmed further that this reaction deserved
its importance in constructing fluorescent oligomers or
dendrimers.4 However, while 1,8-diiodonaphthalene (1) and
2-methylbut-3-yn-2-ol (2a) were used as coupling substrates,
varied from the normal Sonogashira coupling products (4a and
5a) and the enyne formation product,5 an unexpected bicyclized
phenalenone derivative 3a6,7 was generated in the presence of
trace amount of water and air. In this paper, we would like to
report the systematic optimization of the reaction condition for
this transformation, the diversity of the substrates, the possible
mechanism, and its potential application of the product as
fluorescent chemosensor for fluoride anion.
Yield (%)
3a
4a
5a
Entry Catalyst
Solvent
T/1C
1
Pd(PPh3)2Cl2 Et3N
80
80
80
80
80
65
64 o5 18
2
3
4
5
6
7
Pd(PPh3)2Cl2 i-Pr2EtN
Pd(PPh3)2Cl2 i-Pr2NH
Pd(PPh3)2Cl2 Pyrrolidine
Pd(PPh3)2Cl2 Piperidine
Pd(PPh3)2Cl2 THF/Bu4NFb
58
37
o5
o5
0
23 14
32 23
35 46
38 40
75 12
26 63
23 18
12 63
56 10
Pd(PPh3)2Cl2 THF/Bu4NOHc 65
0
8
9
Pd(PPh3)4
Pd(OAc)2
Et3N
Et3N
80
80
rt
50
80
80
80
80
53
20
0
10
11
12d
13e
14f
15g
Pd(PPh3)2Cl2 Et3N
Pd(PPh3)2Cl2 Et3N
Pd(PPh3)2Cl2 Et3N
Pd(PPh3)2Cl2 Et3N
Pd(PPh3)2Cl2 Et3N
Pd(PPh3)2Cl2 Et3N
36
0
0
52
94
92
6
5
3
Exhaustive studies of reaction conditions for the formation of
3a from 1 and 2a were firstly processed. Pd(PPh3)2Cl2 was found
to be an efficient catalyst in comparison with other palladium
catalysts, such as Pd(PPh3)4 and Pd(OAc)2 (Table 1, entries 1, 8
and 9). Triethylamine was determined to be the most suitable
solvent (Table 1, entries 1–5). When diisopropylethylamine or
diisopropylamine was used as a solvent, 3a could be obtained,
but in relatively lower yields (Table 1, entries 2 and 3). However,
when the reaction was conducted in pyrrolidine or piperidine,
only trace amount of 3a was detected by TLC (Table 1, entries 4
and 5). When the solvent was changed to THF adding with
0
58 22
—
12 o5
a
Unless otherwise specified, the reaction was carried out in a sealed
flask with the existence of water (10 mL) and air, and using 1 (1 mmol),
2a (4 mmol), Pd catalyst (0.05 mmol), CuI (0.1 mmol), and PPh3
b
(0.1 mmol) in solvent (40 mL). Bu4NOH (1.0 M in H2O, 4 mmol).
c
d
Bu4NF (1.0 M in THF, 4 mmol). In the absence of water
e
and air. In the absence of water. In the absence of air.
f
g
1,8-Dibromonaphthalene was used as the substrate instead of 1.
tetrabutylammonium fluoride or hydroxide, we didn’t detect 3a
except that the normal Sonogashira products were obtained in
different ratios (Table 1, entries 6 and 7). Further, 3a could not
be afforded either at room temperature (Table 1, entry 10), or in
the absence of water and/or air (Table 1, entry 12–14). When 1
was altered as 1,8-dibromonaphthalene, 3a was isolated in a
yield of 12%, while 1-bromo-8-(phenylethynyl)naphthalene was
isolated as a major product (Table 1, entry 15).
Department of Chemistry, Zhejiang University, Hangzhou 310027,
P. R. China. E-mail: orgwyg@zju.edu.cn, pinglu@zju.edu.cn;
Fax: +86 571-87952543; Tel: +86 571-87952543
w Electronic supplementary information (ESI) available: Detailed
experimental procedures, characterization data, and copies of H and
1
13C NMR spectra for all products. See DOI: 10.1039/c0cc04875e
c
2628 Chem. Commun., 2011, 47, 2628–2630
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Table 2 Palladium catalyzed reaction of 1 with propynols 2a–2ga
formations of 5h–5j (Scheme 1) because the aldehyde cleavage
is more difficult than ketone cleavage,9 similar to the relative
reactivity of retro-aldol condensation. In this point of view,
reactions of 5a with 2a–2g were conducted and bicyclized
products 3a–3g (Table 3) were obtained as we predicted.
Based on the literature and the above substrate-controlled
investigations, we proposed a possible mechanistic pathway
shown in Scheme 3. 5a, formed via normal Sonogoshira
coupling, was firstly postulated to undergo a base-catalyzed
deacetonization to afford I, that is similar to retro-aldol
condensation.9 Then I reacted further with 2a to form II.
Afterward, hydration of II and a sequential intramolecular aldol
condensation generated the cyclized a,b-unsaturated ketone IV.10
A cyclic ether (VI) was obtained soon via Pd-catalyzed allylic
oxidation11 and immediate intramolecular dehydration.
Sequentially, lactone (VII) was formed by further palladium
catalyzed allylic oxidation of VI.11,12 Finally, by orientation of
the carbonyl of ester group, palladium was inserted into aromatic
Csp2–H bond, and a palladium participated six membered ring
was generated. Coordination with water in solution and followed
by reductive elimination, 3a was obtained.13
Yield
(%)
Entry Propynol
Product
1
2
3
4
5
6
7
2a (R1 = R2 = Me)
2b (R1 = Me, R2 = Et)
2c (R1 = Me, R2 = Pr-n) 3c (R1 = Me, R2 = Pr-n) 58
2d (R1 = R2 = Et)
2e (R1,R2 = –(CH2)4–)
2f (R1,R2 = –(CH2)5–)
3a (R1 = R2 = Me)
3b (R1 = Me, R2 = Et)
64
62
3d (R1 = R2 = Et)
3e (R1,R2 = –(CH2)4–)
3f (R1,R2 = –(CH2)5–)
45
59
60
2g (R1 = Me, R2 = Bu-i) 3g (R1 = Me, R2 = Bu-i) 54
a
The reaction was carried out in a sealed flask with the existence of
water (10 mL) and air, and using 1 (1 mmol), 2 (4 mmol), Pd(PPh3)2Cl2
(0.05 mmol), CuI (0.1 mmol), and PPh3 (0.1 mmol) in Et3N (40 mL).
In order to survey the substrate diversity of this one-pot
reaction, various propynols 2a–2k were examined under the
optimized reaction condition. To tertiary propynols 2a–2g
(Table 2), bicyclized products 3a–3g were obtained as major
products in yields of 45–64%, respectively. However, when the
secondary propynols 2h, 2i or 2j (Scheme 1) were used as
coupling substrates, the mono-Sonogashira coupling product
5h, 5i or 5j were isolated as major products in moderate yields
(72–75%). When primary propynol 2k (Scheme 2) was used,
an unexpected acenaphthylene product 6 was isolated in a
yield of 76% (ESIw). The skeleton of 6 deserved multiple
biological activities.8 More interestingly, 4a did not go
further bicyclization at all under the optimized reaction
condition and was mostly recovered.
Not only the synthesis of 3a is fascinating, but also its
photophysical properties. 3a (1 Â 10À5 M in THF) absorbs
light at 432 nm and 454 nm, and emits light at 478 nm (Fig. 1).
It might be assigned to the p–p* transition of the phenalenone
skeleton. Theoretical calculation supported this assignment
(Table S1 in ESIw). Gradual addition of the fluoride anion
produces a decreasing intensity of the absorption peaks
at 432 nm and 454 nm, but an increasing intensity of the
absorbance peaks at 502 nm and 536 nm. A clear isosbestic
point is found to be at 468 nm, which suggests an interconversion
between two species (Fig. S27, ESIw). At the same time, a
noticeable change is also observed by the fluorescent
measurement. No obvious change is found at 478 nm, but
a new emission peak appears at 550 nm accompanied by a
remarkable increment in intensity with the gradual addition of
the fluoride anion (Fig. S28, ESIw). It might be explained that
a photoinduced charge transfer (PCT) process occurs by the
According to above investigations, it might be preliminarily
concluded that the cleavage of one molar ketone from the
mono-coupling intermediate 5a5 played an important role in
the reaction progress. It also well explained the majority
Table 3 Main products of palladium catalyzed reactions of 5a with
propynols 2a–2ga
Scheme 1 Palladium catalyzed reaction of 1 with propynols 2h–2j.
Entry
Propynol
Product
Yield (%)
1
2
3
4
5
6
7
2a
2b
2c
2d
2e
2f
3a (R1 = R2 = Me)
68
65
62
43
61
60
55
3b (R1 = Me, R2 = Et)
3c (R1 = Me, R2 = Pr-n)
3d (R1 = R2 = Et)
3e (R1,R2 = –(CH2)4–)
3f (R1,R2 = –(CH2)5–)
3g (R1 = Me, R2 = Bu-i)
2g
a
The reaction was carried out in a sealed flask with the existence of
water (10 mL) and air, and using 5a (1 mmol), 2 (4 mmol), Pd(PPh3)2Cl2
(0.05 mmol), CuI (0.1 mmol), and PPh3 (0.1 mmol) in Et3N (40 mL).
Scheme 2 Palladium catalyzed reaction of 1 with propynols 2k.
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 2628–2630 2629

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In conclusion, phenalenone derivatives could be efficiently
constructed from 1,8-diiodonaphthalene and tertiary
propynols via
a one-pot reaction which was catalyzed
by Pd(PPh3)2Cl2/CuI in the presence of water and air.
This domino process eventually combines nine sequential
steps, including Pd-catalyzed Sonogoshira coupling (Csp–H
activation), Pd-catalyzed allylic oxidation (Csp3–H activation)
and Pd-catalyzed ortho activation of aromatic rings (Csp2–H
activation). Moreover, the resulting phenalenone derivatives
could be a potential fluorescent chemosensor for the fluoride
anion with high sensitivity and selectivity.15 Further studies to
clearly understand the reaction mechanism and applications of
this approach to phenalenones are ongoing in our laboratory.
This work has been supported by the National Nature Science
Foundation of China (20972137; J0830413). Contributions
from Prof. Shengmin Ma and Jinquan Yu in mechanism
postulation and Jianming Gu and Xiurong Wu in structure
elucidation are greatly appreciated.
Notes and references
1 For
a review of palladium-catalyzed Sonogashira coupling
Scheme 3 The postulated mechanism.
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(b) R. Chinchilla and C. Najera, Chem. Rev., 2007, 107, 874.
´
2 Selected examples of the application of the Sonogashira coupling
reaction: (a) M. Bock, R. Dehn and A. Kirschning, Angew. Chem.,
2008, 120, 9274 (Angew. Chem., Int. Ed., 2008, 47, 9134);
(b) K. Kanda, T. Koike, K. Endo and T. Shibata, Chem.
Commun., 2009, 1870; (c) Z. Chen, J. Zhu, H. Xie, S. Li, Y. Wu
and Y. Gong, Chem. Commun., 2010, 46, 4184.
3 (a) T. J. J. Muller and U. H. F. Bunz, Functional Organic Material,
¨
Wiley VCH, 2007, pp. 179–223, and references cited therein; (b)
T. J. J. Muller and D. M. D’Souza, Pure Appl. Chem., 2008, 80, 609.
¨
4 (a) Z. Zhao, J.-H. Li, P. Lu and Y. Yang, Adv. Funct. Mater., 2007,
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´ ´
5 J. J. Gonzalez, A. Francesch, D. J. Cardenas and A. M.
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6 Patent of the compound 3a: H. Wang and P. Lu, CN 101230267 A,
2008.
7 CCDC 712668 contains the supplementary crystallographic data
of 3a.
8 N. Haddad and E. Abu-Shqara, J. Org. Chem., 1994, 59, 6090.
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Fig. 1 (a) The absorption changes of 3a (1 Â 10À5 M in THF) with
addition of FÀ. Inset figure present the absorption intensity at 536 nm
and 454 nm versus the concentration of FÀ, respectively; (b) the
fluorescent changes of 3a (1 Â 10À5 M in THF, excited at 454 nm)
with addition of FÀ. Inset figure present the emission at 550 nm versus
the concentration of FÀ.
11 (a) M. S. Chen and M. C. White, Science, 2007, 318, 783;
(b) D. J. Covell and M. C. White, Angew. Chem., 2008, 120, 6548
(Angew. Chem., Int. Ed., 2008, 47, 6448).
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addition of a fluoride anion which leads to a noticeably enhanced
red-shifted emission and the red-shifted absorption as well.14
Furthermore, there were no significant changes in the emission
2À
14 (a) D. Tanaka, S. Horike, S. Kitagawa, M. Ohba, M. Hasegaw,
Y. Ozawa and K. Toriumi, Chem. Commun., 2007, 3142; (b) R. M.
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spectraÀwhen other anions, such as AcOÀ, ClÀ, BrÀ, HPO4
,
H2PO4 were added (Fig. S29, ESIw). So we assume that 3a
might be used as a remarkable fluorescent chemosensor for the
fluoride anion.15
15 M. Cametti and K. Rissanen, Chem. Commun., 2009, 2809.
c
2630 Chem. Commun., 2011, 47, 2628–2630
This journal is The Royal Society of Chemistry 2011