One-Shot Double Amination of Sondheimer-Wong Diynes: Synthesis of Photoluminescent Dinaphthopentalenes

Article abstract of DOI:10.1021/acs.orglett.5b01293

Photoluminescent diamino-substituted dinaphthopentalenes were synthesized successfully by the treatment of in situ prepared dinaphthocyclooctadiyne with lithium amide. This reaction involves a series of transformations including the nucleophilic addition

Full text of DOI:10.1021/acs.orglett.5b01293

Letter
pubs.acs.org/OrgLett
One-Shot Double Amination of Sondheimer−Wong Diynes:
Synthesis of Photoluminescent Dinaphthopentalenes
Feng Xu,† Lifen Peng,† Kenta Shinohara,† Takanori Nishida,† Kan Wakamatsu,‡ Motoyuki Uejima,§
Tohru Sato,§ Kazuyoshi Tanaka,*,§ Norihiko Machida,∥ Haruo Akashi,*,∥ Akihiro Orita,*,†
and Junzo Otera†
†Department of Applied Chemistry, Okayama University of Science, 1-1 Ridai-cho, Kita-ku, Okayama 700 0005, Japan
‡Department of Chemistry, Okayama University of Science, 1-1 Ridai-cho, Kita-ku, Okayama 700 0005, Japan
§Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoyo 615 8510, Japan
∥Research Institute of Natural Sciences, Okayama University of Science, 1-1 Ridai-cho, Kita-ku, Okayama 700 0005, Japan
S
* Supporting Information
ABSTRACT: Photoluminescent diamino-substituted
dinaphthopentalenes were synthesized successfully by the
treatment of in situ prepared dinaphthocyclooctadiyne with
lithium amide. This reaction involves a series of trans-
formations including the nucleophilic addition of the lithium
amide to a triple bond of the cyclooctadiyne moiety,
transannulation, protonation of the resulting pentalene anion, and the nucleophilic substitution of the pentalene core with
the lithium amide. In this procedure, a novel double amination step plays a key role. When the diamino-substituted
dinaphthopentalenes were irradiated with UV light in toluene, fluorescence was observed at around 580 nm (ΦF < 0.03).
xpanded π-systems have attracted much attention because
they can be used as the organic material in a range of
E
useful devices such as organic light-emitting diodes (OLED),
organic field effect transistors (OFET), and organic photo-
voltaic cells (OPV).1 A number of polycyclic aromatic
compounds have been synthesized, and their optoelectronic
properties have been extensively explored. In recent times,
much attention has been paid to antiaromatic compounds to
explore new optoelectronic properties of extended π-systems
and their applications.2 In this context, synthetic methods for
the preparation of arenopentalenes such as dibenzo- and
dinaphthopentalenes have been developed,3−8 and several
derivatives of these materials have been applied in OFETs
because of their relatively low-lying lowest unoccupied
molecular orbital (LUMO) energy levels and small highest
occupied molecular orbital (HOMO)−LUMO gaps.4b,d On the
other hand, only a few pentalene derivatives exhibiting
photoluminescence have been reported.9 To explore the
possibility of light-emitting pentalene, we performed time-
dependent density functional theory (TD-DFT) calculations on
the photoexcited transitions of several dibenzo- and dinaphtho-
pentalenes (Figure 1). The calculations demonstrated that
diamino-substituted dinaphthopentalene 1a exhibits a positive
oscillator strength for the first transition (f = 0.300), which is
mainly composed of the HOMO−LUMO transition (69.3%),
giving rise to the possibility of photoluminescence in 1a. In
sharp contrast, the HOMO−LUMO transition is prohibited in
dinaphthopentalene 2 and dibenzopentalenes 3a and 4; the
oscillator strengths (f) of the first transition for 2, 3a, and 4 are
zero.
Figure 1. Structures of pentalenes and calculated wavelengths of
photoexcitation.
Transition-metal-catalyzed couplings are most commonly
used for the synthesis of arenopentalenes.4 Saito synthesized
bis(trimethylsilyl)-substituted dibenzopentalene by the reduc-
tion of trimethylsilylethynylbenzene with lithium and success-
fully isolated the di- and monoanions of dibenzopentalene.5
More recently, Xi synthesized a variety of pentalenes by treating
7a
1,4-diiodo-1,3-butadiene with t-BuLi/Ba[N(SiMe3)2]2 and
Rieke Ca.7b We reported new methodologies for the syntheses
of 5,10-unsymmetrically substituted dibenzopentalenes by
successive additions of a nucleophile and an electrophile to
dibenzocyclooctadiyne 5 (Sondheimer−Wong diyne)10 (reac-
tion 1 in Scheme 1)8a and by nucleophilic substitution of halo-
substituted pentalene 6 (reaction 2).8c
Received: May 2, 2015
Published: June 8, 2015
© 2015 American Chemical Society
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DOI: 10.1021/acs.orglett.5b01293
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Organic Letters
Letter
Scheme 1. Syntheses of 5,10-Substituted Dibenzopentalenes
Scheme 4. Elimination of LiH in Substitution of 9
that, in the substitution of diethylamino pentalene 9 with BuLi,
lithium hydride might have been generated, which then reduced
the aldehyde.11,12
This double amination protocol also served in the synthesis
of diamino-benzonaphthopentalene 11. When benzonaphtho-
cyclooctadiyne 12 was treated with lithium methyl(phenyl)-
amide, the desired pentalene 11 was obtained in 79% yield
(Scheme 5).
Our initial synthetic plan for 1a using dinaphthocyclo-
octadiyne 7 as a starting compound is shown in Scheme 2. This
Scheme 2. Initial Synthetic Plan for 1a
Scheme 5. Double Amination of 12
In light of these preliminary results, the addition of lithium
ethyl(phenyl)amide to dinaphthocyclooctadiyne 7 was inves-
tigated (Scheme 6). Because dinaphthocyclooctadiyne 7 is
synthetic route of 1a involves three transformations: (i)
nucleophilic addition of lithium amide to the alkyne moiety
of 7 followed by transannulation; (ii) bromination of the
resulting pentalene anion (similar to reaction 1); and (iii)
substitution of the bromine with lithium amide (similar to
reaction 2).
Scheme 6. One-Shot Synthesis of 1b
To optimize the reaction conditions for step (i),
dibenzocyclooctadiyne 5 was treated with lithium methyl-
(phenyl)amide as a model reaction (Scheme 3). Surprisingly,
Scheme 3. Double Amination of 5
when 1.5 equiv of PhMeNLi and PhMeNH were added to a
THF solution of 5, diamino-substituted dibenzopentalene 3a
was obtained in 30% yield along with the expected monoamine
derivative 8 (37%). When the reagent amounts were increased
(PhMeNLi (2.2 equiv)/PhMeNH (1.8 equiv)), 3a was
obtained as the sole product in 79% yield. Similarly, methoxy-
and chloro-substituted derivatives 3b and 3c were synthesized
in 72% and 42% yields, respectively.
To shed light on the mechanism of this novel double
amination, diethylamino pentalene 9 was treated with 1.0 equiv
of BuLi followed by 3.0 equiv of 2-naphthaldehyde (Scheme 4).
In this reaction, butyl- and diethylamino-substituted pentalene
10 and 2-naphthyl methanol were obtained in 35% and 27%
yields, respectively. Because the latter product could be
prepared from the reduction of 2-naphthaldehyde, it is assumed
poorly soluble due to its highly expanded π-system,13 7 was
generated in situ by treating the cyclic vinylsulfone precursor 14
with lithium amide. Thus, the diyne obtained was used in the
following transformations without purification.14 When the
cyclic vinylsulfone 14, which had been prepared from the
corresponding formylsulfone 13, was treated with PhEtNLi (8.0
equiv)/PhEtNH (6.0 equiv) in THF, the desired diamino-
substituted dinaphthopentalene 1b was obtained in 56% yield.
Remarkably, the process, which was composed of a series of
transformations including (1) the elimination of PhSO2H
affording dinaphthocyclooctadiyne 7, (2) the addition of
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Organic Letters
Letter
PhEtNLi to the in situ-prepared dinaphthocyclooctadiyne 7
followed by (3) the subsequent transannulation, (4) the
protonation of the resulting pentalene anion 15, (5) the
nucleophilic addition of PhEtNLi to the resulting pentalene 16,
and (6) the elimination of lithium hydride, proceeded smoothly
in a one-shot manner. It should be noted that the 56% overall
yield in the six steps corresponds to an average yield of 91% for
each step despite the demanding reaction conditions. By
changing the lithium amide, the corresponding diamino-
substituted dinaphthopentalenes 1c−f were obtained in
moderate yields. The structure of bisaminopentalene 1b was
confirmed by single-crystal X-ray analysis (Figure S1). The
bisaminopentalene 1b exhibits a monoclinic crystal system
(P21/n) with the center of symmetry residing on the midpoint
of C1−C1′.
spectra were recorded. When the dinaphthopentalenes 1c−f
were irradiated with UV light in toluene, all the derivatives
emitted fluorescence, although the emission quantum yields
were less than 0.03. The emission maxima of 1c, 1e, and 1f
were observed around 580 nm, and the emission of
methoxyphenyl derivative 1d was at 594 nm (Figure 2 inset,
Table 1). To gain further insight into the photochemistry of
1c−f, the HOMO and LUMO of 1a were investigated at the
B3LYP/6-31G(d) level. The results indicated that, in 1a, the
HOMO was expanded over the dinaphthopentalene moiety
and two phenyl groups through the lone pairs of amino
nitrogens (Figure 3a). In contrast, the LUMO orbital was
The UV−vis absorption spectra of these four pentalenes 1c−
f were recorded in CH2Cl2 (Figure 2). Table 1 summarizes the
Figure 3. (a) HOMO and (b) LUMO of 1a.
located mainly on the dinaphthopentalene core (Figure 3b).
Fragment molecular orbital (FMO) analysis revealed that the
HOMO(135) of 1a was composed by a linear combination of
the HOMO(78) of the dinaphthopentalene (DNP) fragment
and the LUMO(58) of a pair of PhMeN fragments, while the
LUMO(136) of 1a was composed by the LUMO+1(80) of
DNP and HOMO(57) of PhMeN fragments (Figure S2). In
1a, the symmetries of the HOMO and LUMO are ag and au,
respectively, and the HOMO−LUMO transition (S1, Au) is
allowed, enabling the photoluminescence of 1c−f.15 Nucleus-
independent chemical shifts (NICS(1)) were also computed to
survey the (anti)aromaticity in 1a (Figure S3). Naphtho
moieties maintained the aromaticities (NICS(1) values =
−10.3, −8.2), and the pentalene core maintained antiaroma-
ticity despite the substitution of a pair of amino groups
(NICS(1) values = 1.4).16
In summary, photoluminescent diamino-substituted penta-
lenes were synthesized. The synthesis was realized by
employing Sondheimer−Wong diynes as key starting materials.
The integration of six steps including a novel diamination
process led to the straightforward synthesis of the desired
compounds. Thus, the bisaminopentalenes obtained emitted
photoluminescence when irradiated with UV light in toluene.
Further synthesis of the amino-pentalenes and their application
to organic materials is under investigation, particularly with the
aim of increasing the quantum yield of photoluminescence.
Figure 2. UV−vis absorption (CH2Cl2, 1.0 × 10−4 M) and
photoluminescence spectra (inset, toluene, 9.7 × 10−7 M) of 1c−f.
spectral data and their plausible excitation wavelengths along
with the oscillator strengths, which were calculated for the first
excitation energies at the B3LYP/6-31G(d)//B3LYP/6-
31G(d) level. All the derivatives 1c−f exhibited weak and
strong absorption bands centered at around 510 (ε < 23 ×
1000) and 336 nm (ε > 63 × 1000), respectively. The methoxy
phenyl- and naphthyl-substituted derivatives 1d and 1f
exhibited slight bathochromic shifts in comparison with 1c
and 1e; for instance, the longest wavelength of the absorption
bands were observed at 519 and 514 nm for 1d and 1f,
respectively, and at 507 and 506 nm for 1c and 1e, respectively.
These absorption bands around 510 nm were consistent with
the calculated wavelengths for the first excitation of 1c−f and
could thus be characterized as HOMO−LUMO transitions
within these molecules.
As the ab initio calculations suggested that HOMO−LUMO
transitions were allowed in 1c−f, their photoluminescence
a
b
c
Table 1. Summarized UV−vis Absorption and Photoluminescence Data and TDDFT Calculations of 1c−f
1c
1d
1e
1f
λmax [nm] (εmax ×1000 [L mol−1 cm−1])
507 (22)
336 (103)
521 (0.30)
575
519 (18)
334 (71)
544 (0.30)
594
506 (21)
336 (102)
522 (0.31)
572
514 (17)
336 (63)
531 (0.70)
577
d
first excitation [nm] (f)
e
Emax [nm]
a
b
c
In CH2Cl2, 1.0 × 10−4 M. In toluene, 9.7 × 10−7 M. Calculations were performed for the corresponding ArMeN derivatives at the B3LYP/6-
d
e
31G(d)//B3LYP/6-31G(d) level. Oscillator strength f. Photoluminescence quantum yields (ΦF) of 1c−f were <0.03.
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Organic Letters
Letter
(b) Zhang, H.; Karasawa, T.; Yamada, H.; Wakamiya, A.; Yamaguchi,
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(7) (a) Li, H.; Wang, X.-Y.; Wei, B.; Xu, L.; Zhang, W.-X.; Pei, J.; Xi,
Z. Nat. Commun. 2014, 5, 4508. (b) Li, H.; Wei, B.; Wu, L.; Zhang,
W.-X.; Xi, Z. Angew. Chem., Int. Ed. 2013, 125, 11022.
ASSOCIATED CONTENT
■
S
* Supporting Information
Experimental details, characterization of all the products, DFT
results, oxidation and reduction potentials, and crystallographic
data for 1b (CIF, CCDC 1011864). The Supporting
Information is available free of charge on the ACS Publications
website at DOI: 10.1021/acs.orglett.5b01293.
(8) (a) Babu, G.; Orita, A.; Otera, J. Chem. Lett. 2008, 37, 1296.
(b) Xu, F.; Peng, L.; Orita, A.; Otera, J. Org. Lett. 2012, 14, 3970. For
nucleophilic substitution of halopentalenes: (c) Xu, F.; Peng, L.;
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(9) Triazapentalene; Namba, K.; Mera, A.; Osawa, A.; Sakuda, E.;
Kitamura, N.; Tanino, K. Org. Lett. 2012, 14, 5554. See refs 4b, f for
dianthracenopentalenes.
(10) For syntheses of Sondheimer−Wong diynes (a) Xu, F.; Peng,
L.; Shinohara, K.; Morita, T.; Yoshida, S.; Hosoya, T.; Orita, A.; Otera,
J. J. Org. Chem. 2014, 79, 11592. (b) Chaffins, S.; Brettreich, M.; Wudl,
F. Synthesis 2002, 1191. (c) Man, Y.-M.; Mak, T. C. W.; Wong, H. N.
C. J. Org. Chem. 1990, 55, 3214. (d) Wong, H. N. C.; Garratt, P. J.;
Sondheimer, F. J. Am. Chem. Soc. 1974, 96, 5604.
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: ktanaka@moleng.kyoto-u.ac.jp.
*E-mail: akashi@rins.ous.ac.jp.
*E-mail: orita@dac.ous.ac.jp.
Notes
(11) Nuclephilic substitution of hydrogen in aromatic compounds
was reported. (a) Terrier, F. Nucleophilic Aromatic Displacement; Verlag
Chemie, Weinheim, 1991. (b) Chupakhin, O. N.; Charushin, V. N.;
van der Plas, H. C. Nucleophilic Aromatic Substitution of Hydrogen;
Academic Press: San Diego, CA, 1994. (c) Makosza, M.;
Wojciechowski, K. Chem. Rev. 2004, 104, 2631.
(12) When naphthalenecarboaldehyde was treated with commercially
available LiH (Alderich or TCI), no formation of 2-naphthylmethanol
was observed. Similar results had been reported by Ashby: LiH which
was freshly prepared from hydrogenolysis of t-BuLi could reduce
benzophenone although commercial LiH did not. Ashby, E. C.;
Noding, S. A. J. Org. Chem. 1980, 45, 1041.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by a Grant-in-Aid for Scientific
Research on Innovative Areas “Organic Synthesis based on
Reaction Integration. Development of New Methods and
Creation of New Substances” (No. 2105), a matching fund
subsidy for private universities from the Ministry of Education,
Culture, Sports, Science and Technology, Japan, JSPS through
its “Funding Program for World-Leading Innovative R&D on
Science and Technology (FIRST Program)” and KAKENHI
(15K05440), and Okayama Prefecture Industrial Promotion
Foundation.
(13) When 14 was treated with LDA, the formation of 7 was
observed on TLC analysis, but the isolation of 7 was unsuccessful
because of its poor solubility.
(14) For reviews of space-integrated one-pot reactions: (a) Yoshida,
J.; Saito, K.; Nokami, T.; Nagaki, A. Synlett 2011, 1189. (b) Suga, S.;
Yamada, D.; Yoshida, J. Chem. Lett. 2010, 39, 404.
(15) Oxidation and reduction potentials electrochemically recorded
for 1c-f, 3a, and 11 were shown in the Supporting Information.
(16) Calculations of NICS(1) values for dinaphthopentalene
presented 2.5 for the pentalene core and −7.1 and −10.0 for the
naphtho moieties.
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