Pd-Catalyzed Annulation of 1-Halo-8-arylnaphthalenes and Alkynes Leading to Heptagon-Embedded Aromatic Systems

Article abstract of DOI:10.1002/chem.201805746

A palladium-catalyzed heptagon-forming annulation reaction between 1-halo-8-arylnaphthalene and diarylacetylene is reported. The reaction is promoted using a catalytic system comprised of Pd(OAc)₂, moderately electron-deficient triarylphosphine P(4-ClC₆H₄)₃, and Ag₂CO₃ to afford benzo[4,5]cyclohepta[1,2,3-de]naphthalene derivatives in moderate to good yields, in preference to fluoranthene as a competing byproduct. Twofold annulation can also be achieved to access a novel heptagon-embedded polycyclic aromatic hydrocarbon compound.

Full text of DOI:10.1002/chem.201805746

A Journal of
Accepted Article
Title: Pd-Catalyzed Annulation of 1-Halo-8-arylnaphthalenes and
Alkynes Leading to Heptagon-Embedded Aromatic Systems
Authors: Jianming Yan, Md. Shafiqur Rahman, and Naohiko Yoshikai
This manuscript has been accepted after peer review and appears as an
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published online in Early View as soon as possible and may be different
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the VoR from the journal website shown below when it is published
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content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201805746
Link to VoR: http://dx.doi.org/10.1002/chem.201805746
Supported by

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Pd-Catalyzed Annulation of 1-Halo-8-arylnaphthalenes and
Alkynes Leading to Heptagon-Embedded Aromatic Systems**
Jianming Yan+, Md. Shafiqur Rahman+, Naohiko Yoshikai*
Abstract:
A
palladium-catalyzed heptagon-forming annulation
heptagons have been elusive.[9] Herein, we disclose
a
reaction between 1-halo-8-arylnaphthalene and diarylacetylene is
palladium-catalyzed heptagon-forming annulation reaction
between 1-halo-8-arylnaphthalene and diarylacetylene. The
reaction affords benzo[4,5]cyclohepta[1,2,3-de]naphthalenes
bearing a variety of aryl groups on the 7- and 8-positions, and
thus complements the scope of Lin/Kwong's annulation.
reported. The reaction is promoted using
a
catalytic system
electron-deficient
comprised
of
Pd(OAc)2,
moderately
and Ag2CO3
triarylphosphine
P(4-ClC6H4)3,
to
afford
benzo[4,5]cyclohepta[1,2,3-de]naphthalene derivatives in moderate
to good yields, in preference to fluoranthene as a competing
byproduct. Twofold annulation can also be achieved to access a
novel heptagon-embedded polycyclic aromatic hydrocarbon
compound.
(a) [2 + 2 + 2] annulation
R
R
R
R
X
H
R
R
cat. MLn
+
R
Polycyclic aromatic hydrocarbons (PAHs) are among
quintessential structural elements in functional molecules for
optoelectronic applications, and therefore the development of
efficient methods for the construction of PAHs from readily
available starting materials represents an important subject in
synthetic chemistry.[1] In this context, transition metal-catalyzed
annulation reactions of aromatic substrates with alkynes have
been extensively explored as means to achieve extension of the
π-system,[2] among which those involving C–H activation have
attracted significant attention due to the greater availability of the
starting materials. Thus, [2 + 2 + 2] annulation reactions of a
monofunctionalized benzene derivative with two molecules of
alkyne have been developed for the synthesis of naphthalene,
anthracene, and related acenes (Scheme 1a).[3] Meanwhile, [4 +
2] annulation reactions of a 2-functionalized biaryl with an alkyne
have been achieved to enable expedient synthesis of
R
X = halogen, metal, H etc.
(b) [4 + 2] annulation
R
cat. MLn
R
X
H
+
R
R
X = halogen, CO2H, metal
(c) This work: [5 + 2] annulation
Ar
Ar
Ar
cat. Pd–PAr3
Ag2CO3
Ar
X
H
+
phenanthrene-type
(Scheme 1b).[4,5]
hexagonal
polyaromatic
compounds
X = Br or I
Scheme 1. Transition metal-catalyzed alkyne annulations for π-extension.
Recently, PAHs that contain
a
seven-membered ring
comprised of all sp2-carbon atoms have gained increasing
attention for their warped structures that could lead to unique
optoelectronic properties.[6.7] However, the synthesis of such
heptagon-embedded PAHs usually requires multiple steps, and
direct construction of heptagons from simple and readily
available fragments has been rare. Recently, Lin, Kwong, and
coworkers disclosed a Pd-catalyzed three-component annulation
reaction of aryl iodide, 8-bromo-1-naphthoic acid, and
The present study commenced with a screening of reaction
conditions for the annulation of 1-bromo-8-phenylnaphthalene
(1a) and diphenylacetylene (2a) (Table 1). The reaction in the
presence of Pd(OAc)2 (10 mol%) and Ag2CO3 (1 equiv) in
dichloroethane at 80 °C afforded, after 18 h, the desired
heptagon product 3aa in a low yield of 18% (entry 1). The
addition of triphenylphosphine (30 mol%) decreased the yield of
3aa while affording a trace amount of fluoranthene 4 (entry 2).[10]
The use of less electron-donating triphenylarsine promoted full
conversion of 1a and improved the yield of 3aa to 59%, albeit
with increased amount (20%) of 4 (entry 3). At the reaction time
of 1.5 h, the yields of 3aa and 4 reached 29% and 21%,
respectively, indicating that the formation of 4 stopped at the
early stage. Moderately electron-deficient triarylphosphines such
as P(4-ClC6H4)3, P(3-ClC6H4)3, and C(4-FC6H4)3 were found to
promote the annulation to afford 3aa in up to 78% yield, while
suppressing the fluoranthene formation (entries 4–6). Note that
the reaction using P(4-ClC6H4)3 reached full conversion at 1.5 h
(entry 4). The annulation reaction became sluggish with more
electron-deficient phosphines such as P(4-CF3C6H4)3 and
norbornadiene
to
afford
a
heptagon-containing
benzo[4,5]cyclohepta[1,2,3-de]naphthalene derivative, in which
naphthalene and benzene rings are linked by a cis-ethenyl
(C2H2) bridge.[8] Except this report, annulative approaches to
[*]
Dr. J. Yan+, M. S. Rahman+, Prof. N. Yoshikai
Division of Chemistry and Biological Chemistry, School of Physical
and Mathematical Sciences
Nanyang Technological University
Singapore 637371, Singapore
E-mail: nyoshikai@ntu.edu.sg
These authors equally contributed to the work.
[+]
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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10.1002/chem.201805746
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P(C6F5)3 (entries 7 and 8), and no annulation was observed with
electron-rich P(4-MeOC6H4)3 (entry 9). Other monophosphines
such as tri(2-furyl)phosphine and SPhos did not improve the
reaction (entries 10 and 11). The reaction using AgOAc instead
of Ag2CO3 afforded 3aa in a slightly lower but comparable yield
(entry 12), while removal of Ag2CO3 resulted in sluggish
conversion (entry 13).
as
5-decyne,
1-phenyl-1-butyne,
and
diethyl
acetylenedicarboxylate failed to undergo the annulation with 1a
under the present conditions.
Table 2. Annulation of 1a with various diaryl alkynes.[a]
Pd(OAc)2 (10 mol%)
P(4-ClC6H4)3 (30 mol%)
Ag2CO3 (1 equiv)
Ar
Ar
Ar
Br
+
Table 1. Optimization of reaction conditions.[a]
DCE, 80 °C, 18 h
Ar
Pd(OAc)2 (10 mol%)
Ph ligand (30 mol%)
Ag2CO3 (1 equiv)
Ph
1a
2a–2k
3aa–3ak
Ph
Br
+
+
Entry
1
Ar
Product
Yield [%]
79
DCE, 80 °C, 18 h
Ph
Ph
3aa
3ab
3ac
3ad
3ae
3af
1a
Entry
2a
3aa
4
2
4-MeOC6H4
4-MeC6H4
4-Me3SiC6H4
4-ClC6H4
75 (68)[b]
63
Ligand[b]
Conv of 1a [%][b]
3aa [%][b]
4 [%][b]
3
1
None
45
18
0
4
58
2
PPh3
58
8
3
5
53
3
AsPh3
100 (60)
100 (100)
100
100
55
59 (29)
78 (75)
77
20 (21)
6
4-FC6H4
60
4
P(4-ClC6H4)3
P(3-ClC6H4)3
P(4-FC6H4)3
P(4-CF3C6H4)3
P(C6F5)3
3 (4)
3
7
4-F3CC6H4
3,4-(MeO)2C6H3
3-MeC6H4
2-MeOC6H4
2-thienyl
3ag
3ah
3ai
55
5
8
57[c]
67
6
65
0
9
7
37
4
10
11
3aj
77
8
29
15
0
3ak
70
9
P(4-MeOC6H4)3
P(2-furyl)3
SPhos
20
0
1
[a] Unless otherwise noted, the reaction was performed using 0.1 mmol of 1a
and 0.2 mmol of 2 according to the conditions in Table 1, entry 4. [b] The yield
of a 0.5 mmol-scale reaction is shown in the parentheses. [c] The reaction was
performed on a 0.6 mmol scale.
10
11
12[c]
13[d]
85
38
2
83
10
3
P(4-ClC6H4)3
P(4-ClC6H4)3
100
40
72
4
Next, a variety of 1-halo-8-arylnaphthalenes were tested for
the annulation with 2a (Scheme 2). The substrate bearing 4-
methoxyphenyl and iodo groups (1b) smoothly underwent the
annulation to afford the desired product 3ba in 66% yield. The
nonplanar structure of 3ba was unambiguously confirmed by X-
ray crystallographic analysis (see the box in Scheme 2).[11]
Likewise, naphthalene substrates bearing different para-
substituted phenyl groups (1c–1f) furnished the desired
annulation products 3ca–3fa in moderate to good yields. The
substrate bearing a meta-tolyl group (1g) underwent exclusive
annulation on the less hindered aryl C–H bond, thus affording
3ga as the single regioisomer. By contrast, the substrate bearing
a 2-naphthyl group (1h) afforded a mixture of the regioisomeric
products 3ha and 3ha' with low regioselectivity, which would
reflect the difficulty in controlling the regioselectivity of
naphthalene C–H palladation.[12] The ortho-tolyl-substituted
substrate reacted rather sluggishly (see 3ia), presumably due to
steric clash between the methyl group and the naphthyl ring.
The reaction tolerated the substrate bearing 4-pyridyl group,
albeit with low reaction efficiency (see 3ja).
30
0
[a] The reaction was performed using 0.1 mmol of 1a and 0.2 mmol of 2a. [b]
Determined by GC using n-tridecane as an internal standard. The conversion
and yield in the parentheses were determined at the reaction time of 1.5 h. [c]
AgOAc was used instead of Ag2CO3. [d] The reaction was performed in the
absence of Ag2CO3.
Having established the optimal catalytic system, various
diarylacetylenes were subjected to the annulation reaction with
1a (Table 2). Besides 2a (entry 1), diarylacetylenes bearing
electron-donating groups such as methoxy, methyl, and silyl
groups or electron-withdrawing groups such as halogen and
trifluoromethyl groups at the para positions participated in the
reaction to afford the corresponding products 3ab–3ag in
moderate to good yields (entries 2–7). Diarylacetylenes bearing
meta-substituents also afforded the desired products 3ah and
3ai in moderate yields (entries
8
and 9). Di(2-
methoxyphenyl)acetylene smoothly participated in the reaction
to afford 3aj in 77% yield (entry 10), while di(1-
naphthyl)acetylene reacted rather sluggishly (< 5% GC yield)
presumably due to steric hindrance. Di(2-thienyl)acetylene was
also amenable to the annulation, affording the product 3ak in
good yield (entry 11). Unfortunately, other types of alkynes such
Table 3. Annulation of various 1-aryl-8-halonaphthalenes with 2a.[a]
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(a)
R
R
Pd(OAc)2 (10 mol%)
P(4-ClC6H4)3 (30 mol%)
Ag2CO3 (1 equiv)
Ph
Pd(OAc)2 (20 mol%)
P(4-ClC6H4)3 (60 mol%)
Ag2CO3 (2 equiv)
Ph
Br
Ph
Ph
Ph
X
+
+
DCE, 80 °C, 18 h
Br
DCE, 80 °C, 18 h
Ph
5
2a
3ba–3ja
Ph
1b–1j
Ph
R
Ph
Me
Ph
Ph
3ba (R = OMe), 66%
3ca (R = Cl), 63%
3da (R = CF3), 85%
3ea (R = CN), 82%
3fa (R = COMe), 85%
Ph
Ph
Ph
6, 47%
3ga, 76%
(b)
OMe
OMe
Ph
Ph
Ph
Ph
Ph
Ph
Br
Ph
Ph
Ph
Ph
+
Me
as above
+
9a
1
Br
Ph
Ph
3ia, 12%
3ha + 3ha’, 74% (1.4:1)
Ph
N
Ph
Ph
OMe
OMe
7
8, 10%
Scheme 3. Attempts on twofold annulation.
3ja, 15%
(top view)
(side view)
3ba
Exposure of the heptagon products 3aa and 3ab to
DDQ/methanesulfonic acid, which is among typical conditions
for the Scholl reaction,[13] did not cause expected
dehydrogenative C–C coupling between the aryl substitutents or
between the aryl substituent and the benzo[4,5]cyclohepta[1,2,3-
de]naphthalene core. Instead, oxidative fragmentation and ring
contraction took place to afford 4H-benzo[de]anthracen-4-one
derivatives 9a and 9b in moderate yields.[11,14] Further
exploration of transformations of the present heptagon
compounds is under way.
Scheme 2. Pd-catalyzed annulation of various 1-halo-8-arylnaphthalenes (1b–
1j) with diphenylacetylene (2a). X = Br except for 1b (X = I). The products 3ha
and 3ha' were obtained as a mixture, and their ratio was determined by 1H
NMR (see the Supporting Information for more detail).
The present catalytic system proved also effective for
twofold annulation between a teraryl substrate 5 bearing two 1-
bromonaphthyl moieties and 2a, which afforded the double
heptagon product 6 in a respectable yield of 47% (Scheme 3a).
X-ray crystallographic analysis of 6 revealed its highly nonplanar
and Ci-symmetric structure and the lack of significant π-π
stacking in the crystal packing.[11] By contrast, we could not
detect a twofold annulation product in the reaction between 1,5-
dibromo-9,10-diarylanthracene 7 and 2a. The reaction gave
multiple products, among which only an unusual 1:3 coupling
product 8 could be isolated and unambiguously characterized by
X-ray analysis (Scheme 4b).[11] Thus, one of the two reaction
sites of 7 underwent the expected heptagon formation, while the
other site reacted with two molecules of diphenylacetylene to
give rise to the peculiar bridged polycyclic moiety through
cleavage of the C1–C9a bond of the anthracene moiety.
R
R
DDQ (2 equiv)
R
MeSO3H, CH2Cl2
rt, 12 h
O
3aa (R = H)
9a (R = H), 50%
3ab (R = OMe)
9b (R = OMe), 28%
Scheme 4. Dehydrogenative cyclization leading to an extended conjugated
system.
UV-vis absorption spectra of selected mono-heptagon
compounds in CH2Cl2 featured the longest wavelength
absorption maximum (λmax
) around 350–360 nm, showing
moderate impact of the peripheral substituents on λmax (see
Figures S7 and S8). None of them showed visible fluorescence
in dilute solution presumably due to nonradiative decay of the
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excited state through facile rotation of the aryl–aryl bonds. On
the other hand, the bis-heptagon compound 6 showed λmax of
284, 320, and 380 nm and moderate fluorescence at 558 nm (Φ
= 0.38) (Figure S9). All the heptagon compounds are more
distinctly emissive in the solid state, with λem of 489, 496, and
508 nm for 3ab, 3fa, and 6, respectively (Figure S10). The
aggregation-induced emission (AIE)[15] behavior of 3ab was also
observed using THF/water mixture samples (Figure S11). These
fluorescence behaviors would be ascribed to the nonplanar
geometry that prevents π-π stacking as well as the aryl–aryl
bonds that freely rotate in solution but are rotationally restricted
in the aggregated state.
subsequent C–H palladation of B and reductive elimination of C
occurred with lower barriers. The formation of D was endergonic
by 21.9 kcal mol–1. While reductive elimination of D was feasible
(ΔG‡ = 8.5 kcal mol–1), alkyne insertion into D required an
exceedingly higher barrier (ΔG‡ = 30.1 kcal mol–1). Thus, D is
unlikely to be responsible for the product 3, and the selectivity
between 3 and 4 would be determined by the competition
between alkyne insertion and C–H palladation pathways of A. In
agreement with this implication, the reaction of pentadeuterated
substrate [D5]-1a with 2a using AsPh3 or P(4-ClC6H4)3 resulted in
a markedly diminished yield of 4 (Scheme 6), as compared with
the reaction of parent 1a (Table 1, entries 3 and 4).
D4
D4
D5
Proposed reaction pathways of the present annulation
reaction are shown in Scheme 5. Oxidative addition of the C–Br
bond of 1 to Pd0, followed by halide abstraction by Ag2CO3,[3a]
would generate a naphthylpalladium species A (X = carbonate).
Insertion of the alkyne 2 into A and subsequent intramolecular
C–H palladation of the alkenylpalladium species B, presumably
via the concerted metallation-deprotonation mechanism, would
lead to an eight-membered palladacycle C. Finally, reductive
elimination of C would furnish the heptagon product 3 while
Pd(OAc)2 (10 mol%)
ligand (30 mol%)
Ag2CO3 (1 equiv)
Ph
Ph
Ph
Br
+
+
DCE, 80 °C, 1.5 h
Ph
[D5]-1a
[D4]-3aa
[D4]-4
2a
ligand = AsPh3
41%
81%
6%
0%
ligand = P(4-ClC6H4)3
regenerating Pd0. The species
A
could also undergo
Scheme 6. Reaction of pentadeuterated substrate [D5]-1a.
intramolecular C–H palladation to give
a
six-membered
palladacycle D. Reductive elimination of
D would afford
fluoranthene 4, while D might also undergo alkyne insertion into
either of the Pd–C bonds, leading to C or its isomer.
In summary, we have developed a palladium-catalyzed
annulation reaction between 1-halo-8-arylnaphthalenes and
diarylacetylenes. The reaction represents a rare example of
direct heptagon formation from simple aromatic precursors,
enabling facile preparation of PAHs with warped geometries.
Further extension of the scope of heptagon-forming annulation
and its application to the synthesis of novel heptagon-embedded
PAHs are underway.
1, Ag2CO3
3
[Pd0]
ΔG‡ = 1.7
AgBr
ΔG‡ = 8.5
4
Ph
ΔG‡ = 30.1
ΔG‡ = 35.6
[Pd]
[Pd]
Ph
[Pd]X
2
Acknowledgements
HX
D (21.9)
Ph
This work was funded by the Ministry of Education (Singapore)
and Nanyang Technological University (RG 114/15 and
MOE2016-T2-2-043). We thank Drs. Yongxin Li and Rakesh
Ganguly (Nanyang Technological University) for assistance with
X-ray crystallographic analysis, and Prof. Qichun Zhang and Dr.
Changjiang Yao (Nanyang Technological University) for
assistance with measurement of solid state fluorescence.
C (17.7)
A (0.0)
Ph
X[Pd]
2
HX
ΔG‡ = 21.6
ΔG‡ = 33.6
B (–3.2)
Keywords: polycyclic aromatic hydrocarbons • alkyne • C–H
Scheme 5. Proposed reaction pathways for the Pd-catalyzed annulation.
Relative free energies (in parentheses) and activation energies (kcal mol–1
were calculated for a model system with [Pd] = PdP(4-ClC6H4)3 and X = OAc.
)
activation • palladium • annulation
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phenylnaphthylpalladium complex A bearing P(4-ClC6H4)3 and
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energy (ΔG‡) of 33.6 kcal mol–1, which was slightly lower than
that of intramolecular C–H palladation of A (35.6 kcal mol–1).
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10.1002/chem.201805746
Chemistry - A European Journal
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Jianming Yan, Md. Shafiqur Rahman,
Naohiko Yoshikai*
Page No. – Page No.
Pd-Catalyzed Annulation of 1-Halo-8-
arylnaphthalenes and Alkynes
Leading to Heptagon-Embedded
Aromatic Systems
A palladium-catalyzed annulation reaction between 1-halo-8-arylnaphthalene and
diarylalkyne is reported. Using a moderately electron-poor triarylphosphine, the
reaction takes place in preference to fluoranthene formation, affording
benzo[4,5]cyclohepta[1,2,3-de]naphthalene derivatives in moderate to good yields.
Twofold annulation is also achieved to access a novel heptagon-embedded
polycyclic aromatic hydrocarbon.
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