Three-bond breaking of cyclic anhydrides: Easy access to polyfunctionalized naphthalenes and phenanthrenes

Article abstract of DOI:10.1021/ol401318v

Benzannulation of phthalic anhydrides with alkynes to polyfunctionalized naphthalenes and phenanthrenes was confirmed to be straightforward using a palladium catalytic system. Sequential liberation of CO₂ and CO occurred via oxidative decomposition of anhydride. In the case of 1,8-naphthalenedicarboxylic anhydrides, both aryls were encompassed in the annulation reaction to afford acenaphthylenes.

Full text of DOI:10.1021/ol401318v

ORGANIC
LETTERS
XXXX
Vol. XX, No. XX
000–000
Three-Bond Breaking of Cyclic
Anhydrides: Easy Access to
Polyfunctionalized Naphthalenes
and Phenanthrenes
Farnaz Jafarpour,* Hamideh Hazrati, and Sorour Nouraldinmousa
School of Chemistry, College of Science, University of Tehran, 14155-6455 Tehran, Iran
jafarpur@khayam.ut.ac.ir
Received May 11, 2013
ABSTRACT
Benzannulation of phthalic anhydrides with alkynes to polyfunctionalized naphthalenes and phenanthrenes was confirmed to be straightforward
using a palladium catalytic system. Sequential liberation of CO2 and CO occurred via oxidative decomposition of anhydride. In the case of 1,8-
naphthalenedicarboxylic anhydrides, both aryls were encompassed in the annulation reaction to afford acenaphthylenes.
Polycyclic aromatic hydrocarbons (PAHs) such as
naphthalene and phenanthrene derivatives are an impor-
tant class of materials because of their application in mate-
rial science, nanotubes, light emitters, semiconductors,
light-absorption dyes, and liquid crystals.1 In addition,
polyfunctionalized PAHs have attracted much attention
because of their solubility, stability, and enhanced charge
transfer and fluorescence properties.2 Accordingly, the
chemists continue to devise new synthetic methods to
efficiently construct these structural motifs. Among var-
ious synthetic routes to π-conjugated naphthalenes,3
(4) Recent examples: (a) Liu, H.; Cao, L.; Fossey, J. S.; Deng, W.-P.
Chem. Commun. 2012, 48, 2674–2676. (b) Ilies, L.; Matsumoto, A.;
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Oishi, S.; Fujii, N.; Ohno, H. J. Org. Chem. 2012, 77, 4907–4916. (b)
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r
10.1021/ol401318v
XXXX American Chemical Society

homologation of mono-4 or difunctionalized5 arenes have
attracted much attention. Cyclotrimerization of arynes,
benzannulation of biaryls, and cyclization of certain di-
arylethenes are developed synthetic strategies to phenan-
threnes as well.6 Limited functional group compatibility,
low regioselectivity, and harsh reaction conditions for the
in situ generation of arynes and the requisite use of
prefunctionalized precursors are some drawbacks of the
stated methods.
anhydrides with alkynes to form isocoumarins (Scheme 1,
path a).9 They also developed the reaction to allenes to
construct δ-lactones.10 We now report our new findings
that sterically hindered polycyclic aromatic hydrocarbons
such as naphthalenes and phenanthrenes can be produced
via consecutive decarboxylativeÀdecarbonylative cross-
coupling of phthalic anhydrides followed by alkyne inser-
tion using palladium in place of nickel (Scheme 1, path b).
On the other hand, carboxylic anhydrides as cheap, safe,
and widely accessible starting materials are precious com-
ponents in metal-catalyzed cross-coupling reactions. In-
sertion of low-valent late transition metals into the
carbonylÀoxygen bond and further CO liberation should
be one of the most useful transformations for the regiose-
lective construction of CÀC bonds.7
Scheme 1. Coupling of Phthalic Anhydrides with Alkynes
Despite the high potential, anhydrides have rarely been
added to the substrate scope of palladium-catalyzed de-
carbonylative transformations.8 Furthermore, there is no
precedent for consecutive decarboxylativeÀ decarbonyla-
tive cross-coupling of cyclic anhydrides via a palladium-
benzyne intermediate. Recently, Kurahashi reported a
nickel-catalyzed decarbonylative cycloaddition of phthalic
This protocol features attractive synthetic aspects such
as employment of inexpensive anhydrides, mild reaction
conditions, and various functional group tolerances.
Furthermore, it is an unprecedented construction of a
PdÀbenzyne intermediate from a cyclic anhydride as most
disubstituted benzyne precursors are unsymmetrical.11
Extrusion of both CO2 and CO molecules under mild
reaction conditions and lower temperatures12 provides a
straightforward and experimentally simple new route to
either phenanthrene or naphthalene derivatives from
phthalic anhydrides, depending on the reaction stoichio-
metry as well as acenaphthylene derivatives in the case of
naphthalenedicarboxylic anhydride. Furthermore, this
protocol opens the opportunity for the waste-minimized
construction of PAHs with only volatile side products.
To begin we attempted the addition of anhydride 1a to
diphenylacetylene 2a applying reaction conditions in a
similar way to the pioneering work of Stephan and de
Vries for the decarbonylative Heck reaction of acid anhy-
drides (Table 1, entry 1):8o However this resulted in the
formation of only traces of the desired naphthalene 3a.
Further optimization showed that addition of a phosphine
ligand and 2 equiv of Ag2CO3 slightly improved the yield
(entry 2). Among the various palladium sources examined,
PdCl2 showed superior catalytic reactivity (entries 2À4).
The catalytic efficiency was further improved when
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B
Org. Lett., Vol. XX, No. XX, XXXX

Ag2CO3 was replaced with K2CO3 (entry 5). Screening
reactions with respect to additives and solvents proved
TBAB and DMF as the most effective ones, respectively
(entries 6À12). A slow dropwise addition of alkyne also
proved to be effective in reducing the alkyne polymeriza-
tion side reaction and improving the yield of phthalic
anhydride benzannulation (entry 10). The control experi-
ment in the absence of the catalyst resulted in the recov-
ery of starting materials (see Supporting Information).
Using PdCl2 (10 mol %), K2CO3 (2.0 equiv), and TBAB
(20 mol %) in DMF at 140 °C for 2 h led to the formation
of the highly substituted naphthalene 3a in 78% yield.
Scheme 2. Palladium Catalyzed Benzannulation of Phthalic
Anhydrides with Alkynes to Construct Naphthalenesa
Table 1. Optimization of Catalyzed Benzannulation Reactiona
entry
[Pd]
base
add.
solv.
yield (%)b
1c
2
PdCl2
;
NaBr
NaBr
NaBr
NaBr
NaBr
ZnCl2
LiOAc
TBAB
TBAB
TBAB
TBAB
TBAB
NMP
11
PdCl2
Ag2CO3
Ag2CO3
Ag2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
NMP
28
3
Pd(OAc)2
Pd(acac)2
PdCl2
NMP
20
4
NMP
10
5
NMP
47
6
PdCl2
NMP
37
a Optimized conditions. bReaction conditions: Pd(OAc)2 (10 mol %),
PPh3 (20 mol %), Ag2CO3 (2 equiv) in NMP (0.2 M) at 160 °C for 24 h.
7
PdCl2
NMP
30
8
PdCl2
NMP
50
9
PdCl2
toluene
DMF
DMSO
Dioxane
62
10
11
12
PdCl2
PdCl2
70 (78)d
55
three possible regioisomeric products 3i with a 63% yield.
Notably, an anhydride bearing two chloride substituents
went through benzannulation and afforded 3j with intact
halo groups providing an opportunity for the construction
of highly functionalized naphthalenes. A sterically hin-
dered anhydride bearing a tert-butyl group also tolerated
the reaction conditions to afford naphthalene 3k in 65%
yield. Finally, our attempts to extend the scope of the
reaction to the phthalic anhydride bearing a nitro group
was not successful and only a trace of the desired naphtha-
lene 3l was obtained. A nonaromatic precursor such as
maleic anhydride and dialkyl acetylenes proved to be
ineffective in this annulation reaction.
Intriguingly, we found that naphthalenedicarboxylic
anhydride 4 participated in a selective benzannulation
reaction with diphenylacetylene to provide 1,2-diphenyla-
cenaphthylene 5a in excellent yield (Scheme 3). The annu-
lation reactions also proceeded smoothly with dialkyl
acetylene derivatives leading to the construction of dialkyl
acenaphthylenes 5b and 5c in satisfactory yields. These
cyclopentene-fused polycyclic aromatic hydrocarbons are
useful intermediates in the construction of curve-shaped
PAHs.13
PdCl2
10
a Reaction conditions: Phthalic anhydride (0.1 mmol, 1 equiv), diphe-
nylacetylene (3 equiv), palladium catalyst (10 mol %), PPh3 (20 mol %),
base (2 equiv), additive (20 mol %), solvent (0.2 M), 140 °C, 24 h.
b Isolated yields. c Ligand-free. d The reactionwas conducted for 2 h. Yield
in parentheses refers to a 2 h slow dropwise addition of alkyne.
Having thus found the optimized reaction condition for
the construction of tetraphenyl substituted naphthalene,
we next investigated the effect of electronic and structural
variations of both substrates. Scheme 2 outlines the scope
of the benzannulation reaction where both electron-rich
and -deficient phthalic anhydrides were well tolerated.
Phthalic anhydrides containing methyl groups afforded
the desired naphthalenes 3b and 3d in 67À81% yields.
The dihalogenated anhydride 1c also survived the
reaction conditions and afforded 3c as a good partner
for further functionalization in moderate yield. 1,2-Di-p-
tolylethyne 2b was employed next, and an up to 80% yield
of the desired naphthalene 3e was gratefully obtained.
Alkynes with electron-withdrawing methyl- and ethyles-
ter groups 2c and 2d also resulted in tetraalkyl ester
substituted naphthalenes 3f, 3g, and 3h albeit in lower
yields. This would provide multiple points for further
synthetic diversification. Employing an asymmetric aryl
alkyl acetylene 2e pleasingly resulted in only one of the
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Org. Lett., Vol. XX, No. XX, XXXX
C

Scheme 3. Annulation Reactions of Diphenylacenaphthylene
Scheme 4. Palladium Catalyzed Benzannulation of Phthalic
Anhydrides with Alkynes To Construct Phenanthrenesa
During the course of these studies, we discovered that
with slightly altered reaction conditions, phenanthrenes
were constructed (Scheme 4). Benzannulation of anhy-
dride 1a with a reduced amount of alkyne 2a and increased
amount of solvent led to 9,10-diphenyl phenanthrene 6a
in 53% yield. With methyl substituted anhydride, a mix-
ture of the regioisomeric products 6b were obtained
with no selectivity. We were pleased to see that dialkyl
acetylene derivatives which usually display lower reac-
tivity compared to diaryl acetylenes14 were also tolerated
under the reaction conditions and selectively afforded
9,10-dialkyl substituted phenanthrenes 6cÀ6e in yields
exceeding 60%. Reduced amounts of DMAD alsoresulted
in the corresponding phenanthrene albeit in a lower yield.
p-Tolyl-substituted alkynes also afforded PAHs 6g and 6h
in good yields.
a Reaction conditions: Anhydride (0.1 mmol), alkyne (2 equiv), PdCl2
(10 mol %), PPh3 (20 mol %), K2CO3 (2 equiv), TBAB (20 mol %),
DMF(0.1M), 140°C for 24 h. bReaction conditions: Pd(OAc)2 (10mol%),
PPh3 (20 mol %), Ag2CO3 (2 equiv), NMP (0.1 M), 160 °C for 24 h.
A plausible mechanism for the benzannulation reaction
of anhydrides is proposed in Scheme 5. Oxidative addition
of palladium to the carbonylÀoxygen bond leads to the
formation of acylpalladium carboxylate metallacycle A as
the key intermediate. Next, to discriminate between two
competitive paths of CO2 or CO extrusion, indenone 7 was
isolated in the course of the reaction (path a). The evidence
suggests that CO2 extrusion followed by alkyne insertion
precedes CO extrusion. Finally, CO liberation followed by
the insertion of the second alkyne molecule leads to
naphthalene 3 (path b). On the other hand, our preliminary
investigation revealed that despite the participation of 1,8-
naphthalic anhydride in this reaction, the possibility of
intermediate formation of an aryne with cyclic anhydrides
could not be definitely ruled out. An aryne trimerization
of anhydride 1b proceeded in the absence of an alkyne
coupling partner to afford triphenylene 8 in 31% isolated
yield.
Scheme 5. Plausible Mechanism
In conclusion, we have developed a new method for
decarboxylative and decarbonylative addition of cyclic
anhydrides to alkynes. The protocol allows for the waste-
minimized construction of sterically congested naphtha-
lenes and phenanthrenes employing a palladium catalyst.
The practical construction of disubstituted acenaphthy-
lenes is also realized using 1,8-naphthalenedicarboxylic
anhydride. The reaction shows generality and good
functional group tolerance. Further efforts to expand the
scope of the reaction are ongoing.
Supporting Information Available. Detailed experimen-
tal procedures and spectroscopic data for all compounds.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(14) Platon, M. L.; Amardeil, R.; Djakovitchb, L.; Hierso, J. C.
Chem. Soc. Rev. 2012, 41, 3929–3968.
The authors declare no competing financial interest.
D
Org. Lett., Vol. XX, No. XX, XXXX