Synthesis of 8,9-disubstituted fluoranthenes by domino two-fold Heck/electrocyclization/dehydrogenation of 1,2-dibromoacenaphthylene

Article abstract of DOI:10.1016/j.tetlet.2011.02.032

Fluoranthenes were prepared by domino two-fold Heck/electrocyclization/ dehydrogenation reactions of 1,2-dibromoacenaphthylene.

Full text of DOI:10.1016/j.tetlet.2011.02.032

Tetrahedron Letters 52 (2011) 1888–1890
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis of 8,9-disubstituted fluoranthenes by domino two-fold
Heck/electrocyclization/dehydrogenation of 1,2-dibromoacenaphthylene
Ihsan Ullah a, Muhammad Nawaz a, Alexander Villinger a, Peter Langer a,b,
⇑
a Institut für Chemie, Universität Rostock, Albert-Einstein-Str. 3a, 18059 Rostock, Germany
b Leibniz-Institut für Katalyse e. V. An der Universität Rostock, Albert-Einstein-Str. 29a, 18059 Rostock, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Fluoranthenes were prepared by domino two-fold Heck/electrocyclization/dehydrogenation reactions of
1,2-dibromoacenaphthylene.
Received 11 December 2010
Revised 5 February 2011
Accepted 7 February 2011
Available online 12 February 2011
Ó 2011 Published by Elsevier Ltd.
Keywords:
Catalysis
Palladium
Heck reaction
Domino reaction
Fluoranthenes
Polycyclic aromatic hydrocarbons (PAHs) are formed by incom-
plete combustion of organic materials.1a,b They possess useful appli-
cations in the field of material sciences, due to their optical
properties, thermo- and light-sensitivity, conductivity, liquid crys-
tal properties, and their heat and corrosion resistance.2a–f Polycyclic
aromatic hydrocarbons containing a five-membered ring constitute
an important subclass of PAHs.3a–e Fluoranthene, the parent core
structure of such molecules,4 is the third most abundant constituent
of coal tar (after naphthalene and phenanthrene).5a–d Fluoranthene
derivatives are also found in oil, cigarette smoke and smoke derived
from open fires, smoked and grilled foods, and in waste water.6
cycloadditions of acenaphthene with thiophenes or 2,3,4,5-tetra-
phenylcyclopentadienone (tetracyclone). Despite their great util-
ity, some syntheses lack general applicability (with regard to the
substitution pattern) or suffer from harsh conditions and/or low
yields. Therefore, the development of alternative synthetic strate-
gies to substituted fluoranthenes is an important task.
Benzene derivatives have been prepared by double Heck reac-
tions of aliphatic 1,2-dibromoalkenes to give hexatrienes and sub-
sequent thermal 6p
-electrocyclization of the latter.12 In recent
years, we have studied the synthesis of various heterocycles, such
as carbazoles, benzothiophenes, dibenzofurans, and benzimidaz-
oles, by the application of this approach.13 The electrocyclization
can proceed smoothly, if the central double bond of the triene sys-
Fluoranthenes have been used as a ligand in chromium(0)-p-com-
plexes.7a,b Fluoranthene derivatives possess characteristic lumines-
cence properties such as anomalous fluorescence quenching,5a–d
and have been used as molecular sensors5e and organic semiconduc-
tors.5f Some fluoranthene derivatives have been employed as organ-
ic light emitting devices,5g as a dopant of molecular crystals for laser
spectroscopy,5h as efficient blue-light-emitting electroluminescent
devices,5i and as dyes.5j Parent fluoranthenes serve as synthetic
building blocks.8a,b Some fluoranthene derivatives have been
reported to possess antiviral activities.9 It should be noted that
fluoranthene constitutes a partial structure of corannulene and,
thus, of C60 fullerene and its higher homologues.10a,b
tem is not involved in a stable aromatic 6p system. It occurred to us
that 1,2-dibromoacenaphthene might be an interesting substrate
for domino Heck/electrocyclization reactions and could allow a
convenient synthesis of fluoranthene derivatives. While Suzuki–
Miyaura reactions of 1,2-dibromoacenaphthene are known,14 Heck
reactions have, to the best of our knowledge, not been reported so
far.15 Herein, we report that domino two-fold Heck/electrocycliza-
tion/dehydrogenation reactions of 1,2-dibromoacenaphthene pro-
vide a convenient access to 8,9-disubstituted fluoranthenes which
are not readily available by other methods.
A number of methods for the synthesis of fluoranthenes have
1,2-Dibromoacenapthylene (2) was prepared, following a
been reported.11 For example, they have been prepared by [4+2]
known procedure,16 by reaction of 1,2-dihydroacenaphthylene
(1) with NBS and dibenzoyl peroxide (Scheme 1).
The Heck reaction of 2 with acrylates and styrenes afforded the
fluoranthenes 3a–q in 54–82% yields (Scheme 2, Table 1). The for-
mation of the products can be explained by two-fold Heck reaction
⇑
Corresponding author. Fax: +49 381 4986412.
E-mail address: peter.langer@uni-rostock.de (P. Langer).
0040-4039/$ - see front matter Ó 2011 Published by Elsevier Ltd.
doi:10.1016/j.tetlet.2011.02.032

I. Ullah et al. / Tetrahedron Letters 52 (2011) 1888–1890
1889
Table 2
Br
Br
Optimization of the synthesis of 3e and 3i
i
No.
3
T (°C)
Catalyst
Solvent
t (h)
Yielda (%)
b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
e
e
e
e
e
e
e
e
e
e
i
i
i
i
i
i
i
90
90
90
110
90
110
90
110
90
90
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
X-Phos/Pd(OAc)2
X-Phos/Pd(OAc)2
X-Phos/Pd(OAc)2
X-Phos/Pd(OAc)2
X-Phos/Pd(OAc)2
X-Phos/Pd(OAc)2
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
X-Phos/Pd(OAc)2
X-Phos/Pd(OAc)2
X-Phos/Pd(OAc)2
X-Phos/Pd(OAc)2
DMF
36
36
36
48
18
36
12
8
12
36
36
36
36
48
36
12
8
—
—
-
b
Dioxane
MeCN
DMF
Dioxane
MeCN
DMF
2
1
b
b
—
Scheme 1. i, NBS, CCl4, dibenzoyl peroxide, reflux, 2 h.
Traces
c
—
82
c
DMF
—
R
R
MeCN
Benzene
DMF
35
R
b
Br
Br
—
—
—
—
b
90
i
b
110
110
110
90
110
120
DMF
b
Dioxane
Dioxane
DMF
DMF
DMF
Traces
b
—
2
3a-q
66
c
—
a
b
c
Yields of isolated products.
No conversion.
Formation of a complex mixture.
R
R
R
R
A
B
Scheme 2. Synthesis of 4a–o. Reagents and Conditions: (i) Method 1, Pd(OAc)2
(5 mol %), X-Phos (10 mol %), NEt3, DMF, 90 °C, 12 h. Method 2, Pd(OAc)2 (5 mol %),
X-Phos (10 mol %), NEt3, DMF, 110 °C, 12 h.
Table 1
Synthesis of 3a–o
3
R
% (3)a Method 1
% (3)a Method 2
Tracesc
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
CO2Me
CO2Et
CO2nBu
CO2iBu
CO2tBu
CO2nHex
CO2(2-Ethylhexyl)
CO2iOct
4-MeC6H4
4-tBuC6H4
4-(MeO)C6H4
4-FC6H4
2-Pyr
68
73
77
81
82
69
71
65
b
—
—
b
Tracesc
Figure 1. Crystal structure of 3l.
Tracesc
b
—
—
—
b
The use of acetonitrile resulted in the formation of the desired
products, albeit, in low yields. The successful employment of
DMF can be explained by its polarity and high boiling point. As
the major side-product the formation of bis(alkenyl)acenaphth-
enes A was observed (5–10% by NMR of the crude product
mixture).
b
Traces
Traces
Traces
66
72
74
59
56
54
63
b
—
Traces
b
Ph
CH2Ph
—
—
Better yields were generally obtained for reactions of acrylates
(products 3a–h, 65–82% entries) than for styrenes (products 3i–
o, 54–74%). This can be explained by the fact that the double bond
of acrylates is more electron-deficient and thus more reactive than
the double bond of styrenes. Most of the products proved to be
fluorescence active.
b
a
b
c
Yields of isolated products.
Experiment not carried out.
Formation of complex mixture.
The structure of compound 3l was independently confirmed by
to give intermediate A, electrocyclization (B) and subsequent
dehydrogenation. The reaction conditions were optimised for the
synthesis of 3e (derived from an acrylate) and 3i (derived from a
styrene) (Table 2).17 The best yields of 3e and i were obtained
when Pd(OAc)2 was used as the catalyst together with the ligand
X-Phos and when the reaction was carried out at 90 °C in DMF.
The temperature played an important role. The reactions of acry-
lates were carried out at 90 °C (product 3e), while reactions of sty-
renes were performed at 110 °C (product 3i). A slight increase or
decrease of the temperature resulted in dramatically lower yields.
The reactions failed when Pd(PPh3)4 was used as the catalyst. The
choice of the solvent also played an important role. No conversion
was observed for nonpolar solvents such as benzene or toluene.
X-ray crystal structure analysis (Fig. 1).18
In conclusion, we have reported a new synthesis of fluoranth-
enes by domino two-fold Heck/electrocyclization/dehydrogenation
reactions of 1,2-dibromoacenaphthene. For electrocyclization reac-
tions to occur smoothly, the central double bond of the triene sys-
tem must not be involved in a stable aromatic 6 system. Because
the double bond C1–C2 of acenaphthene possesses the character
of an alkene, the electrocyclization proceeds in good yields.
Acknowledgements
Financial support by the State of Pakistan and by the DAAD
(HEC-DAAD scholarship for I. U.) is gratefully acknowledged.

1890
I. Ullah et al. / Tetrahedron Letters 52 (2011) 1888–1890
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m = 3051, 2980 (w), 1704 (m), 1453, 1391, 1257, 1160 (w), 1057, 971
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18. CCDC 811880 contain all crystallographic details of this publication and is
available free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html or can
be ordered from the following address: Cambridge Crystallographic Data
Centre, 12 Union Road, GB-Cambridge CB21EZ; Fax: (+44)1223-336-033; or
deposit@ccdc.cam.ac.uk.