Synthesis of a library of fluorescent 2-aryl-3-trifluoromethylnaphthofurans from naphthols by using a sequential pummerer-annulation/cross-coupling strategy and their photophysical properties

Article abstract of DOI:10.1002/chem.201201261

A library of 2-aryl-3-trifluoromethylnaphthofurans was synthesized with high efficiency from simple naphthols. In this synthesis, the Pummerer-type annulation of naphthols with 3-(2,2,2-trifluoroethylidene)-2,4-dithiapentane 2-oxide was followed by a cross-coupling of the resulting 2-methylthio-3- trifluoromethylnaphthofurans with a variety of arylzinc reagents. A palladium complex, Pd-PEPPSI-IPr, was the most efficient catalyst for the arylation step, which represents the first cross-coupling of aryl sulfides by using an N-heterocyclic-carbene-ligated palladium complex. This library consists of new π-expanded molecules, all of which are fluorescent in the solid state as well as in solution. Their photophysical properties, such as absorption and emission, fluorescence quantum yields, and fluorescence lifetimes, were thoroughly investigated. This library was also useful to identify acidochromic molecules. Generation next: Pummerer annulation of simple naphthols followed by cross-coupling with various arylzinc reagents allows the concise and diversity-oriented synthesis of a library of fluorescent naphthofurans (see scheme). Copyright

Full text of DOI:10.1002/chem.201201261

FULL PAPER
DOI: 10.1002/chem.201201261
Synthesis of a Library of Fluorescent 2-Aryl-3-trifluoromethylnaphthofurans
from Naphthols by Using a Sequential Pummerer-Annulation/Cross-
Coupling Strategy and their Photophysical Properties
Yuuya Ookubo,[a] Atsushi Wakamiya,[b] Hideki Yorimitsu,*[a] and Atsuhiro Osuka[a]
Abstract: A library of 2-aryl-3-trifluo-
ACHTUNGTRENNUNGromethylnaphthofurans was synthe-
PEPPSI-IPr, was the most efficient cat-
alyst for the arylation step, which rep-
resents the first cross-coupling of aryl
sulfides by using an N-heterocyclic-car-
bene-ligated palladium complex. This
library consists of new p-expanded
molecules, all of which are fluorescent
in the solid state as well as in solution.
Their photophysical properties, such as
absorption and emission, fluorescence
quantum yields, and fluorescence life-
times, were thoroughly investigated.
This library was also useful to identify
acidochromic molecules.
sized with high efficiency from simple
naphthols. In this synthesis, the Pum-
merer-type annulation of naphthols
with 3-(2,2,2-trifluoroethylidene)-2,4-
dithiapentane 2-oxide was followed by
a cross-coupling of the resulting 2-
methylthio-3-trifluoromethylnaphtho-
furans with a variety of arylzinc re-
Keywords: aryl sulfides · cross-cou-
pling · fluorescence · naphthofur-
ans · palladium
agents.
A
palladium complex, Pd-
Introduction
Naphthofurans are an important class of oxygen-containing
p-rich heteroaromatic compounds that are found in biologi-
cally active compounds[1] and in organic functional materi-
als.[2] Hence, considerable efforts have been devoted to de-
velop efficient methods for constructing naphthofuran skele-
tons, as well as for introducing substituents onto the cores.[3]
Although naphthols are promising starting materials for
constructing naphthofurans, the transformations usually re-
quire multistep procedures and are inherently inefficient.[4,5]
Therefore, new, straightforward approaches to naphthofur-
ans are desired.
In the context of our research on the utility of sulfoxides
in the synthesis of heteroaromatic compounds,[6] we have
very recently developed a straightforward synthesis of 2-
methylthio-3-trifluoromethylbenzofurans from phenols and
sulfoxide 1 under Pummerer conditions (Scheme 1).[7] This
transformation is easy to perform in a single operation and,
thus, is highly efficient, although it comprises multistep
Scheme 1. Previous work on the short synthesis of 2-aryl-3-trifluorome-
thylbenzofurans from phenol; see reference [7].
bond-formation/-cleavage events. These benzofurans feature
a methylthio group at the 2-position, which allows for fur-
ther functionalization. Indeed, the palladium-catalyzed
cross-coupling of BEN01 with three arylzinc reagents has
provided 2-aryl-3-trifluoromethylbenzofurans.[8,9] In addi-
tion, the arylated benzofurans were blue-light fluorescent in
solution, which indicates that the 2-aryl-3-trifluoromethyl-
benzofuran scaffold would be a useful fluorophore.
In light of the importance of naphthofurans as promising
functional organic materials, we envisioned the application
of this Pummerer-annulation/cross-coupling strategy to the
synthesis of naphthofuran-based fluorescent molecules.
Naphthofurans have a larger p-extended system than benzo-
furans and, therefore, are expected to show more interesting
photophysical properties. Because naphthofuran-formation
should occur efficiently in one step and because the subse-
quent cross-coupling would introduce a wide range of aryl
groups, the two-step sequence would be concise enough to
create a library of naphthofuran derivatives.[10] First, herein,
we report the efficient synthesis of a library of fluorescent
2-aryl-3-trifluoromethylnaphthofurans. These products are
solid at room temperature owing to their planar structures
and are fluorescent in the solid state as well as in solution.
[a] Y. Ookubo, Prof. Dr. H. Yorimitsu, Prof. Dr. A. Osuka
Department of Chemistry
Graduate School of Science
Kyoto University
Sakyo-ku, Kyoto 606-8502 (Japan)
Fax : (+)81-75-753-3970
E-mail: yori@kuchem.kyoto-u.ac.jp
[b] Prof. Dr. A. Wakamiya
Institute for Chemical Research
Kyoto University
Uji, Kyoto 611-0011 (Japan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201201261.
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
1
&
ÞÞ
These are not the final page numbers!

A detailed investigation of their photophysical properties, as
well as the discovery of acidochromic molecules from the li-
brary, is also reported.
(CN2NAP01). The reactions of 2-naphthols proceeded re-
gioselectively to construct a naphtho[2,1-b]furan framework
(2NAP01 and CN2NAP01) whilst, the annulation of more
p-expanded phenanthren-9-ol efficiently proceeded to yield
phenanthrofuran (9PHEN01).
AHCTUNGTRENNUNG
Results and Discussion
Next, the methylthio-substituted naphthofurans were aryl-
AHCTUNGTRENNUNG
ated under palladium catalysis.[11] Treatment with a variety
Synthesis of a library of naphthofurans: Four naphthol de-
rivatives were subjected to Pummerer annulation in the
presence of Tf2O and compound 1 in CH2Cl2 (Scheme 2).
Compared to a previous report,[7] the reactions of 1- and 2-
naphthol were slightly improved by changing the reaction
temperature (2NAP01 and 1NAP01). The cyano group of 6-
cyano-2-naphthol was tolerated under these conditions
of arylzinc-halide/lithium-chloride complexes[12] in the pres-
ence of a catalytic amount of [PdCl2A
(dppf)][7,13] or Pd-
PEPPSI-IPr[14] in MeCN for 3 h at 608C provided their cor-
responding arylated naphthofurans ([Eq. (1)] and
CTHUNGTRENNUNG
Scheme 3). Owing to the facile and reliable preparation of
Knochel’s arylzinc reagents, as well as the high catalytic ac-
tivities of the palladium catalysts, the scope of the intro-
duced aryl groups is wide, including p-expanded aryl groups,
such as naphthyl, phenanthryl, and anthranyl groups
(2NAP03-06, 1NAP03), ortho-disubstituted aryl groups
(2NAP07), electron-deficient (2NAP08, 1NAP08) and elec-
tron-rich aryl groups (2NAP09, 1NAP09), and heteroaryl
groups (2NAP10-12).
Scheme 2. Pummerer annulation of naphthol derivatives.
Scheme 3. List of arylated naphthofuran derivatives and catalysts used.
&
2
&
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Fluorescent 2-Aryl-3-trifluoromethylnaphthofurans
FULL PAPER
Although [PdCl
G
do(naphthofuryl)nickel, which was formed by b-hydride
step efficiently, the reactions with sterically demanding
(2NAP06, 2NAP07) and heteroaryl zinc reagents (2NAP10)
resulted in poor yields. Pd-PEPPSI-IPr, which contained a
bulky N-heterocyclic carbene ligand, was the outstandingly
efficient catalyst in such cases. The higher yields of the aryl-
elimination from the initial oxidative adduct, methylthio-
AHCTUNGTREG(NNUN naphthofuryl)nickel. Zinc chloride is crucial to minimize
the formation of the reduced byproduct, presumably by fa-
cilitating transmetalation step, in which the methylthio
group on the nickel center is replaced with a naphthofuryl
moiety. Investigations to improve the efficiency of this reac-
tion are underway in our laboratory.
ACHTUNGTRENNUNGated naphthofurans (2NAP02, 2NAP03, 9PHEN02) were
obtained by using Pd-PEPPSI-IPr. This synthesis is the first
example of the cross-coupling of aryl sulfides by using an N-
heterocyclic-carbene-ligated palladium complex.
To examine the effect of the CF3 group on the photophys-
ical properties of these compounds, we also synthesized un-
substituted-, CH3-substituted-, and CMe3-substituted ana-
logues of 2NAP02 ([Eq. (2)] and Scheme 4). Unsubstituted
Crystal structures: Of the naphthofuran derivatives,
2NAP05, 2NAP06, 2NAP08, 2NAP09, 1NAP08, and 2NAP-
dimer gave crystals that were suitable for X-ray analysis.[20]
Figure 1 shows ORTEPs of 2NAP08 and 2NAPdimer as
Scheme 4. Unsubstituted and CH3-substituted analogues.
H2NAP02[15] and CH3-substituted Me2NAP02[16] were pre-
pared according to the literature. CMe3-substituted
tBu2NAP02 was prepared by trimethylaluminum-mediated
three-fold methylation of the CF3 group.[17]
Figure 1. ORTEPs of a,b) 2NAP08 and c,d) 2NAPdimer; thermal ellip-
soids are set at 50% probability.
We also tried to synthesize a naphthofuran dimer, 2NAP-
dimer. To this end, a new dimerization reaction was devel-
oped because few methods were available for the catalytic
reductive dimerization[18] of aryl sulfides[19] to form biaryl
compounds. Specifically, the nickel-catalyzed zinc-mediated
reductive homo-coupling of 2NAP01 provided 2NAPdimer
in moderate yield (Scheme 5). The modest yield was due to
a competitive reduction reaction that proceeded via hydri-
representative examples. The dihedral angle between the 4-
cyanophenyl group and the naphthofuran plane in 2NAP08
is 328, thus indicating steric repulsion between the aryl
group and the CF3 group. The dihedral angles for 2NAP09
and 1NAP08 are 428 and 168, respectively (see the Support-
ing Information, Figures S6-4 and S6-5). On the other hand,
2NAP05, 2NAP06, and 2NAPdimer, which contained a
bulky aryl group, adopted substantially twisted structures,
with dihedral angles of 698, 678, and 768, respectively (see
the Supporting Information, Figures S6-1, S6-2, and 1). Ro-
tation of the bulky pendant aryl groups would be highly re-
stricted, not only in the ground states but also in the excited
states. These twisted structures are responsible for their flu-
orescence properties (see below). In all cases, the distances
between the two neighboring parallel aromatic rings are
3.3–3.6 ꢁ,[20] which shows that effective p p interactions
À
serve to pack the molecules.[21]
Photophysical properties: Table 1 summarizes the photo-
Scheme 5. Reductive dimerization of 2NAP01.
physical properties of the naphthofuran derivatives, includ-
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
3
&
ÞÞ
These are not the final page numbers!

H. Yorimitsu et al.
Table 1. Photophysical properties of naphthofuran derivatives.[a]
kr[f]
knr
[ꢂ108 sÀ1
lemPW
FfPW
[b]
2
[c]
[d]
2
[e]
[g]
[c]
[h]
Entry
Compound
labs CH Cl
lem CH Cl
Ff CH Cl
tF
2
2
2
2
[nm] (e)
[nm]
[ns]
G
]
G
]
[nm]
1
2
3
4
5
6
7
8
BEN01[i]
2NAP01
1NAP01
CN2NAP01
9PHEN01
BEN02[i]
2NAP02
1NAP02
CN2NAP02
9PHEN02
2NAP03
2NAP04
2NAP05
2NAP06
2NAP07
2NAP08
2NAP09
2NAP10
2NAP11
2NAP12
2NAPdimer
1NAP03
287 (16400)
331 (16100)
337 (3400)
339 (9900)
356 (1700)
292 (13300)
329 (14200)
336 (6400)
338 (7800)
352 (4000)
331 (18100)
324 (13500)
324 (15100)
387 (10500)
324 (8400)
334 (18600)
344 (29800)
332 (10900)
336 (20200)
336 (22700)
332 (18600)
341 (15500)
348 (9300)
350 (32800)
348 (34400)
340 (18500)
328 (10000)
–
–
–
–
–
–
–
353
359
385
368
331[k]
383
362
359[k]
361
398
419
425
451
332[k]
425
425
419
403
365[k]
412[k]
378
402
409
352
370
375
0.20
0.08
0.17
0.17
0.66
0.51
0.78
0.81
0.48
0.92
0.56
0.51
0.46
0.39
0.46
0.72
0.36
0.27
0.74
0.61
0.79
0.63
0.96
0.95
0.57
0.50
0.97
3.05
3.31
5.71
1.56
1.59
2.75
2.81
3.31
1.38
1.51
1.37
2.74
2.38
1.22
1.21
1.53
0.77
1.57
1.29
1.95
1.96
1.39
1.74
2.75
1.46
2.06
0.26
0.51
0.30
4.23
3.21
2.84
2.88
1.45
6.67
3.71
3.72
1.68
1.64
3.77
5.95
2.37
3.52
4.71
4.72
4.05
3.21
6.91
5.45
2.07
3.42
8.25
3.02
2.51
1.45
2.17
3.08
0.80
0.68
1.57
0.57
2.91
3.58
1.97
2.56
4.43
2.31
4.16
9.48
1.66
3.02
1.08
1.89
0.29
0.28
1.56
3.42
NM[j]
NM[j]
NM[j]
NM[j]
–
0.02
0.04
0.04
0.06
–
394
361
393
387
400
414
398
471
348
417
428
422
420
418
429
403
420
438
368
401
369
0.28
0.27
0.14
0.17
0.21
0.21
0.19
0.41
0.30
0.41
0.07
0.08
0.12
0.05
0.36
0.42
0.19
0.20
0.15
0.06
0.19
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
1NAP08
1NAP09
H2NAP02
Me2NAP02
tBu2NAP02
[a] CH2Cl2 was used for measurements in solution. [b] Only the longest absorption maxima are shown; e values are measured in mÀ1 cmÀ1. [c] Only the
shortest emission maxima are shown, some of which appear as a shoulder; irradiation at the absorption maximum was used for each excitation. [d] Abso-
lute fluorescence quantum yields in CH2Cl2. [e] Fluorescence lifetime. [f] Rate constant for radiative decay: kr =Ff CH Cl /tF. [g] Rate constant for nonra-
2
2
diative decay: knr =(1ÀFf CH Cl )/tF. [h] Absolute fluorescence quantum yields as powders (PWs). [i] Liquid. [j] NM=Not measured because the S/N ratios
2
2
are too small. [k] Shoulder. For details, also see the Supporting Information, Figure S5.
ing their absorption and emission properties, fluorescence
quantum yields, fluorescence lifetimes, and decay constants.
Benzofuran derivatives BEN01 and BEN02 are colorless liq-
uids at room temperature and methylthio-substituted
BEN01 is not fluorescent. In contrast, all of the naphthofur-
an derivatives are solids at ambient temperature and blue-
light fluorescent in the solid state, as well as in CH2Cl2,
upon UV irradiation.
The emission maxima of the naphthofuran derivatives in
solution are generally on the UV/violet-light boundary. In
the solid state, the emission bands of CN2NAP02,
9PHEN02, 2NAP06, 2NAP11, 2NAP12, 1NAP03, 1NAP09,
and Me2NAP02 are apparently red-shifted (see the Sup-
porting Information, Figure S5) by 17–38 nm with longer
emission maxima. These small-yet-obvious red-shifts in the
solid state are suitable for organic visible-light-emitting
solids.
Next, the effect of the naphthofuran cores on the photo-
physical properties of these materials was investigated (Fig-
ure 2a) by comparing the phenyl-substituted derivatives
(Table 1, entries 6–10). As the p-conjugation becomes
larger, the absorption maximum is red-shifted; 9PHEN02
shows the longest absorption maximum at 352 nm. In the
fluorescence spectra, BEN02 displays apparently blue-shift-
ed fluorescence and the other compounds display fluores-
cence bands from about 340 nm; 2NAP02 has an emission
maximum at 383 nm. Considering the small overlap between
the absorption and emission bands, which would be favora-
ble for optoelectronic organic materials, we mainly investi-
gated the 2NAP series in terms of the substituent effects.
With the progressive expansion of the size of the naphtho-
furan rings from BEN02 to 9PHEN02, the lifetime of the
excited state becomes longer (from 1.56 to 3.31 ns) and the
The fluorescence quantum yields of methylthio-substitut-
ed naphthofuran derivatives are much lower than those of
their phenyl-substituted analogues, both in solution and in
the solid state, albeit the replacement of the methylthio
group with a phenyl group has little influence on their ab-
sorption and emission bands (Table 1, entries 2–5 versus 7–
10; also see the Supporting Information, Figure S5). In gen-
eral, aryl-substituted naphthofuran derivatives exhibit high
fluorescence quantum yields in CH2Cl2, as exemplified by
2NAP03 (FfCH Cl =0.92; Table 1, entry 11) and 1NAP09
2
2
(FfCH Cl =0.96, Table 1, entry 24). Notably, the fluorescence
2
2
quantum yields of 2NAP06 and 2NAP08 in the solid state
(FfPW =0.41 for both) are almost as high as those in CH2Cl2
(FfCH Cl =0.46 for both; Table 1, entries 14 and 16).
2
2
1NAP03 shows the highest fluorescence quantum yield
(0.42) in the solid state of the compounds that we tested
(Table 1, entry 22).
&
4
&
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Fluorescent 2-Aryl-3-trifluoromethylnaphthofurans
FULL PAPER
Figure 2. Absorption (solid lines) and fluorescence spectra (dashed lines) of naphthofuran derivatives in CH2Cl2: a) Phenyl-substituted naphthofuran de-
rivatives; b) polycyclic aromatic hydrocarbon-substituted naphthofurans; c) naphthofurans that contain a substituted phenyl group; d) five-membered
heteroaromatic-substituted naphthofurans; e) 2-phenylnaphthofurans that contain a different substituent at the 3-position.
rate constant for radiative decay (kr) decreases from 4.23ꢂ
108 to 1.45ꢂ108 sÀ1. The larger p-nuclei decelerate the fluo-
rescence emission.
substituent at the excited state and emission without consid-
erable structural change. The introduction of an electron-
withdrawing (2NAP08) or -donating group (2NAP09) on
the phenyl ring resulted in significant red-shifting of the
emission bands, probably owing to enhanced internal charge
transfer (see below).
For 2NAP11 and 2NAP12, which contain a five-mem-
bered heteroaromatic substituent, red-shifted and enhanced
absorption bands were observed (Figure 2d). These red-
shifts are probably due to the smaller torsion angles and to
the resulting more effective conjugation between the naph-
thofuran ring and the compact thiophene/furan ring. Al-
though 2NAPdimer adopts a twisted conformation in the
crystal (Figure 1), it exhibits an absorption spectrum that is
similar to that of 2NAP12. The emission band of 2NAPdim-
er is rather broad and much more red-shifted than that of
2NAP12. The intense fluorescence of 2NAPdimer in the
solid state is also interesting.
In the 2NAP series that contain a polycyclic aromatic hy-
drocarbon substituent (Table 1, entries 7, 11–14), increases
in p-conjugation and in the steric hindrance of the substitu-
ents from 2NAP02 to 2NAP06 cause gradual red-shifts in
the emission bands (Figure 2b). The multipeak absorption
band of 2NAP06 strongly reflects the absorption of the an-
thracene moiety[22] and the emission band appears in the
most red-shifted region (lemCH Cl =451 nm) in the com-
2
2
pounds that were synthesized.
The absorbances of 2NAP02 and 2NAP07-09 are likely to
be related to the effectiveness of the p-conjugation through
the substituents (Figure 2c and Table 1, entries 7, 15–17).
Specifically, the sterically demanding 2,6-dimethylphenyl
group in 2NAP07 would be perpendicular to the naphtho-
furan ring, thereby leading to the formation of the smallest
p-system with the smallest absorbance. A very small differ-
ence between lemCH Cl and labsCH Cl was observed in
In general, the fluorescence bands are broad and very dif-
ferent to the mirror images of their corresponding absorp-
tion bands, thereby indicating that twisted internal charge
2
2
2
2
2NAP07, thus also implying limited rotation of the bulky
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
5
&
ÞÞ
These are not the final page numbers!

H. Yorimitsu et al.
transfer may contribute to the emission.[23] However, we
only observed small solvent effects on the absorption and
emission spectra (see the Supporting Information, Figur-
es S5-53 and S5-54). DFT calculations of 2NAP02, 2NAP08,
and 2NAP09 were performed to acquire information about
the excitation (Figure 3; also see the Supporting Informa-
Me2NAP02 showed a smaller difference between lemCH Cl
2
2
and labsCH Cl than 2NAP02 because a methyl group is small-
2
2
er than a trifluoromethyl group[24] and, thus, would provide
less twisted conformations in Me2NAP02. Compound
tBu2NAP02 exhibits a smaller shift between lemCH Cl and
2
2
labsCH Cl than 2NAP02, which is ascribed to the bulkier tert-
2
2
butyl group that more effectively restricts rotation in the ex-
cited state. The CF3 group is modestly large and, hence, is
the best substituent, thereby balancing small overlap be-
tween the absorption and emission bands and high fluores-
cence quantum yield in the solid state. Detailed analysis of
the absorption and emission processes is now underway in
our laboratory.
Nitrogen-containing naphthofurans exhibit acidochrom-
ism.[25] The addition of trifluoroacetic acid to a solution of
2NAP09 in CH2Cl2 effected blue-shifts of the absorption
and emission bands, as well as a decrease in the intensity of
the absorption band (Figure 4a). The protonation would
Figure 3. Energy diagrams of Kohn–Sham HOMOs and LUMOs of
2NAP08, 2NAP02, and 2NAP09 at the B3LYP/6-31G(d) level (isoval-
ue=0.04).
tion, Figure S7). For 2NAP02, although the HOMOÀ1 is
highly localized on the naphthofuran ring, the HOMO is
partly delocalized over the phenyl substituent. In the
LUMO, the phenyl ring plays a considerable role. Therefore,
upon irradiation, the CF3-substituted naphthofuran core and
the phenyl ring would serve as a weak electron donor and
acceptor, respectively; this conclusion is also supported by
the TD-DFT calculations (see the Supporting Information,
Figures S7-4–9). Thus, weak internal charge transfer would
operate. For cyano-substituted 2NAP08, as the phenyl ring
becomes electron-deficient, the donor–acceptor relationship
is enhanced. In contrast, 2NAP09 contains the highly elec-
tron-rich dimethylanilino group, which behaves as an elec-
tron-donor. DFT calculations of 2NAP09 reveal that the in-
tramolecular donor–acceptor relationship is reversed.
Figure 4. Absorption (solid lines) and fluorescence spectra (dashed lines)
of a) 2NAP09 and its protonated species in CH2Cl2 and of b) 2NAP10
and its protonated species in CH2Cl2.
To examine the effect of the CF3 group on the photophys-
ical properties of these compounds, we compared the ab-
sorption and emission spectra of 2NAP02 with those of its
unsubstituted analogue H2NAP02, methyl analogue
Me2NAP02, and tert-butyl analogue tBu2NAP02 (Figure 2e
and Table 1, entries 7, 25–27). Compound H2NAP02 shows
the largest absorption band, a mirror image of the absorp-
tion band in the fluorescent spectrum, a small Stokes shift,
and a high fluorescence quantum yield (0.95) in solution.
These observations suggest that the rather flat, untwisted
structural character of H2NAP02 would allow emission
without significant structural change in the excited state.
The small Stokes shift may result in low fluorescence quan-
tum yield in the solid state (FfPW =0.15). Similarly,
prohibit the dimethylaminophenyl group from serving as an
electron donor to reverse the original donor–acceptor rela-
tionship. A similar change was also observed in the case of
1NAP09 (see the Supporting Information, Figure S5-56). In
contrast, similar treatment of pyridyl-substituted 2NAP10
led to a slight red-shift in the absorption band by enhancing
the accepting nature of the pyridyl group and lowering the
LUMO level (Figure 4b). The emission band has its maxi-
mum significantly red-shifted by 3210 cmÀ1 and the acidic
solution of 2NAP10 emits a yellow color. Notably, the addi-
tion of triethylamine to these acidified solutions results in
&
6
&
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Fluorescent 2-Aryl-3-trifluoromethylnaphthofurans
FULL PAPER
fication by column chromatography on silica gel (EtOAc/n-hexane, 1:10)
the recovery of the initial absorption and emission proper-
ties.
provided 1,1’-bis(trifluoromethyl)-2,2’-binaphtho
er, 19 mg, 41.4 mmol, 46%).
ACHTUNGERTN[NUNG 2,1-b]furan (2NAPdim-
Crystallographic data for 2NAP08: C20H10F3NO; Mr =337.29; triclinic;
space group P-1; a=7.344(4), b=8.338(6), c=12.709(8) ꢁ; a=100.51(2),
b=92.37(2), g=1103.06(2)8; V=741.6(8) ꢁ3; 1cald =1.510 gcmÀ3; Z=2;
T=93 K; R1 =0.0387 (I>2s(I)); wR2 =0.1104 (all data); GOF=1.058
(I>2s(I)).
Conclusion
By taking advantage of our unique and concise approach to
naphthofuran scaffolds and by applying the state-of-the-art
palladium catalyst to the cross-coupling substitution of
methylthio groups with arylzinc reagents, a library of 2-aryl-
3-trifluoromethylnaphthofurans was efficiently synthesized
from simple naphthols. These naphthofurans primarily
showed small overlap between their absorption and emis-
sion bands, were all fluorescent solids, and some were acido-
chromic. Applications of these new p-expanded molecules
to organic optoelectronic devices, such as organic electrolu-
minescence devices, are underway in our laboratory.
Crystallographic data for 2NAPdimer: C26H12F6O2; Mr =470.36; mono-
clinic; space group C2/c; a=18.2975(5), b=10.3028(2), c=11.2081(2) ꢁ;
b=113.673(2)8; V=746.029 ꢁ3; 1cald =1.615 gcmÀ3; Z=4; T=93 K; R1 =
0.0660 (I>2s(I)); wR2 =0.2292 (all data); GOF=1.111 (I>2s(I)).
Acknowledgements
This work was supported by Grants-in-Aid (20108006 “pi-Space”,
22106523 “Reaction Integration”, and 23655037) from MEXT. H.Y. ac-
knowledges financial support from Kinki Invention Center. Professors
Masahide Terazima (Kyoto University), Masaaki Baba (Kyoto Universi-
ty), and Hiroshi Miyasaka (Osaka University) are acknowledged for
their fruitful discussions.
Experimental Section
Typical procedure for the Pummerer annulation reaction: The prepara-
tion of 2NAP01 is described as a representative example. A solution of
2-naphthol (2.16 g, 15.0 mmol) and sulfoxide 1 (1.53 g, 7.50 mmol) in
[1] a) R. Le Guꢃvel, F. Oger, A. Lecorgne, Z. Dudasova, S. Chevance,
A. Bondon, P. Barath, G. Simonneaux, G. Salbert, Bioorg. Med.
´
Chem. 2009, 17, 7021 and references cited therein; b) H. Kwiecien,
CH2Cl2ACHTUNGTRENNUNG(4 mL) was placed in a flask under an argon atmosphere. Trifluor-
M. Witczak, M. Kowalewska, M. Augustyniak, Chem. Heterocycl.
Comp. 2010, 46, 20 and references cited therein; c) A. K. Debnath,
C. Hansch, K. H. Kim, Y. C. Martin, J. Med. Chem. 1993, 36, 1007;
d) R. Ribeiro-Rodrigues, W. G. dos Santos, A. B. Oliveira, V.
Snieckus, C. L. Zani, A. J. Romanha, Bioorg. Med. Chem. Lett.
1995, 5, 1509; e) V. Leclerc, P. Depreux, D. Lesieur, D. H. Caignard,
P. Renard, P. Delagrange, B. Guardiola-Lemaitre, P. Morgan,
Bioorg. Med. Chem. Lett. 1996, 6, 1071; f) V. Srivastava, A. S. Negi,
J. K. Kumar, U. Faridi, B. S. Sisodia, M. P. Darokar, S. Luqman,
S. P. S. Khanuja, Bioorg. Med. Chem. Lett. 2006, 16, 911; g) M. Z. A.
Badr, A. M. K. El-Dean, O. S. Moustafa, R. M. Zaki, J. Chem. Res.
2006, 748.
omethanesulfonic anhydride (2.46 mL, 15 mmol) was added to the solu-
tion at À788C and the resulting mixture was stirred at À308C for 30 min.
The mixture was poured into a saturated aqueous solution of NaHCO3
and the product was extracted with CH2Cl2 (3ꢂ20 mL). The combined
organic layer was dried over anhydrous sodium sulfate and concentrated
in vacuo. Purification by column chromatography on silica gel (EtOAc/n-
hexane, 1:10) provided 2-methylthio-1-(trifluoromethyl)naphthoACTHNUTRGNE[NUG 2,1-
b]furan (2NAP01, 1.64 g, 5.84 mmol, 78%).
Typical procedure for the palladium-catalyzed arylation reaction: The
preparation of 2NAP02 is described as a representative example. Pd-
PEPPSI-IPr (258 mg, 0.38 mmol) and 2NAP01 (705 mg, 2.50 mmol) were
placed in a flask under an argon atmosphere and MeCN (30 mL) was
added at RT. PhZnBr·LiCl (9.62 mL, 7.5 mmol, 0.78m in THF) was
added at 608C and the whole mixture was stirred at the same tempera-
ture for 3 h. The mixture was poured into 1m HCl and extracted with
EtOAc (3ꢂ20 mL). The combined organic layer was dried over anhy-
drous sodium sulfate and concentrated in vacuo. Purification by column
chromatography on silica gel (EtOAc/n-hexane, 1:10), followed by gel-
[2] a) A. M. Piloto, S. P. G. Costa, M. S. T. Goncalves, Tetrahedron Lett.
2005, 46, 4757; b) A. S. Klymchenko, T. Ozturk, V. G. Pivovarenko,
A. P. Demchenko, Can. J. Chem. 2001, 79, 358; c) P. K. Frederiksen,
M. Jorgensen, P. R. Ogilby, J. Am. Chem. Soc. 2001, 123, 1215.
[3] For reviews, see: a) T. Graening, F. Thrun, In Comprehensive Heter-
ocyclic Chemistry III (Eds.; A. R. Katritzky, C. A. Ramsden, E. F. V.
Scriven, R. J. K. Taylor), Elsevier: 2008, Vol. 3, Chapter 3.07; b) W.
Friedrichsen, In Comprehensive Heterocyclic Chemistry II (Eds.:
A. R. Katritzky, C. W. Rees, E. F. V. Scriven), Elsevier: 1996, Vol. 2,
Chapter 2.07; c) D. M. X. Donnelly, M. J. Meegan, In Comprehensive
Heterocyclic Chemistry (Eds.: A. R. Katritzky, C. W. Rees), Elsevier:
1984, Vol. 4, Chapter 3.12; d) M. G. Kadieva, ꢄ. T. Oganesyan,
Chem. Heterocyclic Compds. 1997, 33, 1245.
[4] a) T. Satoh, T. Tsuda, Y. Kushino, M. Miura, M. Nomura, J. Org.
Chem. 1996, 61, 6476; b) A. R. Katritzky, L. Serdyuk, L. Xie, J.
Chem. Soc. Perkin Trans. 1 1998, 1059; c) M. Jørgensen, F. C. Krebs,
K. Bechgaard, J. Org. Chem. 2000, 65, 8783; d) K. K. Park, J. Jeong,
Tetrahedron 2005, 61, 545; e) C. Pan, J. Yu, Y. Zhou, Z. Wang, M.-
M. Zhou, Synlett 2006, 11, 1657; f) C. G. Pancote, B. S. de Carvalha,
C. V. Luchez, J. P. S. Fernandes, M. J. Politi, C. A. Brandt, Synthesis
2009, 23, 3963; g) R. Okamoto, E. Okazaki, K. Noguchi, K. Tanaka,
Org. Lett. 2011, 13, 4894.
permeation
chromatography
(CHCl3),
provided
2-phenyl-1-
(trifluoromethyl)naphtho
91%).
ACHTUNGTRENN[UNG 2,1-b]furan (2NAP02, 709 mg, 2.28 mmol,
Transformation of 2NAP02 into tBu2NAP02: (Equation (2)). A solution
of 2NAP02 (40.0 mg, 0.13 mmol) in 1,2-dichloroethane (0.4 mL) was
added under an argon atmosphere. Trimethylaluminum (0.36 mL,
0.64 mmol, 1.8m in toluene) was added at 258C. The resulting mixture
was allowed to warm to 508C and stirred for 20 h. The reaction mixture
was quenched with 1m HCl at 08C. The mixture was warmed to 258C
and a saturated solution of NaHCO3 was added. The product was extract-
ed three times with EtOAc, dried over anhydrous sodium sulfate, and
evaporated to give the crude product. Purification by column chromatog-
raphy on silica gel (EtOAc/n-hexane, 1:10) provided 1-tert-butyl-2-
phenylnaphtho
Transformation of 2NAP01 into 2NAPdimer: (Scheme 5). In a dry,
argon-flushed vial (5 mL), 2-methylthio-1-(trifluoromethyl)naphtho[2,1-
b]furan (2NAP01, 50.0 mg, 0.18 mmol), [NiCl2A(dppf)] (18 mg,
ACHTUNGTRENNUNG[2,1-b]furan (tBu2NAP02, 32.4 mg, 0.109 mmol, 85%).
E
[5] For the one-step synthesis of naphthofurans from naphthols, see:
a) M. T. Baumgartner, A. B. Pierini, R. A. Rossi, J. Org. Chem.
1993, 58, 2593; b) I. Yavari, M. Anary-Abbasinejad, A. Alizadeh,
Tetrahedron Lett. 2002, 43, 4503; c) T. C. Tempesti, A. B. Pierini,
M. T. Baumgartner, J. Org. Chem. 2005, 70, 6508; d) Z. Liu, L. Liu,
Z. Shafiq, Y.-C. Wu, D. Wang, Y.-J. Chen, Synthesis 2007, 1961; e) X.
CTHUNGTRENNUNG
0.027 mmol), ZnCl2 (48 mg, 0.36 mmol), and Zn powder (23 mg,
0.36 mmol) were mixed in THF (0.6 mL). The resulting mixture was
heated at reflux and stirred for 36 h. The mixture was filtered through a
pad of silica gel and the filtrate was evaporated to yield a crude oil. Puri-
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
7
&
ÞÞ
These are not the final page numbers!

H. Yorimitsu et al.
Guo, R. Yu, H. Li, Z. Li, J. Am. Chem. Soc. 2009, 131, 17387; f) L.
Arias, Y. Vara, F. P. Cossꢅo, J. Org. Chem. 2011, 77, 266; g) C.-L.
Chung, C.-H. Han, H.-M. Wang, R.-S. Hou, L.-C. Chen, J. Chin.
Chem. Soc. 2011, 58, 90; h) D. Kundu, M. Samim, A. Majee, A.
Hajra, Chem. Asian J. 2011, 6, 406.
Despotopoulou, P. Knochel, Org. Lett. 2009, 11, 4228; g) A. Metzg-
er, L. Melzig, P. Knochel, Synthesis 2010, 16, 2853; h) L. Melzig, A.
Metzger, P. Knochel, Chem. Eur. J. 2011, 17, 2948.
[12] a) A. Krasovskiy, V. Malakhov, A. Gavryushin, P. Knochel, Angew.
Chem. 2006, 118, 6186; Angew. Chem. Int. Ed. 2006, 45, 6040;
b) F. M. Piller, A. Metzger, M. A. Schade, B. A. Haag, A. Gavryush-
in, P. Knochel, Chem. Eur. J. 2009, 15, 7192.
[13] T. Koshiba, T. Miyazaki, H. Tokuyama, T. Fukuyama, Heterocycles
2009, 77, 233.
[6] a) S. Yoshida, H. Yorimitsu, K. Oshima, Org. Lett. 2009, 11, 2185;
b) T. Kobatake, S. Yoshida, H. Yorimitsu, K. Oshima, Angew. Chem.
2010, 122, 2390; Angew. Chem. Int. Ed. 2010, 49, 2340; c) S. Yoshida,
H. Yorimitsu, K. Oshima, Org. Lett. 2007, 9, 5573; d) S. Yoshida, H.
Yorimitsu, K. Oshima, Chem. Lett. 2008, 37, 786.
[14] a) C. J. OꢈBrien, E. A. B. Kantchev, C. Valente, N. Hadei, G. A.
Chass, A. Lough, A. C. Hopkinson, M. G. Organ, Chem. Eur. J.
2006, 12, 4743; b) M. G. Organ, S. Avola, I. Dudovyk, N. Hadei,
E. A. B. Kantchev, C. J. OꢈBrien, C. Valente, Chem. Eur. J. 2006, 12,
4749; c) S. Sase, M. Jaric, A. Metzger, V. Malakhov, P. Knochel, J.
Org. Chem. 2008, 73, 7380; d) M. G. Organ, G. A. Chass, D. C. Fang,
A. C. Hopkinson, C. Valente, Synthesis 2008, 2776; e) C. Valente,
M. E. Belowich, N. Hadei, M. G. Organ, Eur. J. Org. Chem. 2010,
4343; f) C. Valente, S. C¸ alimsiz, K. H. Hoi, D. Mallik, M. Sayah,
M. G. Organ, Angew. Chem. 2012, 124, 3370; Angew. Chem. Int. Ed.
2012, 51, 3314.
[15] R. Wang, S. Mo, Y. Lu, Z. Shen, Adv. Synth. Catal. 2011, 353, 713.
[16] C. Eidamshaus, J. D. Burch, Org. Lett. 2008, 10, 4211.
[17] J. Terao, M. Nakamura, N. Kambe, Chem. Commun. 2009, 6011.
[18] a) J. Hassan, M. Sꢃvignon, C. Gozzi, E. Schulz, M. Lemaire, Chem.
Rev. 2002, 102, 1359; b) K. Lee, P. H. Lee, Tetrahedron Lett. 2008,
49, 4302 and references cited therein.
[19] To the best of our knowledge, the reductive dimerization of 2-meth-
ylthiopyrimidine is the only example that has been reported thus
far. However, the reaction conditions used herein failed to yield
2NAPdimer; see: K. Itami, D. Yamazaki, J. Yoshida, J. Am. Chem.
Soc. 2004, 126, 15396.
[20] For details, see the Supporting Information, Figure S6.
[21] a) C. Janiak, J. Chem. Soc. Dalton Trans. 2000, 3885; b) E. A.
Meyer, R. K. Castellano, F. Diederich, Angew. Chem. 2003, 115,
1244; Angew. Chem. Int. Ed. 2003, 42, 1210.
[7] T. Kobatake, S. Yoshida, H. Yorimitsu, K. Oshima, J. Am. Chem.
Soc. 2010, 132, 2340.
[8] Approaches to 2-arylbenzofuran derivatives that are based on con-
ventional cross-coupling reactions. For the Stille reaction, see: a) S.-
Y. Lin, C.-L. Chen, Y.-J. Lee, J. Org. Chem. 2003, 68, 2968; b) K.
Ishibashi, K. Nakajima, T. Nishi, Heterocycles 1998, 48, 2669;
c) M. L. Curtin, S. K. Davidsen, H. R. Heyman, R. B. Garland, G. S.
Sheppard, A. S. Florjancic, L. Xu, G. M. Carrera, Jr., D. H. Stein-
man, J. A. Trautmann, D. H. Albert, T. J. Magoc, P. Tapang, D. A.
Rhein, R. G. Conway, G. Luo, J. F. Denissen, K. C. Marsh, D. W.
Morgan, J. B. Summers, J. Med. Chem. 1998, 41, 74; d) S. Wende-
born, S. Berteina, W. K.-D. Brill, A. De Mesmaeker, Synlett 1998,
671; e) K. Yamamura, T. Yamane, H. Takagi, H. Miyake, Heterocy-
cles 1997, 45, 467; For the Negishi reaction, see:f) A. N. Ryabov,
V. V. Izmer, A. A. Tzarev, D. V. Uborsky, A. F. Asachenko, M. V.
Nikulin, J. A. M. Canich, A. Z. Voskoboynikov, Organometallics
2009, 28, 3614; For very recent examples of the Suzuki–Miyaura re-
action, see: g) Y.-L. Chen, J. Tang, M. J. Kesler, Y. Y. Sham, R.
Vince, R. J. Geraghty, Z. Wang, Bioorg. Med. Chem. 2012, 20, 467;
h) J. Riedl, R. Pohl, L. Rulisek, M. Hocek, J. Org. Chem. 2012, 77,
1026; i) N. Ortega, S. Urban, B. Beiring, F. Glorius, Angew. Chem.
Int. Ed. 2012, 51, 1710; Angew. Chem. 2012, 124, 1742; j) J. R.
Donald, R. R. Wood, S. F. Martin, ACS Comb. Sci. 2012, 14, 135.
À
[9] For approaches that use efficient C H arylation steps, see: a) S.
Tanaka, D. Tanaka, A. Sugie, A. Mori, Tetrahedron Lett. 2012, 53,
1173; b) O. Vakuliuk, B. Koszarna, D. T. Gryko, Adv. Synth. Catal.
2011, 353, 925; c) T. Truong, O. Daugulis, J. Am. Chem. Soc. 2011,
133, 4243; d) S. Yanagisawa, K. Itami, Tetrahedron 2011, 67, 4425;
e) F. Shibahara, E. Yamaguchi, T. Murai, Chem. Commun. 2010, 46,
2471; f) T. Bresser, M. Mosrin, G. Monzon, P. Knochel, J. Org.
Chem. 2010, 75, 4686; g) C.-Y. He, S. Fan, X. Zhang, J. Am. Chem.
Soc. 2010, 132, 12850; h) S. Tamba, Y. Okubo, S. Tanaka, D. Mongu-
chi, A. Mori, J. Org. Chem. 2010, 75, 6998; i) K. Kim, I. Kim, Org.
Lett. 2010, 12, 5314; j) B. Liegault, D. Lapointe, L. Caron, A. Vlasso-
va, K. Fagnou, J. Org. Chem. 2009, 74, 1826; k) N. S. Nandurkar,
M. J. Bhanushali, M. D. Bhor, B. M. Bhanage, Tetrahedron Lett.
2008, 49, 1045; l) H.-Q. Do, R. M. K. Khan, O. Daugulis, J. Am.
Chem. Soc. 2008, 130, 15185; m) A. Ohta, Y. Akita, T. Ohkuwa, M.
Chiba, R. Fukunaga, A. Miyafuji, T. Nakata, N. Tani, Y. Aoyagi,
Heterocycles 1990, 31, 1951.
[22] Y. Suzaki, Y. Tsuchido, K. Osakada, Tetrahedron Lett. 2011, 52,
3883.
[23] a) A. P. de Silva, H. Q. N. Gunaratne, T. Gunnlaugsson, A. J. M.
Huxley, C. P. McCoy, J. T. Rademacher, T. E. Rice, Chem. Rev. 1997,
97, 1515; b) C. Reichardt, Chem. Rev. 1994, 94, 2319; c) A. C. Ben-
niston, A. Harriman, D. J. Lawrie, A. Mayeux, Phys. Chem. Chem.
Phys. 2004, 6, 51; d) A. Wakamiya, K. Mori, S. Yamaguchi, Angew.
Chem. 2007, 119, 4271; Angew. Chem. Int. Ed. 2007, 46, 4193;
e) Z. R. Grabowski, K. Rotkiewicz, W. Rettig, Chem. Rev. 2003, 103,
3899.
[24] a) W. K. Hagmann, J. Med. Chem. 2008, 51, 4359; b) C. Wolf, W. A.
Konig, C. Roussel, Liebigs Ann. 1995, 781; c) K. Mikami, Y. Itoh,
M. Yamanaka, Chem. Rev. 2004, 104, 1.
[25] For aniline-based chromophores, see: a) S. J. K. Pond, O. Tsutsumi,
M. Rumi, O. Kwon, E. Zojer, J. L. Brꢃdas, S. R. Marder, J. W. Perry,
J. Am. Chem. Soc. 2004, 126, 9291; b) H. Detert, V. Schmitt, J. Phys.
Org. Chem. 2006, 19, 603; c) A. Baheti, P. Singh, C. P. Lee, K. R. J.
Thomas, K. C. Ho, J. Org. Chem. 2011, 76, 4910; d) P. Singh, A.
Baheti, K. R. J. Thomas, J. Org. Chem. 2011, 76, 6134; e) C. Dou, L.
Han, S. Zhao, H. Zhang, Y. Wang, J. Phys. Chem. Lett. 2011, 2, 666;
For pyridine-based chromophores, see: f) C. J. Kelley, K. Ansu, W.
Budisusetyo, A. Ghiorghis, Y. Qin, J. M. Kauffman, J. Heterocycl.
Chem. 2001, 38, 11; g) H. Detert, O. Sadovski, E. Sugiono, J. Phys.
Org. Chem. 2004, 17, 1046; h) D. Jacquemin, A. Lewalle, E. A. Per-
pꢃte, Chem. Phys. Lett. 2008, 457, 91; For the acidochromism of ani-
line-pyridine hybrids, see: i) A. J. Zucchero, P. L. Mcgrier, U. H. F.
Bunz, Acc. Chem. Res. 2010, 43, 397; j) J. Tolosa, K. M. Solntsev,
L. M. Tolbert, U. H. F. Bunz, J. Org. Chem. 2010, 75, 523.
[10] For reviews on combinatorial approaches to fluorescent molecules,
see: a) M.-S. Schiedel, C. A. Briehn, P. Bꢆuerle, Angew. Chem. 2001,
113, 4813; Angew. Chem. Int. Ed. 2001, 40, 4677; b) T. J. J. Mꢇller,
D. M. D’Souza, Pure Appl. Chem. 2008, 80, 609; c) K. Itami, J. Yosh-
ida, Bull. Chem. Soc. Jpn. 2006, 79, 811; d) M.-S. Schiedel, C. A.
Briehn, P. Bꢆuerle, J. Organomet. Chem. 2002, 653, 200; e) C. A.
Briehn, P. Bꢆuerle, Chem. Commun. 2002, 1015; f) E. Kim, S. B.
Park, Chem. Asian J. 2009, 4, 1646; g) T. J. J. Mꢇller, Functional Or-
ganic Materials: Syntheses, Strategies, and Applications, Wiley-VCH,
Weinheim, 2007, p. 179.
[11] The Pd-catalyzed cross-coupling of arylzinc reagents with aryl
methyl sulfides has been reported; see: a) J. Srogl, W. Liu, D. Mar-
shall, L. S. Liebeskind, J. Am. Chem. Soc. 1999, 121, 9449; b) M. E.
Angiolelli, A. L. Casalnuovo, T. P. Selby, Synlett 2000, 6, 905; c) I.
Ghosh, P. A. Jacobi, J. Org. Chem. 2002, 67, 9304; d) I. Ghosh, P. A.
Jacobi, Can. J. Chem. 2004, 82, 279; e) K. Lee, C. M. Counceller,
J. P. Stambuli, Org. Lett. 2009, 11, 1457; f) A. Metzger, L. Melzig, C.
Received: April 13, 2012
Published online: && &&, 2012
&
8
&
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Fluorescent 2-Aryl-3-trifluoromethylnaphthofurans
FULL PAPER
Fluorescent Compounds
Y. Ookubo, A. Wakamiya,
H. Yorimitsu,* A. Osuka . . . &&&& — &&&&
Synthesis of a Library of Fluorescent
2-Aryl-3-trifluoromethylnaphthofurans
from Naphthols by Using a Sequential
Pummerer-Annulation/Cross-Coupling
Strategy and their Photophysical Prop-
erties
Generation next: Pummerer annula-
tion of simple naphthols followed by
cross-coupling with various arylzinc
reagents, allows the concise- and diver-
sity-oriented synthesis of a library of
fluorescent naphthofurans (see
scheme).
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
9
&
ÞÞ
These are not the final page numbers!