Synthesis and photophysical studies of new fluorescent indole derivatives obtained from β-bromodehydroamino acids - Interaction with fluoride anions

Article abstract of DOI:10.1002/ejoc.200900737

Several, new indole derivatives were synthesised from β-brominated dehydroamino acids and arylboronic acids by using a strategy developed in our research group that involves a sequential Suzuki-Miyaura cross-coupling reaction and a metal-assisted C-N intramolecular cyclisation. The cyclised products were obtained either by direct: cyclisation or by isomerisation followed by cyclisation. The photophysical properties of these compounds were studied in four solvents of different polarity (cyclohexane, diethyl ether, acetonitrile and ethanol). All these compounds have reasonably high fluorescence quantum yields (between 16 and 85%) and show different solvent sensitivity in their fluorescence emission. These results indicate that the indole derivatives prepared are good candidates for fluorescent probes. The response of the new synthesised compounds towards fluoride ion (F^-) was evaluated. It was found that methyl 3-methyl1H-dibenzo[e,g]indole-2-carboxylate, methyl 3-(phenanthren-9-yl)-1H-dibenzo[e,g]indole-2-carboxylate and methyl 1-(naphthalen-1-yl)-3H-benzo[e]mdole-2-carboxylate showed, significant spectral, changes in fluorescence emission upon F^- addition with a decrease in intensity and the appearance of a new band at longer wavelengths. No detectable emission spectral changes were observed when several other anions were added, to these compounds, which indicates their selectivity towards F^-.

Full text of DOI:10.1002/ejoc.200900737

FULL PAPER
DOI: 10.1002/ejoc.200900737
Synthesis and Photophysical Studies of New Fluorescent Indole Derivatives
Obtained from β-Bromodehydroamino Acids – Interaction with Fluoride Anions
Goreti Pereira,[a] Elisabete M. S. Castanheira,*[b] Paula M. T. Ferreira,*[a] and
Maria-João R. P. Queiroz[a]
Keywords: Suzuki–Miyaura coupling / Metal-assisted cyclization / Indoles / Fluorescent probes / Fluorides / Nitrogen
heterocycles / Cyclization
Several new indole derivatives were synthesised from β-bro- pared are good candidates for fluorescent probes. The re-
minated dehydroamino acids and arylboronic acids by using
a strategy developed in our research group that involves a
sequential Suzuki–Miyaura cross-coupling reaction and a
metal-assisted C–N intramolecular cyclisation. The cyclised
products were obtained either by direct cyclisation or by iso-
merisation followed by cyclisation. The photophysical prop-
erties of these compounds were studied in four solvents of
different polarity (cyclohexane, diethyl ether, acetonitrile
and ethanol). All these compounds have reasonably high
fluorescence quantum yields (between 16 and 85%) and
show different solvent sensitivity in their fluorescence emis-
sion. These results indicate that the indole derivatives pre-
sponse of the new synthesised compounds towards fluoride
ion (F–) was evaluated. It was found that methyl 3-methyl-
1H-dibenzo[e,g]indole-2-carboxylate,
anthren-9-yl)-1H-dibenzo[e,g]indole-2-carboxylate
methyl
3-(phen-
and
methyl 1-(naphthalen-1-yl)-3H-benzo[e]indole-2-carboxyl-
ate showed significant spectral changes in fluorescence
emission upon F– addition with a decrease in intensity and
the appearance of a new band at longer wavelengths. No
detectable emission spectral changes were observed when
several other anions were added to these compounds, which
indicates their selectivity towards F–.
moieties to be studied as fluorescent probes and also to
Introduction
evaluate
their
behaviour in
the
presence of
fluoride (F–). Thus, several β,β-disubstituted dehydroamino
acids were prepared in good to high yields from pure stereo-
isomers of a β-bromodehydroaminobutyric acid and a β-
bromodehydrophenylalanine or a β,β-dibromodehydroalan-
ine and arylboronic acids. These compounds were then
treated with palladium and copper acetate to give the corre-
sponding pyrrole-fused compounds. The photophysical
properties of the latter were studied in several solvents.
Since neutral F– sensors usually have hydrogen-bonding
units such as pyrrole, urea, amide or phenol in their re-
cognition sites,[3] we decided to study the behaviour of the
compounds prepared towards this anion. Due to the impor-
tance of F– in biology, medicine, food and environmental
sciences, as it is a common ingredient in anaesthetics, hyp-
notics, psychiatric drugs, several poisons and is a contami-
nant in water,[4] there is growing interest in the development
of new molecules capable of selectively sensing F– in solu-
tion. These molecules contain a binding site that interacts
with the anion and a signaling subunit with the ability of
converting the binding event into a readable signal.[5]
In our laboratories, we have been interested in the syn-
thesis of new fluorescent indole derivatives as fluorescent
probes for peptides and proteins. These compounds were
obtained from brominated dehydroamino acids and aryl- or
heteroarylboronated compounds by using a Suzuki–Mi-
yaura cross coupling followed by a metal-mediated C–N in-
tramolecular cyclisation developed in our research group.[1]
Recently, we have used this strategy to synthesise a phen-
alenoindole and a pyrenylindole from a β-bromodehydro-
phenylalanine or a β-bromodehydroaminobutyric acid and
pyren-1-boronic acid, respectively. The fluorescence proper-
ties of these compounds in solution and in lipid membranes
showed their potential as fluorescent probes for biological
systems.[2] In this work, we report the synthesis of several
new compounds having the pyrrole unit fused with benzene,
phenanthrene, 1,2-dihydroacenaphthylene and anthracene
[a] Centro de Química (CQ-UM), University of Minho,
Campus de Gualtar, 4710-057 Braga, Portugal
Fax: +351-253-604382
E-mail: pmf@quimica.uminho.pt
[b] Centro de Física (CFUM), University of Minho, Campus de
Gualtar,
4710-057 Braga, Portugal
Fax: +351-253-604061
Results and Discussion
E-mail: ecoutinho@fisica.uminho.pt
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.200900737.
We treated the pure stereoisomers of a β-bromodehyd-
roaminobutyric acid [(Z)- or (E)-1] and a β-bromodehydro-
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New Fluorescent Indole Derivatives
phenylalanine [(Z)- or (E)-2] with 9-phenanthracenyl- Table 1. 1H NMR chemical shifts of β-aryldehydroaminobutyric
acid
and
dehydrophenylalanine
derivatives
in
CDCl3
boronic acid, (1,2-dihydroacenaphthylen-5-yl)boronic acid
or 1-naphthylboronic acid under Suzuki–Miyaura coupling
conditions to afford in good yields the corresponding β-
substituted dehydroamino acids (Scheme 1). We determined
the stereochemistry of these compounds using NOE differ-
ence experiments by irradiating the α-NH and OCH3 pro-
tons. In the case of the (Z) isomers, when we irradiated the
OCH3 protons, we observed an NOE enhancement on the
β-CH3 protons of dehydroaminobutyric acid derivatives or
on the phenyl protons of dehydrophenylalanines. We con-
firmed the configuration of the (E) isomers by the observa-
tion of a positive NOE of the β-CH3 or β-phenyl reso-
nances when we irradiated the α-NH group. As reported by
other authors and us also, it was possible to correlate the
chemical shifts of the OCH3, α-NH and β-CH3 protons
with the stereochemistry of the compounds.[6] Thus, we ob-
served the NMR chemical shifts of the OCH3 and β-CH3
protons of the (Z) isomers of the dehydroaminobutyric acid
derivatives at lower fields than those of the (E) isomers
(Table 1). We also found this relation in the case of the
OCH3 protons of dehydrophenylalanines (Table 1). The α-
NH resonances of all the (Z) isomers of β-aryldehydroami-
nobutyric acids and dehydrophenylalanines appeared at
higher field than those of the (E) isomers. This is probably
due to the shielding anisotropic effect of the aryl moiety.
(5ϫ10–3 moldm–3).
Entry
Compound
δ [ppm]
OCH3
α-NH
β-CH3
1
2
3
4
5
6
7
8
9
(Z)-3
(E)-3
(Z)-4
(E)-4
(Z)-5
(E)-5
(Z)-6
(E)-6
(Z)-7
(E)-7
(Z)-8
(E)-8
5.61
6.28
5.77
6.42
5.56
6.16
5.76
6.31
5.48
6.22
5.67
6.35
3.95
3.24
3.70
3.23
3.91
3.30
3.64
3.33
3.92
3.25
3.66
3.23
2.38
2.27
–
–
2.32
2.23
–
–
2.32
2.24
–
10
11
12
–
Scheme 2. Synthesis of β,β-diaryldehydroalanine derivatives. (i)
PdCl2dppf·CH2Cl2 (1:1) (10 mol-%); Cs2CO3 (1.4 equiv.); THF/
H2O (1:1).
We then submitted some of these disubstituted dehydro-
amino acid derivatives (3–12) to a Pd/Cu-assisted C–N in-
tramolecular cyclisation to afford the corresponding indole
derivatives (Table 2). This reaction involved the electrophilic
attack of PdII on the aromatic ring and a nucleophilic at-
tack of N, forming a palladacycle.[1] The only products iso-
lated from the cyclisation of (Z)-4 and (Z)-8 resulted from
isomerisation followed by cyclisation giving 14 and 20,
respectively. Compounds (E)-4 and (E)-8 gave 14 and 20 in
similar yields to those obtained by using (Z)-4 and (Z)-8 as
starting materials. In the case of (Z)-6, although the major
product (17, 52%) resulted from isomerisation followed by
cyclisation, we also isolated 18 (13%) resulting from a direct
cyclisation. In this case, the cyclisation of (E)-6 afforded the
Scheme 1. Synthesis of β-aryldehydroaminobutyric acid and dehy-
drophenylalanine derivatives. (i) PdCl2dppf·CH2Cl2 (1:1) (10 mol-
%); Cs2CO3 (1.4 equiv.); THF/H2O (1:1).
When we used β,β-dibromodehydroalanine (9)[1a] as a same ratio of 17 and 18.
substrate, we obtained the corresponding disubstituted de-
Jones and Mathews[7] synthesised compounds similar to
hydroalanines 10–12 in good yields (between 63 and 71%, 15 with a 1H-dibenzo[e,g]indole moiety. The synthesis in-
Scheme 2).
volved the formylation of a 9-bromophenanthrene followed
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465

G. Pereira, E. M. S. Castanheira, P. M. T. Ferreira, M.-J. R. P. Queiroz
Table 2. Yields of the cyclisation products and H NMR chemical shifts of the NH signals in [D6]DMSO (5ϫ10–3 moldm–3).
FULL PAPER
1
[a] Cyclisation conditions: Pd(OAc)2 (50 mol-%), Cu(OAc)2·H2O (3 equiv.), DMF, 160 °C, 3–4 h.
by the transformation of the aldehyde into an azidocinn-
We studied the absorption and fluorescence properties of
amate using a Rees–Moody protocol. The latter gave the 13–21 in four solvents of different polarity (cyclohexane,
methyl 1H-dibenzo[e,g]indole-2-carboxylate by thermolysis. diethyl ether, acetonitrile and ethanol). The maximum ab-
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New Fluorescent Indole Derivatives
sorption (λabs) and emission wavelengths (λem), molar ab- of 5500 –1 cm–1.[12] A methyl carboxylate group is present
sorption coefficients (ε) and fluorescence quantum yields in our compounds, and it is known that many carbonyl
(ΦF) of these indole derivatives are presented in Tables 3 compounds present a low-lying nǞπ* state. The πǞπ* and
and 4. The normalised absorption and fluorescence spectra nǞπ* electronic transitions can also be nearby in energy,
of 13–21 are presented in Figures 1, 2 and 3.
resulting in state mixing.[13] The higher ε values observed
All indole derivatives 13–21 presented relatively high mo- here can be explained by a predominance of πǞπ* charac-
lar absorption coefficients at the lowest energy maximum (ε ter in these compounds (Tables 3 and 4).
Ն 5.3ϫ103 –1 cm–1) in all the solvents studied (Tables 3
The absorption spectra of the indole derivatives 14, 17
and 4). The near-UV absorption of indole and its deriva- and 20 presented a broad and unstructured lowest-energy
tives was attributed to two strongly overlapping πǞπ* tran- band, due to the strong conjugation of the indole moiety
sitions,[9–11] with an average ε value for unsubstituted indole with the adjacent aromatic rings. A similar behaviour has
Table 3. Maximum absorption (λabs) and emission (λem) wavelengths, molar absorption coefficients (ε) and fluorescence quantum yields
(ΦF) for 13–16.
[a] Relative to 9,10-diphenylanthracene in ethanol (Φ = 0.95 at 25 °C).[8] The error was approximately 10%. Diethyl ether cut-off: 215 nm.
Table 4. Maximum absorption (λabs) and emission (λem) wavelengths, molar absorption coefficients (ε) and fluorescence quantum yields
(ΦF) for 17–21.
[a] Relative to 9,10-diphenylanthracene in ethanol (Φ = 0.95 at 25 °C).[8] The error was approximately 10%. Diethyl ether cut-off: 215 nm.
Eur. J. Org. Chem. 2010, 464–475
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G. Pereira, E. M. S. Castanheira, P. M. T. Ferreira, M.-J. R. P. Queiroz
FULL PAPER
Figure 1. Normalised absorption (in the lowest energy peak) and
fluorescence spectra of solutions (2ϫ10–5  for absorption and
2ϫ10–6  for fluorescence) of 13–15, in several solvents.
Figure 3. Normalised absorption (in the lowest energy peak) and
fluorescence spectra of solutions (2ϫ10–5  for absorption and
2ϫ10–6  for fluorescence) of 19–21, in several solvents.
previously been observed in a pyrenylindole-2-carboxylate
compound.[2] All other compounds, which had the indole
moiety condensed in an extended aromatic system, pre-
sented a structured absorption spectrum in the lower-en-
ergy region, as observed for a phenalenoindole[2] and pyr-
ene[2,1-b]pyrrole derivatives.[14]
The fluorescence spectra of indoles 14, 17 and 20 were
mainly unstructured bands, with large Stokes’ shifts and ap-
preciable solvatochromic behaviour, typical of the charge-
transfer (CT) character of the excited state, even in nonpo-
lar solvents. The influence of the solvent on the absorption
spectral shape was negligible. The effect on the emission
spectra was more pronounced for 17, where the spectral
shift between cyclohexane and ethanol was 44 nm. We ob-
served a similar behaviour due to a high CT character of
the excited state for a pyrenylindole-2-carboxylate.[2] Com-
pound 14 exhibited a slightly structured emission and a
small peak on the higher-energy side (at 359 nm), indicating
that there was a small contribution from the locally excited
(LE) state.
All the other compounds (13, 15, 16, 18, 19 and 21),
displayed fluorescence spectra with well-defined vibrational
structure, especially in solvents of low polarity (Figures 1,
2 and 3). Compounds 13 and 15 had similar absorption and
fluorescence spectra (Figure 1), with a low influence of the
solvent on the emission spectra. This behaviour indicates
that the substituent attached to the dibenzo[e,g]indole-2-
Figure 2. Normalised absorption (in the lowest energy peak) and
fluorescence spectra of solutions (2ϫ10–5  for absorption and
2ϫ10–6  for fluorescence) of 16–18, in several solvents.
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New Fluorescent Indole Derivatives
carboxylate moiety (a methyl group in 13 and a phen- and 15 exhibited noticeable spectral changes at intervals of
anthracenyl group in 15) had a small contribution to the 10 and 5 equiv. of F–, respectively (Figures 4 and 5),
lowest excited state.
whereas for 21, the spectral changes were significantly
We observed a pronounced loss of vibrational structure smaller (Figure 6). The addition of F– to solutions of 13
in polar solvents for 18 and 21 (Figures 2 and 3), indicating and 15 led to an intensely coloured fluorescence (blue and
the CT character of the excited state in polar solvents. The green, respectively) upon irradiation with near-UV light
effect was more significant in ethanol, probably due to con- (see the Supporting Information).
tribution of hydrogen bonding from this protic solvent,
through the α-NH group (donor) or carboxylate group (ac-
ceptor). The extension of the conjugation by the substitu-
tion of a methyl group (16 and 19) by an aromatic moiety
(18 and 21, respectively) provides a significant increase in
excited-state CT character.
All compounds had reasonable to high fluorescence
quantum yields in almost all the solvents studied (Tables 3
and 4), attaining 70–80% in some cases. We observed the
lowest ΦF values (between 16 and 42%) for 15, which is the
largest molecule with seven aromatic rings and showed a
predominance of the nonradiative pathways of deactivation.
The generally high fluorescence quantum yields of these
new indole derivatives and the different solvent sensitivity
of their fluorescence emission make them good candidates
for fluorescent probes.
It has been established that compounds containing pyr-
role, urea, amide, amine or phenol units can act as F– sen-
Figure 5. Fluorescence emission spectra (λex = 335 nm) of 15
(5ϫ10–6  in acetonitrile) in the presence of different amounts of
sors.[3] We also evaluated the response of 13–21 toward F–
F– (0, 5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 130, 150,
ions. We performed fluorescence titration experiments on
5ϫ10–6  solutions in acetonitrile with the incremental ad-
dition of F– (as the tetrabutylammonium salt). We observed
significant spectral changes in emission upon F– addition
for 13, 15 and 21 (Figures 4, 5 and 6), especially for 13 and
15. The emission spectrum of each compound decreased in
intensity, and a new unstructured band appeared at longer
wavelengths (maximum at ca. 465 nm for 13, 515 nm for 15
and ca. 510 nm for 21). In all cases, we observed a clear
isoemissive point [at 423 nm for 13 (Figure 4), 432 nm for
15 (Figure 5) and 440 nm for 21 (Figure 6)]. Compounds 13
200 and 250 equiv.).
Figure 6. Fluorescence emission spectra (λex = 325 nm) of 21
(5ϫ10–6  in acetonitrile) in the presence of different amounts of
F– (0, 20, 40, 60, 80, 100, 150, 200, 250, 300, 350, 400, 450 and
500 equiv.).
The corresponding UV/Vis absorption titrations caused
smaller spectral changes, but we observed clear changes for
larger amounts of F–, with the appearance of a new band
in the higher-wavelength region of the absorption spectrum
(see the Supporting Information). The excitation spectrum
obtained at the compound emission region was always very
Figure 4. Fluorescence emission spectra (λex = 325 nm) of 13
(5ϫ10–6  in acetonitrile) in the presence of different amounts of
F– (0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300,
350, 400, 450 and 500 equiv.).
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G. Pereira, E. M. S. Castanheira, P. M. T. Ferreira, M.-J. R. P. Queiroz
FULL PAPER
similar to the absorption spectrum in the absence of F–.
The excitation spectrum recorded at the maximum of the
new fluorescence band (where the compound emission is
negligible) also resembled the absorption spectrum (for the
same F– content), considering that the latter has a contri-
bution from the pure compound absorption (see the Sup-
porting Information).
We observed no detectable emission spectral changes
with F– addition to indoles 14, 16–18 and 20. For 19, we
detected a small new emission band in the presence of F–,
but only with large amounts of the anion (Ն300 equiv.),
and changes with further increases of F– content were negli-
gible.
The 1H NMR spectra in [D6]DMSO of 13 and 15
showed the appearance of a triplet at δ ≈ 16 ppm, character-
istic of the FHF moiety formed upon the addition of
2 equiv. of F–.[15] This clearly shows that the mechanism of
F– recognition was the deprotonation of the indole group
by the F– ion in the ground state. This explains why in these
new compounds the F– recognition is stronger for com-
pounds with a higher NH chemical shift (13, 15 and 21; see
Table 2). The higher NH acidity in these three compounds
can facilitate the hydrogen abstraction process and the for-
mation of the FHF species.
The formation of a compound anion also justifies the
anomalously large spectral shifts between the compound
emission (first peak) and the new fluorescence band[16]
(104 nm for 13, 157 nm for 15 and 159 nm for 21). The fluo-
rescence titration of a solution of 15 with OH– in acetoni-
trile revealed similar spectral changes as those observed
with F– (see the Supporting Information), with the new un-
structured band arising at the same emission wavelengths
(maximum at 515 nm), indicating that this new emission is
due to an indole 15 anion. The absorption spectra in the
presence of OH– and F– were also roughly similar (see the
Supporting Information), pointing to the formation of
identical species in the ground state, in the presence of
either of the two anions. A similar behaviour was reported
for the pyreno[2,1-b]pyrrole interaction with F– and OH– in
acetonitrile.[16] Intermolecular excited-state proton-transfer
processes have been reported in several indoles, with strong
hydrogen bonding with polar solvent molecules leading to
ion-pair formation.[17] However, in our new indole deriva-
tives, the proton abstraction from the NH group occurred
in the ground state (for an F– amount above 2 equiv.).
To examine the F– selectivity of these compounds, we
Figure 7. Response of 13, 15 and 21 to different anions in fluores-
cence titrations.
Conclusions
Several new pyrrole-fused compounds were prepared in
good yields from brominated dehydroamino acids and aryl-
boronic acids by a Suzuki–Miyaura cross coupling followed
by a Pd/Cu-mediated C–N intramolecular cyclisation. As
expected, the Suzuki products maintained the stereochemis-
try of the β-brominated dehydroamino acid starting mate-
rial. The cyclisation of (Z)-β-aryldehydrophenylalanines
gave mainly the product that results from isomerisation fol-
lowed by cyclisation.
The photophysical properties of the new indole deriva-
tives were studied in four solvents of different polarity. All
compounds showed reasonably high quantum yields in all
solvents (16–85%) and different solvent sensitivity of their
fluorescence emission, which indicated their potential use
as fluorescent probes.
Of all the compounds prepared, three (13, 15 and 21)
showed significant spectral changes in the fluorescence
emission upon F– addition with a decrease in intensity and
the appearance of a new band at longer wavelengths. Selec-
–
tivity tests performed with other anions (Cl–, Br–, HSO4
and CH3COO–) revealed no emission spectral changes, indi-
cating a selectivity of these compounds towards F–.
Experimental Section
Materials and Methods: Melting points [°C] were determined with
a Gallenkamp apparatus and are uncorrected. 1H and 13C NMR
spectra were recorded with a Bruker Avance II+ spectrometer at
performed fluorescence titrations of solutions of 13, 15 and
–
21 in acetonitrile with various anions (Cl–, Br–, HSO4 and 400 and 100.6 MHz, respectively. Chemical shifts and coupling
constants are given in ppm and Hz, respectively. 1H-13C heteronuc-
lear correlations, HMQC, HMBC and NOE experiments were also
performed. HRMS (EI or ESI) data were recorded by the mass
spectrometry service of the University of Vigo, Spain. Elemental
analysis was performed with a LECO CHNS 932 elemental ana-
lyser. The reactions were monitored by thin layer chromatography
(TLC). Column chromatography was performed on Macherey–Na-
gel silica gel (230–400 mesh). Petroleum ether refers to the fraction
that boils at 40–60 °C. When a solvent gradient was used, polarity
was increased from that of neat petroleum ether with diethyl ether
in 10% steps until the isolation of the product. PdCl2dppf·CH2Cl2
CH3COO– as the tetrabutylammonium salts). For each of
the compounds, we observed no emission spectral changes
for any of these anions, demonstrating the selectivity for
F–. Figure 7 displays the ratio of the maximum emission
intensities at the new band (Icompound–F–) and first peak
(Icompound) for the several anions tested. The corresponding
intensity ratio for the free compounds (without anion) at
the same wavelengths is shown for comparison. The high
electronegativity and basicity of F– may justify this selectiv-
ity.
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New Fluorescent Indole Derivatives
(1:1) refers to [1,1Ј-bis(diphenylphosphanyl)ferrocene]dichlorido-
palladium(II)–dichloromethane complex adduct.
[C(CH3)3], 52.22 (OCH3), 81.27 [OC(CH3)3], 122.58 (CH), 123.11
(CH), 125.85 (CH), 126.95 (CH), 127.06 (CH), 127.36 (CH), 127.44
(CH), 127.84 (CH), 127.90 (C), 128.18 (CH), 128.34 (CH), 128.87
(CH), 129.01 (CH), 129.41 (C), 130.36 (C), 130.80 (C), 131.29 (C),
134.50 (C), 139.44 (C), 152.50 (C=O), 166.27 (C=O) ppm. HRMS
(micrOTOF): calcd. for C29H28NO4 [M + H]+ 454.20183; found
454.20128.
Synthesis of (Z)-1, (E)-1, (Z)-2, (E)-2 and 9: The synthesis of these
compounds is described elsewhere.[18–20]
General Procedure for the Synthesis of β-Substituted Dehydroamino
Acid Derivatives: To a solution of the β-bromodehydroamino acid
derivative in THF/H2O (1:1) (0.05 ) boronic acid (1.5 or 5 equiv.),
PdCl2dppf·CH2Cl2 (1:1) (10 mol-%) and Cs2CO3 (1.4 equiv.) were
added. The reaction mixture was heated at 90 °C, and the reaction
was monitored by TLC until all of the β-bromodehydroamino acid
was consumed (1–3 h). The solvent was removed under reduced
pressure, and the residue was dissolved in ethyl acetate (100 mL).
The organic layer was washed with water and brine (2ϫ30 mL
each), dried with MgSO4, and the solvent was removed. The resi-
due was submitted to column chromatography.
Methyl (E)-2-(tert-Butoxycarbonylamino)-3-(phenanthracen-9-yl)-3-
phenylacrylate [(E)-4]: Compound (E)-4 was prepared from (E)-2
(0.50 mmol, 178 mg) and 9-phenanthracenylboronic acid according
to the general procedure described above and with heating for 2 h.
Column chromatography with diethyl ether/petroleum ether (1:4)
gave (E)-4 (132 mg, 58%) as a white solid. M.p. 173.0–174.0 °C
(from diethyl ether/petroleum ether). 1H NMR (400 MHz, CDCl3):
δ = 1.52 (s, 9 H, CH3 Boc), 3.23 (s, 3 H, OCH3), 6.42 (br. s, 1 H,
NH), 7.24–7.28 (m, 1 H, ArH), 7.31–7.35 (m, 2 H, ArH), 7.42–
7.49 (m, 3 H, ArH), 7.57–7.69 (m, 4 H, ArH), 7.88–7.94 (m, 2 H,
ArH), 8.67 (d, J = 8.4 Hz, 2 H, ArH) ppm. 13C NMR (100.6 MHz,
CDCl3): δ = 28.17 [C(CH3)3], 51.82 (OCH3), 81.36 [OC(CH3)3],
122.49 (CH), 122.63 (CH), 126.46 (CH), 126.62 (CH), 126.71 (CH),
126.91 (CH), 127.16 (CH), 127.75 (C), 128.02 (CH), 128.30 (CH),
128.70 (CH), 128.83 (CH), 129.03 (CH), 130.37 (C), 130.58 (C),
130.74 (C), 131.17 (C), 132.32 (C), 135.76 (C), 137.65 (C), 152.86
(C=O), 166.12 (C=O) ppm. HRMS (micrOTOF): calcd. for
C29H27NNaO4 [M]+ 476.18378; found 476.18323.
Methyl (Z)-2-(tert-Butoxycarbonylamino)-3-(phenanthracen-9-yl)-
but-2-enoate [(Z)-3]: Compound (Z)-3 was prepared from (Z)-1
(0.5 mmol, 147 mg) and 9-phenanthracenylboronic acid according
to the general procedure described above and with heating for 1 h.
Column chromatography with diethyl ether/petroleum ether (1:4)
gave (Z)-3 (120 mg, 61%) as a white solid. M.p. 159.0–160.0 °C
(from diethyl ether/petroleum ether). 1H NMR (400 MHz, CDCl3):
δ = 1.27 (s, 9 H, CH3 Boc), 2.38 (s, 3 H, CH3), 3.95 (s, 3 H, OCH3),
5.61 (br. s, 1 H, NH), 7.59–7.73 (m, 5 H, ArH), 7.89 (d, J = 8.0 Hz,
2 H ArH), 8.72 (d, J = 8.4 Hz, 1 H, ArH), 8.77 (d, J = 8.0 Hz, 1
H, ArH) ppm. 13C NMR (100.6 MHz, CDCl3): δ = 21.03 (CH3),
27.98 [C(CH3)3], 52.08 (OCH3), 80.67 [OC(CH3)3], 122.58 (CH),
123.22 (CH), 125.28 (CH), 125.53 (CH), 126.06 (C), 126.95 (CH),
127.05 (CH), 127.06 (CH), 127.30 (CH), 128.48 (C), 128.64 (CH),
130.10 (C), 130.77 (C), 131.38 (C), 131.93 (C), 136.22 (C), 152.96
(C=O), 165.54 (C=O) ppm. HRMS (micrOTOF): calcd. for
C24H26NO4 [M + H]+ 392.18618; found 392.18563.
Methyl (Z)-2-(tert-Butoxycarbonylamino)-(1,2-dihydroacenaphth-
ylen-5-yl)but-2-enoate [(Z)-5]: Compound (Z)-5 was prepared from
(Z)-1 (0.5 mmol, 147 mg) and (1,2-dihydroacenaphthylen-5-yl)bo-
ronic acid according to the general procedure described above and
with heating for 1 h. Column chromatography with diethyl ether/
petroleum ether (3:7) gave (Z)-5 (133 mg, 72%) as a white solid.
M.p. 106–107 °C (from diethyl ether/petroleum ether). 1H NMR
(400 MHz, CDCl3): δ = 1.32 (s, 9 H, CH3 Boc), 2.32 (s, 3 H, CH3),
3.43 (s, 4 H, 2 CH2), 3.91 (s, 3 H, OCH3), 5.56 (br. s, 1 H, NH),
7.25–7.33 (m, 3 H, ArH), 7.43–7.49 (m, 2 H, ArH) ppm. 13C NMR
(100.6 MHz, CDCl3): δ = 21.15 (CH3), 28.04 [C(CH3)3], 30.11
(CH2), 30.44 (CH2), 51.96 (OCH3), 80.50 [OC(CH3)3], 119.15
(CH), 119.74 (CH), 119.94 (CH), 125.36 (C), 126.91 (CH), 128.00
(C), 128.61 (CH), 131.53 (C), 132.74 (C), 139.50 (C), 146.44 (C),
146.53 (C), 153.10 (C=O), 165.76 (C=O) ppm. C22H25NO4
(367.44): calcd. C 71.91, H 6.86, N 3.81; found C 71.46, H 6.34, N
3.75.
Methyl (E)-2-(tert-Butoxycarbonylamino)-3-(phenanthracen-9-yl)-
but-2-enoate [(E)-3]: Compound (E)-3 was prepared from (E)-1
(0.5 mmol, 147 mg) and 9-phenanthracenylboronic acid according
to the general procedure described above and with heating for 1 h.
Column chromatography with diethyl ether/petroleum ether (1:3)
gave (E)-3 (128 mg, 65%) as a white solid. M.p. 143.0–144.0 °C
(from diethyl ether/petroleum ether). 1H NMR (400 MHz, CDCl3):
δ = 1.57 (s, 9 H, CH3 Boc), 2.27 (s, 3 H, CH3), 3.24 (s, 3 H, OCH3),
6.28 (br. s, 1 H, NH), 7.46 (s, 1 H, ArH), 7.56–7.69 (m, 4 H, ArH),
7.83 (dd, J = 7.8, 1.2 Hz, 1 H, ArH), 7.94 (d, J = 8.0 Hz, 1 H,
ArH), 8.68 (d, J = 8.4 Hz, 1 H, ArH), 8.73 (d, J = 8.4 Hz, 1 H,
ArH) ppm. 13C NMR (100.6 MHz, CDCl3): δ = 22.32 (CH3), 28.28
[C(CH3)3], 51.63 (OCH3), 80.75 [OC(CH3)3], 122.51 (CH), 122.86
(CH), 124.18 (CH), 125.33 (C), 126.11 (CH), 126.46 (CH), 126.62
(CH), 126.76 (CH), 128.50 (CH), 129.88 (C), 130.32 (C), 131.43
(C), 138.20 (C), 140.93 (C), 153.41 (C=O), 165.11 (C=O) ppm.
HRMS (micrOTOF): calcd. for C24H26NO4 [M + H]+ 392.18618;
found 392.18563.
Methyl (E)-2-(tert-Butoxycarbonylamino)-(1,2-dihydroacenaphth-
ylen-5-yl)but-2-enoate [(E)-5]: Compound (E)-5 was prepared from
(E)-1 (0.5 mmol, 147 mg) and (1,2-dihydroacenaphthylen-5-yl)bo-
ronic acid according to the general procedure described above and
with heating for 1 h. Column chromatography with diethyl ether/
petroleum ether (3:7) gave (E)-5 (149 mg, 81%) as a white solid.
M.p. 131.0–132.0 °C (from diethyl ether/petroleum ether). 1H
NMR (400 MHz, CDCl3): δ = 1.53 (s, 9 H, CH3 Boc), 2.23 (s, 3
H, CH3), 3.03 (s, 3 H, OCH3), 3.40 (s, 4 H, 2 CH2), 6.16 (br. s, 1
H, NH), 7.17 (d, J = 7.2 Hz, 1 H, ArH), 7.22–7.28 (m, 2 H, ArH),
7.40–7.45 (m, 1 H, ArH), 7.54 (d, J = 8.1 Hz, 1 H, ArH) ppm. 13C
NMR (100.6 MHz, CDCl3): δ = 22.42 (CH3), 28.28 [C(CH3)3],
30.07 (CH2), 30.48 (CH2), 51.63 (OCH3), 80.62 [OC(CH3)3], 118.70
(CH), 119.28 (CH), 120.29 (CH), 124.86 (C), 125.83 (CH), 127.96
(CH), 129.02 (C), 134.68 (C), 139.19 (C), 140.46 (C), 145.44 (C),
146.12 (C), 153.41 (C=O), 165.21 (C=O) ppm. C22H25NO4
(367.44): calcd. C 71.91, H 6.86, N 3.81; found C 71.97, H 6.48, N
3.74.
Methyl (Z)-2-(tert-Butoxycarbonylamino)-3-(phenanthracen-9-yl)-3-
phenylacrylate [(Z)-4]: Compound (Z)-4 was prepared from (Z)-2
(0.50 mmol, 178 mg) and 9-phenanthracenylboronic acid according
to the general procedure described above and with heating for 1 h.
Column chromatography with diethyl ether/petroleum ether (1:3)
gave (Z)-4 (185 mg, 82%) as a white solid. M.p. 168.0–169.0 °C
(from diethyl ether/petroleum ether). 1H NMR (400 MHz, CDCl3):
δ = 1.33 (s, 9 H, CH3 Boc), 3.70 (s, 3 H, OCH3), 5.77 (br. s, 1 H,
NH), 7.26–7.30 (m, 5 H, ArH), 7.60–7.65 (m, 3 H, ArH), 7.69–
7.74 (m, 2 H, ArH), 7.85 (d, J = 7.6 Hz, 1 H, ArH), 8.12 (d, J =
8.4 Hz, 1 H, ArH), 8.74 (d, J = 8.0 Hz, 1 H, ArH), 8.78 (d, J =
Methyl (Z)-2-(tert-Butoxycarbonylamino)-3-phenyl-3-(1,2-dihydro-
8.0 Hz, 1 H, ArH) ppm. 13C NMR (100.6 MHz, CDCl3): δ = 27.99 acenaphthylen-5-yl)acrylate [(Z)-6]: Compound (Z)-6 was prepared
Eur. J. Org. Chem. 2010, 464–475
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
471

G. Pereira, E. M. S. Castanheira, P. M. T. Ferreira, M.-J. R. P. Queiroz
FULL PAPER
from (Z)-2 (0.5 mmol, 178 mg) and (1,2-dihydroacenaphthylen-5-
yl)boronic acid according to the general procedure described above
and with heating for 1.5 h. Column chromatography with diethyl
ether/petroleum ether (1:3) gave (Z)-6 (170 mg, 79%) as a white
solid. M.p. 160.0–161.0 °C (from diethyl ether/petroleum ether). 1H
NMR (400 MHz, CDCl3): δ = 1.37 (s, 9 H, CH3 Boc), 3.41–3.46
(m, 4 H, 2 CH2), 3.64 (s, 3 H, OCH3), 5.76 (br. s, 1 H, NH), 7.17–
7.21 (m, 3 H, ArH), 7.24–7.28 (m, 4 H, ArH), 7.32 (d, J = 6.8 Hz,
1 H, ArH), 7.44 (t, J = 7.6 Hz, 1 H, ArH), 7.60 (d, J = 8.4 Hz, 1
H, ArH) ppm. 13C NMR (100.6 MHz, CDCl3): δ = 28.03 [C-
(CH3)3], 30.17 (CH2), 30.42 (CH2), 52.06 (OCH3), 80.98 [OC-
(CH3)3], 119.22 (CH), 119.73 (CH), 120.45 (CH), 126.92 (C),
127.64 (C), 128.03 (CH), 128.61 (CH), 128.81 (CH), 129.05 (C),
130.40 (CH), 131.15 (C), 139.54 (C), 140.32 (C), 146.42 (C), 147.24
(C), 152.76 (C=O), 166.51 (C=O) ppm. HRMS (micrOTOF):
calcd. for C27H28NO4 [M + H]+ 430.20183; found 430.20128.
153.36 (C=O), 165.04 (C=O) ppm. HRMS (EI): calcd. for
C20H23NNaO4 [M]+ 364.15193; found 364.15159.
Methyl
(Z)-2-(tert-Butoxycarbonylamino)-3-(naphthalen-1-yl)-3-
phenylacrylate [(Z)-8]: Compound (Z)-8 was prepared from (Z)-2
(0.5 mmol, 178 mg) and (naphthalen-1-yl)boronic acid according
to the general procedure described above and with heating for 1 h.
Column chromatography with diethyl ether/petroleum ether (1:2)
gave (Z)-8 (149 mg, 74%) as a white solid. M.p. 165.0–166.0 °C
(from diethyl ether/petroleum ether). 1H NMR (400 MHz, CDCl3):
δ = 1.35 (s, 9 H, CH3 Boc), 3.66 (s, 3 H, OCH3), 5.67 (br. s, 1 H,
NH), 7.18–7.30 (m, 6 H, ArH), 7.47–7.54 (m, 3 H, ArH), 7.86–
7.92 (m, 2 H, ArH), 8.02 (d, J = 8.0 Hz, 1 H, ArH) ppm. 13C NMR
(100.6 MHz, CDCl3): δ = 28.00 [C(CH3)3], 52.14 (OCH3), 81.17
[OC(CH3)3], 125.07 (CH), 125.62 (CH), 126.27 (CH), 127.06 (CH),
127.57 (C), 127.75 (CH), 128.12 (CH), 128.36 (CH), 128.56 (CH),
128.89 (CH), 130.57 (C), 133.90 (C), 135.66 (C), 139.74 (C), 152.53
(C=O), 166.30 (C=O) ppm. HRMS (micrOTOF): calcd. for
C25H26NO4 [M + H]+ 404.18618; found 404.18563.
Methyl (E)-2-(tert-Butoxycarbonylamino)-3-(1,2-dihydroacenaphth-
ylen-5-yl)-3-phenylacrylate [(E)-6]: Compound (E)-6 was prepared
from (E)-2 (0.5 mmol, 178 mg) and (1,2-dihydroacenaphthylen-5-
yl)boronic acid according to the general procedure described above
and with heating for 2 h. Column chromatography with diethyl
ether/petroleum ether (1:4) gave (E)-6 (154 mg, 72%) as a white
solid. M.p. 157.0–158.0 °C (from diethyl ether/petroleum ether). 1H
NMR (400 MHz, CDCl3): δ = 1.48 (s, 9 H, CH3 Boc), 3.33 (s, 3
H, OCH3), 3.39 (s, 4 H, 2 CH2), 6.31 (br. s, 1 H, NH), 7.23–7.38
(m, 10 H, ArH) ppm. 13C NMR (100.6 MHz, CDCl3): δ = 28.17
[C(CH3)3], 30.06 (CH2), 30.44 (CH2), 51.82 (OCH3), 81.13
[OC(CH3)3], 118.61 (CH), 119.29 (CH), 120.98 (CH), 126.95 (C),
127.92 (CH), 128.05 (C), 128.12 (CH), 128.74 (CH), 129.21 (CH),
129.25 (CH), 130.24 (C), 132.54 (C), 138.68 (C), 139.48 (C), 145.94
(C), 146.54 (C), 152.94 (C=O), 166.31 (C=O) ppm. HRMS (EI):
calcd. for C27H27NNaO4 [M]+ 452.18323; found 452.18279.
Methyl
(E)-2-(tert-Butoxycarbonylamino)-3-(naphthalen-1-yl)-3-
phenylacrylate [(E)-8]: Compound (E)-8 was prepared from (E)-2
(0.5 mmol, 178 mg) and (naphthalen-1-yl)boronic acid according
to the general procedure described above and with heating for 1 h.
Column chromatography with diethyl ether/petroleum ether (1:2)
gave (E)-8 (157 mg, 78%) as a white solid. M.p. 155.0–156.0 °C
(from diethyl ether/petroleum ether). 1H NMR (400 MHz, CDCl3):
δ = 1.48 (s, 9 H, CH3 Boc), 3.23 (s, 3 H, OCH3), 6.35 (br. s, 1 H,
NH), 7.24–7.46 (m, 9 H, ArH), 7.80–7.85 (m, 3 H, ArH) ppm. 13
C
NMR (100.6 MHz, CDCl3): δ = 28.20 [C(CH3)3], 51.74 (OCH3),
81.17 [OC(CH3)3], 124.99 (CH), 125.76 (CH), 126.06 (CH), 126.15
(CH), 127.33 (CH), 127.54 (C), 128.12 (CH), 128.22 (CH), 128.44
(CH), 128.81 (CH), 129.04 (CH), 131.85 (C), 132.48 (C), 133.71
(C), 137.10 (C), 138.24 (C), 152.89 (C=O), 166.06 (C=O) ppm.
C25H25NO4 (403.47): calcd. C 74.42, H 6.25, N 3.47; found C
74.52, H 6.07, N 3.43.
Methyl (Z)-2-(tert-Butoxycarbonylamino)-3-(naphthalen-1-yl)but-2-
enoate [(Z)-7]: Compound (Z)-7 was prepared from (Z)-1
(0.5 mmol, 147 mg) and (naphthalen-1-yl)boronic acid according
to the general procedure described above and with heating for 1 h.
Column chromatography with diethyl ether/petroleum ether (3:7)
gave (Z)-7 (125 mg, 73%) as a white solid. M.p. 88.0–89.0 °C (from
diethyl ether/petroleum ether). 1H NMR (400 MHz, CDCl3): δ =
1.30 (s, 9 H, CH3 Boc), 2.32 (s, 3 H, CH3), 3.92 (s, 3 H, OCH3),
5.48 (br. s, 1 H, NH), 7.30 (s, 1 H, ArH), 7.49–7.52 (m, 3 H, ArH),
7.78–7.85 (m, 2 H, ArH), 7.88–7.90 (m, 1 H, ArH) ppm. 13C NMR
(100.6 MHz, CDCl3): δ = 21.19 (CH3), 27.99 [C(CH3)3], 52.03
(OCH3), 82.57 [OC(CH3)3], 124.55 (CH), 124.83 (CH), 125.66
(CH), 125.72 (C), 126.26 (CH), 126.82 (CH), 128.24 (CH), 128.61
(CH), 129.48 (C), 132.16 (C), 133.83 (C), 137.51 (C), 152.95 (C=O),
165.58 (C=O) ppm. C20H23NO4 (341.40): calcd. C 70.36, H 6.79,
N 4.10; found C 70.32, H 6.80, N 4.07.
Methyl 2-(tert-Butoxycarbonylamino)-3,3-bis(phenanthracen-9-yl)-
acrylate (10): Compound 10 was prepared from 9 (0.5 mmol,
178.4 mg) and 9-phenanthracenylboronic acid (5 equiv., 2.5 mmol)
according to the general procedure described above and with heat-
ing for 2 h. Column chromatography with diethyl ether/petroleum
ether (1:3) gave 10 (175 mg, 63%) as a white solid. M.p. 212.0–
213.0 °C (from ethyl acetate/petroleum ether). 1H NMR (400 MHz,
CDCl3): δ = 1.37 (s, 9 H, CH3 Boc), 3.36 (s, 3 H, OMe), 5.84 (br.
s, 1 H, NH), 7.17–7.21 (m, 1 H, ArH), 7.45–7.54 (m, 3 H, ArH),
7.59–7.80 (m, 8 H, ArH), 7.89–7.91 (m, 2 H, ArH), 8.00–8.02 (m,
1 H, ArH), 8.64–8.70 (m, 2 H, ArH), 8.81–8.83 (m, 1 H, ArH)
ppm. 13C NMR (100.6 MHz, CDCl3): δ = 28.06 [(CH3)3C], 52.13
(OCH3), 81.21 [(CH3)3C], 122.40 (CH), 122.57 (CH), 122.70 (CH),
123.57 (CH), 126.27 (CH), 126.56 (CH), 126.75 (CH), 126.83 (CH),
126.89 (CH), 126.93 (CH), 127.01 (CH), 127.11 (CH), 127.52 (CH),
128.05 (CH), 128.82 (CH), 128.97 (CH), 128.70 (CH), 129.70 (CH),
129.80 (C), 130.13 (C), 130.19 (C), 130.45 (C), 130.54 (C), 130.60
(C), 130.69 (C), 130.94 (C), 131.29 (C), 132.95 (C), 135.71 (C),
136.82 (C), 152.74 (C=O), 166.22 (C=O) ppm. HRMS (micrO-
Methyl (E)-2-(tert-Butoxycarbonylamino)-3-(naphthalen-1-yl)but-2-
enoate [(E)-7]: Compound (E)-8 was prepared from (E)-1
(1.0 mmol, 294 mg) and (naphthalen-1-yl)boronic acid according
to the general procedure described above and with heating for 1 h.
Column chromatography with diethyl ether/petroleum ether (3:7)
gave (E)-7 (250 mg, 73%) as a white solid. M.p. 79.0–80.0 °C (from
diethyl ether/petroleum ether). 1H NMR (400 MHz, CDCl3): δ =
1.55 (s, 9 H, CH3 Boc), 2.24 (s, 3 H, CH3), 3.25 (s, 3 H, OCH3),
TOF): calcd. for C37H32NO4 [M
554.23258.
+
H]+ 554.23313; found
Methyl 2-(tert-Butoxycarbonylamino)-3,3-bis(1,2-dihydroacenaphth-
6.22 (br. s, 1 H, NH), 7.20 (d, J = 6.8 Hz, 1 H, ArH), 7.40–7.49 en-5-yl)acrylate (11): Compound 11 was prepared from
(m, 3 H, ArH), 7.77 (d, J = 8.4 Hz, 1 H, ArH), 7.84–7.88 (m, 2 H, (0.25 mmol, 89.2 mg) and 1,2-dihydroacenaphthylen-5-ylboronic
ArH) ppm. 13C NMR (100.6 MHz, CDCl3): δ = 22.59 (CH3), 28.27
acid (5 equiv., 1.25 mmol) according to the general procedure de-
9
[C(CH3)3], 51.56 (OCH3), 80.70 [OC(CH3)3], 123.80 (CH), 125.15 scribed above and with heating for 2 h. Column chromatography
(CH), 125.27 (CH), 125.74 (CH), 126.13 (CH), 127.42 (CH), 128.22 with diethyl ether/petroleum ether (1:3) gave 11 (85 mg, 67%) as a
1
(CH), 130.58 (C), 133.41 (C), 139.49 (C), 141.11 (C), 150.47 (C),
white solid. M.p. 121.0–122.0 °C (from ethyl acetate/n-hexane). H
472
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 464–475

New Fluorescent Indole Derivatives
NMR (400 MHz, [D6]DMSO): δ = 1.34 (s, 9 H, CH3 Boc), 3.25 (s, ArH), 9.46 (br. s, 1 H, NH) ppm. 13C NMR (100.6 MHz, CDCl3): δ
3 H, OCH3), 3.29–3.39 (m, 4 H, 2 CH2), 7.00 (d, J = 7.2 Hz, 1 H,
= 51.74 (OCH3), 111.81 (CH), 120.84 (CH), 121.89 (C), 121.98
ArH), 7.13–7.25 (m, 6 H, ArH), 7.34 (d, J = 6.8 Hz, 1 H, ArH), (CH), 122.54 (CH), 122.67 (CH), 124.43 (C), 125.86 (CH), 126.24
7.47 (t, J = 8.4 Hz, 1 H, ArH), 7.74 (d, J = 8.0 Hz, 1 H, ArH), (CH), 126.29 (CH), 126.56 (CH), 126.58 (CH), 126.88 (CH), 128.64
8.10 (br. s, 1 H, NH) ppm. 13C NMR (100.6 MHz, [D6]DMSO): δ (CH), 128.99 (CH), 129.03 (C), 130.25 (C), 130.32 (C), 130.39 (C),
= 27.59 [C(CH3)3], 29.22 (CH2), 29.61 (CH2), 50.66 (OCH3), 78.88
[OC(CH3)3], 118.31 (CH), 118.63 (CH), 118.77 (CH), 118.81 (CH),
119.87 (CH), 120.31 (CH), 127.37 (CH), 127.77 (CH), 127.92 (C),
128.18 (CH), 128.23 (C), 129.67 (C), 129.74 (CH), 132.08 (C),
132.98 (C), 134.13 (C), 138.59 (C), 145.33 (C), 145.43 (C), 145.79
(C), 153.00 (C=O), 165.57 (C=O) ppm. HRMS (micrOTOF):
calcd. for C33H32NO4 [M + H]+ 506.23313; found 506.23258.
131.61 (C), 131.85 (C), 135.89 (C), 162.58 (C=O) ppm. HRMS
(micrOTOF): calcd. for C24H18NO2 [M + H]+ 352.13375; found
352.13321.
Methyl 3-(Phenanthren-9-yl)-1H-dibenzo[e,g]indole-2-carboxylate
(15): Compound 15 was prepared from 10 (0.32 mmol, 175 mg)
according to the general procedure described above and with heat-
ing for 4 h (110 mg, 52%). Column chromatography with diethyl
ether/petroleum ether (1:3) afforded 15 as a white solid. M.p.
260.0–261.0 °C (from ethyl acetate/petroleum ether). 1H NMR
(400 MHz, CDCl3): δ = 3.55 (s, 3 H, OCH3), 7.00 (t, J = 8 Hz, 1
H, ArH), 7.35–7.41 (m, 3 H, ArH), 7.65–7.77 (m, 6 H, ArH), 7.91
(s, 1 H, ArH), 7.88 (d, J = 8 Hz, 1 H, ArH), 8.24–8.26 (m, 1 H,
ArH), 8.61 (d, J = 8 Hz, 1 H, ArH), 8.70–8.73 (m, 1 H, ArH), 8.86
(d, J = 8.4 Hz, 2 H, ArH), 10.05 (br. s, 1 H, NH) ppm. 13C NMR
(100.6 MHz, CDCl3): δ = 51.71 (OCH3), 120.33 (C), 120.78 (CH),
122.37 (C), 122.70 (CH), 122.81 (CH), 122.95 (C), 123.30 (CH),
123.94 (CH), 124.04 (CH), 124.66 (CH), 124.84 (C), 126.53 (CH),
126.62 (CH), 126.66 (CH), 126.72 (CH), 126.73 (CH), 126.78 (CH),
127.06 (CH), 127.14 (CH), 127.85 (C), 128.50 (CH), 128.73 (C),
128.89 (CH), 130.21 (C), 130.49 (C), 130.63 (C), 131.92 (C), 131.98
(C), 132.39 (C), 162.14 (C=O) ppm. HRMS (micrOTOF): calcd.
for C32H22NO4 [M + H]+ 452.16505; found 452.16451.
Methyl 2-(tert-Butoxycarbonylamino)-3,3-bis(naphthalen-1-yl)acryl-
ate (12): Compound 12 was prepared from 9 (0.5 mmol, 178 mg)
and (naphthalen-1-yl)boronic acid (5 equiv.) according to the gene-
ral procedure described above and with heating for 2 h. Column
chromatography with diethyl ether/petroleum ether (1:2) gave 12
(160 mg, 71%) as a white solid. M.p. 194.0–195.0 °C (from ethyl
acetate/petroleum ether). 1H NMR (400 MHz, CDCl3): δ = 1.38 (s,
9 H, CH3 Boc), 3.36 (s, 3 H, OCH3), 5.78 (br. s, 1 H, NH), 7.12–
7.18 (m, 1 H, ArH), 7.28–7.36 (m, 3 H, ArH), 7.46–7.50 (m, 2 H,
ArH), 7.53–7.69 (m, 2 H, ArH), 7.72–7.88 (m, 4 H, ArH), 7.93 (d,
J = 7.6 Hz, 1 H, ArH), 8.41 (d, J = 7.2 Hz, 1 H, ArH) ppm. 13C
NMR (100.6 MHz, CDCl3): δ = 28.03 [C(CH3)3], 51.90 (OCH3),
81.15 [OC(CH3)3], 124.90 (CH), 125.34 (CH), 125.54 (CH), 125.77
(CH), 126.06 (CH), 126.20 (CH), 126.51 (CH), 127.29 (CH), 127.34
(CH), 127.60 (CH), 128.15 (CH), 128.78 (CH), 129.12 (CH), 129.23
(CH), 129.27 (C), 129.51 (C), 132.00 (C), 133.78 (C), 133.90 (C),
134.72 (C), 136.61 (C), 138.05 (C), 152.82 (C=O), 166.16 (C=O)
ppm. HRMS (micrOTOF): calcd. for C29H28NO4 [M + H]+
454.20183; found 454.20128.
Methyl 9-Methyl-5,7-dihydro-4H-indeno[7,1-ef]indole-8-carboxylate
(16): Compound 16 was prepared from (Z)-5 (0.27 mmol, 100 mg)
according to the general procedure described above and with heat-
ing for 4 h. Crystallization (ethyl acetate/petroleum ether) gave 16
(50 mg, 70%) as a white solid. M.p. 240.0–241.0 °C (from ethyl
acetate/petroleum ether). 1H NMR (400 MHz, CDCl3): δ = 3.00 (s,
3 H, CH3), 3.39–3.46 (dd, J = 7.6 Hz, 4 H, 2 CH2), 3.97 (s, 3 H,
OCH3), 7.21 (s, 1 H, ArH), 7.31 (d, J = 7.2 Hz, 1 H, ArH), 7.56
(t, J = 7.6 Hz, 1 H, ArH), 8.14 (d, J = 8.0 Hz, 1 H, ArH), 8.97 (br.
s, 1 H, NH) ppm. 13C NMR (100.6 MHz, CDCl3): δ = 12.77 (CH3),
29.58 (CH2), 31.01 (CH2), 51.43 (OCH3), 106.03 (CH), 118.32
(CH), 119.05 (CH), 119.60 (C), 120.57 (C), 127.95 (C), 128.37
(CH), 135.78 (C), 136.14 (C), 145.64 (C), 146.23 (C), 162.95 (C=O)
ppm. C17H15NO2 (265.31): calcd. C 76.96, H 5.70, N 5.28; found
C 76.55, H 5.36, N 4.99.
General Procedure for the Intramolecular Cyclisation: To a solution
of the β-substituted or β,β-disubstituted dehydroamino acid deriva-
tives in DMF, Pd(OAc)2 (50 mol-%) and Cu(OAc)2·H2O (3 equiv.)
were added, and the mixture was heated at 160 °C (the reaction
was moniored by TLC). Ethyl acetate (50 mL) was then added, and
the organic layer was washed with water and brine (2ϫ30 mL,
each), dried with MgSO4, and the solvent was removed.
Methyl 3-Methyl-1H-dibenzo[e,g]indole-2-carboxylate (13): Com-
pound 13 was prepared from (Z)-3 (0.29 mmol, 112 mg) according
to the general procedure described above and with heating for 6 h.
Column chromatography with diethyl ether/petroleum ether (1:4)
afforded 13 (33.4 mg, 40%) as a white solid. M.p. 212.0–213.0 °C
(from ethyl acetate/petroleum ether). 1H NMR (400 MHz, CDCl3):
δ = 3.05 (s, 3 H, CH3), 4.01 (s, 3 H, OCH3), 7.55–7.59 (m, 1 H,
ArH), 7.62–7.68 (m, 3 H, ArH), 8.06–8.08 (m, 1 H, ArH), 8.53 (d,
J = 8.4 Hz, 1 H, ArH), 8.67–8.70 (m, 2 H, ArH), 9.56 (br. s, 1 H,
NH) ppm. 13C NMR (100.6 MHz, CDCl3): δ = 51.60 (OCH3),
119.50 (C), 120.59 (CH), 121.29 (C), 122.37 (C), 123.66 (CH),
123.78 (CH), 123.90 (CH and C), 124.33 (CH), 126.46 (CH), 126.91
(CH), 127.13 (CH), 127.77 (C), 129.96 (C), 130.01 (C), 130.67 (C),
162.71 (C=O) ppm. C19H15NO2 (289.33): calcd. C 78.87, H 5.23,
N 4.84; found C 78.75, H 5.32, N 4.32.
Methyl 3-(1,2-Dihydroacenaphthylen-5-yl)-1H-indole-2-carboxylate
(17) and Methyl 9-phenyl-5,7-dihydro-4H-indeno[7,1-ef]indole-8-
carboxylate (18): A mixture (4:1) of 17/18 was obtained by applying
the general procedure described above to (Z)-6 (0.35 mmol,
150 mg) and heating for 4 h (79 mg, 65%). Column chromatog-
raphy with diethyl ether/petroleum ether (1:3) afforded 17 as a
white solid. M.p. 220.0–221.0 °C (from ethyl acetate/petroleum
ether). 1H NMR (400 MHz, CDCl3): δ = 3.49 (s, 4 H, 2 CH2), 3.65
(s, 3 H, OCH3), 7.09 (t, J = 7.8 Hz, 1 H, ArH), 7.27–7.34 (m, 3 H,
ArH), 7.36–7.40 (m, 3 H, ArH), 7.49–7.54 (m, 2 H, ArH), 9.11 (br.
s, 1 H, NH) ppm. 13C NMR (100.6 MHz, CDCl3): δ = 30.21 (CH2),
30.55 (CH2), 51.70 (OCH3), 111.66 (CH), 118.81 (CH), 119.02
(CH), 120.64 (CH), 121.35 (CH), 122.08 (C), 122.27 (CH), 123.82
(C), 125.79 (CH), 126.54 (C), 127.52 (CH), 128.83 (C), 130.19
(CH), 130.94 (C), 135.77 (C), 139.36 (C), 145.85 (C), 146.00 (C),
Methyl 3-(Phenanthren-9-yl)-1H-indole-2-carboxylate (14): Com-
pound 14 was prepared from (Z)-4 (0.5 mmol, 227 mg) according
to the general procedure described above and with heating for 4 h.
Crystallization (diethyl ether/petroleum ether) gave 14 (137 mg,
78%) as a white solid. M.p. 102.0–103.0 °C (from diethyl ether/ 162.46 (C=O) ppm. HRMS (micrOTOF): calcd. for C22H18NO2
petroleum ether). 1H NMR (400 MHz, CDCl3): δ = 3.59 (s, 3 H, [M + H]+ 328.13375; found 328.13321. Compound 18 was also
OCH3), 7.11 (t, J = 7.6 Hz, 1 H, ArH), 7.36–7.49 (m, 3 H, ArH),
7.54 (d, J = 8.4 Hz, 1 H, ArH), 7.63–7.74 (m, 4 H, ArH), 7.84 (s, petroleum ether). H NMR (400 MHz, CDCl3): δ = 3.43 (s, 4 H, 2
1 H, ArH), 7.92 (d, J = 7.2 Hz, 1 H, ArH), 8.81 (t, J = 7.6 Hz, 2 H, CH2), 3.75 (s, 3 H, OCH3), 7.22–7.24 (m, 3 H, ArH), 7.29 (s, 1 H,
isolated as white solid. M.p. 203.0–204.0 °C (from ethyl acetate/
1
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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473

G. Pereira, E. M. S. Castanheira, P. M. T. Ferreira, M.-J. R. P. Queiroz
FULL PAPER
ArH), 7.47–7.55 (m, 5 H, ArH), 9.21 (br. s, 1 H, NH) ppm. 13C
Fluorescence Quantum Yields: For fluorescence quantum yield de-
NMR (100.6 MHz, CDCl3): δ = 29.63 (CH2), 30.96 (CH2), 51.49 terminations, the solutions were bubbled with ultrapure nitrogen
(OCH3), 105.87 (CH), 118.63 (CH), 118.96 (CH), 119.28 (C), for 40 min before measurement. The fluorescence quantum yields
120.73 (C), 126.83 (C), 127.16 (C), 127.41 (CH), 128.01 (CH), (Φs) were determined by the standard method [Equation (1)].[21,22]
128.16 (CH), 130.31 (CH), 135.68 (C), 135.72 (C), 135.96 (C), 9,10-Diphenylanthracene in ethanol (Φr = 0.95[10]) was the refer-
145.95 (C), 146.06 (C), 162.26 (C=O) ppm. HRMS (micrOTOF):
ence.
calcd. for C22H18NO4 [M + H]+ 328.13375; found 328.133321.
Methyl 1-Methyl-3H-benzo[e]indole-2-carboxylate (19): Compound
19 was prepared from (Z)-7 (0.29 mmol, 112 mg) according to the
general procedure described above and with heating for 6 h. Col-
umn chromatography with diethyl ether/petroleum ether (1:4) af-
forded 19 (33.4 mg, 47%) as a white solid. M.p. 212.0–213.0 °C
(from ethyl acetate/petroleum ether). 1H NMR (400 MHz, CDCl3):
δ = 3.07 (s, 3 H, CH3), 3.99 (s, 3 H, OCH3), 7.45–7.49 (m, 2 H,
ArH), 7.60–7.64 (m, 1 H, ArH), 7.70 (d, J = 9.2 Hz, 1 H, ArH),
7.91–7.93 (m, 1 H, ArH), 8.55 (d, J = 8.0 Hz, 1 H, ArH), 9.56 (br.
s, 1 H, NH) ppm. 13C NMR (100.6 MHz, CDCl3): δ = 51.58
(OCH3), 112.92 (CH), 121.48 (C), 121.54 (C), 122.93 (C), 123.18
(CH), 123.63 (CH), 126.61 (CH), 127.58 (CH), 129.14 (CH), 129.88
(C), 130.20 (C), 133.58 (C), 162.86 (C=O) ppm. HRMS (EI): calcd.
for C15H14NO2 [M + H]+ 240.10191; found 240.10180.
(1)
where A is the absorbance at the excitation wavelength, F the inte-
grated emission area and n the refraction index of the solvents used.
Subscripts refer to the reference (r) or sample (s) compound.
Fluorescence and UV/Vis Absorption Titrations: Stock solutions
(5ϫ10–6 ) were prepared by using spectroscopy-grade acetonitrile.
Solutions of tetrabutylammonium fluoride, tetrabutylammonium
chloride, tetrabutylammonium bromide, tetrabutylammonium hy-
drogen sulfate and tetrabutylammonium acetate were prepared at
1ϫ10–2 . The solution containing the fluorescent compound
(2 mL of stock solution) was placed in a quartz cell (10.0 mm
width), and the tetrabutylammonium salt solution was introduced
in an incremental fashion. The corresponding absorption and fluo-
rescence spectra were recorded at 25 °C and were corrected for di-
lution.
Methyl 3-(Naphthalen-1-yl)-1H-indole-2-carboxylate (20): Com-
pound 20 was prepared from (Z)-8 (0.30 mmol, 120 mg) according
to the general procedure described above and with heating for 3 h.
Crystallization from diethyl ether/petroleum ether gave 20 (78 mg,
87%) as a white solid. M.p. 168.0–169.0 °C (from ethyl acetate/
petroleum ether). 1H NMR (400 MHz, CDCl3): δ = 3.62 (s, 3 H,
OCH3), 7.10 (t, J = 7.6 Hz, 1 H, ArH), 7.27–7.42 (m, 3 H, ArH),
7.47–7.61 (m, 4 H, ArH), 7.66 (d, J = 8.4 Hz, 1 H, ArH), 7.94 (d,
J = 8.0 Hz, 2 H, ArH), 9.32 (br. s, 1 H, NH) ppm. 13C NMR
(100.6 MHz, CDCl3): δ = 51.73 (OCH3), 111.76 (CH), 120.80
(CH), 122.08 (CH), 122.15 (C), 124.12 (C), 125.15 (CH), 125.55
(CH), 125.65 (CH), 125.84 (CH), 126.23 (CH), 127.88 (CH), 128.12
(CH), 128.45 (CH), 128.93 (C), 131.53 (C), 132.69 (C), 133.56 (C),
135.77 (C), 162.52 (C=O) ppm. HRMS (micrOTOF): calcd. for
C20H16NO4 [M + H]+ 302.11810; found 302.11756.
Supporting Information (see footnote on the first page of this arti-
cle): Several figures including the emission observed from a solu-
tion of 13 and 15 and of 13 + F– and 15 + F– in acetonitrile, under
irradiation with 340 nm light; the normalised absorption of 13 and
15 (5ϫ10–6  in acetonitrile) and excitation spectrum of 13 and 15
+ 500 equiv. of F–; the fluorescence emission spectra (λex = 335 nm)
of 15 (5ϫ10–6  in acetonitrile) in the presence of different
amounts of OH– (0, 5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80 and
90 equiv.) and the absorption of 15 (5ϫ10–6  in acetonitrile) in
the absence and presence of OH– (90 equiv.).
Methyl 1-(Naphthalen-1-yl)-3H-benzo[e]indole-2-carboxylate (21):
Compound 21 was prepared from 12 (0.30 mmol, 120 mg) accord-
ing to the general procedure described above and with heating for
3 h. Crystallization from diethyl ether/petroleum ether gave 21
(144 mg, 86%) as a white solid. M.p. 194.0–195.0 °C (from ethyl
acetate/petroleum ether). 1H NMR (400 MHz, CDCl3): δ = 3.56 (s,
3 H, OCH3), 7.04 (t, J = 7.6 Hz, 1 H, ArH), 7.14 (d, J = 8.0 Hz,
1 H, ArH), 7.25–7.32 (m, 2 H, ArH), 7.48 (t, J = 7.2 Hz, 1 H,
ArH), 7.56–7.67 (m, 4 H, ArH), 7.77 (d, J = 8.8 Hz, 1 H, ArH),
7.85 (d, J = 8.0 Hz, 1 H, ArH), 7.98 (d, J = 8.4 Hz, 1 H, ArH),
8.02 (d, J = 7.6 Hz, 1 H, ArH), 9.78 (br. s, 1 H, NH) ppm. 13C
NMR (100.6 MHz, CDCl3): δ = 51.61 (OCH3), 112.91 (CH),
122.04 (C), 122.88 (C), 123.03 (CH), 123.88 (CH), 123.95 (C),
125.52 (CH), 125.74 (CH), 126.03 (CH), 126.47 (CH), 127.85 (CH),
128.01 (CH), 128.13 (CH), 128.75 (CH), 129.10 (C), 129.93 (C),
132.87 (C), 133.49 (C), 133.61 (C), 133.72 (C), 162.31 (C=O) ppm.
C24H17NO2 (351.38): calcd. C 82.03, H 4.88, N 3.99; found C
81.64, H 4.46, N 4.29.
Acknowledgments
We thank the Foundation for the Science and Technology (FCT)
Portugal and FEDER (Fundo Europeu de Desenvolvimento Re-
gional) for financial support of the Centro de Física (CFUM) and
the Centro de Química (CQ-UM) and through Project PTDC/QUI/
81238/2006. The Bruker Avance II 400 NMR spectrometer is part
of the National NMR Network and was acquired with funds from
FCT and FEDER. G. P. acknowledges the FCT for a Ph.D. grant
(SFRH/BD/38766/2007).
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Published Online: December 1, 2009
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