SeCl2-Mediated Approach Toward Indole-Containing Polysubstituted Selenophenes

Article abstract of DOI:10.1021/acs.joc.8b00166

A novel and efficient SeCl₂-mediated chalcogenative cyclization strategy toward 3-selenophen-3-yl-1H-indoles from readily available and conveniently substituted propargyl indoles is described. It entails an unprecedented selenirenium-induced 1,

Full text of DOI:10.1021/acs.joc.8b00166

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Article
A SeCl2-Mediated Approach Toward Indole-
Containing Polysubstituted Selenophenes
Guilherme M. Martins, Davi Fernando Back, Teodoro S. Kaufman, and Claudio Silveira
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b00166 • Publication Date (Web): 02 Mar 2018
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A SeCl2-Mediated Approach Toward Indole-Containing
Polysubstituted Selenophenes
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Guilherme M. Martins,a Davi F. Back,a Teodoro S. Kaufmanb*
and Claudio C. Silveiraa*
aDepartamento de Química, Universidade Federal de Santa Maria, Santa Maria, RS, 97105-900, Brazil.
Tel./fax: +55 55 3220 8754
bInstituto de Química Rosario (CONICET-UNR), Suipacha 531, Rosario, SF, S2002LRK, Argentina.
E-mail: silveira@quimica.ufsm.br
RECEIVED DATE (to be automatically inserted after your manuscript is accepted if
required according to the journal that you are submitting your paper to)
ABSTRACT: A novel and efficient SeCl2-mediated chalcogenative cyclization strategy toward 3-
selenophen-3-yl-1H-indoles from readily available and conveniently substituted propargyl indoles,
is described. It entails an unprecedented selenirenium-induced 1,2-indolyl shift prompted by the
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electrophilic addition of SeCl2 to the triple bond of the propargyl indole, followed by cyclization
through the intermediacy of a 1-seleno-1,3-diene. The reaction takes place at room temperature,
shows excellent selectivity, broad substrate scope and wide functional group tolerance.
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KEYWORDS: SeCl2, heterocycles, cyclization, arylacetylenes, indolo[2,3-b]selenophenes,
substituted selenophenes
▀ INTRODUCTION
The selenophene motif is found in a wide array of compounds, many of which are of
pharmacological interest due to their important biological activities. These include antioxidant,1
anti-inflammatory,2 antitumor and cytostatic,3 as well as antibacterial,4a antinocioceptive,4b
antihypertensive,4c enzyme inhibition,5 photobiological,6 and anticonvulsant,7 among others. The
heterocycle has been embedded into certain natural products and selenophene-containing drug
analogs have also been prepared.8
In addition, selenophenes have been eliciting increasing interest as building blocks in organic
synthesis and materials science, for their potential technological applications in organic light
emitting diodes (OLEDs),9a organic field effect transistors (OFETs),9b organic solar cells,9c and
other electronic components.9d Figure 1 depicts the structures of selected bioactive and
technologically interesting selenophenes.
The synthetic approaches to polysubstituted selenophenes and their condensed congeners have
been repeatedly reviewed.10 An analysis of them revealed that suitable substrates for their access
include alkynes and alkenes, but -diketo compounds, imines and amides have also been used. On
the other hand, the sources of the selenium atom have included mainly inorganic chemicals such
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as selenium itself, Na2Se, NaHSe, SeO2, SeOCl2, P2Se5, KSeCN, SeCl4, SeBr4, and selenium
dihalides, among others, but also alkyl and arylselenium derivatives (ArSeCl/Br, PhSeSePh), as
well as selenoesters and other derivatives.
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Figure 1. Selected examples of bioactive and technologically interesting selenophene derivatives.
However, the known routes are not exempt from some disadvantages, including harsh
conditions, low product yields or the requirement of time-consuming multistep preparations of
rather complex or expensive starting materials. Further, some approaches suffer from severe
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limitations in terms of compatible substituents, which limit their substrate scope.
Therefore, despite the huge progress in this area, the need of efficient syntheses of
functionalized selenophenes still stimulates the development of new, milder and more selective
methods to complement and advance existing technologies.
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The electrophilic cyclization of unsaturated compounds, which is believed to proceed through
an intramolecular, stepwise mechanism involving cationic intermediates, has been confirmed as an
efficient approach for the one-pot construction of heterocycles, offering exciting opportunities for
innovation. On the other hand, the indole nucleus is a privileged structure found in many
biologically or technologically relevant compounds.11
In view of our interest in developing new methods for the elaboration of organochalcogen
compounds,12 and considering our latest results on the synthesis of propargyl indoles,13 we decided
to continue this study.
Scheme 1. Proposed strategy for the SeCl2-mediated synthesis of indole-containing poly-
substituted selenophenes.
Accordingly, herein we report the use of our recently reported approach toward substituted
alkynes in combination with SeCl2 as a suitable selenium source, for the development of an
efficient and operationally straightforward strategy toward indole-containing selenophenes
(Scheme 1).
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The new protocol employs readily available and rather inexpensive starting materials and is
applicable to a wide variety of substrates. To the best of our knowledge, except for an isolated
report on the synthesis of 2-substituted indoles carrying a selenophene moiety,14 the direct
attachment of the indole nucleus to the selenophene motif has not been performed to date.
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▀ RESULTS AND DISCUSSION
The best approach toward 3(3-alkynyl)1H-indoles 1 is the catalytic electrophilic aromatic
substitution of propargylic alcohols.15a-e Hence, the target compounds 1a-i and 1k-q were prepared
in 52-89% yield by reaction of the indole derivatives 3a-f and 3h with propargylic alcohols 4a-i in
refluxing MeNO2 (Table 1), under promotion by CeCl3.7H2O (30 mol%), to which ZnO was
added.13a,b The indole derivative 1j was conveniently prepared by conventional protection of 1k
with (Boc)2O.15f
On the other hand, selenium dihalides are unstable, readily undergoing disproportionation;
therefore, their preparation has traditionally been considered difficult,16 and their use in the
synthesis of organoselenium compounds has been rather limited. Fortunately, a modern alternative
gives ready access to useful, clear brownish red solutions of pure SeCl2. The reagent can be
prepared in situ by resorting to the reaction between SO2Cl2 and selenium.17 Recently, this
approach has been employed in reactions involving addition to alkenes18 and alkynes,19 as well as
in aromatic substitutions, as exemplified by the synthesis of diaryl selenides,17b,20 and ring-forming
processes.21
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Table 1. Synthesis of the starting propargyl indoles.
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propargyl
alcohol
4a
time yield
(h) (%)a
entry indole R1 R2 R3
R4
Ph
R5
Ph
R6 product
1
2
3a Me H
3a Me H
3a Me H
3a Me H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Me
H
H
H
1a
1b
1c
1d
1e
1f
3
4
3
5
4
5
3
3
2
72
71
79
52
78
65
70
85
65
4b
4c
4d
4a
4a
4a
4a
4a
-
4Cl-C6H4
Ph
3
4Me-C6H4
Ph
4
n-Bu
Ph
Ph
5
3b Me H Br
3c Me H CN
3d Me H MeO
Ph
6
Ph
Ph
7
Ph
Ph
1g
1h
1i
8
3e Me Me
3f Bn H
H
H
H
H
H
H
H
Ph
Ph
9
Ph
Ph
10
11
12
13
14
15
16
17
-
Boc H
Ph
Ph
Ph
1jb
1k
1l
24 90
3.5 84
3h
H
H
4a
4e
4f
Ph
3a Me H
3a Me H
3a Me H
Ph
4Cl-C6H4
4MeO-C6H4
Ph
4
3
3
4
4
3
70
75
75
70
89
85
Ph
1m
1n
1o
1p
1q
4a
4h
4g
4i
Ph
3b Me H Br
4Br-C6H4
Ph
H
3a Me H
3a Me H
H
H
Me
Ph
4Me-C6H4
a Yields of pure products isolated by column chromatography (hexane/EtOAc), identified by GC-
MS, 1H and 13C NMR. b Prepared in 90% yield by reaction of 1k with (Boc)2O.
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Therefore, in order to test the feasibility of our strategy, suitable solvent and conditions for the
in situ formation of SeCl2 and the concomitant formation of 2a from 1a were initially sought (Table
2), observing that the process could be accomplished in short time in solvents such as MeCN, THF,
CDCl3 and DMF (entries 1-4).
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Table 2. Optimization of the SeCl2-mediated synthesis of indole-substituted selenophenes.a
reactants ratio
(Se0:SO2Cl2:1a)
1.0:2.0:1.0
reaction time after
addition of 1a (h)
0.5
yield of
entry
1
solvent
MeCN
2a(%)b
c
-
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1.0:2.0:1.0
1.0:2.0:1.0
1.0:2.0:1.0
1.0:1.0:1.0
1.0:1.5:1.0
THF
CHCl3
DMF
DMF
DMF
0.5
overnight
0.5
54
38
90
46
83
1.0
0.5
aThe reactions were run at room temperature, under an inert atmosphere. bReaction time for SeCl2
generation: 1.5 h. Reaction time after SeCl2 generation: 0.5 h. cNo reaction.
In this way, the performance of the model reaction between propargyl indole 1a and the in-
situ-prepared SeCl2 was examined, changing the reaction solvent and the reagent ratios. It was
observed that no reaction took place in MeCN after 0.5 h (entry 1), moderate yields (54%) were
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obtained in THF (entry 2), whereas the use of CHCl3 afforded only 38% of 2a after an overnight
reaction period (entry 3).
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Gratifyingly, however, excellent results (90%) were attained when the transformation was
carried out for 0.5 h in DMF (entry 4). The latter condition also provided the best performance. In
fact, it was observed that equimolar amounts of the reactants gave low (46%) product yield (entry
5), and that the yield improved to 83% in the presence of a 1.5 molar excess of SO2Cl2 (entry 6).
With a view to explore the scope and limitations of this new selenophene-forming reaction,
and in order to obtain complex polysubstituted heterocycles, to evaluate its scope and limitations,
once the optimum conditions were established, the protocol was extended to other propargyl
indoles (1a-p). Changing one variable at a time, six points of diversification were examined. These
included the substituent attached to the terminal position of the alkyne moiety, C-2, C-5 and the N-
substituent of the indole nucleus, as well as the nature of the other two substituents of the
propargylic position.
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Regarding the group directly bonded to the alkyne (Table 3), it was found that, among phenyl
derivatives, the substituent attached to the para position of the ring did not affect the performance
of the transformation (entries 1-3 and 15). However, replacing the aromatic ring with a less reactive
aliphatic group resulted in a substrate that proved unsuitable for this transformation (entry 4).
When modifications were made on the indole nucleus, it was observed that the electronic
characteristics (electron donor or acceptor) of the C-5 substituent did not affect the performance of
the transformation, and the corresponding selenophenes were obtained in very high yields (entries
5-7 and 15). It was also concluded that the transformation accepts 2-substituted indoles, as
demonstrated with 1h, which afforded the corresponding product (2h) in excellent yield (entry 8).
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Table3. Scope of the SeCl2-mediated synthesis of polysubstituted selenophenes.
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propargyl
indole
time yield
(min) (%)a
entry
1
R1 R2 R3
R4
Ph
R5
Ph
R6 product
1a
Me H
Me H
Me H
Me H
Me H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Me
H
H
2a
2b
2c
2d
2e
2f
5
30
5
90
88
91
22
92
88
90
89
93
0
2
3
1b
1c
1d
1e
1f
4Cl-C6H4
Ph
H
4Me-C6H4
Ph
4
H
n-Bu
Ph
Ph
30
5
5
Br
Ph
6
Me H CN
Me H MeO
Ph
Ph
30
30
30
30
24b
7
1g
1h
1i
Ph
Ph
2g
2h
2i
8
Me Me
Bn
Boc H
H
H
H
H
H
H
H
Br
H
Ph
Ph
9
H
Ph
Ph
10
11
12
13
14
15
16
1j
Ph
Ph
Ph
2j
1k
1l
H
H
Ph
2k
2l
15 84c
Me H
Me H
Me H
Me H
Me H
Ph
4Cl-C6H4
4MeO-C6H4
Ph
30
60
10
30
45
94
75
98
92
81
1m
1n
1o
1p
Ph
2m
2n
2o
2p
Ph
4Br-C6H4
Ph
Ph
Me
aYields of pure products isolated by column chromatography (hexane/EtOAc) and identified by
GC-MS, 1H and 13C NMR. bTime in hours. cThe reaction was carried out at 0 ºC.
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On the other hand, it was observed that the nature of the substituent of the indole nitrogen was
relevant to the reaction performance. N-methyl and N-benzyl (entry 9) substituted indoles were
suitable substrates, whereas no reaction product was obtained when their N-Boc congener was used
as the starting indole (entry 10), even after 24 h of reaction.
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Notably, employing the unsubstituted indole (N-H) was also fruitful; the reaction of 1k
afforded a very good yield (84%) of the expected product 2k, in short time (entry 11); however, it
was found that the transformation should be carried out at 0 ºC for the best results, since at room
temperature it resulted in a mixture of inseparable products.
It was also detected that in case of compounds displaying a phenyl ring as the other propargyl
substituent, the presence of an electron donating group (OMe) on the para position of the aromatic
ring, adversely affected the reaction performance when compared with a less electron contributing
counterpart, such as a chloride (entries 12 and 13).
In the presence of a phenyl moiety, the propargylic methyl group could be homologated,
without the performance of the reaction being affected (entry 14). Interestingly, the resulting
product was a tetra-substituted selenophene. However, switching to a couple of methyl groups at
the propargylic position (1p) resulted in good yield of the indolo[2,3-b]selenophene derivative 2p
(81%) which was probably obtained through a different cyclization mechanism (entry 16).
The structures of the products were elucidated by means of an exhaustive analysis of their 1H
13
and C NMR spectra and the interpretation of additional NMR experiments, such as NOESY,
which helped the unambiguous establishment of the corresponding structures. For example, cross-
peaks were found in the NOESY spectrum of 2a between H-2 and H-18, between H-2 and H-14
and between H-12 and H-14 (Scheme 2).
Although the fine details of the reaction mechanism remain unknown, several clues collected
during the experiments suggested that the reactions leading to 2a-o and 2p probably proceeded
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through the formation of a common intermediate, resulting from an initial 1,2-migration of the 3-
indolyl moiety. This enabled the formulation of a multi-pathway mechanism (for 2a-o and 2p)
consistent with all the results, as depicted in Scheme 2.
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Scheme 2. Proposed mechanism for the synthesis of compounds 2a-o and 2p, and key NOE cross-
peaks of 2a.
The proposed sequence begins with the electrophilic addition of SeCl2 to the triple bond of 1,
which should result in the generation of the selenirenium intermediate i. In turn, this would trigger
a cationic cascade that could undego at least three different evolutions, including a chloride-
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mediated nucleophilic ring opening of the selenirenium, and two intramolecular alternatives (A1
and A2). The latter resemble the course of the rearrangements that take place during substitution at
a neopentyl centre. The lack of reactivity of the Boc derivative 1j (Table 3, entry 10) may be
explained by the need of intermediate i to trigger the cyclization process.
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In the route A1, a 1,2-sigmatropic rearrangement of the aryl group (R2) would result in the
tertiary allyl carbocationic intermediate ii, which could gain additional stabilization from the
pendant 3-indolyl moiety. Alternatively, according to route A2, the intermediate i could engage in
a 1,2-indolyl shift with the aid of the lone pair of electrons of the indolic nitrogen, to afford the
polysubstituted spirocycle iii, which in turn would undergo ring opening of the strained
cyclopropane motif, to give the carbocationic common intermediate iv.
The mechanism of the 1,2-migrations varies from stepwise to concerted. However, in this case
it should be assumed that ring opening of the selenirenium and C-C bond formation through SN2’
attack of the indole C-3 position to the electron defficient centre, leading to the spirocyclic
intermediate iii is somehow a concerted process, which would avoid passing through a highly
reactive vinyl cation species.22
The migratory aptitudes of the migrating moieties are typically correlated with their electron-
richness and ability to stabilize a positive charge in the transition state/intermediate.23 The observed
results suggest that, as expected, the indolyl motif exhibits a better migratory aptitude than the
differently substituted benzenoids tested; even in the case of 1m, which carries a 4-methoxy
substituent, the 1,2-migration of the indolyl moiety prevails.
In addition, literature reports indicate that methyl groups have low migratory aptitude and that
the relative aptitudes of phenyl and methyl groups for migration during cationic rearrangements is
> 100:1.24 Therefore, a Nametkin-type rearrangement should not be considered in this scenario.
In case R2 is an aromatic substituent, the reaction mechanism would take path a, where loss
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of a proton from the common intermediate iv would afford the selenodiene v, suitable for
cyclization to the cationic intermediate vi. Finally, the latter would deliver the contiguously
trisubstituted selenophene products 2a-o, after loss of the elements of HCl in the last two steps.
Thus, the overall process is an extremely atom economic transformation. It is plausible that the
presence of an alkyl R3 substituent may fail to provide satisfactory stabilization to the carbocationic
intermediate vi, resulting in lower product yields (Table 3, entry 4).
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On the other side, the intriguing formation of compound 2p suggested the involvement of a
slightly different route. The process could take path b where the common carbocationic
intermediate iv would loss a proton and afford selenodiene vii, a geometric isomer of v. In turn, and
resembling path a, the selenodiene vii would undergo an intramolecular nuclephilic attack by the
indole ring, finally affording the fused selenophene 2p by way of the intermediate viii.
Since no 3-(selenophen-3-yl)-1H-indole like 2a-o accompanied the isolation of 2p, it can be
conjectured that the transformation of iv into v or vii should be reversible, enabling the process to
opt between both structure-dependent cyclization paths. The observed products suggest that path
a would not be favored with 1p, probably because of the relative stability of the intermediates v
and vii, and owing to the fact that the more reactive indolyl moiety would compete successfully
with the isopropenyl residue in completing the reaction sequence toward 2p.
It is worth noting that the 1,2-indolyl shift has very few precedents; it has been reported in the
context of some pinacol-type rearrangements,25 gold-mediated reactions of 3-allenyl and 3-alkynyl
derivatives of indoles, extensively studied by the group of Sanz,26 and in the biosynthesis of
violacein, an antibacterial and anticancer purple pigment, produced by Chromobacterium
violaceum.27
Summing up, the accumulated evidence indicates that the reaction proceeds through the
electrophilic addition of SeCl2 to the triple bond and always involves an initial 1,2-indolyl shift
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(A2), instead of the alternate aryl migration (A1) to afford the common intermediate iv; then,
substrates carrying an extra aromatic ring on the propargylic position (1a-o) would take path a,
whereas path b would be operating in case of the dialkyl substituted propargyl indoles (1p). Since
no mixtures of products have been obtained, it seems that the paths would be mutually exclusive.
On the other hand, despite some seleno[3,4-b]indoles are known,28a the seleno[2,3-b]indole
skeleton of 2p is unprecedented and the analogous thieno[2,3-b]indoles are rare.28b-e However, the
latter acquired importance because thienodolin, a natural product from Streptomyces albogriseolus
MJ286-76F7 (Figure 2), is a nitric oxide synthase inhibitor, with potent plant-growth regulatory
properties on rice seedlings.29
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Other thieno[2,3-b]indoles have shown to display antifungal activity, and are potentially useful
in the treatment of central nervous system diseases (Parkinson’s, senile dementia, brain ischemia,
epilepsy), or for the preparation of conducting polymers,30 suggesting that compounds like 2p may
also exhibit relevant bioactivity.
Figure 2. Thienodolin and an antifungal heterocycle as selected bioactive thieno[2,3-b]indoles.
The observation of the unusual 1,2-indole migration among propargyl indoles 1a-o and the
odd outcome of their congener 1p prompted us to evaluate whether other aromatic substituents
would be able to undergo the 1,2-migration and initiate the cascade toward substituted
selenophenes.
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Hence, the model 3-methyl-substituted 1,3,3-triphenyl-1-butyne derivatives 6a-c were
prepared (Table 4) through the MeI-mediated alkylation of the propargyl carbanions, formed by
exposure of the corresponding 1,3,3-triphenyl-1-propynes (5a-c)31 to n-BuLi in THF. The reaction
performance was rather low, possibly as a result of the concomitant formation of allenes as side
products.32 Gratifyingly, however, when the models 6a-c were subjected to reaction with SeCl2
under the previously optimized conditions, the cyclized products 7a-c were obtained in moderate
to very good yields.
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Table 4. SeCl2-mediated synthesis of 2,3-diaryl benzo[b]selenopheno[3,2-d]selenophenes.
starting
material
5a
substituted
butyne
6a
yield
(%)a
42
cyclized
product
7a
yield
(%)a
85
entry
1
R1
H
2
3
5b
5c
OMe
Cl
6b
6c
17
40
7b
83
7c+7c’
53b
aYield after column chromatography. bMixture of isomers (82:18 by CG-MS analysis).
Despite being quite unexpected, the isolation of 7a-c confirmed that aromatic rings other than
substituted indoles are also capable of undergoing the required initial 1,2-migration, and suggested
that the reaction has a much wider scope. Further, isolation of 7c as a mixture of products resulting
from migration of the phenyl and 4-chlorophenyl moieties reinforces the conjecture that the
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migration aptitude is related to the electronic richness of the potentially migrating groups.
A plausible mechanism for the formation of the benzo[b]selenopheno[3,2-d]selenophene ring
system is depicted in Scheme 3. It is proposed that the initial steps, affording intermediate i, are
analogous to those yielding the contiguously trisubstituted selenophenes 2a-o (Scheme 2).
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Scheme 3. Formation of benzo[b]selenopheno[3,2-d]selenophenes 7a-c. Proposed mechanism.
In turn, in the presence of another equivalent of SeCl2, i could undergo the electrophilic
additions of the reagent, resulting in 7 through the intermediacy of the chloroseleno intermediate
ii. However, the final causes behind the different behavior of compounds 1a-o and their congeners
6a-c remain unknown.
Considering that exposure of 6a-c to SeCl2 resulted in the formation of products 7a-c,
containing two selenium atoms and that the reaction could not be stopped at the first stage, it was
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explored if, starting from 1 or 2 it would be also possible to obtain products carrying two selenium
atoms in their structure. In this way, propargyl indoles 1a, 1l and 1q were made to react with two
successive portions of 1.0 equivalents each of SeCl2.
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Not unexpectedly, it was observed the formation of the corresponding selenopheno[3,2-
d]selenophenenes 8a-c, respectively, in moderate yields (Table 5).
Table 5. SeCl2-mediated synthesis of 1-methyl-3-(2-phenylbenzo[b]selenopheno[3,2-
d]selenophen-3-yl)-1H-indoles.
propargyl
indole
1a
SeCl2
(equiv.)
1.0 + 1.0
reaction
time (min.)
5 + 10
cyclized
product
8a
yield
(%)a
38
entry
1
R
H
2
3
4
2a
1l
H
Cl
1.0
10
8a
8b
8c
64
36
44
1.0 + 1.0
1.0 + 1.0
5 + 10
5 + 10
1q
Me
aYield after column chromatography.
Furthermore, it was observed that the reaction can also accept 2a as substrate. In this case, it
gave 8a in 64% yield (entry 2) after reacting with 1.0 equivalent of SeCl2 during 10 min. These
reactions with SeCl2 proved to be very selective, since no formation of 8 could be observed when
compounds 1a and 1l were employed as starting materials and made to react with only 1.0
equivalent of SeCl2 (Table 3, entries 1 and 12).
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The structures of compounds 7b and 8a were also assessed by single crystal X-ray diffraction
analysis (Figure 3).33 This revealed that the tricyclic core is essentially planar in both compounds.
In the case of 7b, the observed dihedral angles C6–C7–C8–C9, C10–Se2–C1–Se1 and C3–C2–
Se1–C1 are ‒0.2º, +179.7º and +179.9º, respectively. On the other hand, it was found that both
aromatic substituents are contorted away from each other, with observed dihedral angles C10–C9–
C17–C22 and C9–C10–C11–C16 of –102.6º and +113.2º, respectively. In addition, with a dihedral
angle C21–C20–O–C23 of +4.9º, the methoxy substituent is almost coplanar with the aromatic
ring.
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Figure 3. ORTEP representations of X-ray crystal structures of compounds 7b (left) and 8a (right),
with ellipsoids drawn at the 50% probability level.
In line with previous observations, it was also found that the tricyclic core is still essentially
planar in 8a; the observed dihedral angles C6–C7–C8–C9, C10–Se2–C1–Se1 and C3–C2–Se1–C1
are +3.3º, +179.5º and +176.0º, respectively. Opposite to the previous finding, it was observed that
both aromatic substituents are contained in planes rotated in the same direction with regards to the
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tricyclic skeleton, and slightly tilted away from each other. The observed dihedral angles C10–C9–
C17–C24 and C9–C10–C11–C12 are –125.5º and +136.2º, respectively.
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▀ CONCLUSIONS
We have demonstrated that conveniently substituted propargyl indoles can afford contiguously
functionalized trisubstituted selenophenes, through a SeCl2-mediated tandem 1,2-indole
migration/cyclization. The reaction is general for a wide variety of compounds simultaneously
possessing alkyl and aryl substituents at the propargylic position. It provided a number of new
heterocycles potentially useful in medicinal chemistry. However, under the same conditions,
propargyl indoles carrying two pendant alkyl substituents at the propargylic position yielded a
seleno[2,3-b]indole derivative.
The broad scope of the reaction was demonstrated by exploring the chemical space at different
points of diversification; it was also shown that some of the resulting products can be further
transformed, rapidly providing access to polycyclic compounds with increased structural
complexity. Some limitations were also found.
SeCl2 acted as a suitable electrophilic agent for the introduction of selenium, and the
transformation, which entailed the migration of the indole as the most electron-rich propargyl
substituent, proceeded in short times, high yields and under mild experimental conditions. The
scope of the reaction was also demonstrated with 1,3,3-triphenyl-1-butynes, which afforded 2,3-
diaryl benzo[b]selenopheno[3,2-d]selenophenes. The observed migratory aptitudes strongly
support an electrophilic mechanism for this transformation, with involvement of a selenirenium-
type intermediate. Additional efforts to explore synthetic applications of this novel reaction are
currently underway and their results will be reported in due time.
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▀ EXPERIMENTAL SECTION
7
8
9
General considerations. The melting points were taken on a MQAPF-301 melting point apparatus
and are reported uncorrected. 1H and 13C NMR spectra were recorded on Bruker 400 and 600 NMR
spectrometers, with the samples dissolved in CDCl3and DMSO-d6. Chemical shifts are informed
in ppm downfield from the signal of TMS, used as internal standard, and the coupling constants (J)
are expressed in Hertz (Hz). Low resolution mass spectra were obtained from a Shimadzu QP2010
gas-chromatograph coupled to a mass spectrometer. High-resolution mass spectral data were
obtained on a Bruker microTOF-Q IIT instrument, employing sodium formate as reference. X-Ray
diffraction data were acquired with a Bruker Kappa APEX II CCD diffractometer, fit with a
graphite monochromator and a Mo-Kα radiation source (λ = 0.71073 Å). Elemental analyses of the
products were obtained in a Perkin-Elmer CHN 2400 elemental analyzer.
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The reagents for synthesis were obtained commercially. The solvents were purified and dried
according to usual procedures.34 All the other reagents were used as received, without further
purification. Chromatographic purifications were conducted by column chromatography using
silica gel (230–400 mesh, 40-63 μm), eluting with hexane or hexane-EtOAc mixtures of increasing
polarity. Progress of the reactions was monitored by thin layer chromatography, using UV light
(254 and 365 nm), I2 or H2SO4/vanillin solution for detection of the spots.
General Procedure for the Preparation of the Propargylic Alcohols.15g A mixture of the
corresponding ketone (5 mmol) and the alkyne (7.5 mmol), were transferred to a 25 mL flask and
mixed with stirring until a homogeneous solution was obtained. The mixture was treated with t-
BuOK (842 mg, 7.5 mmol) and stirred at room temperature until complete consumption of starting
materials was verified by TLC. The reaction mixture was diluted with water (100 mL) and the
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products were extracted with EtOAc (3 × 100 mL). The combined organic extracts were washed
with water (100 mL) and brine (10 mL), dried over MgSO4, filtered and concentrated under reduced
pressure. The residue was purified by silica gel column chromatography, eluting with
hexane:EtOAc (95:5, v/v).
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General Procedure for the Preparation of the Propargyl Indoles.13b The indole (1.0 mmol) was
added to a stirred solution of the propargyl alcohol (1.1 mmol) in anhydrous MeNO2 (2 mL) and
the mixture was treated with anhydrous CeCl3 (73.5 mg, 0.3 mmol) and ZnO (81 mg, 1.0 mmol).
The mixture was heated under reflux until consumption of starting materials was completed (TLC).
The reaction mixture was partitioned between brine (10 mL) and EtOAc and the products were
extracted with EtOAc (3 × 50 mL). The combined organic extracts were washed with water (50
mL) and brine (10 mL), dried over MgSO4, filtered through a cotton plug and concentrated under
reduced pressure. The residue was purified by silica gel column chromatography eluting with
hexane:EtOAc (98:2, v/v).
3-(2,4-Diphenylbut-3-yn-2-yl)-1-methyl-1H-indole (1a). White solid (241 mg, 72% yield): mp 113
ºC; Lit.:15b 110–112 °C. 1H NMR (400 MHz, CDCl3) δ 7.61–7.59 (m, 2H), 7.50 (d, 1H, J = 8.0),
7.44–7.41 (m, 2H), 7.29–7.32 (m, 6H), 7.21–7.17 (m, 1H), 7.16–7.14 (m, 1H), 6.99 (s, 1H), 6.96
(ddd, J = 8.0, 6.9, 1.0, 1H), 3.74 (s, 3H), 2.10 (s, 3H). 13C{1H} NMR (100 MHz, CDCl3) δ 146.2,
137.8, 131.6, 128.1 (2), 127.6, 126.6, 126.3, 126.2, 126.1, 123.9, 121.5, 121.2, 120.2, 118.8,
109.1, 95.2, 82.9, 39.8, 32.7, 31.0. EIMS (m/z, rel. int., %) 335 (M+, 63), 320 ([M-Me]+, 100).
3-(4-(4-Clorophenyl)-2-phenylbut-3-yn-2-yl)-1-methyl-1H-indole (1b). White solid (263 mg, 71%
1
yield): mp 124–126 ºC; Lit.:15e 122–126 °C. H NMR (400 MHz, CDCl3) δ 7.58–7.55 (m, 2H),
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7.46 (d, J = 8.0, 1H), 7.35–7.32 (m, 2H), 7.29–7.14 (m, 7H), 6.98–6.94 (m, 2H), 3.74 (s, 3H), 2.08
(s, 3H). 13C{1H} NMR (100 MHz, CDCl3) δ 146.0, 137.8, 133.6, 132.8, 128.4, 128.1, 126.5, 126.4,
126.1, 126.0, 122.3, 121.6, 121.1, 119.9, 118.8, 109.2, 96.2, 81.9, 39.9, 32.7, 30.9. EIMS (m/z, rel.
int., %) 371 ([M+2]+, 21), 370 ([M+1]+, 18), 369 (M+, 58), 356 ([M+2-Me]+, 36), 354 ([M-Me]+,
100).
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1-Methyl-3-(2-phenyl-4-(p-tolyl)but-3-yn-2-yl)-1H-indole (1c). White solid (275 mg, 79% yield)
mp 119–120 ºC. 1H NMR (400 MHz, CDCl3) δ 7.61–7.58 (m, 2H), 7.51–7.48 (m, 1H), 7.33–7.30
(m, 2H), 7.29–7.23 (m, 3H), 7.21–7.13 (m, 2H), 7.07–7.04 (m, 2H), 6.98 (s, 1H), 6.95 (ddd, J =
13
8.1, 7.0, 1.1, 1H), 3.73 (s, 3H), 2.30 (s, 3H), 2.09 (s, 3H). C{1H} NMR (100 MHz, CDCl3) δ
146.4, 137.8, 137.6, 131.5, 128.8, 128.0, 126.6, 126.3, 126.2, 121.5, 121.3, 120.9, 120.4, 118.7,
109.1, 94.4, 83.0, 39.8, 32.6, 31.0, 21.3. EIMS (m/z, rel. int., %) 349 (M+, 60), 334 ([M-Me]+, 100).
HRMS (ESI) m/z: [M+Na]+ calcd. for C26H23NNa 372.1723; found: 372.1727.
1
1-Methyl-3-(2-phenyl-oct-3-yn-2-yl)-1H-indole (1d). Yellow oil (186 mg, 59% yield): H NMR
(600 MHz, CDCl3) δ 7.54–7.53 (m, 2H), 7.42 (d, J = 8.0, 1H), 7.25–7.22 (m, 3H), 7.18–7.12 (m,
2H), 6.94–6.92 (m, 2H), 3.70 (s, 3H), 2.24 (t, J = 7.1, 2H), 1.97 (s, 3H), 1.52 (quintet, J = 7.7, 2H),
1.42 (septet, J = 7.4, 2H), 3.70 (s, 3H). 13C{1H} NMR (150 MHz, CDCl3) δ 146.9, 137.7, 127.9,
126.5, 126.2, 126.1, 126.0, 121.4, 121.3, 120.9, 118.5, 109.0, 85.4, 82.9, 39.2, 32.6, 31.4, 31.1,
22.0, 18.6, 13.6. EIMS (m/z, rel. int., %) 315 (M+, 39), 300 ([M-Me]+, 100). HRMS (ESI) m/z:
[M+Na]+ calcd. for C23H25NNa 338.1879; found: 338.1876.
5-Bromo-3-(2,4-diphenylbut-3-yn-2-yl)-1-methyl-1H-indole (1e). White solid (323 mg, 78%
yield): mp 107–108 ºC. 1H NMR (600 MHz, CDCl3) δ 7.68 (s, 1H), 7.56 (d, J = 8.0, 2H), 7.45 (m,
2H), 7.31–7.26 (m, 5H), 7.24–7.20 (m, 2H), 7.10 (d, J = 8.6, 1H), 6.97 (s, 1H), 3.70 (s, 3H), 2.06
(3H). 13C{1H} NMR (150 MHz, CDCl3) δ 145.7, 136.4, 131.6, 128.2, 128.1, 127.7, 127.6, 127.2,
126.6, 126.4, 124.4, 123.6, 119.8, 112.2, 110.7, 94.6, 83.2, 39.7, 32.8, 31.0. EIMS (m/z, rel. int.,
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%) 415 ([M+2]+, 58), 413 (M+, 54), 400 ([M+2-Me]+, 94), 398 ([M-Me]+, 100). HRMS (ESI) m/z:
[M+Na]+ calcd. for C25H20BrNNa 436.0671; found: 436.0671.
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3-(2,4-Diphenylbut-3-yn-2-yl)-1-methyl-1H-indole-5-carbonitrile (1f). White solid (234 mg, 65%
yield): mp 143–145 ºC. 1H NMR (600 MHz, CDCl3) δ 7.82 (s, 1H), 7.55 (d, J = 7.4, 2H), 7.44–
7.42 (m, 2H), 7.36 (dd, J = 8.5, 1.1, 1H), 7.31–7.27 (m, 6H), 7.23 (t, J = 6.9, 1H), 7.14 (s, 1H),
3.78 (s, 3H), 2.08 (s, 3H). 13C{1H} NMR (150 MHz, CDCl3) δ 145.3, 139.2, 131.5, 128.3, 128.3,
128.2, 127.9, 126.8, 126.6, 126.3, 125.8, 124.5, 123.2, 121.6, 120.8, 110.1, 101.8, 93.9, 83.6, 39.6,
32.9, 31.0. EIMS (m/z, rel. int., %) 360 (M+, 14), 345 ([M-Me]+, 29). HRMS (ESI) m/z: [M+Na]+
calcd. for C26H20N2Na 383.1519; found: 383.1520.
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3-(2,4-Diphenylbut-3-yn-2-yl)-5-methoxy-1-methyl-1H-indole (1g). White solid (255 mg, 70%
yield): mp 95–96 ºC. 1H NMR (600 MHz, CDCl3) δ 7.60 (d, J = 7.8, 2H), 7.44–7.46 (m, 2H), 7.30–
7.25 (m, 5H), 7.22–7.19 (m, 1H), 7.14 (d, J = 8.8, 1H), 6.96–6.94 (m, 2H), 6.83 (dd, J = 8.8, 2.1,
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1H), 3.71 (s, 3H), 3.64 (s, 3H), 2.08 (s, 3H). C{1H} NMR (150 MHz, CDCl3) δ 153.2, 146.1,
133.1, 131.6, 128.2, 128.1 (2), 127.6, 126.7, 126.6, 126.3, 123.8, 119.5, 111.7, 109.8, 103.0, 95.0,
82.9, 55.7, 39.7, 32.8, 30.9. EIMS (m/z, rel. int., %) 365 (M+, 63), 350 ([M-Me]+, 100). HRMS
(ESI) m/z: [M+Na]+ calcd. for C26H23NNaO 388.1672; found: 388.1672.
3-(2,4-Diphenylbut-3-yn-2-yl)-1,2-dimethyl-1H-indole (1h). White solid (296 mg, 85% yield): mp
153–155 ºC; Lit.:15b 157–159 °C. 1H NMR (400 MHz, CDCl3) δ 7.65 (d, J = 8.1, 1H), 7.58–7.55
(m, 2H), 7.44–7.41 (m, 2H), 7.28–7.16 (m, 7H), 7.11 (ddd, J = 8.1, 7.0, 1.1, 1H), 6.97 (ddd, J =
8.1, 7.0, 1.1,1H), 3.60 (s, 3H), 2.28 (s, 3H), 2.27 (s, 3H). 13C{1H} NMR (100 MHz, CDCl3) δ 148.3,
136.5, 134.35, 131.5, 128.1, 128.0, 127.5, 126.7, 126.6, 126.2, 124.1, 120.5, 120.1, 118.9, 114.7,
108.7, 96.3, 83.2, 41.6, 32.4, 29.3, 11.8. EIMS (m/z, rel. int., %) 349 (M+, 57), 334 ([M-Me]+, 100).
1-Benzyl-3-(2,4-diphenylbut-3-yn-2-yl)-1H-indole (1i). White solid (267 mg, 65% yield): mp 128–
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129 ºC. H NMR (400 MHz, CDCl3) δ 7.61–7.58 (m, 2H), 7.51 (d, J = 8.0, 1H), 7.44–7.40 (m,
2H), 7.32–7.16 (m, 10H), 7.14–7.07 (m, 4H), 6.95 (ddd, J = 8.0, 7.0, 1.0, 1H), 5.28 (s, 2H), 2.09
(m, 3H). 13C{1H} NMR (100 MHz, CDCl3) δ146.3, 137.6, 131.6, 128.7, 128.2, 128.1, 127.6, 127.5,
126.7, 126.6, 126.5, 126.4, 125.6, 123.9, 121.7, 121.4, 120.9, 119.1, 109.6, 95.2, 83.1, 50.0, 39.9,
31.0. EIMS (m/z, rel. int., %) 411 (M+, 38), 396 ([M-Me]+, 39). HRMS (ESI) m/z: [M+Na]+ calcd.
for C31H25NNa 434.1879; found: 434.1877.
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3-(2,4-Diphenylbut-3-yn-2-yl)-1H-indole (1k). White solid (269 mg, 84% yield): mp 75–76 ºC;
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Lit.:15b 73–75 ºC. H NMR (400 MHz, CDCl3) δ 7.85 (s, 1H), 7.59–7.57 (m, 2H), 7.50–7.48 (m,
1H), 7.43–7.40 (m, 2H), 7.29–7.16 (m, 7H), 7.14–7.12 (m, 1H), 7.10 (d, J= 2.5, 1H), 6.96 (ddd, J
= 8.1, 7.0, 1.0, 1H), 2.09 (s, 3H). 13C{1H} NMR (100 MHz, CDCl3) δ 146.1, 137.0, 131.6, 128.1
(2C), 127.6, 126.6, 126.4, 125.7, 123.8, 122.0, 121.7, 121.4, 121.1, 119.3, 111.0, 95.0, 83.0, 39.8,
30.9. EIMS (m/z, rel. int., %) 321 (M+, 21), 306 ([M-Me]+, 100).
3-(2-(4-Chlorophenyl)-4-diphenylbut-3-yn-2-yl)-1-methyl-1H-indole (1l). Yellow solid (258 mg,
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70% yield): mp 130 ºC; Lit.:15b 128–130 ºC. H NMR (600 MHz, CDCl3) δ 7.53–7.50 (m, 2H),
7.44 (d, J = 8.0, 1H), 7.43–7.41 (m, 2H), 7.28–7.22 (m, 6H), 7.19–7.16 (m, 1H), 7.02 (s, 1H), 6.99–
6.96 (m, 1H), 3.76 (s, 3H), 2.06 (s, 3H). 13C{1H} NMR (150 MHz, CDCl3) δ 144.9, 137.9, 132.1,
131.6, 128.2, 128.1, 128.1, 127.8, 126.1, 125.8, 123.5, 121.6, 121.0, 119.5, 118.9, 109.2, 94.5,
83.2, 39.4, 32.7, 30.9. EIMS (m/z, rel. int., %) 371 ([M+2]+, 21), 369 (M+, 61), 354 ([M-Me]+, 100).
3-(2-(4-Methoxyphenyl)-4-phenylbut-3-yn-2-yl)-1-methyl-1H-indole (1m). White solid (274 mg,
75% yield): mp 116–117 ºC. 1H NMR (600 MHz, CDCl3) δ 7.52–7.49 (m, 3H), 7.43–7.42 (m, 2H),
7.26–7.24 (m, 4H), 7.16 (t, J = 7.5, 1H), 6.98–6.96 (m, 2H), 6.81 (d, J = 8.7, 2H), 3.76 (s, 3H),
3.73 (s, 3H), 2.07 (s, 3H). 13C{1H} NMR (150 MHz, CDCl3) δ 158.0, 138.4, 137.8, 131.3, 128.0,
127.7, 127.7, 126.1, 126.0, 123.9, 121.5, 121.2, 120.4, 118.7, 113.4, 109.1, 95.4, 82.7, 55.1, 39.1,
32.6, 31.0. EIMS (m/z, rel. int., %) 365 (M+, 66), 350 ([M-Me]+, 100). HRMS (ESI) m/z: [M+Na]+
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calcd. for C26H23NNaO 388.1672; found: 388.1670.
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3-(1,3-Diphenylpent-1-yn-3-yl)-1-methyl-1H-indole (1n). White solid (261 mg, 75% yield): mp
123–125 ºC; Lit.:15b 124–126 °C. 1H NMR (400 MHz, CDCl3) δ 7.60–7.57 (m, 2H), 7.53–7.50 (m,
1H), 2.47–7.44 (m, 2H), 7.29–7.22 (m, 6H), 7.20–7.12 (m, 2H), 7.01 (s, 1H), 6.94 (ddd, J = 8.1,
7.0, 1.1, 1H), 3.73 (s, 3H), 2.57 (dq, J = 13.0, 7.2, 1H), 2.32 (dq, J = 13.0, 7.2, 1H), 1.04 (t, J =
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7.2, 3H). C{1H} NMR (100 MHz, CDCl3) δ 144.6, 137.7, 131.6, 128.1, 127.9, 127.6, 127.3,
126.4, 126.3, 126.2, 124.0, 121.4, 121.2, 119.5, 118.7, 109.1, 93.7, 84.7, 45.3, 34.7, 32.6, 9.9.
EIMS (m/z, rel. int., %) 349 (M+, 16), 321 ([M-C2H4]+, 28), 320 ([M-Et]+, 100).
5-Bromo-3-(4-(p-bromophenyl)-2-phenylbut-3-yn-2-yl)-1-methyl-1H-indole (1o). Yellow solid
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(343 mg, 70% yield): mp 119–120 ºC. H NMR (400 MHz, CDCl3) δ 7.65–7.64 (m, 1H), 7.55–
7.52 (m, 2H), 7.41–7.38 (m, 2H), 7.31–7.27 (m, 4H), 7.25–7.19 (m, 2H), 7.11 (d, J = 8.7, 1H),
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6.93 (s, 1H), 3.70 (s, 3H), 2.05 (3H). C{1H} NMR (100 MHz, CDCl3) δ 145.5, 136.5, 133.0,
131.4, 128.3, 127.7, 127.3, 126.7, 126.4, 124.6, 123.6, 122.6, 121.9, 119.7, 112.4, 110.7, 96.0,
82.3, 39.8, 32.8, 30.9. EIMS (m/z, rel. int., %) 492 ([M+2]+, 64), 490 (M+, 33), 479 ([M+2-Me]+,
53), 477 ([M-Me]+, 100). HRMS (ESI) m/z: [M+H]+ calcd. for C25H20Br2N 493.9937; found:
493.9956.
1-Methyl-3-(2-methyl-4-phenylbut-3-yn-2-yl)-1H-indole (1p).15b Yellow oil (243 mg, 89% yield):
1H NMR (400 MHz, CDCl3) δ 8.00–7.97 (m, 1H), 7.43–7.39 (m, 2H), 7.28–7.20 (m, 5H), 7.11
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(ddd, J = 8.1, 6.9, 1.2, 1H), 6.96 (s, 1H), 3.70 (s, 3H), 1.79 (s, 6H). C{1H} NMR (100 MHz,
CDCl3) δ 137.8, 131.6, 128.0, 127.4, 125.9, 124.7, 124.1, 121.4, 121.1, 121.0, 118.6, 109.0, 97.1,
80.4, 32.5, 31.2, 30.7. EIMS (m/z, rel. int., %) 273 (M+, 32), 258 ([M-Me]+, 100).
3-(2-(4-Tolyl)-4-phenylbut-3-yn-2-yl)-1-methyl-1H-indole (1q). White solid (258 mg, 74% yield):
mp 111–112 ºC. 1H NMR (400 MHz, CDCl3) δ 7.53–7.51 (m, 1H), 7.49–7.47 (m, 2H), 7.44–7.41
(m, 2H), 7.27–7.21 (m, 4H), 7.18–7.14 (m, 1H), 7.10–7.07 (m, 2H), 6.99–6.95 (m, 2H), 3.74 (s,
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3H), 2.30 (s, 3H), 2.08 (s, 3H). C{1H} NMR (100 MHz, CDCl3) δ 143.3, 137.8, 135.8, 131.6,
128.8, 128.0, 127.5, 126.5, 126.1, 126.0, 124.0, 121.5, 121.3, 120.3, 118.7, 109.1, 95.4, 82.7, 39.5,
32.6, 31.0, 20.9. EIMS (m/z, rel. int., %) 349 (M+, 60), 334 ([M-Me]+, 100). HRMS (ESI) m/z:
[M+H]+ calcd. for C26H24N 350.1903; found: 350.1916.
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tert-Butyl 3-(2,4-diphenylbut-3-yn-2-yl)-1H-indole-1-carboxylate (1j). A solution of propargyl
indole 1k (1.60 g, 5 mmol) in CH2Cl2 (10 mL) was treated successively with pyridine (0.52 mL,
6.4 mmol), Boc2O (1.19 g, 6.4 mmol) and DMAP (0.061 g, 0.5 mmol). The reaction mixture was
stirred for 24 h at room temperature, then NH4Cl(sat) (125 mL) was added and the products were
extracted with EtOAc (2 × 150 mL). The solvent was removed under vacuo and the residue purified
by column chromatography, eluting with hexanes, to afford 1j (1.90 g, 90% yield), as a white solid:
mp 48–50 °C. 1H NMR (600 MHz, CDCl3) δ 8.19 (s, 1H), 7.68 (s, 1H), 7.58 (d, J = 7.7, 2H), 7.43–
7.42 (m, 2H), 7.36 (d, J = 7.7, 1H), 7.30–7.20 (m, 7H), 7.05 (t, J = 7.5, 1H), 2.08 (s, 3H), 1.69 (s,
9H). 13C{1H} NMR (150 MHz, CDCl3) δ 149.9, 144. 9, 136.0, 131.6, 128.7, 128.2, 128.1, 127.8,
126.7, 126.4, 125.7, 124.1, 123.4, 122.5, 122.2, 121.4, 115.0, 93.5, 83.7, 39.7, 30.8, 28.1. HRMS
(ESI) m/z: [M+Na]+ calcd. for C29H27NNaO2 444.1934; found: 444.1936.
General Procedure for the Preparation of the Indole-substituted Selenophenes (2a-p). A
mixture of Se0 (0.5 mmol) and SO2Cl2 (1.0 mmol), was stirred under argon for 1.0 hour at room
temperature. A brown solution was formed. Then DMF (1.5 mL) was added and the system was
stirred for 0.5 hour, when it was treated dropwise with a DMF (1.5 mL) solution of the aryl
propargyl indole (0.5 mmol). The system was stirred for the prescribed time under the chosen
temperature. The reaction was quenched with brine (10 mL) and extracted with EtOAc (3 × 50
mL). The combined organic extracts were washed with water (50 mL) and brine (10 mL), dried
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over MgSO4, filtered and concentrated under reduced pressure. The residue was purified by silica
gel column chromatography, eluting with hexane.
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3-(4,5-Diphenylselenophen-3-yl)-1-methyl-1H-indole (2a). White solid (186 mg, 90% yield): mp
164–165 ºC. 1H NMR (600 MHz, CDCl3) δ 7.92 (s, 1H), 7.24–7.23 (m, 2H), 7.18 (d, J = 8.2, 1H),
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7.13–7.0 (m, 9H), 7.02 (d, J = 7.9, 1H), 6.81–6.78 (m, 1H), 6.52 (s, 1H), 3.59 (s, 3H). C{1H}
NMR (150 MHz, CDCl3) δ 147.4, 146.2, 139.3, 137.3, 136.5, 132.1, 128.9. 128.8, 128.7, 128.0,
127.6, 127.5, 126.8, 126.5, 126.4, 121.1, 120.5, 118.9, 111.2, 108.6, 32.6. EIMS (m/z, rel. int., %)
413 (M+, 100). HRMS (ESI) m/z: [M+H]+ calcd. for C25H20NSe 414.0761; found: 414.0757.
3-(5-(4-Chlorophenyl)-4-phenylselenophen-3-yl)-1-methyl-1H-indole (2b). White solid (197 mg,
88% yield): mp 179–180 ºC. 1H NMR (400 MHz, CDCl3) δ 7.92 (s, 1H), 7.21–7.19 (m, 1H), 7.18–
7.14 (m, 2H), 7.11–7.04 (m, 8H), 7.02 (dt, J = 8.0, 1.0, 1H), 6.83 (ddd, J = 8.0, 7.0, 1.0, 1H), 6.52
(s, 1H), 3.62 (s, 3H). 13C{1H} NMR (100 MHz, CDCl3) δ 147.6, 144.7, 139.2, 136.6, 135.9, 132.7,
130.0, 128.8, 128.7, 128.3 (x2), 127.6, 127.5, 126.7, 126.5, 121.3, 120.4, 119.1, 111.0, 108.8, 32.7.
EIMS (m/z, rel. int., %) 449 ([M+2]+, 12), 448 ([M+1]+, 45), 447 (M+, 31), 446 ([M-1]+, 100). Anal.
Calcd. for C25H18ClNSe: C, 67.20; H, 4.06; N, 3.13. Found: C, 66.97; H, 4.27; N, 3.11.
1-Methyl-3-(4-phenyl-5-(p-toluyl)selenophen-3-yl)-1H-indole (2c). White solid (194 mg, 91%
yield): mp 193–195 ºC. 1H NMR (400 MHz, CDCl3) δ 7.88 (s, 1H), 7.21–7.04 (m, 10H), 6.89 (d,
J = 7.7, 2H), 6.83–6.79 (m, 1H), 6.53 (s, 1H), 3.60 (s, 3H), 2.21 (s, 3H). 13C{1H} NMR (100 MHz,
CDCl3) δ 147.5, 146.6, 139.5, 136.6, 136.5, 134.5, 131.7, 128.9, 128.8, 128.7 (2C), 127.8, 127.5,
126.4, 126.0, 121.1, 120.6, 118.9, 111.5, 108.6, 32.6, 21.0. EIMS (m/z, rel. int., %) 427 (M+, 100).
HRMS (ESI) m/z: [M+Na]+ calcd. for C26H21NNaSe 450.0731; found: 450.0732.
3-(2-Butyl-4-phenylselenophen-3-yl)-1-methyl-1H-indole (2d). Yellow oil (43 mg, 22% yield): 1H
NMR (600 MHz, CDCl3) δ 7.76 (s, 1H), 7.30 (t, J = 8.0, 1H), 7.26 (t, J = 8.1, 1H), 7.18–7.16 (m,
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1H), 7.09–7.04 (m, 5H), 7.02–6.99 (m, 1H), 6.62 (s, 1H), 3.66 (s, 3H), 2.84–2.70 (m, 2H), 1.66–
1.59 (m, 2H), 1.29 (sextet, J = 7.4, 2H), 0.81 (t, J = 7.4, 3H). 13C{1H} NMR (150 MHz, CDCl3)
δ151.0, 146.3, 139.3, 136.4, 132.0, 128.4 (x2), 128.2, 127.5, 126.1, 123.4, 121.2, 120.2, 119.0,
111.5, 108.9, 35.3, 32.6, 31.2, 22.3, 13.8. EIMS (m/z, rel. int., %) 393 (M+, 100). HRMS (ESI) m/z:
[M+H]+ calcd. for C23H24NSe 394.1068; found: 394.1061.
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5-Bromo-3-(4,5-diphenylselenophen-3-yl)-1-methyl-1H-indole (2e). White solid (225 mg, 92%
yield): mp 170–171 ºC. 1H NMR (600 MHz, CDCl3) δ 7.93 (s, 1H), 7.24–7.21 (m, 2H), 7.14–7.10
(m, 10H), 7.04–7.02 (m, 1H), 6.52 (s, 1H), 3.58 (s, 3H). 13C{1H} NMR (150 MHz, CDCl3) δ 147.2,
146.7, 139.2, 137.1, 135.1, 131.4, 130.0, 129.1, 128.9, 128.7, 128.1, 127.7, 127.1, 126.7, 126.6,
124.0, 123.1, 112.5, 111.0, 110.3, 32.9. EIMS (m/z, rel. int., %) 492 ([M+2]+, 77), 490 (M+, 100).
HRMS (ESI) m/z: [M+H]+ calcd. for C25H19BrNSe 491.9866; found: 491.9852.
3-(4,5-Diphenylselenophen-3-yl)-1-methyl-1H-indole-5-carbonitrile (2f). White solid (193 mg,
88% yield): mp 198–199 ºC. 1H NMR (600 MHz, CDCl3) δ 7.95 (s, 1H), 7.33 (s, 1H), 7.26–7.24
(m, 1H), 7.21–7.19 (m, 3H), 7.14–7.10 (m, 6H), 7.09–7.07 (m, 2H), 6.65 (s, 1H), 3.64 (s, 3H).
13C{1H} NMR (150 MHz, CDCl3) δ147.2, 146.8, 138.9, 137.8, 136.7, 130.9, 130.5, 128.8, 128.6,
128.2, 127.7, 127.2, 127.1, 127.0, 126.7, 126.1, 124.2, 120.5, 112.6, 109.7, 102.0, 32.9. EIMS (m/z,
rel. int., %) 439 ([M+1]+, 21), 438 (M+, 100). Anal.Calcd. for C26H18N2Se: C, 71.40; H, 4.15; N,
6.40. Found: C, 71.20; H, 4.21; N, 6.24.
3-(4,5-Diphenylselenophen-3-yl)-5-methoxy-1-methyl-1H-indole (2g). White solid (199 mg, 90%
yield): mp 158–160 ºC. 1H NMR (600 MHz, CDCl3) δ 7.93 (s, 1H), 7.28–7.25 (m, 2H), 7.15–7.10
(m, 8H), 7.05 (d, J = 8.7, 1H), 6.7 (dd, J = 8.7, 2.2, 1H), 6.45 (s, 1H), 6.39 (d, J = 2.2, 1H), 3.56
(s, 3H), 3.47 (s, 3H). 13C{1H} NMR (150 MHz, CDCl3) δ 153.5, 147.2, 145.6, 139.4, 137.5, 132.2,
131.7, 129.5, 128.8, 128.7, 128.1, 127.6, 127.4, 126.8, 126.6, 126.5, 111.9, 110.6, 109.4, 101.6,
55.4, 32.8. EIMS (m/z, rel. int., %) 443 (M+, 100). Anal. Calcd. for C26H21NOSe: C, 70.59; H, 4.78;
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N, 3.17. Found: C, 69.91; H, 4.93; N, 3.09.
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1H), 7.08–6.99 (m, 10H), 6.82–6.78 (m, 1H), 3.51 (s, 3H), 1.80 (s, 3H). 13C{1H} NMR (100 MHz,
CDCl3) δ 147.7, 147.1, 139.3, 137.5, 136.7, 134.7, 132.4, 128.4, 128.2, 128.0, 127.7, 127.5, 126.7,
126.3, 126.1, 120.2, 119.4, 118.9, 109.0, 108.1, 29.5, 10.7. EIMS (m/z, rel. int., %) 427 (M+, 100).
HRMS (ESI) m/z: [M+Na]+ calcd. for C26H21NNaSe 450.0731; found: 450.0735.
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1-Benzyl-3-(4,5-diphenylselenophen-3-yl)-1H-indole (2i). White solid (227 mg, 93% yield): mp
164–165 ºC. 1H NMR (600 MHz, CDCl3) δ 7.93 (s, 1H), 7.27–7.25 (m, 2H), 7.21–7.19 (m, 3H),
7.16–7.14 (m, 2H), 7.12–7.09 (m, 7H), 7.06 (d, J = 8.1, 1H), 7.02–6.99 (m, 1H), 6.85–6.84 (m,
13
2H), 6.82–6.79 (m, 1H), 6.68 (s, 1H), 5.16 (s, 2H). C{1H} NMR (150 MHz, CDCl3) δ 147.4,
146.6, 139.3, 137.3, 137.2, 135.9, 132.1, 128.9, 128.7, 128.5, 128.4, 128.0, 127.9, 127.6, 127.3,
126.8, 126.6, 126.5, 126.4, 121.4, 120.5, 119.2, 112.0, 109.3, 49.8. EIMS (m/z, rel. int., %) 489
(M+, 66). Anal. Calcd. for C31H23NSe: C, 76.22; H, 4.75; N, 2.87. Found: C, 76.71; H, 4.93; N,
2.85.
3-(4,5-Diphenylselenophen-3-yl)-1H-indole (2k). White solid (167 mg, 84% yield): mp 202–204
1
ºC. H NMR (600 MHz, CDCl3) δ 7.93 (s, 1H), 7.89 (s, 1H), 7.24–7.20 (m, 3H), 7.13–7.02 (m,
10H), 6.82–6.80 (m, 1H), 6.65 (d, J = 2.4, 1H). 13C{1H} NMR (150 MHz, CDCl3) δ 147.4, 146.7,
139.3, 137.3, 135.6, 132.1, 128.9, 128.7, 128.0, 127.6, 127.1, 126.8, 126.5, 126.4, 124.4, 121.7,
120.4, 119.4, 113.0, 110.6. EIMS (m/z, rel. int., %) 399 (M+, 100). Anal. Calcd. for C24H17NSe: C,
72.36; H, 4.30; N, 3.52. Found: C, 71.94; H, 4.47; N, 3.45.
3-(4-(4-Chlorophenyl)-5-phenylselenophen-3-yl)-1-methyl-1H-indole (2l). White solid (210 mg,
94% yield): mp 179–181 ºC. 1H NMR (600 MHz, CDCl3) δ 7.91 (s, 1H), 7.22–7.20 (m, 3H), 7.10–
7.08 (m, 4H), 7.05 (m, 4H), 7.02 (d, 7.9, 1H), 6.84–6.81 (m, 1H), 6.54 (s, 1H), 3.63 (s, 3H). 13C{1H}
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