A flexible metal-catalyzed synthesis of highly substituted aryl phenanthrenyl selenides

Article abstract of DOI:10.1002/ejoc.201201340

An efficient method for the preparation of diaryl selenides, which are important in biology and materials science, is described. Specifically, the development of highly substituted phenanthrenyl phenyl selenides 4 and 6 by metal-catalyzed cyclization of o-phenylarylalkynes species 1 was successfully performed. The selectivity for 9- and 10-selenyl phenanthrenes was perfectly controlled by indium(III) and gold(I) catalysts, and the reactions proceed through different pathways. For the In(OTf)₃ catalyst system, 6-endo cyclization of alkyne 3 gives product 4 in which the selenium group is retained. In contrast, for the AuCl(IPr)/AgSbF₆ catalyst system, transformation of metal-alkyne complex 2 into vinylidene-gold intermediate 5 gives product 6 in which the selenium group is migrated. Various substrates, even electronically poor substrates, can be converted into phenanthrenes with high selectivity in high yield under very mild conditions. Highly substituted 9- and 10-selenylphenanthrenes are easily prepared from the corresponding selenium-containing (o-phenylaryl)alkynes. The selectivity is perfectly controlled by indium(III) and gold(I) catalysts. Various substrates can be converted into phenanthrene derivatives with high selectivity and in good yield under very mild conditions. Copyright

Full text of DOI:10.1002/ejoc.201201340

SHORT COMMUNICATION
DOI: 10.1002/ejoc.201201340
A Flexible Metal-Catalyzed Synthesis of Highly Substituted Aryl
Phenanthrenyl Selenides
Wontaeck Lim[a] and Young Ho Rhee*[a]
Keywords: Homogeneous catalysis / Gold / Aromaticity / Synthetic methods / Selenium
An efficient method for the preparation of diaryl selenides,
which are important in biology and materials science, is de-
scribed. Specifically, the development of highly substituted
phenanthrenyl phenyl selenides 4 and 6 by metal-catalyzed
cyclization of o-phenylarylalkynes species 1 was successfully
performed. The selectivity for 9- and 10-selenyl phen-
anthrenes was perfectly controlled by indium(III) and gold(I)
catalysts, and the reactions proceed through different path-
ways. For the In(OTf)3 catalyst system, 6-endo cyclization of
alkyne 3 gives product 4 in which the selenium group is re-
tained. In contrast, for the AuCl(IPr)/AgSbF6 catalyst system,
transformation of metal–alkyne complex 2 into vinylidene–
gold intermediate 5 gives product 6 in which the selenium
group is migrated. Various substrates, even electronically
poor substrates, can be converted into phenanthrenes with
high selectivity in high yield under very mild conditions.
the migration of the selenyl group from selenyl-substituted
alkynes in the presence of a Ru complex to form metal–
vinylidene complex 5 has been noted.[4b] However, catalytic
reactions that utilize this interesting reactivity are still lim-
ited.[5] On the basis of these precedents, we reasoned that
species 5 might undergo electrocyclization to give isomeric
phenanthrene product 6 in an alternative course of the reac-
tion (Scheme 1, path B).[6] Because it is well established that
metal–alkyne complex 2 and corresponding metal–vinyl-
idene species 5 are in equilibrium,[7] the key issue in this
divergent pathway was to find metal catalysts that can
render selectivity in the formation of the product. Herein,
we wish to report our recent results, which indeed show
that the product can be successfully controlled. Thus, the
generation of cycloisomerized product 3 with retention of
the selenyl group was optimized with the indium catalyst
(path A). In contrast, alternative cycloisomerization with
1,2-migration of the selenyl group to generate isomeric
Introduction
Diaryl selenides are an important class of compounds
because of their utility in biologically related areas and ma-
terials science.[1] Thus, the development of new procedures
to prepare diversely substituted diaryl selenides is an impor-
tant task in organic synthesis.[2] Conventionally, these com-
pounds are synthesized by the substitution reaction of aryl
carbanions with selenium electrophiles or by the reaction
of selenium anions with aryl halides. These traditional
methods require the stoichiometric generation of the reac-
tive intermediates under strongly basic conditions. Thus,
the development of more efficient methods that can operate
under mild conditions is highly desirable. In this context,
we envisioned that diversely substituted aryl phenanthrenyl
selenides could be accessed through transition-metal-cata-
lyzed cycloisomerization of (o-phenylaryl)alkynes species 1
(Scheme 1). We were particularly interested in the possibil-
ity of a divergent pathway. In one path of this scenario,
alkyne 1 can generate cycloisomerized product 4 in the pres-
ence of a suitable metal catalyst that can effectively activate
alkynes towards nucleophilic attack of the phenyl group
(Scheme 1, path A). In fact, generation of alkyl-substituted
and halogen-substituted polyaromatic compounds by
metal-catalyzed cycloisomerization of acyclic precursors
has been studied.[3a,3b] However, the cycloisomerization of
selenium-substituted alkynes is extremely rare.[4a] Moreover,
[a] Department of Chemistry, POSTECH,
Pohang University of Science and Technology.
San 31, Hyoja-dong, Pohang, Kyungbuk 790-784, Korea
Fax: +82-54-279-3399
E-mail: yhrhee@postech.ac.kr
Homepage: http://yhrhee.postech.ac.kr
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201201340.
Scheme 1. Divergent pathways for the synthesis of diaryl selenides
containing a phenanthrene moiety.
460
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Synthesis of Highly Substituted Aryl Phenanthrenyl Selenides
product 5 was optimized with Au catalysts (path B). From used, the reaction was completely unreactive (Table 1, en-
a synthetic viewpoint, this flexible route should provide try 11). Switching to PtCl2 (Table 1, entry 12), however, a
powerful access to diversely substituted phenanthrene ring mixture of products was obtained. When AuCl3 was em-
systems.[8]
ployed, desired compound 8b was obtained in 93% yield
with complete selectivity towards the migratory cycloisom-
erization (Table 1, entry 13). The use of AuCl maintained
the reactivity and the yield of the cycloisomerization
Results and Discussion
At the initial stage of the study, a number of metal cata- (Table 1, entry 14). Again, the competing cycloisomeriza-
lysts (5 mol-%) were screened for the cycloisomerization re- tion reaction was not observed. Lowering the temperature
action with 7 as the substrate. On the basis of the pre- also selectively gave the migratory product in very high
cedents discussed above, we first investigated various Rh[9] yield (Table 1, entry 15). Next, we looked into cationic
and Ru[10] complexes. As shown in Table 1, Wilkinson’s cat- gold(I) complexes. Even though the electrophilic complexes
alyst was found to be completely unreactive even at elevated were inefficient in this case (Table 1, entry 16), the use of a
temperature (Table 1, entry 1). Using RhCl3, the reaction more electron-donating complex gave the desired com-
suffered from poor reactivity, even though a small amount pound in excellent yield (Table 1, entry 17). The optimal re-
of the migrated product[11] was obtained (Table 1, entry 2). sult was obtained when the AuCl(IPr)/AgSbF6 complex was
Other Ru and Rh catalysts also showed poor reactivity used (Table 1, entry 18). Under these conditions, the desired
(Table 1, entries 3–7). In contrast, the use of indium(III) cycloisomerization product was obtained in 97% isolated
chloride gave cycloisomerized product 8a with retention of yield at room temperature within a relatively shorter reac-
phenylselenyl group in 65% yield (Table 1, entry 8). In this tion time than AuCl. Thus, we decided to use AuCl(IPr)/
case, migratory cycloisomerization product 8b was obtained AgSbF6 as the optimal catalyst.
in a trace amount (ca. 9%). Thus, the competition between
With the use of the conditions described in entries 9 and
the two pathways seems to be operating. Switching to in- 18 in Table 1, the divergent pathways for the synthesis of
dium triflate improved the yield of 8a to 93% with no ap- the phenanthrenyl selenides were explored (Tables 2 and
parent involvement of the migratory cycloisomerization Table 3). We first investigated the retentive cycloisomeriza-
(Table 1, entry 9). Lowering the temperature decreased the tion by using the indium catalyst (Table 2). The substituent
reactivity of the catalyst (Table 1, entry 10). Then, we on the aryl ring that attacks the metal-bound alkyne had a
looked into the alternative migratory cycloisomerization significant effect on the reaction outcome. For example, the
pathway. When a phosphane-ligated platinum complex was reaction with a substrate bearing an electron-donating
Table 1. Screening of the metal catalyst for the divergent synthesis of selenyl-substituted phenanthrene.
Entry
Catalyst (5 mol-%)
Solvent
T
[°C]
Time
[h]
Conversion
[%]
8a/8b
Yield[a] [%]
1
2
3
4
5
6
7
8
[RhCl(PPh3)3]
RhCl3
RuCl3
[RuCl2(PPh3)3]
Rh2(OAc)2
[Cp*Ru(MeCN)3]PF6
[RhClcod]2
InCl3
In(OTf)3
In(OTf)3
[PtCl2(PPh3)2]
PtCl2
AuCl3
AuCl
AuCl
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
80
80
80
80
80
80
80
80
80
r.t
80
80
80
80
r.t.
r.t.
r.t.
r.t.
20
19
20
20
14
16
16
20
14
20
19
4
19
2
14
1
5.5
0.25
0
25
0
0
0
0
0
100
100
0
–
0:23
–
–
–
–
–
65:9
93:0
–
9
10
11
12
13
14
15
16
17
18
0
–
100
100
100
100
15
100
100
4:64
0:93
0:94
0:99
0:13
0:99
[AuClP(C6F5)3]/AgSbF6
[Au{(tBu)2P(o-biPh)}](CH3CN)SbF6
[AuCl(IPr)]/AgSbF6
0:98 (97[b]
)
1
[a] Determined by analysis of the crude material by H NMR spectroscopy by using 1,3,5-trimethoxybenzene as an internal standard.
[b] Isolated yield.
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461

W. Lim, Y. H. Rhee
SHORT COMMUNICATION
methoxy group was complete within a short time (Table 2, tion (Table 2, entry 9), whereas a chloride group slowed the
entry 2), whereas the same reaction performed with a sub- reaction (Table 2, entry 10). This result is again consistent
strate bearing the electron-withdrawing fluorine group dras- with the mechanistic rationale shown in Scheme 1.
tically slowed the reaction (Table 2, entry 3). In the latter
Next, we investigated the scope of the migratory cyclo-
case, only about 50% conversion was observed, even if isomerization by using the gold catalyst. As shown in
10 mol-% catalyst was used. This result well addresses the Table 3, this pathway proved more sensitive to the substitu-
carbocationic nature of intermediate 3 generated in the re- ents than the retentive cycloisomerization. For example, the
tentive pathway (Scheme 1). Substrate 13 possessing an un- reaction of substrate 9 was significantly slower than that
substituted aryl ring (Table 2, entry 4) maintained the cata- of substrate 7 and produced only retentive cycloisomerized
lytic activity. Introducing a methoxy or methyl group at product 10a in low yield (Table 3, entry 2). However, sub-
other positions of the phenyl ring also gave the cycloiso- strate 11 produced only migratory cycloisomerization prod-
merized products in good yields (Table 2, entries 5–8). The uct 12b in 86% yield (Table 3, entry 3). Interestingly, intro-
effect of the substituents on the connecting aryl ring was duction of methoxy or methyl substituents at other posi-
then studied. As can be seen from Table 2, the substrate tions of the attacking aryl ring had a less significant effect,
possessing a methoxy group increased the rate of the reac- and the migratory cycloisomerization products were con-
stantly produced in good yield (Table 3, entries 5–8). Sub-
strates 23 and 25 also generated the migratory cycloisomer-
Table 2. Scope of the indium(III)-catalyzed cycloisomerization re-
ization products in good yield. As with the retentive cyclo-
action.[a]
Table 3. Scope of the gold-catalyzed cycloisomerization reaction.[a]
[a] General procedure: A mixture of the substrate and In(OTf)3
(5 mol-%) was stirred at 80 °C. [b] Isolated yield. [c] 10 mol-% of
indium-catalyst was used. [d] The substrate was recovered in 49%
yield. [e] When AuCl (5 mol-%) was used at 80 °C, the product was
formed in 40% yield.
[a] Method A: The reaction was performed at room temperature
with the catalyst (5 mol-%). Method B: The reaction was per-
formed at 80 °C with the catalyst (5 mol-%). [b] Isolated yield.
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Eur. J. Org. Chem. 2013, 460–464

Synthesis of Highly Substituted Aryl Phenanthrenyl Selenides
to give the product (33.9 mg, 0.093 mmol) as a white powder in
isomerization, effects of the substituents on the connecting
aryl ring were observed.
93% yield, m.p. 100.2–101.3 °C. Rf = 0.49 (hexane/diethyl ether =
1
95:5). H NMR (300 MHz, CDCl3): δ = 8.64 (d, J = 8.1 Hz, 1 H),
The result shown above indeed illustrate that various
substituents can be installed in the phenanthrene ring by
exploiting the flexible nature of the cycloisomerization reac-
tion. A higher degree of substituent diversity in the product
could be introduced by varying the phenyl group. Thus, our
final task was to establish a general method that would al-
low introduction of a substituted phenyl group. For this
purpose, we pursued the synthesis of compound 30
(Scheme 2). Substrate 29 was prepared uneventfully from
dehydrogenative coupling of terminal alkyne 27 with diaryl
diselenide 28.[12] Reaction of this substrate by using
In(OTf)3 gave retentive cycloisomerization product 30a in
8.47 (s, 1 H), 7.78 (s, 1 H), 7.63–7.49 (m, 5 H), 7.34–7.32 (m, 4 H),
3.15 (s, 3 H), 2.59 (s, 3 H) ppm. 13C NMR (75 MHz, CDCl3): δ =
136.44, 135.97, 134.05, 133.52, 133.43, 133.16, 132.62, 131.89,
130.25, 130.01, 129.76, 128.32, 127.77, 127.66, 126.81, 126.76,
123.18, 121.77, 25.75, 21.72 ppm. IR (NaCl): ν = 2920, 1577, 1476,
˜
1437, 1022, 850, 756, 734, 689 cm–1. HRMS (EI): calcd. for
C22H18Se [M]+ 362.0574; found 362.0572.
(1,3-Dimethylphenanthren-9-yl)(phenyl)selane (8b): To a solution of
AuCl(IPr) (6.4 mg, 0.01 mmol) in dichloromethane (1.5 mL) was
added a solution of AgSbF6 (3.7 mg, 0.01 mmol) in dichlorometh-
ane (1.5 mL), and the resulting mixture was stirred for 10 min at
room temperature. The precipitate was filtered through a pad of
82% yield, whereas the use of the Au catalyst generated Celite, and the solvent was removed under reduced pressure. The
residual oil was dried under reduced pressure for 2 h. To this resi-
due was added a solution of [(3Ј,5Ј-dimethylbiphenyl-2-yl)ethyn-
yl](phenyl)selane (7) (72.2 mg, 0.2 mmol) in dichloromethane
(4 mL), and the resulting mixture was stirred for 15 min. When
the reaction was complete, the solvent was removed under reduced
pressure, and the resulting yellow solid was purified by flash col-
umn chromatography on silica gel to give the product as a pale
yellow solid. This solid was further purified by recrystallization
from diethyl ether/MeOH to give the product (71.2 mg, 0.19 mmol)
as a white powder in 97% yield, m.p. 69.7–71.2 °C. Rf = 0.51 (hex-
ane/diethyl ether = 95:5). 1H NMR (300 MHz, CDCl3): δ = 8.72
(d, J = 8.1 Hz, 1 H), 8.42 (dd, J = 8.1, 0.6 Hz, 1 H), 8.37 (m, 2 H),
7.65 (ddd, J = 7.7, 7.8, 1.5 Hz, 1 H), 7.57 (ddd, J = 7.7, 7.8, 1.5 Hz,
1 H), 7.36–7.31 (m, 2 H), 7.30 (m, 3 H), 7.19–7.16 (m, 3 H), 2.65
(s, 3 H), 2.59 (s, 3 H) ppm. 13C NMR (75 MHz, CDCl3): δ =
137.01, 134.90, 132.52, 132.28, 131.30, 131.12, 130.97, 130.18,
129.44, 128.90, 127.20, 126.96, 126.65, 126.33, 123.41, 120.75,
isomeric 30b in 97% yield.
Scheme 2. Synthesis of compounds 30a and 30b.
22.33, 19.79 ppm. IR (NaCl): ν = 2924, 1577, 1476, 1437, 1022,
˜
849, 784, 742, 690 cm–1. HRMS (EI): calcd. for C22H18Se [M]+
362.0574; found 362.0569.
Supporting Information (see footnote on the first page of this arti-
cle): Analytical data for all compounds, general procedure for the
preparation of the substrates, determination of structures 8a and
Conclusions
We optimized reaction conditions to synthesize multisub-
stituted phenanthrene derivatives, including derivatives con-
taining an electron-deficient substituent. The AuClIPr/
AgSbF6 complex can be used as a good catalyst under mild
conditions to afford the desired products in short reaction
times. This reaction proceeds via a gold–vinylidene interme-
diate, which has a low transition energy. An electron-rich
N-heterocyclic carbene ligand allowed easier formation of
the metal–vinylidene intermediate. Further investigation of
this reaction for the synthesis of polyaromatic hydrocarbons
is in progress.
1
8b, H NMR and 13C NMR spectra.
Acknowledgments
This work was supported by the Korean Government, National
Research Foundation (grant numbers 2010-0009458 and 2008-
0061957).
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Eur. J. Org. Chem. 2013, 460–464
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W. Lim, Y. H. Rhee
SHORT COMMUNICATION
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Received: October 10, 2012
Published Online: December 10, 2012
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