Reusable visible light photoredox catalysts; Catalyzed benzylic C(sp 3)-H functionalization/carbocyclization reactions

Article abstract of DOI:10.1055/s-0032-1317349

The C(sp³)-H functionalization/carbocyclization reaction through the oxidative quenching of visible light photoredox catalysts is established for constructing functionalized 1H-indenes. The process is general for a wide range of benzylic C(sp

Full text of DOI:10.1055/s-0032-1317349

LETTER
▌2707
lRetteerusable Visible Light Photoredox Catalysts; Catalyzed Benzylic
C(sp3)–H Functionalization/Carbocyclization Reactions
Visible Light Photoredox Catalysts
Jia-Dong Xia,a,b Guo-Bo Deng,a Ming-Bo Zhou,a Wei Liu,a Peng Xie,a,b Jin-Heng Li*a
a
State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University,
Changsha 410082, P. R. of China
b
Key Laboratory of Chemical Biology & Traditional Chinese Medicine Research (Ministry of Education), Hunan Normal University, Changsha
410081, P. R. of China
Fax +86(731)88713642; E-mail: jhli@hnu.edu.cn
Received: 09.08.2012; Accepted after revision: 11.09.2012
cyclization of arylalkynes with aromatic sulfonyl chlo-
Abstract: The C(sp3)–H functionalization/carbocyclization reac-
rides (Scheme 1).6h However, the reaction required
tion through the oxidative quenching of visible light photoredox
25 mol% CuCl and harsh conditions (140 °C), and was
catalysts is established for constructing functionalized 1H-indenes.
The process is general for a wide range of benzylic C(sp3)–H bonds
only applied to substrates bearing the simple benzylic
and is highly compatible with common functional groups. Impor- C(sp3)–H group with Me or Ph substituents. In this proto-
tantly, the visible light photoredox catalysts can be recovered and
reused at least three times without loss of catalytic activity.
col, aromatic sulfonyl chlorides were found to formally
act as a donor of aryl radical groups with loss of the SO2Cl
Key words: photoredox, catalysis, C–H activation, cyclization, al-
kynes, indenes
group by heating with CuCl. In light of these results, we
envisioned that aromatic sulfonyl chlorides may be trans-
ferred to aryl radical groups under visible light irradiation.
As expected, we found that a variety of ortho-alkyl aryl-
Visible light photoredox catalyst initiated organic trans- alkynes could undergo arylative cyclization with arylsul-
formations are emerging as uniquely powerful tools for fonyl chlorides7 through an oxidative quenching cycle of
constructing new chemical bonds in organic synthesis due the visible light photocatalysts (Scheme 1). More impor-
to their more environmentally benign sustainability and tantly, the reaction could be employed to functionalize the
mild operating conditions.1–4 Among these transforma- C(sp3)–H bonds of both a benzyl ether and an acetal. It is
tions, C(sp3)–H functionalization using this visible light noted that the products, indene and their derivatives, are
photoredox catalysis strategy is particularly interesting.2,3 ubiquitous in natural products, functional materials, and
However, despite good progress, C(sp3)–H functionaliza- pharmaceuticals.8
tion methods have focused on the C(sp3)–H bonds adja-
R1
cent to either the nitrogen of amines or the oxygen atom
of ethers through the reductive quenching cycles of the
photocatalysts. To our knowledge, only two papers have
reported on the functionalization of C(sp3)–H bonds using
visible light photoredox catalysis via an oxidative quench-
ing cycle.3
Direct functionalization reactions of unactivated C(sp3)–
H bonds are highly desirable from the atom-economic
point of view, and still remain an important challenge.5,6
As an example, transition-metal-catalyzed selective car-
bocyclization of an alkyne with a benzylic C(sp3)–H bond
for the construction of carbocycles is particularly fascinat-
ing because saturated, less functionalized precursors
would be required.5 However, the carbocyclization reac-
tions of alkynes involving benzylic C(sp3)–H functional-
ization are rare and typically require both the use of 10–
25 mol% transition-metal catalysts and elevated tempera-
ture (60–140 °C). For example, Nakamura and co-work-
CuCl (25 mol%)
Na2CO3 (2.5 equiv)
m-xylene, 140 °C
R3
R2
Ar
Ar
R4
Nakamura's work
ref. 6h
1
R1
ArSO2Cl
2
this work
R2
R4
R3
Ru(bpy)3Cl2 or Ir(ppy)3
Na2CO3, 36 W lightbulb
MeCN, 45 °C, 36 h
Scheme 1 Benzylic C(sp3)–H functionalization and carbocyclization
with aromatic sulfonyl chlorides
We began our studies with the reaction between 1-isopro-
pyl-2-(phenylethynyl)benzene (1a) and 4-nitrobenzene-1-
sulfonyl chloride (2a) to establish the optimal reaction
conditions (Table 1).9 Interestingly, substrate 1a could
successfully react with 2a, [Ru(bpy)3Cl2], and NaOAc in
MeCN at 30 °C under irradiation with a 36 W compact
fluorescent light for 36 h, providing the desired product 3
in 37% yield (entry 1). Further screening revealed that the
amount of [Ru(bpy)3Cl2] affected the reaction; the reac-
tion at 5 mol% [Ru(bpy)3Cl2] afforded an identical yield
ers have reported
a new Cu-catalyzed arylative
SYNLETT 2012, 23, 2707–2713
Advanced online publication: 18.10.2012
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0032-1317349; Art ID: ST-2012-W0673-L
© Georg Thieme Verlag Stuttgart · New York

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J.-D. Xia et al.
LETTER
Table 1 Screening for Optimal Conditionsa
to that obtained with 3 mol% [Ru(bpy)3Cl2] (entry 2), but
the yield was reduced significantly using 10 mol%
[Ru(bpy)3Cl2] due to the occurrence of some side-reac-
tions (entry 3). Subsequently, a series of other solvents,
including CH2Cl2, N-methyl-2-pyrrolidinone (NMP), tol-
uene, dimethyl sulfoxide (DMSO), and N,N-dimethylform-
amide (DMF), were tested; these were found to be less
effective than MeCN (entries 2 and 4–8). Among the bas-
es examined, it turned out that Na2CO3 was more efficient
than NaOAc or K2HPO4 (entries 2, 9 and 10). It is note-
worthy that the yield of 3 increased to 83% by using an-
hydrous MeCN medium at 45 °C (entry 11), and identical
results were observed at 60 °C (entry 12). Gratifyingly,
[Ru(bpy)3Cl2] could be recovered and reused at least three
times without loss of catalytic activity [the reaction mix-
ture was filtered through filter paper and a short silica gel
column (EtOAc), and [Ru(bpy)3Cl2] remained on the filter
paper and silica gel. [Ru(bpy)3Cl2] was then recovered by
washing the filter paper and silica gel with MeOH–MeCN
(5 mL, 1:2 v/v) four times] (entry 12). It was noted that the
reaction proceeded smoothly without base, albeit after a
prolonged reaction time (entry 13). However, [Ir(bpy)3]
displayed less reactivity for the reaction (entry 14). Nota-
bly, the reaction did not take place without irradiation by
the compact fluorescent light (entry 15).
NO2
SO2Cl
NO2
Ph
+
[M]
Ph
visible light
1a
2a
3
Entry [M] (mol%)
Base
Solvent Temp Yield
(°C)
(%)b
1
2
[Ru(bpy)3Cl2] (3)
[Ru(bpy)3Cl2] (5)
NaOAc
NaOAc
MeCN
MeCN
MeCN
30
30
30
37
39
3
[Ru(bpy)3Cl2] (10) NaOAc
17
4
[Ru(bpy)3Cl2] (3)
[Ru(bpy)3Cl2] (3)
[Ru(bpy)3Cl2] (3)
[Ru(bpy)3Cl2] (3)
[Ru(bpy)3Cl2] (3)
[Ru(bpy)3Cl2] (3)
[Ru(bpy)3Cl2] (3)
[Ru(bpy)3Cl2] (3)
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
Na2CO3
K2HPO4
Na2CO3
Na2CO3
–
CH2Cl2 30
5
5
NMP
30
30
30
30
30
30
45
60
45
45
45
trace
trace
trace
trace
60
6
toluene
DMSO
DMF
7
8
9
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
Gratifyingly, the above visible light photocatalysis proto-
col was found to be applicable to a diverse range of sub-
stituted arylsulfonyl chlorides for the reaction with
1-isopropyl-2-(phenylethynyl)benzene (1a; Scheme 2).8
Screening revealed that several substituents, such as NO2,
CF3, CN, acetyl, Cl, F, I, Br, Me or MeO, on the aryl ring
of the arylsulfonyl chlorides were tolerated; the electron-
deficient aryl groups were more reactive than the electron-
rich aryl groups (to give 4–13). Notably, [Ru(bpy)3Cl2]
and [Ir(ppy)3] displayed different catalytic reactivity with
arylsulfonyl chlorides; whereas [Ru(bpy)3Cl2] was more
efficient for 4-nitrobenzene-1-sulfonyl chloride (2a) than
[Ir(ppy)3] (entries 12 and 14 in Table 1), it was inferior to
[Ir(ppy)3] with other arylsulfonyl chlorides, such as 4-nitro-
3-(trifluoromethyl)benzene-1-sulfonyl chloride (to give
4), 4-cyanobenzene-1-sulfonyl chloride (to give 5) or 4-
chlorobenzene-1-sulfonyl chloride (to give 7). Conse-
quently, [Ir(ppy)3] was employed for the arylative cycliza-
tion with other arylsulfonyl chlorides to give products 6
and 8–15. In the presence of [Ir(ppy)3] and Na2CO3 under
irradiation by a 36 W compact fluorescent light, 4-acetyl-
benzene-1-sulfonyl chloride underwent the reaction with
substrate 1a, giving the corresponding product 6 in 94%
yield. Notably, when the recovery and reuse of [Ir(ppy)3]
was tested, 91% yield of 6 was still achieved using the re-
covered catalyst. Halogen substituents (F, I and Br), were
compatible with the optimal conditions, giving products
8–10, thereby facilitating additional modifications at the
halogenated positions. Using electron-neutral or electron-
rich arylsulfonyl chlorides, moderate yields of products
11–14 were still achieved with 10 mol% [Ir(ppy)3]. Inter-
estingly, heterocycle-containing sulfonyl chloride was
suitable for the reaction, giving the expected product 15,
10
11c
37
83
12c,d [Ru(bpy)3Cl2] (3)
84
13c,e
14c
[Ru(bpy)3Cl2] (3)
[Ir(ppy)3] (3)
76
Na2CO3
Na2CO3
21
15c,f
[Ru(bpy)3Cl2] (3)
0
a Reaction conditions: 1a (0.2 mmol), 2a (3 equiv), [M], base (2.5
equiv) and solvent (1 mL) irradiated with 36 W compact fluorescent
light for 36 h under argon atmosphere. [Ru(bpy)3Cl2] = tris(2,2′-bi-
pyridine)ruthenium dichloride, [Ir(ppy)3] = tris(2-phenylpyri-
dine)iridium(III).
b Isolated yield.
c Using anhydrous MeCN.
d The catalyst was recovered and reused three times, and the yields
were 80% (run 1), 81% (run 2), and 78% (run 3).
e Irradiated for 42 h.
f Without additional light.
making this methodology more useful for pharmaceuti-
cals and natural product preparation.
As shown in Scheme 3, the scope of ortho-alkyl aryl-
alkynes was exploited in the presence of 4-nitrobenzene-
1-sulfonyl chloride (2a), [Ru(bpy)3Cl2], and Na2CO3 un-
der irradiation with a 36 W compact fluorescent light. The
results demonstrated that both aryl and aliphatic alkynes
were compatible with the standard conditions, giving
products 16–26. For arylalkynes, a number of substitu-
ents, including Me, MeO, F, Cl, Br and NO2, on the aryl
ring at the terminal alkyne were also well tolerated to give
products 16–22. Substrates with a para-methyl group
Synlett 2012, 23, 2707–2713
© Georg Thieme Verlag Stuttgart · New York

LETTER
Visible Light Photoredox Catalysts
2709
underwent the reaction with sulfonyl chloride 2a, were viable for the arylative cyclization, giving the ex-
[Ru(bpy)3Cl2] and Na2CO3 under irradiation with a 36 W pected products 29–32. It was noted that 1-(dimethoxy-
compact fluorescent light to afford the desired product 16 methyl)-2-(phenylethynyl)benzene, an acetal, could also
in 85% yield. MeO-substituted arylalkyne also provided undergo arylative cyclization to offer the demethylated
good yield of 17 under the same conditions. Although the product 33 in good yield. However, substrates with a pri-
reactivity of substrates with electron-withdrawing groups mary benzylic carbon atom were not suitable for the ary-
or an ortho-methyl group was reduced, moderate to good lative cyclization and only trace amounts of product 34
yields were still achieved to give product 18–22. Interest- were obtained.
ingly, naphthalen-1-yl- or thiophen-2-yl-substituted al-
Arylative cyclization reactions of other alkynes, including
kynes were also viable substrates for the arylative
double cyclization of dialkyne compounds, were also in-
cyclization, giving products 23 and 24 in moderate yield.
vestigated (Scheme 4). In the presence of 4-nitrobenzene-
1-sulfonyl chloride (2a), [Ru(bpy)3Cl2] and Na2CO3 under
irradiation with a 36 W compact fluorescent light, both di-
alkyne compounds 1b and 1c were readily transformed
Notably, aliphatic alkynes, even with a bulky tert-butyl
group, afforded the corresponding 1H-indenes 25 and 26
in moderate to good yields.
Gratifyingly, substrates with Br or Me substituents on the into the corresponding bisindenes 36 and 38 in moderate
aromatic ring of the benzylic moiety were also compatible yields together with monoindenes 35 and 37 in 32 and
with the standard conditions, giving products 27 and 31. 31% yield, respectively. Interestingly, treatment of 1,2-di-
For example, Br-substituted substrate was treated with phenylacetylene (1d) with benzene-1-sulfonyl chloride
sulfonyl chloride 2a, [Ru(bpy)3Cl2], and Na2CO3 under ir- (2b) and [Ir(ppy)3], Na2CO3 and 36 W compact fluores-
radiation with a 36 W compact fluorescent light, to cent light gave (2-chloroethene-1,1,2-triyl)tribenzene
smoothly furnish product 27 in 74% yield. Further screen- (38), a desulfitative and Cl-addition product, in 85%
ing revealed that the secondary benzylic carbon atoms, in- yield, suggesting that a vinyl cation is generated.9
cluding 1-ethyl, 1-benzyl, and 1-(phenoxymethyl) groups,
Ph
SO2Cl
Ru(bpy)3Cl2 or Ir(ppy)3
R
Na2CO3, 36 W lightbulb
+
MeCN, 45 °C, 36 h
Ph
R
2
1a
Cl
NO2
CN
O
CF3
Ph
Ph
Ph
Ph
4
7
5
6
Ru(bpy)3Cl2: 6%
Ir(ppy)3: 61%
Ru(bpy)3Cl2: 34%
Ru(bpy)3Cl2: 52%
Ir(ppy)3: 81%
Ir(ppy)3: 94%a
Ir(ppy)3: 40%
F
I
Br
Ph
10
Ph
11
Ph
Ph
8
9
Ir(ppy)3: 53%b
Ir(ppy)3: 56%
Ir(ppy)3: 44%
Ir(ppy)3: 26%
OMe
S
Ph
Ph
15
Ph
Ph
14
12
13
Ir(ppy)3: 42%c
Ir(ppy)3: 40%c
Ir(ppy)3: 71%
Ir(ppy)3: 52%
Scheme 2 Screening arylsulfonyl chlorides (2). Reagents and conditions: 1a (0.2 mmol), 2 (3 equiv), [Ru(bpy)3Cl2] or [Ir(ppy)3] (3 mol%),
Na2CO3 (2.5 equiv), anhydrous MeCN (1 mL), irradiation with a 36 W compact fluorescent light at 45 °C for 36 h under argon atmosphere.
a [Ir(ppy)3] was recovered and reused to give the 6 in 91% yield. b [Ir(ppy)3] (10 mol%) was used.
© Georg Thieme Verlag Stuttgart · New York
Synlett 2012, 23, 2707–2713

2710
J.-D. Xia et al.
LETTER
Notably, three radical inhibitors, 2,2,6,6-tetramethyl- (2 h every interval), the reaction did not proceed during
piperidine-1-oxyl (TEMPO), 1,1-diphenylalkene, and the ‘off’ periods.
2,6-di-tert-butylphenol, were also employed for the reac-
tion of 1-isopropyl-2-(phenylethynyl)benzene (1a) with
4-nitrobenzene-1-sulfonyl chloride (2a), [Ru(bpy)3Cl2],
Na2CO3 under irradiation with a 36 W compact fluores-
A plausible mechanism, outlined in Scheme 5, is proposed
on the basis of the present results and on literature re-
ports.1–7,10 Aryl radical (Ar·)9 is first formed by a single
electron transfer (SET) from the excited state [Ru(bpy)3]2+
cent light. Under these conditions no reaction was ob-
(or [Ir(ppy)3]3+) to an arylsulfonyl chloride,1–4,10 followed
served with a stoichiometric amount of these radical
by addition of Ar· to the carbon–carbon triple bond in sub-
inhibitors, which is consistent with a radical being in-
strate 1, generating radical intermediate A. This interme-
volved in the present reaction mechanism. In addition, a
diate is readily transformed into vinyl cation intermediate
control on/off switching of the light source was tested;2k
B10 by two pathways:1–4 oxidation of radical intermediate
when the lamp was switched off at appropriate intervals
A by (i) [Ru(bpy)3]3+ (or [Ir(ppy)3]4+) cation, and (ii) aryl-
NO2
R1
SO2Cl
Ru(bpy)3Cl2 (3 mol%)
Na2CO3, 36 W lightbulb
R3
+
MeCN, 45 °C, 36 h
R2
R1
R4
NO2
1
2a
R2
NO2
R4
R3
NO2
NO2
16 R5 = Me, 85%
17 R5 = MeO, 87%
18 R5 = F, 78%a
19 R5 = Cl, 65%b
20 R5 = Br, 40%
21 R5 = NO2, 39%
R5
22 38%
23 46%
NO2
NO2
NO2
NO2
Ph
S
Br
25 54%
27 74%
24 48%
NO2
26 71%
NO2
NO2
NO2
Ph
Ph
Ph
Ph
Ph
Ph
Ph
28 80%
Ph
31 53%
29 63%a
30 67%
NO2
NO2
NO2
Ph
Ph
Ph
HO
OPh
32 50%
OMe
34 tracea
33 73%c
Scheme 3 [Ru(bpy)3Cl2]-Catalyzed Arylative Cyclization of ortho-Alkyl Arylalkynes (1) with Sulfonyl Chloride (2a). Reagents and condi-
tions: 1 (0.2 mmol), 2a (3 equiv), [Ru(bpy)3Cl2] (3 mol%), Na2CO3 (2.5 equiv), anhydrous MeCN (1 mL) with 36 W compact fluorescent light
at 45 °C for 36 h under argon atmosphere. a [Ru(bpy)3Cl2] (10 mol%). b 2a (4 equiv). c An acetal, 1-(dimethoxymethyl)-2-(phenylethynyl)ben-
zene, was employed as the substrate.
Synlett 2012, 23, 2707–2713
© Georg Thieme Verlag Stuttgart · New York

LETTER
Visible Light Photoredox Catalysts
2711
O2N
SO2Cl
2a (5 equiv)
NO2
35 32%
+
O2N
Ru(bpy)3Cl2 (3 mol%)
Na2CO3, 36 W lightbulb
MeCN, 45 °C, 36 h
1b
NO2
36 52%
O2N
SO2Cl
Ph
Ph
Ph
2a (5 equiv)
+
Ru(bpy)3Cl2 (3 mol%)
Na2CO3, 36 W lightbulb
MeCN, 45 °C, 36 h
Ph
Ph
Ph
1c
O2N
NO2
NO2
37 31%
38 50%
Ph
Cl
Ph
Ir(ppy)3 (3 mol%)
Na2CO3, 36 W lightbulb
SO2Cl
Ph
Ph
+
MeCN, 45 °C, 36 h
1d (0.2 mmol)
2b (3 equiv)
39 85%
Scheme 4 Arylative cyclization of other alkynes 1
In summary, we have described a general and mild route
that enables the construction of functionalized 1H-in-
denes via photoredox catalyzed arylative cyclization of
ortho-alkyl arylalkynes with arylsulfonyl chlorides using
a visible light photoredox catalysis strategy. This new
protocol has several attractive features: (a) a low operat-
ing temperature (45 °C) and lower loading of catalyst is
required, (b) high functional group tolerance and broad
substrate scope, and (c) simple operation by reusable vis-
ible light photoredox catalysis. Applications of this mild
photoredox catalyst-catalyzed arylative cyclization trans-
formation in organic synthesis are underway in our labo-
ratory.
SET
R
SO2 + Cl– + Ar
ArSO2Cl
2+
3+
Ru(bpy)3
Ru(bpy)3
Ar
Ar
4+
3+
(Ir(ppy)3
)
(Ir(ppy)3
)
1
R
R
ArSO2Cl
2+
Ru(bpy)3
visible light
A
3+
(Ir(ppy)3
)
Ar
+
+ SO2 + Cl–
B
– H+
Ar
Acknowledgment
R
We thank the National Natural Science Foundation of China (No.
21172060) and the Fundamental Research Funds for the Central
Universities (Hunan University) for financial support.
Scheme 5 Possible mechanism
sulfonyl chlorides in a radical chain transfer mechanism.
Finally, deprotonation and carbocyclization of the unsta-
ble intermediate B takes place to furnish the desired 1H-
indenes. The presence of base facilitates the reaction by
removing HCl formed in situ from the reaction (Table 1,
entries 11 and 13).
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.SnuIpofoiprmntgirStanoIuifpog
r
t
iornat
References
(1) For reviews, see: (a) Zeitler, K. Angew. Chem. Int. Ed. 2009,
48, 9785. (b) Yoon, T. P.; Ischay, M. A.; Du, J. Nature
© Georg Thieme Verlag Stuttgart · New York
Synlett 2012, 23, 2707–2713

2712
J.-D. Xia et al.
LETTER
Chem. 2010, 2, 527. (c) Narayanam, J. M. R.; Stephenson,
C. R. J. Chem. Soc. Rev. 2011, 40, 102. (d) Teplý, F. Collect.
Czech. Chem. Commun. 2011, 76, 859. (e) Tucker, J. W.;
Stephenson, C. R. J. J. Org. Chem. 2012, 77, 1617.
S.; Li, Z.; Jian, X.; He, C. Angew. Chem. Int. Ed. 2009, 48,
3999. (c) Tobisu, M.; Nakai, H.; Chatani, N. J. Org. Chem.
2009, 74, 5471. (d) For Ru, see: Datta, S.; Odedra, A.; Liu,
R.-S. J. Am. Chem. Soc. 2005, 127, 11606. (e) Odedra, A.;
Datta, S.; Liu, R.-S. J. Org. Chem. 2007, 72, 3289. (f) For
Rh, see: Shikanai, D.; Murase, H.; Hata, T.; Urabe, H. J. Am.
Chem. Soc. 2009, 131, 3166. (g) For Pd, see: Zhao, S.-C.;
Shu, X.-Z.; Ji, K.-G.; Zhou, A.-X.; He, T.; Liu, X.-Y.; Liang,
Y.-M. J. Org. Chem. 2011, 76, 1941. (h) For Cu, see: Zeng,
X.; Ilies, L.; Nakamura, E. J. Am. Chem. Soc. 2011, 133,
17638. (i) For Au, see: Bhunia, S.; Ghorpade, S.; Huple, D.
B.; Liu, R.-S. Angew. Chem. Int. Ed. 2012, 51, 2939.
(7) For representative reviews and papers on the use of
arylsulfonyl chlorides as aryl group resources, see:
(2) For papers on C(sp3)–H functionalization using visible-light
photoredox catalysis via a reductive quenching cycle, see:
(a) Condie, A. G.; González-Gómez, J.; Stephenson, C. R. J.
J. Am. Chem. Soc. 2010, 132, 1464. (b) Freeman, D. B.;
Furst, L.; Condie, A. G.; Stephenson, C. R. J. Org. Lett.
2012, 14, 94. (c) Zou, Y.-Q.; Lu, L.-Q.; Fu, L.; Chang, N.-J.;
Rong, J.; Chen, J.-R.; Xiao, W.-J. Angew. Chem. Int. Ed.
2011, 50, 7171. (d) Xuan, J.; Cheng, Y.; An, J.; Lu, L.-Q.;
Zhang, X.-X.; Xiao, W.-J. Chem. Commun. 2011, 47, 8337.
(e) Xie, Z.; Wang, C.; de Krafft, K. E.; Lin, W. J. Am. Chem.
Soc. 2011, 133, 2056. (f) Zhu, M.; Zheng, N. Synthesis 2011,
2223. (g) Rueping, M.; Leonori, D.; Poisson, T. Chem.
Commun. 2011, 47, 9615. (h) Hari, D. P.; König, B. Org.
Lett. 2011, 13, 3852. (i) Rueping, M.; Zhu, S.; Koenigs, R.
M. Chem. Commun. 2011, 47, 8679. (j) Rueping, M.; Zoller,
J.; Fabry, D. C.; Poscharny, K.; Koenigs, R. M.; Weirich, T.
E. Chem.–Eur. J. 2012, 18, 3478. (k) Miyake, Y.; Nakajima,
K.; Nishibayashi, Y. J. Am. Chem. Soc. 2012, 134, 3338.
(3) For papers on C(sp3)–H functionalization using visible light
photoredox catalysis via an oxidative quenching cycle, see:
(a) For p-methoxybenzyl (PMB) ethers, see: Tucker, J. W.;
Narayanam, J. M. R.; Shah, P. S.; Stephenson, C. R. J. Chem.
Commun. 2011, 47, 5040. (b) For dialkylamides, see: Dai,
C.; Meschini, F.; Narayanam, J. M. R.; Stephenson, C. R. J.
J. Org. Chem. 2012, 77, 4425.
(a) Morrison, R. T.; Boyd, R. N. Organic Chemistry, 5th ed.;
Allyn and Bacon: Boston, 1987. (b) Dubbaka, S. R.; Vogel,
P. Angew. Chem. Int. Ed. 2005, 44, 7674. (c) Kasahara, A.;
Izumi, T.; Kudou, N.; Azami, H.; Yamamoto, S. Chem. Ind.
(London) 1988, 51. (d) Miura, M.; Hashimoto, H.; Itoh, K.;
Nomura, M. Tetrahedron Lett. 1989, 30, 975. (e) Dubbaka,
S. R.; Vogel, P. J. Am. Chem. Soc. 2003, 125, 15292.
(f) Dubbaka, S. R.; Vogel, P. Tetrahedron Lett. 2006, 47,
3345. (g) Volla, C. M. R.; Vogel, P. Angew. Chem. Int. Ed.
2008, 47, 1305. (h) Volla, C. M. R.; Dubbaka, S. R.; Vogel,
P. Tetrahedron 2009, 65, 504. (i) Chen, J.; Sun, Y.; Liu, B.;
Liu, D.; Cheng, J. Chem. Commun. 2012, 48, 449.
(8) (a) Lopes, L. M. X.; Yoshida, M.; Gottlieb, O. R.
Phytochemistry 1984, 23, 2021. (b) Nagle, D. G.; Zhou, Y.-
D.; Park, P. U.; Paul, V. J.; Rajbhandari, I.; Duncan, C. J. G.;
Pasco, D. S. J. Nat. Prod. 2000, 63, 1431. (c) Sugimoto, H.;
Iimura, Y.; Yamanishi, Y.; Yamatsu, K. J. Med. Chem.
1995, 38, 4821. (d) Dolling, U.-H.; Davis, P.; Grabowski, E.
J. J. J. Am. Chem. Soc. 1984, 106, 446. (e) deSolms, S. J.;
Woltersdorf, O. W. Jr.; Cragoe, E. J. Jr.; Watson, L. S.;
Fanelli, G. M. Jr. J. Med. Chem. 1978, 21, 437. (f) Park, C.
H.; Siomboing, X.; Yous, S.; Gressier, B.; Luyckx, M.;
Chavatte, P. Eur. J. Med. Chem. 2002, 37, 461. (g) Anstead,
G. M.; Wilson, S. R.; Katzenellenbogen, J. A. J. Med. Chem.
1989, 32, 2163. (h) Hajela, K.; Kapil, R. S. Indian J. Chem.,
Sect. B: Org. Chem. Incl. Med. Chem. 1995, 34, 361.
(i) Alcalde, E.; Mesquida, N.; López-Pérez, S.; Frigola, J.;
Mercè, R. J. Med. Chem. 2009, 52, 675. (j) Ito, T.; Tanaka,
T.; Iinuma, M.; Nakaya, K.; Takahashi, Y.; Sawa, R.;
Murata, J.; Darnaedi, D. J. Nat. Prod. 2004, 67, 932.
(9) Typical Experimental Procedure for the Arylative
Cyclization of ortho-Alkyl Arylalkynes with Arylsulfonyl
Chlorides: To a Schlenk tube were added ortho-alkyl
arylalkyne 1 (0.2 mmol), arylsulfonyl chloride 2 (3 equiv),
[Ru(bpy)3Cl2] or [Ir(ppy)3] (3 mol%), Na2CO3 (2.5 equiv),
and anhydrous MeCN (1 mL). The tube was charged with
argon and stirred at 45 °C under irradiation with a 36 W
compact fluorescent light for the indicated time (36 h) until
complete consumption of starting material (reaction
monitored by TLC and GC–MS analysis). When the reaction
was finished, the mixture was diluted in diethyl ether,
filtered through a short crude silica gel column and
(4) For representative papers on other visible light
photocatalysis, see: (a) Pham, P. V.; Nagib, D. A.;
MacMillan, D. W. C. Angew. Chem. Int. Ed. 2011, 50, 6119.
(b) McNally, A.; Prier, C. K.; MacMillan, D. W. C. Science
2011, 334, 1114. (c) Nagib, D. A.; MacMillan, D. W. C.
Nature 2011, 480, 224. (d) Lu, Z.; Shen, M.; Yoon, T. P. J.
Am. Chem. Soc. 2011, 133, 1162. (e) Hurtley, A. E.;
Cismesia, M. A.; Ischay, M. A.; Yoon, T. P. Tetrahedron
2011, 67, 4442. (f) Du, J.; Ruiz Espelt, L.; Guzei, I. A.;
Yoon, T. P. Chem. Sci. 2011, 2, 2115. (g) Lin, S.; Ischay, M.
A.; Fry, C. G.; Yoon, T. P. J. Am. Chem. Soc. 2011, 133,
19350. (h) Zou, Y.-Q.; Chen, J.-R.; Liu, X.-P.; Lu, L.-Q.;
Davis, R. L.; Jørgensen, K. A.; Xiao, W.-J. Angew. Chem.
Int. Ed. 2012, 51, 784. (i) Dai, C.; Narayanam, J. M. R.;
Stephenson, C. R. J. Nat. Chem. 2011, 3, 140. (j) Nguyen, J.
D.; Tucker, J. W.; Konieczynska, M. D.; Stephenson, C. R.
J. J. Am. Chem. Soc. 2011, 133, 3160. (k) Kalyani, D.;
McMurtrey, K. B.; Neufeldt, S. R.; Sanford, M. S. J. Am.
Chem. Soc. 2011, 133, 18566. (l) Maity, S.; Zhu, M.;
Shinabery, R. S.; Zheng, N. Angew. Chem. Int. Ed. 2012, 51,
222.
(5) For selected reviews on C(sp3)–H bond functionalization,
see: (a) Giri, R.; Shi, B.-F.; Engle, K. M.; Maugel, N.; Yu, J.
Q. Chem. Soc. Rev. 2009, 38, 3242. (b) Li, C.-J. Acc. Chem.
Res. 2009, 42, 335. (c) Yoo, W.-J.; Li, C.-J. Top. Curr.
Chem. 2010, 292, 281. (d) Wasa, M.; Engle, K. M.; Yu, J.-
Q. Isr. J. Chem. 2010, 50, 605. (e) Yeung, C. S.; Dong, V.
M. Chem. Rev. 2011, 111, 1215. (f) Newhouse, T.; Baran, P.
S. Angew. Chem. Int. Ed. 2011, 50, 3362. (g) Zhang, S.-Y.;
Zhang, F.-M.; Tu, Y.-Q. Chem. Soc. Rev. 2011, 40, 1937.
(h) Tobisu, M.; Chatani, N. Angew. Chem. Int. Ed. 2006, 45,
1683. (i) Campos, K. R. Chem. Soc. Rev. 2007, 36, 1069.
(j) Jazzar, R.; Hitce, J.; Renaudat, A.; Sofack-Kreutzer, J.;
Baudoin, O. Chem.–Eur. J. 2010, 16, 2654. (k) Li, H.; Li, B.-
J.; Shi, Z.-J. Catal. Sci. Tech. 2011, 1, 191. (l) Ramirez, T.
A.; Zhao, B.; Shi, Y. Chem. Soc. Rev. 2012, 41, 931.
(6) For Pt, see: (a) Bajracharya, G. B.; Pahadi, N. K.; Gridnev,
I. D.; Yamatoto, Y. J. Org. Chem. 2006, 71, 6204. (b) Yang,
concentrated under vacuum. The resulting residue was
purified by silica gel column chromatography (hexane–ethyl
acetate) to afford the desired product.
1,1-Dimethyl-3-(4-nitrophenyl)-2-phenyl-1H-indene (3):
Yield: 55.7 mg (83%); yellow solid; mp 128.7–129.5 °C
(uncorrected); 1H NMR (500 MHz, CDCl3): δ = 8.12 (d,
J = 8.5 Hz, 2 H), 7.47–7.43 (m, 3 H), 7.32–7.29 (m, 6 H),
7.13–7.11 (m, 2 H), 1.42 (s, 6 H); 13C NMR (125 MHz,
CDCl3): δ = 156.0, 153.0, 146.6, 142.3, 141.4, 136.1, 135.7,
130.2, 129.5, 128.3, 127.5, 126.8, 126.0, 123.4, 121.9,
120.2, 51.9, 24.3; MS (EI, 70 eV): m/z (%) = 341 (100) [M]+,
Synlett 2012, 23, 2707–2713
© Georg Thieme Verlag Stuttgart · New York

LETTER
326 (46), 279 (15), 132 (8); HRMS (EI): m/z [M]+ calcd for
Visible Light Photoredox Catalysts
2713
Eds.; John Wiley & Sons: Chichester, 1997. (d) Okuyama,
T. Acc. Chem. Res. 2002, 35, 12. (e) Okuyama, T.; Lodder,
G. In Advances in Physical Organic Chemistry; Tidwell, T.
T.; Richard, J. P., Eds.; Elsevier: Amsterdam, 2002, 1–56.
C23H19NO2: 341.1415; found: 341.1411.
(10) (a) Masamune, S.; Sakai, M.; Morio, K. Can. J. Chem. 1975,
53, 784. (b) Hanack, M. Acc. Chem. Res. 1976, 9, 364.
(c) Dicoordinated Carbocations; Rappoport, Z.; Stang, P. J.,
© Georg Thieme Verlag Stuttgart · New York
Synlett 2012, 23, 2707–2713

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