Synthesis of Benzofurans via Tandem Rhodium-Catalyzed C(sp3)-H Insertion and Copper-Catalyzed Dehydrogenation

Article abstract of DOI:10.1002/adsc.201500396

A sequentially catalyzed cascade approach for the synthesis of benzofuran derivatives (up to 88% yield) from 1-sulfonyl-1,2,3-triazoles has been developed. The cascade reaction involves sequential rhodium-catalyzed C(sp³)-H insertion and copper-catalyzed aerobic oxidation. The method was made more convenient towards the synthesis of benzofurans starting from terminal alkynes via a one-pot sequential copper-catalyzed alkyne-azide cycloaddition (CuAAC)/C-H insertion/dehydrogenation cascade reaction. Moreover, the utility of the cascade approach was demonstrated in the synthesis of the indole framework.

Full text of DOI:10.1002/adsc.201500396

FULL PAPERS
DOI: 10.1002/adsc.201500396
Synthesis of Benzofurans via Tandem Rhodium-Catalyzed
3
À
C(sp ) H Insertion and Copper-Catalyzed Dehydrogenation
Lin Li,+a Xiao-Han Xia,+a Yong Wang,a Pranjal P. Bora,a and Qiang Kanga,*
a
Key Laboratory of Coal to Ethylene Glycol and Its Related Technology, Fujian Institute of Research on the Structure of
Matter, Chinese Academy of Sciences, 155 Yangqiao Road West, Fuzhou 350002, Peopleꢀs Republic of China
Fax: (+86)-591-6317-3548; phone: (+86)-591-6317-3548; e-mail: kangq@fjirsm.ac.cn
+
These authors contributed equally to this work.
Received: April 22, 2015; Revised: May 14, 2015; Published online: June 10, 2015
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201500396.
Abstract: A sequentially catalyzed cascade approach quential copper-catalyzed alkyne-azide cycloaddition
À
for the synthesis of benzofuran derivatives (up to (CuAAC)/C H insertion/dehydrogenation cascade
88% yield) from 1-sulfonyl-1,2,3-triazoles has been reaction. Moreover, the utility of the cascade ap-
developed. The cascade reaction involves sequential proach was demonstrated in the synthesis of the
3
À
rhodium-catalyzed C(sp ) H insertion and copper- indole framework.
catalyzed aerobic oxidation. The method was made
more convenient towards the synthesis of benzofur- Keywords: benzofurans; C H insertion; dehydrogen-
ans starting from terminal alkynes via a one-pot se- ation; rhodium catalysis
À
Introduction
Benzofuran is a privileged structural motif found in
a number of natural products, biologically active mol-
Direct and selective functionalization of C H bond is ecules and pharmaceuticals.[10] Therefore, the develop-
of great importance in organic synthesis and the tran- ment of an efficient and mild approach towards ben-
À
sition metal-catalyzed insertion of carbenes into C H zofuran derivatives is highly desirable.[11] In this paper
À
bonds plays a crucial role in this context.[1] Early we present an efficient approach towards benzofuran
work in this area focused on the transition metal-cata- derivatives from the transition metal-catalyzed
3
À
lyzed generation of metal carbenoids from diazo com- tandem intramolecular C(sp ) H insertion of azavinyl
À
pounds and their insertion into various C H bonds in- carbenes, derived from 1-sulfonyl-1,2,3-triazoles and
3
[2]
À
cluding C(sp ) H bonds. Recently, N-sulfonyl-1,2,3- aerobic
oxidation
via
sequential
catalysis
triazoles have emerged as a convenient and stable (Scheme 1).[12]
precursor of rhodium(II) azavinyl carbenes for a varie-
ty of synthetically useful transformations[3] such as X
À
H (X=C, N, O) functionalization,[4] transannulation
reactions to generate heterocycles,[5] cyclopropana-
tion,[6] ring expansion,[7] or ylide formation with subse-
quent rearrangement.[8] However, the insertion of
a
metal-bound imino carbene intermediate into
3
À
a C(sp ) H bond is quite limited. The Fokin group
demonstrated a highly enantioselective insertion of
3
À
azavinyl carbenes into the C(sp ) H bond catalyzed
by chiral Rh(II) carboxylates.[4a] Very recently, Wang
and Chen reported a one-pot synthesis of 2,3-substi-
tuted benzofurans via a rhodium-catalyzed intramo-
À
lecular C H insertion reaction and subsequent palla-
dium-catalyzed dehydrogenation.[9]
Scheme 1. Construction of benzofuran derivatives from N-
sulfonyl-1,2,3-triazoles via Rh/Cu sequential catalysis.
Adv. Synth. Catal. 2015, 357, 2089 – 2097
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2089

FULL PAPERS
Lin Li et al.
Results and Discussion
be inferior as compared to the Rh2(Oct)4-CuTC com-
bination (entries 6 and 7, Table 1). As expected, the
To start with, we chose N-Ts-1,2,3-triazole 1a as reaction did not proceed in the absence of Rh2(Oct)4
model substrate to facilitate the formation of the (entry 9, Table 1), while only 11% of 2a could be iso-
À
metal-bound imino carbene and intramolecular C H lated without CuTC, (entry 8, Table 1). Moreover, the
insertion. The N-Ts-1,2,3-triazole 1a on treatment product could be achieved in a moderate yield, when
with 1 mol% of Rh2(TFA)4 and 10 mol% of copper(I) the reaction was carried out under air (entry 10,
thiophene-2-carboxylate (CuTC) in the presence of Table 1). Various solvents were then screened to fur-
4Š MS in toluene at 1008C under an O2 atmosphere, ther optimize the reaction conditions (entries 11–17,
À
underwent the C H insertion/dehydrogenation reac- Table 1). Among the tested solvents, toluene was the
tion to afford the desired product 2a in 14% isolated optimal one. Investigations on the effect of substrate
yield (entry 1, Table 1). Inspired by this promising concentration revealed that a higher concentration of
result, several rhodium catalysts with different car- 1a (0.15M, entry 18, Table 1) decreased the yield of
boxylates were tested under the same reaction condi- the desired product 2a. It should be noted that an a-
tions (entries 2–5, Table 1). Among the Rh catalysts amino ketone was the major by-product which was
tested, Rh2(Oct)4 displayed an optimal catalytic activi-
À
ty towards C H insertion and afforded the corre-
sponding product 2a in 88% yield (entry 5, Table 1).
The catalytic combinations of Rh2(Oct)4 with other
copper catalysts such as CuCl2 and CuBr2 were also
tested for the pilot reaction, but they were found to
Table 2. Substrate scope with different R1 groups.[a]
Table 1. Optimization of the reaction conditions.[a]
Entry Rh2L4
(1 mol%)
[Cu]
(10 mol%)
Solvent
Yield
[%][b]
1
2
3
4
Rh2(TFA)4
Rh2(OAc)4
Rh2(esp)4
Rh2(pfb)4
Rh2(Oct)4
Rh2(Oct)4
Rh2(Oct)4
Rh2(Oct)4
–
CuTC
CuTC
CuTC
CuTC
CuTC
CuCl2
CuBr2
–
CuTC
CuTC
CuTC
CuTC
CuTC
CuTC
CuTC
CuTC
CuTC
CuTC
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
xylene
PhCF3
PhCl
14
<5
71
N.R.
88
67
43
11
N.R.
55
58
5
6[c]
7[c]
8[c]
9[c]
10[d] Rh2(Oct)4
11
12
13
14
Rh2(Oct)4
Rh2(Oct)4
Rh2(Oct)4
Rh2(Oct)4
31
58
59
43
ODCB
CHCl3
DCE
cyclohexane 35
toluene 61
15[e] Rh2(Oct)4
16[e] Rh2(Oct)4
17[e] Rh2(Oct)4
39
18[f]
Rh2(Oct)4
[a]
Triazole 1a (0.30 mmol, 1.0 equiv.), Rh2Ln (0.0030 mmol,
0.01 equiv.) and copper catalyst (0.03 mmol, 0.1 equiv.)
were combined in solvent (6.0 mL) with under an oxygen
[a]
balloon at 1008C for 2 h.
Isolated yields.
12 h.
Triazole
1 (0.3 mmol, 1.0 equiv.), CuTC (0.03 mmol,
[b]
[c]
[d]
[e]
[f]
0.1 equiv.), Rh2(Oct)4 (0.003 mmol, 0.01 equiv.) and 4Š
MS were combined in toluene (6.0 mL) under an oxygen
balloon.
Triazoles were consumed, but only a mixture with non-
identifiable products could be obtained.
Air balloon.
808C.
Concentration of 1a is 0.15M.
[b]
2090
asc.wiley-vch.de
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2015, 357, 2089 – 2097

3
À
FULL PAPERS
Synthesis of Benzofurans via Tandem Rhodium-Catalyzed C(sp ) H Insertion
Table 3. Substrate scope using different R2 groups.[a]
generated from the reaction of 1a with H2O[4a] in the
absence of 4Š MS as additive.
With the optimized reaction conditions in hand
[1 mol% of Rh2(Oct)4 and 10 mol% of CuTC as cata-
lysts, 4Š MS as additive, toluene at 1008C under an
oxygen atmosphere for 2 h], we then investigated the
substrate scope of the method (Table 2). We were
pleased to see that a wide range of substrates could
be tolerated under these reaction conditions to afford
the desired benzofuran derivatives in moderate to
good yields. Triazoles 1b, 1c and 1d with methyl
group on different position of the phenyl ring were
converted to the corresponding products 2b, 2c and
2d with 60–84% yields. The intramolecular cascade
reaction of the substrate bearing a 4-OMe group on
the phenyl moiety went smoothly to afford product 2e
in moderate yield (49%). Likewise, substrates with
electron-withdrawing substituents on different posi-
tions of the phenyl ring were also converted to the de-
sired products in moderate to good yields (2f–2k,
Table 2). Substrates with sensitive functional groups
such as ester and nitrile were also tolerated under the
optimal reaction conditions, affording the correspond-
ing products in 74% and 51% yield, respectively (2l
and 2m, Table 2). Interestingly, the cascade reaction
of the alkyl-substituted substrates also proceed
smoothly under these reaction conditions to give the
corresponding products 2o and 2p in 64% and 27%
yield, respectively. However, the desired products 2q
(R1 =H) and 2r (R1 =CH=CH2) could not be ob-
tained from the corresponding starting triazoles.
[a]
Triazole
1 (0.3 mmol, 1.0 equiv.), CuTC (0.03 mmol,
0.1 equiv.), Rh2(Oct)4 (0.003 mmol, 0.01 equiv.) and 4Š
MS were combined in toluene (6.0 mL) under an oxygen
balloon.
(Scheme 2), so demonstrating efficiency of the se-
À
In order to demonstrate the generality of this pro- quential CuAAC/Rh-catalyzed C H insertion/Cu-cat-
tocol further, reactions of some representative benzy- alyzed dehydrogenation cascade reactions.
loxytriazole substrates with different substituents (R2)
Indole is a ubiquitous heterocyclic motif present in
on the aryl ring were also performed (Table 3). Irre- a wide range of natural products and biologically
spective of the electronic nature of the substituents active compounds. In a bid to explore the synthetic
on the aryl ring (R2), all the tested triazoles gave the utility of our protocol we have demonstrated the syn-
corresponding benzofuran derivatives with moderate thesis of the 2,3-substituted indole derivative 7
to good yields. It is important to note that substrates (Scheme 3). The CuTC-catalyzed azide-alkyne cyclo-
with either an ester or an ether group could also be addition (CuAAC) of teminal alkyne 5 and TsN3 re-
tolerated in our reaction conditions to afford the de- sulted the corresponding triazole 6, which on treat-
sired product in moderate yields (2v and 2x, Table 3). ment with 1 mol% of Rh2(Oct)4 and 10 mol% of
As N-sulfonyl-1,2,3-triazoles can be achieved easily CuTC in the presence of 4Š MS in toluene at 1008C
from the CuTC-catalyzed azide-alkyne cycloaddition under O2 atmosphere underwent the intramolecular
À
of terminal alkynes with sulfonyl azide, we envisioned C H insertion/dehydrogenation cascade reaction to
that the benzofuran derivatives could be synthesized furnish the desired 2,3-substituted indole 7 in 30%
starting from terminal alkynes in one-pot via Cu/Rh/ yield.
Cu sequential catalysis. For that purpose, we carried
out the reaction of terminal alkyne 3 with tosyl azide
4 in the presence of CuTC (10 mol%), Rh2(Oct)4
(1.0 mol%), 4Š MS in toluene at room temperature.
The terminal alkyne 3 completely was converted to
N-sulfonyl-1,2,3-triazole 1a within 2 h. The reaction
mixture was then heated to 1008C and stirred under
an oxygen atmosphere for additional 2 h. To our de-
light, the reaction proceed smoothly to give the de-
sired benzofuran derivative 2a in 71% yield from terminal alkyne 3 via sequential Cu/Rh/Cu catalysis.
Scheme 2. One-pot synthesis of benzofuran derivative 2a
Adv. Synth. Catal. 2015, 357, 2089 – 2097
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
2091

FULL PAPERS
Lin Li et al.
synthesis of benzofuran starting from terminal alkyne
À
has been also realized via CuAAC/Rh-catalyzed C H
insertion/Cu-catalyzed dehydrogenation cascade reac-
tions. Furthermore, the reaction protocol has also
been explored towards the synthesis of indole deriva-
tives.
Experimental Section
Scheme 3. One-pot synthesis of indole derivative 7 from ter-
minal alkyne 5 via sequential Cu/Rh/Cu catalysis.
General Information
All reactions were performed under nitrogen using oven-
dried glassware and standard Schlenk techniques. DCM,
DCE and CHCl3 were freshly distilled over calcium hydride
under nitrogen. Toluene was distilled from sodium under ni-
trogen and stored under nitrogen. Other solvents were used
without further purification. Other substrates were obtained
from commercial suppliers and used without further purifi-
cation. The progress of the reactions was monitored by thin-
layer chromatography. Flash column chromatography was
carried out using silica gel 300–400 mesh. All other reagents
were purchased from TCI, Sigma–Aldrich, Alfa Aesar,
Acros, Frontier and Sino compound and used without fur-
ther purification. Rh(II) acetate (Strem Chemicals), Rh(II)
octanoate (Adamas), Rh2(esp)4 (Aldrich), Rh2(TFA)4
(Strem Chemicals), and Rh2(pfb)4 (Aldrich), CuTC (Matrix)
À
A plausible mechanism for the Rh-catalyzed C H
insertion/Cu-catalyzed dehydrogenation process is
presented in Scheme 4. As reported earlier, an equi-
librium is established between the N-sulfonyl-1,2,3-tri-
azole 1 and the imino diazo species I via a reversible
ring-chain tautomerization.[13] Imino diazo species I
then reacts with rhodium(II) with the release of mo-
lecular nitrogen to give imino rhodium carbenoid II
and subsequent intramolecular insertion of the carbe-
noid into the C(sp ) H bond leads to the formation
3
À
of a-imino dihydrobenzofuran III, regenerating the
rhodium(II) catalyst. The a-imino dihydrobenzofuran
III then undergoes imine-enamine tautomerization to
the Z-selective enamine IV, which on CuTC-catalyzed
dehydrogenation furnishes the desired product 2. To
support our proposed mechanism, we have isolated
the intermediate enamine IV-2b from the Rh2(Oct)4
(1 mol%)-catalyzed reaction of triazole 1b which on
treatment with 10 mol% of CuTC under an oxygen
atmosphere in toluene at 1008C delivered the desired
product 2b in 66% yield.
were used as received from the commercial sources. Rh2(S-
[15]
PTTL)4,[14] Rh2(S-NTTL)4
were prepared via literature
procedures. The 1H NMR and 13C NMR spectra were ob-
tained in CDCl3 using a Bruker AVANCE III spectrometer
at 400 and 100 MHz, respectively. Chemical shifts are re-
ported in units of parts per million (ppm) downfield from
tetramethylsilane (TMS), and all coupling constants are re-
ported in hertz. Peak multiplicity is indicated as follows:
br=broad, s=singlet, d=doublet, t=triplet, m=multiplet.
The infrared spectra were recorded on a VERTEX70 infra-
red spectrometer as KBr pellets with absorption in cmÀ1.
HR-MS were obtained on a Thermo Fisher Scientific LTQ
FT Ultra.
Conclusions
In conclusion, we have developed a novel cascade ap-
proach towards the synthesis of benzofuran deriva-
tives from a-imino rhodium carbenoids generated in
Preparation of Triazole Compounds
N-Sulfonyl-1,2,3-triazoles were prepared according to
a modified version of the literature procedure.[16] A Schlenk
vial was charged with copper(I) thiophene-2-carboxylate
(CuTC, 0.011 g, 0.06 mmol, 0.1 equiv. with respect to
situ from N-sulfonyl-1,2,3-triazoles through a sequen-
3
À
tial C(sp ) H insertion/aerobic oxidation. A one-pot
Scheme 4. Proposed mechanism for the formation of benzofurans.
2092
asc.wiley-vch.de
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2015, 357, 2089 – 2097

3
À
FULL PAPERS
Synthesis of Benzofurans via Tandem Rhodium-Catalyzed C(sp ) H Insertion
alkyne) and toluene (3 mL). Subsequently, the alkyne
(0.6 mmol, 1 equiv.) and sulfonyl azide (0.6 mmol, 1 equiv.)
were added and the mixture was stirred at room tempera-
ture until the reaction was complete (as judged by TLC and
LC/MS analysis). The reaction mixture was then diluted
with saturated aqueous NH4Cl solution (5 mL) and extract-
ed into EtOAc (2”5 mL). The combined organics were
dried (Na2SO4), filtered through celite and concentrated
under vacuum. The resulting solid was pulverized in cold cy-
clohexane and collected by filtration to afford the desired
product.
4-Methyl-N-{[2-(o-tolyl)benzofuran-3-yl]methylene}ben-
zenesulfonamide (2c): white solid; yield: 92 mg (0.237 mmol,
79%); mp 117–1188C; H NMR (400 MHz, CDCl3): d=9.01
1
(s, 1H), 8.29 (d, J=7.1 Hz, 1H), 7.90 (d, J=7.5 Hz, 2H),
7.47 (d, J=7.6 Hz, 1H), 7.42 (t, J=7.2 Hz, 1H), 7.37–7.24
(m, 7H), 2.43 (s, 3H), 2.41 (s, 3H); 13C NMR (100 MHz,
CDCl3): d=162.65, 153.71, 143.22, 137.44, 134.88, 130.59,
130.37, 130.32, 128.72, 126.81, 126.15, 125.28, 125.23, 123.83,
123.43, 122.39, 113.68, 110.25, 20.61, 19.36; IR (KBr plate):
nmax =3059, 2923, 1717, 1699, 1684, 1653, 1585, 1541, 1508,
1448, 1321, 1259, 1202, 1159, 1089, 1075, 1019, 919, 849, 804,
774, 763, 748, 669, 626, 548 cmÀ1; HR-MS (MALDI-DHB):
m/z=390.1150, calcd. C23H20NO3S (M+H)+: 390.1158.
4-Methyl-N-{[2-(m-tolyl)benzofuran-3-yl]methylene}ben-
zenesulfonamide (2d)): white solid; yield: 70 mg (0.18 mmol,
Preparation of Benzofuran and Indole Derivatives
Triazole derivative 1 (0.3 mmol), 4ŠMS (20 mg), CuTC
(0.03 mmol, 0.1 equiv.) and Rh2(Oct)4 (0.003 mmol,
0.01 equiv.) were added to an oven-dried Schlenk tube
equipped with a stir bar. The reaction vessel was evacuated
and backfilled with O2 three times before adding freshly dis-
tilled toluene (6.0 mL, 0.05M). The reaction mixture was
stirred under an O2 (balloon) atmosphere at 1008C (checked
by TLC). The residue was purified by flash column chroma-
tography with ethyl acetate and petroleum ether as eluents
to afford 2.
1
60%); mp 146–1498C; H NMR (400 MHz, CDCl3): d=9.34
(s, 1H), 8.29 (d, J=7.3 Hz, 1H), 7.92 (d, J=8.2 Hz, 2H),
7.60–7.54 (m, 3H), 7.47 (t, J=7.6 Hz, 1H), 7.42–7.32 (m,
5H), 2.48 (s, 3H), 2.43 (s, 3H); 13C NMR (100 MHz,
CDCl3): d=166.84, 163.64, 154.45, 144.26, 139.34, 135.89,
132.35, 129.79, 129.58, 129.31, 128.18, 127.89, 126.46, 126.38,
125.21, 124.88, 123.65, 113.13, 111.19, 21.66, 21.51; IR (KBr
plate): nmax =2921, 1595, 1578, 1447, 1397, 1359, 1330, 1259,
1213, 1183, 1159, 1111, 1082, 1015, 936, 874, 827, 800, 775,
764, 710, 688, 676, 666, 626, 593, 567, 546 cmÀ1; HR-MS
(MALDI-DHB): m/z=390.1149, calcd. C23H20NO3S (M+
H)+: 390.1158.
N-{[2-(4-Methoxyphenyl)benzofuran-3-yl]methylene}-4-
methylbenzenesulfonamide (2e): white solid; yield: 60 mg
(0.147 mmol, 49%); mp 181–1848C; 1H NMR (400 MHz,
CDCl3): d=9.35 (s, 1H), 8.26 (d, J=7.2 Hz, 1H), 7.92 (d,
J=8.0 Hz, 2H), 7.75 (d, J=8.5 Hz, 2H), 7.52 (d, J=7.8 Hz,
1H), 7.41–7.30 (m, 4H), 7.09 (d, J=8.6 Hz, 2H), 3.92 (s,
3H), 2.43 (s, 3H); 13C NMR (100 MHz, CDCl3): d=166.89,
163.64, 162.38, 154.27, 144.14, 136.15, 130.79, 129.75, 127.80,
126.12, 125.37, 124.80, 123.49, 120.67, 115.00, 112.20, 111.05,
55.61, 21.65; IR (KBr plate): nmax =3288, 3059, 2871, 2097,
1623, 1589, 1558, 1507, 1472, 1451, 1434, 1333, 1274, 1252,
1217, 1147, 1082, 1073, 1040, 1018, 802, 750, 731, 698, 671,
610 cmÀ1; HR-MS (MALDI-DHB): m/z=406.1098, calcd.
C23H20NO4S (M+H)+: 406.1108.
N-{[2-(3-Fluorophenyl)benzofuran-3-yl]methylene}-4-
methylbenzenesulfonamide (2f): white solid; yield: 61 mg
(0.153 mmol, 51%); mp 156–1638C; 1H NMR (400 MHz,
CDCl3): d=9.32 (s, 1H), 8.28 (d, J=7.6 Hz, 1H), 7.93 (d,
J=8.0 Hz, 2H), 7.59–7.51 (m, 3H), 7.48 (d, J=9.2 Hz, 1H),
7.41 (t, J=7.6 Hz, 1H), 7.38–7.32 (m, 3H), 7.28 (d, J=
8.5 Hz, 1H), 2.43 (s, 3H); 13C NMR (100 MHz, CDCl3): d=
164.34, 164.32, 164.19, 162.85, 161.71, 154.47, 144.52, 135.53,
131.27, 131.19, 130.18, 130.10, 129.87, 127.97, 126.81, 125.10,
125.02, 124.99, 124.96, 123.75, 118.59, 118.38, 115.92, 115.69,
113.74, 111.31, 21.67; 19F NMR (376 MHz, CDCl3): d=
À110.36; IR (KBr plate): nmax =2921, 1595, 1572, 1479, 1454,
1359, 1321, 1303, 1292, 1221, 1188, 1155, 1109, 1087, 1016,
944, 884, 826, 777, 748, 706, 671, 628, 566, 545 cmÀ1; HR-MS
(MALDI-DHB): m/z=394.0899, calcd. C22H17FNO3S (M+
H)+: 394.0908.
Preparation of Intermediate IV-2b
To a solution of triazole 1b (0.3 mmol) in toluene at 238C
was added Rh2(Oct)4 (0.003 mmol, 0.01 equiv.) under an N2
atmosphere. The resulting mixture was stirring at 908C for
3 h before it was quenched with NH4Cl (2 mL, saturated
aqueous solution). The layers were separated and the aque-
ous layer was extracted with EtOAc (3”5 mL). The com-
bined organic layers were washed with brine (10 mL), dried
(Na2SO4) and concentrated under vacuum. The residue was
purified by flash column chromatography with ethyl acetate
and petroleum ether as eluents to afford IV-2b.
4-Methyl-N-[(2-phenylbenzofuran-3-yl)methylene]ben-
zenesulfonamide (2a): white solid; yield: 99 mg
(0.264 mmol, 88%); mp 165–1678C; 1H NMR (400 MHz,
CDCl3): d=9.39 (s, 1H), 8.32 (d, J=7.5 Hz, 1H), 7.98 (d,
J=8.1 Hz, 2H), 7.82 (d, J=9.1 Hz, 2H), 7.62–7.57 (m, 4H),
7.43–7.36 (m, 4H), 2.46 (s, 3H); 13C NMR (100 MHz,
CDCl3): d=166.48, 163.52, 154.50, 144.28, 135.92, 131.48,
129.78, 129.41, 129.14, 128.27, 127.88, 126.45, 125.19, 124.92,
123.66, 113.22, 111.22, 21.63; IR (KBr plate): nmax =1594,
1569, 1317, 1306, 1154, 1088, 783, 738, 669, 543 cmÀ1; HR-
MS (MALDI-DHB): m/z=376.0994, calcd. for C22H18NO3S
(M+H)+: 376.1002.
4-Methyl-N-{[2-(p-tolyl)benzofuran-3-yl]methylene}ben-
zenesulfonamide (2b): white solid; yield: 98 mg
(0.252 mmol, 83%); mp 158–1638C; 1H NMR (400 MHz,
CDCl3): d=9.36 (s, 1H), 8.29–8.26 (m, 1H), 7.92 (d, J=
8.3 Hz, 2H), 7.68 (d, J=8.1 Hz, 2H), 7.54 (d, J=7.7 Hz,
1H), 7.41–7.32 (m, 6H), 2.48 (s, 3H), 2.43 (s, 3H); 13C NMR
(100 MHz, CDCl3): d=166.96, 163.68, 154.40, 144.20, 142.25,
136.04, 130.16, 129.76, 129.07, 127.84, 126.27, 125.45, 125.27,
124.84, 123.59, 112.80, 111.15, 21.65; IR (KBr plate): nmax
=
N-{[2-(3-Chlorophenyl)benzofuran-3-yl]methylene}-4-
methylbenzenesulfonamide (2g): light green solid; yield:
83 mg (0.201 mmol, 67%); mp 145–1518C; 1H NMR
(400 MHz, CDCl3): d=9.29 (s, 1H), 8.28 (d, J=7.5 Hz, 1H),
7.93 (d, J=8.2 Hz, 2H), 7.76 (s, 1H), 7.63 (d, J=7.2 Hz,
3032, 2921, 1581, 1565, 1480, 1452, 1410, 1353, 1318, 1289,
1255, 1198, 1184, 1156, 1198, 1184, 1156, 1110, 1088, 1077,
1017, 916, 848, 818, 794, 777, 749, 670, 645, 610, 551 cmÀ1
;
HR-MS (MALDI-DHB): m/z=390.1149, calcd. for
C23H20NO3S (M+H)+: 390.1158.
Adv. Synth. Catal. 2015, 357, 2089 – 2097
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
2093

FULL PAPERS
Lin Li et al.
1H), 7.56–7.48 (m, 3H), 7.42 (td, J=7.9, 1.2 Hz, 1H), 7.38–
7.33 (m, 3H), 2.43 (s, 3H); 13C NMR (100 MHz, CDCl3):
d=164.19, 162.73, 154.51, 144.52, 135.54, 135.47, 131.41,
130.69, 129.89, 128.75, 127.99, 127.27, 126.83, 125.11, 125.00,
123.74, 113.82, 111.32, 21.69; IR (KBr plate): nmax =2921,
1595, 1580, 1564, 1481, 1454, 1412, 1356, 1319, 1301, 1289,
1200, 1152, 1120, 1076, 1017, 933, 889, 865, 803, 788, 780,
758, 770, 742, 704, 668, 626, 602, 567, 544 cmÀ1; HR-MS
(MALDI-DHB): m/z=410.0602, calcd. C22H17ClNO3S (M+
H)+: 410.0612.
N-{[2-(3-Bromophenyl)benzofuran-3-yl]methylene}-4-
methylbenzenesulfonamide (2h): white solid; yield: 89 mg
(0.195 mmol, 65%); mp 160–1638C; 1H NMR (400 MHz,
CDCl3): d=9.29 (s, 1H), 8.27 (d, J=7.5 Hz, 1H), 7.93 (d,
J=7.9 Hz, 3H), 7.67 (t, J=9.2 Hz, 2H), 7.54 (d, J=8.1 Hz,
1H), 7.42 (ddd, J=10.7, 9.6, 4.7 Hz, 2H), 7.36 (dd, J=7.3,
3.9 Hz, 3H), 2.43 (s, 3H); 13C NMR (100 MHz, CDCl3): d=
164.05, 162.71, 154.50, 144.52, 135.46, 134.32, 131.61, 130.88,
130.10, 129.90, 128.00, 127.72, 126.85, 125.12, 124.98, 123.74,
123.48, 113.83, 111.32, 21.70; IR (KBr plate): nmax =2974,
1598, 1584, 1559, 1541, 1446, 1359, 1329, 1195, 1159, 1080,
1049, 924, 856, 798, 785, 763, 670, 624, 565, 546 cmÀ1; HR-
MS (MALDI-DHB): m/z=454.0104, calcd. C22H17BrNO3S
(M+H)+: 454.0107.
N-{[2-(4-Fluorophenyl)benzofuran-3-yl]methylene}-4-
methylbenzenesulfonamide (2i): white solid; yield: 77 mg
(0.195 mmol, 65%); mp 197–2098C; 1H NMR (400 MHz,
CDCl3): d=9.32 (s, 1H), 8.28 (d, J=7.8 Hz, 1H), 7.92 (d,
J=8.2 Hz, 2H), 7.80 (dd, J=8.7, 5.2 Hz, 2H), 7.55 (d, J=
8.0 Hz, 1H), 7.41 (td, J=7.2, 1.2 Hz, 1H), 7.39–7.33 (m,
3H), 7.29 (t, J=8.5 Hz, 2H), 2.44 (s, 3H); 13C NMR
(100 MHz, CDCl3): d=165.91, 165.26, 163.38, 163.09, 154.40,
144.39, 135.80, 131.29, 131.20, 129.82, 127.89, 126.55, 125.10,
125.02, 124.55, 124.52, 123.63, 116.94, 116.72, 113.11, 111.21,
21.66; 19F NMR (376 MHz, CDCl3): d=À106.86; IR (KBr
plate): nmax =1596, 1578, 1499, 1481, 1452, 1412, 1351, 1322,
1306, 1233, 1197, 1159, 1092, 1077, 1014, 917, 853, 836, 809,
779, 747, 706, 693, 671, 641, 608, 595, 551, 534 cmÀ1; HR-MS
(MALDI-DHB): m/z=394.0900, calcd. C22H17FNO3S (M+
H)+: 394.0908.
154.64, 144.51, 135.51, 132.40, 132.16, 130.46, 129.85, 128.95,
127.97, 126.93, 125.14, 125.04, 123.82, 114.23, 111.34, 52.59,
21.68; IR (KBr plate): nmax =2947, 1720, 1578, 1565, 1452,
1435, 1411, 1357, 1319, 1279, 1203, 1185, 1158, 1116, 1105,
1088, 1078, 1016, 916, 861, 815, 784, 776, 743, 702, 685, 667,
642, 622, 578, 545 cmÀ1; HR-MS (MALDI-DHB): m/z=
434.1046, calcd. C24H20NO5S (M+H)+: 434.1057.
N-{[2-(4-Cyanophenyl)benzofuran-3-yl]methylene}-4-
methylbenzenesulfonamide (2l): white solid; yield: 61 mg
(0.153 mmol, 51%); mp 219–2258C; 1H NMR (400 MHz,
CDCl3): d=9.36 (s, 1H), 8.30 (d, J=7.6 Hz, 1H), 7.95–7.85
(m, 6H), 7.58 (d, J=8.1 Hz, 1H), 7.46 (t, J=7.5 Hz, 1H),
7.42–7.34 (m, 3H), 2.45 (s, 3H); 13C NMR (100 MHz,
CDCl3): d=162.73, 162.22, 154.73, 144.69, 135.38, 133.04,
132.35, 129.90, 129.40, 127.99, 127.32, 125.36, 124.95, 123.92,
117.86, 114.78, 114.73, 111.43, 21.69; IR (KBr plate): nmax
=
2921, 2859, 1733, 1717, 1699, 1684, 1653, 1594, 1558, 1541,
1507, 1456, 1396, 1324, 1285, 1252, 1196, 1176, 1185, 1149,
1095, 1028, 993, 815, 798, 742, 700, 671, 594, 538 cmÀ1; HR-
MS (MALDI-DHB): m/z=401.0947, calcd. C23H17N2O3S
(M+H)+: 401.0954.
4-Methyl-N-({2-[3-(trifluoromethyl)phenyl]benzofuran-3-
yl}methylene)benzenesulfonamide (2m): white solid; yield:
55 mg (0.123 mmol, 41%); mp 148–1508C; 1H NMR
(400 MHz, CDCl3): d=9.31 (s, 1H), 8.31 (dd, J=7.6, 0.8 Hz,
1H), 8.07 (s, 1H), 7.95 (d, J=8.6 Hz, 1H), 7.92 (d, J=
8.4 Hz, 2H), 7.85 (d, J=7.9 Hz, 1H), 7.74 (t, J=7.8 Hz,
1H), 7.59 (d, J=8.1 Hz, 1H), 7.45 (td, J=7.3, 1.4 Hz, 1H),
7.41–7.34 (m, 3H), 2.44 (s, 3H); 13C NMR (100 MHz,
CDCl3): d=163.85, 162.52, 154.61, 144.58, 135.38, 132.23,
131.92, 130.08, 129.88, 129.14, 128.00, 127.85, 127.82, 126.98,
125.73, 125.69, 125.21, 124.98, 124.86, 123.79, 114.07, 111.37,
21.67; 19F NMR (376 MHz, CDCl3): d=À62.88; IR (KBr
plate): nmax =1598, 1583, 1481, 1454, 1426, 1328, 1304, 1199,
1158, 1122, 1091, 1075, 928, 960, 797, 771, 762, 700, 672, 640,
619, 565, 543 cmÀ1
;
HR-MS (MALDI-DHB): m/z=
444.0866, calcd. C23H17F3NO3S (M+H)+: 444.0876.
4-Methyl-N-{[2-(naphthalen-2-yl)benzofuran-3-yl]methy-
lene}benzenesulfonamide (2n): white solid; yield: 75 mg
(0.177 mmol, 59%); mp 170–1748C; 1H NMR (400 MHz,
CDCl3): d=9.44 (s, 1H), 8.33 (d, J=7.4 Hz, 1H), 8.27 (s,
1H), 8.04 (d, J=8.6 Hz, 1H), 8.02–7.97 (m, 1H), 7.97–7.91
(m, 3H), 7.87 (dd, J=10.2, 1.7 Hz, 1H), 7.67–7.61 (m, 2H),
7.59 (d, J=8.2 Hz, 1H), 7.43 (td, J=7.4, 1.3 Hz, 1H), 7.40–
7.32 (m, 3H), 2.43 (s, 3H); 13C NMR (100 MHz, CDCl3):
d=166.44, 163.58, 154.59, 144.34, 135.77, 134.37, 132.96,
129.94, 129.83, 129.37, 129.02, 128.30, 127.96, 127.37, 126.52,
125.50, 125.29, 124.97, 124.93, 123.69, 113.43, 111.24, 21.66;
IR (KBr plate): nmax =2974, 1595, 1566, 1451, 1362, 1313,
1287, 1187, 1152, 1088, 1071, 953, 916, 877, 858, 818, 760,
N-{[2-(4-Chlorophenyl)benzofuran-3-yl]methylene}-4-
methylbenzenesulfonamide (2j): white solid; yield: 86 mg
(0.21 mmol, 70%); mp 186–1918C; 1H NMR (400 MHz,
CDCl3): d=9.32 (s, 1H), 8.28 (d, J=7.5 Hz, 1H), 7.92 (d,
J=8.3 Hz, 2H), 7.73 (d, J=8.6 Hz, 2H), 7.59–7.53 (m, 3H),
7.42 (td, J=7.4, 1.4 Hz, 1H), 7.39–7.33 (m, 3H), 2.44 (s,
3H); 13C NMR (100 MHz, CDCl3): d=164.90, 162.92,
154.48, 144.42, 137.98, 135.72, 130.22, 129.82, 129.81, 127.91,
126.68, 125.09, 125.06, 123.70, 113.48, 111.25, 21.67; IR (KBr
plate): nmax =2822, 1583, 1479, 1450, 1406, 1354, 1324, 1303,
1291, 1196, 1157, 1092, 1075, 1013, 915, 847, 816, 782, 746,
749, 705, 669, 648, 620, 606, 551, 470 cmÀ1
; HR-MS
727, 706, 689, 670, 636, 620, 583, 545 cmÀ1
;
HR-MS
(MALDI-DHB): m/z=426.1150, calcd. C26H20NO3S (M+
(MALDI-DHB): m/z=410.0605, calcd. C22H17ClNO3S (M+
H)+: 426.1158.
H)+: 410.0612.
N-[(2-Cyclohexylbenzofuran-3-yl)methylene]-4-methyl-
benzenesulfonamide (2o): white solid; yield: 73 mg
(0.192 mmol, 64%); mp 180–1838C; 1H NMR (400 MHz,
CDCl3): d=9.28 (s, 1H), 8.15 (d, J=7.1 Hz, 1H), 7.93 (d,
J=8.0 Hz, 2H), 7.45 (d, J=7.6 Hz, 1H), 7.37–7.27 (m, 4H),
3.22 (t, J=11.8 Hz, 1H), 2.43 (s, 3H), 2.05–1.74 (m, 7H),
1.52–1.23 (m, 3H); 13C NMR (100 MHz, CDCl3): d=175.81,
161.54, 154.32, 144.16, 136.20, 129.73, 127.72, 125.56, 124.57,
124.42, 123.02, 111.86, 110.98, 37.02, 31.41, 25.86, 25.51,
Methyl
4-{3-[(tosylimino)methyl]benzofuran-2-yl}ben-
zoate (2k): white solid; yield: 96 mg (0.222 mmol, 74%); mp
227–2308C; 1H NMR (400 MHz, CDCl3): d=9.38 (s, 1H),
8.32 (d, J=7.7 Hz, 1H), 8.26 (d, J=8.2 Hz, 2H), 7.95 (d, J=
8.1 Hz, 2H), 7.89 (d, J=8.2 Hz, 2H), 7.59 (d, J=8.1 Hz,
1H), 7.46 (t, J=7.5 Hz, 1H), 7.41 (d, J=7.9 Hz, 1H), 7.38
(d, J=11.4, 8.1 Hz, 2H), 4.02 (s, 3H), 2.46 (s, 3H);
13C NMR (100 MHz, CDCl3): d=166.07, 164.45, 162.87,
2094
asc.wiley-vch.de
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2015, 357, 2089 – 2097

3
À
FULL PAPERS
Synthesis of Benzofurans via Tandem Rhodium-Catalyzed C(sp ) H Insertion
21.66; IR (KBr plate): nmax =2930, 2854, 1583, 1481, 1451,
1355, 1317, 1286, 1188, 1154, 1088, 1015, 957, 888, 848, 822,
809, 785, 752, 725, 667, 626, 595, 555, 534 cmÀ1; HR-MS
(MALDI-DHB): m/z=382.1465, calcd. C22H24NO3S (M+
H)+: 382.1471.
Methyl 2-phenyl-3-[(tosylimino)methyl]benzofuran-5-car-
boxylate (2v): white solid; yield: 66 mg (0.153 mmol, 51%);
mp 201–2038C; 1H NMR (400 MHz, CDCl3): d=9.37 (s,
1H), 8.95 (d, J=0.7 Hz, 1H), 8.14 (dd, J=8.6, 1.4 Hz, 1H),
7.96 (d, J=8.1 Hz, 2H), 7.80 (dd, J=7.8, 2.3 Hz, 2H), 7.67–
7.57 (m, 4H), 7.37 (d, J=7.9 Hz, 2H), 3.97 (s, 3H), 2.44 (s,
3H); 13C NMR (100 MHz, CDCl3): d=167.33, 166.78,
162.98, 156.82, 144.49, 135.56, 131.84, 129.85, 129.52, 129.18,
128.24, 127.99, 127.80, 127.24, 125.82, 125.35, 113.23, 111.23,
52.35, 21.69; IR (KBr plate): nmax =3028, 2950, 1726, 1715,
1587, 1574, 1448, 1391, 1321, 1288, 1246, 1184, 1158, 1086,
1064, 985, 926, 865, 812, 768, 744, 681, 647, 624, 612, 584,
550 cmÀ1; HR-MS (MALDI-DHB): m/z=434.1046, calcd.
C24H20NO5S (M+H)+: 434.1057.
4-Methyl-N-[(2-methylbenzofuran-3-yl)methylene]ben-
zenesulfonamide (2p): white solid; yield: 26 mg
(0.081 mmol, 27%); mp 150–1558C; 1H NMR (400 MHz,
CDCl3): d=9.22 (s, 1H), 8.12 (d, J=6.3 Hz, 1H), 7.92 (d,
J=7.8 Hz, 2H), 7.44 (d, J=7.0 Hz, 1H), 7.37–7.26 (m, 4H),
2.74 (s, 3H), 2.43 (s, 3H); 13C NMR (100 MHz, CDCl3): d=
168.12, 161.84, 154.41, 144.22, 136.05, 129.75, 127.79, 125.64,
124.65, 124.47, 122.63, 113.76, 110.88, 21.65, 13.36; IR (KBr
plate): nmax =2924, 1597, 1559, 1481, 1453, 1381, 1355, 1315,
1291, 1256, 1196, 1154, 1089, 1025, 945, 847, 815, 804, 788,
757, 671, 646, 609, 571, 551, 537 cmÀ1; HR-MS (MALDI-
DHB): m/z=314.0841, calcd. C17H16NO3S (M+H)+:
314.0845.
N-[(5-Fluoro-2-phenylbenzofuran-3-yl)methylene]-4-
methylbenzenesulfonamide (2s): light green solid; yield:
102 mg (0.258 mmol, 86%); mp 217–2218C; 1H NMR
(400 MHz, CDCl3): d=9.35 (s, 1H), 7.97–7.90 (m, 3H),
7.80–7.75 (m, 2H), 7.63–7.56 (m, 3H), 7.49 (dd, J=8.9,
4.0 Hz, 1H), 7.36 (d, J=8.1 Hz, 2H), 7.12 (td, J=9.0,
2.6 Hz, 1H), 2.44 (s, 3H); 13C NMR (101 MHz, CDCl3): d=
167.68, 163.10, 161.46, 159.06, 150.62, 144.47, 135.67, 131.74,
129.86, 129.50, 129.10, 127.99, 127.91, 126.33, 126.21, 114.33,
114.07, 113.22, 113.18, 112.14, 112.05, 109.72, 109.45, 21.68;
19F NMR (376 MHz, CDCl3): d=À117.20; IR (KBr plate):
nmax =3067, 2922, 1597, 1568, 1471, 1457, 1445, 1391, 1359,
1319, 1303, 1290, 1266, 1216, 1155, 1136, 1113, 1088, 1064,
955, 874, 814, 781, 770, 742, 681, 663, 632, 613, 593,
554 cmÀ1; HR-MS (MALDI-DHB): m/z=394.0900, calcd.
C22H17FNO3S (M+H)+: 394.0908.
N-[(5-Chloro-2-phenylbenzofuran-3-yl)methylene]-4-
methylbenzenesulfonamide (2t): white solid; yield: 105 mg
(0.255 mmol, 85%); mp >2308C; 1H NMR (400 MHz,
CDCl3): d=9.34 (s, 1H), 8.26 (d, J=1.8 Hz, 1H), 7.92 (d,
J=8.2 Hz, 2H), 7.81- 7.75 (m, 2H), 7.63–7.55 (m, 3H), 7.48
(d, J=8.7 Hz, 1H), 7.39–7.33 (m, 3H), 2.45 (s, 3H);
13C NMR (100 MHz, CDCl3): d=167.34, 163.11, 152.81,
144.53, 135.53, 131.82, 130.65, 129.89, 129.75, 129.52, 129.14,
127.96, 127.85, 126.74, 126.55, 126.50, 123.29, 112.65, 112.28,
21.70; IR (KBr plate): nmax =2974, 1699, 1684, 1653, 1635,
1589, 1561, 1541, 1522, 1507, 1453, 1438, 1359, 1319, 1304,
1289, 1259, 1198, 1153, 1121, 1085, 1054, 929, 859, 812, 778,
698, 679, 655, 627, 611, 551 , cmÀ1; HR-MS (MALDI-DHB):
m/z=410.0603, calcd. C22H17ClNO3S (M+H)+: 410.0612.
N-[(5,7-Dichloro-2-phenylbenzofuran-3-yl)methylene]-4-
methylbenzenesulfonamide (2u): white solid; yield: 85 mg
(0.192 mmol, 64%); mp 199–2038C; 1H NMR (400 MHz,
CDCl3): d=9.33 (s, 1H), 8.16 (d, J=1.8 Hz, 1H), 7.92 (d,
J=8.2 Hz, 2H), 7.83- 7.78 (m, 2H), 7.66–7.58 (m, 3H), 7.41–
7.35 (m, 3H), 2.45 (s, 3H); 13C NMR (100 MHz, CDCl3):
d=167.47, 162.75, 148.96, 144.73, 135.25, 132.16, 130.92,
129.95, 129.61, 129.26, 128.03, 127.60, 127.36, 126.59, 121.83,
117.45, 112.91, 21.72; IR (KBr plate): nmax =3032, 2921,
1581, 1565, 1480, 1452, 1410, 1353, 1318, 1289, 1255, 1198,
1184, 1156, 1110, 1088, 1077, 1017, 916, 848, 819, 794, 777,
749, 670, 645, 610, 598, 551 cmÀ1; HR-MS (MALDI-DHB):
m/z=444.0214, calcd. C22H16Cl2NO3S (M+H)+: 444.0222.
4-Methyl-N-[(5-methyl-2-phenylbenzofuran-3-yl)methy-
lene]benzenesulfonamide (2w): light green solid; yield:
68 mg (0.174 mmol, 58%); mp 187–1918C; 1H NMR
(400 MHz, CDCl3): d=9.33 (s, 1H), 8.08 (s, 1H), 7.92 (d,
J=8.2 Hz, 2H), 7.77 (dd, J=6.3, 2.8 Hz, 2H), 7.61–7.54 (m,
3H), 7.43 (d, J=8.4 Hz, 1H), 7.35 (d, J=8.1 Hz, 2H), 7.21
(d, J=8.4 Hz, 1H), 2.46 (s, 3H), 2.44 (s, 3H); 13C NMR
(100 MHz, CDCl3): d=166.76, 163.85, 152.97, 144.26, 135.86,
134.77, 131.39, 129.80, 129.39, 129.12, 128.38, 127.90, 127.67,
125.13, 123.41, 113.03, 110.72, 21.67, 21.52; IR (KBr plate):
nmax =2920, 1653, 1563, 1472, 1444, 1358, 1321, 1303, 1288,
1198, 1153, 1088, 1072, 945, 867, 843, 809, 781, 681, 663, 629,
613, 595, 552 cmÀ1
;
HR-MS (MALDI-DHB): m/z=
390.1153, calcd. C23H20NO3S (M+H)+: 390.1158.
N-{[5-(2-Methoxyethyl)-2-phenylbenzofuran-3-yl]methy-
lene}-4-methylbenzenesulfonamide (2x): white solid; yield:
87 mg (0.201 mmol, 67%); mp 106–1098C; 1H NMR
(400 MHz, CDCl3): d=9.33 (s, 1H), 8.12 (s, 1H), 7.92 (d,
J=8.2 Hz, 2H), 7.80- 7.73 (m, 2H), 7.63–7.56 (m, 3H), 7.47
(d, J=8.3 Hz, 1H), 7.35 (d, J=7.6 Hz, 2H), 7.30–7.26 (m,
1H), 3.64 (t, J=6.5 Hz, 2H), 3.36 (s, 3H), 3.00 (t, J=6.3 Hz,
2H), 2.44 (s, 3H); 13C NMR (100 MHz, CDCl3): d=166.82,
163.72, 153.39, 144.27, 135.99, 135.86, 131.44, 129.78, 129.40,
129.13, 128.32, 127.90, 127.51, 125.28, 123.37, 113.09, 110.96,
73.78, 58.70, 36.11, 21.66; IR (KBr plate): nmax =3073, 2937,
2867, 1585, 1471, 1449, 1386, 1353, 1326, 1290, 1197, 1181,
1156, 1107, 1087, 1071, 976, 866, 813, 775, 704, 679, 666, 629,
614, 597, 559, 546 cmÀ1; HR-MS (MALDI-DHB): m/z=434.
1411, calcd. C25H24NO4S (M+H)+: 434.1421.
N-{[5-(tert-Butyl)-2-phenylbenzofuran-3-yl]methylene}-4-
methylbenzenesulfonamide (2y): yellow solid; yield: 85 mg
(0.198 mmol, 66%); mp 130–1348C; 1H NMR (400 MHz,
CDCl3): d=9.33 (s, 1H), 8.31 (s, 1H), 7.94 (d, J=8.2 Hz,
2H), 7.77 (dd, J=6.5, 3.0 Hz, 2H), 7.60–7.55 (m, 3H), 7.47
(s, 2H), 7.34 (d, J=8.1 Hz, 2H), 2.43 (s, 3H), 1.38 (s, 9H);
13C NMR (100 MHz, CDCl3): d=166.66, 163.36, 152.78,
148.25, 144.21, 136.14, 131.36, 129.71, 129.39, 129.07, 128.43,
127.79, 124.95, 124.36, 119.73, 113.38, 110.56, 34.98, 31.72,
21.65; IR (KBr plate): nmax =2957, 2867, 1583, 1570, 1477,
1393, 1320, 1261, 1205, 1184, 1154, 1089, 1065, 1019, 974,
941, 894, 866, 813, 772, 700, 682, 656, 625, 593, 552 cmÀ1
;
HR-MS (MALDI-DHB): m/z=432.1619, calcd. C26H26NO3S
(M+H)+: 432.1628.
N-[(2,5-Diphenylbenzofuran-3-yl)methylene]-4-methyl-
benzenesulfonamide (2z): white solid; yield: 75 mg
(0.165 mmol, 55%); mp 155–1608C; 1H NMR (400 MHz,
CDCl3): d=9.38 (s, 1H), 8.48 (s, 1H), 7.92 (d, J=8.2 Hz,
2H), 7.80 (dd, J=6.5, 3.0 Hz, 2H), 7.66–7.57 (m, 7H), 7.48
Adv. Synth. Catal. 2015, 357, 2089 – 2097
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
2095

FULL PAPERS
Lin Li et al.
(t, J=7.5 Hz, 2H), 7.38 (t, J=7.3 Hz, 1H), 7.33 (d, J=
8.1 Hz, 2H), 2.42 (s, 3H); 13C NMR (100 MHz, CDCl3): d=
167.03, 163.56, 154.09, 144.33, 141.05, 138.64, 135.81, 131.57,
129.81, 129.46, 129.16, 128.86, 128.22, 127.89, 127.61, 127.31,
126.07, 125.76, 121.99, 113.32, 111.41, 21.67; IR (KBr plate):
nmax =3058, 1652, 1584, 1568, 1541, 1457, 1346, 1327, 1205,
1161, 1153, 1091, 1078, 922, 888, 855, 817, 780, 768, 750, 726,
695, 665, 638, 576, 550 cmÀ1; HR-MS (MALDI-DHB): m/z=
452.1304, calcd. C28H22NO3S (M+H)+: 452.1315.
N-[(1-Acetyl-2-phenyl-1H-indol-3-yl)methylene]-4-meth-
ylbenzenesulfonamide (7): white solid; yield: 37 mg
(0.09 mmol, 30%); mp 191–1978C; 1H NMR (400 MHz,
CDCl3): d=8.78 (s, 1H), 8.43 (d, J=7.5 Hz, 1H), 8.24 (s, J=
8.1 Hz, 1H), 7.85 (d, J=8.0 Hz, 2H), 7.65–7.55 (m, 3H),
7.50–7.36 (m, 4H), 7.33–7.27 (m, 2H), 2.41 (s, 3H), 2.00 (s,
3H); 13C NMR (100 MHz, CDCl3): d=171.09, 164.26,
150.00, 144.10, 136.91, 135.98, 130.93, 130.38, 129.71, 129.62,
129.43, 127.77, 126.83, 125.44, 125.31, 122.80, 116.27, 115.43,
27.73, 21.64; HR-MS (MALDI-DHB): m/z=417.1259, calcd.
C24H21N2O3S (M+H)+: 417.1267.
(Z)-4-Methyl-N-{[2-(p-tolyl)benzofuran-3(2H)-ylidene]-
methyl}benzenesulfonamide (IV-2b): 1H NMR (400 MHz,
CDCl3): d=7.84 (s, 2H), 7.46–7.40 (m, 3H), 7.31 (d, J=
8.0 Hz, 2H), 7.19 (d, J=7.9 Hz, 2H), 7.14 (t, J=7.4 Hz,
1H), 6.97–6.91 (m, 2H), 6.87 (d, J=10.0 Hz, 1H), 6.62 (d,
J=8.0 Hz, 1H), 5.26 (d, J=10.6 Hz, 1H), 2.46 (s, 3H), 2.37
(s, 3H); 13C NMR (100 MHz, CDCl3): d=158.95, 143.68,
138.43, 132.43, 131.62, 130.21, 129.57, 129.49, 129.34, 127.49,
125.45, 123.65, 121.59, 119.90, 110.62, 87.05, 21.64, 21.38; IR
(KBr plate): nmax =2920, 1716, 1699, 1683, 1653, 1636, 1558,
1541, 1521, 1508, 1473, 1457, 1437, 1340, 1319, 1202, 1158,
1086, 911, 812, 743, 697, 672, 606, 555 cmÀ1; HR-MS (DART
positive): m/z=392.1309, calcd. C23H22NO3S (M+H)+:
392.1315.
[3] For recent reviews, see: a) B. Chattopadhyay, V. Ge-
vorgyan, Angew. Chem. 2012, 124, 886–896; Angew.
Chem. Int. Ed. 2012, 51, 862–872; b) A. V. Gulevich, V.
Gevorgyan, Angew. Chem. 2013, 125, 1411–1413;
Angew. Chem. Int. Ed. 2013, 52, 1371–1373; c) Q. Xiao,
Y. Zhang, J. Wang, Acc. Chem. Res. 2013, 46, 236–247;
d) H. M. Davies, J. S. Alford, Chem. Soc. Rev. 2014, 43,
5151–5162.
[4] a) S. Chuprakov, J. A. Malik, M. Zibinsky, V. V. Fokin,
J. Am. Chem. Soc. 2011, 133, 10352–10355; b) T. Miura,
T. Biyajima, T. Fujii, M. Murakami, J. Am. Chem. Soc.
2012, 134, 194–196; c) S. Chuprakov, B. T. Worrell, N.
Selander, R. K. Sit, V. V. Fokin, J. Am. Chem. Soc.
2014, 136, 195–202; d) J. M. Yang, C. Z. Zhu, X. Y.
Tang, M. Shi, Angew. Chem. 2014, 126, 5242–5246;
Angew. Chem. Int. Ed. 2014, 53, 5142–5146.
[5] a) T. Miura, M. Yamauchi, M. Murakami, Chem.
Commun. 2009, 1470–1471; b) T. Horneff, S. Chupra-
kov, N. Chernyak, V. Gevorgyan, V. V. Fokin, J. Am.
Chem. Soc. 2008, 130, 14972–14974; c) B. Chattopad-
hyay, V. Gevorgyan, Org. Lett. 2011, 13, 3746–3749;
d) B. T. Parr, S. A. Green, H. M. L. Davies, J. Am.
Chem. Soc. 2013, 135, 4716–4718; e) S. Chuprakov,
S. W. Kwok, V. V. Fokin, J. Am. Chem. Soc. 2013, 135,
4652–4655; f) J. E. Spangler, H. M. Davies, J. Am.
Chem. Soc. 2013, 135, 6802–6805; g) E. E. Schultz, R.
Sarpong, J. Am. Chem. Soc. 2013, 135, 4696–4699; h) T.
Miura, K. Hiraga, T. Biyajima, T. Nakamuro, M. Mura-
kami, Org. Lett. 2013, 15, 3298–3301; i) Y. Shi, V. Ge-
vorgyan, Org. Lett. 2013, 15, 5394–5396; j) J. S. Alford,
J. E. Spangler, H. M. L. Davies, J. Am. Chem. Soc.
2013, 135, 11712–11715; k) T. Miura, Y. Funakoshi, M.
Murakami, J. Am. Chem. Soc. 2014, 136, 2272–2275;
l) C. E. Kim, S. Park, D. Eom, B. Seo, P. H. Lee, Org.
Lett. 2014, 16, 1900–1903; m) R. Q. Ran, J. He, S. D.
Xiu, K. B. Wang, C. Y. Li, Org. Lett. 2014, 16, 3704–
3707; n) X. Ma, S. Pan, H. Wang, W. Chen, Org. Lett.
2014, 16, 4554–4557; o) K. Chen, Z. Z. Zhu, Y. S.
Zhang, X. Y. Tang, M. Shi, Angew. Chem. 2014, 126,
6763–6767; Angew. Chem. Int. Ed. 2014, 53, 6645–6649;
p) H. Shang, Y. Wang, Y. Tian, J. Feng, Y. Tang,
Angew. Chem. 2014, 126, 5768–5772; Angew. Chem.
Int. Ed. 2014, 53, 5662–5666; q) Y.-Z. Zhao, H.-B.
Yang, X.-Y. Tang, M. Shi, Chem. Eur. J. 2015, 21, 3562–
3566.
Acknowledgements
We thank the National Natural Science Foundation of China
(21302183) and the “Strategic Priority Research Program” of
the Chinese Academy of Sciences (Grant No. XDA09030102)
for financial support.
References
[6] a) S. Chuprakov, V. Gevorgyan, Org. Lett. 2007, 9,
4463–4466; b) S. Chuprakov, S. W. Kwok, L. Zhang, L.
Lercher, V. V. Fokin, J. Am. Chem. Soc. 2009, 131,
18034–18035; c) N. Grimster, L. Zhang, V. V. Fokin, J.
Am. Chem. Soc. 2010, 132, 2510–2511; d) M. Zibinsky,
V. V. Fokin, Org. Lett. 2011, 13, 4870–4872; e) J. S.
Alford, H. M. Davies, Org. Lett. 2012, 14, 6020–6023.
[7] a) N. Selander, B. T. Worrell, V. V. Fokin, Angew.
Chem. 2012, 124, 13231–13234; Angew. Chem. Int. Ed.
2012, 51, 13054–13057; b) T. Miura, Y. Funakoshi, M.
Morimoto, T. Biyajima, M. Murakami, J. Am. Chem.
Soc. 2012, 134, 17440–17443; c) R. Liu, M. Zhang, G.
Winston-McPherson, W. Tang, Chem. Commun. 2013,
49, 4376–4378; d) F. Medina, C. Besnard, J. Lacour,
Org. Lett. 2014, 16, 3232–3235.
[1] For recent reviews, see: a) H. M. L. Davies, R. E. J.
Beckwith, Chem. Rev. 2003, 103, 2861–2904;
b) H. M. L. Davies, J. R. Manning, Nature 2008, 451,
417–424; c) M. M. Díaz-Requejo, P. J. PØrez, Chem.
Rev. 2008, 108, 3379–3394; d) H. L. Davies, A. Dick, in:
À
C H Activation, Vol. 292, (Eds.: J.-Q. Yu, Z. Shi),
Springer, Berlin, Heidelberg, 2010, pp 303–345; e) M. P.
Doyle, R. Duffy, M. Ratnikov, L. Zhou, Chem. Rev.
2010, 110, 704–724; f) C.-M. Che, V. K.-Y. Lo, C.-Y.
Zhou, J.-S. Huang, Chem. Soc. Rev. 2011, 40, 1950–
1975; g) H. M. L. Davies, D. Morton, Chem. Soc. Rev.
2011, 40, 1857–1869; h) H. Lu, X. P. Zhang, Chem. Soc.
Rev. 2011, 40, 1899–1909.
[2] a) H. M. L. Davies, T. Hansen, J. Am. Chem. Soc. 1997,
119, 9075–9076; b) H. M. L. Davies, T. Hansen, M. R.
Churchill, J. Am. Chem. Soc. 2000, 122, 3063–3070.
[8] a) M. Zibinsky, V. V. Fokin, Angew. Chem. 2013, 125,
1547–1550; Angew. Chem. Int. Ed. 2013, 52, 1507–1510;
2096
asc.wiley-vch.de
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2015, 357, 2089 – 2097

3
À
FULL PAPERS
Synthesis of Benzofurans via Tandem Rhodium-Catalyzed C(sp ) H Insertion
b) T. Miura, T. Tanaka, K. Hiraga, S. G. Stewart, M.
Murakami, J. Am. Chem. Soc. 2013, 135, 13652–13655;
c) T. Miura, T. Tanaka, T. Biyajima, A. Yada, M. Mura-
kami, Angew. Chem. 2013, 125, 3975–3978; Angew.
Chem. Int. Ed. 2013, 52, 3883–3886; d) T. Miura, T.
Tanaka, A. Yada, M. Murakami, Chem. Lett. 2013, 42,
1308–1310; e) A. Boyer, Org. Lett. 2014, 16, 1660–1663;
f) Y.-S. Zhang, X.-Y. Tang, M. Shi, Chem. Commun.
2014, 50, 15971–15974; g) Y. Jiang, X.-Y. Tang, M. Shi,
Chem. Commun. 2015, 51, 2122–2125; h) X.-Y. Tang,
Y.-S. Zhang, L. He, Y. Wei, M. Shi, Chem. Commun.
2015, 51, 133–136; i) H. D. Xu, Z. H. Jia, K. Xu, H.
Zhou, M. H. Shen, Org. Lett. 2015, 17, 66–69.
Zeng, R. Zhang, X. Li, H. Jiang, Org. Lett. 2012, 14,
1098–1101; g) Y. Liu, S. Ma, Org. Lett. 2012, 14, 720–
723; h) H. Yuan, K.-J. Bi, B. Li, R.-C. Yue, J. Ye, Y.-H.
Shen, L. Shan, H.-Z. Jin, Q.-Y. Sun, W.-D. Zhang, Org.
Lett. 2013, 15, 4742–4745; i) Z. Zhou, G. Liu, Y. Shen,
X. Lu, Org. Chem. Front. 2014, 1, 1161–1165.
[12] For selected reports on sequential catalysis, see: a) S.
Beligny, S. Eibauer, S. Maechling, S. Blechert, Angew.
Chem. 2006, 118, 1933–1937; Angew. Chem. Int. Ed.
2006, 45, 1900–1903; b) Q. Cai, Z.-A. Zhao, S.-L. You,
Angew. Chem. 2009, 121, 7564–7567; Angew. Chem. Int.
Ed. 2009, 48, 7428–7431; c) Q. Cai, X.-W. Liang, S.-G.
Wang, J.-W. Zhang, X. Zhang, S.-L. You, Org. Lett.
2012, 14, 5022–5025; d) D.-F. Chen, Z.-Y. Han, X.-L.
Zhou, L.-Z. Gong, Acc. Chem. Res. 2014, 47, 2365–
2377.
[13] a) P. Grünanger, P. Vita Finzi, Tetrahedron Lett. 1963,
4, 1839–1840; b) R. E. Harmon, F. Stanley, S. K. Gupta,
J. Johnson, J. Org. Chem. 1970, 35, 3444–3448; c) M. A.
McKinney, P. P. Patel, J. Org. Chem. 1973, 38, 4059–
4064; d) S. W. Kwok, L. Zhang, N. P. Grimster, V. V.
Fokin, Angew. Chem. 2014, 126, 3520–3524; Angew.
Chem. Int. Ed. 2014, 53, 3452–3456.
[9] X. Ma, F. Wu, X. Yi, H. Wang, W. Chen, Chem.
Commun. 2015, 51, 6862–6865.
[10] For selected reviews, see: a) D. A. Horton, G. T.
Bourne, M. L. Smythe, Chem. Rev. 2003, 103, 893–930;
b) G. Zeni, R. C. Larock, Chem. Rev. 2006, 106, 4644–
4680.
[11] For selected reports on the synthesis of benzofurans,
see: a) D. Ma, Q. Cai, X. Xie, Synlett 2005, 2005, 1767–
1770; b) Y. Liao, M. Reitman, Y. Zhang, R. Fathi, Z.
Yang, Org. Lett. 2002, 4, 2607–2609; c) Y. Liao, J.
Smith, R. Fathi, Z. Yang, Org. Lett. 2005, 7, 2707–2709;
d) G. Stork, A. Yamashita, J. Adams, G. R. Schulte, R.
Chesworth, Y. Miyazaki, J. J. Farmer, J. Am. Chem.
Soc. 2009, 131, 11402–11406; e) S. Ye, G. Liu, S. Pu, J.
Wu, Org. Lett. 2012, 14, 70–73; f) B. Yin, C. Cai, G.
[14] H. Tsutsui, T. Abe, S. Nakamura, M. Anada, S. Hashi-
moto, Chem. Pharm. Bull. 2005, 53, 1366–1368.
[15] P. Müller, Y. Allenbach, E. Robert, Tetrahedron: Asym-
metry 2003, 14, 779–785.
[16] J. Raushel, V. V. Fokin, Org. Lett. 2010, 12, 4952–4955.
Adv. Synth. Catal. 2015, 357, 2089 – 2097
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
2097