Organocatalytic C-H/C-H' cross-biaryl coupling: C-selective arylation of sulfonanilides with aromatic hydrocarbons

Article abstract of DOI:10.1021/ja407944p

The hypervalent iodine-mediated C-C selective coupling of N-methanesulfonyl anilides with aromatic hydrocarbons has been developed. The first organocatalytic oxidative cross-biaryl-coupling was achieved by the catalyst control in defining specific 2,2′-diiodobiphenyls for the direct C-C bond formations.

Full text of DOI:10.1021/ja407944p

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Communication
Organocatalytic C-H/C-H’ Cross-Biaryl-Coupling: C-Selective
Arylation of Sulfonanilides with Aromatic Hydrocarbons
Motoki Ito, Hiroko Kubo, Itsuki Itani, Koji Morimoto, Toshifumi Dohi, and Yasuyuki Kita
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/ja407944p • Publication Date (Web): 06 Sep 2013
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Organocatalytic C-H/C-H’ Cross-Biaryl-Coupling: C-Selective
Arylation of Sulfonanilides with Aromatic Hydrocarbons
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Motoki Ito, Hiroko Kubo, Itsuki Itani, Koji Morimoto, Toshifumi Dohi and Yasuyuki Kita*
College of Pharmaceutical Sciences, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga, 525-8577, Japan
Supporting Information Placeholder
ABSTRACT: The hypervalent iodine-mediated C-C selective
coupling of N-methanesulfonyl anilides with aromatic hydrocar-
bons (AHs) has been developed. The first organocatalytic oxida-
tive cross-biaryl-coupling was achieved by the catalyst control in
defining specific 2,2’-diiodobiphenyls for the direct C-C bond
formations.
Direct coupling between two aromatic substrates that accompa-
nies the double C-H bond transformation, that is called oxidative
cross-coupling or cross dehydrogenative coupling (CDC), is now
being extensively investigated as the short step and greener alter-
native to the well-established transition metal-catalyzed coupling
of metallated and halogenated arenes represented by Negishi cou-
pling and Suzuki-Miyaura coupling.1-3 In general, the develop-
ment of oxidative couplings has been severely hampered by vari-
ous problematic side-reactions, i.e., homo-coupling, over-
oxidation, and polymerization, especially under catalytic condi-
tions, while a significant advancement in transition metal chemis-
try has realized a variety of controlled reactions in recent years.1,2
SCHEME 1. 2,2‘-diiodobiphenyl catalysed cross-coupling of
anilides 1 with AHs 2.
undesired by-products. On the other hand, the yield of the biaryl
products 3 was dramatically improved by employing the 1-
naphthylamine derivative 1b as the substrate. Regarding the
nucleophiles, the C-C coupling selectively occurred with the pa-
ra-substituted phenyl ether 2g as good as p-xylene 2a to give a
considerable yield of the corresponding biaryls, 3aa, 3ba, and 3bg.
We have also devoted a great deal of effort to establish a green
system for the synthesis of biaryls through the development of
metal-free couplings using hypervalent iodine(III) reagents, such
as PhI(OAc)2 (PIDA) and PhI(OCOCF3)2 (PIFA), as the specific
oxidants.4 One of the important goals of this area is the develop-
ment of organocatalytic oxidative cross-coupling, however, it has
still remained as a big challenge, especially for the coupling of
unfunctionalized aromatic hydrocarbons (AHs).
In this report, we describe the discovery of a novel C-C selec-
tive cross-coupling of aniline derivatives with AHs under the first
organocatalytic conditions (Scheme 1). The investigation of the
protecting groups and AH (2a: p-xylene) as the nucleophile under
stoichiometric conditions was initially studied in which the
reaction of N-methanesulfonyl (Ms) anilide 1a promptly afforded
the biaryl product 3aa by the C-C coupling under PIDA-HFIP
(hexafluoroisopropanol)5 reagent-solvent conditions (Scheme 2).
The use of other protecting groups, such as Me, Ac, CF3CO, Boc,
and Tf groups, instead of the Ms group did not afford any of the
desired coupling products.6 Even the Ts group provided a signifi-
cantly reduced yield (less than 30% yield) by forming
SCHEME 2. Cross-coupling of anilides 1 with AHs 2 under
stoichiometric conditions.
While the iodine(III)-mediated N-selective couplings of aniline
derivatives with aromatic substrates have emerged in recent
years,7,8 at the outset of our studies, there were no reported exam-
ples of the C-C coupling with AH nucleophiles. AH nucleophiles,
such as halobenzene and mesitylene, with N-acyl anilides were
reported to predominantly provide diarylamines by the C-N bond
formation over C-C coupling.7 As an indirect example via formal
[4+3] intermediates, Canesi and co-worker reported that the cou-
pling of N-Ms anilides with thiophenes afforded biaryls through
the C-N bond formation and successive cleavage for the fomation
of the aromatics.9a More recently, an AH nucleophile, naphthalene,
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was demonstrated to provide a C-C coupling product through a
in the catalyst. Nonetheless, the coupling did not proceed at all in
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similar indirect way to that for thiophenes in utilizing our
dearomatizing [2+3] cyclization10-isomerization process.9b These
methods seem not to have a promising prospect for converting to
a catalytic version due to the narrow reaction scope and rather low
coupling productions.
the absence of the iodoarene catalysts (Entry 10).
With the optimized catalyst 4e in hand, we then examined the
scope of the reaction with respect to the AH components (Table 2).
The coupling of 1b with AHs 2b-d afforded the biaryl product
3bb-bd in good to high yields (entries 1-3). The unsymmetrical
2d reacted at the less hindered ortho-position of the methyl group
with a high regioselectivity. Toluene 2e was also applicable as a
nucleophile (entry 4). The coupling with naphthalene 2f exclu-
sively occurred at the α-position (entry 5). para-Substituted phe-
nyl ether 2g afforded the biaryl 3bg in quantitative yield by cou-
pling at the ortho-position of the methoxy group (entry 6). The
benzyl alcohol 2h gave the desired biaryls 3bh without any unde-
sired oxidative side-reactions (entry 7). For the electron- with-
drawing bromine and ester substituted 2i and 2j, biaryls
Once the new coupling of the AHs was launched, we next
envisioned extending the coupling to
a catalytic version.
Organoiodine compounds had been introduced as a unique class
of organocatalysts for developing the oxidative bond-forming
reactions by us11e and others.11f However, standard catalytic
conditions using 10 mol% iodobenzene with mCPBA as the
oxidant did not work well for the present oxidative cross-coupling
and only afforded the biaryl 3ba in a low yield. (Table 1, entry 1).
However, the catalytic reactions might become realistic by some
catalyst control. We have recently reported that 2,2’-
diiodobiphenyls are efficient precursors of highly reactive
iodine(III) species not aggregating with each other under mild
oxidation conditions.12 Therefore, we attempted to use the 2,2’-
diiodobiphenyl catalysts 4a-d and its new derivative 4e for the
coupling. To our delight, simple 2,2’-diiodobiphenyl 4a showed
an extremely high catalytic activity within a 5 mol% loading
which corresponds to a 10 mol% loading of the iodine moiety
(entry 2). It should be emphasized that the catalytic amount of 4a
gave a result comparable to the stoichiometric use of the PIDA in
HFIP, even in a more practical solvent, TFE (trifluoroethanol)
(entry 3). Further tuning of the catalyst revealed the significant
effect of the substituent. The yield slightly decreased with
catalysts 4b and 4c by introducing alkyl substituents, probably
due to their steric hindrance (entries 4 and 5).13 While the lower
catalytic activity was observed for the electron-withdrawing
chlorine substituted 4d (entry 6),
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Table 2. Catalytic coupling of 1b with aromatic hydrocarbons
2
Entry
1
Entry
5
Biaryl 3, Yielda
Biaryl 3, Yielda
3bf, 82%
3bb, 94%
Table 1. Optimization of conditions for the catalytic coupling
of 1b with 2a
2
3
R‘ = tBu, R‘‘ = Me;
3bc, 83%b
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7
R‘ = Me; 3bg, 99%
R‘ = CH2OH; 3bh, 67%
R‘ = Br; 3bi, 92%
2a
Iodoarene
(y mol%)
R‘ = R‘‘ = iPr;
3bd, 54%
8c
9c
Entry
Yielda
Fluoroalcohol
R‘ = CO2Me; 3bj, 74%
(x equiv)
1
2
3
4
5
6
7
8
9
10
10
10
10
10
10
10
5
PhI (10 mol%)
4a (5 mol%)
4a (5 mol%)
4b (5 mol%)
4c (5 mol%)
4d (5 mol%)
4e (5 mol%)
4e (5 mol%)
o-PhC6H4I
(10 mol%)
none
HFIP
HFIP
TFE
TFE
TFE
TFE
TFE
TFE
HFIP
38%
94%
89%
78%
81%
81%
99%
76%
49%
4
3be, 66%
10
11
R’ = Bn; 3bk, 99%
R’ = TBDPS; 3bl, 92%
a Isolated yield based on 1b. b 9:1 mixture of regioisomeres. c HFIP was
used instead of TFE.
10
3bi and 3bj were obtained in high yields, respectively, using
HFIP as solvent (entries 8 and 9). The benzyl and silyl groups
could also be used as protecting groups of the phenols (entries 10
and 11).
10
10
HFIP
ND
a Isolated yield based on 1b.
the introduction of an electron-donating methoxy group in the
catalyst 4e gave the best result (99% yield, entry 7).14 Lowering
the amount of 2a to 5 equiv led to a decrease in product yield
(entry 8).15 The use of mono-iodobiphenyl, which has a structure
related to the diiodide catalyst 4a, resulted in a sharp drop in the
product yield (entry 9). This result indicated the importance of the
second iodine moiety at the ortho-position of biaryl substructure
We then investigated the scope of the anilides 1 in the coupling
with AH 2a (Table 3). The 1-naphthylamine derivatives 1c and 1d
with protections by the benzylsulfonyl and cyclopropylsulfonyl
groups produced the desired products 3ca and 3da in good yields
(entries 1 and 2). The 2-naphthylamine derivative 1e was also
applicable as a substrate by using HFIP instead of TFE and the
coupling occurred only at the 1-position of 1e (entry 3). The in-
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troduction of bromine and acetoxymethyl groups at the 6-position
accerelation of the re-oxidation step for regeneration of the
1
2
3
of 1e slightly affected the yields (entries 4 and 5). The more elec-
tron-rich phenanthrene 1h afforded the biaryl 3ha without causing
any undesired oxidation (entry 6).
catalytic active species with mCPBA.
4
5
Table 3. Scope of anilides 1 in the coupling with 2a a
6
7
Entry
Anilide 1
Biaryl 3
Yieldb
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It is worth mentioning that our metal-free method provides mild
conditions of tempearture compared to the recently reported Pd-
catalyzed oxidative coupling of aniline derivatives within the
same level of the loading of catalyst and substrates.16
1
2
R = Br, R‘ = Bn (1c) R = Br, R‘ = Bn (3ca)
76%
67%
R = Br,
R = Br,
Amino-substituted arenes often serve as organocatalysts, lig-
ands, functionalized materials and their precursors.17 To apply the
synthesized N-Ms biaryls as precursors of these compounds, a
mild and high-yielding deprotection method of the Ms group is
required due to the rare removal of the Ms group.18 We achieved
deprotection of the Ms group under nBuLi or LDA-mediated con-
ditions, which were originally reported by Carreira and Urabe,19
by utilizing the Boc group as a proxy protecting group of the sul-
fonamide N-H group (Scheme 4, eq 2). The (R)-(+)-
camphorsulfonyl (Cs*) group was also deprotected by this three-
step protocol. As a result, the synthesis of a useful chiral 2-
aminobinaphthyl 7jf17d-f becomes possible after separation of a
1:1 diastereomixture of the produced 3jf, which was obtained by
our coupling of 1j and 2f by the usual SiO2 chromatography (eq
3).
R‘ = c-propyl (1d)
R‘ = c-propyl (3da)
3c
4c
5c
R = H (1e)
R = Br (1f)
R = H (3ea)
R = Br (3fa)
62%
50%
54%
R = CH2OAc (1g)
R = CH2OAc (3ga)
6c
71%
(1h)
(3ha)
a Reactions were performed by using the catalyst 4e (5 mol%) with dry
mCPBA (1.5 equiv.) in TFE-CH2Cl2 (2:1) at room temperature for 3 hours.
b Isolated yield based on 1. c HFIP was used instead of TFE.
Furthermore, our new catalytic system is applicable for the
coupling of 1b with thiophene 5 to afford the biaryl product 6a in
high yield (Scheme 3). The coupling product 6b was obtained
from 2,4-dimethylanilide 1i in higher yield by the catalyst 4e than
that reported with the use of stoichiometric PIDA in HFIP.9a
The more activated intermediate than the catalyst 4e‘ itsself
might be generated during the catalytic cycle. Thus, the reaction
with a stoichiometric amount of the isolated hypervalent iodine
4e‘ provided the same product 3ba in a slightly lower yield (68%,
see eq 1) than that under catalytic conditions. We also ascertained
the comparably faster consumption of anilides 1 with the 2,2’-
diiodobiphenyl
SCHEME 4. Deprotection of N-sulfonylamino biaryls 3.
In summary, by defining unique 2,2’-diiodobiphenyls 4 as a
specific catalyst, we have developed for the first time the novel
iodine(III)-mediated coupling of anilides 1 with AHs 2 by cataly-
sis of the organoiodine. This is the first report of the organocata-
lytic intermolecular oxidative cross-biaryl-coupling and thus the
catalyst-controlled methodology would provide a new opportunity
for developing greener synthetic methods of the valuable biaryl
motifs.
ASSOCIATED CONTENT
Supporting Information
Scheme 3. Catalytic coupling of anilides 1 and thiophene 5
Experimental details and characterization data. This material is
available free of charge via the Internet at http://pubs.acs.org.
catalyst 4e than 4e‘ even though the loading of the iodine content
in the catalyst is ten-times lower (10 mol% for the catalyst 4e vs
150 mol% I(III) for 4e‘). The substitution of the electron-donating
methoxy groups in the catalyst 4e seems to contribute to the
AUTHOR INFORMATION
Corresponding Author
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(10)Tohma H.; Watanabe H.; Takizawa S.; Maegawa T.; Kita Y.
Heterocycles 1999, 51, 1785.
kita@ph.ritsumei.ac.jp
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(11)Reviews: (a) Dohi T.; Kita Y. Chem. Commun. 2009, 2073. (b)
Richardson, R. D.; Wirth, T. Angew. Chem., Int. Ed. 2006, 45, 4402. (c)
Ochiai, M.; Miyamoto, K. Eur. J. Org. Chem. 2008, 4229. (d) Yusubov,
M. S.; Zhdankin, V. V. Mendeleev Commun. 2010, 20, 185. For the
original papers, see: (e) Dohi T.; Maruyama A.; Yoshimura M.; Morimoto
K.; Tohma H.; Kita Y. Angew. Chem. Int. Ed. 2005, 44, 6193. (f) Ochiai
M.; Takeuchi Y.; Katayama T.; Sueda T.; Miyamoto K. J. Am. Chem. Soc.
2005, 127, 12244.
(12)(a) Dohi T.; Takenaga N.; Fukushima K.; Uchiyama T.; Kato D.;
Shiro M.; Fujioka H.; Kita Y. Chem. Commun. 2010, 46, 7697. (b) Dohi
T.; Kato D.; Hyodo R.; Yamashita D.; Shiro M.; Kita Y. Angew. Chem.
Int. Ed. 2011, 50, 3784. (c) Dohi T.; Nakae T.; Ishikado Y.; Kato D.; Kita
Y. Org. Biomol. Chem. 2011, 9, 6899.
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
This work was finantially supported by Grant-in-Aid for Scien-
tific Research (A) and Encouragement of Young Scientist (A)
from the Japan Society for the Promotion of Science (JSPS), a
grant-in-Aid for Scientific Research on Innovative Areas “Ad-
vanced Molecular Transformation by Organocatalysts” from The
Ministry of Education, Culture, Sports, Science and Technology
(MEXT), and Ritsumeikan Global Innovation Research Organiza-
tion (R-GIRO) project. M.I. acknowledges the Research Activity
Start-up from JSPS.
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(13)Antonchick et al. used our catalyst 4c for the catalytic C-N couplings
of acetoanilides with AHs. See ref. 7b.
(14)A greener co-oxidant, AcOOH, could also be used, but the yields
were substantially lower (up to 52% for 3ba) than that using mCPBA. See
ref. 12a.
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Journal of the American Chemical Society
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Organocatalytic C-H/C-H’ Cross-Biaryl-Coupling: C-Selective Arylation of Sulfonanilides with Aromatic Hydrocar-
bons
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ACS Paragon Plus Environment