Rh(III)-catalyzed oxidative olefination of N-(1-naphthyl)sulfonamides using activated and unactivated alkenes

Article abstract of DOI:10.1021/ol2023856

Rhodium(III)-catalyzed oxidative olefination of N-(1-naphthyl)sulfonamides has been achieved at the peri position. Three categories of olefins have been successfully applied. Activated olefins reacted to afford five-membered azacycles as a result of oxida

Full text of DOI:10.1021/ol2023856

ORGANIC
LETTERS
2011
Vol. 13, No. 21
5808–5811
Rh(III)-Catalyzed Oxidative Olefination of
N-(1-Naphthyl)sulfonamides Using
Activated and Unactivated Alkenes
Xuting Li,†,‡ Xue Gong,† Miao Zhao,† Guoyong Song,† Jian Deng,‡ and Xingwei Li*,†
Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023,
China, and School of Chemistry and Chemical Engineering, University of South China,
Hengyang 421001, China
xwli@dicp.ac.cn
Received September 6, 2011
ABSTRACT
Rhodium(III)-catalyzed oxidative olefination of N-(1-naphthyl)sulfonamides has been achieved at the peri position. Three categories of olefins
have been successfully applied. Activated olefins reacted to afford five-membered azacycles as a result of oxidative olefinationÀhydroamination.
Unactivated olefins reacted to give the olefination product. 2-fold oxidative CÀC and CÀN coupling was achieved for allylbenzenes.
The oxidative coupling of unreactive CÀH bonds with
olefins (the Fujiwara-Moritani reaction)1 represents an
atom-economic strategy to directly functionalize arenes
without prior activation and has received increasing atten-
tion since 1967. It has become an attractive alternative to
the Heck reaction. Achieving oxidative CÀC coupling in
high catalytic efficiency using readily available starting
materials should increase sustainability in synthesis.2 A
common strategy to achieve selective CÀH oxidative
olefination is the use of a neighboring directing group.
Palladium,2,3 ruthenium,4 and rhodium5 have been re-
ported to effectively catalyze this transformation with the
assistance of directing groups such as amide, oxime,
pyridyl, ketone, carboxyl, and ester. In contrast to the
well-studied palladium catalysts, rhodium(III) complexes
have been recently explored and have been found to effect
at low catalyst loading with high functional group
tolerance.6À10 Despite the success, nearly all oxidative
olefination required somewhat activated alkenes such as
† Chinese Academy of Sciences.
‡ University of South China.
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r
10.1021/ol2023856
Published on Web 10/11/2011
2011 American Chemical Society

acrylates and styrenes. Glorius8a and Bergman and
Ellman11 reported the only two examples of Rh(III)-
catalyzedolefination using unactivatedolefins. In Bergman
and Ellman’s report,11 various unactuvated alkenes such as
1-hexene are smoothly coupled with O-methyl oximines.
We now report a general method of Rh(III)-catalyzed oxi-
dative olefination of the sulfonamides of 1-naphthylamine
at the peri position using activated and unactivated alkenes.
Although the sulfonamide group can act as a directing
group in facilitating CÀH activation, only very limited
examples have been reported.12 In this context, given that
sulfonamide groups can be readily installed and removed,
it is important to explore this type of substrate for selective
CÀH activation. We initiated our investigation on the
oxidative olefination of N-(1-naphthyl)sulfonamide 1a
with benzyl acrylate. Our initial screening indicated that
the coupled product 3aa was isolated in 70% yield when a
combination of [RhCp*Cl2]2 (2.5 mol %) and Cu(OAc)2
(2.1 equiv) was used in DCE (120 °C). Replacing the
solvent with DMF resulted in significant decomposition
under the same conditions. Gratifyingly, by lowering the
temperature to 100 °C, a clean reaction was achieved and
3aa was isolated in 89% yield (Scheme 1). Notably, no
silver salt additive is necessary under these conditions.
This product was characterized as a five-membered
azacycle as a result of olefination followed by intramo-
lecular hydroamination.7a,10a,10b,13
readily coupled with 1a to afford the cyclization products
in high yields (87À90%). In addition, both electron-donat-
ing (3cc and 3dc) and -withdrawing (3bb) groups in the
naphthyl ring are well tolerated. Furthermore, no Heck-
type product was generated for a halogen-functionalized
substrate (see 3bb). This specific feature highlights an
advantage of Rh(III)-catalyzed CÀC coupling reactions
compared to many palladium-catalyzed ones in that the
halogen is retained. In addition, other activated olefins
such as acrylonitrile and enones are all efficient coupling
partners. Thus, all the coupled products were isolated in
comparably high yields (87À95%) for all monosulfona-
mides examined. In contrast, only unidentifiable products
were isolated when PhNHTs was used as a substrate under
the same conditions. CÀH activation at both the ortho and
peri position of 1-substituted naphthalenes has been noted
using rhodium and palladium catalysts.14 To better define
the substrate scope, a centrosymmetric disulfonamide has
been applied. Although two equivalents of olefin were
oxidatively incorporated, NMR analyses indicated that
monocyclization occurred. Thus, products 3fb and 3fc
were isolated in good yields. In these reactions, failure of
the second hydroamination is likely caused by the change
of electronic effects induced by the first cyclization.
The scope of the olefin was successfully expanded.
Simple styrene and 4-chlorostyrene readily coupled with
1a to give products 4a (93%) and 4b (82%), respectively
(Scheme 2). Significantly, unactivated simple olefins such
as 1-hexene, vinylcyclohexane, and 4-methyl-1-pentene are
also efficient coupling partners, and all the coupled pro-
ducts were isolated in high yield (72À93%). In line with the
scope of sulfonamides in their coupling with acrylates,
both electron-donating and halide substituents in the
naphthyl ring can be tolerated, indicating the general
applicability of the sulfonamide substrate. We noted that
only two reports deals with rhodium-catalyzed oxidative
olefination using unactivated alkenes.8a,11
Scheme 1. Oxidative Olefination Using Activated Alkenesa,b
(9) (a) Guimond, N.; Gorelsky, S. I.; Fagnou, K. J. Am. Chem. Soc.
2011, 133, 6449. (b) Tsai, A. S.; Tauchert, M. E.; Bergman, R. G.;
Ellman, J. A. J. Am. Chem. Soc. 2011, 133, 1248. (c) Li, Y.; Li, B.-J.;
Wang, W.-H.; Huang, W.-P.; Zhang, X.-S.; Chen, K.; Shi, Z.-J. Angew.
Chem., Int. Ed. 2011, 50, 2115. (d) Gong, T.-J.; Xiao, B.; Liu, Z.-J.; Wan,
J.; Xu, J.; Luo, D.-F.; Fu, Y.; Liu, L. Org. Lett. 2011, 13, 3235. (e) Park,
S. H.; Kim, J. Y.; Chang, S. Org. Lett. 2011, 13, 2372.
(10) (a) Wang, F.; Song, G.; Li, X. Org. Lett. 2010, 12, 5430. (b)
Wang, F.; Song, G.; Du, Z.; Li, X. J. Org. Chem. 2011, 76, 2926. (c)
Chen, J.; Song, G.; Pan, C.-L.; Li, X. Org. Lett. 2010, 12, 5426.
(11) Tsai, A. S.; Brasse, M.; Bergman, R. G.; Ellman, J. A. Org. Lett.
2011, 13, 540.
(12) (a) Dai, H.-X.; Stepan, A. F.; Plummer, M. S.; Zhang, Y.-H.;
Yu, J.-Q. J. Am. Chem. Soc. 2011, 133, 7222. (b) Youn, S. W.; Bihn, J. H.;
Kim, B. S. Org. Lett. 2011, 13, 3738. (c) Miura, M.; Tsuda, T.; Pivsa-Art,
S.; Nomura, M. J. Org. Chem. 1998, 63, 5211.
(13) (a) Zhu, C.; Falck, J. R. Org. Lett. 2011, 13, 1214. (b) Li, J.-J.;
Mei, T.-S.; Yu, J.-Q. Angew. Chem., Int. Ed. 2008, 47, 6452. (c) Lu, Y.;
Wang, D.-H.; Engle, K. M.; Yu, J.-Q. J. Am. Chem. Soc. 2010, 132, 5916.
(d) Willwacher, J.; Rakshit, S.; Glorius, F. Org. Biomol. Chem. 2011, 9,
4736.
a Conditions: sulfonamide (0.5 mmol), alkene (0.75 mmol),
[RhCp*Cl2]2 (0.0125 mmol), Cu(OAc)2 (1.05 mmol), DMF (3 mL),
100 °C, 16 h, under N2, isolated yield. b 2a = benzyl acrylate, 2b =
n-butyl acrylate, 2c = tert-butyl acrylate, 2d = acrylonitrile, 2e =
1-penten-3-one. c Conditions: sulfonamide (0.5 mmol), alkene (1.5 mmol),
[RhCp*Cl2]2 (0.0125 mmol), Cu(OAc)2 (2.1 mmol), DMF (3 mL), 100 °C,
18 h, under N2, isolated yield.
(14) (a) Kim, B. S.; Jang, C.; Lee, D. J.; Youn, S. W. Chem. Asian J.
2010, 5, 2336. (b) Mochida, S.; Shimizu, M.; Hirano, K.; Satoh, T.;
Miura, M. Chem. Asian J. 2010, 5, 847. (c) Chen, X.; Li, J.-J.; Hao, X.-S.;
Goodhue, C. E.; Yu, J.-Q. J. Am. Chem. Soc. 2006, 128, 78. (d) Kaım,
¨
With these optimized conditions in hand, we first ex-
amined the scope of activated olefins in their coupling with
N-(1-naphthyl)sulfonamides (Scheme 1). Several acrylates
L. E.; Gamez-Montano, R.; Grimaud, L.; Ibarra-Riverab, T. Chem.
Commun. 2008, 1350. (e) Harayama, T.; Sato, T.; Hori, A.; Abeand, H.;
Takeuchi, Y. Synthesis 2004, 9, 1446.
Org. Lett., Vol. 13, No. 21, 2011
5809

Given the proximity of the sulfonamide NH group and
the olefin unit in products 4, we reasoned that allylic olefin
products could potentially undergo further intramolecular
oxidative amidation via formal allylic CÀH activation.13a
In order to validate this possibility, an excess of Cu(OAc)2
(4.1 equiv) was applied to the coupling of a 4-bromo
substituted sulfonamide (1b) and 4-methyl-1-pentene. In-
deed, the expected 2-fold oxidative coupling product (6)
was isolated in 52% yield (eq 2), together with the direct
olefination product 4h (18%). Alternatively, 6 could also
beobtainedwhen4hwassubjectedtothestandardreaction
conditions, suggesting that 4h is an intermediate in the
formation of 6.
Scheme 2. Olefination Using Unactivated Alkenesa
a Conditions: sulfonamide (0.5 mmol), alkene (0.75 mmol), [RhCp*-
Cl2]2 (0.125 mmol), Cu(OAc)2 (1.05 mmol), DMF (3 mL), 100 °C, 16 h,
under N2, isolated yield.
The generality of this formal allylic CÀH oxidation
follows from the coupling of allylbenzenes and 1a. The
reaction of allylbenzenes and 1a under the same conditions
afforded 7a,b in high yield, with no direct olefination
product being isolable (Scheme 3). When allyl acetate
was employed, product 8 was isolated in 89% yield.
Formation of related terminal olefins starting from allyl
acetate has been reported.11,16
Scheme 3. Olefination Using Allylic Olefins
Surprisingly, when we attempted to carry out the reac-
tion of 1a and tert-butyl acrylate (2 equiv) under aerobic
conditions (O2 (1 atm) and Cu(OAc)2 (20 mol %)) (eq 1),
no olefination product such as 3ac was detected. Instead, a
formal oxidative carbonylation reaction occurred. On the
basis of NMR, IR spectroscopy, and mass spectrometry,
the product 5a was determined as a lactam. In particular,
the carbonyl carbon resonates characteristically at δ 165.1
in the 13C NMR spectrum (CDCl3), and a characteristic IR
signal was alsodetected (1747cmÀ1). Thus products5a, 5b,
and 5e were isolated in 50À54% yield under these unopti-
mized conditions. Our preliminary studies indicated that
the Cu(OAc)2 co-oxidant is necessary, and using a smaller
amount of tert-butyl acrylate resulted in lower efficiency.
Using n-butyl acrylate also resulted in lower yield. When
DMA was used as a solvent for the reaction of 1a under the
same conditions (tert-butyl acrylate), 5a was also isolated
albeit at a lower yield. Although the carbonyl likely
originates from DMF, no solid conclusion on the role of
tert-butyl acrylate can be drawn at this stage.15
To explore the mechanism of this transformation, a
stoichiometric reaction between 1b and [RhCp*Cl2]2 has
been carried out in the presence of an access of NaOAc
(25 °C). NMR analysis of the reaction product 9 indicated
that the coordination sphere of the rhodium complex include
a Cp* ring, a sulfonamidate, and an acetate (eq 3).
Although the sixth coordination site and identity of 9
cannot be unambiguously established, IR spectroscopy
suggested that the acetate likely adopts the η2 binding
mode in the sold state (no intense absorption in the range
(15) Even though 5a was also obtained using DMA as a solvent, no
solid conclusion on the souce of carbonyl group of 5a can be drawn. For
example, Jiao recently reported that both DMF and DMA can be the
souce of a cyanide group in the reaction with indole, where the CN group
originates mainly from the NMe2 group. See: (a) Ding, S.; Jiao, N. J. Am.
Chem. Soc. 2011, 133, 12374. (b) Kim, J.; Chang, S. J. Am. Chem. Soc.
2010, 132, 10272. Labeling experiments are underway.
(16) (a) Lautens, M.; Tayama, E.; Herse, C. J. Am. Chem. Soc. 2005,
127, 72. (b) Steinig, A. G.; de Meijere, A. Eur. J. Org. Chem. 1999, 1333.
(c) Menard, F.; Perez, D.; Roman, D. S.; Chapman, T. M.; Lautens, M.
J. Org. Chem. 2010, 75, 4056. (d) Mariampillai, B.; Herse, C.; Lautens,
M. Org. Lett. 2005, 7, 4745.
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Org. Lett., Vol. 13, No. 21, 2011

of 1600À2100 cmÀ1). Subjection of 9 (4 mol %) to the
coupling of 1a and tert-butyl acrylate under the standard
conditions afforded product 3ac in comparably high yield
(86%), suggesting that 9 could be an active intermediate in
this catalytic process. In addition, migratory insertion of
Rh-bound amido groups to olefins has been reported.17
were isolated in moderate yields. Despite the lower cataly-
tic efficiency, these products are complementary to those
obtained from sulfonamides. The absence of any further
aza-Michael reaction might be ascribed to both electronic
and steric effects. Electronically, the NH proton is less
acidic in products 10aÀc, and previous reports seem to
indicate that acidic OH and NH groupstend to add to
activated olefins.7a,b,10a Sterically, the bulky tBu group in
the amide renders the NH group less accessible.
A plausible pathway for the formation of 7 is given in
Scheme 4. Rhodation at the peri position (A) followed by
insertion of the olefin affords a rhodium(III) alkyl species
(B). Subsequent β-hydrogen elimination generates the
direct olefination intermediate (C). This intermediate is
proposed to undergo allylic CÀH activation, leading to
anη3-allyl species (D) followed by nucleophilic CÀN bond
formation.18 Formation of 8 starting from 1a and ally
acetate may likely follow the β-oxygen elimination of B
that is generated after allyl acetate insertion, and olefin E is
thus a likely intermediate.11,16
Insummary, wehavesuccessfullyachieved the rhodium-
(III)-catalyzed oxidative olefination of N-(1-naphthyl)-
sulfonamides at the peri position. This coupling process
proceeded under simple conditions in high selectivity and
high efficiency. Three categories of olefins have been success-
fully applied. Activated olefins reacted to afford new five-
membered azacycles as a result of oxidative olefination-
hydroamination sequence. Unactivated olefins coupled
smoothly with N-(1-naphthyl)sulfonamides to afford the
direct olefination product, which could undergo further intra-
molecular oxidative allylicamidation. 2-fold oxidation was
successfully achieved for allylic olefins such as allylbenzene
and allyl acetate. In contrast, although N-(1-naphthyl)-
pivalamide also coupled with acrylate esters, only the
direct olefination products were isolated. Thus, by intro-
ducing an appropriate directing group, CÀH activation
and oxidative functionalization using unactivated as well
as activated terminal olefins can be achieved in high yield
and high selectivity. Given the wide scope of substrates and
cleavability of sulfonamide NÀS and carboxamide NÀC
bonds in the coupled products, the current reactions are
likely to find important synthetic utility. Studies on the
mechanistic details of the CÀH activation and of the
oxidative carbonylation are currently underway in our
laboratory.
Scheme 4. Possible Mechanisms of the Formation of 7 and 8
The scope of amide substrates was successfully extended
to a pivalamide (eq 4). Although unactivated olefins are
not appliable, acrylates did couple with this pivalamide
under modified conditions in MeCN ([RhCp*Cl2]2 (4mol%)
and Ag2CO3 (2.1 equiv). Thus, olefination products 10aÀc
Acknowledgment. This work was supported by the
Dalian Institute of Chemical Physics, Chinese Academy
of Sciences.
(17) Zhao, P.; Krug, C.; Hartwig, J. F. J. Am. Chem. Soc. 2005, 127,
12066.
(18) An alternative mechanism of Wacker-type amidation followed
by β-hydrogen elimination is also possible (see ref 10b).
Supporting Information Available. Synthetic proce-
dures, characterization data, and NMR spectra of all
coupled products. This material is available free of charge
via the Internet at http://pubs.acs.org.
Org. Lett., Vol. 13, No. 21, 2011
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