Rhodium(III)-catalyzed dehydrogenative Heck reaction of salicylaldehydes

Article abstract of DOI:10.1002/anie.201203224

Your CHOice! An efficient Rh^III-catalyzed dehydrogenative Heck reaction (DHR) of salicylaldehydes with different classes of olefins extends the oxidative Heck reaction to aldehyde C-H bonds. Several structural motifs similar to natural products and bioactive molecules such as aurones, flavones, 2'-hydroxychalcones, and flavanones could be efficiently produced. Initial mechanistic studies give insight into the reaction mechanism. Copyright

Full text of DOI:10.1002/anie.201203224

Angewandte
Chemie
DOI: 10.1002/anie.201203224
À
C H Functionalization
Rhodium(III)-Catalyzed Dehydrogenative Heck Reaction of
Salicylaldehydes**
Zhuangzhi Shi, Nils Schrçder, and Frank Glorius*
Dedicated to Professor Hans J. Schꢀfer on the occasion of his 75th birthday
The transition-metal-catalyzed Mizoroki–Heck reaction is
À
one of the most popular and powerful tools for C C bond
formation and offers a straightforward approach for the
construction of olefination products.[1] Three kinds of sub-
strates are typically utilized as the coupling partner for the
olefin in this reaction: aryl halides or pseudohalides, organ-
ometallic reagents, and non-preactivated (hetero)arenes. In
terms of atom economy the third type of substrate is the most
attractive. Initial studies on the PdII-catalyzed dehydrogen-
ative Heck reaction[2] (DHR) of benzene with styrene were
reported by Fujiwara and Moritani.[3] Compared with the
traditional Mizoroki–Heck reaction, this method faces three
fundamental challenges: 1) how to expand the scope of
substrates; 2) how to control positional selectivity in mole-
À
cules that contain diverse C H bonds; and 3) how to make
the reaction mild and efficient and, thus, applicable in
synthesis.
catalyzed carbonylative Heck reaction of halides,[10] this
methodology affords another way to complete the Heck
Much effort has been devoted to solving these problems
and significant improvements have been made in recent
reaction on carbonyl groups.[11] Most importantly, it provides
access to the structural motifs of valuable natural products
and bioactive molecules such as aurone,[12] flavone,[13] 2’-
hydroxychalcone,[14] and flavanone[15] (Scheme 1).
years.[4] Yu et al. have developed DHR reactions for unac-
3
À
À
tivated C(sp ) H bonds, electron-deficient aryl C H bonds,
and remote C(sp ) H bonds. In 2010, the same group
developed an unprecedented cascade reaction consisting of
a Pd -catalyzed alcohol-directed aryl C H olefination and an
2
[5]
À
II
À
oxidative intramolecular cyclization which afforded pyran
products in the presence of amino acid ligands [Eq. (1)].[5b]
Recently, Satoh and Miura et al.,[6] other groups,[7] and we[8]
have shown that {RhIIICp*} complexes[9] catalyzed the DHR
of substrates including acetanilides, benzhydroxamic acids,
benzoic acids, phenol carbamates, and ketones, and olefins.
We report herein on a RhIII-catalyzed regioselective DHR
Scheme 1. Structures of biologically active natural products.
À
À
of aldehyde C H bonds with different classes of olefins
The selective functionalization of aldehyde C H bonds
[Eq. (2)]. In combination with a recent report on the PdII-
has been quite an active research area.[16] To date, there have
been two main strategies for the direct functionalization of
À
aldehyde C H bonds with olefins: 1) oxidative addition of
[*] Dr. Z. Shi, N. Schrçder, Prof. Dr. F. Glorius
Universitꢀt Mꢁnster, Organisch-Chemisches Institut
Corrensstrasse 40, 48149 Mꢁnster (Germany)
E-mail: glorius@uni-muenster.de
low-valent transition-metal complexes (especially RhI cata-
[17]
À
lysts) to aldehyde C H bonds and 2) umpolung of alde-
hydes with N-heterocyclic carbenes (NHCs).[18] In the context
À
Homepage: http://www.uni-muenster.de/Chemie.oc/glorius/
index.html
of either of these methods, aldehyde C H bonds can add to
=
C C bonds yielding ketone derivatives by hydroacylation.
[**] We thank Dr. Matthew Hopkinson and Dr. Honggen Wang for
helpful discussions. This work was supported by the Alexander von
Humboldt Foundation (Z.S.). Generous financial support by the
DFG (IRTG Mꢁnster–Nagoya) and by the European Research
Council under the European Community’s Seventh Framework
Program (FP7 2007–2013)/ERC grant agreement no. 25936 is
gratefully acknowledged.
À
However, extending the DHR to aldehyde C H bonds
remains undeveloped, with no examples reported to date.
Satoh and Miura demonstrated the Rh-catalyzed oxidative
coupling between salicylaldehydes and internal alkynes,
À
involving the cleavage of the aldehyde C H bond and
producing chromone derivatives.[6f] Inspired by this work,
we envisioned that salicylaldehydes should be a suitable class
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201203224.
À
of substrates to achieve DHR with aldehyde C H bonds.
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!

.
Angewandte
Communications
With this hypothesis in mind, we selected salicylaldehyde
(1a) and ethyl acrylate (2a) as substrates and Cu(OAc)2 as
the oxidant in tert-amyl alcohol as the solvent at a reaction
temperature of 1208C. In our initial studies, the efficiency of
several catalysts like [{RuCl2(p-cymene)}2], [Cp*Rh-
(CH3CN)3](SbF6)2, and [(Cp*RhCl2)2] was tested (see the
Supporting Information). Interestingly, the cyclization prod-
uct 3aa was produced in 23% yield in the presence of the
latter catalyst; this product may result from DHR of the
desired products using these olefins. Electron-donating
groups such as methoxy (1c), ethoxy (1d), and methylthio
(1e) as well as electron-withdrawing groups such as carbox-
ylate (1n) and nitro (1o) were tolerated on the salicylalde-
hyde. In particular, the halogen-containing substrates (1 f–k)
reacted efficiently. Substrates 1l and 1m derived from 1h by
Suzuki and Heck reactions, respectively, are also compatible
with the process. As expected, the naphthaldehyde substrates
1q and 1r and the benzopyran substrate 1s can also be
converted into interesting products (3qa–sa). Interestingly,
when we selected 1t as the substrate, the desired product 3ta
was obtained only in 30% yield. The uncyclized product 4ta,
which was isolated in 28% yield, may act as an intermediate
in this reaction [Eq. (3)]. To prove this hypothesis, we
employed 4ta as the starting material under our standard
reaction conditions and, indeed, observed the formation of
3ta in 40% yield [Eq. (4)].
À
aldehyde C H bond and subsequent intramolecular oxidative
cyclization. Gratifyingly, 3aa was obtained in 48% yield when
we increased the amount of oxidant. The product yield was
increased to 63% when the solvent was changed to DCE.
1,2,3,4-Tetraphenyl-1,3-cyclopentadiene was found to be an
effective ligand,[6f,19] affording 3aa in 76% yield. Under these
conditions, decreasing either the catalyst loading or the
reaction temperature led to lower yields of 3aa.
With a set of optimized conditions in hand, we examined
À
the scope of the DHR of aldehyde C H bonds and the
À
subsequent oxidative cyclization of C O bonds (Scheme 2).
We were pleased to find that electron-deficient olefins such as
butyl acrylate (2b) and methyl vinyl ketone (2c) were also
suitable substrates for this transformation. Furthermore,
a variety of salicylaldehydes could be converted to the
Other olefin substrates such as styrene and ethylene were
also investigated with salicylaldehydes as reaction partners
(Scheme 3). We found that electron-neutral and electron-rich
salicylaldehydes (1a, 1b, and 1d) afforded only olefinated
products without further cyclization even when the amount of
oxidant was increased. The successive oxidative cyclization
was inhibited presumably because styrene is less electrophilic
than ethyl acrylate. The reaction with moderately electron-
poor salicylaldehydes (like 1n) can also produce chalcone
derivatives (4nd) with some flavone-type by-products. Halide
functional groups on either the salicylaldehydes or styrene
were tolerated (4 fd, 4gd, and 4af). The most electron-poor
substrate, 5-nitrosalicylaldehyde, selectively afforded 5od in
44% yield. When Ag2CO3 was used as the oxidant, only
À
flavanone 6ad resulting from DHR of the aldehyde C H
bond and subsequent Michael addition. In addition, when
ethylene gas (5 bar) was used as a substrate only the
hydroacylation product 7bg was obtained in 29% yield.
Lonchocarpin (4sd) and 4-methoxylonchocarpin (4se)
are isolated from Lonchocarpus utilus and L. subglaucescens,
plants found in tropical America, Africa, and the Caribbean
islands. They exhibit a range of biological and pharmacolog-
ical properties including antimutagenic, antimicrobial, anti-
ulcer, and antitumor activities.[20] Compounds 4sd and 4se
could be synthesized using this methodology in just two steps
from commercially available reagents.
Scheme 2. RhIII-catalyzed cyclization of salicylaldehydes and electron-
deficient olefins. General reaction conditions: 1 (0.2 mmol), 2
(0.4 mmol), [(Cp*RhCl2)2] (2.5 mol%), C5H2Ph4 (10 mol%), Cu(OAc)2
(0.8 mmol), DCE (1.0 mL), 1208C, 18 h, under Ar; values in parenthe-
In order to gain insight into the mechanism of the
reaction, we performed parallel experiments with deute-
rium-labeled substrates (see the Supporting Information).
1
ses indicate the Z/E ratios, which were determined by H NMR
À
analysis of the crude products. [a] Reaction temperature 908C.
The kinetic isotope effect (KIE) value for the C H olefina-
2
www.angewandte.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
These are not the final page numbers!

Angewandte
Chemie
Scheme 4. Plausible reaction mechanism.
On the basis of these investigations, a mechanism is
proposed in Scheme 4. Coordination of the 2-hydroxy group
of salicylaldehydes to a RhIIILn species appears to be the key
À
for the selective cleavage of the aldehyde C H bond to afford
A.[6f,22] This rhodacycle can coordinate one equivalent of
alkene to form B, which undergoes alkene insertion giving
intermediate C. Subsequently, b-hydride elimination of C
generates the uncyclized product and a RhIIIH species. This
species can undergo reductive elimination to yield a RhI
complex, which is then reoxidized by CuII to RhIIILn (catalytic
cycle I). If this resulting olefination product contains an
electron-withdrawing group on the alkene (i.e., R2 = COOR,
COR) or the salicylaldehyde (i.e., R1 = NO2), a subsequent
alkoxyrhodation cyclization will take place by a 5-exo or 6-
endo-trig pathway generating E or E’. Similar to Yuꢀs work,[5b]
we observed the Z-type product,[23] which means this cycliza-
tion process proceeds by anti addition and then syn-b-hydride
elimination to afford the oxidized cyclization product and the
RhIIIH species. In the presence of another two equivalents of
Cu(OAc)2, the resulting RhI species can transfer to the
catalytically active RhIIILn (catalytic cycle II).
À
Scheme 3. C H olefination of salicylaldehydes with other olefins.
General reaction conditions: 1 (0.2 mmol), 2 (0.4 mmol), [(Cp*RhCl2)2]
(2.5 mol%), C5H2Ph4 (10 mol%), Cu(OAc)2 (0.4 mmol), DCE (1.0 mL),
1208C, 18 h, under Ar. [a] Determined by 1H NMR analysis of crude
products. [b] 4.0 equiv Cu(OAc)2 was used. [c] 2.0 equiv Ag2CO3 was
used as oxidant instead of Cu(OAc)2. [d] Ethylene atmosphere (5 bar).
tion of 1a with ethyl acrylate 2a and styrene 2d were 1.3 and
À
1.2, respectively, suggesting that the C H cleavage is fast and
not involved in the rate-determining step.[21] When the
simpler benzaldehyde (1u) was utilized as the substrate, the
corresponding chalcone was not formed [Eq. (5)]. 2-Methox-
ybenzaldehyde (1v) underwent DHR only at the CHO-
À
directed ortho aromatic C H bond [Eq. (6)]. Therefore, the
presence of a hydroxy group in the substrate was critical in
triggering the initial C H bond-functionalization event.
Meanwhile, when imine 1w was subjected to the standard
reaction conditions, no desired products were observed, thus
indicating the important role of the carbonyl group for this
transformation [Eq. (7)].
À
In summary, we have developed a catalytic DHR with
À
aldehyde C H bonds, complementing the Heck reaction on
carbonyl substrates. This methodology is attractive because
the starting materials are readily available and the products
are valuable. Moreover, we have applied this methodology to
the synthesis of lonchocarpin and 4-methoxylonchocarpin,
showing the practicality and value of this method.
Received: April 26, 2012
Published online: && &&, &&&&
À
Keywords: C H functionalization ·
dehydrogenative Heck reaction · heterocycles · rhodium ·
salicylaldehydes
.
[1] S. Brꢁse, A. de Meijere, Metal-Catalyzed Cross-Coupling
Reactions (Eds.: A. de Meijere, F. Diederich), Wiley-VCH,
New York, 2004, Chap. 5.
[2] a) J. Le Bras, J. Muzart, Chem. Rev. 2011, 111, 1170; b) E. M.
Ferreira, H. Zhang, B. M. Stoltz, Tetrahedron 2008, 64, 5987.
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3
These are not the final page numbers!

.
Angewandte
Communications
[3] a) I. Moritani, Y. Fujiwara, Tetrahedron Lett. 1967, 8, 1119; b) Y.
Fujiwara, I. Moritani, M. Matsuda, S. Teranishi, Tetrahedron
Lett. 1968, 9, 3863.
ange.201203792; Angew. Chem. Int. Ed. 2012, DOI: 10.1002/
anie.201203792.
À
[9] For reviews of rhodium (III)-catalyzed oxidative C H function-
[4] Recent examples of palladium (II)-catalyzed DHR: a) N. P.
Grimster, C. Gauntlett, C. R. A. Godfrey, M. J. Gaunt, Angew.
Chem. 2005, 117, 3185; Angew. Chem. Int. Ed. 2005, 44, 3125;
b) E. M. Beck, N. P. Grimster, R. Hatley, M. J. Gaunt, J. Am.
Chem. Soc. 2006, 128, 2528; c) G. Cai, Y. Fu, Y. Li, X. Wan, Z.
Shi, J. Am. Chem. Soc. 2007, 129, 7666; d) E. M. Beck, R. Hatley,
M. J. Gaunt, Angew. Chem. 2008, 120, 3046; Angew. Chem. Int.
Ed. 2008, 47, 3004; e) A. Garcꢂa-Rubia, R. G. Arrayꢃs, J. C.
Carretero, Angew. Chem. 2009, 121, 6633; Angew. Chem. Int. Ed.
2009, 48, 6511; f) C. Aouf, E. Thiery, J. Bras, J. Muzart, Org. Lett.
2009, 11, 4096; g) Y. Yang, K. Cheng, Y. Zhang, Org. Lett. 2009,
11, 5606; h) H. Jiang, Z. Feng, A. Wang, X. Liu, Z. Chen, Eur. J.
Org. Chem. 2010, 1227; i) J. Wu, X. Cui, L. Chen, G. Jiang, Y. Wu,
J. Am. Chem. Soc. 2009, 131, 13888; ruthenium(II)-catalyzed
DHR: j) K. Padala, J. Masilamani, Org. Lett. 2012, 14, 1134;
k) L. Ackermann, L. Wang, R. Wolfram, A. V. Lygin, Org. Lett.
2012, 14, 728; l) B. Li, J. Ma, N. Wang, H. Feng, S. Xu, B. Wang,
Org. Lett. 2012, 14, 736; m) K. Padala, M. Jeganmohan, Org.
Lett. 2011, 13, 6144; n) L. Ackermann, J. Pospech, Org. Lett.
2011, 13, 4153; o) T. Ueyama, S. Mochida, T. Fukutani, K.
Hirano, T. Satoh, M. Miura, Org. Lett. 2011, 13, 706.
[5] a) D.-H. Wang, K. M. Engle, B.-F. Shi, J.-Q. Yu, Science 2010,
327, 315; b) Y. Lu, D.-H. Wang, K. M. Engle, J-.Q. Yu, J. Am.
Chem. Soc. 2010, 132, 5916; c) M. Ye, G.-L. Gao, J.-Q. Yu, J. Am.
Chem. Soc. 2011, 133, 6964; d) D.-H. Wang, J.-Q. Yu, J. Am.
Chem. Soc. 2011, 133, 5767; e) K. M. Engle, D.-H. Wang, J.-Q.
Yu, J. Am. Chem. Soc. 2010, 132, 14137; f) K. M. Engle, D.-H.
Wang, J.-Q. Yu, Angew. Chem. 2010, 122, 6305; Angew. Chem.
Int. Ed. 2010, 49, 6169; g) M. Wasa, K. M. Engle, J-.Q. Yu, J. Am.
Chem. Soc. 2010, 132, 3680; h) B.-F. Shi, Y.-H. Zhang, J. K. Lam,
D.-H. Wang, J-.Q. Yu, J. Am. Chem. Soc. 2010, 132, 460; i) Y.-H.
Zhang, B.-F. Shi, J.-Q. Yu, J. Am. Chem. Soc. 2009, 131, 5072.
[6] a) N. Umeda, K. Hirano, T. Satoh, M. Miura, J. Org. Chem. 2009,
74, 7094; b) M. Miura, T. Tsuda, T. Satoh, S. Pivsa-Art, M.
Nomura, J. Org. Chem. 1998, 63, 5211; c) K. Ueura, T. Satoh, M.
Miura, Org. Lett. 2007, 9, 1407; d) K. Ueura, T. Satoh, M. Miura,
J. Org. Chem. 2007, 72, 5362; e) K. Morimoto, K. Hirano, T.
Satoh, M. Miura, Org. Lett. 2010, 12, 2068. See also: f) M.
Shimizu, H. Tsurugi, T. Satoh, M. Miura, Chem. Asian J. 2008, 3,
881.
alization: a) T. Satoh, M. Miura, Chem. Eur. J. 2010, 16, 11212;
b) G. Song, F. Wang, X. Li, Chem. Soc. Rev. 2012, 41, 3651;
c) F. W. Patureau, J. Wencel-Delord, F. Glorius, Aldrichimica
Acta 2012, 45, 31.
[10] a) X.-F. Wu, H. Jiao, H. Neumann, M. Beller, ChemCatChem
2011, 3, 726; b) X.-F. Wu, H. Neumann, A. Spanenberg, T.
Schulz, H. Jiao, M. Beller, J. Am. Chem. Soc. 2010, 132, 14596;
c) P. Hermange, T. M. Gøgsig, A. T. Lindhardt, R. H. Taaning, T.
Skrydstrup, Org. Lett. 2011, 13, 2444; d) K. S. Bloome, E. J.
Alexanian, J. Am. Chem. Soc. 2010, 132, 12823.
[11] An earlier work on palladium-catalyzed Heck reactions of
benzoyl chloride with olefins: C. Andersson, A. Hallberg, J. Org.
Chem. 1988, 53, 4257.
[12] T. Nakayama, J. Biosci. Bioeng. 2002, 94, 487.
[13] a) E. Azzini, R. Bugianesi, F. Romano, D. Venere, S. Miccadei,
A. Durazzo, M. S. Foddai, G. Catasta, V. Linsalata, G. Maiani,
Br. J. Nutr. 2007, 97, 963; b) U. Justesen, P. Knuthsen, T. Leth, J.
Chromatogr. A 1998, 799, 101; c) H. Sakakibara, Y. Honda, S.
Nakagawa, H. Ashida, K. Kanazawa, J. Agric. Food Chem. 2003,
51, 571.
[14] B. Madan, S. Batra, B. Ghosh, Mol. Pharmacol. 2000, 58, 526.
[15] J. J. Peterson, J. T. Dwyer, G. R. Beecher, S. A. Bhagwat, S. E.
Gebhardt, D. B. Haytowitz, J. M. Holden, J. Food Compos. Anal.
2006, 19, S66.
[16] Some recent examples of the selective metal-catalyzed function-
À
alization of aldehyde C H bonds: a) S. K. Murphy, M. M.
Coulter, V. M. Dong, Chem. Sci. 2012, 3, 355; b) H. A. Khan,
K. G. M. Kou, V. M. Dong, Chem. Sci. 2011, 2, 407; c) M. M.
Coulter, K. G. M. Kou, B. Galligan, V. M. Dong, J. Am. Chem.
Soc. 2010, 132, 16330; d) D. H. T. Phan, K. G. M. Kou, V. M.
Dong, J. Am. Chem. Soc. 2010, 132, 16354; e) B.-X. Tang, R.-J.
Song, C.-Y. Wu, Y. Liu, M.-B. Zhou, W.-T. Wei, G.-B. Deng, D.-L.
Yin, J.-H. Li, J. Am. Chem. Soc. 2010, 132, 8900; f) D. Crꢄpin, J.
Dawick, C. Aꢅssa, Angew. Chem. 2010, 122, 630; Angew. Chem.
Int. Ed. 2010, 49, 620; g) J. D. Osborne, H. E. Randell-Sly, G. S.
Currie, A. R. Cowley, M. C. Willis, J. Am. Chem. Soc. 2008, 130,
17232; h) P. ꢆlvarez-Bercedo, A. Flores-Gaspar, A. Correa, R.
Martin, J. Am. Chem. Soc. 2010, 132, 466.
[17] a) G. C. Fu in Modern Rhodium-Catalyzed Reactions (Ed.: P. A.
Evans), Wiley-VCH, New York, 2005, pp. 79 – 91; b) M. C.
Willis, Chem. Rev. 2010, 110, 725.
[7] a) S. H. Park, J. Y. Kim, S. Chang, Org. Lett. 2011, 13, 2372; b) T.-
J. Gong, B. Xiao, Z.-J. Liu, J. Wan, J. Xu, D.-F. Luo, Y. Fu, L. Liu,
Org. Lett. 2011, 13, 3235; c) C. Feng, T.-P. Loh, Chem. Commun.
2011, 47, 10458; d) F. Wang, G. Song, X. Li, Org. Lett. 2010, 12,
5430; e) Y. Su, M. Zhao, K. Han, G. Song, X. Li, Org. Lett. 2010,
12, 5462; f) F. Wang, G. Song, Z. Du, X. Li, J. Org. Chem. 2011,
76, 2926; g) C. Zhu, J. Falck, Chem. Commun. 2012, 48, 1674;
h) J. Chen, G. Song, C.-L. Pan, X. Li, Org. Lett. 2010, 12, 5426.
[8] a) F. Patureau, F. Glorius, J. Am. Chem. Soc. 2010, 132, 9982;
b) S. Rakshit, C. Grohmann, T. Besset, F. Glorius, J. Am. Chem.
Soc. 2011, 133, 2350; c) T. Besset, N. Kuhl, F. Patureau, F.
Glorius, Chem. Eur. J. 2011, 17, 7167; d) F. Patureau, T. Besset, F.
Glorius, Angew. Chem. 2011, 123, 1096; Angew. Chem. Int. Ed.
2011, 50, 1064; e) F. Patureau, C. Nimphius, F. Glorius, Org. Lett.
2011, 13, 6346; f) N. Schrçder, T. Besset, F. Glorius, Adv. Synth.
Catal. 2012, 354, 579; See also: g) J. Wencel-Delord, C.
Nimphius, F. W. Patureau, F. Glorius, Angew. Chem. 2012, 124,
2290; Angew. Chem. Int. Ed. 2012, 51, 2247; h) J. Wencel-Delord,
C. Nimphius, F. W. Patureau, F. Glorius, Chem. Asian J. 2012, 7,
1208; i) C. Grohmann, H. Wang, F. Glorius, Org. Lett. 2012, 14,
656; j) F. W. Patureau, T. Besset, N. Kuhl, F. Glorius, J. Am.
Chem. Soc. 2011, 133, 2154; k) S. Rakshit, F. W. Patureau, F.
Glorius, J. Am. Chem. Soc. 2010, 132, 9585; l) N. Kuhl, M. N.
Hopkinson, F. Glorius, Angew. Chem. 2012, DOI: 10.1002/
[18] a) D. Enders, O. Niemeier, A. Henseler, Chem. Rev. 2007, 107,
5606; b) V. Nair, S. Vellalth, B. P. Babu, Chem. Soc. Rev. 2008, 37,
2691; c) J. L. Moore, T. Rovis, Top. Curr. Chem. 2009, 291, 77;
d) A. T. Biju, N. Kuhl, F. Glorius, Acc. Chem. Res. 2011, 44, 1182;
e) P.-C. Chiang, J. W. Bode, TCI MAIL 2011, 149, 2; f) K. A.
Scheidt, D. T. Cohen, Chem. Sci. 2012, 3, 53; g) X. Bugaut, F.
Glorius, Chem. Soc. Rev. 2012, 41, 3511.
[19] This bulky Cp ligand can improve the reactivity; a) N. Umeda,
H. Tsurugi, T. Satoh, M. Miura, Angew. Chem. 2008, 120, 4083;
Angew. Chem. Int. Ed. 2008, 47, 4019; b) T. K. Hyster, T. Rovis,
Chem. Commun. 2011, 47, 11846; c) T. K. Hyster, T. Rovis,
Chem. Sci. 2011, 2, 1606.
[20] K. Nicolaou, J. Pfefferkorn, G.-Q. Cao, Angew. Chem. 2000, 112,
750; Angew. Chem. Int. Ed. 2000, 39, 734.
[21] a) W. Jones, Acc. Chem. Res. 2003, 36, 140; b) E. Simmons, J.
Hartwig, Angew. Chem. 2012, 124, 3120; Angew. Chem. Int. Ed.
2012, 51, 3066.
[22] The coordination mode of the hydroxy group to an RhIIILn
species is still unclear. Miura et al. proposed that the phenolic
oxygen atom in salicylaldehyde coordinates with the RhIII
species as an anionic ligand: a) K. Kokubo, K. Matsumasa, M.
Miura, M. Nomura, J. Org. Chem. 1997, 62, 4564; b) K. Kokubo,
K. Matsumasa, Y. Nishinaka, M. Miura, M. Nomura, Bull. Chem.
4
www.angewandte.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
These are not the final page numbers!

Angewandte
Chemie
Soc. Jpn. 1999, 72, 303; Liu et al. obtained clear evidence by X-
ray structure analysis of an intermedate in a PdII-catalyzed
reaction that the phenol group coordinated as a neutral ligand:
c) B. Xiao, T.-J. Gong, Z.-J. Liu, J.-H. Liu, D.-F. Luo, J. Xu, L.
Liu, J. Am. Chem. Soc. 2011, 133, 9250. In Scheme 4 we depict
the phenol group coordinated with RhIII as a neutral s donor;
however, anionic coordination cannot be ruled out at present
stage.
[23] We found that Z-type products can isomerize to E-type ones at
room temperature. For example (Z)-3pa:
Thus, the small amounts of the E isomer might arise from this
equilibrium rather than from b-hydride elimination.
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

.
Angewandte
Communications
Communications
À
C H Functionalization
Z. Shi, N. Schrçder,
F. Glorius*
&&&& — &&&&
Rhodium(III)-Catalyzed Dehydrogenative
Heck Reaction of Salicylaldehydes
Your CHOice! An efficient RhIII-catalyzed
dehydrogenative Heck reaction (DHR) of
salicylaldehydes with different classes of
olefins extends the oxidative Heck reac-
ucts and bioactive molecules such as
aurones, flavones, 2’-hydroxychalcones,
and flavanones could be efficiently pro-
duced. Initial mechanistic studies give
insight into the reaction mechanism.
À
tion to aldehyde C H bonds. Several
structural motifs similar to natural prod-
6
www.angewandte.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
These are not the final page numbers!