Synthesis of Phosphabenzenes by an Iron-Catalyzed [2+2+2] Cycloaddition Reaction of Diynes with Phosphaalkynes

Article abstract of DOI:10.1002/anie.201502531

A method for the synthesis of phosphabenzenes under iron catalysis is described. Thus, the FeI₂-catalyzed [2+2+2] cycloaddition of diynes with phosphaalkynes in m-xylene gave a variety of phosphabenzenes in good to high yields (up to 87 % yield

Full text of DOI:10.1002/anie.201502531

Angewandte
Chemie
International Edition: DOI: 10.1002/anie.201502531
German Edition: DOI: 10.1002/ange.201502531
Synthetic Methods
Synthesis of Phosphabenzenes by an Iron-Catalyzed [2+2+2]
Cycloaddition Reaction of Diynes with Phosphaalkynes**
Kazunari Nakajima, Shohei Takata, Ken Sakata,* and Yoshiaki Nishibayashi*
Abstract: A method for the synthesis of phosphabenzenes
under iron catalysis is described. Thus, the FeI2-catalyzed
[2+2+2] cycloaddition of diynes with phosphaalkynes in
m-xylene gave a variety of phosphabenzenes in good to high
Scheme 1. Strategy for the synthesis of phosphabenzenes by a transi-
tion-metal-catalyzed [2+2+2] cycloaddition reaction.
yields (up to 87% yield).
T
he development of novel methods for the construction of
aromatic rings is important in enabling access to new drugs,
materials, and other useful molecules.[1] In sharp contrast to
benzenes and pyridines, which have been synthesized by
a broad range of organic reactions, the synthesis of phospha-
benzenes has received relatively little attention.[2–6] Phospha-
benzenes are attractive motifs as heavier-atom-containing
benzene analogues, and have been utilized as ligands for
transition-metal complexes.[2,3] Since the first synthesis of
phosphabenzenes by the treatment of pyrylium salts with
phosphine equivalents,[4] a number of other synthetic methods
have been investigated.[2,5,6] However, to the best of our
knowledge, no transition-metal-catalyzed reactions have been
reported for the synthesis of phosphabenzenes.
At first, we carried out reactions of 4,4-bis(ethoxycarbo-
nyl)hepta-1,6-diyne (1a) with 1-adamantylphosphaethyne
(2a) in the presence of a variety of transition-metal com-
plexes, such as cobalt, nickel, ruthenium, rhodium, and
iridium complexes, which were previously reported to func-
tion as effective catalysts of various [2+2+2] cycloaddition
reactions.[7] Unfortunately, these transition-metal complexes
did not act as effective catalysts (see Table S1 in the
Supporting Information for details). However, when FeI2
was used as a catalyst in toluene at 908C for 18 h, the desired
phosphabenzene 3a was obtained in 60% yield (Scheme 2).
This result prompted us to investigate the iron-catalyzed
reaction in detail.
Transition-metal-catalyzed [2+2+2] cycloaddition has
been studied extensively as a powerful strategy for the
selective preparation of benzenes and pyridines.[7] Recently,
a variety of transition-metal catalysts have been applied to
[2+2+2] cycloaddition reactions of two alkynes with nitriles
to produce pyridines with high selectivity. Against this
background, we envisaged the use of phosphaalkynes[8,9] as
substrates for [2+2+2] cycloaddition reactions catalyzed by
transition-metal complexes as a novel synthetic method
toward phosphabenzenes (Scheme 1). Herein we disclose
our preliminary results on the use of iron-catalyzed[10,11]
[2+2+2] cycloaddition reactions of diynes with phospha-
alkynes to synthesize the corresponding phosphabenzenes in
good to high yields.
Scheme 2. Initial investigation of the transition-metal-catalyzed
[2+2+2] cycloaddition reaction. Ad=adamantyl.
The reaction of 1a with 2a (2 equiv) in the presence of
FeI2 (10 mol%) in m-xylene at 1408C (bath temperature) for
18 h gave 3a in 83% yield (Table 1, entry 1). In this reaction
system, no formation of benzene derivatives by the trimeri-
zation of 1a was observed. The use of FeBr2 and FeCl2 as
catalysts, in place of FeI2, gave 3a in 16 and 17% yield,
respectively (Table 1, entries 2 and 3). No reaction occurred
in the presence of iron(II) trifluoromethanesulfonate (Fe-
(OTf)2; Table 1, entry 4); however, the addition of KI
(20 mol%) led to the formation of 3a (Table 1, entry 5).
These results indicate that the iodide ligand at the iron center
plays an important role in promoting the present reaction.
When o- and p-xylene were used as solvents, 3a was
obtained in slightly lower yield (Table 1, entries 6 and 7). The
reaction did not proceed smoothly in the solvents anisole and
ortho-dichlorobenzene (Table 1, entries 8 and 9). When 1,3-
bis(diphenylphosphino)propane (dppp) and 2,2’-bipyridyl
(bpy) were added as ligands to the iron complex, the yield
of 3a decreased dramatically (Table 1, entries 10 and 11).
Reduced iron complexes generated in situ by the reduction of
[*] Dr. K. Nakajima, S. Takata, Prof. Dr. Y. Nishibayashi
Institute of Engineering Innovation, School of Engineering
The University of Tokyo
Yayoi, Bunkyo-ku, Tokyo, 113-8656 (Japan)
E-mail: ynishiba@sogo.t.u-tokyo.ac.jp
Prof. Dr. K. Sakata
Faculty of Pharmaceutical Sciences, Hoshi University
Ebara, Shinagawa-ku, Tokyo, 142-8501 (Japan)
E-mail: sakata@hoshi.ac.jp
[**] We thank the Japan Society for the Promotion of Science (JSPS) and
the Ministry of Education, Culture, Sports, Science and Technology
of Japan (MEXT) for Grants-in-Aid for Scientific Research (Nos.
26288044, 26620075, 26105708, and 26870120).
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201502351.
Angew. Chem. Int. Ed. 2015, 54, 7597 –7601
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
7597

.
Angewandte
Communications
Table 1: Optimization of the reaction conditions with substrates 1a and
2a.[a]
We investigated the reactions of a variety of diynes 1 with
2a (Table 2). The use of 20 mol% of FeI2 was necessary to
Table 2: Reactions of diynes 1 with 1-adamantylphosphaethyne (2a).[a]
Entry
[Fe]
Additive
Solvent
T
Yield [%][b]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
FeI2
–
–
–
m-xylene
m-xylene
m-xylene
m-xylene
m-xylene
o-xylene
p-xylene
anisole
o-C6H4Cl2
m-xylene
m-xylene
m-xylene
m-xylene
m-xylene
m-xylene
m-xylene
m-xylene
1408C
1408C
1408C
1408C
1408C
1408C
1408C
1408C
1408C
1408C
1408C
1408C
908C
83
16
17
0
50
71
74
0
FeBr2
FeCl2
Fe(OTf)2
Fe(OTf)2
FeI2
FeI2
FeI2
FeI2
FeI2
FeI2
FeI2
FeI2
FeI2
FeI2
FeI2
–
–
KI[c]
–
–
–
–
3
12
0
dppp[c]
bpy[c]
Zn[c]
–
0
64
42
0
80
0
–
–
–
–
608C
RT
1408C
1408C
[c]
[a] Reaction conditions: 1a (0.15 mmol), 2a (0.30 mmol), iron catalyst
(0.015 mmol), solvent (1.5 mL), 18 h. [b] Yield of the isolated product.
[c] 20 mol%. Tf = trifluoromethanesulfonyl.
FeII salts with Zn have been reported to act as efficient
catalysts in iron-catalyzed [2+2+2] cycloaddition reactions.[10-
d,e,11c] However, no reaction took place when Zn was added to
the present reaction system (Table 1, entry 12). As the
reaction temperature was lowered, the product yield
decreased (Table 1, entries 13–15). The use of 20 mol% of
FeI2 did not improve the yield of 3a, but no formation of 3a
was observed at all in the absence of FeI2 (Table 1, entries 16
and 17). These results clearly indicate that FeI2 plays a critical
role in promoting the [2+2+2] cycloaddition of the diyne with
the phosphaalkyne.
The molecular structure of 3a was determined unambig-
uously by X-ray crystallographic analysis (Figure 1). The
bond lengths and angles of the phosphabenzene ring in 3a are
similar to those of phosphabenzene derivatives previously
reported by other research groups.[12]
Figure 1. ORTEP drawing of 3a. Thermal ellipsoids are shown at the
50% probability level. Hydrogen atoms are omitted for clarity. Selected
[a] Reaction conditions: 1 (0.15 mmol), 2a (0.30 mmol), FeI2
(0.030 mmol), m-xylene (1.5 mL), 1408C (bath temperature), 18 h.
[b] Yield of the isolated product. [c] The reaction was carried out at 808C
in toluene. Bn=benzyl, Ts = p-toluenesulfonyl.
À
À
bond lengths [Š] and angles [8]: P1 C1 1.7588(15), C1 C2 1.388(3),
À
À
À
À
C2 C3 1.397(3), C3 C7 1.396(2), C7 C8 1.394(3), P1 C8 1.7159(19);
C1-P1-C8 102.60(8), P1-C1-C2 122.04(13), C1-C2-C3 124.54(14), C2-C3-
C7 123.36(15), C3-C7-C8 122.42(16), P1-C8-C7 124.84(13).
7598
www.angewandte.org
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2015, 54, 7597 –7601

Angewandte
Chemie
obtain the corresponding phosphabenzenes 3 in high yields.[13]
Diynes bearing methyl, n-propyl, n-butyl, and benzyl ester
moieties were successfully converted into the corresponding
phsophabenzenes 3b–e in high yields (Table 2, entries 1–4).
The presence of a phenyl group instead of an ester group in
substrate 1 f enabled the synthesis of 3 f in 51% yield (Table 2,
entry 5). Diynes derived from a b-ketoester (substrate 1g)
and 1,3-diketones (substrates 1h–j) were also applicable, and
the desired phosphabenzenes 3g–j were obtained in good
yields (Table 2, entries 6–9). Phosphabenzenes 3k and 3l
containing ether and sulfonamide moieties were also obtained
in good yields (Table 2, entries 10 and 11). The use of diynes
1m and 1n with an internal alkyne moiety afforded 3m and
3n in only 22 and 26% yield (Table 2, entries 12 and 13), thus
indicating that only diynes with two terminal alkyne moieties
can be transformed into the corresponding phosphabenzenes
in good to high yields. When we used a 1,7-octadiyne
derivative, the corresponding product 3o with a fused six-
membered ring was obtained in 15% yield (Table 2, entry 14).
Unfortunately, when 1,6-heptadiyne and 1,7-octadiyne were
used as substrates, no formation of the corresponding
phosphabenzenes was observed. These results indicate that
the Thorpe–Ingold effect[14] plays an important role in the
present reaction system.
Next, we investigated reactions of 1a with other phos-
phaalkynes 2 as substrates (Table 3). When (3,5-dimethyl-1-
adamantyl)phosphaethyne (2b) was used under the standard
reaction conditions, the corresponding phosphabenzene 3p
was obtained in 63% yield (Table 3, entry 1). The use of
phosphaalkyne 2c bearing a 1-methyl-1-phenylethyl group
gave 3q in 80% yield (Table 3, entry 2). The introduction of
methyl and alkoxy groups on the benzene ring of 2c was also
possible, and the corresponding products 3r–t were obtained
in high yields (Table 3, entries 3–5). The reaction of phos-
phaalkyne 2g bearing a very bulky trityl group gave 3u in
73% yield (Table 3, entry 6). However, trimethylsilylphos-
phaethyne (2h) was not applicable in this reaction system:
only a trace amount of 3v was obtained under the same
reaction conditions (Table 3, entry 7). The decomposition of
2h may occur under the catalytic reaction conditions at
1408C, as 2h has been reported to have low thermal
stability.[15] These results suggest that the use of phosphaal-
kynes bearing a tertiary alkyl group is necessary for the
synthesis of the corresponding phosphabenzenes in the
present reaction system.
To evaluate the thermodynamic nature of the present
reaction, we calculated the Gibbs free energy (DG298K) of the
reactions of 1,6-heptadiyne with phosphaethyne, hydrogen
cyanide, and acetylene at the B3LYP/6-311G** level of theory
(Scheme 3). The reaction free energy for the formation of
Table 3: Reactions of 4,4-bis(ethoxycarbonyl)hepta-1,6-diyne (1a) with
phosphaalkynes 2.[a]
Scheme 3. Calculated reaction free energies (B3LYP/6-311G**).
phosphabenzenes is more exergonic than that for pyridines,
but less exergonic than that for benzenes. Notably, the
thermodynamic nature of the [2+2+2] cycloaddition for the
formation of phosphabenzenes is similar to that of other
[2+2+2] cycloaddition reactions, although the thermody-
namic stability of phosphaalkynes is quite different from that
of alkynes and nitriles.[8]
Next, we applied the present reaction conditions with FeI2
(20 mol%) as a catalyst to [2+2+2] cycloaddition reactions
for the formation of benzenes and pyridines (Scheme 4).
When 1a was treated with 1-hexyne in the presence of FeI2,
[a] Reaction conditions: 1a (0.15 mmol), 2 (0.30 mmol), FeI2
(0.030 mmol), m-xylene (1.5 mL), 1408C (bath temperature), 18 h.
[b] Yield of the isolated product.
Scheme 4. Reactions of 1a with 1-hexyne and valeronitrile.
Angew. Chem. Int. Ed. 2015, 54, 7597 –7601
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
7599

.
Angewandte
Communications
benzene derivatives 4 and 3a’ were formed in good yields
(Scheme 4a). On the other hand, when we examined the
reaction of 1a with valeronitrile, the formation of 3a’ was
observed, but no pyridine derivative 5 was detected at all
(Scheme 4b). It is known that the electronic structure of
phosphaalkynes is similar to that of alkynes rather than
nitriles.[2b, 8] Therefore, the present reaction system for the
synthesis of phosphabenzenes might be related to [2+2+2]
cycloaddition for the synthesis of benzenes. Moreover, the
formation of benzene derivatives suggests the existence of
ferracyclopentadiene species as key reactive intermediates[16]
in the present reaction system, because ferracyclopentadiene
intermediates have been proposed for iron-catalyzed [2+2+2]
cycloaddition processes to form benzenes.[11c,d,f]
Scheme 6. Gibbs free energy diagram for oxidative cyclization.
To obtain further information on the reaction pathway, we
investigated the stoichiometric reactivity of FeI2 toward 1a.
When FeI2 was treated with 1a in m-xylene/THF (1:1) at
room temperature, the corresponding p-alkyne complex 6
was obtained in 32% yield (Scheme 5a). The treatment of 6
with 2a at 14088C for 12 h afforded the phosphabenzene 3a in
40% yield (Scheme 5b). These results indicate that the p-
alkyne–iron complex 6 may be involved in the present
reaction system.
Scheme 7. A plausible reaction pathway.
phabenzene 3. At present, however, we cannot exclude
another reaction pathway via a 3-phospha-1-ferracyclopenta-
diene species C[18] as a key reactive intermediate.
In summary, we have developed an efficient method for
the synthesis of phosphabenzenes by the iron-catalyzed
[2+2+2] cycloaddition of diynes with phosphaalkynes. With
this reaction system, 2,4,5-trisubstituted phosphabenzenes
can be obtained in high yields. We believe the method
described herein provides a useful platform for the explora-
tion of functional molecules containing a phosphabenzene
moiety.
Scheme 5. Synthesis and reactivity of the p-alkyne complex 6.
DFT calculations with the B3LYP* hybrid functional[17]
support the oxidative cyclization of a p-alkyne–iron complex
to give a ferracyclopentadiene complex (Scheme 6). The
Keywords: [2++2+2] cycloaddition · homogeneous catalysis ·
iron · phosphaalkynes · phosphabenzenes
5
quintet state of the complex I, in which 1,6-heptadiyne is
How to cite: Angew. Chem. Int. Ed. 2015, 54, 7597–7601
Angew. Chem. 2015, 127, 7707–7711
coordinated to FeI2, is much lower in Gibbs free energy than
3
5
the triplet-state complex I. The complex I is transformed
into the ferracyclopentadiene 5II via the transition state 5TS(I-
II). The activation free energy is 16.6 kcalmolÀ1, and the
reaction is slightly endergonic (3.1 kcalmolÀ1). In the ferra-
cyclopentadiene, the free energy of the triplet state 3II is
[1] Modern Arene Chemistry (Ed.: D. Astruc), Wiley-VCH, Wein-
heim, 2002.
[2] a) A. J. Ashe III, Acc. Chem. Res. 1978, 11, 153; b) F. Mathey,
Angew. Chem. Int. Ed. 2003, 42, 1578; Angew. Chem. 2003, 115,
1616.
[3] a) P. Le Floch, F. Mathey, Coord. Chem. Rev. 1998, 179 – 180,
771; b) P. Le Floch, Coord. Chem. Rev. 2006, 250, 627; c) L.
Kollµr, G. Keglevich, Chem. Rev. 2010, 110, 4257; d) C. Müller,
L. E. E. Broeckx, I. de Krom, J. J. M. Weemers, Eur. J. Inorg.
Chem. 2013, 187.
[4] G. Märkl, Angew. Chem. Int. Ed. Engl. 1966, 5, 846; Angew.
Chem. 1966, 78, 907.
[5] For examples of the preparation of phosphabenzenes from
phosphaalkynes, see: a) W. Rçsch, M. Regitz, Z. Naturforsch. B
1986, 41, 931; b) K. H. Dçtz, A. Tiriliomis, K. Harms, M. Regitz,
U. Annen, Angew. Chem. Int. Ed. Engl. 1988, 27, 713; Angew.
5
slightly lower than that of the quintet state II. Thus, the
following reaction with phosphaalkynes is considered to
proceed from the triplet-state ferracyclopentadiene 3II,
which is formed through intersystem crossing, or the quintet
state 5II.
A plausible reaction pathway based on the experimental
results and DFT calculations is shown in Scheme 7. First, an
iron complex A containing 1 as a p-alkyne ligand is formed
from FeI2 and 1. Next, oxidative cyclization of the diyne in A
affords a ferracyclopentadiene intermediate B,[16] which reacts
with the phosphaalkyne 2 to give the corresponding phos-
7600 www.angewandte.org
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2015, 54, 7597 –7601

Angewandte
Chemie
Chem. 1988, 100, 725; c) G. Märkl, A. Kallmünzer, Tetrahedron
Lett. 1989, 30, 5245; d) U. Annen, M. Regitz, H. Kluge, Chem.
Ber. 1990, 123, 935; e) J.-D. Andriamizaka, C. Couret, J. EscudiØ,
J. Organomet. Chem. 1991, 419, 57; f) K. H. Dçtz, A. Tiriliomis,
K. Harms, Tetrahedron 1993, 49, 5577; g) M. Julino, M. Slany, U.
Bergsträßer, F. MerÅier, F. Mathey, M. Regitz, Chem. Ber. 1995,
128, 991; h) D. Bçhm, H. Geiger, F. Knoch, F. Kremer, S.
Kummer, P. Le Floch, F. Mathey, U. Schmidt, U. Zenneck,
Phosphorus Sulfur Silicon Relat. Elem. 1996, 109 – 110, 173; i) B.
Wrackmeyer, U. Klaus, J. Organomet. Chem. 1996, 520, 211;
j) M. A. Hofmann, A. Nachbauer, U. Bergsträßer, M. Regitz,
Eur. J. Org. Chem. 1999, 1041; k) S. G. Ruf, J. Dietz, M. Regitz,
Tetrahedron 2000, 56, 6259; l) B. Breit, R. Winde, T. Mackewitz,
R. Paciello, K. Harms, Chem. Eur. J. 2001, 7, 3106; m) X. Chen,
[10] a) U. Schmidt, U. Zenneck, J. Organomet. Chem. 1992, 440, 187;
b) F. Knoch, F. Kremer, U. Schmidt, U. Zenneck, P. Le Floch, F.
Mathey, Organometallics 1996, 15, 2713; c) K. FerrØ, L. Toupet,
V. Guerchais, Organometallics 2002, 21, 2578; d) B. R. DꢀSouza,
T. K. Lane, J. Louie, Org. Lett. 2011, 13, 2936; e) C. Wang, X. Li,
F. Wu, B. Wan, Angew. Chem. Int. Ed. 2011, 50, 7162; Angew.
Chem. 2011, 123, 7300; f) T. K. Lane, B. R. DꢀSouza, J. Louie, J.
Org. Chem. 2012, 77, 7555; g) C. Wang, D. Wang, F. Xu, B. Pan,
B. Wan, J. Org. Chem. 2013, 78, 3065; h) V. Richard, M. Ipouck,
D. S. MØrel, S. Gaillard, R. J. Whitby, B. Witulski, J.-L. Renaud,
Chem. Commun. 2014, 50, 593.
[11] a) H. tom Dieck, R. Diercks, Angew. Chem. Int. Ed. Engl. 1983,
22, 1138; Angew. Chem. 1983, 95, 1138; b) C. Breschi, L. Piparo,
P. Pertici, A. M. Caporusso, G. Vitulli, J. Organomet. Chem.
2000, 607, 57; c) N. Saino, D. Kogure, S. Okamoto, Org. Lett.
2005, 7, 3065; d) N. Saino, D. Kogure, K. Kase, S. Okamoto, J.
Organomet. Chem. 2006, 691, 3129; e) A. Fürstner, K. Majima,
R. Martin, H. Krause, E. Kattnig, R. Goddard, C. W. Lehmann,
J. Am. Chem. Soc. 2008, 130, 1992; f) Y. Liu, X. Yan, N. Yang, C.
Xi, Catal. Commun. 2011, 12, 489.
[12] a) J. C. J. Bart, J. J. Daly, J. Chem. Soc. A 1970, 567; b) P.
Le Floch, D. Carmichael, L. Ricard, F. Mathey, J. Am. Chem.
Soc. 1993, 115, 10665; c) C. Müller, D. Wasserberg, J. J. M.
Weemers, E. A. Pidko, S. Hoffmann, M. Lutz, A. L. Spek, S. C. J.
Meskers, R. A. J. Janssen, R. A. van Santen, D. Vogt, Chem. Eur.
J. 2007, 13, 4548.
[13] With 10 mol% of FeI2, the corresponding phosphabenzenes
were obtained in moderate to good yields (3b: 63%, 3i: 52%).
[14] M. E. Jung, G. Piizzi, Chem. Rev. 2005, 105, 1735.
[15] J. C. Guillemin, T. Janati, P. Guenot, P. Savignac, J. M. Denis,
Angew. Chem. Int. Ed. Engl. 1991, 30, 196; Angew. Chem. 1991,
103, 191.
[16] J. M. Hoyt, K. T. Sylvester, S. P. Semproni, P. J. Chirik, J. Am.
Chem. Soc. 2013, 135, 4862.
[17] a) M. Reiher, O. Salomon, B. A. Hess, Theor. Chem. Acc. 2001,
107, 48; b) O. Salomon, M. Reiher, B. A. Hess, J. Chem. Phys.
2002, 117, 4729.
˝
S. Alidori, F. F. Puschmann, G. Santiso-Quinones, Z. Benko, Z.
Li, G. Becker, H.-F. Grützmacher, H. Grützmacher, Angew.
Chem. Int. Ed. 2014, 53, 1641; Angew. Chem. 2014, 126, 1667.
[6] For selected examples of the preparation of phosphabenzenes,
see: a) N. Avarvari, N. MØzailles, L. Ricard, P. Le Floch, F.
Mathey, Science 1998, 280, 1587; b) N. Avarvari, N. Maigrot, L.
Ricard, F. Mathey, P. Le Floch, Chem. Eur. J. 1999, 5, 2109; c) P.
de Koe, F. Bickelhaupt, Z. Naturforsch. B 2003, 58, 782; d) R. A.
Hunter, R. J. Whitby, M. E. Light, M. B. Hursthouse, Tetrahe-
dron Lett. 2004, 45, 7633; e) J. Grundy, F. Mathey, Angew. Chem.
Int. Ed. 2005, 44, 1082; Angew. Chem. 2005, 117, 1106; f) N. H. T.
Huy, B. Donnadieu, F. Mathey, Organometallics 2008, 27, 4005;
g) H. Wang, C. Li, D. Geng, H. Chen, Z. Duan, F. Mathey, Chem.
Eur. J. 2010, 16, 10659; h) Y. Mao, F. Mathey, Org. Lett. 2010, 12,
3384; i) H. Chen, J. Li, H. Wang, H. Liu, Z. Duan, F. Mathey, Eur.
J. Inorg. Chem. 2011, 1540; j) Y. Mao, F. Mathey, Chem. Eur. J.
2011, 17, 10745; k) Y. Mao, F. Mathey, Org. Lett. 2012, 14, 1162;
l) Y. Mao, K. M. H. Lim, R. Ganguly, F. Mathey, Org. Lett. 2012,
14, 4974.
[7] a) S. Saito, Y. Yamamoto, Chem. Rev. 2000, 100, 2901; b) J. A.
Varela, C. Saµ, Chem. Rev. 2003, 103, 3787; c) B. Heller, M.
Hapke, Chem. Soc. Rev. 2007, 36, 1085; d) J. A. Varela, C. Saµ,
Synlett 2008, 2571; e) G. Domínguez, J. PØrez-Castells, Chem.
Soc. Rev. 2011, 40, 3430; f) D. L. J. Broere, E. Ruijter, Synthesis
2012, 44, 2639; g) Transition-Metal-Mediated Aromatic Ring
Construction (Ed.: K. Tanaka), Wiley, Hoboken, 2013.
[8] a) M. Regitz, P. Binger, Angew. Chem. Int. Ed. Engl. 1988, 27,
1484; Angew. Chem. 1988, 100, 1541; b) M. Regitz, Chem. Rev.
1990, 90, 191.
[18] P. Binger, B. Biedenbach, A. T. Herrmann, F. Langhauser, P.
Betz, R. Goddard, C. Krüger, Chem. Ber. 1990, 123, 1617.
[9] a) J. F. Nixon, Chem. Rev. 1988, 88, 1327; b) J. F. Nixon, Coord.
Chem. Rev. 1995, 145, 201.
Received: March 18, 2015
Published online: May 15, 2015
Angew. Chem. Int. Ed. 2015, 54, 7597 –7601
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
7601