Silver triflate catalyzed tandem heterocyclization/alkynylation of 1-((2-tosylamino)aryl)but-2-yne-1,4-diols to 2-alkynyl indoles

Article abstract of DOI:10.1002/chem.201200578

Don't cross me! 2-Alkynyl indoles were prepared efficiently by the AgOTf-catalyzed tandem heterocyclization/alkynylation of 1-(2-tosylamino)aryl) but-2-yne-1,4-diols under mild conditions (see scheme). The attractiveness of this approach lies in the fact that both the indole ring and alkyne side chain of the N-heterocycle are sequentially formed from low cost, readily available, and ecologically benign starting materials. It also provides the first route to this synthetically valuable class of compounds that is not based on a cross-coupling strategy. Copyright

Full text of DOI:10.1002/chem.201200578

COMMUNICATION
DOI: 10.1002/chem.201200578
Silver Triflate Catalyzed Tandem Heterocyclization/Alkynylation of
1-((2-Tosylamino)aryl)but-2-yne-1,4-diols to 2-Alkynyl Indoles
Srinivasa Reddy Mothe, Prasath Kothandaraman, Sherman Jun Liang Lauw,
Samuel Ming Wei Chin, and Philip Wai Hong Chan*[a]
Indoles are a key structural component in many natural
and pharmaceutical products as well as functional materi-
als.[1–3] Because of this, and their ability to serve as a versatile
building block in organic synthesis, a myriad of impressive
methods for the construction of indole derivatives have
been developed over the years. Recently, this has hitherto
included transition-metal-catalyzed cross-coupling of an
indole with an alkyne, either preformed or generated in situ,
to access synthetically valuable 2-alkynyl indole deriva-
tives.[3] However, the reactions were shown to require stoi-
chiometric or excess amounts of various reagents, which can
lead to equimolar or more amounts of waste products.
Added to this is the need to introduce structural elements to
(Scheme 1).[6] In contrast, a process involving a Lewis acid-
À
triggered C OH bond activation of a propargylic diol,
which results in the formation of an N-heterocycle with the
À
direct the C C bond-forming process to occur regioselec-
Scheme 1. Lewis and Brønsted acid-catalyzed reactivities of propargylic
diols.
tively at the C2 position of the indole ring. For this reason,
establishing synthetic methods to this immensely important
nitrogen heterocycle in an efficient manner and with control
of substitution patterns from readily accessible substrates
continues to be actively pursued.
liberation of two molecules of H2O as potentially the only
by-product is not known. As part of ongoing efforts to de-
velop this type of reaction, our discovery that inexpensive,
ecologically benign, and readily available simple AgI salts
can effect tandem heterocyclization/alkynylation of propar-
gylic 1,4-diols of the type 1 with an appropriately placed ani-
line moiety is reported herein (Scheme 1). This provides
a convenient route to 2-alkynyl indoles 2 that assembles
both the indole ring and alkyne moiety in one step for
a wide range of substrates. Achieved under mild conditions,
it also represents the first synthetic method for the prepara-
tion of this N-heterocycle that does not rely on a cross-cou-
pling strategy.
The 1-((2-tosylamino)aryl)but-2-yne-1,4-diols studied in
this work were prepared from the reaction of the corre-
sponding aldehyde and substituted N-tosyl-1-(2-aminophe-
nyl)prop-2-yn-1-ol pretreated with LDA following literature
procedures.[7] By using N-tosyl-1-(2-aminophenyl)-1,3-di-
phenyl-prop-2-yn-1-ol 1a as the probe substrate, we began
by examining a variety of Lewis and Brønsted acid catalysts
to establish the reaction conditions (Table 1). This study ini-
tially revealed treating a solution of 1a in toluene with
AgOTf (5 mol%) at room temperature for 7 h gave 3-
phenyl-2-(phenylethynyl)-1-tosyl-1H-indole 2a and 3-
phenyl-2-(2-phenylvinylidene)-1-tosyl indolin-3-ol 3a in 45
and 30% yields, respectively (Table 1, entry 1). The struc-
ture of the 2-alkynyl indole product was determined by
Lewis and Brønsted acid-catalyzed reactions of unsaturat-
ed alcohols have emerged over the years as efficient and
À
À
convenient synthetic strategies for C C and C X (X=N, O,
S) bond formation.[4–6] For example, we recently reported
a method for the synthesis of indenyl-fused and 2,3-disubsti-
tuted indoles that relied on the cycloisomerization of 2-tosyl-
aminophenylprop-1-yn-3-ols in the presence of a gold(I) cat-
alyst.[2b] We subsequently demonstrated that the synthetic
method could be fine-tuned to provide 1H-indole-2-carbal-
dehydes and (E)-2-(iodomethylene)indolin-3-ols by intro-
ducing N-iodosuccinimide into the reaction conditions.[2a]
Further exploration of this field led us to investigate the po-
tential Lewis acid-catalyzed reactivity of propargylic diols.
Thus far, the Lewis and Brønsted acid-mediated chemistry
of this class of compounds has been reported to give only
the oxygen heterocycle and an equimolar amount of H2O
[a] S. R. Mothe, Dr. P. Kothandaraman, S. J. L. Lauw, S. M. W. Chin,
Prof. Dr. P. W. H. Chan
Division of Chemistry and Biological Chemistry
School of Physical and Mathematical Sciences
Nanyang Technological University
Singapore 637371 (Singapore)
Fax : (+65)6791-1961
E-mail: waihong@ntu.edu.sg
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201200578.
Chem. Eur. J. 2012, 18, 6133 – 6137
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
6133

Table 1. Optimization of the reaction conditions.[a]
Entry
Catalyst
Solvent
Yield [%][b]
2a
3a
4a
1[c]
2
AgOTf
AgOTf
AgOTf
AgOTf
AgOTf
AgOTf
AgOTf
AgOTf
AgOTf
AgOTf
AgOTf
AgOTf
AgNTf2
AgPF6
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
MeNO2
1,4-dioxane
45
88
78
69
86
85
68
78
79
65
30
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
3[d]
4[e]
5[f]
6[g]
7[h]
8
Figure 1. ORTEP drawing of 2a with thermal ellipsoids at 50% probabil-
ity levels.[8]
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
A
[i]
THF
–
–
[i]
MeCN
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
tries 13–19). Moreover, in reactions where AgPF6, AgSbF6
or AgBF4 was employed as the catalyst, the Meyer–Schuster
rearrangement adduct 4a was also afforded as a side prod-
uct in 15–55% yield (Table 1, entries 14–16).[9] The analo-
gous AgOAc-mediated reaction was the only instance in
which the substrate was recovered in near quantitative yield
(Table 1, entry 17). Low product yields of 20–35% were ad-
ditionally afforded in control experiments with the Brønsted
acid catalysts TFA, TfOH and Tf2NH, whereas p-
TsOH·H2O led to decomposition of the substrate (Table 1,
entries 20–23). A similar outcome was found when the
Brønsted-acid-mediated reactions were re-examined in a va-
riety of solvents and at various catalyst loadings and temper-
atures.[7] Under these various conditions, the 2-alkynyl
indole product was furnished in 25–48% yield and/or with
recovery of 1a in up to 68% yield and/or substrate decom-
position. Along with the above results of reaction in the
presence of a base, the possibility of a hidden Brønsted acid
catalyst was shown to be unlikely based on further control
experiments with AgOTf at 1 and 5 mol% heated to reflux
in 1,2-dichloroethane prior to use or 5 mol% of AgOTf in
the presence of 10 mol% of tBuCl, which furnished 2a in
low yields of 13–38%.[7,10] On the basis of the above results,
the reaction of 1a in the presence of AgOTf (5 mol%) in
toluene at 708C for 2 h provided the optimal conditions.
With the optimized conditions in hand, we next turned to
evaluating their generality for a series of propargylic 1,4-
diols and the results are summarized in Table 2. These reac-
tions demonstrated that by using AgOTf as catalyst, the
conditions proved to be broad and a variety of 2-alkynyl in-
doles could be afforded in good to excellent yields from the
corresponding substrates 1b–x. Starting alcohols with a pend-
ant phenyl moiety and their derivatives with electron-with-
drawing or electron-donating groups in the para position at
R1 or R2 were found to react well, affording 2b–f in excel-
lent yields of 87–94%. Likewise, 2-alkynyl indoles 2g–m,
38
30
20
35
–
18
55
15
–
–
–
–
–
–
–
AgSbF6
AgBF4
AgOAc
[i]
–
Cu
A
68
50
Yb
A
[j]
p-TsOH·H2O
TFA
TfOH
–
20
32
35
Tf2NH
[a] All reactions were performed at the 0.1 mmol scale with catalyst/1a
ratio=1:20 in 4 mL of solvent at 708C for 2 h. [b] Isolated product yield.
[c] Reaction carried out at room temperature for 7 h. [d] Reaction car-
ried out in the presence of 5 mol% of Et3N. [e] Reaction carried out in
the presence of 10 mol% of Et3N. [f] Reaction carried out in the pres-
ence of 5 mol% of K2CO3. [g] Reaction carried out in the presence of
10 mol% of K2CO3. [h] Reaction carried out in the presence of 1 equiv
of K2CO3. [i] No reaction based on TLC and 1H NMR analysis of the
crude reaction mixture. [j] Decomposition products obtained based on
1
TLC and H NMR analysis of the crude reaction mixture.
1H NMR
spectroscopy
and
X-ray
crystallography
(Figure 1).[8] Our studies subsequently showed that forma-
tion of the 2-vinylidene indolin-3-ol byproduct could be sup-
pressed to give 2a as the only product in 88% yield by in-
creasing the reaction temperature to 708C for 2 h (Table 1,
entry 2). Slightly lower product yields were obtained when
the reaction was repeated in the presence of 5 or 10 mol%
of Et3N or K2CO3 as well as 1 equiv of the latter inorganic
base (Table 1, entries 3–7). Likewise, changing the solvent
from toluene to MeNO2, 1,4-dioxane or 1,2-dichloroethane
gave slightly lower product yields of 65–79% (Table 1, en-
tries 8–10). In contrast, replacing toluene with THF or
MeCN as the solvent was found to result in recovery of the
substrate in near quantitative yield (Table 1, entries 11 and
12). Similarly, a survey of other low cost silver(I) salts and
Lewis acids did not provide any improvements (Table 1, en-
6134
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 6133 – 6137

Silver Triflate-Catalyzed Tandem Heterocyclization/Alkynylation
COMMUNICATION
which R2 = pClC6H4 and R4 =Cl and 1x where R2 =H, were
the only examples found to give the corresponding 2-alkynyl
indoles 2q and 2x in lower yields of 45 and 38%, respective-
ly.
Table 2. Tandem heterocyclization/alkynylation of 1b–x catalyzed by
AgOTf.[a]
A tentative mechanism for the present AgI-catalyzed 2-al-
kynyl indole forming reaction is outlined in Scheme 2. This
could initially involve activation of 1 through coordination
Scheme 2. Proposed reaction pathway for the formation of 2-alkynyl in-
doles.
of the metal catalyst with the sterically less hindered secon-
dary alcohol moiety of the substrate to give the silver(I)-co-
ordinated intermediate A. It is possible that this could sub-
sequently trigger 5-exo-dig cyclization of the pendant aniline
group to the alkyne moiety and formation of 2-vinylidene
indolin-3-ol 3. Further coordination of this newly formed
[a] All reactions were performed at the 0.1 mmol scale with AgOTf/
1 ratio=1:20 in toluene (4 mL) at 708C for 2 h. Values in parenthesis
denote isolated product yields. [b] Reaction performed at 408C for 0.5 h.
[c] Reaction performed for 0.5 h.
À
adduct to AgOTf, which is re-generated from [Ag] OH by
protonolysis and also affords a molecule of H2O, gives AgI-
À
activated allene species B. A second C OH bond activation
step that initiates deprotonation of the allene moiety fol-
[11]
À
lowed by elimination of [Ag] OH,
which releases the
containing a 1-napthyl, heteroaryl, alkyl, or cycloalkane sub-
stituent on the alkyne side chain, were obtained in excellent
yields of 74–94% from the corresponding alcoholic sub-
strates 1g–m. The presence of an electron-withdrawing or
electron-donating group or benzofused ring on the aniline
moiety was found to have no influence on the course of the
reaction with 2n–p and 2r–s obtained in 80–93% yield. Ad-
ditionally, substrates where both the carbinol carbon centers
are secondary alcohols, as in 1t and 1u, were found to pro-
ceed well and provide 2t and 2u in 92 and 72% yields, re-
spectively. This is noteworthy as these adducts cannot be
prepared following a cross-coupling approach due to the
need for the C3 position of the indole ring to be occupied
metal catalyst once again by protonolysis, would then pro-
vide 2 and another molecule of water.
While fortuitous, the competitive formation of 3a for the
cyclization of 1a at room temperature under the conditions
mentioned earlier in entry 1, Table 1 argues in favor of the
mechanism put forward in Scheme 2. This argument was fur-
ther corroborated by the observation that when a solution
of 3a in toluene was treated with 5 mol% of AgOTf under
the conditions shown in Scheme 3, the expected 2-alkynyl
indole 2a was obtained as the sole product in 92% yield.
À
The role of the silver catalyst in facilitating the two C OH
bond activation steps could also be shown by repeating the
À
by a functional group so that the C C bond-forming process
can only occur at the C2 position of the N-heterocyclic sub-
strate.[3] Starting 1,4-diols 2v and 2w, with a pendant thio-
phene or alkyne moiety at R1, were also found to be well
tolerated under the reaction conditions, giving the corre-
sponding 2-alkynyl indoles in respective yields of 67 and
61%. Under the standard conditions, reaction of 1q in
Scheme 3. Dehydrative alkynylation of 3a catalyzed by AgOTf.
Chem. Eur. J. 2012, 18, 6133 – 6137
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6135

P. W. H. Chan et al.
[2] For selected recent examples: a) P. Kothandaraman, S. R. Mothe,
S. S. M. Toh, P. W. H. Chan, J. Org. Chem. 2011, 76, 7633–7640; b) P.
Kothandaraman, W. Rao, S. J. Foo, P. W. H. Chan, Angew. Chem.
2010, 122, 4723–4727; Angew. Chem. Int. Ed. 2010, 49, 4619–4623;
c) P. Buchgraber, M. M. Domostoj, B. Scheiper, C. Wirtz, R.
Mynott, J. Rust, A. Fꢂrstner, Tetrahedron 2009, 65, 6519–6534; d) S.
Sato, M. Shibuya, N. Kanoh, Y. Iwabuchi, Chem. Commun. 2009,
6264–6266; e) Y. Yamane, X. Liu, A. Hamasaki, T. Ishida, M.
Haruta, T. Yokoyama, M. Tokunaga, Org. Lett. 2009, 11, 5162–
5165; f) D. Ye, J. Wang, X. Zhang, Y. Zhou, X. Ding, E. Feng, H.
Sun, G. Liu, H. Jiang, H. Liu, Green Chem. 2009, 11, 1201–1208;
g) B. Gabriele, R. Mancuso, G. Salerno, E. Lupinacci, G. Ruffolo,
M. Costa, J. Org. Chem. 2008, 73, 4971–4977; h) I. Nakamura, U.
Yamagishi, D. Song, S. Konta, Y. Yamamoto, Angew. Chem. 2007,
119, 2334–2337; Angew. Chem. Int. Ed. 2007, 46, 2284–2287; i) K.
Cariou, B. Ronan, S. Mignani, L. Fensterbank, M. Malacria, Angew.
Chem. 2007, 119, 1913–1916; Angew. Chem. Int. Ed. 2007, 46, 1881–
1884; j) Y. Zhang, J. P. Donahue, C.-J. Li, Org. Lett. 2007, 9, 627–
630; k) K. O. Hessian, B. L. Flynn, Org. Lett. 2006, 8, 243–246.
[3] For selected recent examples: a) N. A. Danilkina, S. Brꢄse, I. A.
Balova, Synlett 2011, 517–520; b) L. Yang, L. Zhao, C.-J. Li, Chem.
Commun. 2010, 46, 4184–4186; c) B. P. Berciano, S. Lebrequier, F.
Besseliꢅvre, S. Piguel, Org. Lett. 2010, 12, 4038–4041; d) A. S.
Dudnik, V. Gevorgyan, Angew. Chem. 2010, 122, 2140–2142;
Angew. Chem. Int. Ed. 2010, 49, 2096–2098; e) S. H. Kim, S. Chang,
Org. Lett. 2010, 12, 1868–1871; f) T. Kawano, N. Matsuyama, K.
Hirano, T. Satoh, M. Miura, J. Org. Chem. 2010, 75, 1764–1766;
g) F. Besseliꢅvre, S. Piguel, Angew. Chem. 2009, 121, 9717–9720;
Angew. Chem. Int. Ed. 2009, 48, 9553–9556; h) J. P. Brand, J. Char-
pentier, J. Waser, Angew. Chem. 2009, 121, 9510–9513; Angew.
Chem. Int. Ed. 2009, 48, 9346–9349; i) N. Matsuyama, K. Hirano, T.
Satoh, M. Miura, Org. Lett. 2009, 11, 4156–4159; j) M. Tobisu, Y.
Ano, N. Chatani, Org. Lett. 2009, 11, 3250–3252; k) Y. Gu, X. M.
Wang, Tetrahedron Lett. 2009, 50, 763–766; l) I. V. Seregin, V. Rya-
bova, V. Gevorgyan, J. Am. Chem. Soc. 2007, 129, 7742–7743;
m) M. Nagamochi, Y.-Q. Fang, M. Lautens, Org. Lett. 2007, 9, 2955–
2958.
reactions of 1a and 3a under similar conditions but in the
absence of the catalyst. In both instances, this test led to the
recovery of the respective starting alcohols in near quantita-
tive yield.
In summary, we have demonstrated for the first time that
À
the silver(I)-mediated C OH bond activation of 1,4-propar-
gylic diols is an effective and chemoselective strategy for the
construction of 2-alkynyl indoles. The reaction was shown to
tolerate a diverse set of starting alcohols and afford the N-
heterocycle for applications in natural product synthesis and
medicinal and materials chemistry. Previous methods to this
immensely important member of the indole family of com-
pounds have mainly relied on synthetic strategies that re-
quire a cross-coupling step and structural elements to regio-
selectively direct alkynylation to occur at the C2 position of
the nitrogen ring. Our approach is rapid, forming the indole
ring and alkyne side chain of the N-heterocycle sequentially
from a wide variety of starting materials and a catalytic
system that are low cost, readily available, and ecologically
benign.
Experimental Section
General Procedure: A solution of propargylic 1,4-diol 1a (0.1 mmol) in
toluene (2 mL) was added dropwise to a solution of AgOTf (5 mmol) in
anhydrous toluene (2 mL) at room temperature. The resulting mixture
was stirred at 708C for 2 h and monitored by TLC analysis. On comple-
tion, the reaction mixture was brought to room temperature and concen-
trated under reduced pressure. Purification by flash column chromatogra-
phy on silica gel (eluent: n-hexane/EtOAc=9:1) gave the 2-akynyl
indole compound.
[4] For selected recent examples by us, refer to refs. [2a], [2b], and:
a) P. Kothandaraman, C. Huang, D. Susanti, W. Rao, P. W. H. Chan,
Chem. Eur. J. 2011, 17, 10081–10088; b) S. R. Mothe, P. Kothandara-
man, W. Rao, P. W. H. Chan, J. Org. Chem. 2011, 76, 2521–2531;
c) X. Zhang, W. T. Teo, Sally, P. W. H. Chan, J. Org. Chem. 2010, 75,
6290–6293; d) W. Rao, P. Kothandaraman, C. B. Koh, P. W. H.
Chan, Adv. Synth. Catal. 2010, 352, 2521–2530.
[5] For reviews: a) B. Biannic, A. Aponick, Eur. J. Org. Chem. 2011,
6605–6617; b) E. Emer, R. Sinisi, M. G. Capdevila, D. Petruzziello,
F. D. Vincentiis, P. G. Cozzi, Eur. J. Org. Chem. 2011, 647–666;
c) M. Bandini, N. Tragni, Org. Biomol. Chem. 2009, 7, 1501–1507;
d) N. Ljungdahl, N. Kann, Angew. Chem. 2009, 121, 652–654;
Angew. Chem. Int. Ed. 2009, 48, 642–644; e) J. Muzart, Tetrahedron
2008, 64, 5815–5849; f) J. Muzart, Eur. J. Org. Chem. 2007, 3077–
3089; g) J. Muzart, Tetrahedron 2005, 61, 4179–4212; h) Y. Tamaru,
Eur. J. Org. Chem. 2005, 2647–2656.
Acknowledgements
This work was supported by a University Research Committee Grant
(RG55/06) from Nanyang Technological University and a Science and
Engineering Research Council Grant (092 101 0053) from A*STAR, Sin-
gapore. An Undergraduate Research Experience on Campus stipend (to
SJLL) from NTU is also gratefully acknowledged and we thank Dr.
Yongxin Li of this Division for providing the X-ray crystallographic data
reported in this work.
Keywords: alcohols
·
heterocyclization/alkynylation
·
homogeneous catalysis · indoles · silver
[6] For recent examples: a) F. Yang, T. Jin, M. Bao, Y. Yamamoto, Tet-
rahedron 2011, 67, 10147–10155; b) K. Ravindar, M. S. Reddy, P.
Deslongchamps, Org. Lett. 2011, 13, 3178–3181; c) K.-G. Ji, H.-T.
Zhu, F. Yang, A. Shaukat, X.-F. Xia, Y.-F. Yang, X.-Y. Liu, Y.-M.
Liang, J. Org. Chem. 2010, 75, 5670–5678; d) X. Zhang, Z. Lu, C.
Fu, S. Ma, J. Org. Chem. 2010, 75, 2589–2598; e) A. Aponick, C.-Y.
Li, J. Malinge, E. F. Marques, Org. Lett. 2009, 11, 4624–4627; f) A.
Aponick, C.-Y. Li, J. A. Palmes, Org. Lett. 2009, 11, 121–124.
[7] Please refer to the Supporting Information for further details.
[8] CCDC-844472 (2a) contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif.
[1] For selected reviews: a) V. Sharma, P. Kumar, D. Pathak, J. Hetero-
´
cycl. Chem. 2010, 47, 491–502; b) J. Barluenga, F. Rodrguez, F. J.
´
Fananꢁs, Chem. Asian J. 2009, 4, 1036–1048; c) O. Miyata, N.
Takeda, T. Naito, Heterocycles 2009, 78, 843–871; d) K. Krꢂger (nꢃe
Alex), A. Tillack, M. Beller, Adv. Synth. Catal. 2008, 350, 2153–
2167; e) K. Higuchi, T. Kawasaki, Nat. Prod. Rep. 2007, 24, 843–
868; f) Comprehensive Heterocyclic Chemistry III, Vol.
3 (Eds.:
A. R. Katritzky, C. A. Ramsden, E. F. V. Scriven, R. J. K. Taylor),
Pergamon Press, Oxford, UK, 2007; p 1; g) G. R. Humphrey, J. T.
Kuethe, Chem. Rev. 2006, 106, 2875–2911; h) S. Cacchi, G. Fabrizi,
Chem. Rev. 2005, 105, 2873–2920; i) M. Somei, F. Yamada, Nat.
Prod. Rep. 2005, 22, 73–103; j) M. Somei, F. Yamada, Nat. Prod.
Rep. 2004, 21, 278–311.
[9] For recent reviews: a) V. Cadierno, P. Crochet, S. E. Garcꢆa-Garrido,
J. Gimeno, Dalton Trans. 2010, 39, 4015–4031; b) D. A. Engel, G. B.
Dudley, Org. Biomol. Chem. 2009, 7, 4149–4158.
6136
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 6133 – 6137

Silver Triflate-Catalyzed Tandem Heterocyclization/Alkynylation
COMMUNICATION
[10] For selected examples: a) T. T. Dang, F. Boeck, L. Hintermann, J.
Org. Chem. 2011, 76, 9353–9361; b) C.-L. Deng, T. Zou, Z.-Q.
Wang, R.-J. Song, J.-H. Li, J. Org. Chem. 2009, 74, 412–414; c) M.
Bandini, A. Eichholzer, P. Kotrusz, M. Tragni, S. Troisi, A. Umani-
Ronchi, Adv. Synth. Catal. 2009, 351, 319–324; d) A. Arcadi, M. Al-
fonsi, F. Marinelli, J. Organomet. Chem. 2007, 692, 5322–5326;
e) S. W. Youn, J. I. Eom, J. Org. Chem. 2006, 71, 6705–6707; f) C. G.
Yang, N. W. Reich, Z. Shi, C. He, Org. Lett. 2005, 7, 4553–4556;
g) T. J. Harrison, G. R. Dake, Org. Lett. 2004, 6, 5023–5026; h) H.
Jona, H. Mandai, W. Chavasiri, K. Takeuchi, T. Mukaiyama, Bull.
Chem. Soc. Jpn. 2002, 75, 291–309.
[11] a) D. Lee, S. J. Danishefsky, J. Am. Chem. Soc. 2010, 132, 4427–
4430; b) K. Komeyama, N. Saigo, M. Miyagi, K. Takaki, Angew.
Chem. 2009, 121, 10059–10062; Angew. Chem. Int. Ed. 2009, 48,
9875–9878; c) C. P. Khulbe, R. S. Mann, Can. J. Chem. 1978, 56,
2791–2796.
Received: February 22, 2012
Published online: April 18, 2012
Chem. Eur. J. 2012, 18, 6133 – 6137
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6137