Gold-Catalyzed Domino Synthesis of Functionalized Benzofurans and Tetracyclic Isochromans via Formal Carboalkoxylation

Article abstract of DOI:10.1021/acs.orglett.6b02159

A domino synthesis of benzofurans with the modification of side chains from α-alkoxyalkyl o-alkynylaryl ethers (n = 0) and electron-rich arenes has been developed. In the present domino reaction, which would proceed via the α-alkoxyalkylation of arenes with an intermediate in the migratory cycloisomerization of o-alkynylaryl ethers followed by the nucleophilic addition of benzofurans to benzyl ethers, a cationic Au(III) catalyst activates the C-C π bond and the C-O σ bond. The present method could be extended to Au(I)-catalyzed domino synthesis of tetracyclic isochromans from α-alkoxyalkyl (o-alkynylaryl)methyl ethers (n = 1) and aryl methoxymethyl ethers.

Full text of DOI:10.1021/acs.orglett.6b02159

Letter
pubs.acs.org/OrgLett
Gold-Catalyzed Domino Synthesis of Functionalized Benzofurans
and Tetracyclic Isochromans via Formal Carboalkoxylation
Tomoyuki Obata,† Sho Suzuki,† Asuka Nakagawa,† Ryota Kajihara,† Keiichi Noguchi,‡ and Akio Saito*,†
†Division of Applied Chemistry, Institute of Engineering and ‡Instrumentation Analysis Center, Tokyo University of Agriculture and
Technology, 2-24-16 Naka-cho, Koganei, Tokyo 184-8588, Japan
S
* Supporting Information
ABSTRACT: A domino synthesis of benzofurans with the
modification of side chains from α-alkoxyalkyl o-alkynylaryl
ethers (n = 0) and electron-rich arenes has been developed. In
the present domino reaction, which would proceed via the α-
alkoxyalkylation of arenes with an intermediate in the
migratory cycloisomerization of o-alkynylaryl ethers followed
by the nucleophilic addition of benzofurans to benzyl ethers, a
cationic Au(III) catalyst activates the C−C π bond and the C−
O σ bond. The present method could be extended to Au(I)-catalyzed domino synthesis of tetracyclic isochromans from α-
alkoxyalkyl (o-alkynylaryl)methyl ethers (n = 1) and aryl methoxymethyl ethers.
ransition-metal-catalyzed migratory cycloisomerization of
o-alkynylaryl ethers and amines having a migrating group
formation of o-alkynylphenols followed by the cycloisomeriza-
tion to benzofuran has been reported by Hashmi et al.,13 to our
knowledge, the carboalkoxylation-type migratory cycloisomeri-
zation concomitant with the modification of side chains
(including the formal reaction) has not been achieved. Herein,
we report the unprecedented domino synthesis of benzofurans
and isochromans with the modification of side chains from α-
alkoxyalkyl o-alkynylaryl ethers and α-alkoxyalkyl (o-
alkynylaryl)methyl ethers with arenes.
T
on the heteroatoms provides a powerful approach to the
synthesis of 2,3-disubstituted benzofurans and indoles (eq 1),1
We have developed migratory cycloisomerizations of
alkynes14 and domino reactions via the formation of α,β-
enone intermediates15 for novel and efficient synthetic methods
of heterocycles. As part of our research, we focused on the
structure of products 2 formed by the carboalkoxylation of o-
alkynylaryl ethers 1 with the migration of α-alkoxyalkyl groups
(Scheme 1). Thus, the elimination of the alkoxy group in 2
would proceed even by weak Lewis acidity of the catalyst due to
the electron donation of an oxygen atom, thereby leading to an
oxonium ion intermediate B having an α,β-enone structure
(path a).16 Furthermore, in the presence of a nucleophile 3, the
intermediate B would be converted to benzofurans 4 with the
modification of side chains by the subsequent nucleophilic
addition of 3. In the reaction of 1 and 3, the nucleophilic
addition of 3 to a zwitterionic intermediate A prior to the
migration of the α-alkoxyalkyl group would be expected as an
alternative route (path b). As a similar substitution reaction, a
cationic gold(I)-catalyzed alkylation of alcohols, amines, and
anisole with alkyl o-alkynylbanzoates have been reported by
Asao et al.17 One the other hand, the generated benzyl ethers 6
from 1 with electron-rich aromatics 3 (Nu = aryl) as a
nucleophile would undergo the subsequent nucleophilic
which are often found in biologically active compounds.2 In
these reactions, generally, the π-acidic metal catalyst (Pd, Pt,
Au, etc.) activates the alkyne π-bond to generate an (alkenyl)
metal intermediate bearing an electrophilic migrating group,
which then shifts to the most nucleophilic 3-position of
heterocycles. As a migrating group, α-alkoxyalkyl,3,4 allyl,3b,5
benzyl,3b,6 acyl,7 methyl,8 sulfonyl,9 boryl groups, and so on10
have been employed.11 Recently, Oh and co-workers reported
an elegant synthesis of 2,3-disubstituted indoles via silver-
catalyzed condensation of N-(o-alkynylaryl)formimidates and
active methylene compounds followed by the migratory
cycloisomerization based on the carboamination of alkynes
with 1,3-alkenyl shifts (eq 2).12 Such a domino procedure
brings about not only (i) the construction of heterocyclic
frameworks and (ii) the introduction of side chains but also
(iii) the modification of side chains (migrating groups) in a
single step and in an atom-economical manner. However,
although an interesting domino reaction via the gold-catalyzed
Received: July 22, 2016
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.6b02159
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Letter
Scheme 1. Proposed Mechanism
Table 1. Substrate Scope for the Formation of 4
a
b
entry
1
3
4/Xn
yield (%)
1
1a
1b
1c
1d
1e
1f
3a
3a
3a
3a
3a
3a
3a
3b
3c
3d
3e
4aa/2,4,6-(MeO)3
4ba/2,4,6-(MeO)3
4ca/2,4,6-(MeO)3
4da/2,4,6-(MeO)3
4ea/2,4,6-(MeO)3
4fa/2,4,6-(MeO)3
4ga/2,4,6-(MeO)3
4ab/2,4,5-(MeO)3
4ac/2,4,5,6-(MeO)4
4ad/2,4-(MeO)2
4ae/2,4,6-Me3
76
2
67
3
67
4
26
5
81
6
28
7
1g
1a
1a
1a
1a
57
8
52
addition of benzofurans 5 to form 4 due to the stability of the
benzylic carbocation of C by electron-rich aromatic rings.18
Accordingly, in both paths a and b, a good balance of π- and σ-
acidity of catalytic systems would be required.
Initially, based on Yamamoto’s procedure for the carboalkox-
ylation with the migration of α-alkoxyalkyl groups,3a PtCl2 (20
mol %) with 1,5-cyclooctadiene (COD, 80 mol %) ligand was
employed for the reaction of o-alkynylaryl ether 1a with 1,3,5-
trimethoxybenzene (3a, 1.2 equiv) in toluene or CH2Cl2 as a
preliminary examination. Unfortunately, in these reactions, 3-
(methoxymethyl)benzofuran 2a was only obtained as a main
product (Scheme 2). On the other hand, the use of the cationic
9
53
10
00 (5a: 87)
c
11
17
a
3a: 1,3,5-(MeO)3C6H3, 3b: 1,3,4-(MeO)3C6H3, 3c: 1,3,4,5-
b
(MeO)4C6H2, 3d: 1,3-(MeO)2C6H4, 3e: mesitylene. Isolated yields.
c
3 equiv of 3e was used.
AuCl3 (5 mol %) and AgOTf (15 mol %) at room temperature
to give 4ba, 4ca, and 4ea in good yields (entries 2, 3, and 5).
Although the reaction of tert-butyl-substituted 1d with 3a
afforded a slightly complicated mixture, the desired 4da was
obtained (entry 4). Furthermore, not only other α-alkoxyalkyl
ether 1f but also aniline 1g could be employed as a substrate
(entries 6 and 7). In addition, the present method could be
applied to the reaction of 1a with various electron-rich arenes
such as 1,3,4-trimethoxybenzene (3b, entry 8), 1,3,4,5-
tetramethoxybenzene (3c, entry 9), and mesitylene (3e, entry
11). On the other hand, the cases of 1,3-dimethoxybenzene
(3d) gave benzofuran 5a in 86% yield (entry 10), which was
considered to be indicative of path b (Scheme 1) of these
domino reactions.
Scheme 2. Optimization of Reaction Conditions for the
Domino Reaction of 1a with 3a
To gain a better understanding of the involvement of path b
in the present domino reaction, we carried out the cationic
Au(III)-catalyzed reaction of benzofuran 5a with benzyl ether
6a or 6d (Scheme 3a), which would be expected as an
intermediate of path b (Scheme 1). Thus, the corresponding
product 4aa was found to be obtained in 79% yield from 5a and
6a, while 5a was recovered in 94% in the reaction of 5a and 6d.
These observations are in agreement with results in the domino
reaction of 1a with 3a or 3d (Table 1, entries 1 and 10). Also,
considering the possibility of path a (Scheme 1), we examined
reactions of 3-(methoxymethyl)benzofuran 2a with arene 3a or
3d under the cationic Au(III)-catalyzed conditions (Scheme
3b). However, the reaction of 2a with 3a gave 4aa, and that
with 3d gave 4ad. Thus, the present domino reactions would
proceed via path b rather than path a (Scheme 1).
Furthermore, since the reaction of 5a and 6a without any
catalyst did not proceed at all (Scheme 3a), the Au(III) catalyst
would activate the C−O σ bond of 6a.
gold catalysts in CH2Cl2 led to the formation of the desired 3-
benzylbenzofuran 4aa at room temperature. In particular,
gold(III) catalysts, which shows relatively high σ-electro-
philicity,19 brought about superior results to gold(I) catalysts
(Supporting Information). Among tested catalysts, the catalyst
derived from AuCl3 (5 mol %) and AgOTf (15 mol %) afforded
4aa in good yield (76%, Scheme 2). It should be mentioned
that a sole addition of AuCl3 or AgOTf resulted in the recovery
of a considerable amount of 1a (more than 86%, Supporting
Information).
Under the optimized reaction conditions, the scope for the
formation of 4 from o-alkynylaryl ethers 1 and various arenes 3
is summarized in Table 1. Similar to 1a bearing an n-butyl
substituent at the alkyne terminus (entry 1), benzyloxyethyl-,
cyclopropyl-, and phenyl-substituted 1b, 1c, and 1e reacted
with 1,3,5-trimethoxybenzene (3a, 1.2 equiv) in the presence of
Next, we attempted to extend the present method to a
domino reaction of α-alkoxyalkyl (o-alkynylaryl)methyl ethers
7. As a 6-membered ring formation based on the carboalkox-
B
DOI: 10.1021/acs.orglett.6b02159
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Scheme 3. Control Experiments
Scheme 5. Reactions of 7a−d with 10a or 10b
inferior results to the Gagosz catalyst (Supporting Informa-
tion).
ylation, the migratory cycloisomerization of o-alkynylbenzoates
bearing α-alkoxyalkyl3b and other migrating groups11a−c has
been known, while that of (o-alkynylaryl)methyl ethers bearing
allyl groups only has been known.11d Therefore, we checked
whether the corresponding product 8a was formed by the
migratory cycloisomerization of 7a (Scheme 4). Interestingly,
In conclusion, we have developed the cationic gold(III)-
catalyzed domino synthesis of benzofurans with the mod-
ification of side chains from α-alkoxyalkyl o-alkynylaryl ethers
and electron-rich arenes. Mechanistic studies imply that the
present domino reactions proceed via nucleophilic addition of
benzofurans to benzyl ethers, which are formed by the α-
alkoxyalkylation of arenes (path b). The present method could
be extended to gold(I)-catalyzed domino synthesis of
tetracyclic isochromans from α-alkoxyalkyl (o-alkynylaryl)-
methyl ethers and arenes. Further investigations will focus on
extending this strategy to other heterocyclic synthesis.
Scheme 4. Reaction of 7a without Nucleophiles
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.6b02159.
Screening of catalysts for the domino reactions of 1a and
7a, experimental procedures, and spectral data (PDF)
Crystallographic data of 11aa (CIF)
the cationic gold(I) catalyst derived from (Ph3P)AuCl (5 mol
%) and AgSbF6 (5 mol %) led to the formation of tetracyclic
isochroman 9a, although Yamamoto’s Pt-catalytic systems
(PtCl2−COD in toluene)3a resulted in the quantitative
recovery of 7a. This result, which would be regarded as a
formal annulation of 8a with methoxymethyl-deprotected
compound of 7a, encouraged us to examine the cationic
gold-catalyzed domino reaction of 7 with various arenes
(Scheme 5 and the Supporting Information).
AUTHOR INFORMATION
Corresponding Author
■
*E-mail: akio-sai@cc.tuat.ac.jp.
Notes
The authors declare no competing financial interest.
At the outset, it turned out that the reaction of (o-
alkynylaryl)methyl ether 7a with 1,3,5-trimethoxybenzene (3a,
1.2 equiv) under gold-catalyzed conditions gave a complicated
mixture (Supporting Information). However, when 7a reacted
with aryl methoxymethyl ether 10a in the presence of
(Ph3P)AuNTf2 (Gagosz catalyst)20 in CH2Cl2 at room
temperature, tetracyclic isochroman 11aa was obtained in
71% yield (Scheme 5). Furthermore, Gagosz catalyst could be
applied to reactions of 7a−c with 10a or 10b, thereby leading
to the corresponding tetracyclic isochromans 11 in 51−83%
yields. The obtained tetracyclic isochromans 9a and 11 were
single cis-isomers that were determined by the X-ray structure
analysis of 11aa21 and by NOE experiments of other products.
It should be mentioned that cationic Au(III) catalyst showed
ACKNOWLEDGMENTS
■
This work was partially supported by JSPS Grants-in-Aid for
Scientific Research (C) (Grant No. 15K07852) and by the
Naito Foundation.
REFERENCES
■
(1) For recent reviews, see: (a) Dudnik, A.; Chernyak, N.;
Gevorgyan, V. Aldrichimica Acta 2010, 43, 37. (b) Gulevich, A. V.;
Dudnik, A. S.; Chernyak, N.; Gevorgyan, V. Chem. Rev. 2013, 113,
3084. (c) Weibel, J.-M.; Blanc, A.; Pale, P. Chem. Rev. 2008, 108, 3149.
(d) Cacchi, S.; Fabrizi, G. Chem. Rev. 2005, 105, 2873. (e) Shapiro, N.
D.; Toste, F. D. Synlett 2010, 2010, 675. (f) Pflasterer, D.; Hashmi, A.
S. K. Chem. Soc. Rev. 2016, 45, 1331.
̈
C
DOI: 10.1021/acs.orglett.6b02159
Org. Lett. XXXX, XXX, XXX−XXX

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Letter
(2) Recent examples: (a) Lu, Z.; Ott, G. R.; Anand, R.; Liu, R.-Q.;
Covington, M. B.; Vaddi, K.; Qian, M.; Newton, R. C.; Christ, D. D.;
Trzaskos, J.; Duan, J. J.-W. Bioorg. Med. Chem. Lett. 2008, 18, 1958.
(b) Gessner, G.; Macianskiene, R.; Starkus, J. G.; Schoenherr, R.;
Heinemann, S. H. Eur. J. Pharmacol. 2010, 632, 52. (c) Suresh, N.;
Vasanthi, N. S. J. Proteomics Bioinf. 2010, 3, 20. (d) Li, J.; Pan, L.;
Kim, S. Y.; Piao, L. Synlett 2014, 25, 579. (c) See also: Kusama, H.;
Miyashita, Y.; Takaya, J.; Iwasawa, N. Org. Lett. 2006, 8, 289.
(d) Kamijo, S.; Yamamoto, Y. J. Am. Chem. Soc. 2002, 124, 11940.
(13) This reaction is a first example for gold-catalyzed cyclo-
isomerization of o-alkynylphenols. See: (a) Hashmi, A. S. K.; Frost, T.
M.; Bats, J. W. Org. Lett. 2001, 3, 3769. The author succeeded
isolating the organogold intermediates of these cycloisomerization. See
also: (b) Hashmi, A. S. K.; Ramamurthi, T. D.; Rominger, F. Adv.
Synth. Catal. 2010, 352, 971.
(14) (a) Saito, A.; Kanno, A.; Hanzawa, Y. Angew. Chem., Int. Ed.
2007, 46, 3931. (b) Saito, A.; Oda, S.; Fukaya, H.; Hanzawa, Y. J. Org.
Chem. 2009, 74, 1517. (c) Saito, A.; Konishi, T.; Hanzawa, Y. Org. Lett.
2010, 12, 372. (d) Saito, A.; Iimura, K.; Hanzawa, Y. Tetrahedron Lett.
2010, 51, 1471. (e) Saito, A.; Enomoto, Y.; Hanzawa, Y. Tetrahedron
Lett. 2011, 52, 4299.
(15) (a) Saito, A.; Umakoshi, M.; Yagyu, N.; Hanzawa, Y. Org. Lett.
2008, 10, 1783. (b) Saito, A.; Kasai, J.; Odaira, Y.; Fukaya, H.;
Hanzawa, Y. J. Org. Chem. 2009, 74, 5644. (c) Saito, A.; Kasai, J.;
Konishi, T.; Hanzawa, Y. J. Org. Chem. 2010, 75, 6980.
(16) (a) Box, V. G. S.; Jackson, Y. A. Heterocycles 1983, 20, 753.
(b) Jackson, Y. A.; Marriott, K.-S. C.; Anderson, M. Heterocycles 2001,
55, 91. (c) Maguire, A. R.; Plunkett, S. J.; Papot, S.; Clynes, M.;
O’Connor, R.; Touhey, S. Bioorg. Med. Chem. 2001, 9, 745.
(d) Campbell, J. A.; Bordunov, V.; Broka, C. A.; Dankwardt, J.;
Hendricks, R. T.; Kress, J. M.; Walker, K. A. M.; Wang, J.-H.
Tetrahedron Lett. 2004, 45, 3793.
Deng, Y.; Munoz-Acuna, U.; Yuan, C.; Lai, H.; Chai, H.; Chagwedera,
̃
̃
T. E.; Farnsworth, N. R.; Carcache de Blanco, E. J.; Li, C.; Soejarto, D.
D.; Kinghorn, A. D. J. Org. Chem. 2013, 78, 10166. (e) Saravanan, B.;
Saravanan, R. R.; Manivannan, V. J. Chem. Pharm. Res. 2012, 4, 3057.
(3) (a) Nakamura, I.; Mizushima, Y.; Yamamoto, Y. J. Am. Chem. Soc.
2005, 127, 15022. (b) Furstner, A.; Davies, P. W. J. Am. Chem. Soc.
̈
2005, 127, 15024. (c) Furstner, A.; Heilmann, E. K.; Davies, P. W.
̈
Angew. Chem., Int. Ed. 2007, 46, 4760. (d) Nakamura, I.; Chan, C. S.;
Araki, T.; Terada, M.; Yamamoto, Y. Adv. Synth. Catal. 2009, 351,
1089. Examples of sulfide analogues: (e) Nakamura, I.; Sato, T.;
Yamamoto, Y. Angew. Chem., Int. Ed. 2006, 45, 4473. (f) Nakamura, I.;
Okamoto, M.; Sato, T.; Terada, M. Heterocycles 2010, 82, 689.
(4) Representative examples for the gold-catalyzed reactions of
alkynes and acetals: (a) Zhang, G.; Zhang, L. J. Am. Chem. Soc. 2008,
130, 12598. (b) Bae, H. J.; Jeong, W.; Lee, J. H.; Rhee, Y. H. Chem. -
Eur. J. 2011, 17, 1433. (c) Zhang, M.; Wang, Y.; Yang, Y.; Hu, X. Adv.
Synth. Catal. 2012, 354, 981. (d) Zi, W.; Toste, F. D. J. Am. Chem. Soc.
2013, 135, 12600. (e) Schultz, D. M.; Babij, N. R.; Wolfe, J. P. Adv.
Synth. Catal. 2012, 354, 3451. (f) Yu, Y.; Yang, W.; Rominger, F.;
Hashmi, A. S. K. Angew. Chem., Int. Ed. 2013, 52, 7586.
(17) (a) Asao, N.; Aikawa, H.; Tago, S.; Umetsu, K. Org. Lett. 2007,
9, 4299. (b) Aikawa, H.; Tago, S.; Umetsu, K.; Haginiwa, N.; Asao, N.
Tetrahedron 2009, 65, 1774. See also: (c) Li, Y.; Yang, Y.; Yu, B.
Tetrahedron Lett. 2008, 49, 3604. (d) Tang, Y.; Li, J.; Zhu, Y.; Li, Y.;
Yu, B. J. Am. Chem. Soc. 2013, 135, 18396.
(18) In the transition-metal-catalyzed benzylation of indoles with
benzyl alcohol, the stability of the benzylic carbocation is critical to the
success of these reactions. (a) Au(III) catalyst: Hikawa, H.; Suzuki,
H.; Azumaya, I. J. Org. Chem. 2013, 78, 12128. (b) Ru(II) catalyst:
Putra, A. E.; Takigawa, K.; Tanaka, H.; Ito, Y.; Oe, Y.; Ohta, T. Eur. J.
Org. Chem. 2013, 2013, 6344. (c) Ir(I) catalyst: Whitney, S.; Grigg,
R.; Derrick, A.; Keep, A. Org. Lett. 2007, 9, 3299.
(19) (a) Gorin, D. J.; Toste, F. D. Nature 2007, 446, 395.
(b) Yamamoto, Y. J. Org. Chem. 2007, 72, 7817. (c) See also ref 18a.
́
(20) Mezailles, N.; Ricard, L.; Gagosz, F. Org. Lett. 2005, 7, 4133.
(21) CCDC 1481371 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.ac.uk/
data_request/cif.
(5) (a) Cacchi, S.; Fabrizi, G.; Moro, L. Synlett 1998, 1998, 741.
(b) Monteiro, N.; Balme, G. Synlett 1998, 1998, 746. (c) Cacchi, S.;
Fabrizi, G.; Moro, L. Tetrahedron Lett. 1998, 39, 5101. (d) Liang, Z.;
Ma, S.; Yu, J.; Xu, R. J. Org. Chem. 2007, 72, 9219. (e) Cacchi, S.;
Fabrizi, G.; Pace, P. J. Org. Chem. 1998, 63, 1001. (f) Majumdar, K. C.;
Hazra, S.; Roy, B. Tetrahedron Lett. 2011, 52, 6697. (g) Propargyl
groups: Cacchi, S.; Fabrizi, G.; Moro, L. Tetrahedron Lett. 1998, 39,
5101. (h) See: Furstner, A.; Szillat, H. J. Am. Chem. Soc. 2001, 123,
̈
11863.
(6) Examples of sulfide and selenide analogues: (a) Nakamura, I.;
Sato, T.; Terada, M.; Yamamoto, Y. Org. Lett. 2008, 10, 2649. (b) Sato,
T.; Nakamura, I.; Terada, M. Eur. J. Org. Chem. 2009, 2009, 5509.
(7) (a) Shimada, T.; Nakamura, I.; Yamamoto, Y. J. Am. Chem. Soc.
2004, 126, 10546. (b) Nakamura, I.; Mizushima, Y.; Yamagishi, U.;
Yamamoto, Y. Tetrahedron 2007, 63, 8670. (c) Nakamura, I.; Sato, Y.;
Konta, S.; Terada, M. Tetrahedron Lett. 2009, 50, 2075. (d) Wu, C. Y.;
Hu, M.; Liu, Y.; Song, L. J.; Lei, Y.; Tang, B. X.; Li, R. J.; Li, J. H.
Chem. Commun. 2012, 48, 3197.
(8) Zeng, X.; Kinjo, R.; Donnadieu, B.; Bertrand, G. Angew. Chem.,
Int. Ed. 2010, 49, 942.
(9) (a) Nakamura, I.; Yamagishi, U.; Song, D.; Konta, S.; Yamamoto,
Y. Angew. Chem., Int. Ed. 2007, 46, 2284. (b) Nakamura, I.; Yamagishi,
U.; Song, D.; Konta, S.; Yamamoto, Y. Chem. - Asian J. 2008, 3, 285.
(c) Zhu, Z.; Chen, K.; Xu, Q.; Shi, M. Adv. Synth. Catal. 2015, 357,
3081.
(10) (a) Hirner, J. J.; Faizi, D. J.; Blum, S. A. J. Am. Chem. Soc. 2014,
136, 4740. (b) Chong, E.; Blum, S. A. J. Am. Chem. Soc. 2015, 137,
10144. (c) Faizi, D. J.; Issaian, A.; Davis, A. J.; Blum, S. A. J. Am. Chem.
Soc. 2016, 138, 2126. (d) Silyl migration of sulfide analogues:
Nakamura, I.; Sato, T.; Terada, M.; Yamamoto, Y. Org. Lett. 2007, 9,
4081.
(11) Migratory cycloisomerizations of o-alkynylbenzoates: (a) Allyl
groups: Shi, Y.; Roth, K. E.; Ramgren, S. D.; Blum, S. A. J. Am. Chem.
Soc. 2009, 131, 18022. (b) Benzyl and cinnamyl groups: Hashmi, A. S.
K.; Lothschutz, C.; Dopp, R.; Ackermann, M.; De Buck Becker, J.;
̈
̈
Rudolph, M.; Scholz, C.; Rominger, F. Adv. Synth. Catal. 2012, 354,
133. (c) Benzyl group: Komeyama, K.; Takahashi, K.; Takaki, K. Org.
Lett. 2008, 10, 5119. (d) A migratory cycloisomerization of (o-
alkynylaryl)methyl ethers with the migration of allyl groups:
Ackermann, M.; Bucher, J.; Rappold, M.; Graf, K.; Rominger, F.;
Hashmi, A. S. K. Chem. - Asian J. 2013, 8, 1786.
(12) (a) Oh, C. H.; Karmakar, S.; Park, H. S.; Ahn, Y. C.; Kim, J. W.
J. Am. Chem. Soc. 2010, 132, 1792. (b) Oh, C. H.; Park, H. S.; Park, N.;
D
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