Gold-catalyzed [1,5]-hydride shift onto unactivated alkynes to trigger an intermolecular Diels-Alder reaction

Article abstract of DOI:10.1021/ol5017355

A [1,5]-hydride shift of sp³ C-H onto an unactivated carbon-carbon triple bond catalyzed by a gold(I) complex enabled N-propargylisoindolines to be latent dienes and therefore triggered an intermolecular Diels-Alder reaction with dienophiles. This protocol provides an atom-economical and straightforward approach to access a wide range of polycyclic skeletons in high yields and with excellent diastereoselectivities from easily accessible molecules.

Full text of DOI:10.1021/ol5017355

Letter
pubs.acs.org/OrgLett
Gold-Catalyzed [1,5]-Hydride Shift onto Unactivated Alkynes To
Trigger an Intermolecular Diels−Alder Reaction
Xiang Wu, Shu-Sen Chen, Yue Hu, and Liu-Zhu Gong*
Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemistry, University of Science and
Technology of China, Hefei 230026, China
Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072, China
S
* Supporting Information
ABSTRACT: A [1,5]-hydride shift of sp3 C−H onto an unactivated
carbon−carbon triple bond catalyzed by a gold(I) complex enabled N-
propargylisoindolines to be latent dienes and therefore triggered an
intermolecular Diels−Alder reaction with dienophiles. This protocol
provides an atom-economical and straightforward approach to access a
wide range of polycyclic skeletons in high yields and with excellent
diastereoselectivities from easily accessible molecules.
Scheme 1. Alkynes Served as Hydride Acceptors in the
Cascade Reactions
he direct functionalization of inactive C−H bonds
Tundoubtedly represents one of the most ideal strategies
for the synthesis of structurally complex molecules.1 [1,n]-
Sigmatropic hydrogen shift/cyclization reactions have been a
redox-economical strategy to functionalize sp3 C−H bonds and
have turned out to be very useful in organic synthesis.2−4 In most
cases, an activated hydride acceptor, basically an electronically
deficient unsaturated bond, is required to be located in an
appropriate position to a hydride donor. Previous elegant studies
have indicated that the presence of π-Lewis acid catalysts has
enabled unactivated alkynes to serve as hydride acceptors to
participate in cascade [1,5]-hydride shift/ring-closing reactions
(Scheme 1A−1).5 Additionally, [1,5]-hydride shift/elimination
reactions, very unique methods for the preparation of allenes,
have been established by Che, Gagosz, Ma, and others (Scheme
1A-2).6 Moreover, the zwitterionic intermediates, generated
from the [1,5]-hydride shift of propargylic amines, were also able
to react with terminal alkynes and isonitriles, furnishing products
A and B, respectively (Scheme 1A-3).7 Herein, we will describe
that a [1,5]-hydride shift of sp3 C−H onto the unactivated
carbon−carbon triple bond catalyzed by a gold(I) complex
enabled N-propargylisoindolines to be latent dienes capable of
undergoing an intermolecular Diels−Alder reaction with
dienophiles,8 directly giving rise to polycyclic molecules (Scheme
1B).
During our continuous endeavors directed toward the C−H
functionalization reaction by using [1,n]-hydride shift strategy,9
we initially investigated a transformation of 1a under the catalysis
of a gold(I) complex to identify if it was possible to undergo a
hydride shift/cyclization reaction2a,b and to generate tricyclic
product C under degassed conditions (eq 1). However, the
proposed product C was not detected. On the contrary, an
unanticipated molecule D was isolated in a 14% yield, which was
presumably generated from a reaction between a diene species,
cinnamylisoindole IIa in situ formed from [1,5]-hydride shift of
1a, with trace amounts of residual oxygen in glassware and
solvent (eq 1).10 Indeed, the yield of D could be improved to
67% by conducting the reaction under the atmosphere of air,
Received: June 16, 2014
Published: July 2, 2014
© 2014 American Chemical Society
3820
dx.doi.org/10.1021/ol5017355 | Org. Lett. 2014, 16, 3820−3823

Organic Letters
Letter
a
Table 1. Optimization of Reaction Conditions
Table 2. Scope of Arylalkynylisoindoline Substrates
a
b
entry
[M] (5 mol %)
soln
temp (°C) time (h) yield (%)
entry
1 (R)
3
yield (%)
1
t-BuXPhosAuNTf2
PdCl2
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
THF
MeCN
PhMe
60
60
60
60
60
60
60
60
20
60
60
60
60
3
24
24
24
24
3
89
<5
<5
b
1
1b (2-MeC6H4)
1c (3-MeC6H4)
1d (4-MeC6H4)
1e (2-MeOC6H4)
1f (3-MeOC6H4)
1g (4-MeOC6H4)
1h (2-ClC6H4)
3b
3c
3d
3e
3f
88
84
95
91
92
89
53
77
84
77
78
75
82
89
2
2
3
PtCl2
3
4
Ph3PAuCl
4
5
JohnPhosAuCl
JohnPhosAuSbF6
IPrAuSbF6
b
5
6
40
81
88
47
51
39
24
38
6
3g
3h
3i
7
3
7
8
IPrAuNTf2
3
8
1i (3-ClC6H4)
9
t-BuXPhosAuNTf2
t-BuXPhosAuNTf2
t-BuXPhosAuNTf2
t-BuXPhosAuNTf2
t-BuXPhosAuNTf2
24
24
24
24
24
9
1j (4-ClC6H4)
3j
10
11
12
13
10
11
12
13
14
1k (2-MeO2CC6H4)
1l (3-MeO2CC6H4)
1m (4-MeO2CC6H4)
1n (E-C6H5CHCH)
1o (H)
3k
3l
3m
3n
3o
CHCl3
b
a
Yield of the isolated product. No reaction was observed. DCE = 1,2-
dichloroethane.
a
The reaction was carried out with 1 (0.1 mmol) and N-
benzylmaleimide 2a (1.2 equiv) in the presence of 5 mol % of t-
BuXPhosAuNTf2 in DCE (1.0 mL) under N2. The resulting solution
was stirred for 3 h at 60 °C. Yield of the isolated product.
which could clearly indicate the occurrence of the reaction
between cinnamylisoindole IIa and oxygen, leading to the
generation of oxidized product D. In addition, 1H NMR studies
identified the intermediate IIa to confirm the hypothesis on the
[1,5]-hydride transfer occurred in 1a under the catalysis of
gold(I), leading to the efficient formation of cinnamylisoindole
b
(Table 2). Generally, the introduction of an electron-rich
substituent to the arylalkynyl moiety of the substrate 1 led to a
relatively cleaner reaction in comparison with those bearing an
electron-withdrawing group (entries 1−6 vs 10−12). Interest-
ingly, in the cases of alkynylisoindolines with a chlorophenyl
substituent, the substitution pattern exerted an apparent impact
on the conversion. As a consequence, the m- and p-
chlorophenylalkynylisoindolines 1i and 1j resulted in consid-
erably higher yields than o-chlorophenylalkynylisoindoline 1h
(entries 8 and 9 vs 7). Moreover, E-styrylalkynylisoindoline 1n
could furnish the product 3n in 82% yield (entry 13). More
significantly, an unsubstituted substrate, 2-(prop-2-yn-1-yl)-
isoindoline 1o, could also be nicely tolerated to give
corresponding polycyclic product in an 89% yield (entry 14).
Additionally, the variation of substituent on the isoindoline
moiety was also tolerated to undergo the cascade reaction cleanly
and furnished polycyclic heterocycles in high yields (Table
3).Basically, either the electronic feature of the substituent or the
11
1
IIa (see the Supporting Information for H NMR spectra).
Interestingly, the allene resulting from the [1,5]-hydride shift/
elimination process, which commonly occurred in other
processes,6 was not observed in this case.
The findings inspired us to envisage that if a dienophile was
introduced to the reaction, a cascade [1,5]-hydride shift/
intermolecular Diels−Alder reaction12 would be created. To
our delight, a reaction of 1a with N-benzylmaleimide (2a) was
indeed able to undergo the desired cascade reaction to give endo-
adduct 3a as a single diastereomer in a high yield (89%) under
the promotion of t-BuXPhosAuNTf213 at 60 °C under N2 (Table
1, entry 1). Other commonly used π-Lewis acids, such as PdCl2
and PtCl2,14 showed no catalytic activity for this transformation
(entries 2 and 3). Either the counterion or ligand of gold(I)
complexes exerted significant effect on the catalytic activity. For
instance, gold chloride complexes were unable to promote the
reaction (entries 4 and 5), and JohnPhosAuSbF615 gave a poor
yield (entry 6). In sharp contrast, the highly cationic gold
complexes enabled the reaction to proceed smoothly, in
particular, under the assistance of an appropriate ligand (entries
1, 7, and 8). When the reaction was performed at 20 °C in 1,2-
dichloroethane (DCE), a lower yield (47%) was obtained,
prolonging the reaction time to 24 h (entry 9). A final evaluation
of solvents showed that DCE is the most suitable media to allow
the reaction and gives the highest yield (entries 1 and 10−13).
Having established the optimal reaction conditions, the
generality of the transformation for arylalkynylisoindolines 1
was subsequently examined (Table 2). A variety of substrates
1b−o with different substituents adjacent to the carbon−carbon
triple bond were treated with N-benzylmaleimide (2a) in the
presence of 5 mol % of t-BuXPhosAuNTf2 in DCE at 60 °C. All
of the arylalkynylisoindolines underwent the [1,5]-hydride shift/
intermolecular Diels−Alder cycloaddition very smoothly and
gave 3b−o in high yields and with excellent endo-selectivity
a
Table 3. Scope of Isoindoline Substrates
b
entry
1 (R)
3
yield (%)
1
2
3
4
5
6
7
1p (4-Cl)
3p
3q
3r
3s
3t
90
91
88
89
88
89
78
1q(5-Cl)
1r (5-Me)
1s (5,6-Me2)
1t (5-OMe)
1u (5-CF3)
1v (5-NO2)
3u
3v
a
The reaction was carried out with 1 (0.1 mmol) and N-
benzylmaleimide 2a (1.2 equiv) in the presence of 5 mol % of t-
BuXPhosAuNTf2 in DCE (1.0 mL) under N2. The resulting solution
b
was stirred for 3 h at 60 °C. Yield of the isolated product.
3821
dx.doi.org/10.1021/ol5017355 | Org. Lett. 2014, 16, 3820−3823

Organic Letters
Letter
Scheme 2. Scope of Dienophiles
Scheme 3. Deuterium-Labeling Experiments
a
The reaction was carried out with 1 (0.1 mmol) in the presence of 5
mol % of t-BuXPhosAuNTf2 in DCE (1.0 mL) at 60 °C under N2 for 3
h. The solution was then cooled to 20 °C, dimethyl acetylenedicarbox-
ylate was added, and the resulting solution was stirred for 1 h.
substitution pattern has little influence on the reaction
performance. Thus, the presence of electron-donating or
electron-withdrawing groups on the isoindoline led to the
generation of desired products in almost identical yields (entries
1−6) except that the 5-NO2-substituted isoindoline (1v) gave a
relatively lower, but still good, yield (78%, entry 7).
Scheme 4. Proposed Mechanism
In addition to showing excellent generality for the
arylalkynylisoindolines 1, the protocol could also be amenable
to a wide scope of dienophiles 2 (Scheme 2). The use of N-
methylmaleimide (2b) as a dienophile furnished the correspond-
ing product 4a16 in an 85% yield with perfect endo-selectivity,
while 4b was isolated in an 84% yield with a 15/1 diastereomeric
ratio in favor of endo-product when N-phenylmaleimide (2c) was
used. The cascade reaction with dimethyl fumarate (2d) also
proceeded cleanly to give 4c as a single diastereomer, whereas a
1/1 endo/exo-mixture of 4d was created from a similar reaction
with dimethyl maleate (2e). However, benzylidene malononitrile
(2f) showed less reactivity to afford the desired product 4e in a
lower yield (52%). In contrast, the use of dimethyl
acetylenedicarboxylate (2g) as a dienophile at 60 °C was unable
to generate the desired polycyclic product although the [1,5]-
hydride transfer indeed occurred, presumably because the
dimethyl acetylenedicarboxylate is highly active and undergoes
some unidentified reactions. Alternatively, after 1a was initially
transformed into isoindole catalyzed by t-BuXPhosAuNTf2 in
DCE at 60 °C under N2 for 3 h, the solution was cooled down to
20 °C and treated with dimethyl acetylenedicarboxylate (2g) to
enable the generation of the desired product 4f in an 81% yield.
To get insight into reaction mechanism, some deuterium
labeling experiments were performed (Scheme 3). The exposure
of deuterated [D4]-1a to the optimal conditions led to [D4]-3a in
88% yield with a 100% deuterium at vinyl carbon a (eq 3),
indicating the clean occurrence of [1,5]-hydride transfer.
Surprisingly, a significant deuterium loss was observed at carbon
c (D3), and only 38% deuterium was found at vinyl carbon b,
which we presumed might arise from protonation of the
intermediate with residual water. Indeed, the addition of 3
equiv of water led to an even more significant deuterium loss at
carbon-c (D3, 75% vs 35%) and much less deuterium at vinyl
carbon-b (D2, 38% vs 9%) while the deuterium at vinyl carbon-a
remained 100% (eq 4). As a comparison, a similar reaction of
[D4]-1a conducted in the presence of D2O led to [D4]-3a with a
considerable improvement in carbon b and c (eq 5). Moreover,
when the cascade reaction of 1a was conducted with D2O (3.0
equiv) under the otherwise identical conditions, a [D3]-3a was
isolated in an 84% yield, with 25% and 63% deuterium content
for the carbon b and c, but no deuterium was observed at carbon a
(eq 6). These facts clearly demonstrated that the external water
participated in the protonation of the isoindole and vinylgold
parts of the key intermediate generated from the gold catalyzed
[1,5]-hydride shift step.
On the basis of the deuterium-labeling experiments, a plausible
mechanism was proposed (Scheme 4). Initially, a [1,5]-hydride
shift of [D4]-1a occurred under the promotion of gold(I) to
generate an intermediate [D4]-I, which subsequently underwent
reversible protonation and deprotonation reaction sequences
with external water (or D2O) under the assistance of the resultant
bis((trifluoromethyl)sulfonyl)amide (Tf2N−),17 leading to the
formation of equilibrium mixture of various deuterated N-
cinnamylisoindole [Dn]-IIa by protodemetalation of corre-
sponding vinylgold species [Dn]-III. Finally, the Diels−Alder
reaction of [Dn]-IIa with the N-benzylmaleimide would occur to
afford [Dn]-3a with various deuterium ratios at the deuteratable
carbons.
In conclusion, we have demonstrated that the gold(I) appears
to be an efficient catalyst for the hydride shift of sp3 C−H onto
the unactivated carbon−carbon triple bond in the context of the
3822
dx.doi.org/10.1021/ol5017355 | Org. Lett. 2014, 16, 3820−3823

Organic Letters
Letter
Peennings, M. L. M. J. Am. Chem. Soc. 1983, 105, 4775. (c) De Boeck, B.;
Jiang, S.; Janousek, Z.; Viehe, H. G. Tetrahedron 1994, 50, 7075. (d) De
Boeck, B.; Janousek, Z.; Viehe, H. G. Tetrahedron 1995, 51, 13239.
(e) Zhang, C.; Kanta De, C.; Mal, R.; Seidel, D. J. Am. Chem. Soc. 2008,
130, 416. (f) Che, X.; Sheng, L.; Dang, Q.; Bai, X. Synlett 2008, 2373.
substrate to enable alkynylisoindolines to act as latent dienes
capable of participating in an intermolecular Diels−Alder
reaction with various dienophiles. This protocol provides an
atom-economical synthesis of structurally complex polycyclic
products in high yields from easily accessible molecules by redox-
economical functionalization of sp3 C−H bonds under mild
conditions. The deuterium-labeling experiments indicate that the
reaction involves a [1,5]-hydride shift onto the gold-activated
alkyne to generate a N-cinnamylisoindole, which undergoes the
subsequent Diels−Alder reaction.
́ ́ ́
(g) Foldi, A. A.; Ludanyi, K.; Benyei, A. C.; Matyus, P. Synlett 2010,
̈
2109. (h) Mori, K.; Sueoka, S.; Akiyama, T. J. Am. Chem. Soc. 2011, 133,
2424.
(5) For hydride transfer to alkynes with platinum catalysts, see:
(a) Bajracharya, G. B.; Pahadi, N. K.; Gridnev, I. D.; Yamamoto, Y. J. Org.
Chem. 2006, 71, 6204. (b) Vadola, P. A.; Sames, D. J. Am. Chem. Soc.
2009, 131, 16525. (c) Tobisu, M.; Nakai, H.; Chatani, N. J. Org. Chem.
2009, 74, 5471. (d) Yang, S.; Li, Z.; Jian, X.; He, C. Angew. Chem., Int. Ed.
2009, 48, 3999. For hydride transfer to alkynes with gold catalysts, see:
(e) Jurberg, I. D.; Odabachian, Y.; Gagosz, F. J. Am. Chem. Soc. 2010,
132, 3543. (f) Bhunia, S.; Ghorpade, S.; Huple, D. B.; Liu, R.-S. Angew.
Chem., Int. Ed. 2012, 51, 2939. (g) Vasu, D.; Das, A.; Liu, R.-S. Chem.
ASSOCIATED CONTENT
* Supporting Information
■
S
Experimental details and characterization data. This material is
available free of charge via the Internet at http://pubs.acs.org.
Commun. 2010, 46, 4115. (h) Barluenga, J.; Sigueiro, R.; Vicente, R.;
̈
AUTHOR INFORMATION
Corresponding Author
́
Ballesteros, A.; Tomas, M.; Rodríguez, M. Angew. Chem., Int. Ed. 2012,
51, 10377. For hydride transfer to alkynes with other catalysts, see:
(i) Shikanai, D.; Murase, H.; Hata, T.; Urabe, H. J. Am. Chem. Soc. 2009,
■
*E-mail: gonglz@ustc.edu.cn.
Notes
131, 3166. (j) Barluenga, J.; Fananas
́
-Mastral, M.; Aznar, F.; Valdes
Angew. Chem., Int. Ed. 2008, 47, 6594. (k) Cambeiro, F.; Lopez, S.;
Varela, J. A.; Saa, C. Angew. Chem., Int. Ed. 2012, 51, 723.
́
, C.
̃
́
́
The authors declare no competing financial interest.
(6) For selected examples, see: (a) Lo, V. K.-Y.; Wong, M.-K.; Che, C.-
M. Org. Lett. 2008, 10, 517. (b) Kuang, J.; Ma, S. J. Am. Chem. Soc. 2010,
132, 1786. (c) Bolte, B.; Odabachian, Y.; Gagosz, F. J. Am. Chem. Soc.
2010, 132, 7294. (d) Lo, V. K.-Y.; Zhou, C.-Y.; Wong, M.-K.; Che, C.-M.
Chem. Commun. 2010, 46, 213. (e) Periasamy, M.; Sanjeevakumar, N.;
Dalai, M.; Gurubrahamam, R.; Reddy, P. O. Org. Lett. 2012, 14, 2932.
(f) Tang, X.; Zhu, C.; Cao, T.; Kuang, J.; Lin, W.; Ni, S.; Zhang, J.; Ma, S.
Nat. Commun. 2013, 4, 2450. (g) Jiang, G.-J.; Zheng, Q.-H.; Dou, M.;
Zhuo, L.-G.; Meng, W.; Yu, Z.-X. J. Org. Chem. 2013, 78, 11783.
(7) (a) Sugiishi, T.; Nakamura, H. J. Am. Chem. Soc. 2012, 134, 2504.
(b) Odabachian, Y.; Wang, Q.; Zhu, J. Chem. −Eur. J. 2013, 19, 12229.
(8) For selected reviews on Diels−Alder reactions, see: (a) Nicolaou,
K. C.; Snyder, S. A.; Montagnon, T.; Vassilikogiannakis, G. Angew.
Chem., Int. Ed. 2002, 41, 1668. (b) Fringuelli, F.; Taticchi, A. The Diels−
Alder Reaction: Selected Practical Methods; Wiley: Chichester, 2002.
(9) (a) He, Y.-P.; Du, Y.-L.; Luo, S.-W.; Gong, L. Z. Tetrahedron Lett.
2011, 52, 7064. (b) Chen, D.-F.; Han, Z.-Y.; He, Y.-P.; Yu, J.; Gong, L.-
Z. Angew. Chem., Int. Ed. 2012, 51, 12307. (c) He, Y. P.; Wu, H.; Chen,
D. F.; Yu, J.; Gong, L. Z. Chem.Eur. J. 2013, 19, 5232.
ACKNOWLEDGMENTS
■
We are grateful for financial support from the NSFC (Nos.
21172207, 21232007, and 21302177), the Ministry of Education,
and the China Postdoctoral Science Foundation (No.
2014M551807).
REFERENCES
■
(1) For recent reviews on C−H activation, see: (a) Kakiuchi, F.;
Chatani, N. Adv. Synth. Catal. 2003, 345, 1077. (b) Godula, K.; Sames,
D. Science 2006, 312, 67. (c) Bergman, R. G. Nature 2007, 446, 391.
(d) Alberico, D.; Scott, M. E.; Lautens, M. Chem. Rev. 2007, 107, 174.
(e) Chen, X.; Engle, K. M.; Wang, D.-H.; Yu, J.-Q. Angew. Chem., Int. Ed.
2009, 48, 5094. (f) Lyons, T. W.; Sanford, M. S. Chem. Rev. 2010, 110,
1147. (g) Jazzar, R.; Hitce, J.; Renaudat, A.; Sofack-Kreutzer, J.; Baudoin,
O. Chem.Eur. J. 2010, 16, 2654. (h) Sun, C.-L.; Li, B.-J.; Shi, Z.-J.
Chem. Rev. 2011, 111, 1293. (i) Davies, H. M. L.; Du Bois, J.; Yu, J.-Q.
Chem. Soc. Rev. 2011, 40, 1855. (j) Bruckl, T.; Baxter, R. D.; Ishihara, Y.;
Baran, P. S. Acc. Chem. Res. 2012, 45, 826. (k) Haibach, M. C.; Seidel, D.
Angew. Chem., Int. Ed. 2014, 53, 5010.
(2) For examples of 1,4-hydride shift/cyclization, see: (a) Yang, S.; Li,
Z.; Jian, X.; He, C. Angew. Chem., Int. Ed. 2009, 48, 3999. (b) Alajarin,
M.; Martin-Luna, M.; Vidal, A. Adv. Synth. Catal. 2011, 353, 557.
(c) Mori, K.; Kurihara, K.; Yabe, S.; Yamanaka, M.; Akiyama, T. J. Am.
Chem. Soc. 2014, 136, 3744. (d) Mori, K.; Kurihara, K.; Akiyama, T.
Chem. Commun. 2014, 50, 3729.
(3) For selected examples of 1,5-hydride shift/cyclization, see:
(a) Pastine, S. J.; McQuaid, K. M.; Sames, D. J. Am. Chem. Soc. 2005,
127, 12180. (b) Pastine, S. J.; Sames, D. Org. Lett. 2005, 7, 5429.
(c) Tobisu, M.; Chatani, N. Angew. Chem., Int. Ed. 2006, 45, 1683.
(d) Murarka, S.; Deb, I.; Zhang, C.; Seidel, D. J. Am. Chem. Soc. 2009,
131, 13226. (e) McQuaid, K. M.; Sames, D. J. Am. Chem. Soc. 2009, 131,
402. (f) Zhou, G.; Zhang, J. Chem. Commun. 2010, 46, 6593. (g) Kang,
Y. K.; Kim, S. M.; Kim, D. Y. J. Am. Chem. Soc. 2010, 132, 11847.
(h) Mori, K.; Kawasaki, T.; Sueoka, S.; Akiyama, T. Org. Lett. 2010, 12,
1732. (i) Bolte, B.; Gagosz, F. J. Am. Chem. Soc. 2011, 133, 7696.
(j) Zhou, G.; Liu, F.; Zhang, J. Chem. −Eur. J. 2011, 17, 3101. (k) Cao,
W.; Liu, X.; Wang, W.; Lin, L.; Feng, X. Org. Lett. 2011, 13, 600. (l) Jiao,
Z.-W.; Zhang, S.-Y.; He, C.; Tu, Y.-Q.; Wang, S.-H.; Zhang, F.-M.;
Zhang, Y.-Q.; Li, H. Angew. Chem., Int. Ed. 2012, 51, 8811. (m) Mori, K.;
Ehara, K.; Kurihara, K.; Akiyama, T. J. Am. Chem. Soc. 2011, 133, 6166.
(4) For examples of [1,6]-hydride shift/cyclization, see: (a) Verboom,
W.; Reinhoudt, D. N.; Visser, R.; Harkema, S. J. Org. Chem. 1984, 49,
269. (b) Reinhoudt, D. N.; Visser, G. W.; Verboom, W.; Beenders, P. H.;
̈
(10) (a) Stobaugh, J. F.; Repta, A. J.; Sternson, L. A. J. Org. Chem. 1984,
49, 4306. (b) Kricka, L. J.; Vernon, J. M. J. Chem. Soc. C 1971, 2667.
(c) Duan, S.; Sinha-Mahapatra, D. K.; Herndon, J. W. Org. Lett. 2008,
10, 1541.
(11) (a) Pahadi, N. K.; Paley, M.; Jana, R.; Waetzig, S. R.; Tunge, J. A. J.
Am. Chem. Soc. 2009, 131, 16626. (b) Xue, X. S.; Yu, A.; Cai, Y.; Cheng,
J.-P. Org. Lett. 2011, 13, 6054.
(12) (a) Kreher, R.; Use, G. Heterocycles 1982, 19, 637. (b) Bonnett, R.;
North, S. A.; Newton, R. F.; Scopes, D. I. C. Tetrahedron 1983, 39, 1401.
(c) Kreher, R. P.; Hildebrand, T. Chem. Ber. 1988, 121, 81. (d) Grigg, R.;
Somasunderam, A.; Sridharan, V.; Keep, A. Synlett 2009, 97.
(e) Yanagimoto, T.; Toyota, T.; Matsuki, N.; Makino, Y.; Uchiyama,
S.; Ohwada, T. J. Am. Chem. Soc. 2007, 129, 736.
(13) Fehr, C.; Vuagnoux, M.; Buzas, A.; Arpagaus, J.; Sommer, H.
Chem.Eur. J. 2011, 17, 6214.
(14) (a) Nakamura, H.; Kamakura, T.; Ishikura, M.; Biellmann, J.-F. J.
Am. Chem. Soc. 2004, 126, 5958. (b) Nakamura, H.; Onagi, S.;
Kamakura, T. J. Org. Chem. 2005, 70, 2357.
(15) Nieto-Oberhuber, C.; Lop
́
ez, S.; Munoz, M. P.; Car
́
denas, D. J.;
Bunuel, E.; Nevado, C.; Echavarren, A. M. Angew. Chem., Int. Ed. 2005,
̃
44, 6146.
(16) The endo configuration was identified by its X-ray structure; see
the Supporting Information.
(17) Deb, I.; Das, D.; Seidel, D. Org. Lett. 2011, 13, 812.
3823
dx.doi.org/10.1021/ol5017355 | Org. Lett. 2014, 16, 3820−3823