Au-catalyzed intramolecular annulations toward fused tricyclic [1,3]oxazino[3,4-a]indol-1-ones under extremely mild conditions

Full text of DOI:10.1039/c5ra21109c

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: Z. Chen, X. Zeng,
B. Yan, Y. zhao and Y. Fu, RSC Adv., 2015, DOI: 10.1039/C5RA21109C.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Please do not adjust margins
RSC Advances
Page 1 of 5
View Article Online
DOI: 10.1039/C5RA21109C
RSC Advances
COMMUNICATION
Au-catalyzed Intramolecular Annulations Toward Fused Tricyclic
[1,3]oxazino[3,4-a]indol-1-ones under Extremely Mild Conditions
Zhiyuan Chen,*,a Xingping Zeng,a Bingyu Yan,a Yanlu Zhao, and Yang Fu*,a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
We report a general and efficient method for the rapid generation Scheme 1. (a) 1.3-Oxazinane. (b) fused indole-based tetracyclic compound
of tricyclic [1,3]oxazino[3,4-a]indol-1-ones under extremely mild that containing an 1.3-oxazinane. (c) fused tricyclic 1.3-oxazinane derivative.
conditions. The reaction is compatible with a wide range of
functionalized indoles with different electronic natures. The blue
light fluorescent emission properties of some titled fused-tricyclic
compounds are briefly studied.
We recently published studies regarding the transition-metal-
catalyzed electrophilic cycloisomerization reaction of multiple
alkynes 1 (Scheme 2a) to prepare functionalized carbocyclic and
heterocyclic
molecules
B
such
as
halo-substituted
benzo[a]fluorenols,6a densely trisubstituted naphathelenes,6b 3-
CF3S-1-metheleneindenes,6c 2-vinyl-3-OAc-indenes,6d etc. The
reactions were supposed to proceed by a stepwise mechanism and
involve metal-coordination and activation of the alkyne triple bond
(intermediate I), intramolecular nucleophilic attack on the cationic
species to form the ring skeleton A1 and A2, and subsequent de-
metallation reactions by the in situ generated electrophiles E+
(Scheme 2a).
Substituted 1.3-oxazinane alkaloids are an important subclass of
heterocycles due to their presence in a wide range of natural or
bioactive molecules (Scheme 1a).1 1.3-Oxazinanes are versatile
synthetic building blocks for organic synthesis, and they can be
readily converted to N-alkyl- or N-H-functionalized 1,3-
aminoalcohols in concise transformations.2 1.3-Oxazinanes with
fused aromatic analogues are very closely related to optoelectronic
material fields (Scheme 1b).3 For instance, 1.3-oxazinane with a
fused 3H-indole structure was found to be stable enough to
tolerate hundreds of switching cycles in photochemical experiments
with no sign of decomposition even in oxygenation conditions. Their
excellent fatigue resistance has made the indole-based 1,3-
E+
(in situ)
[M]
E
a)
R
R
Nu
[M]
Nu
(a)
(b)
[M]
b
X
X
R
[M]
oxazinanes attractive as photoresponsive photochromic filters and
A1
B1
R
4
X
Nu
photonic devices.
Moreover, because the indole-based
E+
(in situ)
a
[M]
X
E
Nu
R
R
1
heterocycles generally display potent biological or medicinal
activities, we envisioned that the incorporation of the indole moiety
into the scaffold of 1,3-oxazinanes would be beneficial for
subsequent biological evaluation or chemical genetic studies. While
there are reports of polycyclic indole skeletons containing
oxazinane structures,5 there are currently lack of general method
describing the synthesis of fused tricyclic [1,3]oxazino[3,4-a]indol-1-
ones (Scheme 1c).
I
Nu
[M]
Nu
X
X
b)
A2
B2
R'
N
Boc
M
O
2
R'
H+
R'
[M]
N
N
O
[M]
[M]
O
(favored!)
(a)
(b)
O
C
R'
N
b
H+
a
O
N
( in situ)
O
O
N
HN
(a)
O
M
O
R'
R'
II
(b)
(c)
H+
N
O
N
O
[M]
O
O
D (disfavored!)
a.Key Laboratory of Functional Small Organic Molecules, Ministry of Education, and
College of Chemistry & Chemical Engineering, Jiangxi Normal University, Ziyang
Road 99, Nanchang, Jiangxi 330022 (P. R. China). E-mail: zchen@jxnu.edu.cn;
yangfu@jxnu.edu.cn
Scheme 2. (a) Published results in transition-metal-catalyzed electrophilic
cyclization reactions. (b) Proposed synthethic route.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
The facile nature of catalytic cycloisomerization strategies
prompted us to imagine that a similar reaction using Boc-protected
This journal is © The Royal Society of Chemistry 20xx
RSC Advances, 2015, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 2 of 5
View Article Online
DOI: 10.1039/C5RA21109C
COMMUNICATION
Journal Name
2-alkylindole 2 as a starting material would lead to the indole-based reaction medium (Table 1 entries 14-18). Finally, the concentration
tricyclic product C or D (Scheme 2b). As shown in Scheme 2b, the of this intramolecular annulation reaction was also tested (Table 1
reaction would commence with a 6-endo-dig (path a) or 5-exo-dig entries 19-20). Impressively, this reaction is easily handled and only
(path b) cyclization of a tethered carbamate onto a metalla-alkyne requires the catalyst and environmentally friendly solvent to
complex II followed by the formation of tricyclic ring systems with promote the expected transformation at room temperature.
concurrent elimination of the carbocation tBu+. Isobutene would be
Table 1. Optimization of the reaction conditions.[a]
released from the tert-butyl group and the in situ-generated proton
could in turn work as an electrophile to induce the demetallation
reaction to close the catalytic cycle. In this regard, we suggest that
bond angles of 120° rather than 109.5° in the rigid indole-C2 atom
in intermediacy II should force the putative 6-endo-dig cyclization
pathway to be a more favored one. This shows that product C is the
entry cat. (x mol%)
additive (1.0
eq.)
solv.
time
/h
3a/%a
major outcome.
The transition-metal-catalyzed intramolecular cyclizations of
alkynes for the rapid generation of five-membered dioxolan-2-
ones7a,b and 1,3-oxazolidin-2-ones8a,b,9 and oxazinones have been
realized. Gagosz et al reported a one-pot Cu(II) and Au(I) co-
catalyzed sequential reaction of bromoalkyne with tert-
1
2
3
4
5
AuCl3 (5)
AuCl3 (5)
AuCl3 (5)
AgOTf (5)
-
DCM
24
24
24
24
2
9
-
Toluene
EtOH
0
-
21
0
butyloxycarbamate to give
a
diverse set of 1,5-disubstituted
gold-catalyzed
oxazolones. 9 Asao and co-workers reported
a
-
EtOH
alkylation reaction of alcohols and aromatic compounds using
ortho-alkynylbenzoic acid alkyl esters as starting materials.10,11
Occhiato and co-workers reported a cyclic urethane derivatives
synthesis via gold(I)-catalyzed cyclization of N-Boc-protected 6-
alkynyl-3,4-dihydro-2H-pyridines.12 However, the development of
practical and efficient methods to prepare six-membered and
indole-based fused tricyclic ring systems, especially from readily
available starting materials and simple processing reactions, are still
of highly desirable.
Ph3PAuCl (2.5) +
AgBF4 (5)
p-TsOH
EtOH
58
6
AuCl3 (5)
AuCl3 (5)
AuCl3 (5)
AuCl3 (5)
AuCl3 (5)
HAuCl4 (5)
HAuCl4 (2)
-
p-TsOH
EtOH
EtOH
EtOH
EtOH
DCM
EtOH
EtOH
EtOH
DCM
2.5
4
75
43
37
68
72
92
75
0
7
MsOH
8
HOAc
10
4.5
4
9
TFA
10
11
12
13
14
15
p-TsOH
Results and Discussion
-
2.5
5
-
The NBoc-2-alkynylindole 2a was first selected as a test substrate.
Initially, the model reaction of indole 2a under the catalysis of AuCl3
in dichloromethane was examined.13 To our delight, the desired
product (compound 3a) was isolated at very low yields (Table 1,
entry 1). The targeted by-product 3a’ was not detected. Preliminary
study indicated that alcoholic solvent was an optimal reaction
medium; the yield of compound 3a could be improved to 21% in
ethanol (Table 1, entry 3). Notably, the silver catalyst was totally
inert (Table 1, entry 4). We reasoned that the acidic condition
would be necessary for the formation of the carbenium ion species
because it was assumed to be involved in the annulation process.
To this end, we were delighted to find that the addition of p-TsOH
dramatically accelerated the transformation, and the desired
compound 3a was isolated in 58% or 75% yield when catalyzed via
Ph3PAuBF4 or AuCl3, respectively (Table 1, entries 5-6). No improved
performance was observed when Brønsted acids such as MsOH,
HOAc, or TFA were used (Table 1 entries 7-9). A similar result of 72%
yield was obtained when using DCM as the solvent under the
catalysis of AuCl3 (Table 1 entry 10). Good results were obtained
when a commercially available acidic gold catalyst, HAuCl4, was
evaluated. The desired product 2a was isolated in 92% yield even in
the absence of external acid additives (Table 1 entry 11). We next
screened some other laboratory solvents using HAuCl4 as the
catalyst. The results indicate that ethanol was the most optimal
p-TsOH
24
4
HAuCl4 (5)
HAuCl4 (5)
-
-
88
84
1,4-
dioxane
4
16
17
18
19
20
HAuCl4 (5)
HAuCl4 (5)
HAuCl4 (5)
HAuCl4 (5)
HAuCl4 (5)
-
-
-
-
-
HFIP
4
54
MeOH
iPrOH
EtOH
EtOH
4
87
14
12
1.5
86
92b
85c
[a] reaction conditions: 1a (0.20 mmol), catalyst (x mol%), additive (y eq.),
solvent (2.0 mL, 0.10 M), room temp. [b] EtOH (3.0 mL); [c] EtOH (1.0 mL). p-
TsOH = 4-methylbenzenesulfonic acid. MsOH = methanesulfonic acid. TFA =
2,2,2-trifluoroacetic acid. HFIP = 1,1,1,3,3,3-hexafluoropropan-2-ol.
Having defined the conditions needed for efficient
transformation, we next examined a wide variety of NBoc-2-
alkynylindoles (2; Table 2).14 The reaction was found to have a
good functional group tolence with respect to variation of the R2
2 | RSC Advances, 2015, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 3 of 5
View Article Online
DOI: 10.1039/C5RA21109C
Journal Name
COMMUNICATION
groups in substrate
2 as well as the existence of aryl-, Therefore, the existence of these groups suggest that further
heteroaryl-, alkyl, and cycloalkyl groups at this position. For elaborations on the resulting products may be easily achieved
example, when R1 = H and the aryl group on R2 contained via palladium-catalyzed cross-coupling reactions.
electron-donating or -withdrawing substituents, the expected
Interestingly, when substrate 4 contained a nucleophilic free
products 3b to 3i were obtained in 52-86% yields. Notably, the hydroxoy group at the C3 position of the indole core structure,
photoelectronically important CN group (2f) 15 and 2-thienyl the cyclization reaction selectively occurred at the ester moiety,
16
group (2j)
can also be tolerated. This indicates that and the free OH group was alkylated with the alcoholic solvent
photochromic property studies might be conducted in the future to afford product 5. Only modest yield of 63% could be obtained
with fluorescence spectroscopy.4 The presence of a heteroaryl when using HAuCl4 (5 mol%) as the cataylst for reaction of 4a to
goup on the 2-thienyl substituent was also tolerated under 5a, however, this could be improved to 75% yield when AuCl3
standard conditions. This afforded the expected product 3j in 77% (5.0 mol%) was used as the catalyst, p-TsOH (1.0 equiv.) as the
yield. The efficiency of this reaction was not compromised when acidic additive and DCM as the solvent. We presumed the
substrates containg alkyl groups such as n-hexyl or cyclopropyl HAuCl4 should be too acidic as compared with p-TsOH for the
substituent were added at the R2 position. The corresponding reaction of 4a to 5a. The structure of compound 5 was identified
products 3k and 3l were isolated in 86% and 72% yields, unambiguously by X-Ray diffraction analysis. 17 It should be
respectively.
noted that when running the reaction of 4 in nonalcoholic
solvents such as dichloromethane or 1,4-dioxane, which were
potential solvents for the cyclization reaction of 2a (Table 1),
the reaction became black soon and a complex mixture were
observed. This result indicated that for the reaction of 4 to 5,
the etherization process of substrate 4 with alcohol should
possibly happen first before the 6-endo-dig cyclization.
Table 2. Scope of NBoc-2-alkynylindoles 2.[a]
R1
R1
R2
HAuCl4 (5 mol%)
N
R2
N
EtOH (0.1 mol/L);
room temp. time.
O
COOtBu
O
2
3
Table 3. Annulation reaction of NBoc-3-hydroxymethylindoles 4.[a]
nBu
C6H4-p-OMe
3d, 81%, 1h
Me
O
O
O
, 77%, 4h
, 86%, 2h
N
NHAc
CN
F
O
O
3f, 71%, 34h
O
O
3g, 67%, 10h
, 76%, 20h
Cl
Br
S
O
O
O
3h, 70%, 8h
, 52%, 12h
, 77%, 2h
Me
Ph
O
O
O
3k, 86%, 2h
3l, 72%, 15h
, 88%, 3h
S
N
N
Cl
Cl
Cl
nBu
O
O
O
O
O
3o, 76%, 3h
3p, 67%, 2h
, 80%, 12h
Br
Br
O
O
3r, 90%, 2h
, 72%, 3h
[a] reaction conditions: compound 4 (0.20 mmol, 1.0 equiv), AuCl3 (5 mol%),
p-TsOH (1.0 equiv), EtOH (2.0 mL, 0.10 M), rt, open air; isolated yields based
on compound 4. [b] MeOH (2.0 mL) instead of EtOH as the solvent.
[a] Reaction conditions: 2 (0.20 mmol), HAuCl4 (5 mol%), EtOH (2.0 mL, 0.10
M), rt; isolated yields based on 2.
This result is significant and deserves notice because it is
widely accepted that the nucleophilic ability of the free OH
group is much stronger than the oxygen atom in carbamate. 18
However, the 6-endo-dig cyclization product 5 was found to be
the only product, and compound 5’ was not observed. This
result confirmed our hypothesis that the NBoc-2-alkynylindole
structure is very rigid (scheme 1b) such that the nucleophilic
oxygen is positioned and should be held close to the alkyne
For the various substituents attached at the benzoid ring of
the indole core structure, we were delighted to find that the
electron-rich alkyl group and the electron-deficient halogen
group (6-Cl and 5-Br) can be tolerated to give a structually
divergent 1H-[1,3]oxazino[3,4-a]indol-1-ones (3m-3r) in good to
excellent yields. Halogen groups such as chloro and bromo
atoms are versatile synthetic handles in organic synthesis.
This journal is © The Royal Society of Chemistry 20xx
RSC Advances, 2015, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 4 of 5
View Article Online
DOI: 10.1039/C5RA21109C
COMMUNICATION
Journal Name
d
Hamamatsu Quantaurus-QY system. Fluorescence life time studies were
recorded on a Hamamatsu Quantaurus-Tau system.
reaction center. Therefore, the relative nucleophilicity is not
necessarily the determining factor for the annulation reaction.
For the hydroxyl group to attack the alkyne-gold complex, an
anti relationship is needed, which might be sterically
disfavoured by the Boc group. The yields of the alkyl substituted
products 5g and 5h were only moderate, and were presumably
due to the relatively low reactivity or the inherent strain of the
corresponding starting materials.
To demonstrate the utility of the resulting tricyclic
[1,3]oxazino[3,4-a]indol-1-ones, the fluorescence of compounds
3a, 3d, 3f, 3g, and 3j were briefly studied (Figure 1). These
compounds were selected to be representative because the
fluorescence emission behaviours were largely dependent on
the fluorophore with influence on the substituted groups.20 The
results showed that all of the compounds emitted from 400 nm
to 450 nm (the maxinum emission wavelength were shown in
table 4). In addition, distinct electronic effects in the emission
spectra were also observed. For example, compound 3d has an
electron-donating methoxy group at the phenyl moiety, and it
displayed a red-shift in emission wavelength versus 3a (from
408 to 413 nm). Compound 3g has an electron-deficient halogen
group, and it produced a minor blue shift (406 nm) in the
emission spectrum. Compounds 3f and 3j had an obvious red-
shift because the largest emission peaks were located at 435 nm
and 440 nm, respectively. The solution quantum yields of
compounds 3a, 3d, 3g and 3f displayed efficiencies ranged from
0.49 to 0.76 (Table 4). This result indicated that flexible emission
band tuning might be achieved simply by changing the
electronic nature of the substituents. These were attached at
the fluorophore core structure. In addition, lumophores based
on 3a as a matrix may play a crucial role in light emitting
materials, environmental sensors or bio-probes in future work.
More detailed photophysical characterization is currently
underway.
The aldehyde group in the C3 position of the indole substrate
can be successfully tolerated (Scheme 3, eq 1). When aldehyde 6
was cyclized, the expected product 7 was isolated in 80% yield.
The aldehyde group was very reactive in organic synthesis, and
the tolerance of this functional group suggested that additional
transformations such as the Seyferth-Gilbert homologation19 or
reductive amination reactions should be possible to introduce
diversity and complexity. Moreover, the 2-(1H-indol-2-yl)-1-
phenylethanone 8 could be obtained in 63% yield when treating
the compound 3a in KOH-EtOH (Scheme 3, eq 2).
Scheme 3. Annulation reaction of the aldehyde substituted indole 6.
And ring expansion reaction of product 3a.
Conclusions
1.0
3a
3d
In conclusion, photophysically and pharmaceutically important
tricyclic [1,3]oxazino[3,4-a]indol-1-ones were constructed
efficiently via a gold-catalyzed intramolecular cyclization of N-
Boc-2-alkynylindoles under room temperature in alcoholic
solvent. This reaction is easily handled because only the
catalyst and environmentally friendly solvent are needed to
promote the formal annulation. In addition, the reaction
shows a high chemical selectivity toward 6-endo-dig cyclization
because no 5-exo-dig cyclization was observed. This method
0.8
3f
3g
3j
0.6
0.4
0.2
0.0
350
375
400
425
450
475
500
525
550
575
highlights
a facile one-step transformation from easily
Wavelength nm
available starting materials to structurally diverse
[1,3]oxazino[3,4-a]indol-1-ones. These are not readily available
via conventional synthetic methods. The preliminary
photophysical examinations revealed that some of the tricyclic
products have blue fluorescence. This indicated that the fused
polyaromatic compounds might be used as optoelectronic
materials in future work.
Figure 1. The fluorescence spectrum of compounds 3a, 3d, 3f, 3g, and 3j.
Experiments were carried out in a dilute solution of CHCl3 (10-5 mol/L) at
room temperature.
Table 4. Photophysical Properties Measured in CHCl3 (10-5 mol/L).
c
compound
λmax,em/nm
ΦF
τF (ns) d
1.24
1.18
1.53
3a
3d
3g
3j
386, 409a, 432b
389, 412a, 437b
384, 407a, 431b
413, 434a, 462b
0.572
0.666
0.496
Acknowledgements
0.76
2.12
We thank the National Natural Science Fundation of China
(21202065, 21462022), and the Natural Science Foundation of
Jiangxi Province (20142BAB203005) for financial support.
a
b
Referenced to the maximum emission peak. referenced to the shoulder
c
peak.
Absolute fluorescence quantum yields were recorded on a
4 | RSC Advances, 2015, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 5 of 5
View Article Online
DOI: 10.1039/C5RA21109C
Journal Name
COMMUNICATION
Keywords: gold-catalysis • intramolecular annulation • indole • 1H-
[1,3]oxazino[3,4-a]indol-1-one • tricyclic compounds
Notes and references
14 We have also screened the reaction of NCbz-2-phenylethynyl-1H-indole
and NFmoc-2-phenylethynyl-1H-indole under the optimized conditions,
however, only far inferior yield of product 3a was obtained.
15 (a) R. García, S. More, M. Melle-Franco, and A. Mateo-Alonso, Org. Lett.
2014, 16, 6096. (b) E. Donckele, A. Finke, L. Ruhlmann, C. Boudon, N.
Trapp, and F. Diederich, Org. Lett. 2015, 17, 3506. (c) S. Park, S. Varghese,
J. Kim, S. Yoon, O. Kwon, B. An, J. Gierschner, and S. Park, J. Am. Chem.
Soc. 2013, 135, 4757.
1 (a) A. Frank, V. Sylvia, and B. Stefan, Tetrahedron 2003, 59, 6785. (b) C.
Kuroda, S. Shimizu, and J. Satoh, J. Chem. Soc., Chem. Commun., 1987,
286. (c) O. Meth-Cohn, and S. Rhouat, J. Chem. Soc., Chem. Commun.
1981, 5. 241.
16 (a) Y. Wang, J. Ma, and Y. Jiang, J. Phys. Chem. A, 2005, 109, 7197. (b) N.
Tanifuji, M. Irie, and K. Matsuda, J. Am. Chem. Soc. 2005, 127, 13344.
17 CCDC 1400834 (5d) contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
2 For selected examples, see: (a) M. P. Sibi, Z. Ma, and C. Jasperse, J. Am.
Chem. Soc. 2005, 127, 5764 (b) W. J. Humenny, P. Kyriacou, K. Sapeta, A.
Karadeolian, and M. A. Kerr, Angew. Chem., Int. Ed. 2012, 51, 11088. (c)
Y.-B. Kang, X. Sun, and Y. Tang, Angew. Chem., Int. Ed. 2007, 46, 3918.. (d)
I. S. Young, and M. A. Kerr, Org. Lett. 2004, 6, 139.
Cambridge
www.ccdc.cam.ac.uk/data_request/cif.
18 The nucleophilic ability of oxygen group should be weakened when
linked with strong electron-withdrawing carbonyl group. For
Crystallographic
Data
Centre
via
3 E. Deniz, M. Tomasulo, S. Sortino, and F. Raymo, J. Phys. Chem. C. 2009,
113, 8491.
a
selected examples using alcohol as nucleophiles in transition-metal
catalysis, see: (a) B. M. Trost, M. R. Machacek, H. C. Tsui, J. Am. Chem.
Soc. 2005, 127, 7014. (b) B. M. Trost, H. C. Tsui, F. D. Toste, J. Am.
Chem. Soc. 2000, 122, 3534.
4 R. A. Evans, and G. K. Such. Coloration Tech. 2005, 58, 825.
5 (a) S. Raghao, and G. Milind, J. Chem. Res., Synopses, 1996, 11, 496. (b) A.
Javier, D. Francisca, V. Juan, L. Jose, and L. Carlos, Tetrahedron Lett. 2002,
43, 8025. (b) J. Liu, M. Shen, Y. Zhang, G. Li, A. Khodabocus, S. Rodriguez,
B. Qu, V. Farina, C. Senanayake, and B. Lu, Org. Lett. 2006, 8, 3573.
6 Benzofluorenol: (a) Z. Chen, M. Zeng, J. Yuan, Q. Yang, and Y. Peng, Org.
Lett. 2012, 14, 3588. Naphthelene: (b) Z. Chen, X. Jia, C. Ye, G. Qiu, and J.
Wu, Chem. Asian. J. 2014. 9, 126. Methyleneindene: (c) Q. Xiao, H. Zhu, G.
Li, and Z. Chen, Adv. Synth. Catal. 2014, 356, 3809. (d) H. Zhu, J. Huang, C.
Fan, and Z. Chen, Chem. Asian. J. 2015. 10, 1463.
19 (a) J. C. Gilbert, and U. Weerasooriya, J. Org. Chem., 1982, 47, 1837. (b) G.
J. Roth, B. Liepold, S. G. Müller, and H. J. Bestmann, Synthesis, 2004, 59.
20 Z. Chi, X. Zhang, B. Xu, X. Zhou, C. Ma, Y. Zhang, S. Liu, and J. Xu, Chem.
Soc. Rev. 2012, 41, 3878.
7 (a) A. Buzas, and F. Gagosz, Org. Lett. 2006, 8, 515. (b) C. Lim, J. Kang, J.
Lee, and S. Shin, Org. Lett. 2007, 9, 3539.
8 (a) A. Buzas, and F. Gagosz, Synlett 2006, 2727. (b) R. Robles-Machin, J.
Adrio, and J. C. Carretero, J. Org. Chem. 2006, 71, 5023. (c) E. Lee,H.
Yeom, J. Hwang, and S. Shin, Eur. J. Org. Chem. 2007, 3503. (d) A. S. K.
Hashmi, R. Salathe, and W. Frey, Synlett, 2007, 1763.
9 F. Istrate,; A. Buzas, I. Jurberg, Y. Odabachian, and F. Gagosz, Org. Lett.
2008, 10, 925.
10 N. Asao, H. Aikawa, S. Tago, and K. Umetsu, Org. Lett. 2007, 9, 4299.
11 For recent reviews of gold catalysis, see: (a) Modern Gold-Catalyzed
Synthesis; A. S. K. Hashmi, and F. D. Toste, Eds.; Wiley-VCH, Weinheim,
Germany, 2012. (b) M. Rudolph, and A. S. K. Hashmi, Chem. Soc. Rev. 2012,
41, 2448. (c) A. Fürstner, Chem. Soc. Rev. 2009, 38, 3208. (d) Z. Li, C.
Brouwer, and C. He, Chem. Rev. 2008, 108, 3239.
12 A. Oppedisano, C. Prandi, P. Venturello, A. Deagostino, G. Goti, D. Scarpi,
E. G. Occhiato, J. Org. Chem. 2013, 78, 11007.
13 (a) N. Patil, R. D. Kavthe, and Y. Yamamoto, Adv. Heterocycl. Chem. 2010,
101, 75. (b) H. V. Adcock, and P. W. Davies, Synthesis, 2012, 44, 3401.
This journal is © The Royal Society of Chemistry 20xx
RSC Advances, 2015, 00, 1-3 | 5
Please do not adjust margins