Gold-Catalyzed Cyclization of Furan-Ynes bearing a Propargyl Carbonate Group: Intramolecular Diels–Alder Reaction with In Situ Generated Allenes

Article abstract of DOI:10.1002/chem.201603055

Gold-catalyzed cyclization of various furan-ynes with a propargyl carbonate or ester moiety results in the formation of a series of polycyclic aromatic ring systems. The reactions can be rationalized through a tandem gold-catalyzed 3,3-rearrangement of the propargyl carboxylate moiety in furan-yne substrates to form an allenic intermediate, which is followed by an intramolecular Diels–Alder reaction of furan and subsequent ring-opening of the oxa-bridged cycloadduct. It was found that the steric and electronic properties of phosphine ligands on the gold catalyst had a significant impact on the reaction outcome. In the case of 1,5-furan-yne, the cleavage of the oxa-bridge in the cycloadduct with concomitant 1,2-migration of the R¹group occurs to furnish anthracen-1(2H)-ones bearing a quaternary carbon center. For 1,4-furan-yne, a facile aromatization of the cycloadduct takes place to give 9-oxygenated anthracene derivatives.

Full text of DOI:10.1002/chem.201603055

DOI: 10.1002/chem.201603055
Communication
&
Gold Catalysis
Gold-Catalyzed Cyclization of Furan-Ynes bearing a Propargyl
Carbonate Group: Intramolecular Diels–Alder Reaction with In
Situ Generated Allenes
Ning Sun, Xin Xie, Haoyi Chen, and Yuanhong Liu*[a]
multistep synthesis,[7] or using terminal allenes formed in situ
through base-assisted propargyl-allenyl rearrangement.[8]
Abstract: Gold-catalyzed cyclization of various furan-ynes
with a propargyl carbonate or ester moiety results in the
formation of a series of polycyclic aromatic ring systems.
The reactions can be rationalized through a tandem gold-
catalyzed 3,3-rearrangement of the propargyl carboxylate
moiety in furan-yne substrates to form an allenic inter-
mediate, which is followed by an intramolecular Diels–
Alder reaction of furan and subsequent ring-opening of
the oxa-bridged cycloadduct. It was found that the steric
and electronic properties of phosphine ligands on the
gold catalyst had a significant impact on the reaction out-
come. In the case of 1,5-furan-yne, the cleavage of the
oxa-bridge in the cycloadduct with concomitant 1,2-mi-
gration of the R1 group occurs to furnish anthracen-1(2H)-
ones bearing a quaternary carbon center. For 1,4-furan-
yne, a facile aromatization of the cycloadduct takes place
to give 9-oxygenated anthracene derivatives.
Therefore, the development of efficient and convenient meth-
ods for IMDAF reactions of furans with allenes from easily ac-
cessible starting materials with wide structural diversity is
highly desirable. During our work on the utilization of the
gold-catalyzed 3,3-rearrangement of propargyl carbonates or
esters as an efficient tool for the generation of carboxyal-
lenes,[9] we envisioned that the thus-formed allenes might
react with a tethered furan through the Diels–Alder reaction. It
was noted that under the gold or platinum catalysis, the furan-
allenes usually undergo the metal-promoted intramolecular
[4+3] cycloaddition by forming a metal-allyl cation intermedi-
ate, which often competes with the [4+2] cycloaddition pro-
cess (Scheme 1). The reaction selectivity depends on the differ-
ent catalysts, substitution pattern of the substrates, and the re-
action conditions. For example, MascareÇas et al. found that
the use of PtCl2/CO or IPrAuCl/AgSbF6 (IPr=1,3-bis(2,6-diiso-
propylphenyl)imidazol-2-ylidene) could direct a route of [4+3]
cycloaddition.[10] They also showed in one case that the use of
AuCl3 or AuCl gave the [4+2] cycloadduct predominately at
elevated temperature (1108C).[10a] Toste et al. found that [4+2]
and [4+3] cycloadditions of diene-allenes could be controlled
by the gold catalyst with different ligands; p-acceptor ligands
such as triarylphosphite, favored the formation of a [4+2] cy-
cloadduct.[11] However, most of the successful substrates used
in these studies were diene-allenes, with only limited results
Furan rings widely occur as a key structural subunit in numer-
ous natural products and pharmaceuticals.[1] Substituted furans
also serve as synthetic intermediates and building blocks in or-
ganic synthesis.[2] In this regard, the intramolecular Diels–Alder
reactions of furan (IMDAF), as the diene component, with a va-
riety of dienophiles, such as activated alkenes, alkynes, or al-
lenes,[3] have been proved to be a powerful methodology in
the synthesis of polycyclic skeletons and in the total synthesis
of natural products.[4] In addition, the resulting oxygen-bridged
norbornenes or norbornadienes are valuable precursors for fur-
ther manipulations,[5] leading to a wide range of functionalized
molecules with biological interest.[6] Generally, allenes are more
reactive than alkenes as dienophiles, however, the utilization
of allenes in IMDAF reactions is largely unexplored. Most of
studies rely on the reactivity of activated allenes bearing an
electron-withdrawing group, which need to be pre-installed by
derived from furan-allenes.
A gold-catalyzed transannular
[4+3] cycloaddition of furan-allenes has been explored by
Gung et al.,[12] including the use of propargyl esters as the
allene precursors. They also disclosed that the gold-catalyzed
intermolecular reaction of terminal propargyl esters with
furans proceeded through the [4+3] process. During our stud-
ies on gold-catalyzed cyclization of furan-ynes,[13] we found
that ligands played an important role in achieving [4+2] cyclo-
addition of furans with in situ generated allenes. We now
report facile gold-catalyzed cascade reactions of furan-ynes
bearing a propargyl carbonate moiety, involving 3,3-rearrange-
ment and IMDAF reactions as the key steps, which provide
synthetically valuable anthracen-1(2H)-ones and 9-oxygenated
anthracenes with wide functional group tolerance (Scheme 2,
Eq. (1) and (2)). The cycloaddition step occurred exclusively by
a [4+2] process using bulky biphenyl-di-tert-butyl phosphine
derivatives as the ligands. Especially, in the case of 1,5-furan-
ynes, bearing a four-carbon linkage between furan and alkyne
moiety, a facile 1,2-migration of the R1 group occurred to fur-
[a] Dr. N. Sun, X. Xie, H. Chen, Prof. Y. Liu
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Or-
ganic Chemistry
Chinese Academy of Sciences
345 Lingling Lu, Shanghai 200032 (People’s Republic of China)
Fax: (+86) 021-64166128
E-mail: yhliu@sioc.ac.cn
Supporting information for this article can be found under
http://dx.doi.org/10.1002/chem.201603055.
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bulky phosphine ligands such as Sphos (2-dicyclohexylphos-
phino-2’,6’-dimethoxybiphenyl, catalyst C) catalyzed this reac-
tion less efficiently, leading to 2a in 42% yield (entry 6). Inter-
estingly, the use of (Me)4tBuXphos as the ligand (catalyst D) re-
sulted in the formation of a diastereomeric mixture of [4+2]
cycloadducts 4a and 4a’ in high yield (entry 7). These results
indicated that the steric and electronic properties of phosphine
ligands on gold catalysts had a significant impact on the reac-
tion outcome. When the reaction was run at room tempera-
ture using catalyst B, the cycloadduct 4 could also be ob-
served, along with 27% of 2a (entry 9). This suggests that 4
might be the intermediate leading to product 2. Decreasing
the amount of catalyst B to 2 mol% gave 2a in a lower yield
of 59% (entry 10). Changing the solvent to toluene or THF af-
forded 2a also in lower yields of 49 or 33% (entries 11,12, re-
spectively). We then investigated the effect of the protecting
groups on this reaction. Acetyl- (Ac), pivaloyl- (Piv), or benzoyl-
protected (Bz) substrates 5a–c, respectively, resulted in remark-
able decreases in product yields (24–46%), along with the for-
mation of several byproducts (entries 13–15). These results
reveal that the nature of the protecting groups on the alcohol
is also crucial for successful transformation. In this reaction,
a carbonate substrate is converted into 2a more efficiently
than those of esters, possibly due to the enhanced stability of
the carboxyallene intermediate for the carbonate cases.
Scheme 1. Metal-catalyzed [4+3] cycloaddition of furan-allenes.
Scheme 2. Gold-catalyzed [4+2] cycloaddition of furans with in situ
generated allenes.
nish the anthracenones containing
(Scheme 2, eq 1).
a quaternary carbon
Recently, we developed various gold-catalyzed intramolecu-
lar cyclizations of benzene-tethered furan-ynes, initiated by
attack of the furan on the gold-activated alkyne, followed by
furan ring-opening.[13] These initial results make the current
target 3,3-rearrangement/IMDAF reactions with high selectivity
a challenging task. To initiate an allene formation, 3,3-rear-
rangement of the propargyl carbonate moiety in designed
substrates 1 should occur more rapidly than the furan-yne cyc-
lization.[14] Here, we expected that the desired transformation
might be achieved through variation of the different ligands
on gold. To test the feasibility of our hypothesis, we initially ex-
amined the gold-catalyzed reactions of 1,5-furan-yne 1a bear-
ing a phenyl substituent at the alkyne terminus; the results are
shown in Table 1. Treatment of 1a in DCE (1,2-dichloroethane)
with cationic gold(I) complex PPh3AuSbF6, generated in situ, af-
forded only a complex reaction mixture (Table 1, entry 1). To
our delight, the use of a gold catalyst with an N-heterocyclic
carbene (NHC) ligand, after stirring the reaction mixture in DCE
at 508C for 2 h, provided the desired anthracen-1-(2H)-one 2a
in 56% yield, along with 7% of byproduct anthracene 3a
(entry 2). The structure of 2a was unambiguously confirmed
by X-ray crystallography.[15] The results indicated that an inter-
esting 1,2-migration of the phenyl group occurred during the
reaction process, resulting in the assembly of a quaternary
carbon center adjacent to a carbonyl functionality in 2a. De-
composition of the substrate was observed only in the pres-
ence of AgSbF6 (entry 3). When [JohnphosAu(MeCN)]SbF6 (cat-
alyst A) was used (Johnphos=(2-biphenyl)di-tert-butylphos-
phine), the yield of 2a increased to 67%, along with 9% of 3a
(entry 4). Gratifyingly, it was found that gold catalyst B with
tBuXphos (2-di-tert-butylphosphino-2’,4’,6’-triisopropylbiphenyl)
as the ligand was more efficient for this transformation, lead-
ing to 84% yield of 2a, whereas the formation of 3a was com-
pletely inhibited (entry 5). Gold complexes possessing other
Next, the scope of the gold-catalyzed cascade reaction was
evaluated under the conditions shown in Table 1, entry 5 (con-
ditions a); the results are shown in Table 2. We first investigat-
ed the electronic effect of the aryl substituents on the alkyne
terminus. We were pleased to find that a series of electron-
withdrawing groups substituted on the aryl alkynes such as p-
F, p-Cl, p-CF3, and p-CO2Et underwent the cyclization smoothly
to provide the corresponding anthracenones 2b,c,e,f in 64–
86% yields in short reaction times. However, when aryl alkynes
bearing substituents such as p-Br or p-OMe were employed,
the desired products were obtained only in low yields under
conditions a, possibly due to the rapid decomposition of the
starting materials. We then made efforts to re-optimize the re-
action conditions for those particular alkynes. Gratifyingly, we
À
found that simply changing the counterion from SbF6 to OTfÀ
(Tf=trifluoromethanesulfonyl) in the gold catalyst led to 70%
yield of 2g bearing a p-OMe-substituted aryl group (condi-
tions b, 5 mol% tBuXphosAuCl/AgOTf). Under these conditions,
p-Br-substituted 1d afforded 2d in a high yield of 88%. Elec-
tron-rich aryl alkynes with p-Me, p-tBu, 3-OMe, or 3,4,5-(OMe)3
substituents were also well suited under these conditions, fur-
nishing 2h–k in 42–78% yields. A thienyl group was well toler-
ated under conditions b, leading to the desired product 2l in
73% yield. The use of alkynes with an alkyl substituent such as
nBu resulted in a complex mixture of products, in DCE. In con-
trast, when the reaction was carried out in THF, this substrate
isomerized rapidly within 30 minutes at room temperature to
give allenyl carbonate 6m in 69% yield. A cyclopropyl-substi-
tuted alkyne also afforded allene product 6n in 79% yield in
THF. However, extending the reaction time formed a complex
reaction mixture, and the desired anthracen-1(2H)-ones were
not observed in these cases. Cyclization of substrate 1o with
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Table 1. Optimization studies for the formation of 2a.
Yield [%][a]
Entry
Substrate
Catalyst
Solvent
T [8C]
t [h]
2a
3a
4a/4a’
[b]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
R=CO2Me (1a)
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
PPh3AuCl/AgSbF6
IPrAuCl/AgSbF6
AgSbF6
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
toluene
THF
RT
50
RT
50
50
50
50
50
RT
50
50
50
50
50
50
2
2
2
4
2
2
6
6
12
5
–
56
–
–
7
–
9
–
7
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
[b]
A
B
C
D
E
B
B
B
B
B
B
B
67
84[c]
42
–
47/44
10/14
13/20
–
27
59[d]
49
33
24
44
46
–
–
–
–
–
–
3
3
5
3
R=Ac (5a)
R=Piv (5b)
R=Bz (5c)
DCE
DCE
DCE
3
1
[a] NMR yields determined by H NMR using CH2Br2 as an internal standard. [b] A complex reaction mixture was observed. [c] Yield of isolated product was
80%. [d] 2 mol% of catalyst B was used.
a C-5 unsubstituted furan ring occurred smoothly to give 1-
phenylanthracen-2-ol (7) in 63% yield under conditions b. The
structure of 7 was confirmed by the X-ray crystallography anal-
ysis of its OAc derivative,[15] in which no 1,2-phenyl migration
occurred.
We propose the following reaction mechanism for the
above-mentioned transformations (Scheme 3). Initially, gold-
catalyzed 3,3-rearrangement of the propargyl carbonate
moiety affords carboxyallene intermediate 6. This is followed
Scheme 3. Possible reaction mechanism for the formation of anthracenones
2.
by IMDAF reaction to give an oxa-bicyclic alkene intermediate
4. Then, gold-assisted cleavage of the oxa-bridge in cycload-
duct 4 takes place to give alcohol intermediate 9.[14] Subse-
quent 1,2-migration of the R1 group, followed by reaction of
the resulting oxocarbenium ion 11 with a LAuOH (L=ligand)
species furnishes the anthracenone products 2.[16] In the case
of 1o (R2 =H), elimination of the carbonate group occurred to
afford 7, due to the ease of aromatization.
To understand the reaction mechanism, we carried out the
following control experiments (Scheme 4). Treatment of cyclo-
adduct 4a or 4a’ in the presence of gold catalyst B in DCE af-
forded ring-opened product 2a in high yields. However, with-
out gold catalyst, no reaction occurred. It was therefore con-
cluded that ring opening of the oxa-bridge in intermediate 4
proceeded with the assistance of Lewis acid.
After the success of the transformation of 1,5-furan-ynes 1,
we next attempted to extend this cyclization reaction to 1,4-
furan-yne substrates 12 with a three-carbon linkage between
the furan and alkyne moieties. A brief optimization of reaction
conditions was carried out, the results of which are shown in
Table 3. It turned out that the use of gold catalysts with bulky
phosphine ligands afforded the desired 9-oxygenated anthra-
cenes 13a in generally good to high yields, and the best result
was achieved using [tBuXphosAu(MeCN)]SbF6 (catalyst B)
(Table 3, entries 1–4). When frequently used gold complexes
such as PPh3AuNTf2 or PPh3AuSbF6 were employed as the cata-
lyst, only low product yields of 37 and 10%, respectively, were
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Table 2. Synthesis of antracen-1(2H)-ones 2 through gold-catalyzed cyclization reactions of 1.
Substrate
Product[a]
Substrate
Product[a]
[a] Conditions used (a or b), reaction time, and yields of isolated product are shown. [b] The reaction was carried out at room temperature in THF.
tected (o-alkynyl)phenyl 2-furylcarbinols leading to protected
1-naphthols reported by us.[13d] This result, in which 14 was ob-
tained, indicated that the furan-yne cyclization occurred more
rapidly than 3,3-rearrangement of the propargyl carbonate
moiety. In addition to the carbonate substrates, propargyl
acetate or benzoate were also well suited for this reaction,
Scheme 4. Control experiments.
providing 13m and 13n in 91% and 94% yields, respectively.
observed (Table 3, entries 5,6). The scope of this reaction is
shown in Table 4. In most cases, the 3,3-rearrangement/cyclo-
addition cascade of substrates 12 proceeded quite efficiently,
catalyzed by 5 mol% of catalyst B (DCE, 508C, 1–3 h), leading
to 13 in good to excellent yields. In the present reaction, both
electron-withdrawing [p-Cl, p-CF3, p-CN, o-Br, o-F, 3,5-di-Cl] and
electron-donating [p-Me, 3-OMe, 3,5-di(OMe), 3,4,5-tri(OMe)]
aryl substituents were well-tolerated during the process, fur-
nishing the corresponding anthracene derivatives 13b–k in
50–96% yields. In particular, sterically encumbered o-Br-substi-
tuted substrate 12 f was smoothly converted into the corre-
sponding 13 f in a high yield of 89%. When a substrate bear-
ing an alkyl group, such as a n-butyl group at the propargylic
position (12l), was employed, a completely different product
of naphthalene 14 with a cis-enone moiety was obtained in
70% yield. In this case, a competitive gold-catalyzed cyclization
of furan-ynes with ring-opening of the furan moiety occurred,
similar to that of gold-catalyzed cycloisomerization of TBS-pro-
Table 3. Optimization studies for the formation of 13a.
Entry
Catalyst
t
Yield
[%][a]
[h]
1
2
3
4
5
6
7
B
A
C
D
1
1
1
6
4
4
1
93[b]
84
89
75
PPh3AuNTf2
PPh3AuCl/AgSbF6
AgSbF6
37
10
–
[c]
[a] NMR yields determined by 1H NMR using CH2Br2 as an internal
standard. [b] Yield of isolated product was 91%. [c] A complex reaction
mixture was observed.
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Table 4. Synthesis of functionalized anthracenes 13 through gold-catalyzed reactions of 12.[a]
Substrate
Product[a]
Substrate
Product[a]
[a] Yields of isolated product.
We propose the following reaction mechanism for the
formation of products 13 (Scheme 5). In the first step, an effi-
cient gold-catalyzed 3,3-rearrangement occurs to afford the
carboxyallene intermediate 15. This is followed by the IMDAF
reaction to give an oxa-bicyclic intermediate 16, ring-opening
of 16, and aromatization, which delivers the anthracene prod-
ucts 13.
In conclusion, we have developed an efficient and cascade
approach for IMDAF reactions with allenes. The allene moiety
can be constructed conveniently by a gold-catalyzed 3,3-rear-
rangement of the propargyl carbonates or in some cases,
esters, which undergo subsequent IMDAF reaction followed by
ring-opening of the oxa-bridged cycloadduct to afford polycyc-
lic aromatic skeletons. In the case of 1,5-furan-yne, the cleav-
The synthetic utility of these functionalized anthracene prod-
ucts was also briefly investigated (Scheme 6). Interestingly, in
the presence of ceric ammonium nitrate (CAN), a deprotection
followed by oxidation of 13m occurred smoothly in air, lead-
ing to anthraquinone 17 and its dimer 18 in 61% and 30%
yields, respectively. To our surprise, when the reaction was car-
ried out in CH3CN, 18 was formed as the only product in 95%
yield. Anthraquinones are an important class of naturally oc-
curring substances,[17] and they are also known as efficient
building blocks in the synthesis of polysubstituted acenes for
usage in organic functional materials.[18] Thus, our method
provides a facile route for these compounds.
Scheme 5. Possible reaction mechanism for the formation of anthracenes
13.
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[9] a) Y. Chen, M. Chen, Y. Liu, Angew. Chem. Int. Ed. 2012, 51, 6493; Angew.
Chem. 2012, 124, 6599; b) M. Chen, J. Liu, L. Wang, X. Zhou, Y. Liu,
Chem. Commun. 2013, 49, 8650.
[10] a) B. Trillo, F. Lꢁpez, M. Gulꢂas, L. Castedo, J. L. MascareÇas, Angew.
Chem. Int. Ed. 2008, 47, 951; Angew. Chem. 2008, 120, 965; b) B. Trillo, F.
Lꢁpez, S. Montserrat, G. Ujaque, L. Castedo, A. Lledꢁs, J. L. MascareÇs,
Chem. Eur. J. 2009, 15, 3336.
[11] P. Mauleꢁn, R. M. Zeldin, A. Z. Gonzꢃlez, F. D. Toste, J. Am. Chem. Soc.
2009, 131, 6348.
[12] a) B. W. Gung, D. T. Craft, Tetrahedron Lett. 2009, 50, 2685; b) B. W. Gung,
L. N. Bailey, J. Wonser, Tetrahedron Lett. 2010, 51, 2251; c) B. W. Gung,
D. T. Craft, L. N. Bailey, K. Kirschbaum, Chem. Eur. J. 2010, 16, 639.
[13] a) Y. Chen, Y. Lu, G. Li, Y. Liu, Org. Lett. 2009, 11, 3838; b) Y. Chen, Y. Liu,
J. Org. Chem. 2011, 76, 5274; c) Y. Chen, G. Li, Y. Liu, Adv. Synth. Catal.
2011, 353, 392; d) C. Wang, Y. Chen, X. Xie, J. Liu, Y. Liu, J. Org. Chem.
2012, 77, 1915; e) Y. Chen, M. Chen, Y. Liu, Angew. Chem. Int. Ed. 2012,
51, 6181; Angew. Chem. 2012, 124, 6285; f) N. Sun, X. Xie, Y. Liu, Chem.
Eur. J. 2014, 20, 7514; g) Y. Chen, L. Wang, N. Sun, X. Xie, X. Zhou, H.
Chen, Y. Li, Y. Liu, Chem. Eur. J. 2014, 20, 12015; h) C. Wang, X. Xie, J.
Liu, Y. Liu, Y. Li, Chem. Eur. J. 2015, 21, 559.
Scheme 6. Transformation of anthracene 13m (d.r.=diastereomeric ratio).
age of the oxa-bridge in the cycloadduct with concomitant
1,2-migration of an aryl group occurs to furnish anthracen-
1(2H)-ones bearing a quaternary carbon center. In the case of
1,4-furan-yne, a facile aromatization of the cycloadduct takes
place to give 9-oxygenated anthracene derivatives. Further ap-
plications of this cascade reaction to the synthesis of diverse
complex molecules are currently under way.
[14] For Pd-catalyzed reactions of similar types of furan-ynes with organo-
borons to anthracenes involving IMDAF reaction of furans with in situ-
formed allenes, see: C. Wang, L. Kong, Y. Li, Y. Li, Eur. J. Org. Chem.
2014, 3556.
[15] CCDC 1479103 (catalyst B), 1479104 (2a), 1479105 (3a), 1479106 (4a),
1494304 (OAc derivative of 7), 1479107 (13a), 1479108 (17), and
1479109 (18) contain the supplementary crystallographic data for this
paper. These data are provided free of charge by The Cambridge Crys-
tallographic Data Centre.
[16] The unusual formation of 3a shown in Table 1, entries 2, 4, and 6 might
be rationalized by following the tandem reaction: Initially, a propargyl
carbocation is formed by decarboxylation,[9a] which may equilibrate
with the allenyl carbocation. A hydride transfer from AuOMe produces
the allene, which undergoes a Diels–Alder reaction followed by ring-
opening, and aromatization to afford 3a.
Acknowledgements
We thank the National Natural Science Foundation of China
(Grant Nos. 21372244, 21572256, 21421091), Chinese Academy
of Science for financial support.
Keywords: allenes
· diels–alder reaction · furans · gold
catalysis · propargyl carbonates
[1] a) A. Boto, L. Alvarez in Heterocycles in Natural Product Synthesis, Wiley-
VCH, Weinheim, 2011, pp. 97–152; b) J. F. Kratochvil, R. H. Burris, M. K.
Seikel, J. M. Harkin, Phytochemistry 1971, 10, 2529; c) Y.-L. Lin, Y.-L. Tsai,
Y.-H. Kuo, Y.-H. Liu, M.-S. Shiao, J. Nat. Prod. 1999, 62, 1500; d) T. Krause,
M. U. Gerbershagen, M. Fiege, R. Weißhorn, F. Wappler, Anaesthesia
2004, 59, 364; e) Q.-Z. Ye, S.-X. Xie, M. Huang, W.-J. Huang, J.-P. Lu, Z.-Q.
Ma, J. Am. Chem. Soc. 2004, 126, 13940; f) H. Tan, X. Chen, Z. Liu, D. Z.
Wang, Tetrahedron 2012, 68, 3952.
[2] a) J. A. Joule, K. Mills, Heterocyclic Chemistry, 5th ed., Wiley-Blackwell,
Hoboken, 2010, pp. 347–368; b) H. Heaney, J. S. Ahn in Comprehensive
Heterocyclic Chemistry II, Vol. 2 (Eds.: A. R. Katritzky, C. W. Rees, E. F. V.
Scriven), Pergamon Press, Oxford, 1996, pp. 297–350.
[3] For reviews, see: a) B. H. Lipshutz, Chem. Rev. 1986, 86, 795; b) C. O.
Kappe, S. S. Murphree, A. Padwa, Tetrahedron 1997, 53, 14179.
[4] For the total synthesis of natural products using IMDAF reactions, see:
a) A. Padwa, M. A. Brodney, S. M. Lynch, J. Org. Chem. 2001, 66, 1716;
b) J. D. Ginn, A. Padwa, Org. Lett. 2002, 4, 1515; c) S. Claeys, D. V. Haver,
P. J. De Clercq, M. Milanesio, D. Viterbo, Eur. J. Org. Chem. 2002, 1051;
d) S. E. Wolkenberg, D. L. Boger, J. Org. Chem. 2002, 67, 7361; e) Q.
Wang, A. Padwa, Org. Lett. 2004, 6, 2189; f) C.-C. Li, S. Liang, X.-H.
Zhang, Z.-X. Xie, J.-H. Chen, Y.-D. Wu, Z. Yang, Org. Lett. 2005, 7, 3709;
g) A. Padwa, Q. Wang, J. Org. Chem. 2006, 71, 7391; h) A. Padwa, H.
Zhang, J. Org. Chem. 2007, 72, 2570.
[5] For reviews, see: a) P. Vogel, D. Fattori, F. Gasparini, C. L. Drian, Synlett
1990, 173; b) M. Lautens, K. Fagnou, S. Hiebert, Acc. Chem. Res. 2003,
36, 48; c) D. K. Rayabarapu, C.-H. Cheng, Acc. Chem. Res. 2007, 40, 971.
[6] a) M. Lautens, J.-L. Renaud, S. Hiebert, J. Am. Chem. Soc. 2000, 122,
1804; b) R. M. Bimwala, P. Vogel, J. Org. Chem. 1992, 57, 2076.
[7] a) S. G. Cauwberghs, P. J. De Clercq, Tetrahedron Lett. 1988, 29, 6501;
b) M. P. S. Ishar, A. Wali, R. P. Gandhi, J. Chem. Soc., Perkin Trans. 1 1990,
2185; c) M. E. Jung, S.-J. Min, J. Am. Chem. Soc. 2005, 127, 10834.
[8] a) K. Kanematsu, I. Kinoyama, J. Chem. Soc., Chem. Commun. 1992, 735;
b) H.-J. Wu, F.-H. Ying, W.-D. Shao, J. Org. Chem. 1995, 60, 6168; c) G. O.
Torosyan, Russ. J. Org. Chem. 2002, 38, 1489; d) A. G. Lohse, R. P. Hsung,
Org. Lett. 2009, 11, 3430.
[17] a) P. A. Cohen, G. H. N. Towers, Phytochemistry 1995, 40, 911; b) L. P. Mai,
F. Gꢄuritte, V. Dumontet, M. V. Tri, B. Hill, O. Thoison, D. Guꢄnard, T. Sꢄv-
enet, J. Nat. Prod. 2001, 64, 1162; c) Y. Deng, Y.-W. Chin, H. Chai, W. J.
Keller, A. D. Kinghorn, J. Nat. Prod. 2007, 70, 2049; d) Y.-B. Wu, C.-J.
Zheng, L.-P. Qin, L.-N. Sun, T. Han, L. Jiao, Q.-Y. Zhang, J.-Z. Wu, Mole-
cules 2009, 14, 573; e) S.-X. Feng, J. Hao, T. Chen, S. X. Qiu, Helv. Chim.
Acta 2011, 94, 1843; f) T. Ruksilp, J. Sichaem, S. Khumkratok, P. Siripong,
S. Tip-pyang, Chem. Nat. Compd. 2013, 49, 746.
[18] a) C. D. Sheraw, T. N. Jackson, D. L. Eaton, J. E. Anthony, Adv. Mater.
2003, 15, 2009; b) S. A. Odom, S. R. Parkin, J. E. Anthony, Org. Lett. 2003,
5, 4245; c) Y. Sakamoto, T. Suzuki, M. Kobayashi, Y. Gao, Y. Fukai, Y.
Inoue, F. Sato, S. Tokito, J. Am. Chem. Soc. 2004, 126, 8138; d) R. Mondal,
B. K. Shah, D. C. Neckers, J. Org. Chem. 2006, 71, 4085; e) D. Lehnherr,
R. R. Tykwinski, Org. Lett. 2007, 9, 4583; f) Z. Liang, W. Zhao, S. Wang, Q.
Tang, S.-C. Lam, Q. Miao, Org. Lett. 2008, 10, 2007; g) D. Lehnherr, A. H.
Murray, R. McDonald, M. J. Ferguson, R. R. Tykwinski, Chem. Eur. J. 2009,
15, 12580; h) D. Matsumura, K. Kitazawa, S. Terai, T. Kochi, Y. Ie, M.
Nitani, Y. Aso, F. Kakiuchi, Org. Lett. 2012, 14, 3882.
Received: June 27, 2016
Published online on && &&, 0000
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Chem. Eur. J. 2016, 22, 1 – 7
www.chemeurj.org
6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Communication
COMMUNICATION
&
Gold Catalysis
N. Sun, X. Xie, H. Chen, Y. Liu*
&& – &&
Gold-Catalyzed Cyclization of Furan-
Ynes bearing a Propargyl Carbonate
Group: Intramolecular Diels–Alder
Reaction with In Situ Generated
Allenes
The power of gold: Gold-catalyzed
cyclization of various furan-ynes with
a propargyl carbonate or ester moiety
results in the formation of a series of
polycyclic aromatic ring systems. The
reaction consists of a tandem gold-cata-
lyzed 3,3-rearrangement of the proparg-
yl carboxylate in the furan-ynes to form
an allenic intermediate, followed by an
intramolecular Diels–Alder reaction of
furan and subsequent ring-opening of
the oxa-bridged cycloadduct. The steric
and electronic properties of phosphine
ligands on the gold catalyst had a signifi-
cant impact on the reaction outcome.
Chem. Eur. J. 2016, 22, 1 – 7
www.chemeurj.org
7
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ