Gold Catalysis of Non-Conjugated Haloacetylenes

Article abstract of DOI:10.1055/s-0040-1706606

Gold-catalyzed reactions of conjugated haloacetylenes are well known and usually result in the formation of addition or dimerization products. Herein, we report a gold-catalyzed reaction of non-conjugated haloacetylenes, which leads exclusively to the hal

Full text of DOI:10.1055/s-0040-1706606

SYNTHESIS
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart
2020, 52, A–N
paper
A
en
H. Siera et al.
Paper
Synthesis
Gold Catalysis of Non-Conjugated Haloacetylenes
Hannah Siera
R
R
R
Nina Semleit
Mathis Kreuzahler
Christoph Wölper
Gebhard Haberhauer*
1,2-arylshift and
cycloisomerization
X
X
+
R
X
0
0
0
0
-
0
0
0
2
-
5
4
2
7
-
7
5
1
0
R
R
gold catalyst (5 mol%)
CDCl3 or (CH2Br)2
Institut für Organische Chemie, Universität Duisburg-Essen,
Universitätsstraße 7, 45117 Essen, Germany
gebhard.haberhauer@uni-due.de
R'
R'
8 examples
up to 83% yield
R'
9 examples
up to 73% yield
X = Br, Cl, H
CIenMhsrtaiisitCltuogtrpefrhbüehrsWapOroördngl.pdhaenianrbigsecrAhhueatuChehorer@muine,i-Udnuiev.edresität Duisburg-Essen, Universitätsstraße 7, 45117 Essen, Germany
Received: 28.07.2020
Accepted after revision: 21.10.2020
Published online: 26.11.2020
show via dual gold catalysis16,17 that head-to-tail dimers 4–
6 can be obtained from haloacetylenes 1–3 (Scheme 1a).11
Recently, we were able to show that the mono gold(I)-cata-
lyzed dimerization of chloro- and bromoarylacetylenes 2
and 3 delivers the head-to-head products 7 and 8 (Scheme
1b).8 In the presence of arylacetylenes a haloalkynylation
reaction of the acetylene can be achieved instead of di-
merization.5 Both quantum chemical calculations and in-
vestigations by means of 13C-labeled compounds have
shown that the formation of the addition products takes
place via at least one rearrangement.6 Haloacetylenes can
also be added to alkenes via gold catalysis.4,7,9,10 Depending
on the substrate and the catalyst, the corresponding [2+2]
cycloaddition10 or 1,2-haloalkynylation products9 are
formed.
DOI: 10.1055/s-0040-1706606; Art ID: ss-2020-t0402-op
Abstract Gold-catalyzed reactions of conjugated haloacetylenes are
well known and usually result in the formation of addition or dimeriza-
tion products. Herein, we report a gold-catalyzed reaction of non-
conjugated haloacetylenes, which leads exclusively to the halogenated
cyclization products. Remarkable is the gold-catalyzed reaction of trityl-
haloacetylenes to haloindene derivatives, as mechanistic studies reveal
that an 1,2-aryl shift occurs in the initially formed gold complex. The
potential functionalization at the halogen atom and the wide scope of
these cyclization reactions make them an attractive method for the
construction of cyclic systems.
Key words gold catalysis, haloacetylenes, indene, chromene, chro-
mane, 1,2-aryl shift, cyclization
Until now, mainly aryl-substituted haloacetylenes have
been used in gold catalysis.4–12 Here, we investigated the
behavior of the readily available1 non-conjugated haloacet-
ylenes in the presence of different gold catalysts. In all three
non-conjugated systems including (homo)propargylic
ethers and tritylhaloacetylenes neither the formation of the
addition products nor the reaction to dimerization prod-
ucts was observed. Interestingly, in all cases an intramolec-
ular cyclization took place. The gold-catalyzed conversion
of the tritylhaloacetylenes is of special interest, as investi-
gations by means of NMR spectroscopy, X-ray structure
analysis and quantum chemical calculations show that an
aryl shift occurred in the initially formed gold complex.
Furthermore, we describe mechanistic studies and the wide
scope of these new gold-catalyzed cyclization reactions
(Scheme 1c).
Halogenated compounds are among the most used re-
agents for carbon–carbon bond forming reactions in organ-
ic chemistry. In contrast to alkyl, vinyl, and aryl halides,
haloacetylenes1 are rarely employed for the linking of car-
bon–carbon bonds. This is astonishing as they are readily
available from the corresponding terminal acetylenes and
decompose, with the exception of fluoroacetylenes,2 only at
higher temperatures.3 There are a few examples of conver-
sions of haloacetylenes, whereby the halogen moiety is re-
tained during the reaction, allowing a further transforma-
tion of the reactive halogen-substituted center.4–12
In the field of homogenous gold catalysis,13 alkynes are
probably the most frequently used substrates due to their
high reactivity. At the beginning, only the formation of new
carbon–heteroatom bonds was reported.14 Nowadays, there
are many examples of gold-catalyzed carbon–carbon bond
forming reactions of alkynes,15 and yet haloacetylenes have
been rarely employed in gold catalysis. One of the first reac-
tions was carried out by Hashmi et al.11,12 They were able to
For the investigation of the gold(I)-catalyzed reaction of
non-conjugated haloacetylenes, we chose compounds 9 and
10 as model systems (Scheme 2). These systems can be pre-
pared in only two steps: The propargylic ether is synthe-
sized starting from the corresponding phenol and aniline
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Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany

B
H. Siera et al.
Paper
Synthesis
cyclization (Scheme 2). An analogous gold(I)-catalyzed cy-
clization has already been observed for terminal propargyl-
ic ethers.20–23
a) Hashmi
R
X
X
X
[Au]+
X
Y
Cl
R
Y
[JohnPhosAu(NCMe)]SbF6 (5 mol%)
R
X = I, Br, Cl
R
X = I, Br, Cl
R
R
DCM
4, 5, 6
Cl
1, 2, 3
b) Our previous work
R
r.t., 2 h
Y = NTs, O
Y = NTs, O
9a, 10a–d
11a, 12a–d
X
R = p-Me
o-Me
11a (84%), 12a (33%)
12b (33%)
X
X
[Au]+
R
+
p-OMe
12c (56%)
X
R
p-COOMe
12d (73%)
R
X = Br, Cl
Scheme 2 Gold(I)-catalyzed cyclization of chloroacetylenes 9, 10 to
1,2-dihydroquinoline 11a and 2H-chromenes 12
X = Br, Cl
7, 8
2, 3
c) This work
The experiment was repeated on a preparative scale
with different propargylic chloroacetylenes to evaluate the
scope of the reaction (Scheme 2). The highest yield was ob-
tained for the conversion of chloroacetylene 9a to dihydro-
quinoline 11a (84%). Using a propargylic ether led to the
formation of 2H-chromene in a significantly lower yield
(12a, 33%). Changing the substitution position from para
(12a, 33%) to ortho (12b, 33%) had no effect on the yield.
However, a methoxy group in the para position increased
the yield to 56% (12c). The conversion of 10d leads to an
even higher yield (12d, 73%).
Y
Cl
[Au]+
Y
R
R
Y = NTs, O
Y = NTs, O
Cl
11, 12
9, 10
O
R
[Au]+
R
O
Cl
Cl
13
14
As second model, the non-conjugated acetylenes 13
were chosen (Scheme 3). The synthesis of these homoprop-
argylic ethers was accomplished via a Mitsunobu reaction24
and followed by chlorination19 with N-chlorosuccinimide.
Fortunately, the reaction of 13a with [JohnPhosAu(NCMe)]SbF6
in deuterated chloroform also showed a complete conver-
sion into one main product with an NMR yield of 93%.
R
R
R
[Au]
R
X
+
X
R
X
R
1
R'
Based on the aromatic signals in the H NMR spectrum, a
R'
R'
X = Br, Cl, H
X = Br, Cl, H
X = Br, Cl, H
ring formation was assumed. Further 1D and 2D NMR spec-
troscopic studies confirmed a 6-exo-dig cyclization. The
evaluation of the NOESY spectrum shows that the main
product represents the Z isomer of 14a (Scheme 3 and
Figure S8).
18, 19, 20
21, 22, 23
15, 16, 17
Scheme 1 Gold(I)-catalyzed dimerization of haloarylacetylenes 1–3
leads to head-to-tail products 4–6 (a) and to head-to-head dimers 7, 8
(b). The gold(I)-catalyzed reaction of propargylic and homopropargylic
chloroacetylenes 9, 10, 13 leads to cyclization products 11, 12, 14,
whereas the gold-catalyzed conversion of trityl compounds 15–17 re-
sults in the formation of indenes 18–23 (c).
O
[JohnPhosAu(NCMe)]SbF6 (5 mol%)
R
DCM
r.t., 2 h
O
R
Cl
derivatives and propargyl bromide.18 The resulting com-
pounds were then converted into the chloroacetylenes 9 and
10 with N-chlorosuccinimide.19 First, we investigated the con-
version of 10a with the gold(I) catalyst [JohnPhosAu(NCMe)]SbF6
(S1) in deuterated chloroform, which was monitored by
1H NMR spectroscopy. Fortunately, we could observe a
complete conversion into one main product with a yield of
90%. By analyzing the 1D and 2D NMR spectra, we could
confirm the formation of 2H-chromene 12a via a 6-endo-dig
Cl
13a–e
14a–e
R = p-Me
o-Me
(Z)-14a (60%)
(E)-14b (10%)
(Z)-14c (70%)
(Z)-14d (83%)
p-Cl
p-OMe
p-COOMe (Z)-14e (45%)
Scheme 3 Gold(I)-catalyzed cyclization of chloroacetylenes 13 to chro-
manes 14
© 2020. Thieme. All rights reserved. Synthesis 2020, 52, A–N

C
H. Siera et al.
Paper
Synthesis
In the next step, the reaction was carried out on a pre-
parative scale (Scheme 3). Changing the methyl group from
para to ortho position leads to a significant decrease in the
reaction yield from 60% (14a) to 10% (14b). Here, the reac-
tion of the ortho-substituted homopropargylic ether 13b
surprisingly results in the formation of the E isomer. With a
chlorine atom in para position, the corresponding cycliza-
tion product 14c could be isolated in 70% yield. The highest
yield delivers the chloroacetylene with a methoxy group in
the para position (83%, 14d). Using a methyl ester as sub-
stituent (13e) results in the formation of the chromane 14e
in lower yield (45%). The molecular structure of 14e ob-
tained via X-ray diffraction shows that the Z isomer was
formed, which agrees with our findings from the NMR
spectroscopic investigations (Figure 1).
1
3
X
+
X
X
1
3
2
2
catalyst
conditions
MeO
OMe
OMe
16a X = Cl
17a X = H
19a X = Cl
20a X = H
22a X = Cl
23a X = H
Scheme 4 Gold-catalyzed reaction of alkynes 16a and 17a under dif-
ferent conditions
carbene gold and to phosphine gold complexes. As solvents
chloroform, acetonitrile, and benzene were tested. In order
to monitor the reaction process, the experiments were car-
ried out in NMR tubes. The conversion of the reactant and
the yield of the products were determined using hexa-
methylbenzene as internal standard. The thus obtained
results are summarized in Table 1.
A glance at the NMR investigations shows that two
products were formed (Scheme 4). Both exhibit an 1H NMR
signal in the range of  = 5–6, which is typical for an olefinic
or benzylic proton. The conversion and the ratio of the
products 19a and 22a strongly depend on the catalyst and
the reaction conditions. In general, phosphine ligands deliv-
ered conversions up to 93% and product 22a is preferential-
ly formed (entries 1–6, 8, 9, and 13). The yield of 22a was as
high as 59% (entry 8). When using carbene ligands, the for-
mation of 19a prevails in one case (entry 12), however, the
yield of 43% is moderate. The best yields were obtained
with the gold(III) complex dichloro(2-picolinato)gold(III) in
chloroform at 65 °C (22a, 72%; entry 14).
Figure 1 Molecular structure of the chromane 14e in the solid state.
Displacement ellipsoids are drawn at the 70% probability level, and hy-
drogen atoms as spheres of arbitrary radii.
For structural analysis 2D NMR spectra of 19a and 22a
were recorded. According to NOESY and HMBC spectra, 19a
and 22a are indene derivatives showing a methoxyphenyl
group in the C2 position. Both indenes 19a and 22a differ
only in the position of the halogen atom and the phenyl
group. In 19a, the phenyl group is attached to the C1 atom
and thus 19a represents a vinylic chloride. In the case of
22a, the phenyl group and the chlorine atom are changed
compared to 19a. Thus, 22a is a benzylic chloride. This as-
signment is clearly plausible based on the coupling of the
benzylic protons in the NOESY spectra. In the NOESY spec-
trum of 22a a coupling between the benzylic proton ( =
5.80) and both the protons of the para-substituted ring ( =
7.25) and the protons of the six-membered ring of the in-
dene ( = 7.71) is found (see Figure S10). The NOESY spec-
trum of 19a exhibits in addition to the above described cou-
plings an interaction of the benzylic proton ( = 5.03) with
the unsubstituted phenyl group ( = 7.16) (see Figure S9).
Please note, that the treatment of a mixture of 19a and 22a
with different bases (sodium ethoxide and triethylamine)
does not lead to selective interconversion of the two iso-
mers.
Furthermore, we synthesized different tritylchloro- and
-bromoacetylenes and treated them with arylalkynes in the
presence of gold catalysts. The tritylacetylenes 15 and 16
(see the Supporting Information) were synthesized from
the corresponding tritylacetylenes 17 by reaction with N-
chlorosuccinimide (NCS) and N-bromosuccinimide (NBS),
respectively, according to known procedures.19,25 Besides
the phenyl group, we used p-tolyl and p-methoxyphenyl as
aryl groups. For the first investigation, we chose 16a as a
model system (Scheme 4). The characteristic 1H NMR signal
of the methyl group, which is separated from other signals
at a chemical shift of about  = 3.8, can be used as reference
signal to determine the conversion of 16a and the yield of
possible haloalkynylation products.
The initial gold(I)-catalyzed reaction of 16a with 1-
phenylprop-1-yne showed only a conversion of the chloride
16a. Since no reaction of the arylalkyne was observed, the
arylalkyne was omitted for further investigations. To opti-
mize yields, the experiment was carried out at room tem-
perature and at 65 °C using different solvents, ligands, and
counterions. The catalyst selection ranged from gold(III) to
© 2020. Thieme. All rights reserved. Synthesis 2020, 52, A–N

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H. Siera et al.
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Synthesis
Table 1 Optimization of the Reaction Conditions for the Gold-Catalyzed Reaction of Alkyne 16a Using 1H NMR Experimentsa
Entry
Catalyst
Conditions
Yield (%)
Conversion (%)
19a
22a
26
1
2b
3c
[JohnPhosAu(NCMe)]SbF6
[JohnPhosAu(NCMe)]SbF6
[JohnPhosAu(NCMe)]SbF6
[JohnPhosAu(NCMe)]SbF6
[JohnPhosAu(NCMe)]SbF6
r.t., 7 d, CDCl3
19
30
11
–
42
30
28
–
86
93
55
14
32
91
92
88
92
70
36
91
58
84
r.t., 24 h, CDCl3
r.t., 24 h, CDCl3
4
r.t., 24 h, CD3CN
5
r.t., 24 h, C6D6
8
10
43
–
27
6
JohnPhosAuNTf2
r.t., 7 d, CDCl3
29
37
7
27
7
tBuXPhosAuNTf2
r.t., 7 d, CDCl3 then 65 °C, 24 h, CDCl3
r.t., 7 d, CDCl3
28
8d
9d
10d
11d
12d
13d
14
CyJohnPhosAuCl/AgNTf2
CyJohnPhosAuCl/AgSbF6
59
56
21
16
7
r.t., 7 d, CDCl3 then 65 °C, 24 h, CDCl3
r.t., 7 d, CDCl3
9
29
IPrAuCl/AgNTf2
16
9
IPrAuCl/AgSbF6
r.t., 7 d, CDCl3 then 65 °C, 24 h, CDCl3
r.t., 24 h, CDCl3
IPrAuCl/NaBArF24
43
–
30
Ph3PAuCl/AgNTf2
r.t., 24 h, CDCl3
30
72
dichloro(2-picolinato)gold(III)31
r.t., 7 d, CDCl3 then 65 °C, 24 h, CDCl3
5
a If not stated otherwise, the concentration of the alkyne 16a was 0.1 M and 5 mol% of the catalyst was used.
b The concentration of the alkyne 16a was 0.5 M.
c 2.5 mol% of the catalyst was used.
d 10 mol% of the silver or sodium salt, respectively, was used.
Furthermore, we were able to grow single crystals of
19a and 22a, which were analyzed via X-ray diffraction. The
molecular structures of 19a and 22a confirmed the indene
structures (see Figure 2). In both cases, the methoxyphenyl
unit and the indene moiety are almost parallel to each oth-
er, which suggests a good conjugation of the two aromatic
rings. However, the phenyl group is twisted out of this
plane in both cases. A glance at the products and the start-
ing materials reveals that an 1,2-aryl shift has taken place. A
comparable gold-catalyzed aryl rearrangement has already
been observed in trityl systems,32 whereby two alkyne
units, one terminal and one internal trityl-substituted
alkyne unit, were converted into benzofluorenone deriva-
tives.
In contrast to the previously observed gold-catalyzed
conversions of chloroacetylenes5,8 no chlorine shift takes
place, which raises the question whether the halogen atom
has any importance for the mechanism. To examine this is-
sue, we studied the reaction of the terminal tritylacetylene
17a with different gold catalysts (see Table 2). Analogous to
Figure 2 Molecular structures of the indenes 19a (left) and 22a (right) in the solid state. In the case of indene 19a, two independent molecules are
found in the asymmetric unit; only one of them is displayed. Displacement ellipsoids are drawn at the 70% probability level, and hydrogen atoms as
spheres of arbitrary radii.
© 2020. Thieme. All rights reserved. Synthesis 2020, 52, A–N

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H. Siera et al.
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Synthesis
Table 2 Optimization of the Reaction Conditions for the Gold-Catalyzed Reaction of Alkyne 17a Using 1H NMR Experimentsa
Entry
Catalyst
Conditions
Yield (%)
Conversion (%)
20a
23a
1
2
[JohnPhosAu(NCMe)]SbF6
JohnPhosAuNTf2
r.t., 7 d, CDCl3 then 65 °C, 24 h, CDCl3
r.t., 7 d, CDCl3
88
16
5
9
–
98
26
75
76
90
38
97
0
3
JohnPhosAuNTf2
r.t., 7 d, CDCl3 then 65 °C, 24 h, CDCl3
r.t., 7 d, CDCl3
54
10
73
–
4
tBuXPhosAuNTf2
57
–
5
tBuXPhosAuNTf2
r.t., 7 d, CDCl3 then 65 °C, 24 h, CDCl3
r.t., 7 d, CDCl3
6b
CyJohnPhosAuCl/AgNTf2
CyJohnPhosAuCl/AgNTf2
CyJohnPhosAuCl/AgSbF6
IPrAuCl/AgNTf2
24
4
7b
r.t., 7 d, CDCl3 then 65 °C, 24 h, CDCl3
r.t., 7 d, CDCl3 then 65 °C, 24 h, CDCl3
r.t., 7 d, CDCl3
89
–
8b
–
9b
26
4
10
71
–
42
88
0
10b
11b
12b
13b
14b
15
IPrAuCl/AgNTf2
r.t., 7 d, CDCl3 then 65 °C, 24 h, CDCl3
r.t., 7 d, CDCl3 then 65 °C, 24 h, CDCl3
r.t., 24 h, CDCl3
IPrAuCl/AgSbF6
–
IPrAuCl/NaBArF24
75
14
4
–
93
22
76
0
Ph3PAuCl/AgNTf2
r.t., 7 d, CDCl3
8
Ph3PAuCl/AgNTf2
r.t., 7 d, CDCl3 then 65 °C, 24 h, CDCl3
r.t., 7 d, CDCl3 then 65 °C, 24 h, CDCl3
72
–
dichloro(2-picolinato)gold(III)
–
a If not stated otherwise, the concentration of the alkyne 17a was 0.1 M and 5 mol% of the catalyst was used.
b 10 mol% of the silver or sodium salt, respectively, was used.
the reaction of chloroalkyne 16a, the corresponding in-
denes 20a and 23a were formed. Interestingly, the reaction
with the gold(III) complex dichloro(2-picolinato)gold(III)
did not lead to any conversion (entry 15). The highest yield
of 20a was obtained with [JohnPhosAu(NCMe)]SbF6 at 65 °C
(88%; entry 1), whereas the best reaction conditions for the
preparation of 23a are CyJohnPhosAuNTf2 as catalyst at a
temperature of 65 °C (89%; entry 7). Comparing the ratio of
both products, it becomes obvious that the tendencies are
strongly dependent on the temperature. In addition, a
change of the ratio can be observed during the reaction. For
example, if tBuXPhosAuNTf2 is used as catalyst, the ratio of
20a to 23a amounts to 57:10 after one week at room tem-
perature (entry 4). Subsequent heating of this sample to 65
°C for 24 hours causes a reverse of the ratio to 0:73 (entry
5); i.e. a conversion of 20a into 23a must have occurred.
After the NMR experiments, we performed the reaction
on a preparative scale. To evaluate the scope of the gold-cat-
alyzed cyclization of tritylacetylenes, different trityl sys-
tems were converted into the corresponding indenes 18–23
(Scheme 5). Besides the methoxy-substituted compounds
15a–17a, the unsubstituted systems 15b–17b and the
trimethyl- and trimethoxy-substituted compounds 15c–
17c and 15d–17d were tested. The conversion of the termi-
nal alkynes 17 were conducted using [JohnPhosAu(NCMe)]SbF6
as catalyst. For the reaction of the tritylhaloalkynes 15 and
16 different catalysts were used (see Scheme 5).
In the case of the terminal alkynes 17, the indene for-
mation can only be observed when the trityl system con-
tains electron-rich aromatic rings. Thus, alkyne 17b shows
no reaction. The conversion of the other terminal alkynes
always shows the preferred formation of 20 over 23. For ex-
ample, the reaction of the methyl-substituted system only
delivers indene 20c. The indenes 20 and 23 could be isolat-
ed in total yields (20 and 23 together) up to 83–95%.
The chloroacetylenes 16 are more reactive than the cor-
responding terminal alkynes 17; the gold-catalyzed reac-
tion therefore leads to the corresponding indenes in all cas-
es. The total yields (19 and 22 together) are in the range of
28–60%, whereby indene 22 is always preferentially
formed. The higher reactivity could also be a reason for the
lower total yields compared to the terminal alkynes. In the
case of the trimethyl-substituted system 16c, the formation
of 22c is strongly preferred. Therefore, the amount of com-
pound 19c was too small to be isolated. Due to their high
reactivity the indenes 22d and 19d could only be identified
in NMR experiments. Any attempt to isolate and character-
ize them failed.
Interestingly, the substitution of chlorine by bromine,
leads to the formation of only one indene product using di-
chloro(2-picolinato)gold(III) as catalyst. In three cases, the
benzylic bromide (21a–21c) and in one case the vinylic bro-
mide (18d) were isolated. Unfortunately, compounds 21b
and 21c could not be separated from byproducts. The latter
could be identified as the chloroindenes 22b and 22c,
© 2020. Thieme. All rights reserved. Synthesis 2020, 52, A–N

F
H. Siera et al.
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Synthesis
R
R
R
gold catalyst
X
X
X
R
+
R
R
R'
R'
R'
X = Br, Cl, H
X = Br, Cl, H
X = Br, Cl, H
R = H, R' = OMe
R = H, R' = H
R = Me, R' = Me
R = OMe, R' = OMe
a
b
c
d
15, 16, 17
18, 19, 20
21, 22, 23
Cl
Cl
Br
19b (13%)
C, r.t., 4 db
22b (28%)
21b (53%)
A, 65 °C, 3 da
Cl
Cl
Br
Br
OMe
OMe
OMe
OMe
OMe
OMe
20a (65%)
A, 65 °C, 24 h
23a (25%)
19a (13%)
A, r.t., 4 d
22a (15%)
18a (70%)
D, r.t., 5 hb
21a (73%)
B, 65 °C, 24 h
Cl
Br
Cl
20c (83%)
A, 65 °C, 24 h
22c (60%)
B, 65 °C, 24 h
21c
A, 65 °C, 24 ha (58%, 83:17 ratio 21c/22c)
22c
OMe
OMe
OMe
OMe
Cl
OMe
Br
Cl
MeO
MeO
MeO
MeO
MeO
OMe
OMe
OMe
OMe
OMe
20d (65%)
23d (30%)
19d
B, 65 °C, 24 h
22d
18d (15%)
A, 65 °C, 24 h
B, 65 °C, 24 h
Scheme 5 Gold-catalyzed reaction of alkynes 15–17 leads to the indenes 18–23. If not stated otherwise, CDCl3 was used as solvent and 5 mol% of
the catalyst was employed. Compounds listed in one box were formed as isomers in the same reaction. The following catalysts were used:
[JohnPhosAu(NCMe)]SbF6 (A), dichloro(2-picolinato)gold(III) (B), IPrAuCl/AgSbF6 (C), IPrAuCl/NaBArF24 (D). a 1,2-Dibromoethane was employed as
solvent. b 10 mol% of the silver or sodium salt, respectively, was used.
respectively. They were formed during the reaction with
dichloro(2-picolinato)gold(III) in chloroform via a bro-
mine–chlorine exchange. Repeating the reactions with
[JohnPhosAu(NCMe)]SbF6 in dibromoethane only led in the
case of alkyne 15b to the selective formation of the bromo-
substituted indene 21b. Using the bromoacetylene 15a, it
could be shown that the conversion with IPrAuCl/NaBArF24
leads to the selective formation of the vinylic bromide 18a.
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This is in contrast to the results obtained by dichloro(2-pi-
colinato)gold(III), where selectively the benzylic bromide
21a was formed.
In addition to the bromo- and chloroacetylenes 15a and
16a the corresponding iodoacetylene was treated with a
gold(III) and gold(I) catalyst, respectively. However, the con-
version of the starting material proceeded very slowly and
after workup only an indenone derivative instead of the
corresponding iodoindene could be isolated (see Support-
ing Information).
Furthermore, the energies of the stationary points were
calculated using the density functional B3LYP, the addition-
al dispersion correction D3BJ and the basis set 6-
311++G(d,p) for C, H, Cl, and P. For Au the def2-TZVP basis
set was employed. To determine the solvent effect, single
point calculations were performed using chloroform as sol-
vent. The thus obtained data are summarized in Figure 3
and in the Supporting Information (Figures S1–S4 and Ta-
bles S1 and S2).
Let us consider the values obtained by means of B3LYP-
D3BJ/6-311++G(d,p),def2-TZVP(SMD) with JohnPhos as li-
gand of the gold catalyst. The first step is the formation of
the alkyne gold complexes 24a,b from the alkynes 16a,b
and the cationic gold catalysts. These complexes undergo
rearrangement via an 1,2-aryl shift to form the cations
26a,b (Figure 3). The activation barrier for this rearrange-
ment is strongly dependent on the migrating aryl group. If a
shift of the electron-rich methoxyphenyl moiety takes
place, the free energy for transition state 25a amounts to
9.0 kcal/mol. By contrast, the shift of the unsubstituted
phenyl group exhibits a significant higher activation barrier
(25b: 12.6 kcal/mol). For this reason, the gold-catalyzed re-
action of 16a results selectively in a shift of the electron-
rich methoxyphenyl group. A comparison of the activation
barriers for the 1,2-aryl shift (9.0 kcal/mol for 25a and 12.6
kcal/mol for 25b) and the gold-catalyzed dimerization of
16a,b (29.6 kcal/mol for 29a and 30.7 kcal/mol for 29b cal-
culated on the same level of theory; see left side of Figure 3)
In the next step, we wanted to gain insight into the reac-
tion mechanism. As model systems we have chosen the me-
thoxy-substituted tritylchloroacetylene 16a and the unsub-
stituted tritylchloroacetylene 16b. Compound 16a was
used for the NMR experiments and 16b is the simplest rep-
resentative of the tritylchloroacetylenes. For the quantum
chemical calculations, we only considered a mono gold(I)-
catalyzed mechanism, in which the activation of the alkyne
takes place by only one gold center. This approach is insofar
justified, as a dual gold catalysis can be ruled out for the re-
action of chloroacetylenes with phosphine gold(I) complex-
es.8 As ligands for the gold(I) complex, the neutral phos-
phine ligands PMe3 and JohnPhos were chosen. The geo-
metrical parameters of all stationary points were optimized
using the density functional B3LYP33–35 with additional dis-
persion correction with Becke–Johnson damping (D3BJ).36
As basis sets 6-31G(d) was used for the light elements C, H,
Cl, and P, whereas def2-TZVP37,38 basis was employed for Au.
Figure 3 Free energy (ΔG) profile of the gold(I)-catalyzed reaction of alkynes 16a (R = OMe) and 16b (R = H) calculated by means of
B3LYP-D3BJ/6-311++G(d,p),def2-TZVP(SMD). [Au]+ = JohnPhosAu+.
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H. Siera et al.
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reveals that the 1,2-aryl shift exhibits considerably smaller
values. Thus, no dimerization reaction is observed. The sec-
ond step is a cyclization to cations 28a,b, which are only
slightly more stable than cations 26a,b. The activation bar-
riers for both systems are similar and amount to 11.0
kcal/mol and 10.4 kcal/mol, respectively. After rearomatiza-
tion via deprotonation, the last step is a protodesauration.
Depending on the regioselective attack of the proton, either
indenes 19a,b or indenes 22a,b are formed. Whether the ra-
tio of 19 to 22 is only determined by the attack of the pro-
ton, can not be answered, since subsequent isomerization
of 19 and 22 is also conceivable (see Table 2).
In conclusion, we have developed a gold-catalyzed reac-
tion method to synthesize chromene, dihydroquinoline,
chromane, indene, and haloindene derivatives with yields
up to 83% starting from terminal and halogen-substituted
non-conjugated acetylenes. Advantages of this reaction are
the readily available starting materials and the retainment
of the halogen atom in the product allowing a further func-
tionalization of the cyclization products. According to
quantum chemical calculations, the reaction of tritylhalo-
acetylenes catalyzed by gold complexes proceeds via a dif-
ferent mechanism compared to the gold-catalyzed reaction
of other haloacetylenes. Instead of rearrangement via a
chloronium ion, a 1,2-aryl shift takes place. In the next step,
a Friedel–Crafts type-cyclization and the following protode-
sauration leads to the formation of the indenes. This reac-
tion represents a new possibility to achieve halogen-substi-
tuted cycles starting from simple systems.
Gold(I)-Catalyzed Cyclization of Chloroacetylenes 9, 10, and 13;
General Procedure
In a 2-mL screw-capped vial, chloroacetylene (0.4 mmol, 1.0 equiv)
was dissolved in dry DCM (0.4 mL, 1 M). The gold catalyst (0.02 mmol,
0.05 equiv) was added. The mixture was stirred at r.t. until full con-
version (TLC monitoring). The solvent was removed under reduced
pressure and the residue purified by flash chromatography to yield
the desired heterocycles.
4-Chloro-6-methyl-1-tosyl-1,2-dihydroquinoline (11a)
According to the general procedure, acetylene 9a (133.5 mg, 0.4 mmol, 1.0
equiv) was dissolved in dry DCM (0.4 mL, 1 M). [JohnPhosAu(NCMe)]SbF6
(15.4 mg, 20 mol, 5 mol%) was added. The mixture was stirred at r.t.
for 2 h and then the solvent was removed in vacuo to give a residue
which was purified by flash chromatography (silica gel, cyclo-
hexane/EtOAc 95:5) to yield 11a (112 mg, 0.34 mmol, 84%) as a color-
less solid; Rf (cyclohexane/EtOAc 95:5) = 0.24.
1H NMR (CDCl3, 600 MHz):  = 7.60–7.57 (d, 3JH,H = 8.2 Hz, 1 H, CarH),
7.29–7.27 (s, 2 H, CarH), 7.24–7.22 (s, 1 H, CarH), 7.20–7.17 (d, 1 H,
CarH), 7.12–7.10 (d, 3JH,H = 8.2 Hz, 2 H, CarH), 5.62–5.59 (t, 3JH,H = 4.6 Hz,
1 H, CH=CCl), 4.44–4.41 (d, 3JH,H = 4.6 Hz, 2 H, CH2), 2.37 (s, 3 H, CH3),
2.36 (s, 3 H, CH3).
13C NMR (CDCl3, 151 MHz):  = 143.9 (q, Car), 137.2 (q, Car), 135.7 (q,
Car), 133.2 (q, Car), 130.2 (t, Car), 129.4 (t, Car), 129.1 (q, CCl), 128.0 (q,
Car), 127.4 (t, Car), 127.2 (t, Car), 125.1 (t, Car), 121.1 (t, CH=CCl), 46.1 (s,
CH2), 21.7 (p, CH3), 21.4 (p, CH3).
The NMR data agree with those in the literature.39
4-Chloro-6-methyl-2H-chromene (12a)
According to the general procedure, acetylene 10a (72.3 mg, 0.4 mmol, 1.0
equiv) was dissolved in dry DCM (0.4 mL, 1 M). [JohnPhosAu(NCMe)]SbF6
(15.4 mg, 20 mol, 5 mol%) was added. The mixture was stirred at r.t.
for 2 h and then the solvent was removed in vacuo to give a residue
which was purified by flash chromatography (silica gel, n-hexane) to
yield 12a (23 mg, 0.13 mmol, 33%) as a colorless oil; Rf (n-hexane) =
0.20.
All chemicals were reagent grade and were used as purchased from
ABCR, Alfa Aesar, Acros Organics, Carbolution, TCI, or Sigma-Aldrich.
Reactions were monitored by TLC analysis with silica gel 60 F254
thin-layer plates. Flash chromatography was carried out on silica 60
(40–63 m, 230–400 mesh). 1H and 13C NMR spectra were measured
with Bruker Avance DRX 500, Avance NEO 400, DMX 300 and Avance
HD 600 spectrometers. The spectra were referenced to the peak for
the protium impurity in the deuterated solvents indicated in brackets
in the analytical data (CD2Cl2, 1H:  = 5.32, 13C:  = 53.84; CD3CN, 1H:
 = 1.94, 13C:  = 1.32; CDCl3, 1H:  = 7.26, 13C:  = 77.16). 13C NMR
spectra were measured with 1H decoupling. 13C assignment was
achieved via HSQC, HMBC and COSY spectra. The 13C signals were re-
ferred to p (primary), s (secondary), t (tertiary), q (quaternary) carbon
atoms. HRMS spectra were recorded with a Bruker BioTOF III mass
spectrometer with electrospray ionization (ESI) and atmospheric
pressure chemical ionization (APCI) as ionization source. UV/Vis ab-
sorption spectra were obtained with a Jasco V-550 spectrophotome-
ter. IR absorption spectra were recorded with a Varian 3100 FT-IR
spectrophotometer. Melting points were measured with a Büchi
melting point apparatus Model B-540 with an open capillary and are
uncorrected. [JohnPhosAu(NCMe)]SbF6 (S1)26 was synthesized ac-
cording to the literature procedure. Haloacetylenes were prepared
from the corresponding terminal acetylenes, see the Supporting In-
formation for details.
IR (ATR): 2920, 2834, 2729, 1746, 1694, 1632, 1578, 1489, 1414, 1371,
1321, 1283, 1273, 1234, 1211, 1152, 1130, 1088, 1059, 974, 936, 882,
864, 818, 789, 762, 735, 698, 683, 638, 604 cm–1
.
1H NMR (CDCl3, 600 MHz):  = 7.25–7.22 (d, 3JH,H = 2.0 Hz, 1 H, CarH),
7.00–6.97 (dd, 3JH,H = 2.0 Hz, 1 H, CarH), 6.73–6.70 (d, 1 H, CarH), 5.90–
3
3
5.88 (t, JH,H = 4.0 Hz, 1 H, ClC=CH), 4.82–4.78 (d, JH,H = 4.0 Hz, 2 H,
OCH2), 2.30 (s, 3 H, CH3).
13C NMR (CDCl3, 151 MHz):  = 152.5 (q, Car), 131.1 (q, Car), 131.0 (t,
Car), 128.4 (q, Car), 125.1 (t, Car), 121.1 (q, Car), 119.0 (t, ClC=CH), 115.7
(t, Car), 66.1 (s, OCH2), 20.8 (p, CH3).
HRMS (APCI): m/z [M + H]+ calcd for C10H1035ClO+: 181.0415; found:
181.0413.
UV/Vis (CH3CN): max (log ) = 219 (4.28), 264 (3.57), 319 nm (3.38).
4-Chloro-8-methyl-2H-chromene (12b)
According to the general procedure, acetylene 10b (72.3 mg, 0.4 mmol, 1.0
equiv) was dissolved in dry DCM (0.4 mL, 1 M). [JohnPhosAu(NCMe)]SbF6
(15.4 mg, 20 mol, 5 mol%) was added. The mixture was stirred at r.t.
for 2 h and then the solvent was removed in vacuo to give a residue
which was purified by flash chromatography (silica gel, n-hexane) to
yield 12b (23 mg, 0.13 mmol, 33%) as a colorless oil; Rf (n-hexane) =
0.30.
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IR (ATR): 2839, 1634, 1601, 1516, 1495, 1466, 1433, 1379, 1329, 1300,
1263, 1242, 1225, 1198, 1163, 1098, 1080, 1053, 1007, 978, 943, 901,
(Z)-4-(Chloromethylene)-6-methylchromane (14a)
According to the general procedure, acetylene 13a (77.9 mg, 0.4 mmol, 1.0
equiv) was dissolved in dry DCM (0.4 mL, 1 M). [JohnPhosAu(NCMe)]SbF6
(15.4 mg, 20 mol, 5 mol%) was added. The mixture was stirred at r.t.
for 2 h and then the solvent was removed in vacuo to give a residue
which was purified by flash chromatography (silica gel, cyclo-
hexane/EtOAc 95:5) to yield 14a (47 mg, 0.24 mmol, 60%) as a color-
less oil; Rf (cyclohexane/EtOAc 95:5) = 0.63.
827, 787, 775, 739, 710 cm–1
.
1H NMR (CDCl3, 600 MHz):  = 7.30–7.28 (dd, 3JH,H = 7.7 Hz, 1 H, CarH),
7.07–7.05 (dd, 3JH,H = 7.7 Hz, 1 H, CarH), 6.87–6.84 (t, 3JH,H = 7.7 Hz, 1 H,
CarH), 5.90–5.88 (t, 3JH,H = 4.0 Hz, 1 H, ClC=CH), 4.87–4.83 (d, 3JH,H = 4.0
Hz, 2 H, CH2), 2.18 (s, 3 H, CH3).
13C NMR (CDCl3, 151 MHz):  = 152.7 (q, Car), 132.3 (t, Car), 128.7 (q,
CCl), 125.3 (q, Car), 122.5 (t, Car), 121.0 (q, Car), 120.9 (t, Car), 118.6 (t,
ClC=CH), 66.1 (s, CH2), 15.7 (p, CH3).
IR (ATR): = 2971, 2928, 2878, 1487, 1464, 1418, 1377, 1327, 1296,
1277, 1254, 1229, 1217, 1169, 1128, 1076, 1042, 1001, 945, 905, 883,
806, 781, 745, 735, 696, 648 cm–1
.
HRMS (APCI): m/z [M + H]+ calcd for C10H1035ClO+: 181.0415; found:
181.0409.
1H NMR (CDCl3, 600 MHz):  = 8.10–8.07 (d, 3JH,H = 2.0 Hz, 1 H, CarH),
7.06–7.01 (dd, 3JH,H = 2.0 Hz, 8.4 Hz, 1 H, CarH), 6.78–6.75 (d, 3JH,H = 8.4
UV/Vis (CH3CN): max (log ) = 192 (4.27), 217 (4.18), 267 (3.61), 314
nm (3.25).
4
Hz, 1 H, CarH), 6.02–5.99 (t, JH,H = 1.3 Hz, 1 H, C=CHCl), 4.28–4.25 (t,
3JH,H = 5.6 Hz, 2 H, OCH2), 2.62–2.58 (td, 3JH,H = 5.6 Hz, 4JH,H = 1.3 Hz, 2
H, CH2), 2.30 (s, 3 H, CH3).
4-Chloro-6-methoxy-2H-chromene (12c)
13C NMR (CDCl3, 151 MHz):  = 152.6 (q, Car), 131.1 (t, Car), 130.0 (q,
C=CHCl), 129.2 (q, Car), 128.5 (t, Car), 118.7 (q, Car), 116.9 (t, Car), 110.8
(t, C=CHCl), 66.7 (s, OCH2), 31.9 (s, CH2), 20.9 (p, CH3).
HRMS (APCI): m/z [M + H]+ calcd for C11H1235ClO+: 195.0571; found:
195.0568.
According to the general procedure, acetylene 10c (78.6 mg, 0.4 mmol, 1.0
equiv) was dissolved in dry DCM (0.4 mL, 1 M). [JohnPhosAu(NCMe)]SbF6
(15.4 mg, 20 mol, 5 mol%) was added. The mixture was stirred at r.t.
for 2 h and then the solvent was removed in vacuo to give a residue
which was purified by flash chromatography (silica gel, cyclo-
hexane/EtOAc 95:5) to yield 12c (44 mg, 0.22 mmol, 56%) as a yellow
oil; Rf (cyclohexane/EtOAc 95:5) = 0.19.
UV/Vis (CH3CN): max (log ) = 216 (4.37), 256 (4.16), 312 nm (3.77).
IR (ATR): 2834, 1732, 1688, 1653, 1626, 1607, 1578, 1483, 1402, 1383,
1348, 1310, 1294, 1265, 1204, 1153, 1086, 1032, 1017, 972, 936, 912,
(E)-4-(Chloromethylene)-8-methylchromane (14b)
According to the general procedure, acetylene 13b (77.9 mg, 0.4 mmol, 1.0
equiv) was dissolved in dry DCM (0.4 mL, 1 M). [JohnPhosAu(NCMe)]SbF6
(15.4 mg, 20 mol, 5 mol%) was added. The mixture was stirred at r.t.
for 2 h and then the solvent was removed in vacuo to give a residue
which was purified by flash chromatography (silica gel, cyclo-
hexane/EtOAc 95:5) to yield 14b (8 mg, 0.04 mmol, 10%) as a colorless
oil; Rf (cyclohexane/EtOAc 95:5) = 0.28.
868, 849, 822, 793, 766, 743, 725, 700, 691, 669, 638, 623 cm–1
.
1H NMR (CDCl3, 600 MHz):  = 7.00–6.99 (dd, 1 H, CarH), 6.76–6.74 (m,
3
2 H, CarH), 5.95–5.93 (t, JH,H = 4.1 Hz, 1 H, CH=CCl), 4.79–4.77 (d,
3JH,H = 4.1 Hz, 2 H, CH2), 3.79 (s, 3 H, OCH3).
13C NMR (CDCl3, 151 MHz):  = 154.4 (q, Car), 148.5 (q, Car), 128.3 (q,
Car), 122.2 (q, Car), 119.8 (t, CH=CCl), 116.6 (t, Car), 116.0 (t, Car), 109.9
(t, Car), 66.1 (s, CH2), 56.0 (p, OCH3).
HRMS (ESI): m/z [M + H]+ calcd for C10H1035ClO2+: 197.0364; found:
197.0361.
IR (ATR): 2974, 2916, 2872, 1734, 1659, 1616, 1541, 1470, 1456, 1425,
1377, 1341, 1308, 1275, 1254, 1206, 1171, 1119, 1086, 1069, 1042,
1003, 945, 912, 893, 874, 810, 766, 733, 677, 646 cm–1
.
1H NMR (CDCl3, 600 MHz):  = 7.29–7.26 (d, 3JH,H = 7.5 Hz, 1 H, CarH),
UV/Vis (CH3CN): max (log ) = 221 (4.34), 330 nm (3.54).
7.07–7.04 (d, 3JH,H = 7.5 Hz, 1 H, CarH), 6.82–6.77 (t, 3JH,H = 7.5 Hz, 1 H,
CarH), 6.60 – 6.59 (t, 4JH,H = 1.8 Hz, 1 H, C=CHCl), 4.26 – 4.22 (d, 3JH,H
=
Methyl 4-Chloro-2H-chromene-6-carboxylate (12d)
5.9 Hz, 2 H, OCH2), 2.84–2.81 (td, 3JH,H = 5.9 Hz, 4JH,H = 1.8 Hz, 2 H, CH2),
According to the general procedure, acetylene 10d (89.9 mg, 0.4 mmol, 1.0
equiv) was dissolved in dry DCM (0.4 mL, 1 M). [JohnPhosAu(NCMe)]SbF6
(15.4 mg, 20 mol, 5 mol%) was added. The mixture was stirred at r.t.
for 2 h and then the solvent was removed in vacuo to give a residue
which was purified by flash chromatography (silica gel, cyclo-
hexane/EtOAc 95:5) to yield 12d (66 mg, 0.29 mmol, 73%) as a color-
less solid; mp 107 °C; Rf (cyclohexane/EtOAc 95:5) = 0.25.
2.20 (s, 3 H, CH3).
13C NMR (CDCl3, 151 MHz):  = 152.5 (q, Car), 132.0 (q, C=CCl), 130.8 (t,
Car), 127.2 (q, Car), 121.2 (t, Car), 120.5 (t, Car), 119.8 (q, Car), 111.8 (t,
C=CHCl), 65.7 (s, OCH2), 26.4 (s, CH2), 16.2 (p, CH3).
HRMS (APCI): m/z [M + H]+ calcd for C11H1235ClO+: 195.0571; found:
195.0569.
UV/Vis (CH3CN): max (log ) = 192 (4.33), 219 (4.48), 262 (4.27), 308
nm (3.90).
IR (ATR): 2955, 2866, 1715, 1647, 1605, 1578, 1489, 1458, 1435, 1424,
1389, 1331, 1316, 1261, 1248, 1240, 1192, 1173, 1128, 1105, 1059,
1013, 988, 972, 920, 907, 866, 839, 797, 781, 758, 731, 706, 646, 613
cm–1
.
(Z)-4-(Chloromethylene)-6-chlorochromane (14c)
1H NMR (CDCl3, 600 MHz):  = 8.10–8.09 (d, 3JH,H = 2.1 Hz, 1 H, CarH),
7.90–7.87 (dd, 3JH,H = 2.1 Hz, 8.5 Hz, 1 H, CarH), 6.83–6.80 (d, 3JH,H = 8.5
Hz, 1 H, CarH), 5.93–5.92 (t, 3JH,H = 3.9 Hz, 1 H, CH=CCl), 4.96–4.94 (d,
3JH,H = 3.9 Hz, 2 H, CH2), 3.90 (s, 3 H, OCH3).
13C NMR (CDCl3, 151 MHz):  = 166.5 (q, COOMe), 158.4 (q, Car), 132.6
(t, Car), 127.6 (q, CCl), 126.5 (t, Car), 123.6 (q, Car), 120.7 (q, Car), 119.3
(t, CH=CCl), 116.0 (t, Car), 66.8 (s, CH2), 52.2 (p, OCH3).
According to the general procedure, acetylene 13c (86.0 mg, 0.4 mmol, 1.0
equiv) was dissolved in dry DCM (0.4 mL, 1 M). [JohnPhosAu(NCMe)]SbF6
(15.4 mg, 20 mol, 5 mol%) was added. The mixture was stirred at r.t.
for 2 h and then the solvent was removed in vacuo to give a residue
which was purified by flash chromatography (silica gel, cyclo-
hexane/EtOAc 95:5) to yield 14c (61 mg, 0.28 mmol, 70%) as a yellow
oil; Rf (cyclohexane/EtOAc 95:5) = 0.39.
IR (ATR): = 2882, 1626, 1560, 1458, 1429, 1216, 1377, 1323, 1289,
1267, 1248, 1221, 1192, 1169, 1125, 1098, 1074, 1040, 945, 903, 882,
HRMS (APCI): m/z [M + H]+ calcd for C11H1035ClO3+: 225.0313; found:
225.0311.
862, 816, 733, 718, 673, 625 cm–1
.
UV/Vis (CH3CN): max (log ) = 195 (4.23), 241 (4.58), 281 nm (3.68).
© 2020. Thieme. All rights reserved. Synthesis 2020, 52, A–N

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H. Siera et al.
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1H NMR (CDCl3, 600 MHz):  = 8.27–8.26 (d, 3JH,H = 2.6 Hz, 1 H, CarH),
7.18–7.15 (dd, 3JH,H = 2.6 Hz, 8.8 Hz, 1 H, CarH), 6.81–6.78 (d, 3JH,H = 8.8
UV/Vis (CH3CN): max (log ) = 191 (4.19), 246 (4.51), 304 nm (3.53).
Hz, 1 H, CarH), 6.08 (t, 4JH,H = 1.2 Hz, 1 H, C=CHCl), 4.30–4.25 (t, 3JH,H
=
Gold-Catalyzed Synthesis of Indenes; General Procedure
5.6 Hz, 2 H, OCH2), 2.62–2.58 (td, 3JH,H = 5.6 Hz, 4JH,H = 1.2 Hz, 2 H, CH2).
The acetylene (1.0 equiv) was dissolved in CDCl3 or 1,2-dibro-
moethane and the gold catalyst (0.05 equiv) was added. The mixture
was stirred until 1H NMR spectra or TLC showed complete conversion.
The solvent was removed in vacuo to give a residue which was puri-
fied by flash chromatography.
13C NMR (CDCl3, 151 MHz):  = 153.3 (q, Car), 130.2 (t, Car), 128.9 (q,
C=CCl), 127.9 (t, Car), 125.0 (q, Car), 120.2 (q, Car), 118.5 (t, Car), 112.4 (t,
C=CHCl), 66.8 (s, OCH2), 31.4 (s, CH2).
HRMS (APCI): m/z [M + H]+ calcd for C10H935Cl2O+: 213. 9947; found:
213.9940.
2-(4-Methoxyphenyl)-1-phenyl-1H-indene (20a) and
2-(4-Methoxyphenyl)-3-phenyl-1H-indene (23a)
UV/Vis (CH3CN): max (log ) = 192 (4.27), 219 (4.30), 254 (4.07), 193
nm (3.70).
According to the general procedure acetylene 17a (119.4 mg, 0.4 mmol,
1 equiv) was dissolved in CDCl3 (0.8 mL); [JohnPhosAu(NCMe)]SbF6
(15.4 mg, 0.02 mmol, 0.05 equiv) was added and the mixture was
stirred overnight at 65 °C. The solvent was removed in vacuo and the
residue was purified by flash chromatography (silica gel, n-hexane/
DCM 4:1) to yield 20a (78 mg, 0.26 mmol, 65%) as a white solid and
23a (31 mg, 0.10 mmol, 25%) as an orange solid.
(Z)-4-(Chloromethylene)-6-methoxychromane (14d)
According to the general procedure, acetylene 13d (84.3 mg, 0.4 mmol, 1.0
equiv) was dissolved in dry DCM (0.4 mL, 1 M). [JohnPhosAu(NCMe)]SbF6
(15.4 mg, 20 mol, 5 mol%) was added. The mixture was stirred at r.t.
for 2 h and then the solvent was removed in vacuo to give a residue
which was purified by flash chromatography (silica gel, cyclo-
hexane/EtOAc 95:5) to yield 14d (70 mg, 0.33 mmol, 83%) as a yellow
oil; Rf (cyclohexane/EtOAc 95:5) = 0.32.
2-(4-Methoxyphenyl)-1-phenyl-1H-indene (20a)
Rf (n-hexane/DCM 1:1) = 0.49.
1H NMR (CDCl3, 600 MHz):  = 7.45–7.43 (m, 2 H, CarH), 7.39–7.37 (m,
1 H, CarH), 7.24–7.21 (m, 4 H, CarH + CaliH), 7.17–7.14 (m, 4 H, CarH),
7.09–7.06 (m, 1 H, CarH), 6.80–6.79 (m, 2 H, CarH), 4.93 (s, 1 H, CHPh),
3.76 (s, 3 H, OCH3).
13C NMR (CDCl3, 151 MHz):  = 159.1 (q, CarOCH3), 149.7 (q, C=C),
149.0 (q, Car), 143.7 (q, Car), 140.4 (q, Car), 129.0 (t, Car), 128.0 (t, Car),
128.0 (t, Car), 127.1 (t, Car), 126.8 (t, Car), 126.3 (t, C=C), 125.2 (t, Car),
123.9 (t, Car), 120.8 (t, Car), 114.1 (t, Car), 56.4 (t, CHPh), 55.3 (p, OCH3).
IR (ATR): = 2934, 2874, 2832, 1719, 1622, 1572, 1481, 1462, 1424,
1379, 1339, 1308, 1296, 1271, 1256, 1206, 1167, 1130, 1119, 1072,
1047, 1032, 953, 907, 897, 875, 855, 805, 752, 737, 696, 654, 619, 610
cm–1
.
1H NMR (CDCl3, 600 MHz):  = 7.89–7.88 (d, 4JH,H = 2.9 Hz, 1 H, CarH),
3
3
6.85–6.82 (dd, JH,H = 8.9 Hz, JH,H = 2.9 Hz, 1 H, CarH), 6.81–6.78 (d,
3JH,H = 8.9 Hz, 1 H, CarH), 6.04–6.03 (t, 4JH,H = 1.2 Hz, 1 H, CHCl), 4.25–
3
4.23 (t, JH,H = 5.6 Hz, 2 H, OCH2), 3.79 (s, 3 H, OCH3), 2.61–2.59 (td,
3JH,H = 5.6 Hz, 4JH,H = 1.2 Hz, 2 H, CH2).
HRMS (ESI): m/z [M + H]+ calcd for C22H19O+: 299.1430; found:
299.1426.
The NMR data agree with those in the literature.40
13C NMR (CDCl3, 151 MHz):  = 152.9 (q, Car), 149.0 (q, Car), 129.9 (q,
C=CHCl), 119.1 (q, Car), 117.8 (t, Car), 117.5 (t, Car), 112.2 (t, Car), 111.6
(t, CHCl), 66.7 (s, OCH2), 55.9 (p, OCH3), 31.9 (s, CH2).
HRMS (ESI): m/z [M + H]+ calcd for C11H1235ClO2+: 211.0520; found:
211.0511.
2-(4-Methoxyphenyl)-3-phenyl-1H-indene (23a)
Rf (n-hexane/DCM 1:1) = 0.54.
UV/Vis (CH3CN): max (log ) = 214 (4.27), 250 (4.07), 328 nm (3.74).
1H NMR (CDCl3, 400 MHz):  = 7.35–7.51 (m, 1 H, CarH), 7.46–7.35 (m,
5 H, CarH), 7.28–7.18 (m, 5 H, CarH), 6.78–6.74 (m, 2 H, CarH), 3.90 (s, 2
H, CH2), 3.78 (s, 3 H, OCH3).
13C NMR (CDCl3, 100 MHz):  = 158.7 (q, CarOCH3), 147.3 (q, Car), 142.3
(q, C=C), 140.9 (q, C=C), 138.5 (q, C=C), 136.5 (q, Car), 129.6 (t, Car),
129.3 (q, Car), 129.0 (t, Car), 127.4 (t, Car), 126.6 (t, Car), 124.9 (t, Car),
123.6 (t, Car), 120.2 (t, Car), 113.8 (t, Car), 55.3 (p, OCH3), 41.3 (s, CH2).
Methyl (Z)-4-(Chloromethylene)chromane-6-carboxylate (14e)
According to the general procedure, acetylene 13e (95.5 mg, 0.4 mmol, 1.0
equiv) was dissolved in dry DCM (0.4 mL, 1 M). [JohnPhosAu(NCMe)]SbF6
(15.4 mg, 20 mol, 5 mol%) was added. The mixture was stirred at r.t.
for 2 h and then the solvent was removed in vacuo to give a residue
which was purified by flash chromatography (silica gel, cyclo-
hexane/EtOAc 95:5) to yield 14e (44 mg, 0.18 mmol, 45%) as a color-
less solid; mp 64 °C; Rf (cyclohexane/EtOAc 95:5) = 0.21.
HRMS (ESI): m/z [M + H]+ calcd for C22H19O+: 299.1430; found:
299.1425.
IR (ATR): = 3071, 2947, 2903, 1703, 1634, 1613, 1570, 1487, 1389,
1329, 1285, 1265, 1248, 1231, 1194, 1125, 1107, 1080, 1036, 982,
9499, 916, 899, 885, 835, 816, 806, 785, 760, 739, 719, 679, 638, 613
The NMR data agree with those in the literature.40
1-Bromo-2-(4-methoxyphenyl)-3-phenyl-1H-indene (21a)
cm–1
.
According to the general procedure acetylene 15a (150.9 mg, 0.4
mmol, 1 equiv) was dissolved in CDCl3 (0.8 mL); dichloro(2-picolina-
to)gold(III) (7.8 mg, 0.02 mmol, 0.05 equiv) was added and the mix-
ture was stirred overnight at 65 °C. The solvent was removed in vacuo
and the residue was purified by flash chromatography (silica gel,
n-hexane/DCM 2:1) to yield 21a (111 mg, 0.29 mmol, 73%) as a yellow
solid; mp 157–159 °C; Rf (n-hexane/DCM 2:1) = 0.26.
1H NMR (CDCl3, 600 MHz):  = 8.99–8.96 (d, 3JH,H = 2.2 Hz, 1 H, CarH),
7.91–7.88 (dd, 3JH,H = 2.2 Hz, 8.7 Hz, 1 H, CarH), 6.90–6.87 (d, 3JH,H = 8.7
4
Hz, 1 H, CarH), 6.12–6.11 (t, JH,H = 1.3 Hz, 1 H, C=CHCl), 4.37–4.33 (t,
3JH,H = 5.6 Hz, 2 H, OCH2), 3.90 (s, 3 H, OCH3), 2.65–2.61 (td, 3JH,H = 5.6
Hz, 4JH,H = 1.3 Hz, 2 H, CH2).
13C NMR (CDCl3, 151 MHz):  = 166.9 (q, Car), 158.3 (q, Car), 131.6 (t,
Car), 130.7 (t, Car), 129.0 (q, C=CCl), 122.1 (q, Car), 118.8 (q, Car), 117.3
(t, Car), 112.5 (t, C=CHCl), 67.3 (s, OCH2), 52.2 (p, OCH3), 31.3 (s, CH2).
HRMS (ESI): m/z [M + H]+ calcd for C12H1235ClO3+: 239.0469; found:
239.0463.
IR (ATR): 3026, 2999, 2839, 1599, 1512, 1487, 1460, 1441, 1418, 1298,
1250, 1179, 1152, 1115, 1072, 1047, 1026, 883, 868, 831, 814, 783,
770, 750, 737, 706, 696, 648, 637, 611 cm–1
.
© 2020. Thieme. All rights reserved. Synthesis 2020, 52, A–N

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H. Siera et al.
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Synthesis
1H NMR (CDCl3, 400 MHz):  = 7.65–7.63 (m, 1 H, CarH), 7.44–7.35 (m,
5 H, CarH), 7.32–7.27 (m, 2 H, CarH), 7.20–7.15 (m, 3 H, CarH), 6.82–
6.78 (m, 2 H, CarH), 5.96 (s, 1 H, CHBr), 3.79 (s, 3 H, OCH3).
13C NMR (CDCl3, 101 MHz):  = 159.2 (q, CarOCH3), 143.9 (q, Car), 143.7
(q, Car), 142.0 (q, C=C), 139.3 (q, C=C), 134.7 (q, Car), 130.6 (t, Car),
129.3 (t, Car), 128.9 (t, Car), 128.1 (t, Car), 126.6 (t, Car), 126.3 (q, Car),
125.1 (t, Car), 121.0 (t, Car), 113.8 (t, Car), 55.3 (p, OCH3), 49.9 (t, CHBr).
Car), 126.2 (q, Car), 123.7 (t, Car), 119.3 (t, Car), 113.8 (t, Car), 56.8 (t,
CHPh), 55.3 (p, OCH3).
HRMS (ESI): m/z [M + H]+ calcd for C22H1835ClO+: 333.1041; found:
333.1037; m/z [M –
Cl]+ calcd for C22H17O+: 297.1274; found:
297.1276.
UV/Vis (CH2Cl2): max (log ) = 226 (3.93), 312 nm (4.10).
HRMS (ESI): m/z [M – 79Br]+ calcd for C22H17O+: 297.1274; found:
297.1276.
1-Chloro-2-(4-methoxyphenyl)-3-phenyl-1H-indene (22a)
Mp 169 °C; Rf (n-hexane/DCM 1:1) = 0.41.
UV/Vis (CH2Cl2): max (log ) = 255 (4.39), 304 (3.94), 347 nm (3.81).
IR (ATR): 3077, 3042, 2999, 2940, 2843, 1599, 1514, 1454, 1441, 1416,
1337, 1298, 1285, 1252, 1206, 1182, 1167, 1113, 1072, 1049, 1026,
936, 914, 887, 868, 833, 814, 783, 768, 750, 737, 719, 694, 654, 637,
3-Bromo-2-(4-methoxyphenyl)-1-phenyl-1H-indene (18a)
According to the general procedure acetylene 15a (150.9 mg, 0.4
mmol, 1 equiv) was dissolved in CDCl3 (4 mL); IPrAuCl (12.4 mg, 0.02
mmol, 0.05 equiv) and NaBArF24 (35.4 mg, 0.04 mmol, 0.1 equiv) were
added and the mixture was stirred for 5 h at r.t. The solvent was re-
moved in vacuo and the residue was purified by flash chromatogra-
phy (silica gel, n-hexane/DCM 2:1) to yield 18a (106 mg, 0.28 mmol,
70%) as a colorless oil; Rf (n-hexane/DCM 2:1) = 0.47.
627, 615, 602 cm–1
.
1H NMR (CDCl3, 600 MHz):  = 7.66–7.63 (m, 1 H, CarH), 7.44–7.41 (m,
2 H, CarH), 7.40–7.36 (m, 3 H, CarH), 7.34–7.29 (m, 2 H, CarH), 7.22–
7.20 (m, 2 H, CarH), 7.19–7.16 (m, 1 H, CarH), 6.82–6.79 (m, 2 H, CarH),
5.80 (s, 1 H, CHCl), 3.79 (s, 3 H, OCH3).
13C NMR (CDCl3, 151 MHz):  = 159.1 (q, CarOCH3), 144.1 (q, Car), 143.2
(q, Car), 141.6 (q, CPhOCH3), 139.7 (q, CPh), 134.6 (q, Car), 130.7 (t, Car),
129.3 (t, Car), 129.1 (t, Car), 129.0 (t, Car), 128.1 (t, Car), 126.5 (t, Car),
126.0 (q, Car), 124.6 (t, Car), 120.9 (t, Car), 113.8 (t, Car), 60.4 (t, CHCl),
55.3 (p, OCH3).
IR (ATR): 3059, 3025, 2957, 2930, 2905, 2835, 1601, 1505, 1493, 1441,
1246, 1177, 1042, 1026, 941, 835, 779, 752, 729, 696, 683, 617, 604
cm–1
.
1H NMR (CDCl3, 400 MHz):  = 7.59–7.56 (m, 2 H, CarH), 7.51–7.49 (m,
1 H, CarH), 7.39–7.35 (m, 1 H, CarH), 7.21–7.11 (m, 5 H, CarH), 7.07–
7.05 (m, 2 H, CarH), 6.86–6.82 (m, 2 H, CarH), 4.99 (s, 1 H, CHPh), 3.77
(s, 3 H, OCH3).
13C NMR (CDCl3, 101 MHz):  = 159.2 (q, CarOCH3), 146.1 (q, C=C),
145.8 (q, C=C), 143.3 (q, C=C), 139.1 (q, C=C), 130.3 (t, Car), 128.9 (t,
Car), 128.2 (t, Car), 127.6 (t, Car), 127.1 (t, Car), 126.8 (q, C=C), 126.6 (t,
Car), 123.7 (t, Car), 120.6 (t, Car), 117.3 (q, C=C), 113.8 (t, Car), 58.1 (t,
CHPh), 55.3 (p, OCH3).
HRMS (ESI): m/z [M + Na]+ calcd for C22H1735ClONa+: 355.0860; found:
355.0859; m/z [M – 35Cl]+ calcd for C22H17O+: 297.1274; found:
297.1274.
UV/Vis (CH2Cl2): max (log ) = 251 (4.03), 307 (3.62), 339 nm (3.61).
1-Bromo-2,3-diphenyl-1H-indene (21b)
Acetylene 15b (138.9 mg, 0.4 mmol, 1 equiv) was dissolved in 1,2-di-
bromoethane (0.8 mL); [JohnPhosAu(NCMe)]SbF6 (14.5 mg, 0.02
mmol, 0.05 equiv) was added and the mixture was stirred for 3 d at
65 °C. The solvent was removed in vacuo and the residue was purified
by flash chromatography (silica gel, n-hexane/Et2O 20:1) to yield 21b
(72 mg, 0.21 mmol, 53%) as a yellow solid; mp 157–159 °C; Rf (n-hex-
ane/Et2O 20:1) = 0.49.
HRMS (ESI): m/z [M – 79Br]+ calcd for C22H17O+: 297.1274; found:
297.1274.
UV/Vis (CH2Cl2): max (log ) = 227 (4.25), 310 nm (4.35).
1-Chloro-2-(4-methoxyphenyl)-3-phenyl-1H-indene (22a) and 3-
Chloro-2-(4-methoxyphenyl)-1-phenyl-1H-indene (19a)
IR (ATR): 3057, 3023, 2920, 1603, 1485, 1458, 1441, 1356, 1167, 1121,
1028, 939, 916, 883, 868, 785, 766, 752, 710, 691, 664, 635, 613, 606
According to the general procedure acetylene 16a (133.1 mg, 0.4 mmol,
1 equiv) was dissolved in CDCl3 (0.8 mL); [JohnPhosAu(NCMe)]SbF6
(15.4 mg, 0.02 mmol, 0.05 equiv) was added and the mixture was
stirred for 4 d at r.t. The solvent was removed in vacuo and the residue
was purified by flash chromatography (silica gel, n-hexane/DCM 4:1
to 3:1) to yield 19a (17.6 mg, 0.05 mmol, 13%) as a light brown solid
and 22a (19.4 mg, 0.06 mmol, 15%) as a yellow solid.
cm–1
.
1H NMR (CD3CN, 600 MHz):  = 7.68–7.65 (m, 1 H, CarH), 7.45–7.40
(m, 3 H, CarH), 7.37–7.32 (m, 4 H, CarH), 7.31–7.22 (m, 5 H, CarH), 7.19–
7.16 (m, 1 H, CarH), 6.22 (s, 1 H, CHBr).
13C NMR (CD3CN, 151 MHz):  = 145.0 (q, C=C), 144.2 (q, C=C), 144.0
(q, C=C), 141.3 (q, C=C), 135.2 (q, C=C), 135.0 (q, C=C), 130.3 (t, Car),
130.0 (t, Car), 130.0 (t, Car), 129.8 (t, Car), 129.2 (t, Car), 129.1 (t, Car),
128.7 (t, Car), 127.9 (t, Car), 126.1 (q, Car), 122.0 (t, Car), 51.2 (t, CHBr).
3-Chloro-2-(4-methoxyphenyl)-1-phenyl-1H-indene (19a)
Mp 117 °C; Rf (n-hexane/DCM 1:1) = 0.47.
HRMS (ESI): m/z [M – 79Br]+ calcd for C21H15+: 267.1168; found:
267.1169.
IR (ATR): 2926, 2835, 1603, 1576, 1562, 1506, 1495, 1439, 1418, 1343,
1300, 1267, 1248, 1177, 1074, 1047, 1026, 970, 914, 874, 839, 829,
UV/Vis (CH2Cl2): max (log ) = 249 (4.40), 301 (3.86), 331 nm (3.75).
808, 779, 762, 752, 735, 696, 644, 619, 610 cm–1
.
1-Chloro-2,3-diphenyl-1H-indene (22b) and 3-Chloro-1,2-diphe-
nyl-1H-indene (19b)
1H NMR (CDCl3, 600 MHz):  = 7.64–7.61 (m, 2 H, CarH), 7.52–7.51 (m,
1 H, CarH), 7.38–7.35 (m, 1 H, CarH), 7.21–7.17 (m, 4 H, CarH), 7.16–
7.13 (m, 1 H, CarH), 7.10–7.09 (m, 2 H, CarH), 6.86–6.83 (m, 2 H, CarH),
5.03 (s, 1 H, CHPh), 3.77 (s, 3 H, OCH3).
13C NMR (CDCl3, 151 MHz):  = 159.1 (q, CarOCH3), 145.8 (q, CCl),
142.1 (q, Car), 141.9 (q, CPhOCH3), 139.3 (q, Car), 130.2 (t, Car), 128.9 (t,
Car), 128.1 (t, Car), 127.5 (t, Car), 127.3 (q, Car), 127.1 (t, Car), 126.6 (t,
According to the general procedure acetylene 16b (121.1 mg, 0.4
mmol, 1 equiv) was dissolved in CDCl3 (0.8 mL); IPrAuCl (12.4 mg,
0.02 mmol, 0.05 equiv) and AgSbF6 (15.5 mg, 0.04 mmol, 0.1 equiv)
were added and the mixture was stirred for 4 d at r.t. The solvent was
removed in vacuo and the residue was purified by flash chromatogra-
© 2020. Thieme. All rights reserved. Synthesis 2020, 52, A–N

L
H. Siera et al.
Paper
Synthesis
phy (silica gel, n-hexane/DCM 4:1) to yield 19b (13.7 mg, 0.05 mmol,
UV/Vis (CH2Cl2): max (log ) = 227 (4.08), 321 nm (4.13).
13%) as a yellow oil and 22b (32.4 mg, 0.11 mmol, 28%) as a white sol-
id.
1-Bromo-6-methyl-2,3-di(4-tolyl)-1H-indene (21c) and 1-Chloro-
6-methyl-2,3-di(4-tolyl)-1H-indene (22c)
3-Chloro-1,2-diphenyl-1H-indene (19b)
Rf (n-hexane/DCM 1:1) = 0.58.
Acetylene 15c (155.7 mg, 0.4 mmol, 1 equiv) was dissolved in 1,2-di-
bromoethane (0.8 mL); [JohnPhosAu(NCMe)]SbF6 (14.5 mg, 0.02
mmol, 0.05 equiv) was added and the mixture was stirred overnight
at 65 °C. The solvent was removed in vacuo and the residue was puri-
fied by flash chromatography (silica gel, n-hexane/Et2O 30:1) to yield
21c (74 mg, 0.19 mmol, 48%) and 22c (14 mg, 0.04 mmol, 10%) as an
inseparable mixture (yellow solid).
IR (ATR): 3059, 3025, 2928, 1601, 1578, 1590, 1491, 1458, 1443, 1343,
1296, 1263, 1177, 1152, 1099, 1072, 1026, 1003, 968, 939, 912, 870,
831, 824, 795, 733, 691, 671, 621, 611 cm–1
.
1H NMR (CDCl3, 600 MHz):  = 7.66–7.64 (m, 2 H, CarH), 7.56–7.55 (m,
1 H, CarH), 7.40–7.37 (m, 1 H, CarH), 7.33–7.30 (m, 2 H, CarH), 7.24–
7.18 (m, 5 H, CarH), 7.16–7.13 (m, 1 H, CarH), 7.10–7.08 (m, 2 H, CarH),
5.08 (s, 1 H, CHPh).
13C NMR (CDCl3, 151 MHz):  = 146.0 (q, C=C), 142.4 (q, C=C), 141.9 (q,
C=C), 139.0 (q, C=C), 133.6 (q, C=C), 128.9 (t, Car), 128.9 (t, Car), 128.8
(q, C=C), 128.4 (t, Car), 128.2 (t, Car), 127.8 (t, Car), 127.5 (t, Car), 127.1
(t, Car), 127.0 (t, Car), 123.8 (t, Car), 119.6 (t, Car), 56.9 (t, CHPh).
Mixture 21c and 22c
Mp 141–142 °C; Rf (silica gel, n-hexane/Et2O 30:1) = 0.41.
IR (ATR): 3021, 2916, 2731, 1701, 1607, 1516, 1503, 1478, 1182, 1121,
1036, 1018, 856, 816, 766, 754, 735, 721, 706, 677, 664, 638 cm–1
.
UV/Vis (CH2Cl2): max (log ) = 256 (4.49), 305 (4.02), 341 nm (3.86).
HRMS (ESI): m/z [M – 35Cl]+ calcd for C21H15+: 267.1168; found:
267.1168.
1-Bromo-6-methyl-2,3-di(4-tolyl)-1H-indene (21c)
1H NMR (CD2Cl2, 400 MHz):  = 7.47 (br s, 1 H, CarH), 7.22 (br s, 4 H,
CarH), 7.16–7.05 (m, 6 H, CarH), 5.97 (s, 1 H, CHBr), 2.43 (s, 3 H, CH3),
2.39 (s, 3 H, CH3), 2.32 (s, 3 H, CH3).
13C NMR (CD2Cl2, 101 MHz):  = 144.4 (q, C=C), 141.4 (q, C=C), 141.4
(q, C=C), 140.3 (q, C=C), 138.3 (q, Car), 137.8 (q, Car), 137.1 (q, Car),
131.9 (q, C=C), 131.6 (q, C=C), 129.8 (t, Car), 129.7 (t, Car), 129.5 (t, Car),
129.3 (t, Car), 129.2 (t, Car), 126.2 (t, Car), 121.1 (t, Car), 50.7 (t, CHBr),
21.6 (p, CH3), 21.5 (p, CH3), 21.3 (p, CH3).
UV/Vis (CH2Cl2): max (log ) = 231 (4.03), 303 nm (4.15).
1-Chloro-2,3-diphenyl-1H-indene (22b)
Mp 163 °C; Rf (n-hexane/DCM 1:1) = 0.52.
IR (ATR): 3059, 3025, 2928, 1605, 1497, 1485, 1458, 1441, 1356, 1341,
1292, 1202, 1177, 1152, 1082, 1072, 1047, 1028, 1003, 984, 941, 918,
887, 870, 845, 795, 764, 754, 725, 714, 691, 669, 644, 621 cm–1
.
1H NMR (CDCl3, 600 MHz):  = 7.68–7.65 (m, 1 H, CarH), 7.43–7.31 (m,
7 H, CarH), 7.27–7.21 (m, 6 H, CarH), 5.83 (s, 1 H, CHCl).
13C NMR (CDCl3, 151 MHz):  = 143.9 (q, C=C), 143.5 (q, C=C), 142.0 (q,
C=C), 141.2 (q, C=C), 134.3 (q, C=C), 133.6 (q, C=C), 129.5 (t, Car), 129.3
(t, Car), 129.1 (t, Car), 129.0 (t, Car), 128.3 (t, Car), 128.2 (t, Car), 127.7 (t,
Car), 126.9 (t, Car), 124.6 (t, Car), 121.2 (t, Car), 60.3 (t, CHCl).
HRMS (APCI): m/z [M + H]+ calcd for C24H22Br+: 389.0899; found:
389.0905.
1-Chloro-6-methyl-2,3-di(4-tolyl)-1H-indene (22c)
According to the general procedure acetylene 16c (138.0 mg, 0.4
mmol, 1 equiv) was dissolved in CDCl3 (0.8 mL); the catalyst di-
chloro(2-picolinato)gold(III) (7.8 mg, 0.02 mmol, 0.05 equiv) was add-
ed and the mixture was stirred overnight at 65 °C. The solvent was
removed in vacuo and the residue was purified by flash chromatogra-
phy (silica gel, n-hexane/DCM 4:1) to yield 22c (84 mg, 0.24 mmol,
60%) as a yellow solid; mp 145–148 °C; Rf (n-hexane/DCM 4:1) = 0.32.
HRMS (ESI): m/z [M – 35Cl]+ calcd for C21H15+: 267.1168; found:
267.1168.
UV/Vis (CH2Cl2): max (log ) = 247 (4.38), 309 (3.86), 326 nm (3.84).
5-Methyl-1,2-di(4-tolyl)-1H-indene (20c)
IR (ATR): 3021, 2916, 2859, 2733, 1516, 1503, 1478, 1445, 1348, 1175,
1130, 1018, 932, 856, 835, 820, 797, 777, 764, 741, 723, 712, 675, 631
According to the general procedure acetylene 17c (112.4 mg, 0.36 mmol,
1 equiv) was dissolved in CDCl3 (0.72 mL); [JohnPhosAu(NCMe)]SbF6
(13.2 mg, 0.018 mmol, 0.05 equiv) was added and the mixture was
stirred overnight at 65 °C. The solvent was removed in vacuo and the
residue was purified by flash chromatography (silica gel, n-hexane/
EtOAc 98:2) to yield 20c (93 mg, 0.30 mmol, 83%) as an orange solid;
mp 172–174 °C; Rf (n-hexane/EtOAc 98:2) = 0.21.
cm–1
.
1H NMR (CD2Cl2, 400 MHz):  = 7.47–7.46 (m, 1 H, CarH), 7.23 (m, 4 H,
CarH), 7.16–7.13 (m, 3 H, CarH), 7.09–7.06 (m, 3 H, CarH), 5.80 (s, 1 H,
CHCl), 2.43 (s, 3 H, CH3), 2.40 (s, 3 H, CH3), 2.32 (s, 3 H, CH3).
13C NMR (CD2Cl2, 101 MHz):  = 143.9 (q, C=C), 141.7 (q, C=C), 141.1
(q, C=C), 140.7 (q, C=C), 138.3 (q, Car), 137.8 (q, Car), 137.1 (q, Car),
131.8 (q, C=C), 131.3 (q, C=C), 129.9 (t, Car), 129.8 (t, Car), 129.5 (t, Car),
129.3 (t, Car), 129.2 (t, Car), 125.7 (t, Car), 120.9 (t, Car), 60.9 (t, CHCl),
21.6 (p, CH3), 21.5 (p, CH3), 21.3 (p, CH3).
IR (ATR): 3026, 2916, 2868, 1607, 1510, 1470, 1449, 1377, 1188, 1109,
1036, 1020, 895, 856, 843, 812, 799, 783, 729, 716, 650 cm–1
.
1H NMR (CDCl3, 600 MHz):  = 7.40–7.39 (m, 2 H, CarH), 7.25–7.20 (m,
2 H, CarH + CaliH), 7.06–7.04 (m, 3 H, CarH), 7.03–7.00 (m, 4 H, CarH),
6.91–6.89 (m, 1 H, CarH), 4.89 (s, 1 H, CHAr), 2.36 (s, 3 H, CH3), 2.28 (s,
3 H, CH3), 2.25 (s, 3 H, CH3).
HRMS (ESI): m/z [M + H]+ calcd for C24H2235Cl+: 345.1405; found:
345.1397; m/z [M – Cl]+ calcd for C24H21+: 309.1638; found: 309.1645.
13C NMR (CDCl3, 151 MHz):  = 150.4 (q, C=C), 146.7 (q, C=C), 143.7 (q,
C=C), 137.5 (q, Car), 137.2 (q, Car), 136.6 (q, Car), 136.1 (q, Car), 132.6 (q,
Car), 129.7 (t, Car), 129.3 (t, Car), 127.8 (t, Car), 127.1 (t, Cali), 126.7 (t,
Car), 126.2 (t, Car), 123.5 (t, Car), 121.7 (t, Car), 55.6 (t, CHAr), 21.6 (p,
CH3), 21.3 (p, CH3), 21.2 (p, CH3).
HRMS (ESI): m/z [M + H]+ calcd for C24H23+: 311.1794; found:
311.1793.
UV/Vis (CH2Cl2): max (log ) = 252 (4.55), 306 (4.10), 337 nm (4.01).
6-Methoxy-2,3-bis(4-methoxyphenyl)-1H-indene (23d) and
5-Methoxy-1,2-bis(4-methoxyphenyl)-1H-indene (20d)
According to the general procedure acetylene 17d (143.4 mg, 0.4 mmol,
1 equiv) was dissolved in CDCl3 (0.8 mL); [JohnPhosAu(NCMe)]SbF6
(15.4 mg, 0.02 mmol, 0.05 equiv) was added and the mixture was
© 2020. Thieme. All rights reserved. Synthesis 2020, 52, A–N

M
H. Siera et al.
Paper
Synthesis
stirred overnight at 65 °C. The solvent was removed in vacuo and the
residue was purified by flash chromatography (silica gel, n-hex-
ane/DCM 1:1) to yield 20d (93 mg, 0.26 mmol, 65%) as a white solid
and 23d (42 mg, 0.12 mmol, 30%) as a white solid.
HRMS (ESI): m/z [M + H]+ calcd for C24H2279BrO3+: 437.0747; found:
437.0746; m/z [M – 79Br]+ calcd for C24H21O3+: 357.1485; found:
357.1489.
UV/Vis (CH2Cl2): max (log ) = 227 (4.08), 321 nm (4.13).
5-Methoxy-1,2-bis(4-methoxyphenyl)-1H-indene (20d)
Rf (n-hexane/DCM 1:1) = 0.17.
Funding Information
1H NMR (CD2Cl2, 400 MHz):  = 7.46–7.42 (m, 2 H, CarH), 7.16–7.16
(m, 1 H, CaliH), 7.04–7.00 (m, 3 H, CarH), 6.94–6.93 (m, 1 H, CarH),
6.82–6.78 (m, 2 H, CarH), 6.78–6.74 (m, 2 H, CarH), 6.63–6.61 (m, 1 H,
CarH), 4.87 (s, 1 H, CHPhOCH3), 3.80 (s, 3 H, OCH3), 3.75 (s, 3 H, OCH3),
3.72 (s, 3 H, OCH3).
13C NMR (CD2Cl2, 101 MHz):  = 159.7 (q, CarOCH3), 159.6 (q, CarOCH3),
158.8 (q, CarOCH3), 151.6 (q, Cali), 145.3 (q, Car), 142.0 (q, Car), 132.9 (q,
Car), 129.0 (t, Car), 128.3 (t, Car), 128.2 (q, Car), 126.1 (t, Cali), 124.3 (t,
Car), 114.5 (t, Car), 114.2 (t, Car), 110.9 (t, Car), 106.7 (t, Car), 55.8 (p,
OCH3), 55.6 (p, OCH3), 55.5 (p, OCH3), 55.0 (t, CHPhOCH3).
This work was supported by the Deutsche Forschungsgemeinschaft
(DFG; HA 2973/17-1).
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e
Forsch
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3/17-1)
Acknowledgment
The authors would like to thank Adrian Schützmann, Petra Schneider,
and Katrin Steiger for support.
Supporting Information
HRMS (ESI): m/z [M + H]+ calcd for C24H23O3+: 359.1642; found:
359.1639.
Supporting information for this article is available online at
The NMR data agree with those in the literature.40
https://doi.org/10.1055/s-0040-1706606. Su
p
p
ortingI
n
formatio
n
S
u
p
p
ortingInformati
o
n
6-Methoxy-2,3-bis(4-methoxyphenyl)-1H-indene (23d)
Rf (n-hexane/DCM 1:1) = 0.23.
References
1H NMR (CD3CN, 400 MHz):  = 7.25–7.22 (m, 2 H, CarH), 7.22–7.18
(m, 2 H, CarH), 7.13–7.12 (m, 1 H, CarH), 7.02–6.97 (m, 3 H, CarH), 6.83–
6.82 (m, 1 H, CarH), 6.78–6.74 (m, 2 H, CarH), 3.83 (s, 3 H, OCH3), 3.82
(s, 2 H, CH2), 3.80 (s, 3 H, OCH3), 3.74 (s, 3 H, OCH3).
13C NMR (CD3CN, 101 MHz):  = 156.0 (q, CarOCH3), 159.5 (q, CarOCH3),
159.1 (q, CarOCH3), 145.2 (q, Car), 141.2 (q, Car), 139.5 (q, C=C), 138.2
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121.0 (t, Car), 115.2 (t, Car), 114.5 (t, Car), 112.9 (t, Car), 111.1 (t, Car),
56.1 (p, OCH3), 55.9 (p, OCH3), 55.8 (p, OCH3), 41.7 (s, CH2).
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159.6 (q, CarOCH3), 149.0 (q, C=C), 145.2 (q, C=C), 139.8 (q, C=C), 132.2
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