Platinum- and gold-catalyzed hydroalkoxylation and tetramerization of propiolate esters

Article abstract of DOI:10.1016/j.catcom.2014.07.010

PtCl₂ was found to efficiently catalyze intermolecular additions of propiolate esters with alcohols. The reaction of propiolate esters and alcohols in the presence of PtCl₂ gave (E)-vinyl ethers as the major products at 60 °C, whereas alkyl 3,3-dialkoxypropanoates were predominantly obtained when the reaction temperature was set to 80°C. On the other hand, a novel regioselective tetramerization of propiolate esters catalyzed by AuCl₃ under mild conditions afforded 1,2,5,6-tetrasubstituted- cyclooctatetraene (1,2,5,6-COT) in moderate yields.

Full text of DOI:10.1016/j.catcom.2014.07.010

Platinum- and gold-catalyzed hydroalkoxylation and tetramerization of
propiolate esters
Qian Chen, Changyuan Zhang, Chunxiao Wen, Jin Fang, Zhiyun Du,
Dongling Wu
PII:
DOI:
Reference:
S1566-7367(14)00272-6
doi: 10.1016/j.catcom.2014.07.010
CATCOM 3967
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
16 May 2014
25 June 2014
7 July 2014
Please cite this article as: Qian Chen, Changyuan Zhang, Chunxiao Wen, Jin
Fang, Zhiyun Du, Dongling Wu, Platinum- and gold-catalyzed hydroalkoxylation
and tetramerization of propiolate esters, Catalysis Communications (2014),
doi:
10.1016/j.catcom.2014.07.010
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ACCEPTED MANUSCRIPT
Platinum- and gold-catalyzed hydroalkoxylation and
tetramerization of propiolate esters
Qian Chen*, Changyuan Zhang, Chunxiao Wen, Jin Fang, Zhiyun Du*, Dongling Wu
School of Chemical Engineering and Light Industry, Guangdong University of Technology, Guangzhou
510006, China
*Corresponding authors. Tel.: +86 20 3932 2231; fax: +86 20 3932 2235.
E-mail addresses: qianchen@gdut.edu.cn (Q. Chen), zhiyundu@gdut.edu.cn (Z. Du).
ABSTRACT: PtCl2 was found to efficiently catalyze intermolecular additions of propiolate esters with
alcohols. The reaction of propiolate esters and alcohols in the presence of PtCl2 gave (E)-vinyl ethers as
the major products at 60 oC, whereas alkyl 3,3-dialkoxypropanoates were predominantly obtained when
o
the reaction temperature was set to 80 C. On the other hand, a novel regioselective tetramerization of
propiolate esters catalyzed by AuCl3 under mild conditions afforded 1,2,5,6-tetrasubstituted-
cyclooctatetraene (1,2,5,6-COT) in moderate yields. © 2014 Elsevier B.V. All rights reserved.
Keywords: Hydroalkoxylation; Tetramerization; Propiolate ester; Platinum catalyst; Gold catalyst
1. Introduction
It has been widely known that transition metal complexes catalyze intermolecular additions of
nucleophiles to carbon-carbon multiple bonds [13]. Such addition reactions are perfectly suited to
fulfill today’s need for the atom economy [4] and atom efficiency [5]. The hydroalkoxylation and
bis(hydroalkoxylation) of olefins or alkynes afford vinyl ethers [1,68] or acetals [13,615]. For
examples, when alkyl acrylates or alkyl propiolates are treated with alcohols catalyzed by AgI, CuI or
PdII [68,1415], the reactions give alkyl 3,3-dialkoxypropanoates, which are very important precursors
in organic synthesis and pharmaceutical chemistry [16]. For the alkyne unit of acetylenedicarboxylates,
it is worth to mention that nucleophiles could directly add to the triple bonds in the absence of transition
metal catalysts [17].
1

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Platinum and gold catalysts are efficient reagents for intermolecular and intramolecular additions of
nucleophiles to alkynes [13,18]. The hydration, hydroalkoxylation and hydroarylation of alkynes
catalyzed by Pt and Au have been developed extensively during the last three decades [13,18]. The
use of platinum and gold salts enables these reactions to proceed under mild conditions with high
selectivity. Recently, Reetz [23], He [24] and Biffis [25] reported hydroarylations of electron-deficient
alkynes with Au catalysts. He [26] also found the AuCl3-catalyzed additions of N-methyl indole to ethyl
propiolate. Yu [27] lately reported PtCl2-catalyzed tandem cyclization/intermolecular addition reactions
of o-alkynylanilines with electron-poor alkynes. On the other hand, alkyl propiolate is also an important
material for the synthesis of cyclooctatetraene (COT), which is a highly valuable organic intermediate
[28]. Since Reppe [29] first discovered the Ni-catalyzed tetramerization of ethyne affording COT in
1948, transition-metal mediated synthesis of COT has been of particular interest [30]. However, the
regio- and chemo-selectivity of most tetramerization of alkynes are very low and different
tetrasubstituted isomers are always obtained as a mixture, together with the trimerized and polymerized
products [30]. For example, the reaction of ethyl propiolate catalyzed by Ni(PCl3)4 afforded two isomers
of 1,2,4,6-tetrasubstituted-COT (28% yield) and 1,3,5,7-COT (1% yield) and two trisubstituted benzenes
[31]. Gold catalysts also showed reactivities in the dimerization [32] and trimerization [33] of alkynes.
However, to our knowledge, there are no reports describing gold-catalyzed tetramerization of alkynes to
afford COTs. Herein, we report an efficient PtCl2-catalyzed hydroalkoxylation and
bis(hydroalkoxylation) of propiolate esters and a novel regioselective AuCl3-catalyzed tetramerization of
propiolate esters to afford 1,2,5,6-tetrasubstituted-COT.
2. Experimental
2.1. General
Nuclear magnetic resonance spectra were recorded on a Bruker AVANCE 400 spectrometer. All
reactions were carried out in a sealed high pressure tube. Commercial reagents were used without
purification unless otherwise noted. Flash chromatography was performed using the appropriate eluent
on silica gel standard grade 60 (230-400 mesh).
2.2. General procedure
2.2.1. General procedure for monohydroalkoxylation of propiolate esters
To a solution of ethyl propiolate (98 mg, 1.0 mmol) in methanol (2 mL) was added catalytic PtCl2 (5
o
mg, 0.02 mmol). The mixture was stirred at 60 C for 12 h. The reaction solution was cooled to room
temperature, and CH2Cl2 (20 mL) was added. The mixture was then filtered, and the filtrate was
concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel
with hexanes-ethyl acetate (20:1) as the eluent to give a mixture of (E)-ethyl 3-methoxyacrylate(4) and
2

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ethyl 3,3-dimethoxypropanoate(5) (112 mg, 85% yield, 4:5 = 13:1, the ratio was determined by 1H NMR)
as a colorless oil.
2.2.2. General procedure for bis(hydroalkoxylation) of propiolate esters
To a solution of ethyl propiolate (98 mg, 1.0 mmol) and amyl alcohol (440 mg, 5.0 mmol) in toluene
o
(2 mL) was added catalytic PtCl2 (5 mg, 0.02 mmol). The mixture was stirred at 80 C for 24 h. The
reaction solution was cooled to room temperature. The mixture was then filtered, and the filtrate was
concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel
with hexanes-ethyl acetate (20:1) as the eluent to give ethyl 3,3-bis(pentyloxy)propanoate (187 mg, 68%
yield) as a colorless oil.
2.2.3. General procedure for tetramerization of propiolate esters
To a solution of ethyl propiolate (98 mg, 1.0 mmol) in 1,2-dichloroethane (2 mL) was added catalytic
AuCl3 (6 mg, 0.02 mmol). The mixture was stirred at room temperature for 4 h. The mixture was then
filtered, and the filtrate was concentrated under reduced pressure. The residue was purified by flash
chromatography on silica gel with hexanes-ethyl acetate (20:1) as the eluent to give (1Z,3Z,5Z,7Z)-
tetraethyl cycloocta-1,3,5,7-tetraene-1,2,5,6-tetracarboxylate (41 mg, 42% yield) as a colorless oil.
3. Results and discussion
3.1. Hydroalkoxylation and bis(hydroalkoxylation)
The catalytic activity of PtCl2 (2 mol%) was first tested for the reaction of ethyl propiolate in
methanol at room temperature (Scheme 1). The reaction led to a poor conversion of ethyl propiolate to
afford two isomers including (Z)-ethyl 3-methoxyacrylate 1 and (E)-ethyl 3-methoxyacrylate 4 in 16%
and 26% isolated yields, respectively. Only 1 was detected at the start of the reaction, while 4 was
generated after 3 h [34,35]. Moreover, treatment of (Z)-vinyl ether 1 with catalytic PtCl2 in toluene at 60
oC for 3 h gave (E)-vinyl ether 4 in 90% yield, while no conversion was observed without the addition of
PtCl2. As our consideration, this isomerization can be probablely explained: (1) the complexation of
PtCl2 with 1 afforded Zwitterionic complex 2; (2) the isomerization of cis form 2 gave its trans form 3
because the trans-arrangement is thermodynamically more stable than the initially formed cis form.
Scheme 1. PtCl2-catalyzed hydromethoxylation of ethyl propiolate.
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In order to achieve complete conversion of ethyl propiolate, the reaction temperature was raised to 60
oC. The starting material was consumed within 9 h and afforded a mixture of 1 and 4 (Z:E = 1:7), while
ethyl 3,3-dimethoxypropanoate 5 was also observed. After additional 3 h, (Z)-vinyl ether was converted
to the (E)-vinyl ether completely, and a mixture of 4 and 5 (4:5 = 13:1) was isolated in 85% yield. On
the other hand, terminal alkynes without electron-withdrawing groups such as 1-hexyne,
phenylacetylene and propargyl alcohol did not give the corresponding products under the same
conditions.
We then carried out a brief optimization of experimental conditions, and the results are summarized
in Table 1. With the use of PtCl4 as the catalyst, only trace of hydromethoxylation products was detected
when the reaction was conducted at room temperature for 48 h (entry 3). Switching the catalyst from
platinum to gold catalysts (AuCl, AuCl3 and PPh3AuSbF6) decreased the yield of 4 and the ratio of 4 and
1/5 (entries 46). To avoid the formation of bis(hydroalkoxylation) product 5 at 60 °C, the reaction of
stoichiometric amounts of methanol and ethyl propiolate catalyzed by PtCl2 in an inert solvent (toluene)
was carried out (entries 810). Unfortunately, only trace of 4 was observed when methanol (1 eq., 2 eq.
or 5 eq.) was introduced. Thus, we concluded that the optimized combination for the
monohydroalkoxylation of propiolate esters was to use 2 mol% of PtCl2 as the catalyst and the reaction
was set at 60 °C (entry 2).
Table 1
Platinum- and gold-catalyzed hydromethoxylation of ethyl propiolate.a
Entry
1
Cat.
PtCl2
T (oC)
rt
Time (h) Yield (%)b
1/4/5c
48
12
48
12
12
12
12
24
24
24
42
85
38/62/0
2
PtCl2
60
rt
0/93/7
3
PtCl4
trace
38
-
4
AuCl
rt
65/35/0
5
AuCl3
rt
55
12/48/40
6
PPh3AuCl/AgSbF6
PPh3AuCl
PtCl2
rt
35
45/55/0
7
rt
NR
trace
trace
trace
-
-
-
-
8d
9e
10f
60
60
60
PtCl2
PtCl2
4

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a The reaction of ethyl propiolate (1 mmol) and methanol (2 mL) was carried out in the presence of 2 mol% of catalysts.
b Isolated yields based on ethyl propiolate.
c Ratio was determined by 1H NMR.
d The reaction of ethyl propiolate (1 mmol) and methanol (1 mmol) was carried out in toluene (2 mL).
e The reaction of ethyl propiolate (1 mmol) and methanol (2 mmol) was carried out in toluene (2 mL).
f The reaction of ethyl propiolate (1 mmol) and methanol (5 mmol) was carried out in toluene (2 mL).
To investigate the scope of the monohydroalkoxylation protocol, we applied the optimum reaction
conditions to the addition of variant alcohols to alkynes with electron-withdrawing groups and the
results are illustrated in Table 2. The reactions of ethyl propiolate or benzyl propiolate with alcohols
(MeOH, EtOH, i-PrOH or t-BuOH) afforded the desired products in 22-85% yields and the ratios of (E)-
vinyl ethers and acetals were varied from 3/1 to 24/1 (entries 16). Additions of primary alcohols to
propiolate esters gave the products in good yields, while i-PrOH and t-BuOH led to the formation of the
desired products in low yields due to the steric hindrance of bulkier alcohols. The hydroalkoxylation of
internal alkynes with electron-withdrawing group was also investigated (entries 79). Unfortunately, the
reactions of diethyl acetylenedicarboxylate, ethyl 2-butynoate and ethyl phenylpropiolate under the same
conditions gave the corresponding ketones (42%, 48% and 80% yield, respectively) due to the hydration
of alkynes with trace amount of water in methanol. We then tried the hydroalkoxylation of these internal
alkynes in anhydrous methanol, while no any hydromethoxylation product was detected. As a
comparison with terminal alkynes (propiolate esters), internal alkynes with the substituent of electron-
poor, electron-rich or phenyl group (entries 79) showed no reactivity for hydroalkoxylation, perhaps
due to the steric hindrance.
Table 2
PtCl2-catalyzed monohydroalkoxylation of alkynes.a
Entry
R1
H
H
H
H
H
H
R2
Et
R3OH
MeOH
EtOH
Yield (%)b
(E)-vinyl ether/acetalc
1
2
3
4
5
6
85
82
82
83
38
22
13/1
5/1
Et
Bn
Bn
Bn
Bn
MeOH
EtOH
24/1
7/1
i-PrOH
t-BuOH
4/1
3/1
5

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7
8
9
CO2Et
Me
Et
Et
Et
MeOH
MeOH
MeOH
-
-
-
-
-
-
Ph
a The reaction of alkyne (1 mmol) and alcohol (2 mL) was carried out in the presence of 2 mol% of PtCl2 at 60 oC.
b Isolated yields based on the corresponding alkynes.
c Ratio was determined by 1H NMR.
Having succeeded in monohydroalkoxylation of propiolate esters, we are encouraged to explore their
bis(hydroalkoxylation) reactions to obtain acetals. We first examined the reaction of ethyl propiolate
catalyzed by PtCl2 in refluxing ethanol for 3 days. A mixture of the (E)-vinyl ether and the acetal ((E)-
vinyl ether:acetal = 1:8) was obtained in 56% yield. In order to achieve complete conversion of vinyl
ethers, several conventional solvents for platinum catalysts were then screened and toluene was proved
to be the optimum solvent. Amyl alcohol was chosen as the nucleophile due to its higher boiling point.
When ethyl propiolate and 5 equiv. of amyl alcohol were introduced with 2 mol% of PtCl2 in toluene at
o
80 C for 24 h, the reaction afforded the acetal in 68% yield, while vinyl ethers were consumed
completely.
We then carried out bis(hydroalkoxylation) of propiolate esters with several alcohols and the results
are illustrated in Table 3. Ethyl propiolate and benzyl propiolate underwent acetalization with primary
alcohols to afford the corresponding acetals in 52-76% yields (entries 1). Ethylene glycol also gave
the cyclic acetals in moderate yields using dioxane as the solvent due to its insolubility in toluene
(entries 2 and 5).
Table 3
PtCl2-catalyzed bis(hydroalkoxylation) of propiolate esters.a
Entry
1
R1
Et
R2OH
Product
Yield (%)b
68
AmOH
2
3
Et
Et
HOCH2CH2OH
PhCH2CH2OH
52c
58
6

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4
5
Bn
Bn
AmOH
76
HOCH2CH2OH
54c
65
6
Bn
PhCH2CH2OH
a The reaction of alkyne (1 mmol) and alcohol (5 mmol) was carried out in the presence of 2 mol% of PtCl2 in toluene (2 mL)
at 80 oC
b Isolated yields based on the corresponding alkynes.
c Dioxane was used as the solvent and 2.5 equiv. of ethylene glycol was introduced.
3.2. Tetramerization
During our research on the addition of alcohols to terminal alkynes, we happened to isolate a
tetramerization product (m/z = 393 [M + H]+) when ethyl propiolate was treated with the above catalysts
1
in the absence of alcohols, while all reactions in table 13 did not give this type of by-product. The H
NMR and 13C NMR spectra (Fig. 1) are in good agreement with the structure of 1,2,5,6-tetrasubstituted-
cyclooctatetraene (1,2,5,6-COT). After a brief optimization of reaction conditions (screening Pt(II),
Pt(IV), Au(I), Au(III) or Ag(I) catalysts), 1,2,5,6-COT (when E = CO2Et, Scheme 2) was obtained in
42% yield as the major isomer when ethyl propiolate was catalyzed by AuCl3 in 1,2-dichloroethane
(DCE) at room temperature, while only trace of other isomers was detected. The other two substrates (E
= CO2Bn or CO2CH2CH2Ph, Scheme 2) containing arene ring also gave the corresponding products in
moderate yields, while the reaction temperature need to be raised to 80 oC. It is worth to mention that the
tetramerization of alkyl propiolate catalyzed by Ni catalyst mainly provided 1,2,4,6- and 1,3,5,7-COT
[30] and this novel tetramerization catalyzed by AuCl3 regioselectively afforded a different type of
tetrasubstituted-COT.
7

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Fig. 1. 1H NMR and 13C NMR spectra of 1,2,5,6-tetrasubstituted-COT (with E = CO2Et).
Scheme 2. Tetramerization of propiolate esters catalyzed by AuCl3.
4. Conclusion
These results provide a facile entry to the synthesis of (E)-vinyl ether, alkyl 3,3-dialkoxypropanoates
and 1,2,5,6-tetrasubstituted COT from propiolate esters, which demonstrate that PtCl2 is an efficient
catalyst for the hydroalkoxylation and bis(hydroalkoxylation) of electron-deficient alkynes to afford the
exclusive anti-Markovnikov addition products and the regioselective tetramerization of alkyl propiolates
is smoothly catalyzed by AuCl3 under mild conditions. The previous work [6,8,14] has shown that Ag-,
Pd-, and Cu salts are also active for hydroalkoxylations of electron-poor alkynes or alkenes and in some
cases more effective. For examples, AgOTf catalyzes the stereoselective trans addition of alcohol to
methyl propiolate to afford (Z)-vinyl ethers [6], and Cu(I)-catalyzed acetal formation from ethyl
propiolate also gives ethyl 3,3-dialkoxypropanoates [14]. Our study shows that cationic platinum
complexes are efficient for both mono- and bis(hydroalkoxylation) of propiolate esters when the
o
o
reaction temperature is set to 60 C and 80 C, respectively. In the case of monohydroalkoxylation, our
results are similar to the corresponding Ag-catalysis, whereas Pt-catalysis gives the product of (E)-vinyl
ethers. In the case of oligomerization of alkyl propiolates, the previous work shows that Ni-catalysis
8

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gives 1,3,5,7-, 1,2,4,6- and 1,3,6,8-COT and trisubstituted benzenes with different regio-selectivities
under different conditions [30]. In some cases the tetramerization can proceed selectively and one
isomer then becomes the predominant product, which remain hard to explain and predict [30]. Our study
shows AuCl3 catalyzes a novel type of tetramerization to give 1,2,5,6-COT regioselectively, which is no
published example to our knowledge. This interesting property of gold complexes should lead to new
and useful applications in catalysis and organic synthesis. Further investigations on the oligomerization
of alkynes are ongoing and will be reported in due course.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (21242002 and
21272043), Guangdong Undergraduate Innovation Training Program (1184513178), Guangdong
Industry-University-Research Program (2012B091100342) and Guangzhou Industry-University-
Research Program (2013J4500014).
References
1. A.S.K. Hashmi, Chem. Rev. 107 (2007) 3180–3211.
2. M. Beller, J. Seayad, A. Tillack, H. Jiao, Angew. Chem. Int. Ed. 43 (2004) 3368–3398.
3. M. Rudolph, A.S.K. Hashmi, Chem. Soc. Rev. 41 (2012) 2448–2462.
4. B.M. Trost, Angew. Chem. Int. Ed. 34 (1995) 259–281.
5. R.A. Sheldon, Chemtech 24 (1994) 38–46.
6. Y. Kataoka, O. Matsumoto, K. Tani, Chem. Lett. 25 (1996) 727–728.
7. J.H. Teles, S. Brode, M. Chabanas, Angew. Chem. Int. Ed. 37 (1998) 1415–1418.
8. L. Jia, H. Jiang, J. Li, Chem. Commun. 53 (1999) 985.
9. Y. Fukuda, K. Utimoto, J. Org. Chem. 56 (1991) 3729–3731.
10. S. Antoniotti, E. Genin, V. Michelet, J.P. Genêt, J. Am. Chem. Soc. 127 (2005) 9976–9977.
11. M. Li, R. Hua, J. Org. Chem. 73 (2008) 86588660.
12. M.C.B. Jaimes, C.R.N. Böhling, J.M. Serrano-Becerra, A.S.K. Hashmi, Angew. Chem. Int. Ed. 52 (2013) 7963–
7966.
13. M.C.B. Jaimes, F. Rominger, M.M. Pereira, R.M.B. Carrilho, S.A.C. Carabineiro, A.S.K. Hashmi, Chem. Commun.
50 (2014) 4937–4940.
14. S.H. Bertz, G. Dabbagh, P. Cotte, J. Org. Chem. 47 (1982) 2216.
15. A. Kishi, S. Sakaguchi, Y. Ishii, Org. Lett. 2 (2000) 523.
16. M. Yamashita, H. Asada, Speciality Chemicals Innovation in Industrial Synthesis and Applications, Elsevier
Applied Science, New York, 1991.
17. A.S.K. Hashmi, M.A. Grundl, A.R. Nass, F. Naumann, J.W. Bats, M. Bolte, Eur. J. Org. Chem. 2001, 47054732.
18. A.S.K. Hashmi, Gold Bull. 36 (2003) 39.
19. C. Bruneau, Angew. Chem. Int. Ed. 44 (2005) 2328.
20. L. Zhang, J. Sun, S.A. Kozmin, Adv. Synth. Catal. 348 (2006) 2271.
21. V. Michelet, P.Y. Toullec, J.P. Genêt, Angew. Chem. Int. Ed. 47 (2008) 4268.
9

ACCEPTED MANUSCRIPT
22. F. Alonso, I.P. Beletskaya, M. Yus, Chem. Rev. 104 (2004) 30793160.
23. M.T. Reetz, K. Sommer, Eur. J. Org. Chem. (2003) 34853496.
24. Z. Shi, C. He, J. Org. Chem. 69 (2004) 36693671.
25. C. Tubaro, M. Baron, A. Biffis, M. Basato, Beilstein J. Org. Chem. 9 (2013) 246–253.
26. Z. Li, Z. Shi, C. He, J. Organomet. Chem. 690 (2005) 5049.
27. X. Li, J.Y. Wang, W. Yu, L.M. Wu, Tetrahedron 65 (2009) 1140–1146.
28. K.B. Wiberg, Chem. Rev. 101 (2001) 1317.
29. W. Reppe, O. Schlichting, K. Klager, T. Toepel, Justus Liebigs Ann. Chem. 560 (1948) 1.
30. C. Wang, Z. Xi, Chem. Commun. 43 (2007) 5119–5133.
31. J.R. Leto, M.F. Leto, J. Am. Chem. Soc. 83 (1961) 2944.
32. S. Sun, J. Kroll, Y. Luo, L. Zhang, Synlett (2012) 5456.
33. K.J. Klabunde, T. Groshens, M. Brezinski, W. Kennelly, J. Am. Chem. Soc. 100 (1978) 44374440.
34. A.S.K. Hashmi, J.P. Weyrauch, W. Frey, J.W. Bats, Org. Lett. 6 (2004) 43914394.
35. M. Pernpointner, A.S.K. Hashmi, J. Chem. Theory Comput. 5 (2009) 27172725.
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Graphical Abstract
11

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Highlights
1. PtCl2-catalyzed hydroalkoxylation of propiolate esters affords (E)-vinyl ethers.
2. PtCl2-catalyzed bis(hydroalkoxylation) of propiolate esters affords acetals.
3. AuCl3-catalyzed tetramerization of propiolate esters affords cyclooctatetraenes.
12