Recyclable heterogeneous gold(I)-catalyzed oxidation of internal acylalkynes: Practical access to vicinal tricarbonyls

Article abstract of DOI:10.1016/j.tetlet.2021.152953

A highly efficient heterogeneous gold(I)-catalyzed oxidation of internal acylalkynes has been developed using 2,6-dichloropyridine N-oxide as the oxidant in dichloromethane (CH₂Cl₂) at room temperature, providing a novel and practical approach for the construction of diverse vicinal tricarbonyls such as α,β-diketoesters, 1,2,3-triketones, and α,β-diketoamides in good to excellent yields. The heterogeneous gold(I) catalyst can be readily obtained via a simple preparative procedure from commercially available reagents and recovered by filtration of the reaction mixture and reused up to seven times without significant loss of catalytic efficiency.

Full text of DOI:10.1016/j.tetlet.2021.152953

Tetrahedron Letters 68 (2021) 152953
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Recyclable heterogeneous gold(I)-catalyzed oxidation of internal
acylalkynes: Practical access to vicinal tricarbonyls
⇑
Wenli Hu, Bin Huang, Bingbo Niu, Mingzhong Cai
Key Laboratory of Functional Small Organic Molecule, Ministry of Education and College of Chemistry & Chemical Engineering, Jiangxi Normal University, Nanchang 330022, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A highly efficient heterogeneous gold(I)-catalyzed oxidation of internal acylalkynes has been developed
Received 4 December 2020
Revised 5 February 2021
Accepted 18 February 2021
Available online 23 February 2021
using 2,6-dichloropyridine N-oxide as the oxidant in dichloromethane (CH2Cl2) at room temperature,
providing a novel and practical approach for the construction of diverse vicinal tricarbonyls such as
a,
b-diketoesters, 1,2,3-triketones, and ,b-diketoamides in good to excellent yields. The heterogeneous
a
gold(I) catalyst can be readily obtained via a simple preparative procedure from commercially available
reagents and recovered by filtration of the reaction mixture and reused up to seven times without signif-
icant loss of catalytic efficiency.
Keywords:
Gold
Oxidation
Ó 2021 Elsevier Ltd. All rights reserved.
Acylalkyne
1,2,3-Tricarbonyl
Heterogeneous catalysis
Introduction
these conventional routes, the oxidation of diazo derivatives of b-
dicarbonyl compounds using DMDO [18], t-BuOCl [5,19], epoxides
Vicinal tricarbonyl compounds (VTCs) have drawn considerable
attention from synthetic and medicinal chemists in recent years
because of their presence in various biologically and pharmaceuti-
cally significant compounds, such as the elastase inhibitors YM-
47141 and YM-47142 [1], the potent immunosuppressants FK-
506 and FR-900525 [2], as well as rapamycin and 29-demethoxyra-
pamycin [3]. They are also important building blocks in organic
synthesis due to their highly electrophilic nature, particularly the
central carbonyl, and exhibit significant reactivity toward even
rather weak nucleophiles [4]. These compounds have been suc-
cessfully used for the construction of a variety of carbo- and hete-
rocycles including cyclopentanes [5], pyrroles [6], indoles [7],
isoquinolines [8], quinoxalines [9], triazines [10], imidazoles [11],
furans [12], and benzofurans [13]. Additionally, applications of
VTCs in the total synthesis of natural products have also been
reported [14].
[20], or pyridine N-oxides [21] appears to be one of the most con-
venient and frequently used methods. In spite of significant pro-
gress made in the development of efficient synthetic methods,
these approaches suffer often from disadvantages such as the use
of potentially explosive diazo compounds or toxic reagents, a lim-
ited substrate scope, harsh reaction conditions, and unsatisfactory
yields.
Over the past two decades, catalytic organic reactions involving
gold
organic synthesis [22]. Various transformations of the highly elec-
trophilic gold -oxo carbene intermediates offer an attractive
alternative to the reactions of -diazo carbonyl compounds [23].
Gold -oxo carbene intermediates can be easily formed through
a-oxo carbene intermediates have been widely employed in
a
a
a
intermolecular oxygen transfer under mild conditions from gold
complexes and readily available alkynes with pyridine N-oxides
as safe oxygen carriers [24]. Recently, the gold(I)-catalyzed oxida-
tion of alkynes and internal acylalkynes with pyridine N-oxides as
oxidants was reported as a highly efficient method for the synthe-
sis of 1,2-dicarbonyls and 1,2,3-tricarbonyls, respectively, under
mild conditions [25]. However, homogeneous gold-catalyzed
organic reactions suffer from drawbacks such as the high cost, dif-
ficult separation, and non-recyclability of the gold catalysts as well
as the decay of cationic gold, which largely limit their applications
in large-scale synthesis or in industry. Anchoring homogeneous
gold complexes onto a solid support through covalent bond
formation is one of the possible ways to address these problems;
Based on the synthetic versatility of VTCs, various methods
have been developed for their construction [4]. Conventional syn-
thetic approaches for VTCs include the direct oxidation of b-dicar-
bonyl compounds [15] or their
a-substituted derivatives [16] and
oxidative cleavage of the C@C and C = X (X = N, S, P, and I) double
bonds of a-functionalized b-dicarbonyl compounds [4a,17]. Among
⇑
Corresponding author.
E-mail address: caimzhong@163.com (M. Cai).
https://doi.org/10.1016/j.tetlet.2021.152953
0040-4039/Ó 2021 Elsevier Ltd. All rights reserved.

W. Hu, B. Huang, B. Niu et al.
Tetrahedron Letters 68 (2021) 152953
application of the immobilized catalysts in organic transformations
could result in easy separation, recovery, and reusability of the
gold catalysts, thereby minimizing gold contamination of the tar-
get product and waste derived from the reaction workup [26].
The employment of high-surface-area mesoporous materials as
catalyst supports is particularly attractive in this regard.
afforded the desired product 3a in low yields of 20–47%. We next
evaluated the influence of different heterogeneous gold(I) catalysts
on the model reaction (Entries 6–10). The use of Ph2P-MCM-41-
AuCl as the catalyst did not produce product 3a and substrate 1a
was recovered in 92% yield (Entry 6). When Ph2P-MCM-41-AuOTf,
Ph2P-MCM-41-AuBF4, Ph2P-MCM-41-AuPF6 or Ph2P-MCM-41-
AuSbF6 was used as the catalyst, the reaction afforded product 3a
in 63–77% yield (Entries 7–10), but Ph2P-MCM-41-AuNTf2 gave
the best result (Entry 2). Replacement of chlorobenzene with THF
resulted in a significant decrease in the yield of 3a (Entry 11),
whilst the use of DCE, CHCl3, CH2Cl2 or PhCF3 as the solvent fur-
nished 3a in 72–85% yield (Entries 12–15), with CH2Cl2 at 40 °C
representing the best choice (Entry 14). Gratifyingly, performing
the reaction at room temperature in CH2Cl2 lead to almost com-
plete conversion of the starting material 1a within 1 h, providing
the desired 3a in 89% yield (Entry 16). Reducing the amount of
the gold catalyst to 2.5 mol% led to a decreased yield of 3a even
when the reaction time was prolonged to 5 h (Entry 17). However,
further increasing the amount of the gold catalyst to 10 mol% did
not improve the yield of 3a significantly (Entry 18). When homoge-
neous Ph3PAuNTf2 (5 mol%) was used as the catalyst, the desired
product 3a was also isolated in 88% yield (Entry 19), revealing that
the catalytic efficiency of Ph2P-MCM-41-AuNTf2 was comparable
to that of Ph3PAuNTf2. Thus, the best result was achieved with
5 mol% Ph2P-MCM-41-AuNTf2 and 2,6-dichloropyridine N-oxide
as the oxidant in CH2Cl2 at room temperature for 1 h (Entry 16).
Having established the optimal reaction conditions, the sub-
strate scope of this heterogeneous gold(I)-catalyzed oxidation of
internal acylalkynes was investigated. As seen from Table 2, this
reaction was quite general for a wide variety of diversely substi-
tuted methyl or ethyl 3-phenylpropiolates, and the desired VTCs
3b-w were generally obtained in good to excellent yields. For
example, para- or meta-substituted methyl or ethyl 3-phenylpropi-
olates 1b-q bearing either electron-donating or electron-with-
drawing groups gave the corresponding VTCs 3b-q in 68–90%
yield, indicating that the electronic nature of substituents on the
benzene ring had limited influence on the reaction. A wide range
of substituents such as methyl, tert-butyl, methoxy, trifluo-
romethoxy, fluoro, chloro, bromo, trifluoromethyl, cyano, nitro,
ketone and ester functional groups were tolerated. 3,4-Disubsti-
tuted 3-phenylpropiolates 1r-s were also suitable substrates and
produced the expected products 3r-s in 80–95% yield. Sterically
hindered ortho-substituted 3-phenylpropiolates 1t-w displayed a
relatively lower reactivity than the corresponding para-substituted
ones and gave the desired VTCs 3t-w in 55–71% yield. Notably,
rigid 4-biphenyl- and bulky 1-naphthyl-substituted propiolates
1x and 1y provided the target products 3x and 3y in good yields.
Heteroaryl-substituted propiolates such as 2- or 3-thienyl-substi-
tuted propiolates 1z and 1a’ also gave the desired VTCs 3z and
3a’ in 59% and 85% yield, respectively. Next, various alkynyl
ketones and amides were examined. Alkynyl ketones 1b’ and 1c’
were successfully converted into the corresponding triketo prod-
ucts 3b’ and 3c’ in 75–82% yield, respectively. Similarly, mono-
and di-N-substituted alkynyl amides 1d’ and 1e’ afforded the
desired VTCs 3d’ and 3e’ in 73–91% yield, respectively. It should
Mesoporous MCM-41 has been widely utilized as an ideal sup-
port for the immobilization of homogeneous catalysts owing to its
unique properties, such as large pore volume, ultrahigh surface
area, homogeneity of the pores, and high thermal stability com-
pared to other solid supports [27]. To date, gold(I) or gold(III) com-
plexes anchored onto MCM-41 have been successfully applied to
various organic transformations [28]. Recently, we reported the
synthesis of a diphenylphosphine-modified MCM-41-supported
gold(I) complex [Ph2P-MCM-41-AuNTf2] and its successful applica-
tion to the oxidative ring expansion of 2-alkynyl-1,2-dihydropy-
ridines or -quinolines leading to functionalized azepines or
benzazepines [29]. To further expand the applications of this
heterogeneous gold(I) catalyst, herein we report a highly efficient
heterogeneous gold(I)-catalyzed oxidation of internal acylalkynes
leading to vicinal tricarbonyls in good to excellent yields using
the Ph2P-MCM-41-AuNTf2 complex as a recyclable catalyst under
mild conditions (Scheme 1).
Results and discussion
The diphenylphosphine-modified MCM-41-supported gold(I)
complexes [Ph2P-MCM-41-AuX, X = Cl, OTf, NTf2, BF4, PF6, and
SbF6] could be easily prepared from commercially available start-
ing materials via a simple procedure as depicted in Scheme 2
[29]. The condensation of mesoporous MCM-41 with 2-
(diphenylphosphino)ethyltriethoxysilane in dry toluene at reflux,
followed by silylation with Me3SiCl in dry toluene at room temper-
ature generated the diphenylphosphine-modified MCM-41 mate-
rial [Ph2P-MCM-41]. The latter was reacted with Me2SAuCl in
dichloromethane (CH2Cl2) at room temperature to give the Ph2P-
MCM-41-AuCl complex. Finally, Ph2P-MCM-41-AuCl was treated
with various silver salts (AgX, X = OTf, NTf2, BF4, PF6, SbF6) in CH2-
Cl2 at room temperature to afford the diphenylphosphine-modified
MCM-41-supported gold(I) complexes [Ph2P-MCM-41-AuX,
X = OTf, NTf2, BF4, PF6, SbF6] as grey powders.
The diphenylphosphine-modified MCM-41-supported gold(I)
complexes [Ph2P-MCM-41-AuX, X = Cl, OTf, NTf2, BF4, PF6, SbF6]
were then used as the catalysts for the oxidation of internal acy-
lalkynes to vicinal tricarbonyls. Initial experiments with ethyl 3-
phenylpropiolate (1a) as a model substrate were conducted to
optimize the reaction conditions, and the results are listed in
Table 1. First, the effect of various pyridine N-oxides as oxidants
was examined using Ph2P-MCM-41-AuNTf2 as the catalyst and
chlorobenzene as the solvent at 60 °C (Entries 1–5). The bulky
and electron-deficient 2,6-dichloropyridine N-oxide (2b) was
found to be the most efficient oxidant, while other pyridine N-oxi-
des such as 2-chloropyridine N-oxide (2a), 4-nitropyridine N-oxide
(2c), 8-methylquinoline N-oxide (2d), and pyridine N-oxide (2e)
Scheme 1. Heterogeneous gold(I)-catalyzed oxidation of internal acylalkynes towards vicinal tricarbonyls.
2

W. Hu, B. Huang, B. Niu et al.
Tetrahedron Letters 68 (2021) 152953
Scheme 2. Preparation of the Ph2P-MCM-41-AuX complexes.
Table 1
Optimization of the reaction conditions.a
Entry
X
N-oxide
Solvent
Temp. (°C)
Time (h)
Yield 3a (%)b
1
2
3
4
5
6
7
8
NTf2
NTf2
NTf2
NTf2
NTf2
Cl
OTf
BF4
PF6
SbF6
NTf2
NTf2
NTf2
NTf2
NTf2
NTf2
NTf2
NTf2
–
2a
2b
2c
2d
2e
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
THF
DCE
CHCl3
CH2Cl2
PhCF3
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
60
60
60
60
60
60
60
60
60
60
60
60
60
40
60
25
25
25
25
3
3
3
3
3
12
3
3
3
3
3
3
3
3
3
1
5
0.5
47
82
28
23
20
0
63
75
66
77
31
77
72
85
83
89
75
90
88
9
10
11
12
13
14
15
16
17c
18d
19e
1
a
b
c
d
Reagents and conditions: 1a (0.2 mmol), 2 (0.5 mmol), Ph2P-MCM-41-AuNTf2 (5 mol%), solvent (0.5 mL). Isolated yield. Ph2P-MCM-41-AuNTf2 (2.5 mol%) was used.
e
Ph2P-MCM-41-AuNTf2 (10 mol%) was used. Ph3PAuNTf2 (5 mol%) was used.
be noted that ester and ketone products were obtained as the
hydrate forms 30 or as mixtures of the keto and hydrate forms with
a predominance for the latter. However, in the cases of amide prod-
ucts, keto forms 3 predominate. To further expand the reaction
scope, we also examined the reactivity of internal alkynes such
as 1,2-diphenylacetylene and 1-phenylhexyne under the standard
conditions; unfortunately, the oxidation reaction did not proceed.
As reported by Dubovtsev and co-workers, the gold(I)-catalyzed
oxidation of internal diarylalkynes to 1,2-diketones requires the
use of TfOH (2 equiv.) as an auxiliary reagent to quench the formed
2-methylpyridine and to retain the activity of the gold catalyst
[25b].
tion. To illustrate that alkyl-substituted acylalkynes can also be
employed as precursors of VTCs, we performed the one-pot syn-
thesis of quinoxaline derivatives 4 via the oxidation of alkyl-substi-
tuted acylalkynes 1f’ or 1g’, followed by condensation with o-
phenylenediamine (Scheme 3). Treatment of alkyl-substituted acy-
lalkynes 1f’ or 1g’ (0.2 mmol) with 2b (2.5 equiv.) in PhCF3 in the
presence of Ph2P-MCM-41-AuNTf2 (5 mol%) at room temperature
for 1 h, followed by the reaction with o-phenylenediamine (1.5
equiv.) at 60 °C for 5 h, provided the desired quinoxaline deriva-
tives 4 in overall yields of 62–75%.
Encouraged by the above results, we next applied this method-
ology to the one-pot construction of other heterocyclic systems
using internal acylalkynes as readily available starting materials.
This protocol was proven to be successful for the preparation of
valuable acyl-substituted N-heterocycles including indoles,
It should be noted that, like in Zhang’s and Deng’s works [15a,e],
we were also unable to purify aliphatic VTC products by flash chro-
matography on silica gel, presumably due to facile aldol condensa-
3

W. Hu, B. Huang, B. Niu et al.
Tetrahedron Letters 68 (2021) 152953
Table 2
Heterogeneous gold(I)-catalyzed synthesis of VTCs.a,b
a
b
Reagents and conditions: 1 (0.2 mmol), 2b (0.5 mmol), Ph2P-MCM-41-AuNTf2 (5 mol%), CH2Cl2 (0.5 mL), room temperature, 1 h. Isolated yield.
pyrazines, and benzo[b][1,4]oxazines (Scheme 4). These acyl-sub-
stituted N-heterocycles 5–7 were isolated in good overall yields
of 60–85%.
To confirm the heterogeneous nature of this oxidation reaction
catalyzed by Ph2P-MCM-41-AuNTf2, the reaction of ethyl 3-
phenylpropiolate (1a) with 2b in CH2Cl2 was carried out until
approximately 40% conversion of 1a was reached. Then the gold
catalyst was removed from the reaction mixture by filtration and
the catalyst-free filtrate was stirred at room temperature for an
additional 1 h. In this case, no further increase in the conversion
4

W. Hu, B. Huang, B. Niu et al.
Tetrahedron Letters 68 (2021) 152953
Scheme 3. Heterogeneous gold(I)-catalyzed one-pot synthesis of quinoxalines 4.
Scheme 4. Heterogeneous gold(I)-catalyzed one-pot synthesis of acyl-substituted N-heterocycles 5–7.
From both economic and environmental protection viewpoints,
the recovery and recyclability of heterogeneous precious metal cat-
alysts are significant factors for their practical applications. The
Ph2P-MCM-41-AuNTf2 catalyst can be easily separated from the
product and recovered through a simple filtration process. We next
examined the recyclability of the Ph2P-MCM-41-AuNTf2 catalyst in
the oxidation reaction of ethyl 3-(3-chloro-4-methylphenyl)propi-
olate (1r) with 2b under the standard conditions (Fig. 1). After the
first reaction cycle was completed, the gold(I) catalyst was recov-
ered by filtration of the reaction mixture, followed by washing
with acetone and drying at 60 °C in vacuo for 1 h. In the recycling
experiments, the recovered catalyst was recharged with substrate
1r for the next reaction run under the same conditions. These
results indicated that the Ph2P-MCM-41-AuNTf2 catalyst still
exhibited high catalytic activity even after being reused seven
times and the yield of the desired product 3r was over 91% in eight
consecutive runs. In addition, the gold content of the recovered
gold(I) catalyst after recycling eight times was found to be
0.37 mmol gꢀ1 based on ICP-AES analysis, which revealing negligi-
ble gold leaching.
Fig. 1. Recyclability of the Ph2P-MCM-41-AuNTf2 catalyst.
Conclusion
of 1a was observed, revealing that leached gold species from the
Ph2P-MCM-41-AuNTf2 catalyst was not related to the observed
oxidation. In addition, the filtrate did not contain any gold species
(below the detection limit) based on ICP-AES analysis. These
results showed that the real catalytic species should be Ph2P-
MCM-41-AuNTf2 and not the leached gold species in the solution,
thereby verifying the heterogeneous nature of the oxidation.
In summary, we have developed a novel, facile and practical
method for the synthesis of vicinal tricarbonyls through a recy-
clable heterogeneous gold(I)-catalyzed oxidation reaction of inter-
nal acylalkynes (alkynyl esters, ketones, and amides) with 2,6-
dichloropyridine N-oxide as the oxidant. The current approach
has attractive advantages over the previously reported routes to
5

W. Hu, B. Huang, B. Niu et al.
Tetrahedron Letters 68 (2021) 152953
[12] (a) H.H. Wasserman, G.M. Lee, Tetrahedron Lett. 35 (1994) 9783–9786;
(b) P. Truong, X. Xu, M.P. Doyle, Tetrahedron Lett. 52 (2011) 2093–2096.
[13] Q. Sha, H. Liu, Y. Li, Adv. Synth. Catal. 361 (2019) 1627–1631.
[14] (a) L. Selter, L. Zygalski, E. Kerste, U. Koert, Synthesis 49 (2016) 17–28;
(b) H.H. Wasserman, G.H. Kuo, Tetrahedron Lett. 32 (1991) 7131–7132.
[15] (a) Y. Liu, Z. Zhang, Y. Wan, G. Zhang, Z. Li, J. Bi, N. Ma, T. Liu, Q. Liu, J. Org.
Chem. 82 (2017) 3901–3907;
VTCs including mild reaction conditions, the use of readily avail-
able and safe internal alkynes as substrates, high functional group
tolerance, good to excellent yields, and easy recyclability of the
expensive gold(I) catalyst. Furthermore, our heterogeneous oxida-
tion methodology can be successfully applied to the one-pot con-
struction of various valuable N-heterocycles.
(b) X. Han, T. Lei, X. Yang, L. Zhao, B. Chen, C. Tung, L. Wu, Tetrahedron Lett. 58
(2017) 1770–1774;
(c) J. Cui, Y.N. Duan, J. Yu, C. Zhang, Org. Chem. Front. 3 (2016) 1686–1690;
(d) A. Sivan, A. Deepthi, Tetrahedron Lett. 55 (2014) 1890–1893;
(e) Z. Wang, X. An, L. Ge, J. Jin, X. Luo, W. Deng, Tetrahedron 70 (2014) 3788–
3792;
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
(f) H.H. Wasserman, J.E. Pickett, J. Am. Chem. Soc. 104 (1982) 4695–4696.
[16] (a) J. Sim, H. Jo, M. Viji, M. Choi, J. Jung, H. Lee, J. Jung, Adv. Synth. Catal. 360
(2018) 852–858;
(b) H. Asahara, N. Nishiwaki, J. Org. Chem. 79 (2014) 11735–11739.
[17] (a) S. Santo, F. Coelho, RSC Adv. 2 (2012) 3237–3241;
(b) K. Lee, R.S. Lee, J.S. Lee, Synth. Commun. 50 (2020) 1141–1146.
[18] J. Schutte, F. Kilgenstein, M. Fischer, U. Koert, Eur. J. Org. Chem. (2014) 5302–
5311.
[19] P.M. Truong, P.Y. Zavalij, M.P. Doyle, Angew. Chem. Int. Ed. 53 (2014) 6468–
6472.
[20] L. Meng, J. Org. Chem. 81 (2016) 7784–7789.
[21] Y. Yu, Q. Sha, H. Cui, K.S. Chandler, M.P. Doyle, Org. Lett. 20 (2018) 776–779.
[22] (a) J. Xiao, X. Li, Angew. Chem. Int. Ed. 50 (2011) 7226–7236;
(b) Z. Zheng, Z. Wang, Y. Wang, L. Zhang, Chem. Soc. Rev. 45 (2016) 4448–
4458;
Acknowledgements
We thank the National Natural Science Foundation of China
(No. 21462021), the Natural Science Foundation of Jiangxi Province
of China (No. 20161BAB203086) and Key Laboratory of Functional
Small Organic Molecule, Ministry of Education (No. KLFS-KF-
201704) for financial support.
(c) H.S. Yeom, S. Shin, Acc. Chem. Res. 47 (2014) 966–977;
(d) D.B. Huple, S. Ghorpade, R.S. Liu, Adv. Synth. Catal. 358 (2016) 1348–1367;
(e) N. Rode, F. Marinelli, A. Arcadi, T. Adak, M. Rudolph, F. Rominger, A.S.K.
Hashmi, Adv. Synth. Catal. 360 (2018) 4790–4794;
(f) A.S.K. Hashmi, T. Wang, S. Shi, M. Rudolph, J. Org. Chem. 77 (2012) 7761–
7767;
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tetlet.2021.152953.
(g) V. Claus, L. Molinari, S. Bullmann, J. Thusek, M. Rudolph, F. Rominger, A.S.K.
Hashmi, Chem. Eur. J. 25 (2019) 9385–9389.
References
[23] L. Zhang, Acc. Chem. Res. 47 (2014) 877–888.
[1] (a) K. Yasumuro, Y. Suzuki, M. Shibazaki, K. Teramura, K. Abe, M. Orita, J.
Antibiot. 48 (1995) 1425–1429;
[24] (a) A.S.K. Hashmi, Chem. Rev. 107 (2007) 3180–3211;
(b) L. Ye, L. Cui, G. Zhang, L. Zhang, J. Am. Chem. Soc. 132 (2010) 3258–3259;
(c) L. Ye, W. He, L. Zhang, J. Am. Chem. Soc. 132 (2010) 8550–8551.
[25] (a) S. Shi, T. Wang, W. Yang, M. Rudolph, A.S.K. Hashmi, Chem Eur. J. 19 (2013)
6576–6580;
(b) M. Orita, K. Yasumuro, K. Kukubo, M. Shimizu, K. Abe, T. Tokunaga, H.
Kaniwa, J. Antibiot. 48 (1995) 1430–1434;
(c) H.H. Wasserman, J.-H. Chen, M. Xia, J. Am. Chem. Soc. 121 (1999) 1401–
1402.
(b) A.Y. Dubovtsev, D.V. Dar’in, M. Krasavin, V.Y. Kukushkin, Eur. J. Org. Chem.
(2019) 1856–1864;
(c) A.Y. Dubovtsev, D.V. Dar’in, V.Y. Kukushkin, Org. Lett. 21 (2019) 4116–
4119;
(d) A.Y. Dubovtsev, N.V. Shcherbakov, D.V. Dar’in, V.Y. Kukushkin, J. Org.
Chem. 85 (2020) 745–757.
[2] (a) H. Tanaka, A. Kuroda, H. Marusawa, H. Hatanaka, T. Kino, T. Goto, M.
Hashimoto, T. Taga, J. Am. Chem. Soc. 109 (1987) 5031–5033;
(b) T. Kino, H. Hatanaka, M. Hashimoto, M. Nishiyama, T. Goto, M. Okuhara, M.
Kohsaka, H. Aoki, H. Imanaka, J. Antibiot. 40 (1987) 1249–1255;
(c) H. Hatanaka, T. Kino, M. Asano, T. Goto, H. Tanaka, M. Okuhara, J. Antibiot.
42 (1989) 620–622;
(d) T.K. Jones, S.G. Mills, R.A. Reamer, D. Askin, R. Desmond, R.P. Volante, I.
Shinkai, J. Am. Chem. Soc. 111 (1989) 1157–1159.
[3] (a) C. Vezina, A. Kudelski, S.N. Sehgal, J. Antibiot. 28 (1975) 721–726;
(b) D.C.N. Swindells, P.S. White, J.A. Findlay, Can. J. Chem. 56 (1978) 2491–
2492;
(c) J.A. Findlay, J.-S. Liu, D.J. Burnell, Can. J. Chem. 60 (1982) 2046–2047.
[4] (a) H.H. Wasserman, J. Parr, Acc. Chem. Res. 37 (2004) 687–701;
(b) M.B. Rubin, R. Gleiter, Chem. Rev. 100 (2000) 1121–1164.
[5] P. Truong, C.S. Shanahan, M.P. Doyle, Org. Lett. 14 (2012) 3608–3611.
[6] (a) H.H. Wasserman, L.J. Lombardo, Tetrahedron Lett. 30 (1989) 1725–1728;
(b) Q. Sha, J. Wang, M.P. Doyle, J. Org. Chem. 83 (2018) 11288–11297.
[7] (a) Q. Sha, H. Arman, M.P. Doyle, Org. Lett. 17 (2015) 3876–3879;
(b) L. Wang, J.-L. Zhong, X.-F. Lin, Angew. Chem., Int. Ed. 58 (2019) 15824–
15828.
[8] H.H. Wasserman, R. Amici, R. Frechtte, J.H. van Duzer, Tetrahedron Lett. 30
(1989) 869–872.
[9] (a) C. Foley, A. Shaw, C. Hulme, Org. Lett. 20 (2018) 1275–1278;
(b) R.V. Hoffman, H.-O. Kim, A.L. Wilson, J. Org. Chem. 55 (1990) 2820–2822;
(c) R.M. Adlington, J.E. Baldwin, D. Catterick, G.J. Pritchard, J. Chem. Soc.,
Perkin Trans. 1 (2001) 668–679.
[26] (a) S. Tsupova, A. Cadu, S.A.C. Carabineiro, M. Rudolph, A.S.K. Hashmi, J. Catal.
350 (2017) 97–102;
(b) S. Carrettin, M.C. Blanco, A. Corma, A.S.K. Hashmi, Adv. Synth. Catal. 348
(2006) 1283–1288;
(c) W. Cao, B. Yu, Adv. Synth. Catal. 353 (2011) 1903–1907;
(d) M. Egi, K. Azechi, S. Akai, Adv. Synth. Catal. 353 (2011) 287–290;
(e) X.-Z. Shu, S.C. Nguyen, Y. He, F. Oba, Q. Zhang, C. Canlas, G.A. Somorjai, A.P.
Alivisatos, F.D. Toste, J. Am. Chem. Soc. 137 (2015) 7083–7086;
(f) R. Cai, X. Ye, Q. Sun, Q. He, Y. He, S. Ma, X. Shi, ACS Catal. 7 (2017) 1087–
1092.
[27] (a) C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Nature 359
(1992) 710–712;
(b) A. Corma, Top Catal. 4 (1997) 249–260;
(c) R.M. Martin-Aranda, J. Cejka, Top Catal. 53 (2010) 141–153.
[28] (a) A. Corma, C. Gonzalez-Arellano, M. Iglesias, M.T. Navarro, F. Sanchez,
Chem. Commun. (2008) 6218–6220;
(b) A. Corma, E. Gutierrez-Puebla, M. Iglesias, A. Monge, S. Perez-Ferreras, F.
Sanchez, Adv. Synth. Catal. 348 (2006) 1899–1907;
(c) G. Villaverde, A. Corma, M. Iglesias, F. Sanchez, ACS Catal. 2 (2012) 399–
406;
(d) Q. Nie, F. Yi, B. Huang, M. Cai, Adv. Synth. Catal. 359 (2017) 3968–3976;
(e) W. Yang, R. Zhang, F. Yi, M. Cai, J. Org. Chem. 82 (2017) 5204–5211;
(f) D. Liu, Q. Nie, R. Zhang, M. Cai, Adv. Synth. Catal. 360 (2018) 3940–3948.
[29] B. Niu, Q. Nie, B. Huang, M. Cai, Adv. Synth. Catal. 361 (2019) 4065–4074.
[10] S.P. Stanforth, B. Tarbit, M.D. Watson, Tetrahedron 60 (2004) 8893–8897.
[11] M.F. Brackeen, J.A. Stafford, P.L. Feldman, D.S. Karanewsky, Tetrahedron Lett.
35 (1994) 1635–1638.
6