Lewis Acid Catalyzed Electrophilic Aminomethyloxygenative Cyclization of Alkynols with N, O-Aminals

Article abstract of DOI:10.1021/acs.orglett.9b04630

Lewis acid enables the electrophilic carbooxygenative cyclization of alkynols with N,O-aminals. The new process proceeds efficiently under very mild conditions via a pathway that is opposite to classical carbo-metalation. These reactions exhibit broad substrate generality and functional group compatibility, leading to a wide variety of 5-8-membered oxacycles bearing diverse functional groups. The cyclization products can be elaborated via simple functional group transformations to generate synthetically useful oxacycles.

Full text of DOI:10.1021/acs.orglett.9b04630

pubs.acs.org/OrgLett
Letter
Lewis Acid Catalyzed Electrophilic Aminomethyloxygenative
Cyclization of Alkynols with N,O‑Aminals
Anrong Chen, Houjian Yu, Jiaqi Yan, and Hanmin Huang*
Cite This: https://dx.doi.org/10.1021/acs.orglett.9b04630
Read Online
sı
*
Metrics & More
Article Recommendations
Supporting Information
ACCESS
ABSTRACT: Lewis acid enables the electrophilic carbooxygena-
tive cyclization of alkynols with N,O-aminals. The new process
proceeds efficiently under very mild conditions via a pathway that
is opposite to classical carbo-metalation. These reactions exhibit
broad substrate generality and functional group compatibility,
leading to a wide variety of 5−8-membered oxacycles bearing
diverse functional groups. The cyclization products can be
elaborated via simple functional group transformations to generate synthetically useful oxacycles.
Scheme 1. Proposed Aminomethyloxygenative Cyclization
of Alkynols with N,O-Aminals
he ubiquity of oxygen-heterocycles continues to spark the
development of a number of cyclization reactions.1
T
Among the many ring-forming reactions in oxygen-heterocycle
preparation, metal-catalyzed intramolecular addition of an O−
H bond across an unsaturated carbon−carbon is particularly
attractive.2 While numerous efforts have been devoted to the
development of efficient catalytic systems by turning to the
metal catalyst,2,3 the divergence of products generated from the
documented methods is still limited due to the modes of
cyclization commonly resulting in protonation.4 Moreover, the
construction of medium-sized rings in an efficient and selective
manner is still a challenging task.5
Ynamides are special alkynes attached to a nitrogen atom
bearing an electron-withdrawing substituent, which holds a
unique nature allowing for the regioselective addition of
electrophiles or nucleophiles onto the ynamide.6 These
reactions have emerged as versatile tools for the synthesis of
a number of important chemical products in both academic
and industrial laboratories.7 Arguably, the most prevalent class
of ynamide reactions are π-bond insertion processes in which a
metal catalyst binds to π-orbitals of the alkyne and transfers a
functional group via an external nucleophilic attack (nucleo-
metalation) (Scheme 1, eq 1).8 The resulting nucleophilic
vinylmetal species can undergo a range of further reaction.
However, the formation of vinylmetal species via nucleophilic
β-addition is difficult due to the directing effect of the amido
group of ynamide9 and is restricted to specific examples.10
Compared to the well-established nucleophilic addition
pathway, a “polarity-reversed” electrophilic addition pathway
that is initiated by electrophilic addition has also been
developed (Scheme 1, eq 2) for the addition of acids and
halogen-derived reagents to alkynes.11 However, we are
surprised to find that little attention has been payed to
carbofunctionalization of alkynes by using such method,12
although such a catalytic system would preclude the use of
reactive organometallics, and more importantly, it can generate
a highly reactive keteniminium intermediate. Moreover, the
use of such kind of method for the carbooxygenative
cyclization of alkynols has remained unexplored, which is
presumably due to the lack of suitable carbon electrophiles.
Received: December 24, 2019
https://dx.doi.org/10.1021/acs.orglett.9b04630
© XXXX American Chemical Society
Org. Lett. XXXX, XXX, XXX−XXX
A

Organic Letters
pubs.acs.org/OrgLett
Letter
N,O-Aminals are reactive and versatile electrophiles, which
could be recognized as latent iminiums.13 We reasoned that
the iminium A could be generated from N,O-aminal 2 under
the assistance of Lewis acid. Upon trapping with the π-rich
nucleophile ynamide 1, the active keteniminium intermediate
B could be generated from iminium A. The resulting
keteniminium B could undergo oxygenative cyclization to
produce the desired β-aminomethyl oxacycles. Herein, we
report the development of a Lewis acid−catalyzed electrophilic
aminomethyloxygenative cyclization of alkynols with N,O-
aminals as electrophiles (Scheme 1, eq 3). The reaction
proceeds efficiently under very mild conditions and exhibits
broad substrate generality and functional group compatibility,
leading to a wide variety of 5−8-membered oxacycles bearing
diverse functional groups. The oxacycles can be further
elaborated through conventional functional group trans-
formations and successfully applied to the formal synthesis of
dinotefuran, which is an important insecticide.14
To examine the feasibility of the proposed reaction, we
initiated the investigations by examining the reaction of N-(6-
hydroxyhex-1-yn-1-yl)-N,4-dimethylbenzenesulfonamide (1a)
and N,N-dibenzyl-1-methoxymethanamine (2a). The proposed
cyclization reaction was conducted in CH2Cl2 at 80 °C under
the catalysis of 5 mol % of Lewis acid. After an extensive
screening of Lewis acid catalysts, the commonly used Lewis
acids, including Cu(OTf)2, Zn(OTf)2, Yb(OTf)3, and Fe-
(OTf)3, with OTf− as counteranion stood out as effective
catalysts. The target product 3aa with a seven-membered-ring
containing two amine moieties was obtained in 91% yield
when Zn(OTf)2 served as catalyst. In contrast, relative lower
yields were observed when Cl− or Br− served as the
counteranion (Table 1, entries 1−7). Inspired by this
promising result, we next sought to improve the efficiency of
the reaction by screening other reaction conditions. When the
temperature dropped to 25 °C, the reaction kept its high
activity and selectivity (Table 1, entries 8−10). On the other
hand, Brønsted acids, such as TfOH, MsOH, Tf2NH and 4-
NO2C6H4B(OH)2, can also promote this reaction, but only
moderate yields were achieved (Table 1, entries 11−14).
Screening of the solvent demonstrated that CH2Cl2 and
toluene both are good choices for achieving high reactivity
(Table 1, entries 15−19). Considering the solubility of the
catalyst, we chose to use CH2Cl2 as the solvent. Finally, no
desired product 3aa was observed in the absence of catalyst
(Table 1, entry 20).
With the optimized reaction conditions in hand, we turned
our attention to validating the generality of our strategy under
the catalysis of Zn(OTf)2, and the results are summarized in
Scheme 2. First, the substrate scope of N,O-aminal was
a
Scheme 2. Substrate Scope of Cyclization
a
Table 1. Optimization of Reaction Conditions
b
entry
cat.
solvent
T (°C)
yield (%)
1
2
3
4
5
6
7
8
CuCl2
CuBr2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
MeOH
Toluene
CH3CN
THF
80
80
80
80
80
80
80
60
40
25
25
25
25
25
25
25
25
25
25
25
10
65
81
89
82
91
88
89
87
90
65
63
59
40
59
90
89
84
46
0
Cu(OAc)2
Cu(OTf)2
Fe(OTf)3
Zn(OTf)2
Yb(OTf)3
Zn(OTf)2
Zn(OTf)2
Zn(OTf)2
TfOH
a
Reaction conditions: 1 (0.3 mmol), 2a (0.36 mmol), Zn(OTf)2 (5
b
mol %), CH2Cl2 (1.0 mL), 12 h, isolated yield. 4-NO2C6H4B(OH)2
(5 mol %). DME (1.0 mL).
c
9
10
11
12
13
14
15
16
17
18
19
20
examined with the reaction of 1a between various of N,O-
aminals derived from different amines and methanol. The
desired seven-membered cyclic ethers containing a β-amino-
methyl functional group (3aa−3ak) were obtained in good to
excellent yields. The reactions of N,O-aminals, derived from
methanol and benzylamines bearing a variety of electron-
withdrawing (−F, −Cl, and −Br) and electron-donating
substituents (−CH3 and -OCH3) on the phenyl ring,
proceeded well to deliver the desired products in more than
90% yields (3ab−3ag). However, N,O-aminals prepared from
methanol and simple aliphatic amines, such as dipropylamine,
diisopropylamine, dibutylamine and dicyclohexylamine, could
not react with N-(6-hydroxyhex-1-yn-1-yl)-N,4-dimethylben-
MsOH
Tf2NH
4-NO2C6H4B(OH)2
Zn(OTf)2
Zn(OTf)2
Zn(OTf)2
Zn(OTf)2
Zn(OTf)2
DMF
CH2Cl2
a
Reaction conditions: 1a (0.3 mmol), 2a (0.36 mmol), cat.(5 mol %),
b
solvent (1.0 mL), 12 h. Isolated yield.
B
https://dx.doi.org/10.1021/acs.orglett.9b04630
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
a
zenesulfonamide (1a) under the standard reaction conditions
to give the corresponding products. To our delight, when 4-
NO2C6H4B(OH)2 was utilized as a catalyst, the desired
products could be obtained in moderate yields (Scheme 2,
3ah−3ak). The higher reactivity exhibited here by the boric
acid might be attributed to its capability to generate the
iminium species via formation of B-OMe complex.
Scheme 3. Substrate Scope of Alkynol
Subsequently, the substrate scope of the alkynol was further
explored. As shown in Scheme 2, the 7-endo cyclization of N-
(6-hydroxyhex-1-yn-1-yl)-N,4-dimethylbenzenesulfonamide
derivatives with N,O-aminal 2a performed well to afford the
corresponding seven-membered products in excellent yields
(Scheme 2, 3aa−3ca). For example, two-oxygen-atom-
containing 3ba and bicyclic heterocycle 3ca were obtained in
excellent yields. Similar to the formation of seven-membered
ring products, the five-membered products 3da−3fa were
obtained in excellent yields, and the spirocyclic product 3fa
could be efficiently obtained in 85% yield. As expected, the six-
membered adducts 3ga−3ka could also be produced in good
yields under the standard reaction conditions. The structure of
3ga was further confirmed by single-crystal X-ray analysis.
When the electron-withdrawing group changed from a
sulfonamide to a simple amide, the corresponding six-
membered products were still obtained in good yields (Scheme
2, 3ha and 3ia). The cyclization of 1j bearing a camphor
sultam chiral auxiliary was successful to afford chiral product
3ja in 94% yield. Moreover, the reaction of metaxalone-derived
alkynol 1k was effectively converted into the corresponding
product 3ka in 70% yield. Further prolonging the tether length,
an eight-membered ring product (3la) was produced in 40%
yield.
a
Reaction conditions: 1 (0.3 mmol), 2a (0.36 mmol), Zn(OTf)2 (5
mol %), CH2Cl2 (1.0 mL), 12 h. isolated yield. The ratios of E/Z are
1
given within parentheses and were determined by H NMR.
Scheme 4. Synthetic Transformations
Next, the cyclization reactions with N-alkynylamino alcohols
were examined under the standard reaction conditions. As
shown in Scheme 3, the reaction was found to be compatible
with a series of aliphatic-substituted N-alkynylamino alcohols
(R = Hex, Oct) and diverse aromatic N-alkynylamino alcohols
bearing different substituents on the phenyl ring (R = H, Me,
OMe). The five-membered ring products 3ma−3qa were
successfully obtained in 77−92% yields. The structure of 3pa
was further confirmed by single-crystal X-ray analysis. In
addition, the six- and seven-membered ring products 3ra and
3sa were also obtained in excellent yields. However, the
analogous eight-membered product 3ta was obtained in only
10% isolated yield under the standard reaction conditions. The
lower activity might be attributed to the unfavorable
transannular interactions and entropic factors.
To further demonstrate the utility of this catalytic protocol,
transformation of the resulting heterocycles was explored
(Scheme 4). The Lewis acid enabled electrophilic amino-
methylation/cyclization process proved to be scalable in the
presence of 0.5 mol % of Zn(OTf)2 without lowering the yield
of this transformation (88% yield). The sulfonamide group
could be removed by treatment of 3da with p-TsOH·H2O in
CH2Cl2 to afford the corresponding α-aminomethyl butyr-
olactone 4 in excellent yield.4c Meanwhile, one benzyl group
contained in product 4 could be removed to give 3-
((benzylamino)methyl)dihydrofuran-2(3H)-one 5 in 70%
yield.15 In addition, the product 4 could be easily transformed
into aminodiol 6 by reduction with LiAlH4.16 The aminodiol 6
was successfully converted into N,N-dibenzyl-1-(tetrahydrofur-
an-3-yl)methanamine 7 via cyclization with TsCl in pyridine.17
Finally, the benzyl groups contained in product 7 were
successfully removed to give (tetrahydrofuran-3-yl)-
methanamine 8 in 78% yield through Pd/C-catalyzed hydro-
genolysis in the presence of H2.18 The (tetrahydrofuran-3-
yl)methanamine 8 could be facilely transferred to dinotefuran
9 according to the reported procedure.19
In summary, we have developed a Lewis acid catalyzed
synthesis of highly functionalized oxygen-heterocycles from
readily accessible alkynols and N,O-aminals. This method
operates through an electrophilic carbofunctionalization path-
way that is opposite to the classical carbometalation and could
provide a series of strategic bond-forming processes that will
have broad appeal in synthetic chemistry. This protocol
operates under very mild reaction conditions and exhibits
broad substrate generality and functional group compatibility,
leading to a wide variety of 5−8-membered ring oxacycles
bearing diverse functional groups. The highly functionalized
C
https://dx.doi.org/10.1021/acs.orglett.9b04630
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
Eycken, E.; Medaer, B.; Hoornaert, G. J. Tetrahedron Lett. 2002, 43,
3011. (c) Mullen, C. A.; Gagne, M. R. Org. Lett. 2006, 8, 665.
(d) Smith, J. A.; Moeller, K. D. Org. Lett. 2013, 15, 5818. (e) Fujino,
D.; Yorimitsu, H.; Osuka, A. J. Am. Chem. Soc. 2014, 136, 6255.
oxacycles are versatile synthetic intermediates and can be
readily transformed into important heterocyclic motifs.
ASSOCIATED CONTENT
* Supporting Information
■
̈
(f) Rosner, C.; Hennecke, U. Org. Lett. 2015, 17, 3226. (g) Trost, B.
sı
M.; Xu, S.-Y.; Sharif, E. U. J. Am. Chem. Soc. 2019, 141, 10199.
(5) (a) Molander, G. A. Acc. Chem. Res. 1998, 31, 603. (b) Mehta,
G.; Singh, V. Chem. Rev. 1999, 99, 881. (c) Yet, L. Chem. Rev. 2000,
100, 2963.
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.9b04630.
Experimental details and full spectroscopic data for all
new compounds (PDF)
(6) For selected reviews on ynamide, see: (a) Zificsak, C. A.;
Mulder, J. A.; Hsung, R. P.; Rameshkumar, C.; Wei, L.-L. Tetrahedron
2001, 57, 7575. (b) DeKorver, K. A.; Li, H.; Lohse, A. G.; Hayashi,
R.; Lu, Z.; Zhang, Y.; Hsung, R. P. Chem. Rev. 2010, 110, 5064.
(c) Evano, G.; Coste, A.; Jouvin, K. Angew. Chem., Int. Ed. 2010, 49,
2840. (d) Wang, X.-N.; Yeom, H.-S.; Fang, L.-C.; He, S.; Ma, Z.-X.;
Kedrowski, B. L.; Hsung, R. P. Acc. Chem. Res. 2014, 47, 560. (e) Pan,
F.; Shu, C.; Ye, L.-W. Org. Biomol. Chem. 2016, 14, 9456. (f) Zhou,
B.; Tan, T.-D.; Zhu, X.-Q.; Shang, M.; Ye, L.-W. ACS Catal. 2019, 9,
6393.
Accession Codes
CCDC 1958217−1958218 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(7) For selected examples,see: (a) Couty, S.; Meyer, C.; Cossy, J.
Angew. Chem., Int. Ed. 2006, 45, 6726. (b) Mukherjee, A.; Dateer, R.
B.; Chaudhuri, R.; Bhunia, S.; Karad, S. N.; Liu, R.-S. J. Am. Chem.
Soc. 2011, 133, 15372. (c) Rettenmeier, E.; Schuster, A. M.; Rudolph,
M.; Rominger, F.; Gade, C. A.; Hashmi, A. S. K. Angew. Chem., Int. Ed.
2013, 52, 5880. (d) Adcock, H. V.; Chatzopoulou, E.; Davies, P. W.
Angew. Chem., Int. Ed. 2015, 54, 15525. (e) Shu, C.; Wang, Y.-H.;
Zhou, B.; Li, X.-L.; Ping, Y.-F.; Lu, X.; Ye, L.-W. J. Am. Chem. Soc.
2015, 137, 9567. (f) Lecomte, M.; Evano, G. Angew. Chem., Int. Ed.
2016, 55, 4547. (g) Wang, Y.; Song, L.-J.; Zhang, X.-H.; Sun, J.-W.
Angew. Chem., Int. Ed. 2016, 55, 9704. (h) Patil, D. V.; Kim, S. W.;
Nguyen, Q. H.; Kim, H.; Wang, S.; Hoang, T.; Shin, S. Angew. Chem.,
AUTHOR INFORMATION
Corresponding Author
■
Hanmin Huang − University of Science and Technology of
China, Hefei, P.R. China, and Lanzhou University,
Lanzhou, P.R. China; orcid.org/0000-0002-0108-
6542; Email: hanmin@ustc.edu.cn
Other Authors
Anrong Chen − University of Science and Technology of
China, Hefei, P.R. China
Houjian Yu − University of Science and Technology of
China, Hefei, P.R. China
Jiaqi Yan − University of Science and Technology of China,
Hefei, P.R. China
́
Int. Ed. 2017, 56, 3670. (i) Zhao, Q.; Leon Rayo, D. F.; Campeau, D.;
Daenen, M.; Gagosz, F. Angew. Chem., Int. Ed. 2018, 57, 13603.
(j) Hong, F.-L.; Wang, Z.-S.; Wei, D.-D.; Zhai, T.-Y.; Deng, G.-C.; Lu,
X.; Liu, R.-S.; Ye, L.-W. J. Am. Chem. Soc. 2019, 141, 16961. (k) Xu,
Y.; Sun, Q.; Tan, T.-D.; Yang, M.-Y.; Yuan, P.; Wu, S.-Q.; Lu, X.;
Hong, X.; Ye, L.-W. Angew. Chem., Int. Ed. 2019, 58, 16252. (l) Dutta,
S.; Mallick, R. K.; Prasad, R.; Gandon, V.; Sahoo, A. K. Angew. Chem.,
Int. Ed. 2019, 58, 2289. (m) Zhou, B.; Zhang, Y.-Q.; Zhang, K.-R.;
Yang, M.-Y.; Chen, Y.-B.; Li, Y.; Peng, Q.; Zhu, S.-F.; Zhou, Q.-L.; Ye,
L.-W. Nat. Commun. 2019, 10, 3234.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.orglett.9b04630
Notes
(8) (a) Schore, N. E. Chem. Rev. 1988, 88, 1081. (b) Furstner, A.;
̈
Davies, P. W. Chem. Commun. 2005, 18, 2307. (c) Chinchilla, R.;
Najera, C. Chem. Rev. 2007, 107, 874.
(9) Selected examples: (a) Gourdet, B.; Lam, H. W. J. Am. Chem.
Soc. 2009, 131, 3802. (b) Saito, N.; Katayama, T.; Sato, Y. Adv. Synth.
Catal. 2013, 355, 853. (c) Saito, N.; Saito, K.; Sato, H.; Sato, Y. Org.
Lett. 2008, 10, 3829. (d) Minko, Y.; Pasco, M.; Lercher, L.;
Botoshansky, M.; Marek, I. Nature 2012, 490, 522.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This research was supported by the National Natural Science
Foundation of China (21925111, 21672199, 21790333, and
21702197).
(10) Selected examples of the reactions of ynamides with a gold
catalyst: (a) Davies, P. W.; Cremonesi, A.; Dumitrescu, L. Angew.
Chem., Int. Ed. 2011, 50, 8931. (b) Kramer, S.; Odabachian, Y.;
Overgaard, J.; Rottlander, M.; Gagosz, F.; Skrydstrup, T. Angew.
Chem., Int. Ed. 2011, 50, 5090. (c) Dateer, R. B.; Shaibu, B. S.; Liu, R.-
S. Angew. Chem., Int. Ed. 2012, 51, 113.
(11) (a) Nenitzescu, C. D.; Balaban, A. T. In Friedel-Crafts and
related reactions; Olah, G. A., Ed.; Interscience: New York, 1964; Vol.
3, p 1033. (b) Koser, G. F.; Rebrovic, L.; Wettach, R. H. J. Org. Chem.
1981, 46, 4324. (c) Trost, B. M.; Pinkerton, A. B. J. Am. Chem. Soc.
2002, 124, 7376. (d) Thadani, A. N.; Rawal, V. H. Org. Lett. 2002, 4,
4317. (e) Sun, J.; Kozmin, S. A. J. Am. Chem. Soc. 2005, 127, 13512.
(f) Carey, F. A.; Sundberg, R. J. Advanced Organic Chemistry Part B:
Reactions and Synthesis; Springer: Berlin, 2007.
REFERENCES
■
(1) For selected reviews, see: (a) Alonso, F.; Beletskaya, I. P.; Yus,
M. Chem. Rev. 2004, 104, 3079. (b) Hashmi, A. S. K. Chem. Rev.
2007, 107, 3180. (c) Furstner, A.; Davies, P. W. Angew. Chem., Int. Ed.
̈
2007, 46, 3410. (d) Nakata, T. Chem. Soc. Rev. 2010, 39, 1955.
(e) Shelton, J.; Lu, X.; Hollenbaugh, J. A.; Cho, J. H.; Amblard, F.;
Schinazi, R. F. Chem. Rev. 2016, 116, 14379.
(2) For selected reviews, see: (a) Beller, M.; Seayad, J.; Tillack, A.;
Jiao, H. Angew. Chem., Int. Ed. 2004, 43, 3368. (b) Alonso, F.;
Beletskaya, I. P.; Yus, M. Chem. Rev. 2004, 104, 3079. (c) Larrosa, I.;
Romea, P.; Urpí, F. Tetrahedron 2008, 64, 2683. (d) Garre, M. S.;
Sucunza, D.; Aguilar, E.; García-García, P.; Vaquero, J. J. J. Org. Chem.
2019, 84, 5712.
(3) (a) McDonald, F. E. Chem. - Eur. J. 1999, 5, 3103. (b) Bruneau,
C.; Dixneuf, P. H. Angew. Chem., Int. Ed. 2006, 45, 2176. (c) Trost, B.
M.; McClory, A. Chem. - Asian J. 2008, 3, 164.
(12) (a) Kusama, H.; Yamabe, H.; Onizawa, Y.; Hoshino, T.;
Iwasawa, N. Angew. Chem., Int. Ed. 2005, 44, 468. (b) Suero, M. G.;
Bayle, E. D.; Collins, B. S. L.; Gaunt, M. J. J. Am. Chem. Soc. 2013,
135, 5332. (c) Zhang, F.-Z.; Das, S.; Walkinshaw, A. J.; Casitas, A.;
Taylor, M.; Suero, M. G.; Gaunt, M. J. J. Am. Chem. Soc. 2014, 136,
(4) For a few cyclizations that did not result in protonation, see:
(a) Blandino, M.; McNelis, E. Org. Lett. 2002, 4, 3387.
(b) Compernolle, F.; Mao, H.; Tahri, A.; Kozlecki, T.; Van der
D
https://dx.doi.org/10.1021/acs.orglett.9b04630
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
8851. (d) Romanov-Michailidis, F.; Ravetz, B. D.; Paley, D. W.; Rovis,
T. J. Am. Chem. Soc. 2018, 140, 5370.
(13) (a) Xu, J.; Chen, X.; Wang, M.; Zhang, P.; Song, B.-A.; Chi, Y.
Angew. Chem., Int. Ed. 2015, 54, 5161. (b) Huang, Y.-Y.; Cai, C.;
Yang, X.; Lv, Z.-C.; Schneider, U. ACS Catal. 2016, 6, 5747.
(c) Wang, W.; Huang, H. Chem. Commun. 2019, 55, 3947. (d) Kang,
Z.; Wang, Y.; Zhang, D.; Wu, R.; Xu, X.; Hu, W. J. Am. Chem. Soc.
2019, 141, 1473. (e) Yu, J.; Chen, L.; Sun, J. Org. Lett. 2019, 21,
1664.
(14) Honda, H.; Tomizawa, M.; Casida, J. E. Toxicol. Lett. 2006,
161, 108.
(15) Olofson, R. A.; Martz, J. T.; Senet, P. J.; Piteau, M.; Malfroot,
T. J. Org. Chem. 1984, 49, 2081.
(16) Takekawa, Y.; Shishido, K. J. J. Org. Chem. 2001, 66, 8490.
(17) Nishizawa, M.; Yadav, A.; Iwamoto, Y.; Imagawa, H.
Tetrahedron 2004, 60, 9223.
(18) Qin, G.; Li, L.; Li, J.; Huang, H. J. Am. Chem. Soc. 2015, 137,
12490.
(19) Li, H.-F.; Wang, L.-L. Tetrahedron 2018, 74, 336.
E
https://dx.doi.org/10.1021/acs.orglett.9b04630
Org. Lett. XXXX, XXX, XXX−XXX