A Photocatalyzed Synthesis of Naphthalenes by Using Aniline as a Traceless Directing Group in [4 + 2] Annulation of Amino-benzocyclobutenes with Alkynes

Article abstract of DOI:10.1021/acscatal.7b00716

We report a visible-light-promoted synthesis of substituted naphthalenes via [4 + 2] annulation of amino-benzocyclobutenes with alkynes. Amino-benzocyclobutenes, which are conveniently synthesized by [2 + 2] cycloaddition of arynes with ketenes followed by reductive amination, undergo regioselective opening of the cyclobutenyl ring to reveal a presumably distonic radical cation upon photooxidation by an excited iridium complex. The distonic radical cation undergoes the annulation with terminal and internal alkynes as well as diynes to afford structurally diverse naphthalenes. The regiochemistry of the annulation follows the pattern displayed in the addition of nucleophilic carbon radicals to alkynes. The aniline group plays a dual role in which it not only directs the initial photooxidation to generate the amine radical cation but also serves as a leaving group to complete aromatization.

Full text of DOI:10.1021/acscatal.7b00716

Subscriber access provided by CORNELL UNIVERSITY LIBRARY
Letter
A Photocatalyzed Synthesis of Naphthalenes by Using Aniline as a Traceless
Directing Group in [4+2] Annulation of AminoBenzocyclobutenes with Alkynes
Qile Wang, and Nan Zheng
ACS Catal., Just Accepted Manuscript • Publication Date (Web): 15 May 2017
Downloaded from http://pubs.acs.org on May 15, 2017
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Catalysis is published by the American Chemical Society. 1155 Sixteenth Street
N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 6
ACS Catalysis
1
2
3
4
5
6
7
8
9
A Photocatalyzed Synthesis of Naphthalenes by Using Aniline as a
Traceless Directing Group in [4+2] Annulation of AminoBenzocyclo-
butenes with Alkynes
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Qile Wang, and Nan Zheng *
Department of Chemistry and Biochemistry, University of Arkansas
Fayetteville, Arkansas 72701 United States.
Abstract: We report a visible-light-promoted synthesis of substituted naphthalenes via [4+2] annulation of amino-
benzocyclobutenes with alkynes. Amino-benzocyclobutenes, which are conveniently synthesized by [2+2] cycloaddition
of arynes with ketenes followed by reductive amination, undergo regioselective opening of the cyclobutenyl ring to reveal
a presumably distonic radical cation upon photooxidation by an excited iridium complex. The distonic radical cation un-
dergoes the annulation with terminal and internal alkynes as well as diynes to afford structurally diverse naphthalenes.
The regiochemistry of the annulation follows the pattern displayed in addition of nucleophilic carbon radicals to alkynes.
The aniline group plays a dual role in which it not only directs the initial photooxidation to generate the amine radical
cation but also serves as a leaving group to complete aromatization.
Keywords: substituted naphthalenes, amino-benzocyclobutenes, photocatalysis, annulation, C-C cleavage.
Substituted naphthalenes and their derivatives, such as
naphthoquinones, are ubiquitous in many valuable mole-
cules across a broad spectrum of usage.1 Selected exam-
ples in this class of compounds include 9,10-
anthraquinone-2,7-disulphonic acid (AQDS), an excellent
energy storage material for flow batteries,2 justicidin A, a
potent antitumor natural product,3 and rumexoside, iso-
lated from the roots of a Turkish medicinal plant (Figure
1).4 Synthesis of substituted naphthalenes remains chal-
lenging due to the limitation of functional group toler-
ance as well as regioselectivity.5 Most of these syntheses
fall into two categories: 1) they start from a simple naph-
thalene core and then often require stepwise and lengthy
elaboration to install the requisite functional groups;6 2)
they begin with a suitably functionalized arene and pro-
ceed through annulation or cyclization to install the other
arene.7 Between the two approaches, the later is generally
considered to be more desirable because it is convergent
and modular.
Benzocyclobutenols, which bear a hydroxyl group on the
cyclobutenyl ring, display similar versatility in the ring
opening process.9, 10 Photo-irradiation, base treatment, or
heating generally favors cleavage of the distal C-C bond,
revealing a quinodimethane intermediate that readily
participates in the Diels-Alder reaction to provide dihy-
dronaphthalenes.11 On the other hand, cleavage of the
proximal C-C bond can be realized by transition metal
complexes such as Pd and Rh complexes to furnish aryl-
palladium or -rhodium intermediates that can participate
in a number of C-C bond formation reactions.9a, 12 Alt-
hough amino-benzocyclobutenes can be conveniently
synthesized by [2+2] cycloaddition of arynes with ketenes
followed by reductive amination, they have been much
less exploited than benzocyclobutenols in organic synthe-
sis (Scheme 1).13 Two notable examples using amino-
benzocyclobutenes as precursors to synthesize substitut-
ed arenes and dihydronaphthalenes include Shi’s work on
addition of vinylogous amides to arynes and Hsung’s on
syntheses of chelidonine and norchelidonine. In both
works, a quinodimethane intermediate was proposed to
be generated in situ via the ring opening and then was
intercepted by a nucleophile or underwent the Diels-
Alder reaction.14
Few studies on amino-benzocyclobutenes’ utility as
synthetic building blocks prompted us to examine their
synthetic applications, particularly in the context of visi-
ble light photocatalysis. We envisioned that single elec-
tron photooxidation of amino-benzocyclobutenes would
induce cleavage of the distal C-C bond to furnish a dis-
tonic radical cation.15 This reactive species would then
Figure 1. Selected examples of substituted naphthalenes
The embedded ring strain in benzocyclobutenes ren-
ders the usually inert C-C bonds cleavable under various
conditions, thereby making them a versatile precursor in
the synthesis of naphthalenes and dihydronaphthalenes.8
ACS Paragon Plus Environment

ACS Catalysis
undergo two sequential C-C bond formations mediated
Page 2 of 6
tions examined, concentrated HCl was added during the
workup to ensure completion of the elimination16.
1
2
3
4
5
6
7
8
by radicals to form a dihydronaphthalene. We expected
that its reactivity would be distinct from that of a
quinodimethane and thereby could furnish a completely
different subclass of dihydronaphthalenes. Herein we
report our studies on intermolecular annulations of ami-
no-benzocyclobutenes with alkynes and diynes, which
results in a three-component (benzynes, lithium enolates
or silyl ketene acetals, and alkynes) synthesis of substitut-
ed naphthalenes. Anilines play a dual role in this reaction:
it first engages in the photooxidation to induce the ring
opening and then serves as a leaving group to complete
aromatization.
Table 1. Optimization of the Reaction Conditions.a
Entry
Photocatalyst
Additives
(1eq.)
Yield of 3a [%]b
1
2
3
4
5
6
7
8
[Ir{dF(CF3)ppy}2(dtbpy)][PF6]
[Ir(dtbbpy)(ppy)2][PF6]
[Ir(dtbbpy)(ppy)2][PF6]
[Ir(dtbbpy)(ppy)2][PF6]
[Ir(dtbbpy)(ppy)2][PF6]
[Ir(dtbbpy)(ppy)2][PF6]
[Ir(dtbbpy)(ppy)2][PF6]
22%
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
37%
K2HPO4
K3PO4
48%
36%
K2HPO4
K2HPO4
K2HPO4
K2HPO4
59%c
62%c, d
N.R.c, e
N.R.c, d
aConditions: 1a (0.1 mmol, 0.1 M in degassed toluene), 2a (0.5 mmol),
irradiation with 18 white LED at room temperature for 36 h ，
W
concentrated HCl is added. 20 s later, the mixture is filtered through silica
gel. bYield determined by GC analysis using dodecane as an internal
standard unless noted. c 0.2 M of 1a in degassed toluene. dIrradiation with
6 W blue LED. eNo light.
Scheme 1. Cleavage reactions of benzocyclobutenols
and amino-benzocyclobutenes
Using phenylacetylene (2a) as the alkyne partner, we
examined the scope of amino-benzocyclobutenes (Table
2). Replacement of the -OMe substituent with a more
labile -OBn group had little effect on the product’s yield
(3b). Addition of another -OMe group para to the original
one (1c) furnished 1,4-dimethoxy-7-phenylnaphthalene 3c,
a naphthoquinone precursor in 58% yield. Fusion of a
benzene ring to amino-benzocyclobutene 1d was easily
accomplished by modifying the corresponding benzyne
precursor, and the expected product 9,10-Dimethoxy-2-
phenylanthracene 3d, an anthraquinone precursor was
prepared in 54% yield. Additional substituents were
readily incorporated into amino-benzocyclobutenes by
choosing silyl ketene acetals bearing the substituents for
the [2+2] cycloaddition with the corresponding benzynes.
These substituted amino-benzocyclobutenes (1e: -OMe;
1f: -Et; 1g: -CH2CH2OAc) underwent the annulation with
3-butyn-2-one or phenylacetylene uneventfully, providing
C5-substituted naphthalenes (3e, 3f, and 3g) in 54-68%
yields. Aromatic O-glycosides such as naphthalene sac-
charides are a common structural motif in bioactive natu-
ral products. The common approach for synthesis of this
motif is to form the glycosidic bond between an aglycone
(e.g., naphthol) and a saccharide.17 This method permits
an alternative assembly strategy in which the glycosidic
bond is formed between a simpler aglycone (e.g., a phenol
derivative) and the saccharide and the subsequent annu-
lation completes the synthesis of the more complex agly-
cone. Amino-benzocyclobutene 1h bearing a tetraacetyl
glucose with a β configuration at the anomeric carbon
underwent the annulation with phenylacetylene to afford
3h with the β configuration intact. Lastly, the alkoxy sub-
stituent in amino-benzocyclobutenes helped stabilize the
aryne intermediate and thus improved the efficiency of
the [2+2] cycloaddition to form the cyclobutenyl ring.
Amino-benzocyclobutene 1a and phenylacetylene were
chosen as the representative substrates to optimize the
reaction conditions (Table 1). The substituent on the ani-
line moiety was found to greatly affect the reaction, and
amino-benzocyclobutenes bearing electron-withdrawing
groups performed much better than those bearing elec-
tron-donating ones (see SI). The -CF3 group was selected
as the standard substituent because of its chemical inert-
ness under the photoredox conditions and the availability
of commercially available cheap precursor, 4-
(trifluoromethyl)-aniline. Among the solvents screened,
toluene was found to be the best. Other aromatic solvents
and polar solvents such as methanol and nitromethane all
gave inferior results (see SI). For the photocatalyst, we
focused
on
those
soluble
in
toluene.
[Ir(ppy)2(dtbbpy)][PF6] was more effective than
[Ir{dF(CF3)ppy}2(dtbpy)][PF6] (entries 1 and 2), whereas
Ru(bpy)3(BArF)2 was surprisingly inactive (see SI). Addi-
tion of an inorganic base such as K2HPO4 increased the
yield of 3a from 37% to 48% (entry 3). However, use of
more basic K3PO4 gave a slightly lower yield of 3a (entry
4). Interestingly, use of a more soluble base such as
Cs2CO3 or tetrabutylammonium hydroxide resulted in a
much lower yield of 3a, suggesting a delicate balance of
the base’s strength and solubility in order to achieve the
optimal yield (see SI). Increasing the concentration and
switching from 18 W white LED to 6 W blue LED both
helped the reaction, furnishing product 3a in 62% yield
(entries 5 and 6). Control experiments showed that both
light and the photocatalyst were essential to the reaction
(entries 7 and 8). These results suggested that the Diels-
Alder reaction pathway unlikely operated in the
reaction.14a, 14c It was worth of note that because incom-
plete elimination of the aniline was observed in the condi-
ACS Paragon Plus Environment

Page 3 of 6
ACS Catalysis
hindrance, participated in the annulation to furnish only
However, it was not required for the annulation. Amino-
1
2
3
4
5
6
7
8
benzocyclobutenes (1i and 1j), both lack of the alkoxy
substituent, proceeded in the annulation to furnish 2-
phenylnaphthalene 3i and 3-phenylphenanthrene 3j re-
spectively.
one regioisomer 3q in 58% yield albeit in longer reaction
time. To our surprise, diynes 2i-k worked really well in
this method. Alkynyl naphthalenes 3r-s, which are usually
synthesized by cross coupling of terminal alkynes with
prefunctionalized naphthalenes, were obtained in one
step in 62-63% yield. Not surprisingly, the glycosidic bond
survived in the annulation of 1h with diyne 2k, which
allowed for rapid increase of the structural complexity of
naphthalene saccharide 3t in a respectable yield (61%).
Table 2. Substrate Scope of Amino-
benzocyclobutenes
H
[Ir(dtbbpy)(ppy)2]PF6
N
R1
Toluene, degasssed
K2HPO4
7
CF3 + R1
R
R
Entry[a]
1
9
2
1
3
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table 3. Substrate Scope of Alkynes
Yield[%][b]
58
Substrate
Product
OBn
H
N
OBn
Ph
CF3
CF3
3b
1b
OMe
Ph
OMe
OMe
H
N
58
2
3c
1c
OMe
OMe
OMe
H
N
Ph
CF3
3
4
54
68
1d
3d
OMe
OMe
OMe
OMe
O
H
N
CF3
1e
OMe
3e
OMe
OMe
OMe
OMe
H
N
Ph
5
6
CF3
56
54
Et
1f
3f
Et
OMe
H
N
Ph
3g
OAc
CF3
1g
OAc
OAc
OAc
O
O
AcO
AcO
AcO
AcO
7
3h
O
O
OAc
OAc
H
N
Ph
50
CF3
1h
H
H
Ph
3i
N
56
40
8
9
CF3
1i
1j
H
N
Ph
CF3
3j
1
2
[a] Conditions: (0.1 mmol, 0.2 M in degassed toluene), (0.5 mmol),
after irradiation with 6 W blue LED at room temperature for 60 h,
concentrated HCl is added. 20 s later, the mixture is filtered through
silica gel. [b] Isolated yields.
We next investigated the scope of alkynes (Table 3).
The substituents on the phenyl group of phenylacetylene
were well tolerated. Several groups with various electronic
characters at the para or meta position (2b-e) were com-
patible with the annulation reaction to provide naphtha-
lenes 3k-n in 51-64% yield. In addition to the aryl group at
C7, other functional groups such as thiophene and methyl
esters were easily incorporated into C7 of naphthalenes,
as 3-ethynylthiophene 2f and methyl propiolate 2g both
successfully underwent the annulation with 1a, although
in somewhat lower yields than phenylacetylene. Unsym-
metrical internal alkyne 2h, despite the increase in steric
We believed that the annulation probably proceeds in a
mechanism similar to our previously reported [4+2] annu-
lation of cyclobutylanilines with alkynes, as the reactivity
trend and regiochemistry with respect to alkynes com-
pletely match with those observed for the latter
reaction.15c The photoexcited Ir(III) complex oxidizes
amino-benzocyclobutene 1 to generate amino radical cat-
ACS Paragon Plus Environment

ACS Catalysis
Page 4 of 6
ion 4 followed by ring opening at the distal C–C bond to also acts as a leaving group to complete aromatization.
1
2
3
4
5
6
7
8
form distonic radical cation 5, which subsequently adds to
alkyne to furnish vinyl radical 6. Ring closure is then
achieved via intramolecular addition of the vinyl radical
to the iminium ion to provide amino radical cation 7,
which is reduced by the Ir(II) complex to give 1,4-
dihydronaphthalene 8 after protonation. Finally, elimina-
tion of the aniline group presumably by an E1-like path-
way gives naphthalene 3 via benzylic carbocation 9
(Scheme 2). The [4+2] annulation of amino-
benzocyclobutenes with alkynes was considerably slower
than that of cyclobutylanilines with alkynes. We attribut-
ed the slower annulation of amino-benzocyclobutenes to
the stability and low reactivity of the incipient benzyl
radicals. It has been reported that benzyl radicals add to
alkenes much slower than alkyl radicals.18 To support the
Because a different type of the ring-opening intermediate
(e.g., the distonic radical cation) is involved, amino-
benzocylobutenes display distinct chemistries from ben-
zocyclobutenols in the annulation reaction.
AUTHOR INFORMATION
9
Corresponding Author
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
* E-mail: nzheng@uark.edu
Notes
The authors declare no competing financial interest.
ASSOCIATED CONTENT
proposed
mechanism,
the
uneliminated
1,4-
Supporting Information.
dihydronaphthalene intermediate from 2h was successful-
ly isolated (see SI). UV-Vis absorption spectra of amino-
benzocyclobutene 1a and [Ir(ppy)2(dtbbpy)]PF6 supported
that the Ir complex was photoexcited by the blue LED.
The oxidation half peak potential of 1a was found to be
1.13 V vs. SCE, which is more positive than the reduction
The supporting information is available free of charge via the
Internet at http://pubs.acs.org.
Experimental procedures and spectra data
ACKNOWLEDGMENT
potential of the photoexcited Ir(III) complex (Ir3+*/Ir2+
:
0.66 V vs. SCE).19 Although thermodynamically unfavora-
ble, such SET processes have been reported.15c, 20 Stern-
Volmer quenching studies also showed that amino-
benzocyclobutene 1a was able to quench the photoexcited
Ir(III) complex (see SI). TEMPO completely inhibited the
formation of the uneliminated dihydronaphthalene and
naphthalene.
We thank the University of Arkansas, the Arkansas Biosci-
ence Institute, the National Institutes of Health (NIH) (grant
number P30 GM103450) from the National Institute of Gen-
eral Medical Sciences, and NSF Career Award (Award Num-
ber CHE-1255539) for generous support of this research. We
also thank Jiang Wang and Jean de Dieu Nubundiho for ex-
perimental assistance in discovering this method.
REFERENCES
1.
(a) Granda, M.; Blanco, C.; Alvarez, P.; Patrick, J. W.;
Menéndez, R., Chem. Rev. 2014, 114, 1608-1636; (b) Donner, C. D.,
Nat. Prod. Rep. 2015, 32, 578-604.
2.
Huskinson, B.; Marshak, M. P.; Suh, C.; Er, S.; Gerhardt,
M. R.; Galvin, C. J.; Chen, X.; Aspuru-Guzik, A.; Gordon, R. G.; Aziz,
M. J., Nature 2014, 505, 195-198.
3.
Fukamiya, N.; Lee, K.-H., J. Nat. Prod. 1986, 49, 348-350.
4.
Demirezer, Ö.; Kuruüzüm, A.; Bergere, I.; Schiewe, H. J.;
Zeeck, A., Phytochemistry 2001, 56, 399-402.
5. de Koning, C. B.; Rousseau, A. L.; van Otterlo, W. A. L.,
Tetrahedron 2003, 59, 7-36.
6.
Groom, K.; Hussain, S. M. S.; Morin, J.; Nilewski, C.;
Rantanen, T.; Snieckus, V., Org. Lett. 2014, 16, 2378-2381.
7.
(a) Raviola, C.; Protti, S.; Ravelli, D.; Fagnoni, M., Chem.
Scheme 2. Proposed Reaction Mechanism
Soc. Rev. 2016, 45, 4364-4390; for selected recent intermolecular
examples, see: (b) Zhou, S.; Wang, J.; Wang, L.; Song, C.; Chen, K.;
Zhu, J., Angew. Chem. Int. Ed. 2016, 55, 9384-9388; (c) Fukutani, T.;
Hirano, K.; Satoh, T.; Miura, M., Org. Lett. 2009, 11, 5198-5201; (d)
Jiang, H.; Cheng, Y.; Zhang, Y.; Yu, S., Org. Lett. 2013, 15, 4884-4887;
(e) Naresh, G.; Kant, R.; Narender, T., Org. Lett. 2015, 17, 3446-3449;
(f) Peng, S.; Wang, L.; Wang, J., Chem. Eur. J. 2013, 19, 13322-13327; (g)
Tan, X.; Liu, B.; Li, X.; Li, B.; Xu, S.; Song, H.; Wang, B., J. Am. Chem.
Soc. 2012, 134, 16163-16166; (h) Shu, W.-M.; Zheng, K.-L.; Ma, J.-R.;
Wu, A.-X., Org. Lett. 2016, 18, 3762-3765; (i) Larock, R. C., J.
Organomet. Chem. 1999, 576, 111-124; (j) Asao, N.; Nogami, T.; Lee, S.;
Yamamoto, Y., J. Am. Chem. Soc. 2003, 125, 10921-10925; (k)
Viswanathan, G. S.; Wang, M.; Li, C.-J., Angew. Chem. Int. Ed. 2002,
41, 2138-2141.
In conclusion, we report a visible-light-mediated syn-
thesis of substituted naphthalenes via the [4+2] annula-
tion of amino-benzocyclobutenes with alkynes. Upon
one-electron photooxidation, amino-benzocylobutenes
undergo ring opening to reveal presumably the distonic
radical cation, which then participate in two sequential C-
C bond formations en route to naphthalenes. Amino-
benzocylobutenes tolerate substitution at C-2, C-5, and C-
7 positions including a usually labile glycosidic bond at C-
2. Terminal alkynes, internal alkynes and diynes are all
shown to be a viable annulation partner, affording struc-
turally diverse naphthalenes. The aniline moiety plays a
critical role in the annulation, as it not only functions as a
photo-oxidizable group to induce the ring opening but
8.
9.
Mehta, G.; Kotha, S., Tetrahedron 2001, 57, 625-659.
(a) Yu, J. J.; Yan, H.; Zhu, C., Angew. Chem. Int. Ed. 2016,
55, 1143-1146; (b) Takemura, I.; Imura, K.; Matsumoto, T.; Suzuki, K.,
Org. Lett. 2004, 6, 2503-2505; (c) Kraus, G. A.; Zhao, G., Synlett 1995,
ACS Paragon Plus Environment

Page 5 of 6
ACS Catalysis
1995, 541-542; (d) Kametani, T.; Katoh, Y.; Fukumoto, K., J. Chem.
Soc., Perkin Trans. 1 1974, 1712-1714; (e) Arnold, B. J.; Sammes, P. G., J.
Chem. Soc., Chem. Commun. 1972, 30-31.
1
2
3
4
10.
Sadana, A. K.; Saini, R. K.; Billups, W. E., Chem. Rev. 2003,
103, 1539-1602.
11.
(a) Caubere, P.; Derozier, N.; Loubinoux, B., Bull. Soc.
5
6
7
8
Chim. Fr. 1971, 1, 302; (b) Arnold, B. J.; Sammes, P. G.; Wallace, T. W.,
J. Chem. Soc., Perkin Trans. 1 1974, 409-414; (c) Cava, M. P.; Muth, K.,
J. Am. Chem. Soc. 1960, 82, 652-654; (d) Charlton, J. L.; Alauddin, M.
M., Tetrahedron 1987, 43, 2873-2889; (e) Gokhale, A. a. S. P., Helv.
Chim. Acta 1998, 81, 251--267; (f) Kitaura, Y.; Matsuura, T.,
Tetrahedron 1971, 27, 1597-1606; (g) Oppolzer, W., Synthesis 1978,
1978, 793-802; (h) Segura, J. L.; Martín, N., Chem. Rev. 1999, 99, 3199-
3246; (i) Stevens, R. V.; Bisacchi, G. S., J. Org. Chem. 1982, 47, 2396-
2399; (j) Choy, W.; Yang, H., J. Org. Chem. 1988, 53, 5796-5798; (k)
Iida, K.; Komada, K.; Saito, M.; Yoshioka, M., J. Org. Chem. 1999, 64,
7407-7411.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
12.
(a) Fumagalli, G.; Stanton, S.; Bower, J. F., Chem. Rev. 2017
DOI: 10.1021/acs.chemrev.6b00599; (b) Chtchemelinine, A.; Rosa, D.;
Orellana, A., J. Org. Chem. 2011, 76, 9157-9162; (c) Ding, L.; Ishida, N.;
Murakami, M.; Morokuma, K., J. Am. Chem. Soc. 2014, 136, 169-178;
(d) Ishida, N.; Sawano, S.; Masuda, Y.; Murakami, M., J. Am. Chem.
Soc. 2012, 134, 17502-17504; (e) Ishida, N.; Ishikawa, N.; Sawano, S.;
Masuda, Y.; Murakami, M., Chem. Commun. 2015, 51, 1882-1885; (f)
Li, Y.; Lin, Z., J. Org. Chem. 2013, 78, 11357-11365; (g) Xia, Y.; Liu, Z.;
Liu, Z.; Ge, R.; Ye, F.; Hossain, M.; Zhang, Y.; Wang, J., J. Am. Chem.
Soc. 2014, 136, 3013-3015; (h) Ishida, N.; Sawano, S.; Murakami, M.,
Nat. Commun. 2014, 5, 3111; (i) Zhao, C.; Liu, L.-C.; Wang, J.; Jiang, C.;
Zhang, Q.-W.; He, W., Org. Lett. 2016, 18, 328-331.
13.
Chen, P. H.; Savage, N. A.; Dong, G., Tetrahedron 2014, 70,
4135-4146.
14.
(a) Feltenberger, J. B.; Hayashi, R.; Tang, Y.; Babiash, E. S.
C.; Hsung, R. P., Org. Lett. 2009, 11, 3666-3669; (b) Li, R.; Wang, X.;
Wei, Z.; Wu, C.; Shi, F., Org. Lett. 2013, 15, 4366-4369; (c) Ma, Z.-X.;
Feltenberger, J. B.; Hsung, R. P., Org. Lett. 2012, 14, 2742-2745.
15.
(a) Maity, S.; Zhu, M.; Shinabery, R. S.; Zheng, N., Angew.
Chem. Int. Ed. 2012, 51, 222-226; (b) Nguyen, T. H.; Maity, S.; Zheng,
N., Beilstein J. Org. Chem. 2014, 10, 975-980; (c) Wang, J.; Zheng, N.,
Angew. Chem. Int. Ed. Engl. 2015, 54, 11424-7.
16.
The distribution of the uneliminated dihydronaphthalenes
and naphthalenes varied greatly with the substituents of amino-
benzocyclobutenes as well as the structure of alkynes.
17.
Jacobsson, M.; Malmberg, J.; Ellervik, U., Carbohydr. Res.
2006, 341, 1266-1281.
18.
Héberger, K.; Walbiner, M.; Fischer, H., Angew. Chem. Int.
Ed. 1992, 31, 635-636.
19.
Roth, H. G.; Romero, N. A.; Nicewicz, D. A., Synlett 2016,
27, 714-723.
20.
(a) Yasu, Y.; Koike, T.; Akita, M., Adv. Synth. Catal. 2012,
354, 3414-3420; (b) Primer, D. N.; Karakaya, I.; Tellis, J. C.; Molander,
G. A., J. Am. Chem. Soc. 2015, 137, 2195-2198.
ACS Paragon Plus Environment

ACS Catalysis
Page 6 of 6
SYNOPSIS TOC
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
6
ACS Paragon Plus Environment