Catalyst- and Substituent-Controlled Switching of Chemoselectivity for the Enantioselective Synthesis of Fully Substituted Cyclobutane Derivatives via 2 + 2 Annulation of Vinylogous Ketone Enolates and Nitroalkene

Article abstract of DOI:10.1021/acs.orglett.8b03335

The first regioselective, diastereoselective, and enantioselective organocatalyzed Michael-Michael cascade of vinylogous ketone enolates and nitroalkenes for the construction of fully substituted cyclobutanes is achieved by the deployment of the appropriate chiral squaramide catalyst and the pertinent substituent on the substrate. The domino reaction provided cyclobutanes with four contiguous stereocenters, including a quaternary center in good yields with diastereomeric ratio of >20:1 and with enantioselectivities of mostly up to 98% enantiomeric excess (ee). The structures and the absolute configurations of the adducts were confirmed by single-crystal X-ray crystallographic analyses of the appropriate products.

Full text of DOI:10.1021/acs.orglett.8b03335

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Catalyst- and Substituent-Controlled Switching of Chemoselectivity
for the Enantioselective Synthesis of Fully Substituted Cyclobutane
Derivatives via 2 + 2 Annulation of Vinylogous Ketone Enolates and
Nitroalkene
Pavan Sudheer Akula,† Bor-Cherng Hong,* and Gene-Hsiang Lee‡
†Department of Chemistry and Biochemistry, National Chung Cheng University, Chia-Yi 621, Taiwan, Republic of China
‡Instrumentation Center, National Taiwan University, Taipei 106, Taiwan, Republic of China
S
* Supporting Information
ABSTRACT: The first regioselective, diastereoselective, and enantioselective organocatalyzed Michael−Michael cascade of
vinylogous ketone enolates and nitroalkenes for the construction of fully substituted cyclobutanes is achieved by the
deployment of the appropriate chiral squaramide catalyst and the pertinent substituent on the substrate. The domino reaction
provided cyclobutanes with four contiguous stereocenters, including a quaternary center in good yields with diastereomeric
ratio of >20:1 and with enantioselectivities of mostly up to 98% enantiomeric excess (ee). The structures and the absolute
configurations of the adducts were confirmed by single-crystal X-ray crystallographic analyses of the appropriate products.
yclobutane derivatives stand out for their unique
with iminium catalysis for the synthesis of chiral cyclobutanes
with subsequent ring expansion to give cyclopentanone
derivatives.5 In mechanistic studies of the organocatalytic
Michael addition of aldehydes to nitroalkenes, the research
groups of Blackmond, Seebach, and Hayashi revealed a resting-
state cyclobutane intermediate. These findings led to thought-
provoking questions that encouraged the development of new
methods in the synthesis of cyclobutanes.6,7 Later, Jørgensen
and co-workers designed a bifunctional hydrogen-bonding
catalyst for the double activation of α,β-unsaturated aldehydes
and nitroalkenes to give cyclobutanes as the products, rather
than as reaction intermediates (Scheme 1a).8 Independently,
Vicario et al. reported a cooperative catalyzed enantioselective
formal [2 + 2] cycloaddition of enal and α-hydroxymethyl
nitroalkene, with the catalyst cocktail of arylprolinol ether and
thiourea (Scheme 1b).9 To achieve this reaction, two types of
catalysts produced a synergistic catalysis, with the driving force
arising from the hemiacetal formation. Extending the
discoveries from these early investigations, a series of ingenious
examples of enantioselective synthesis have been presented.10
However, attempts to apply these strategies to other reactant
analogues afforded acyclic products instead of cyclobutanes.
For example, the reaction of allylic ketone and cinnamaldehyde
C
scaffolds in naturally occurring compounds1 and have
long been of interest to chemists, especially as a molecular
building block for subsequent transformations (Figure 1).2
Figure 1. Selected natural products and therapeutic agents containing
chiral cyclobutanes.
While most of the direct synthetic methods give rise to racemic
cyclobutanes, only a few instances of metal-catalyzed3 or
photochemical4 enantioselective approaches have been real-
ized. The pioneering work of Ishihara and his co-workers
described the organocatalytic enantioselective [2 + 2]
cycloaddition of unactivated alkenes and α-acyloxyacroleins
Received: October 18, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b03335
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
Scheme 1. Organocatalytic α/γ-Alkylations
Table 1. Screening of Conditions for the Reactions
yield
yield
c
time,
catalyst t (h)
of 3
of 4
ee of
b
c
d
entry
1, 2
3:4
(%)
(%)
4
(%)
e
g
g
e
1
2
3
4
5
6
7
8
9
1a, 2a
1a, 2a
1a, 2a
1a, 2a
1a, 2a
1a, 2a
1a, 2a
1a, 2a
1a, 2b
1b, 2a
1a, 2a
1a, 2a
1a, 2a
1a, 2a
A
B
C
D
E
F
G
H
F
F
F
F
F
24
24
22
14
20
8
10
20
8
30
12
13
18
48
nd
na
<5
<5
nd
na
f
g
g
f
∼0
∼0
39:61
28:72
36:64
6:94
31
24
29
5
60
70
62
93
89
73
70
−87
−91
−86
98
9:91
6
−93
−98
99
19:81
25:75
80:(20)
12:82
11:89
11:89
9:91
15
22
76
10
10
9
h
i
i
10
15
na
98
96
97
j
11
81
78
76
87
k
12
13
l
m
14
F
4
98
a
Unless otherwise noted, the reactions were performed on a 0.45 M
scale of 2 (1.0 equiv), and 1 (1.5 equiv) with 10 mol % of catalyst in a
derivatives with the Jørgensen−Hayashi catalyst and a
hydrogen-bonding diamine catalyst afforded the direct vinyl-
ogous Michael addition11,12 adduct, 1,7-dioxo products, with
good yields and enantioselectivities (Scheme 1c).13
screw capped vial at ambient temperature (∼25−30 °C).
b
1
Determined by crude H NMR; dr of 4 was observed to be >20:1.
c
d
Isolated yields. The ee of 4 was analyzed by HPLC with column
e
f
g
Chiralpak IC. nd = not determined. na = not available. Most of the
h
Correspondingly, direct diastereoselective and enantioselec-
tive vinylogous Michael additions of enones to enals with the
Jørgensen−Hayashi catalyst, Et3N, and cinnamic acid additives
in aprotic solvents provided the γ-alkylated products (Scheme
1d).14 Palomo and his co-workers described an elegant method
of regioselective, diastereoselective, and enantioselective direct
Michael reaction of β,γ-unsaturated ketones with nitroalkenes
and a tertiary amine/hydrogen-bonding bifunctional catalyst to
proceed in an exclusive α-alkylation of enone, providing the
corresponding α-branched ketones with two vicinal tertiary
carbon stereocenters in good diastereoselectivities and
enantioselectivities (Scheme 1e).15 Thus, variants of [2 + 2]
enantioselective annulations remain compelling subjects for
development. Therefore, we envisioned that the enantiose-
lective annulations of β,γ-unsaturated ketones could be
achieved by introducing the appropriate substituents onto
the nitroalkenes and the applicable bifunctional organocatalysts
(Scheme 1f).16
We initially selected a series of organocatalysts for the
reaction of enone 1a and methylnitrostyrene 2a (Table 1,
entries 1−8). The reaction with the primary amine catalysts A
and B in CH2Cl2 gave a trace or no observation of the products
3a and 4a. Treatment of 1a and 2a with Takemoto catalyst C
afforded a 39:61 ratio of 3a and 4a, as monitored by crude 1H
NMR, and obtained 31% yield of 3a and 60% yield of 4a
(Table 1, entry 3). Interestingly, the reaction with squaramide
catalyst D increased the isolation yield of 4a (70%) and the
ratio of 3a:4a (28:72) (Table 1, entry 4). Exposure of 1a and
1 and 2 was recovered. Analyzed with column Chiralpak IA.
i
Cyclobutane 4c was not observed; instead, the γ-alkylation adduct
j
k
(3c-γ) was isolated in 15% yield. Reaction in toluene. Reaction in
CH3CN. Reaction in THF. A 77:23 Z/E mixture of 2a was used for
l
m
the reaction in CH2Cl2.
2a to cinchona thiourea catalyst E did not improve the yield
and selectivity of 4a over 3a, but gave similar results as the
reaction with diamine thiourea catalyst C (Table 1, entries 5
and 3). We were pleased to observe that the reaction of 1a and
2a with 0.1 equiv of cinchona squaramide catalyst F was
completed in a short period of time (8 h) and provided a 94:6
ratio of 4a:3a and 93% isolated yield of 4a (Table 1, entry 6).
However, the reaction with another cinchona squaramide
catalyst G did not improve the yield of 4a (89%) and the ratio
of 4a:3a (91:9) (Table 1, entry 7). The reaction with
squaramide catalyst H was slow, and lower yields were
observed (Table 1, entry 8). Notably, the nature of
substituents on enone 1 and nitroolefin 2 seemed to be
crucial for the feasibility and selectivity of the [2 + 2]
annulations. For example, the reaction of catalyst F with 1a
and 2b, which lacks the methyl group on the nitrostyrene 2,
gave only 70% yield of 4b with a 75:25 ratio of 4b:3b, after 8 h
reaction (Table 1, entry 9). The regioselectivity of 4/3 of the
reaction with 2b was lower than the reaction with its
counterpart 2a, where a 94:6 ratio was obtained (Table 1,
entries 9 and 6). Interestingly, the dichotomous regioselectivity
was reversed to favor 3 over 4 by replacing the phenyl with the
B
DOI: 10.1021/acs.orglett.8b03335
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
methyl group of R1 on enone 1. For example, the reaction of
enone 1b (where R1 = Me, instead of an aromatic group) and
2a with catalyst F for 30 h, provided a 76% yield of 3c and a
80:20 ratio of 3c:3c-γ, where the γ-alkylation product (3c-γ)
was not even cyclized via the subsequent intramolecular nitro-
Michael reaction, and the expected cyclobutane product 4c
was not observed (Table 1, entry 10). It is noteworthy that the
intramolecular nitro-Michael reaction of 3c-γ to cyclobutane
4c did not occur spontaneously, as did the other counterpart
derivatives (4a and 4b) with only a subtle difference in the R1
substituent.
Table 2. Examples of the Annulation
bc
,
d
time, t
(h)
yield
ee
entry
product
(%)
(%)
1
2
4a: R1 = H; R2 = H; R3 = Ph; R4 = Me
4d: R1 = H; R2 = H; R3 = 4-BrC6H4; R4
= Me
8
12
93
89
98
98
For the enantioselectivities in the above reactions, the
reaction of 1a and 2a with catalyst F gave a 93% isolation yield
of 4a with excellent enantioselectivity (98% ee, Table 1, entry
6), while the reaction with other catalysts, C, D and E,
provided lesser yields of 4a (60%−70% yields) with opposite
and lower enantioselectivities (−86% to −91% ee), (Table 1,
entries 3−5). In addition, the reaction of 1a and 2a with
another cinchona squaramide catalyst G, instead of F, provided
4a with opposite and slightly less enantioselectivity (−93% ee)
(Table 1, entry 7). The high enantioselectivities of the
annulations with catalyst F were inconsistent with nitrostyrene
(2b), where butane 4b was obtained with 99% ee, even though
with a low 4a/3a ratio (Table 1, entry 9). The reaction of 1a
and 2a with catalyst F in other solvents, e.g., toluene, CH3CN,
and THF, did not improve the regioselectivities and the yields
of cyclobutane product 4a (Table 1, entries 11−13). In
addition, the reaction of 1a with a ca. 3:1 Z/E mixture of 2a
under the optimal reaction conditions (catalyst F in CH2Cl2,
the condition in Table 1, entry 6), 4a was isolated with a
similar yield (87%) and enantioselectivity (98%), albeit a much
longer reaction time (48 h) was required for the reaction to
reach completion with the (Z)-2a (Table 1, entry 14). Note
that the (Z)-enriched nitrostyrene 2a was prepared from the
isomerization of (E)-nitrostyrene 2a by photo irradiation with
a 24 W household compact fluorescent light (CFL).17,18 To
the best of our knowledge, the synthesis of these (Z)-
nitroalkenes from the isomerization of (E)-nitroalkenes with
the aid of a household CFL and in the absence of catalyst has
never been realized.19
3
4
5
6
7
8
9
4e: R1 = H; R2 = H; R3 = 4-FC6H4; R4
10
10
10
14
10
10
10
90
90
92
89
92
93
93
98
98
98
98
98
= Me
4f: R1 = H; R2 = H; R3 = 3-BrC6H4; R4
= Me
4g: R1 = H; R2 = H; R3 = 4-ClC6H4; R4
= Me
4h: R1 = H; R2 = H; R3 = 4-MeOC6H4;
R4 = Me
4i: R1 = H; R2 = H; R3 = 2-ClC6H4; R4
= Me
4j: R1 = H; R2 = H; R3 = 2-BrC6H4; R4
= Me
4k: R1 = H; R2 = H; R3 = 4-NO2C6H4;
R4 = Me
4l: R1 = Br; R2 = H; R3 = Ph; R4 = Me
4m: R1 = Cl; R2 = H; R3 =
4-NO2C6H4; R4 = Me
4n: R1 = H; R2 = H; R3 = PhCH2CH2;
R4 = Me
4o: R1 = H; R2 = H; R3 = n-Bu; R4 =
Me
4p: R1 = H; R2 = OMe; R3 = Ph; R4 =
Me
4q: R1 = H; R2 = F; R3 = Ph; R4 = Me
4r: R1 = H; R2 = H; R3 = Ph; R4 = Et
e
96
98
e
10
11
14
14
87
93
93
e
98
e
12
13
14
16
16
10
66
54
95
98
e
99
98
15
16
10
12
89
87
98
98
a
Unless otherwise noted, the reactions were performed on a 0.45 M
scale of 1 (1.5 equiv) and 2 (1.0 equiv) in CH2Cl2 at rt (25−30 °C)
b
c
and in the indicated time. Isolated yields of 4. dr >20:1, determined
d
by 1H NMR of the crude reaction mixture. Unless otherwise
e
addressed, the ee of 4 was analyzed by HPLC with Chiralpak IC. The
ee was analyzed with Chiralpak IA.
With the optimal conditions in hand, the domino reactions.
with respect to enones 1 and alkylnitroolefins 2. were
scrutinized (Table 2). The results are promising and generally
good, with respect to the variants of 1 and 2 tested, providing
the cyclobutanes 4 in good yields (mostly ∼85%−95%) with
consistently excellent enantioselectivities (93%−99%), regard-
less of the electronic substitution pattern. However, the
reaction of nitroalkenes 2 with the aliphatic alkyl substituents
of R3, instead of aryl moieties, required a slightly longer time
for the reaction to be completed and relatively lower yields of
4n and 4o were obtained (66% and 54% yields, respectively),
in comparison to the regular 85%−93% yields (Table 2, entries
12 and 13). A slightly lower enantioselectivity (93% ee) was
observed in the product of 4l, where R1 = Br (Table 2, entry
10). In addition, as expected, all products 4 were obtained in
an excellent diastereomeric selectivity, dr >20:1, and only one
diastereomer in each reaction was observed. The structures of
(+)-4a, (+)-4e, (+)-4i, and (+)-4j, including their absolute
stereochemistry, were explicitly revealed by their single-crystal
X-ray diffraction analyses and the stereo plots of the X-ray
crystal analyses are illustrated in Figure 2.18
Figure 2. Stereo plots of the X-ray analyses of (+)-4a, (+)-4e, (+)-4i,
and (+)-4j. [Legend: C, gray; O, red; N, blue; F, chartreuse; Cl,
green; Br, purple.]
enolization of enone 1a with catalyst F occurs through the
squaramide hydrogen-bonding activation and the protonation
process of the quinuclidine moiety (TS A). Subsequent
conjugate addition of enolized 1a to nitroalkene 2a occurs
via the squaramide-amine-activated process (TS B), in which
the γ-alkylation of 1a occurs. It is noteworthy that replacing the
substituent on the nitroolefin, from 2b to 2a (where H was
replaced by Me), altered the nature of the electrophile 2 and
governed the γ-alkylation of 1a toward 2a to render the
intermediate C, instead of the α-alkylation of 1a to produce the
α-branched ketone 3a, as well as the subsequent intramolecular
nitro-Michael cyclization of C. The stereomodel presented in
the frame above TS B invoked an alternative view to elucidate
To account for the regioselectivity and stereoselectivity, we
propose a plausible mechanism (Scheme 2). The initial
C
DOI: 10.1021/acs.orglett.8b03335
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
52% yields, respectively, with high diastereoselectivity (>20:1)
and enantioselectivity (98% ee) of 4s obtained. (See Figure 3.)
In summary, the efficient organocatalytic enantioselective [2
+ 2] cycloaddition of enones to nitroolefins was realized with
high diastereoselectivities (>20:1), enantioselectivities (93%−
99% ee), and excellent yields. Unlike the previous examples of
enantioselective [2 + 2] cycloaddition of enals and nitroolefins
with the usage of secondary amine organocatalysts, this current
enantioselective [2 + 2] cycloaddition of enone and nitro-
alkene occurred with the aid of the hydrogen-bonding process
and the bifunctional squaramide catalyst. Our study revealed
that the dichotomous regioselectivity (α vs γ) of vinylogous
ketone to nitroolefin was governed by a few factors, including
the organocatalysts, the substituents on the nitroolefin, and the
substituents on the vinylogous carbonyl compounds. With the
appropriate and dexterous arrangement of these elements, the
γ-alkylation of the vinylogous ketone to nitroolefin becomes
feasible, as does the subsequent cyclization to render the [2 +
2] cycloaddition adducts. This domino reaction not only
contributes a concise method for the synthesis of highly
substituted cyclobutanes, but also manifests an example of
deploying suitable catalysts and substituents in cascade
reactions that would be otherwise unattainable. The cyclo-
butanes prepared are relatively stable and are adequate for
further transformation, even at elevated temperatures, e.g., with
SeO2 at 100 °C for prolonged reaction times. The structures of
some products were explicitly determined by X-ray crystallo-
graphic analyses. Furthermore, an unprecedented isomer-
ization of (E)-nitrostyrene 2a to (Z)-2a with a household
compact fluorescent light in the absence of catalyst has been
revealed in this study. Given the limited examples of the highly
enantioselective synthesis of highly substituted cyclobutanes,21
this cascade asymmetric reaction method could provide a
valuable contribution to chemical synthesis.
Scheme 2. Plausible Reaction Mechanism
the observed stereoselectivity. Accordingly, the succeeding
nitro-Michael addition of the intermediate C delivered the
cyclobutane product 4a and regenerated catalyst F to continue
the reaction cycle.
On the other hand, direct asymmetric addition of esters or
the related carboxylic acid derivatives to π electrophiles persists
to be a troublesome task; in this context, Palomo and his co-
workers developed a method by using α-hydroxy ketones as
the masked ester donors in the Brønsted-base-catalyzed
conjugate additions to nitroalkenes.20 Here, we envisioned
that the phenylethanonyl moiety in the cyclobutane 4 could be
considered as the masked ester and the transformation process
would be of interest. Accordingly, ketocyclobutane 4a was
treated with SeO2 and acetic acid in dioxane−H2O (100 °C)
for 18 h, affording diketone 5a in 57% yield (Figure 3).
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b03335.
Experimental procedures and characterization data for
the new compounds (PDF)
Figure 3. Other transformations of the cyclobutane products.
Accession Codes
CCDC 1868867, 1868868, 1868869, 1868870 contains the
supplementary crystallographic 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.
Oxidation of 5a with Pb(OAc)4 in MeOH at room
temperature for 2 h provided ester 6a in 80% yield. In
addition, some of the cyclobutane amino acids have been used
for clinical trials. For example, mirogabalin is in Phase-III
clinical trial for the treatment of diabetic peripheral neuro-
pathic pain, renal impairment, postherpetic neuralgia, etc.
Fluciclovine (18F) is being used for a Phase-III clinical trial in
the treatment of prostate cancer (Figure 1). Accordingly, 4a
and 6a were individually reduced with zinc powder in HOAc−
H2O at room temperature for 24−15 h to give aminobutanes
7a and 8a in 78% and 73% yields, respectively. Lately,
oxidation of 4a with m-CPBA and TFA in CH2Cl2 afforded
88% yield of ester 9a. For further extension of the functionality
in the system, the reaction of the ester-substituted nitroolefin
(2n) and 1e with catalyst F was scrutinized, and a ratio of 4s/
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: chebch@ccu.edu.tw.
ORCID
Bor-Cherng Hong: 0000-0002-4623-3366
Notes
1
3s was found to be 44:56 from the crude H NMR analysis
(Figure 3). Compounds 4s and 3s were isolated in 34% and
The authors declare no competing financial interest.
D
DOI: 10.1021/acs.orglett.8b03335
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(15) Iriarte, I.; Olaizola, O.; Vera, S.; Gamboa, I.; Oiarbide, M.;
Palomo, C. Angew. Chem., Int. Ed. 2017, 56, 8860.
(16) (a) Chauhan, P.; Mahajan, S.; Kaya, U.; Hack, D.; Enders, D.
ACKNOWLEDGMENTS
■
We acknowledge financial support for this study from the
Ministry of Science and Technology (MOST, Taiwan) and
thank the Instrument Center of MOST for analyses of the
compounds.
́
Adv. Synth. Catal. 2015, 357, 253−281. (b) Aleman, J.; Parra, A.;
Jiang, H.; Jørgensen, K. A. Chem. - Eur. J. 2011, 17, 6890. (c) Held, F.
E.; Tsogoeva, S. B. Catal. Sci. Technol. 2016, 6, 645.
(17) (Z)-2-Nitro-1-phenylpropene was reported to be obtained in a
1:1 ratio of (Z)- and (E)- isomeric mixtures from the UV irradiation
of (E)-2-nitro-1-phenylpropene with a Hanau high-pressure mercury
lamp (UV lamp) in petroleum ether; see: Pennings, M. L.; Reinhoudt,
D. N. J. Org. Chem. 1982, 47, 1816−1823 Nevertheless, the
isomerization of the nitroalkenes with the aid of household CFL
has not been previously realized .
REFERENCES
■
(1) (a) Beniddir, M. A.; Evanno, L.; Joseph, D.; Skiredj, A.; Poupon,
E. Nat. Prod. Rep. 2016, 33, 820−842. (b) Dembitsky, V. M.
Phytomedicine 2014, 21, 1559. (c) Hong, Y. J.; Tantillo, D. J. Chem.
Soc. Rev. 2014, 43, 5042. (d) Dembitsky, V. M. J. Nat. Med. 2007, 62,
1.
(18) See the Supporting Information for details.
̈
(2) (a) Poplata, S.; Troster, A.; Zou, Y.-Q.; Bach, T. Chem. Rev.
(19) For recent examples of visible-light induced photoisomerization
of alkenes, see: (a) Metternich, J. B.; Sagebiel, S.; Lueckener, A.;
Lamping, S.; Ravoo, B. J.; Gilmour, R. Chem. - Eur. J. 2018, 24, 4228.
(b) Cai, W.; Fan, H.; Ding, D.; Zhang, Y.; Wang, W. Chem. Commun.
2017, 53, 12918. (c) Metternich, J. B.; Gilmour, R. Synlett 2016, 27,
2541. (d) Zhan, K.; Li, Y. Catalysts 2017, 7, 337.
(20) Olaizola, I.; Campano, T. E.; Iriarte, I.; Vera, S.; Mielgo, A.;
García, J. M.; Odriozola, J. M.; Oiarbide, M.; Palomo, C. Chem. - Eur.
J. 2018, 24, 3893.
(21) For reviews, see: (a) Wang, M.; Lu, P. Org. Chem. Front. 2018,
5, 254. (b) Xu, Y.; Conner, M. L.; Brown, M. K. Angew. Chem., Int. Ed.
2015, 54, 11918. For recent examples, see: (c) Zhong, X.; Tang, Q.;
Zhou, P.; Zhong, Z.; Dong, S.; Liu, X.; Feng, X. Chem. Commun.
2018, 54, 10511. (d) See ref 4d. (e) Kossler, D.; Cramer, N. Chem.
Sci. 2017, 8, 1862.
2016, 116, 9748. (b) Xu, Y.; Conner, M. L.; Brown, M. K. Angew.
Chem., Int. Ed. 2015, 54, 11918. (c) Secci, F.; Frongia, A.; Piras, P. P.
Molecules 2013, 18, 15541. (d) Seiser, T.; Saget, T.; Tran, D. N.;
Cramer, N. Angew. Chem., Int. Ed. 2011, 50, 7740. (e) The Chemistry
of Cyclobutanes, Rappoport, Z.; Liebman, J. F., Eds.; Wiley:
Chichester, U.K., 2005. (f) Lee-Ruff, E.; Mladenova, G. Chem. Rev.
2003, 103, 1449. (g) Namyslo, J. C.; Kaufmann, D. E. Chem. Rev.
2003, 103, 1485. (h) Winkler, J. D.; Bowen, C. M.; Liotta, F. Chem.
Rev. 1995, 95, 2003.
(3) (a) Pagar, V. V.; RajanBabu, T. V. Science 2018, 361, 68.
(b) Conner, M. L.; Xu, Y.; Brown, M. K. J. Am. Chem. Soc. 2015, 137,
3482. (c) Hu, J.-L.; Feng, L.-W.; Wang, L.; Xie, Z.; Tang, Y.; Li, X. J.
Am. Chem. Soc. 2016, 138, 13151. (d) Panish, R.; Chintala, S. R.;
Boruta, D. T.; Fang, Y.; Taylor, M. T.; Fox, J. M. J. Am. Chem. Soc.
2013, 135, 9283. (e) Suarez-Pantiga, S.; Hernandez-Díaz, C.; Rubio,
́
E.; Gonzalez, J. M. Angew. Chem., Int. Ed. 2012, 51, 11552.
(f) Hayashi, Y.; Narasaka, K. Chem. Lett. 1989, 18, 793. (g) Hayashi,
Y.; Niihata, S.; Narasaka, K. Chem. Lett. 1990, 19, 2091. (h) Narasaka,
K.; Hayashi, Y.; Shimadzu, H.; Niihata, S. J. Am. Chem. Soc. 1992, 114,
8869.
(4) (a) Yagishita, F.; Sakamoto, M.; Mino, T.; Fujita, T. Org. Lett.
2011, 13, 6168. (b) Muller, C.; Bauer, A.; Maturi, M. M.; Cuquerella,
̈
M. C.; Miranda, M. A.; Bach, T. J. Am. Chem. Soc. 2011, 133, 16689.
̈
(c) Coote, S. C.; Pothig, A.; Bach, T. Chem. - Eur. J. 2015, 21, 6906.
(d) Miller, Z. D.; Lee, B. J.; Yoon, T. P. Angew. Chem., Int. Ed. 2017,
56, 11891.
(5) Ishihara, K.; Nakano, K. J. Am. Chem. Soc. 2007, 129, 8930.
́
(6) (a) Bures, J.; Armstrong, A.; Blackmond, D. G. J. Am. Chem. Soc.
2011, 133, 8822. (b) Patora-Komisarska, K.; Benohoud, M.; Ishikawa,
H.; Seebach, D.; Hayashi, Y. Helv. Chim. Acta 2011, 94, 719.
́
(c) Bures, J.; Armstrong, A.; Blackmond, D. G. J. Am. Chem. Soc.
2012, 134, 6741.
(7) Parra, A.; Reboredo, S.; Aleman, J. Angew. Chem., Int. Ed. 2012,
51, 9734.
́
(8) Albrecht, Ł.; Dickmeiss, G.; Acosta, F. C.; Rodríguez-Escrich, C.;
Davis, R. L.; Jørgensen, K. A. J. Am. Chem. Soc. 2012, 134, 2543.
(9) Talavera, G.; Reyes, E.; Vicario, J. L.; Carrillo, L. Angew. Chem.,
Int. Ed. 2012, 51, 4104.
(10) (a) Nielsen, A. J.; Jenkins, H. A.; McNulty, J. Chem. - Eur. J.
2016, 22, 9111. (b) Duan, G.-J.; Ling, J.-B.; Wang, W.-P.; Luo, Y.-C.;
Xu, P.-F. Chem. Commun. 2013, 49, 4625.
(11) For review: (a) Yin, Y.; Jiang, Z. ChemCatChem 2017, 9, 4306.
(b) Schneider, C.; Abels, F. Org. Biomol. Chem. 2014, 12, 3531.
(c) Chauhan, P.; Kaya, U.; Enders, D. Adv. Synth. Catal. 2017, 359,
888.
(12) (a) Rout, S. R.; Joshi, H.; Singh, V. K. Org. Lett. 2018, 20, 2199.
(b) Mondal, S.; Mukherjee, S.; Yetra, S. R.; Gonnade, R. G.; Biju, A.
T. Org. Lett. 2017, 19, 4367. (c) Li, X.; Lu, M.; Dong, Y.; Wu, W.;
Qian, Q.; Ye, J.; Dixon, D. J. Nat. Commun. 2014, 5, 4479. (d) Chen,
X.-Y.; Liu, Q.; Chauhan, P.; Li, S.; Peuronen, A.; Rissanen, K.; Jafari,
E.; Enders, D. Angew. Chem., Int. Ed. 2017, 56, 6241.
(13) Gu, Y.; Wang, Y.; Yu, T.-Y.; Liang, Y.-M.; Xu, P.-F. Angew.
Chem., Int. Ed. 2014, 53, 14128.
(14) Guo, Q.; Fraboni, A. J.; Brenner-Moyer, S. E. Org. Lett. 2016,
18, 2628.
E
DOI: 10.1021/acs.orglett.8b03335
Org. Lett. XXXX, XXX, XXX−XXX