Phosphine-catalyzed dearomative [3+2] annulation of 3-nitroindoles and allenoates

Article abstract of DOI:10.1016/j.tetlet.2019.06.016

The efficient phosphine-catalyzed dearomative [3+2] annulation of 3-nitroindoles with allenoates has been successfully developed, providing a facile access to cyclopenta[b]indolines with good to excellent yields and high diastereoselectivities. This strategy features mild reaction conditions, high functional group tolerance, and scalability. Additionally, the 2-nitrobenzofuran and 2-nitrobenzothiophene were good dearomative [3+2] annulation partners.

Full text of DOI:10.1016/j.tetlet.2019.06.016

Tetrahedron Letters xxx (xxxx) xxx
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Phosphine-catalyzed dearomative [3+2] annulation of 3-nitroindoles
and allenoates
Kui Liu a, Gang Wang a, Shao-Jie Cheng a, Wen-Feng Jiang a, Cheng He b, Zhi-Shi Ye a,
⇑
a Zhang Dayu School of Chemistry, Dalian University of Technology, Dalian 116024, China
b State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, China
a r t i c l e i n f o
a b s t r a c t
Article history:
The efficient phosphine-catalyzed dearomative [3+2] annulation of 3-nitroindoles with allenoates has
been successfully developed, providing a facile access to cyclopenta[b]indolines with good to excellent
yields and high diastereoselectivities. This strategy features mild reaction conditions, high functional
group tolerance, and scalability. Additionally, the 2-nitrobenzofuran and 2-nitrobenzothiophene were
good dearomative [3+2] annulation partners.
Received 4 April 2019
Revised 5 June 2019
Accepted 6 June 2019
Available online xxxx
Ó 2019 Elsevier Ltd. All rights reserved.
Keywords:
Dearomatization
Annulation
Phosphine catalysis
3-Nitroindoles
The cyclopenta[b]indoline motif is recognized as a prominent
structural scaffold owing to their prevalence in natural products
and bioactive moleculars (Fig. 1) [1]. For example, vindolinine
exhibits anticancer activity [2]. Polyveoline is a selective inhibitor
of T. brucei PFK [3]. As a result, the development of efficient meth-
ods for synthesis of cyclopenta[b]indolines has received extensive
attention, and great progress has been made on this research area
over the past decades [4]. Among these achievements, catalytic
dearomative annulation of indoles has emerged as one of the effi-
cient and powerful strategies to access various cyclopenta[b]indo-
lines [1c,5]. However, the most of the dearomative annulation for
construction of cyclopenta[b]indolines was mainly focused on the
electron-rich indoles, and the electron-deficient indoles have sel-
dom been explored [6,7]. In 2009, Prieto group disclosed micro-
wave-assisted dearomative annulation of 3-nitroindoles and
cyclopentadiene albeit with low reactivity [8]. Subsequently, Trost
and coworkers developed palladium-catalyzed dearomative
trimethylenemethane [3+2] cycloaddition of 3-nitroindoles with
excellent yields and high diastereoselectivities [9]. Recently, three
elegant examples of dearomative [3+2] cycloaddition of 3-nitroin-
doles and vinylcyclopropanes were independently documented by
Vitale, Shi and Wang [10]. Hence, the construction of cyclopenta[b]
indolines employing dearomative annulation of 3-nitroindoles is
still an active challenging task and highly desirable.
Over the past decades, phosphine-catalysis serves as a powerful
tool for the straightforward construction of diverse cyclic skeletons
[11]. Among the phosphine-catalysis chemistry, the addition of
phosphine to allenoate generates the phosphonium zwitterionic
OH
H
OH
N
H
H
HN
H
H
Me
H
N
H
CO2Me
H
N
H
N
N
H
Vindolinine
Spermacoceine
Polyveoline
Fig. 1. Examples of natural products and bioactive molecules containing cyclopenta
[b]indoline skeleton.
O2N
NO2
cat. PPh3
·
CO2R
CO2R
PPh3
N
PG
N
PG
up to 99% yield
up to >20:1 dr
NO2
[3+2]
PPh3
CO2R
PPh3 Annulation
CO2R
N
PG
⇑
Corresponding author.
E-mail address: yzhsh1984@dlut.edu.cn (Z.-S. Ye).
Scheme 1. Phosphine-catalyzed dearomative [3+2] annulation of 3-nitroindoles
and allenoates.
https://doi.org/10.1016/j.tetlet.2019.06.016
0040-4039/Ó 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: K. Liu, G. Wang, S. J. Cheng et al., Phosphine-catalyzed dearomative [3+2] annulation of 3-nitroindoles and allenoates, Tetrahe-
dron Letters, https://doi.org/10.1016/j.tetlet.2019.06.016

2
K. Liu et al. / Tetrahedron Letters xxx (xxxx) xxx
intermediate, which possesses high reactivity and has been widely
applied in cycloaddition with electrophilic alkene [12]. Considering
that 3-nitroindole can behave as electrophilic alkene, we envi-
sioned that phosphine-catalyzed dearomative [3+2] annulation of
3-nitroindole with allenoate would enable facile construction of
the cyclopenta[b]indoline scaffold Scheme 1. The key challenge
for this proposal is overcoming the high energetic barrier in
dearomatization process which depends upon whether phospho-
nium zwitterionic intermediate has strong nucleophilic capability
to attack the 2-position of 3-nitroindole. Herein, we demonstrated
an efficient and unprecedented phosphine-catalyzed dearomative
[3+2] annulation of 3-nitroindoles and allenoates, providing a
facile access to cyclopenta[b]indolines with excellent yields and
high diastereoselectivities.
Table 1
Condition optimization.a
Entry
Solvent
Cat. PR3
Yield (%)b
Initially, 3-nitroindole (1a) and allenoate (2a) were chosen as
the model substrates to test our hypothesis (Table 1). To our
delight, the dearomative [3+2] annulation of 1a and 2a proceeded
smoothly in the presence of PPh3 as catalyst, affording the desired
cyclopenta[b]indoline 3aa with excellent yield and high diastere-
oselectivity (Table 1, entry 1). Further screening of solvents
showed that benzene was identified as the most favorable solvent
in view of reactivity (Table 1, entry 7). The various phosphine cat-
alysts had dramatic influence on reactivity of the transformation.
When the electron-rich phosphine P(n-Bu)3 and PCy3 took the
place of the PPh3, the reaction displayed low reactivity and failure,
respectively (Table 1, entries 10 and 11). For the electron-deficient
aryl phosphine catalyst, such as tris(pentafluorophenyl)phosphine,
is completely ineffective for annulation. Additionally, introduction
of methyl substituent at the 2-position of phenyl group of PPh3 led
1
2
3
4
5
6
7
8
THF
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
P(n-Bu)3
PCy3
P(o-MeC6H4)3
P(C6F5)3
90
88
88
91
93
96
97
96
60
54
<5
<5
<5
1,4-dioxane
Ethyl ether
DCM
DCE
Ethyl acetate
Benzene
Toluene
Acetonitrile
Benzene
Benzene
Benzene
Benzene
9
10
11
12
13
a
Conditions: 1a (0.10 mmol), 2a (0.15 mmol), cat. PR3 (20 mol %), solvent
(1.0 mL), rt. The diastereoselectivity was determined by 1H NMR. In the all cases,
only one diastereoisomer was isolated.
b
Isolated yield.
NO2
O2N
PPh3
·
Ar
R
Ar
CO2Et
CO2Et
R
PG
Benzene, N2, rt
N
N
PG
1
2a
3
R1
O2N
O2N
1
3ba
3ca
3da
: R = OMe, 91%
1
: R = CO2Me, 64%
CO2Et
1
CO2Et
N
Ac
H
: R = Cl, 59%
N
H
N
Ac
b
3aa
3aa
, 97% (99%)
X-ray of
2
3da
3ea
3fa
3ga
3ha
3ia
: R = Me, 93%
: R = OMe, 93%
: R = F, 92%
: R = Cl, 80%
: R = Br, 77%
: R = OBn, 92%
O2N
3
O2N
2
3ja
: R = Me, 96%
R2
3
2
3ka
: R = F, 78%
CO2Et
3
CO2Et
R3
2
3la
: R = Cl, 80%
H
N
Ac
H
2
Ac
2
O2N
O2N
O2N
O2N
CO2Et
CO2Et
CO2Et
CO2Et
N
H
O
N
H
O
N
Boc
H
N H
Ts
n-pentyl
EtO
3oa
3ma
3na
3pa
, 60%
, 52%
, 90%
, 89%
O2N
4
O2N
3qa
3ra
3sa
3ta
: R = (CH2)4Cl, 88%
4
: R = Cy, 93%
CO2Et
4
CO2Et
: R = C6H5, 60%
N
Me
Ac
: No reaction
N
H
O
4
: R = 3-MeC6H4, 76%
4
R4
3va
3ua
: R = 2-Naphthyl, 73%
Scheme 2. Substrate scope: 3-nitroindoles 1a. a 1 (0.20 mmol), 2a (0.30 mmol), PPh3 (20 mol %), benzene (1.0 mL), rt. The diastereoselectivity was determined by 1H NMR. In
b
the all cases, only one diastereoisomer was isolated. Scale-up reaction: 1 (2.45 mmol) and 2a (3.68 mmol) were employed for reaction.
Please cite this article as: K. Liu, G. Wang, S. J. Cheng et al., Phosphine-catalyzed dearomative [3+2] annulation of 3-nitroindoles and allenoates, Tetrahe-
dron Letters, https://doi.org/10.1016/j.tetlet.2019.06.016

K. Liu et al. / Tetrahedron Letters xxx (xxxx) xxx
3
to no reactivity (Table 1, entry 12). Therefore, the optimal reaction
conditions were established: using PPh3 as catalyst and benzene as
solvent to perform the dearomative [3+2] annulation at room
temperature.
3aa was unambiguously established by X-ray crystallographic
analysis.[13]
In order to further assess the generality of our methodology the
substrate scope of allenoate 2 was explored (Scheme 3). Diverse
allenoate 2 conducted successfully to afford the target product in
58% to 99% yield. In the all cases, only one diastereoisomer was iso-
lated. Remarkably, the transformation is insensitive to the steric
hindrance. For instance, although the sterically crowded allenoate
2c was employed for the annulation, the formation of product 3ac
still was achieved in 99% yield. Unfortunately, phenylbuta-2,3-
dien-1-one (2m) and phenylsulfonylpropa-1,2-diene (2n) were
completely ineffective reaction partners and no desired products
were observed.
Having confirmed the effectiveness of our method for dearoma-
tive [3+2] annulation of 3-nitroindoles with allenoates, we next
turned our attention to dearomative annulation of other heteroaro-
matic ring bearing nitro group Scheme 4. The 2-nitrobenzofuran
and 2-nitrobenzothiophene underwent the transformation suc-
cessfully to furnish the corresponding products in the 75% and
65% yield, respectively. However, the annulation of 2-nitropyrrole
with allenoate 2a suffered failure probably because of higher ener-
getic barrier in dearomatization process.
With the aforementioned optimal reaction conditions, substrate
scope of the 3-nitroindoles 1 was examined and the results were
depicted in Scheme 2. In general, the dearomative [3+2] annulation
of various 3-nitroindoles 1 transformed smoothly, providing the
cyclopenta[b]indolines 3 with good to excellent yields and high
diastereoselectivities. The ether (3ba, 3ea and 3ia), bromide
(3ha), chloride (3da, 3ga and 3la), fluoride (3fa, 3ka) and ester
(3da) functional groups are well tolerated. Particularly, the prod-
ucts with Cl and Br on the phenyl ring are noteworthy, as these
functional groups allow for late-stage cross-coupling reaction.
However, the electronic properties of the substituent at 4-position
of 3-nitroindoles had obviously influence the reactivity of the
transformation, the yield of 3ca dramatically decreased to 64%
yield when the electron-withdrawing group (CO2Me) was intro-
duced. Subsequently, the N-protecting group of the 3-nitroindoles
were intensively investigated. Replacement of Ac with Boc and Ts
groups resulted in low conversion and yield, delivering desired
products 3ma and 3na in the 60% and 52% yield. Aryl and alkyl
substituents for R4 group were also compatible in the process, con-
verting the corresponding products 3pa–3ua in good to excellent
yields. Unfortunately, the 2-methyl-3-nitroindoles (1v) was not
suitable for dearomative [3+2] annulation as a result of steric hin-
drance. To further evaluate the practical utility, the annulation of
3-nitroindole (1a) with allenoate (2a) was carried out on larger-
scale, and the desired product was furnished without loss of yield.
Additionally, the relative stereochemistry of the desired product
Subsequently, further synthetic transformations of 3aa were
conducted Scheme 5. The nitro group of 3aa was efficiently reduced
in the presence of Zn/TMSCl to deliver product 4 in the 72% yield.
The denitration took place smoothly when the 3aa was treated with
AIBN/nBu3SnH. Moreover, employment of DIBAL-H as reductive
reagent resulted in reduction of the ester group and removal of
Ac group. Removal of Boc group was carried out successfully under
the acidic conditions, and 70% yield product was obtained.
NO2
O2N
PPh3
Benzene, N2, rt
·
EWG
EWG
H
Ac
N
N
Ac
1a
2
3
O2N
O2N
O2N
OtBu
OPh
OBn
OMe
N
Ac
H
O
N
Ac
H
N
Ac
H
O
O
3ab
3ac
3ad
, 89%
, 99%
, 73%
O2N
O2N
3ae
, Ar = 4-ClC6H4, 60%
OAr
3af
, Ar = 4-BrC6H4, 58%
H
N
Ac
3ai
3ag
3ah
, Ar = 4-MeOC6H4, 85%
, Ar = 3,5-Me2C6H3, 80%
O
N
Ac
H
O
, 92%
O2N
O2N
O2N
O
Ph
OCH2Ar
S
Ph
H
H
N
N
Ac
N
Ac
H
O
O
O
Ac
3an
, No reaction
3aj
3am
, Ar = 4-ClC6H4, 89%
, No reaction
3ak
, Ar = 4-MeOC6H4, 96%
3al
, Ar = 2-BrC6H4, 84%
Scheme 3. Substrate scope: allenoates 2a. a 1a (0.20 mmol), 2 (0.30 mmol), PPh3 (10 mol %), benzene (1.0 mL), rt. The diastereoselectivity was determined by 1H NMR. In the
all cases, only one diastereoisomer was isolated.
Please cite this article as: K. Liu, G. Wang, S. J. Cheng et al., Phosphine-catalyzed dearomative [3+2] annulation of 3-nitroindoles and allenoates, Tetrahe-
dron Letters, https://doi.org/10.1016/j.tetlet.2019.06.016

4
K. Liu et al. / Tetrahedron Letters xxx (xxxx) xxx
CO2Et
NO2
H
PPh3
Benzene, N2, rt
·
NO2
CO2Et
2a
X
X
1
3
CO2Et
CO2Et
H
CO2Et
H
H
N
Ac
O
NO2
S
NO2
, 75%, >20:1 dr
NO2
3ya
3wa
3xa
, 65%, >20:1 dr
, No reaction
a
a
Scheme 4. Substrate scope: hetroaromatic compounds bearing nitro group
.
Conditions: 1a (0.20 mmol), 2 (0.30 mmol), PPh3 (20 mol %), benzene (1.0 mL), rt. The
diastereoselectivities of the products were determined by 1H NMR.
Scheme 5. Further synthetic transformations of the desired product 3aa and 3na.
Finally, the asymmetric dearomative [3+2] annulation of
cyclopenta[b]indoline with good to excellent yields and high
diastereoselectivities. This method features mild reaction
conditions, high functional group tolerance and scalability.
Moreover, the 2-nitrobenzofuran and 2-nitrobenzothiophene
were subjected to dearomative annulation in the good yields
and high diastereoselectivities. Further studies on the
dearomative annulation of 3-nitroindoles are underway in
our lab.
3-nitroindole and allenoates was also investigated [14]. The
annulation performed very well in the presence of chiral Trost’s
phosphine catalyst, moderate 54% of enantioselectivity, 67% yield
and >20:1 dr were obtained (see Scheme 6).
In summary, we have successfully developed a novel and
efficient phosphine-catalyzed dearomative [3+2] annulation of
3-nitroindoles with allenoates, providing
a facile access to
NO2
N
O2N
O
O
cat.P
benzene, rt
1a
CO2Et
NH HN
Ac
N
Ac
H
PPh2 Ph2P
cat.P
·
2a
3aa
, 54% ee
CO2Et
67% yield, >20:1 dr
Scheme 6. Asymmetric dearomative [3+2] annulation of 3-nitroindole 1a and allenoate 2a.
Please cite this article as: K. Liu, G. Wang, S. J. Cheng et al., Phosphine-catalyzed dearomative [3+2] annulation of 3-nitroindoles and allenoates, Tetrahe-
dron Letters, https://doi.org/10.1016/j.tetlet.2019.06.016

K. Liu et al. / Tetrahedron Letters xxx (xxxx) xxx
5
[7] (a) For selected reports for dearomatizative annulation of electron-
withdrawing indoles, see: B. Biolatto, M. Kneeteman, E. Paredes, P.M.E.
Mancini J. Org. Chem. 66 (2001) 3906;
Acknowledgments
Financial support from Dalian University of Technology and
National Natural Science Foundation of China (21801036), is
acknowledged.
(b) T.L.S. Kishbaugh, G.W. Gribble, Tetrahedron Lett. 42 (2001) 4783;
(c) S. Lee, S. Diab, P. Queval, M. Sebban, I. Chataigner, S.R. Piettre, Chem.-Eur. J.
19 (2013) 7181;
(d) X. Liu, D. Yang, K. Wang, J. Zhang, R. Wang, Green Chem. 19 (2017) 82;
(e) D.J. Rivinoja, Y.S. Gee, M.G. Gardiner, J.H. Ryan, C.J.T. Hyland, ACS Catal. 7
(2017) 1053;
(f) K.-K. Wang, W. Du, J. Zhu, Y.-C. Chen, Chin. Chem. Lett. 28 (2017) 512;
(g) A. Awata, T. Arai, Angew. Chem. Int. Ed. 53 (2014) 10462;
(h) A.L. Gerten, L.M. Stanley, Org. Chem. Front. 3 (2016) 339;
(i) Y. Li, F. Tur, R.P. Nielsen, H. Jiang, F. Jensen, K.A. Jørgensen, Angew. Chem.
Int. Ed. 55 (2016) 1020;
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tetlet.2019.06.016.
(j) Q. Cheng, F. Zhang, Y. Cai, Y.-L. Guo, S.-L. You, Angew. Chem. Int. Ed. 57
(2018) 2134;
(k) J.-J. Suo, W. Liu, J. Du, C.-H. Ding, X.-L. Hou, Chem. Asian J. 13 (2018) 959;
(l) J.-Q. Zhao, M.-Q. Zhou, Z.-J. Wu, Z.-H. Wang, D.-F. Yue, X.-Y. Xu, X.-M. Zhang,
W.-C. Yuan, Org. Lett. 17 (2015) 2238;
(m) J.-Q. Zhao, Z.-J. Wu, M.-Q. Zhou, X.-Y. Xu, X.-M. Zhang, W.-C. Yuan, Org.
Lett. 17 (2015) 5020;
(n) I. Chataigner, S.R. Piettre, Org. Lett. 9 (2007) 4159;
(o) D.-F. Yue, J.-Q. Zhao, X.-Z. Chen, Y. Zhou, X.-M. Zhang, X.-Y. Xu, W.-C. Yuan,
Org. Lett. 19 (2017) 4508.
References
[1] (a) For selected reviews, see: E. Attorusso, O. Taglialatela-Scafati, Alkaloids:
Structure, Isolation, Synthesis and Biology, Wiley-VCH, Weinheim, 2008;
(b) F. Gueritte, J. Fahy, in: Anticancer Agents from Natural Products, CRC Press,
Boca Raton, FL, 2005, p. 123;
(c) N.H. Greig, X.-F. Pei, T.T. Soncrant, D.K. Ingram, A. Brossi, Med. Res. Rev. 15
(1995) 3;
(d) A.M. Balde, L.A. Pieters, A. Gergely, V. Wray, M. Claeys, A.J. Vlietinck,
Phytochem 30 (1991) 997;
(e) I.W. Southon, J. Buckingham, Dictionary of Alkaloids, Chapman and Hall,
New York, 1989;
(f) R. Hocquemiller, G. Dubois, M. Leboeuf, A. Cavé, N. Kunesch, C. Riche, A.
Chiaroni, Tetrahedron Lett. 22 (1981) 5057;
[8] M.V. Gómez, A.I. Aranda, A. Moreno, F.P. Cossío, A. de Cózar, Á. Díaz-Ortiz, A. de
la Hoz, P. Prieto, Tetrahedron 65 (2009) 5328.
[9] B.M. Trost, V. Ehmke, B.M. O’Keefe, D.A. Bringley, J. Am. Chem. Soc. 136 (2014)
8213.
[10] (a) M. Laugeois, J. Ling, C. Férard, V. Michelet, V. Ratovelomanana-Vidal, R.M.
Vitale, Org. Lett. 19 (2017) 2266;
(g) N. Langlois, R.Z. Andriamialisoa, J. Org. Chem. 44 (1979) 2468.
[2] E.M. Maloney, H.H.S. Fong, N.R. Farnsworth, R.N. Blomster, D.J. Abraham, J.
Pharm. Sci. 3 (1991) 997.
[3] I. Ngantchou, B. Nyasse, C. Denier, C. Blonski, V. Hannaert, B. Schneider, Bioorg.
Med. Chem. Lett. 20 (2010) 3495.
[4] (a) For selected reviews, see: T.S. Silva, M.T. Rodrigues Jr., H. Santos, L.A. Zeoly,
W.P. Almeida, R.C. Barcelos, R.C. Gomes, F.S. Fernandes, F. Coelho Tetrahedron
75 (2019) 2063;
(b) Y. Wang, F. Xie, B. Lin, M. Cheng, Y. Liu, Chem.-Eur. J. 24 (2018) 14302;
(c) B.M. Griffiths, J.D. Burl, X. Wang, Synlett 27 (2016) 2039;
(d) E. Manoni, A. De Nisi, M. Bandini, Pure Appl. Chem. 88 (2016) 207;
(e) W. Zi, Z. Zuo, D. Ma, Acc. Chem. Res. 48 (2015) 702;
(f) D. Zhang, H. Song, Y. Qin, Acc. Chem. Res. 44 (2011) 447;
(g) S. Anas, H. Kagan, B, Tetrahedron: Asymmetry 20 (2009) 2193.
[5] (a) For selected reviews for dearomatization of indoles, see: G. Huang, B. Yin
Adv. Synth. Catal. 361 (2019) 405;
(b) M. Sun, Z.-Q. Zhu, L. Gu, X. Wan, G.-J. Mei, F. Shi, J. Org. Chem. 83 (2018)
2341;
(c) J.-Q. Zhang, F. Tong, B.-B. Sun, W.-T. Fan, J.-B. Chen, D. Hu, X.-W. Wang, J.
Org. Chem. 83 (2018) 2882.
[11] (a) For selected reviews, see: H. Ni, W.-L. Chan, Y. Lu Chem. Rev. 118 (2018)
9344;
(b) H. Guo, Y. Fan, Z. Sun, Y. Wu, O. Kwon, Chem. Rev. 118 (2018) 10049;
(c) Y. Wei, M. Shi, Org. Chem. Front. 2017 (1876) 4;
(d) X. Lu, C. Zhang, Z. Xu, Acc. Chem. Res. 34 (2001) 535;
(e) J.L. Methot, W.R. Roush, Adv. Synth. Catal. 346 (2004) 1035;
(f) L.-W. Ye, J. Zhou, Y. Tang, Chem. Soc. Rev. 37 (2008) 1140;
(g) B.J. Cowen, S.J. Miller, Chem. Soc. Rev. 38 (2009) 3102;
(h) S.-X. Wang, X. Han, F. Zhong, Y. Wang, Y. Lu, Synlett (2011) 2766;
(i) Q.-Y. Zhao, Z. Lian, Y. Wei, M. Shi, Chem. Commun. 48 (2012) 1724;
(j) Y.C. Fan, O. Kwon, Phosphine catalysis, in: B. List (Ed.), Science of Synthesis.
Asymmetric Organocatalysis. Lewis Base and Acid Catalysts, Georg Thieme
Verlag KG, Stuttgart New York, 2012, p. 723;
(k) Y.C. Fan, O. Kwon, Chem. Commun. 49 (2013) 11588;
(l) Y. Wei, M. Shi, Chem.-Asian J. 9 (2014) 2720;
(m) Z. Wang, X. Xu, O. Kwon, Chem. Soc. Rev. 43 (2014) 2927;
(n) T. Wang, X. Han, F. Zhong, W. Yao, Y. Lu, Acc. Chem. Res. 49 (2016) 1369;
(o) W. Li, J. Zhang, Chem. Soc. Rev. 45 (2016) 1657.
(b) C. Zheng, S.-L. You, Nat. Prod. Rep. (2019), https://doi.org/10.1039/
C8NP00098K;
(c) W. Sun, G. Li, L. Hong, R. Wang, Org. Biomol. Chem. 14 (2016) 2164;
(d) W.-T. Wu, L. Zhang, S.-L. You, Chem. Soc. Rev. 45 (2016) 1570;
(e) S.P. Roche, J.-J.Y. Tendoung, B. Tréguier, Tetrahedron 71 (2015) 3549;
(f) Q. Ding, X. Zhou, R. Fan, Org. Biomol. Chem. 12 (2014) 4807;
(g) S.L. You (Ed.), Asymmetric Dearomatization Reactions, Wiley-VCH,
Weinheim, 2016;
(h) C.-X. Zhuo, W. Zhang, S.-L. You, Angew. Chem. Int. Ed. 51 (2012) 12662;
(i) Q. Ding, Y. Ye, R. Fan, Synthesis 45 (2013) 1;
(j) S.P. Roche Jr., J.A. Porco, Angew. Chem. Int. Ed. 50 (2011) 4068;
(k) F. López Ortiz, M.J. Iglesias, I. Férnndez, C.M. Andújar Sánchez, G.R. Gómez,
Chem. Rev. 107 (2007) 1580;
[12] (a) For some selected examples for phosphine-catalyzed cycloaddition of
allenoate with electrophilic alkene, see: C. Zhang, X. Lu J. Org. Chem. 60 (1995)
2906;
(b) X.-Y. Guan, Y. Wei, M. Shi, Org. Lett. 12 (2010) 5024;
(c) X.-N. Zhang, M. Shi, ACS Catal. 3 (2013) 507;
(d) X.-C. Zhang, S.-H. Cao, Y. Wei, M. Shi, Org. Lett. 13 (2011) 1142;
(e) J. Zhang, C. Cheng, D. Wang, Z. Miao, J. Org. Chem. 82 (2017) 10121;
(f) B. Baskar, K. Wittstein, M.G. Sankar, V. Khedkar, M. Schürmann, K. Kumar,
Org. Lett. 14 (2012) 5924;
(g) X. Li, F. Wang, N. Dong, J.-P. Cheng, Org. Biomol. Chem. 11 (2013) 1451;
(h) L. Zhou, C. Wang, C. Yuan, H. Liu, C. Zhang, H. Guo, Org. Lett. 20 (2018)
6591;
(i) Z. Gao, C. Wang, L. Zhou, C. Yuan, Y. Xiao, H. Guo, Org. Lett. 20 (2018) 4302;
(j) E. Li, P. Jia, L. Liang, Y. Huang, ACS Catal. 4 (2014) 600;
(l) E. Li, Y. Huang, L. Liang, P. Xie, Org. Lett. 15 (2013) 3138;
(m) J. Zheng, Y. Huang, Z. Li, Org. Lett. 15 (2013) 5758;
(n) J. Zheng, Y. Huang, Z. Li, Org. Lett. 15 (2013) 5064;
(o) Y. Gu, P. Hu, C. Ni, X. Tong, J. Am. Chem. Soc. 137 (2015) 6400;
(p) X. Han, Y. Wang, F. Zhong, Y. Lu, J. Am. Chem. Soc. 133 (2011) 1726;
(q) Z. Yu, Z. Jin, M. Duan, R. Bai, Y. Lu, Y. Lan, J. Org. Chem. 83 (2018) 9729;
(r) F. Zhong, X. Han, Y. Wang, Y. Lu, Chem. Sci. 3 (2012) 1231;
(s) H. Xiao, Z. Chai, D.-D. Cao, H. Wang, J. Chen, G. Zhao, Org. Biomol. Chem. 10
(2012) 3195;
(t) H. Ni, X. Tang, W. Zheng, W. Yao, N. Ullah, Y. Lu, Angew. Chem. Int. Ed. 56
(2017) 14222;
(u) E. Li, H. Jin, P. Jia, X. Dong, Y. Huang, Angew. Chem. Int. Ed. 55 (2016)
11591;
(v) Y.S. Tran, O. Kwon, J. Am. Chem. Soc. 129 (2007) 12632;
(w) G. Zhu, Z. Chen, Q. Jiang, D. Xiao, P. Cao, X. Zhang, J. Am. Chem. Soc. 119
(1997) 3836;
(x) J.E. Wilson, G.C. Fu, Angew. Chem., Int. Ed. 45 (2006) 1426;
(y) B.J. Cowen, S.J. Miller, J. Am. Chem. Soc. 129 (2007) 10988;
(z) W. Yao, Z. Yu, S. Wen, H. Ni, N. Ullah, Y. Lan, Y. Lu, Chem. Sci. 8 (2017) 5196.
(l) A.R. Pape, K.P. Kaliappan, E.P. Kündig, Chem. Rev. 100 (2000) 2917.
[6] (a) For selected reports for dearomatizative annulation of electron-rich
indoles, see: Y. Lian, H.M.L. Davies J. Am. Chem. Soc. 132 (2010) 440;
(b) C. Jing, Q.-Q. Cheng, Y. Deng, H. Arman, M.P. Doyle, Org. Lett. 18 (2016)
4550;
(c) G. Zhang, V.J. Catalano, L. Zhang, J. Am. Chem. Soc. 129 (2007) 11358;
(d) H. Xiong, H. Xu, S. Liao, Z. Xie, Y. Tang, J. Am. Chem. Soc. 135 (2013) 7851;
(e) J. Zhu, Y. Liang, L. Wang, Z.-B. Zheng, K.N. Houk, Y. Tang, J. Am. Chem. Soc.
136 (2014) 6900;
(f) L.-Y. Mei, Y. Wei, X.-Y. Tang, M. Shi, J. Am. Chem. Soc. 137 (2015) 8131;
(g) L. Liao, C. Shu, M. Zhang, Y. Liao, X. Hu, Y. Zhang, Z. Wu, W. Yuan, X. Zhang,
Angew. Chem. Int. Ed. 53 (2014) 10471;
(h) R.-D. Gao, Q.-L. Xu, B. Zhang, Y. Gu, L.-X. Dai, S.-L. You, Chem. Eur. J. 22
(2016) 11601;
(i) B. Bajtos, M. Yu, H. Zhao, B.L. Pagenkopf, J. Am. Chem. Soc. 129 (2007) 9631;
(j) H. Li, R.P. Hughes, J. Wu, J. Am. Chem. Soc. 136 (2014) 6288;
(k) J.E. Spangler, H.M.L. Davies, J. Am. Chem. Soc. 135 (2013) 6802;
(l) J.-M. Yang, P.-H. Li, Y. Wei, X.-Y. Tang, M. Shi, Chem. Commun. 52 (2016)
346;
(m) J. Zhang, Z. Chen, H. Wu, J. Zhang, Chem. Commun. 2012 (1817) 48;
(n) W. Chen, Y. Xia, L. Lin, X. Yuan, S. Guo, X. Liu, X. Feng, Chem.-Eur. J. 21
(2015) 15104;
(o) G. Zhang, V. Catalano, J.L. Zhang, J. Am. Chem. Soc. 129 (2007) 11358;
(p) Z. Chai, Y.-M. Zhu, P.-J. Yang, S. Wang, S. Wang, Z. Liu, G. Yang, J. Am. Chem.
Soc. 137 (2015) 10088;
(q) Q.-J. Liu, J. Zhu, X.-Y. Song, L. Wang, S.R. Wang, Y. Tang, Angew. Chem. Int.
Ed. 57 (2018) 3810.
Please cite this article as: K. Liu, G. Wang, S. J. Cheng et al., Phosphine-catalyzed dearomative [3+2] annulation of 3-nitroindoles and allenoates, Tetrahe-
dron Letters, https://doi.org/10.1016/j.tetlet.2019.06.016

6
K. Liu et al. / Tetrahedron Letters xxx (xxxx) xxx
[13] CCDC 1904193 contains the supplementary crystallographic data for this
paper. These can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk.
(b) K. Li, T. Gonçalves, K.-W. Huang, Y. Lu, Angew. Chem. Int. Ed. 58 (2019)
5427.
[14] (a) During the preparation of this manuscript, two similar asymmetric
dearomative annulation of 3-nitroindoles with allenoates appeared: H.
Wang, J. Zhang, Y. Tu, J. Zhang Angew. Chem. Int. Ed. 58 (2019) 5422;
Please cite this article as: K. Liu, G. Wang, S. J. Cheng et al., Phosphine-catalyzed dearomative [3+2] annulation of 3-nitroindoles and allenoates, Tetrahe-
dron Letters, https://doi.org/10.1016/j.tetlet.2019.06.016