Phosphine-Catalyzed Enantioselective [4 + 3] Annulation of Allenoates with C,N-Cyclic Azomethine Imines: Synthesis of Quinazoline-Based Tricyclic Heterocycles

Article abstract of DOI:10.1021/acs.orglett.6b02885

With the use of a commercially available chiral phosphine as the catalyst, the first catalytic enantioselective [4 + 3] annulation of allenoates with C,N-cyclic azomethine imines is developed. The reaction works efficiently under mild reaction conditions to afford seven-membered ring-fused quinazoline-based tricyclic heterocycles in high yields with good to excellent diastereo- and enantioselectivities.

Full text of DOI:10.1021/acs.orglett.6b02885

Letter
pubs.acs.org/OrgLett
Phosphine-Catalyzed Enantioselective [4 + 3] Annulation of
Allenoates with C,N-Cyclic Azomethine Imines: Synthesis of
Quinazoline-Based Tricyclic Heterocycles
Chunhao Yuan,† Leijie Zhou,† Miaoren Xia,§ Zhanhu Sun,† Dongqi Wang,§ and Hongchao Guo*,†,‡
†Department of Applied Chemistry, China Agricultural University, Beijing 100193, P. R. China
‡Key Laboratory of Green Pesticide and Agricultural Bioengineering, Ministry of Education, Guizhou University, Guiyang 550025,
China
§Institute of High Energy Physics, Chinese Academy of Science, Beijing 100049, P. R. China
S
* Supporting Information
ABSTRACT: With the use of a commercially available chiral
phosphine as the catalyst, the first catalytic enantioselective [4
+ 3] annulation of allenoates with C,N-cyclic azomethine
imines is developed. The reaction works efficiently under mild
reaction conditions to afford seven-membered ring-fused
quinazoline-based tricyclic heterocycles in high yields with
good to excellent diastereo- and enantioselectivities.
Heterocyclic carbene-catalyzed enantioselective cycloaddition
of azomethine imines and enals represented the only asymmetric
[4 + 3] example, providing a simple excess to chiral
hexahydropyrazolodiazepinone derivatives.15 Since seven-mem-
bered heterocyclic moieties play a key role in many biologically
active compounds, and at the same time, the construction of
seven-membered ring is a challenging task,16 developing new
annulation reaction for the synthesis of seven-membered ring-
fused heterocycles is highly desirable.
Chiral phosphine-catalyzed asymmetric annulation reactions
have seen rapidly growing use in the assembly of synthetically
useful or biologically significant complex carbocyclic and
heterocyclic scaffolds17 and natural products.18 A variety of
asymmetric annulation reactions have been achieved for the
construction of four-, five-, and six-membered cyclic skeletons.17
Among these annulation reactions, phosphine-catalyzed [4 + 3]
annulations have less been explored, only limited successful
nonasymmetric examples were reported.19 Especially, to the best
of our knowledge, no asymmetric [4 + 3] annulation catalyzed by
chiral phosphine has yet been developed to access seven-
membered ring in a enantioselective form.
Azomethine imines have successfully been applied in
phosphine-catalyzed asymmetric [3 + 2] and [3 + 3] annulations
for synthesis of chiral dinitrogen-fused heterocycles (Scheme
1a−c),9,14,19b but their asymmetric [4 + 3] annulation under
phosphine catalysis remains unsolved. From a mechanistic
perspective, phosphine-catalyzed annulations are typically
postulated to involve the in situ formation of phosphonium
(di)enolate zwitterions, which subsequently undergo coupling
with electrophiles. However, phosphonium (di)enolate zwitter-
uinazoline occurs as a key heterocyclic motif in a wide
Q range of synthetic drugs, pharmaceuticals, agrochemicals,
bioactive natural products, and materials.1 Quinazoline deriva-
tives have showed extremely diverse biological activities such as
anticancer, anti-inflammatory, antimalarial, antihypertensive,
anticonvulsant, and antituberculosis activities.1 Numerous
quinazoline-based commercial drugs such as Gefitinib, Erlotinib,
Canertinib, Afatinib, and Vandetanib have demonstrated the
importance of quinazoline pharmacophore. Many multicyclic
quinazoline derivatives also displayed exceptional bioactivities
such as insecticidal, antiasthmatic, antitumor, and antihyperten-
sive activity.1 Beyond these bioactive functions, quinazoline and
its derivatives had been used as building blocks for synthesis of
natural alkaloids.2 Since quinazoline derivatives are commonly
evaluated in drug discovery efforts, continuous efforts have been
devoted to the development of synthetic methods for novel
quinazoline derivatives.1
Azomethine imines, which are easily accessible and stable
compounds, have extensively been employed as efficient 1,3-
dipoles in cycloaddition reactions for the synthesis of various
dinitrogen-fused heterocyclic frameworks.3 Their asymmetric [3
+ 2] cycloaddition reactions had been intensely studied.
Numerous metal or organocatalyst-catalyzed asymmetric [3 +
2] cycloaddition reactions of azomethine imines with alkenes,4
alkynes,5 aldehydes,6 cyclobutenone,7 arylacetic acid derivatives,8
allenoates,9 or azlactones10 have been developed to provide five-
membered nitrogen-containing heterocycles. A few metal or
organocatalyst-catalyzed asymmetric [3 + 3] cycloaddition
reactions of azomethine imines have also been reported for
synthesis of six-membered dinitrogen-fused heterocycles.6c,11−14
In contrast, asymmetric higher-order cycloaddition of azome-
thine imines such as [4 + 3] cycloaddition has received much less
attention and successful examples are extremely rare. N-
Received: September 25, 2016
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.6b02885
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
Scheme 1. Phosphine-Catalyzed Asymmetric Annulations of
Azomethine Imines
Table 1. Screening of Reaction Conditions
b
c
c
entry
Px
solvent
t (h)
yield (%)
dr
ee (%)
1
2
3
4
5
6
7
8
9
P1
P2
P3
P4
P5
P1
P1
P1
P1
P1
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
4
90
91
92
76
46
95
70
85
95
97
9:1
80
50
72
80
80
80
60
83
87
94
5
5:1
5
7:1
5
6:1
7
1.3:1
9:1
d
DCE
6
CHCl3
toluene
THF
9
7:1
12
7
8:1
11:1
20:1
e
10
THF
30
a
Unless otherwise specified, all reactions were performed with 1a
(0.125 mmol), 2a (0.19 mmol), and catalyst (0.025 mmol) in 2 mL of
b
c
solvent at room temperature. Isolated yield. Determined by chiral
d
e
HPLC analysis. DCE: 1,2-dichloroethane. The reaction was
performed at 0 °C.
yield with 11:1 dr and 87% ee (entries 6−9). To our delight, a
decrease in temperature to 0 °C could remarkably enhance
stereoselectivities, leading to 3aa in 97% yield with 20:1 dr and
94% ee (entry 10). Notably, even the amount of azomethine
imine 1a was scaled up to 0.6 g, the reaction still proceeded very
well under the optimal conditions to afford the cycloadduct 3aa
in 95% yield with 20:1 dr and 93% ee. Obviously, there was no
significant loss of diastereoselectivity, enantioselectivity, and
yield, compared with the reaction at 0.125 mmol of scale (Table
1).
With the optimal reaction conditions in hand, further studies
were focused on the evaluation of the substrate scope of α-
substituted allenoates in this asymmetric [4 + 3] annulation
(Table 2). Various allenoates bearing both electron-donating and
withdrawing groups on benzene ring reacted with azomethine
imine 1a, providing the seven-membered ring-fused tricyclic
heterocyclic products 3 in excellent yields (93−98%) with good
to excellent diastereoselectivities and excellent enantioselectiv-
ities (90−96%) (entries 1−17). The electronic properties of
substituents on benzene ring have little effect on the yields,
diastereo-, and enantioselectivities (entries 1−17). The steric
properties have also not remarkable effect on the yields and
enantioselectivities but seem to have significant influence on
diastereoselectivities. For example, an ortho-chloro substituent
on benzene ring could lead to relative low diastereoselectivity
(entry 10), which might be caused by the large steric hindrance
between ortho-chloro-substituted aryl group and 3,4-dihydro-
quinazoline ring. 2-Naphthyl-substituted allenoate (2r) dis-
played good compatibility with the standard reaction conditions,
providing the desired product 3ar in good yield with excellent
diastereo- and enantioselectivity (entry 18). A special carbox-
ylate-substituted allenoate 2s also worked well to produce the
cycloadduct 3as in high yield with 20:1 dr and 95% ee (entry 19).
Particularly, alkyl substituted allenoates 2t and 2u were
ions from α-substituted allenoates may act as two- or four-carbon
synthon; the competing [3 + 2] and [4 + 3] paths may
concurrently exist (Scheme 1d), leading to low chemoselectivity
and poor yields for [4 + 3] cycloadducts. Hence, development of
phosphine-catalyzed asymmetric [4 + 3] annulation is certainly
difficult. Herein, we present the first example of chiral phosphine-
catalyzed enantioselective [4 + 3] annulation reaction, affording
chiral seven-membered ring-fused quinazoline-based tricycles
with high chemo-, diastereo-, and enantioselectivity (Scheme
1d).
Since quinazoline derivatives have widely been applied in
discovery of novel bioactive compounds,1 it promoted us to
choose quinazoline-based azomethine-imines as 1,3-dipole for
the phosphine-catalyzed annulations. We initially explored the
reaction of azomethine imine 1a with allenoate 2a with the use of
commercially available chiral phosphines as the catalyst (Table
1). In the presence of Kwon phosphine P1, allenoate 2a reacted
smoothly with azomethine imine 1a in dichloromethane at room
temperature to give the desired product 3aa in 90% yield with
good dr (9:1) and 80% ee (entry 1). In particular, the reaction
displayed excellent chemoselectivity, and no [3 + 2] annulation
product was observed. We next screened other phosphines to
improve diastereo- and enantioselectivity. Benzyl-substituted
Kwon phosphine P2 could catalyze the reaction to afford the
product 3aa in excellent yield, albeit with moderate diastereo-
and enantioselectivity (entry 2). Phosphines P3 and P4 displayed
similar catalytic capability to that of P1 (entries 3−4). Although
spirocyclic phosphine P5 could also deliver 80% ee, it only gave
3aa in 46% yield with poor dr (entry 5). With the use of Kwon
phosphine P1 as the catalyst, the solvent screening revealed that
THF is the optimal solvent, providing the product 3aa in 95%
B
DOI: 10.1021/acs.orglett.6b02885
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
a
Table 2. Substrate Scope with Respect to Allenoates
Table 3. Substrate Scope with Respect to Azomethine Imines
yield
b
c
c
yield
b
ee
entry
R
t (h)
3
(%)
dr
ee (%)
c
c
entry
1
1 (R/R′)
t (h)
3
(%)
dr
(%)
1
Ph (2a)
30
72
72
44
20
36
40
27
30
60
12
43
12
30
12
12
72
72
10
72
96
3aa
3ab
3ac
3ad
3ae
3af
97
97
95
96
95
96
96
95
98
94
98
96
93
96
95
98
98
82
60
70
95
20:1
20:1
25:1
25:1
20:1
25:1
14:1
19:1
33:1
5:1
94
92
92
93
95
94
96
94
94
90
94
93
94
96
94
94
96
94
95
90
70
6-F/4-MeC6H4 (1b)
7-Br/4-MeC6H4 (1c)
6-Me/4-MeC6H4 (1d)
H/Ph (1e)
16
96
72
72
40
16
40
42
3ba
3ca
3da
3ea
3fa
96
85
97
96
95
91
98
96
30:1
8:1
94
83
90
93
92
93
93
92
2
3-MeC6H4 (2b)
4-MeC6H4 (2c)
3-MeOC6H4 (2d)
3,5-MeO2C6H3 (2e)
4-t-BuC6H4 (2f)
2-FC6H4 (2g)
3-FC6H4 (2h)
4-FC6H4 (2i)
d
2
3
3
4
5
6
7
8
30:1
20:1
11:1
20:1
20:1
13:1
4
5
H/2-MeC6H4 (1f)
H/4-MeOC6H4 (1g)
H/4-t-BuC6H4 (1h)
H/4-ClC6H4 (1i)
6
3ga
3ha
3ia
7
3ag
3ah
3ai
8
9
a
Unless otherwise specified, all reactions were performed with 1a
(0.125 mmol), 2 (0.19 mmol), and P1 (0.025 mmol) in THF (2 mL)
at 0 °C. Isolated yield. Determined by chiral HPLC analysis. In
10
11
12
13
14
15
2-ClC6H4 (2j)
3-ClC6H4 (2k)
4-ClC6H4 (2l)
3-BrC6H4 (2m)
4-BrC6H4 (2n)
3-CF3C6H4 (2o)
4-CF3C6H4 (2p)
4-CO2MeC6H4 (2q)
2-naphthyl (2r)
CO2Et (2s)
3aj
3ak
3al
20:1
25:1
20:1
25:1
17:1
30:1
15:1
16:1
20:1
b
c
d
DCM (2 mL) at 5 °C.
3am
3an
3ao
3ap
3aq
3ar
3as
3at
a
Table 4. Oxidation-Ring-Opening of Tricyclic Products 3
d
16
17
18
19
20
21
H (2t)
b
c
c
entry R1 in 4
R2 in 4
Ph
4
yield (%)
dr
ee (%)
Me (2u)
3au
20:1
a
1
2
3
4
5
6
7
8
H
H
H
H
H
H
H
5-F
4aa
4ab
4ac
4ad
4ae
4af
73
85
84
70
78
72
71
86
20:1
20:1
20:1
25:1
20:1
16:1
20:1
30:1
92
92
92
93
96
93
95
94
Unless otherwise specified, all reactions were performed with 1a
(0.125 mmol), 2 (0.19 mmol), and P1 (0.025 mmol) in THF (2 mL)
at 0 °C. Isolated yield. Determined by chiral HPLC analysis. At 5
4-MeC6H4
2-FC6H4
4-ClC6H4
4-BrC6H4
2-naphthyl
CO2Et
b
c
d
°C.
compatible with the current phosphine catalysis conditions
(entries 20−21). α-Methyl allenoate 2t underwent the reaction
to give the product 3at in 70% yield and 90% ee (entry 20), in
contrast, α-ethyl allenoate 2u showed excellent reactivity and
diastereoselectivity but lower enantioselectivity (entry 21). The
absolute configurations of the [4 + 3] annulation products were
determined by the single-crystal X-ray diffraction analysis of the
product 3am.20
4ag
4ba
Ph
a
Unless otherwise specified, all reactions were performed with 3 (0.1
mmol) and mCPBA (0.8 mmol) in DCE (2 mL) at 40 °C for 12 h.
Isolated yield. Determined by chiral HPLC analysis.
b
c
1,2-diazepine derivatives 4 in 70−86% yield and 92−96% ee.
Various tricyclic products (3) succumbed to the oxidation
conditions, giving the diverse chiral monocyclic products with
retention of diastereo- and enantiochemistry. It is worth noting
that the synthesis of 4aa could be achieved through one-pot
sequential annulation/oxidation-ring-opening reaction in 61%
yield with 20:1 dr and 93% ee (Scheme 2). Furthermore,
The scope of azomethine imines was also evaluated, and the
results are shown in Table 3. 6-Fluoro-substitued azomethine
imine 1b performed efficiently to afford the corresponding
product 3ba in excellent yield with 30:1 dr and 94% ee. Strangely,
7-bromo-substitued azomethine imine 1c provided inferior
results, in comparison with the substrate 1b. Although 7-
bromo substituent is far from the reactive center, it displayed
significant negative effect on the reactivity and selectivity, leading
to the product 3ca with lower yield, diastereo-, and
enantioselectivity. The reaction of electron-rich azomethine
imine 1d with allenoate 2a proceeded smoothly to give the
cycloadduct 3da in 97% yield with 30:1 dr and 90% ee. Variation
of arylsulfonyl protecting groups in azomethine imines were well
tolerated, giving the desired cycloadducts (3ea−3ia) in excellent
yields with excellent diastereo- and enantioselectivities.
Scheme 2. Oxidation-Ring-Opening of Tricyclic Products 3
Since diazepines are important bioactive molecules21 and also
functioned as key scaffolds in asymmetric synthesis,22 we
explored their synthesis with the products 3 as the starting
material. As shown in Table 4, treatment of the products 3 with
mCPBA in DCE at 40 °C for 12 h led to oxidation-ring-opening
of tricyclic heterocycles, affording chiral 2,3,4,7-tetrahydro-1H-
C
DOI: 10.1021/acs.orglett.6b02885
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
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reduction of nitro group in 4ae followed by diazotization and
treatment with H3PO2 can remove NO2 to give the compound 5.
Other synthetic utility of the products had also been investigated.
As illustrated in Scheme 3, with the use of NaBH4 as the reducing
Scheme 3. Synthetic Applications of the Products 3
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reduced to give the compound 6. In the presence of LiALH4,
imine and ester moieties were all reduced to afford the alcohol 7
in 72% yield without loss of dr and ee. The addition of the
Grignard reagent to the ester moiety led to the alcohol product 8.
In summary, we have developed the first catalytic
enantioselective [4 + 3] annulation of allenoates with
azomethine imines using a commercially available chiral
phosphine. A wide range of substrates with regard to both the
allenoates and azomethine imines were tolerated. The reaction
worked very well at hundreds of milligram scale. The products
were further transformed into other biologically significant
compounds, specifically, with the use of an oxidation-ring-
opening procedure, chiral monocyclic diazepine derivatives were
synthesized.
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ASSOCIATED CONTENT
* Supporting Information
■
(17) For recent reviews, see: (a) Marinetti, A.; Voituriez, A. Synlett
2010, 174. (b) Wang, S.-X.; Han, X.-Y.; Zhong, F.-R.; Wang, Y.-Q.; Lu,
Y.-X. Synlett 2011, 19, 2766. (c) Zhao, Q.-Y.; Lian, Z.; Wei, Y.; Shi, M.
Chem. Commun. 2012, 48, 1724. (d) Fan, Y. C.; Kwon, O. Chem.
Commun. 2013, 49, 11588. (e) Wang, Z.; Xu, X.; Kwon, O. Chem. Soc.
Rev. 2014, 43, 2927. (f) Xiao, Y.; Guo, H.; Kwon, O. Aldrichimica Acta
2016, 49, 3. (g) Wang, T.; Han, X.; Zhong, F.; Yao, W.; Lu, Y. Acc. Chem.
Res. 2016, 49, 1369.
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.orglett.6b02885.
Experimental procedure, characterization data, HPLC
analysis data, NMR spectra, and X-ray crystallographic
data (PDF)
(18) (a) Wang, J. C.; Krische, M. J. Angew. Chem., Int. Ed. 2003, 42,
5855. (b) Cai, L.; Zhang, K.; Kwon, O. J. Am. Chem. Soc. 2016, 138,
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AUTHOR INFORMATION
Corresponding Author
■
(19) (a) Zheng, S.; Lu, X. Org. Lett. 2009, 11, 3978. (b) Na, R.; Jing, C.;
Xu, Q.; Jiang, H.; Wu, X.; Shi, J.; Zhong, J.; Wang, M.; Benitez, D.;
Tkatchouk, E.; Goddard, W. A., III; Guo, H.; Kwon, O. J. Am. Chem. Soc.
2011, 133, 13337. (c) Zhou, R.; Wang, J.; Duan, C.; He, Z. Org. Lett.
2012, 14, 6134. (d) Jing, C.; Na, R.; Wang, B.; Liu, H.; Zhang, L.; Liu, J.;
Wang, M.; Zhong, J.; Kwon, O.; Guo, H. Adv. Synth. Catal. 2012, 354,
1023. (e) Li, Z.; Yu, H.; Feng, Y.; Hou, Z.; Zhang, L.; Yang, W.; Wu, Y.;
Xiao, Y.; Guo, H. RSC Adv. 2015, 5, 34481.
(20) Crystallographic data for rac-3aa, 3am, and rac-4af have been
deposited with the Cambridge Crystallographic Data Centre as
deposition number CCDC 1485763−1485765.
(21) (a) Danneberg, P.; Weber, K. H. Br. J. Clin. Pharmacol. 1983, 16,
231s. (b) Szucs, T. Drugs 1991, 41, 18.
*E-mail: hchguo@cau.edu.cn.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work is supported by the NSFC (No. 21172253, 21372256,
and 21572264) and the opening foundation of the Key
Laboratory of Green Pesticide and Agricultural Bioengineering,
Ministry of Education, Guizhou University (No.
2014GDGP0103).
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C.; Sahoo, B.; Daniliuc, C. G.; Glorius, F. J. Am. Chem. Soc. 2014, 136,
17402.
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DOI: 10.1021/acs.orglett.6b02885
Org. Lett. XXXX, XXX, XXX−XXX