Copper-catalyzed three-component synthesis of 2-iminodihydrocoumarins and 2-iminocoumarins

Article abstract of DOI:10.1002/adsc.200900890

An efficient synthesis of N-sulfonyl-substituted 2-imino-3,4- dihydrocoumarins and 2-iminocoumarins via a copper-catalyzed multicomponent reaction of sulfonyl azides with terminal alkynes and β-(ortho- hydroxyphenyl)-α β-unsaturated ketones or ortho- hydroxyphenylpropiolates has been developed. The cascade process involves trapping the keteimine by a nucleophilic addition and an intramolecular Michael addition. This methodology could well be extended to the concise synthesis of the polysubstituted piperidine scaffold.

Full text of DOI:10.1002/adsc.200900890

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DOI: 10.1002/adsc.200900890
Copper-Catalyzed Three-Component Synthesis of
2-Iminodihydrocoumarins and 2-Iminocoumarins
Yang Shen,a Sunliang Cui,a Jing Wang,a Xiaopeng Chen,a Ping Lu,a,*
and Yanguang Wanga,b,*
a
Department of Chemistry, Zhejiang University, Hangzhou 310027, Peopleꢀs Republic of China
Fax : (+86)-571-8795-1512; e-mail: pinglu@zju.edu.cn or orgwyg@zju.edu.cn
State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, Peopleꢀs Republic of China
b
Received: December 22, 2009; Revised: March 30, 2010; Published online: April 23, 2010
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.200900890.
Abstract: An efficient synthesis of N-sulfonyl-sub-
stituted 2-imino-3,4-dihydrocoumarins and 2-imino-
coumarins via a copper-catalyzed multicomponent
reaction of sulfonyl azides with terminal alkynes
and b-(ortho-hydroxyphenyl)-a,b-unsaturated ke-
tones or ortho-hydroxyphenylpropiolates has been
developed. The cascade process involves trapping
the keteimine by a nucleophilic addition and an in-
tramolecular Michael addition. This methodology
could well be extended to the concise synthesis of
the polysubstituted piperidine scaffold.
ACHTUNGTRENaNUNG dition (CuAAC) and the generation of ketenimine
intermediate by nucleophiles. Instead of sulfonyl
azides, phosphoryl azides could also participate in the
reaction and afford three component adducts.[6] As an
extension of our previous work, here we use b-(ortho-
hydroxyphenyl)-a,b-unsaturated ketones as substrates,
with both nucleophilicity and electrophilicity, for trap-
ping the ketenimine intermediates. Fortunately, 2-imi-
nocoumarins were ideally obtained in moderate yields
and with trans as the predominant configuration.
The CuI-catalyzed reaction of toluenesulfonyl azide
(1a) with phenylacetylene (2a) and chalcone (3a) was
used to screen the reaction conditions (Table 1). Tri-
Keywords: cascade reactions; copper; coumarins;
ketenimines; multicomponent reactions
ACHTUNGTRENUNeNG thylamine (TEA, 1 equiv.) was proven to be the
Table 1. Optimization of reaction conditions for the synthe-
sis of iminodihydrocoumarin 4a.[a]
Iminocoumarins are one type of protein tyrosine
kinase (PTK) inhibitors that are most valuable for the
treatment of diseases involving excess cell prolifera-
tion as well as the antitumor process.[1] They are also
useful fluorescent dyes in fields as various as cell biol-
ogy, medical analysis and sensors.[2] Classic methods
for synthesis of iminocoumarins, such as Knoevenagel
condensation and modification from coumarins, suffer
from several shortcomings including limited substitu-
ents and troublesome chemical process manage-
ment.[3] In order to overcome these shortages, here
we would like to report a concise synthesis of imino-
coumarins via multicomponent reactions that are ver-
satile with regard to the substrate scope and the syn-
thetic applicability.
Entry Base
Solvent Time [h] Yield[b] [%] dr[c]
1
2
3
4
5
6
Et3N
Et3N
CH2Cl2
CH3CN
CH2Cl2
8
8
8
86
72
83
55
75
47
95:5
95:5
92:8
90:10
95:5
90:10
pyridine
pyridine
2,6-luitidine CHCl3
CH3CN 12
8
K2CO3 CH2Cl2 12
[a]
Reaction conditions: 1a (0.6 mmol), 2a (0.6 mmol), 3a
(0.5 mmol), CuI (0.06 mmol), the indicated base
(0.6 mmol) and solvent (5 mL).
Recently, we[4] and others[5] have developed Cu-cat-
alyzed three-component reactions of sulfonyl azides
with terminal alkynes and a number of nucleophiles,
such as amines, alcohols as well as water. These reac-
tions involve a copper-catalyzed azide-alkyne cyclo-
[b]
[c]
Yield of the isolated product.
The ratio was determined by 1H NMR spectroscopy of
the crude product.
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Table 2. Three-component reaction of azides 1 with alkynes 2 and chalcones 3.[a]
Entry
1 (R1)
2 (R2)
3 (R3/R4)
Product 4/Yield [%][b]
1
2
3
4
5
6
7
8
1a (4-MeC6H4)
1b (Ph)
1c (4-ClC6H4)
1d (5-Me2N-naphth-1-yl)
1a
1a
1e (Me)
1b
1c
1b
1a
1c
1a
1a
1a
1a
2a (Ph)
2b (4-MeOC6H4)
2c (4-MeC6H4)
2d (4-FC6H4)
2e (n-Bu)
2f (1-cyclohexenyl)
2a
2f
2a
2c
2b
2e
3a (H/Ph)
3a
3a
3a
3a
3a
3b (H/4-ClC6H4)
3b
3c (H/2-MeC6H4)
3c
3d (4-Br/Ph)
3d
3d
4a/86[c]
4b/73[c]
4c/81[c]
4d/75[c]
4e/97[d]
4f/88[c]
4g/83[c]
4h/85[c]
4i/71[c]
4j/79[c]
4k/69[c]
4l/74[e]
4m/81[c]
4n/80[c]
4o/85[c]
4p/46[c]
9
10
11
12
13
14
15
16
2g (4-EtC6H4)
2a
2f
2a
3e (3-MeO/Ph)
3e
3f (H/Me)
[a]
Reaction conditions: 1 (0.6 mmol), 2 (0.6 mmol), 3 (0.5 mmol), CuI (0.06 mmol), TEA (0.6 mmol), CH2Cl2 (5 mL), room
temperature, 8 h.
Isolated yield.
dr>95:5 based on H NMR spectroscopy of the crude product.
[b]
[c]
[d]
[e]
1
drꢀ88:12.
drꢀ82:18.
most effective base among those others tested, such lished by a single crystal X-ray analysis (Figure 1),[7]
as pyridine, 2,6-lutidine and potassium carbonate which clearly presented the trans configuration.
(Table 1, entries 1, 3–6). As to the solvent, in compari-
son with acetonitrile, dichloromethane not only pro- was proposed and is shown in Scheme 1. Firstly,
vided a higher isolated yield but also a higher diaste- ketenimine A could be formed by the Cu-catalyzed
reomeric ratio (dr=95:5) in favour of the trans cycloaddition reaction of azides 1a and alkynes 2a via
isomer (Table 1, entries 1 and 2).
a click reaction and a subsequent release of N2.[4,5]
Based on our previous works, a possible mechanism
AHCTUNGTRENNUNG
With the optimized reaction conditions in hand, we Then nucleophile B, deprotonated by triethylamine,
tested the substrate diversity with a variety of azides, could then attack the central carbon of A to form C.
alkynes and chalcones (Table 2). In all cases, the reac-
tions afforded the corresponding N-toluenesulfonyl-
iminodihydrocoumarins 4a–4p in 46–97% yields. The
stereoselectivity of the reaction was related to the
character of alkynes. Arylacetylenes 2a–2d and 2g
(Table 2, entries 1–4, 7, 9–11, 13, 14, and 16) and cy-
clohexenylacetylene (2f) (Table 2, entries 6, 8, and 15)
underwent this cascade reaction smoothly with excel-
lent diastereomeric ratios (dr>95:5) while 1-hexyne
(2e) gave a slightly decreased diastereomeric ratio
(Table 2, entries 5 and 12).
The structures of the products was fully character-
1
ized by H NMR and 13C NMR spectroscopy as well
as high-resolution mass spectrometry (see Supporting
Information). The structure of 4h was further estab- Figure 1. X-ray crystal structure of 4h.
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Copper-Catalyzed Three-Component Synthesis of 2-Iminodihydrocoumarins and 2-Iminocoumarins
Scheme 2. Depiction of the trans stereocontrol of 4a.
Scheme 1. Possible mechanism for the formation of 4a.
Finally, C could undergo an intramolecular Michael
addition and a sequential proton transfer to afford
the iminodihydrocoumarin 4a.
As shown in Figure 1, the iminodihydrocoumarin
ring exists in a twisted planar form. The vicinal cou-
pling constant (3J) for two protons on C-1 and C-2 is Scheme 3. Three-component reaction of 1a, 2a and 5.
1
not clearly shown in the H NMR spectrum because
À
À
À
the dihedral angle of H C-1 C-2 H is 92.778. Based
on the Karplus relation, J is calculated to be 2.07 Hz.
3
Meanwhile, the structures of both trans-4h and cis-4h nent adduct product 6 was obtained in 90% isolated
have been optimized by the RHF/6-31G(d) method. yield (Scheme 3).
À
À
À
The dihedral angles of H C-1 C-2 H in trans-4h and
Rather than altering the ketone to an ester, we
ꢁ
cis-4h are calculated to be 968 and 488, respectively. tried to change C=C into C C. However, many at-
3
Hence, the J values are calculated to be 2.21 Hz for tempts at synthesis of 3-(2-hydroxyphenyl)-1-phenyl-
trans-4h and 8.2 Hz for cis-4h. Based on these calcu- prop-2-yn-1-one failed because this expected com-
1
lated results and H NMR data, we assigned all com- pound was too unstable and would intramolecularly
pounds 4 as having the trans configuration. The ob- cyclize to benzofuran-2-ylACTHNUTRGNEU(GN phenyl)methanone in high
served diastereoselectivity could be rationalized by yield.
two factors. One is the steric hindrance (Scheme 2)
Based on the above survey, we used ortho-hydroxy-
and the second is the result of the thermodynamic phenylpropiolates 7, which couple an ester group and
ꢁ
equilibration. By calculation of the energy potentials a C C bond, to test the reality of this cascade reac-
of trans-4h and cis-4h [RHF/6-31G(d) method], trans- tion. Fortunately, the anticipated iminocoumarins 8
4h is more stable than cis-4h and the energy differ- were obtained in high yields (Table 3). Both aromatic
ence is 3.41 kcal·molÀ1. In comparison to aromatic sulfonyl azides (Table 3, entries 1–8 and 10–17) and
acetylenes (2a–2d) and cyclohexenylacetylene (2g), 1- aliphatic sulfonyl azide (Table 3, entry 9) gave imino-
hexyne (2f) gave a relatively lower diastereoselectiv- coumarins in good to excellent yields. An electronic
ity due to the fact that the steric hindrance has been effect, either by a conjugative effect or by an induc-
released a little when the cis configuration is adopted tive effect, on the aromatic sulfonyl azides 1, aromatic
in the step of the Micheal addition.
acetylenes 2 and phenylpropiolates 7 did not affect
In order to extend the substrate diversity, ortho-hy- the reaction. Hex-1-yne (2e) and 3,3-dimethylbut-1-
droxyphenyl-a,b-unsaturated ester 5 was tested for yne (2j) afforded 9a and 9b in 87% and 95% yields,
this cascade reaction. Unfortunately, although trap- respectively (Scheme 4). In these cases, the basicity of
ping the ketenimine by phenolic anion was observed intermediate E was increased. Therefore it preferred
in this case, we did not detect the sequential intramo- abstraction of a proton instead of a sequential Mi-
lecular Michael addition product. The three-compo- chael addition.
Adv. Synth. Catal. 2010, 352, 1139 – 1144
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Table 3. Three-component reaction of azides 1 with alkynes 2 and phenylpropiolates 7.[a]
Entry
1 (R1)
2 (R2)
7 (R3/R4)
Product 8/Yield[b] [%]
1
2
3
4
5
6
7
8
1a (4-MeC6H4)
1b (Ph)
1a
1a
1a
1a
1f (4-O2NC6H4)
1g (4-AcNHC6H4)
1e (Me)
2a (Ph)
2a
2b (4-MeOC6H4)
2c (4-MeC6H4)
2g (4-EtC6H4)
2a
2a
2a
7a (H/Me)
7a
7a
7a
7a
7a
7a
7a
8a/92
8b/91
8c/90
8d/96
8e/98
8f/95
8g/92
8h/93
8i/87
9
2a
7a
10
11
12
13
14
15
16
17
1c (4-ClC6H4)
2c
2b
7a
7a
7a
7a
8j/92
8k/81
8l/96
8m/90
8n/94
8o/93
8p/91
8q/93
1f
1a
1a
1a
1a
1a
1a
2h (4-t-BuC6H4)
2i (3-ClC6H4)
2a
2a
2a
2a
7b (H/Et)
7c (H/Bn)
7d (4-Cl/Me)
7e (4-Me/Me)
[a]
Reaction conditions: 1 (1.2 mmol), 2 (1.2 mmol), 7 (1.0 mmol), CuI (0.1 mmol), CH2Cl2 (10 mL) , TEA (1.2 mmol), room
temperature, 24 h.
Isolated yield.
[b]
Scheme 4. Three-component reaction of propiolate 7a with azide 1a and alkynes 2.
To highlight the utility of this methodology, typical- peridine 12 could be prepared in six steps and with a
ly with high diasteroselectivity in the case of (ortho- total yield of 43%.
hydroxyphenyl)-a,b-unsaturated ketones, we synthe-
In conclusion, we have developed an efficient and
sized 4a on a gram scale and converted it into syn- highly diastereoselective synthesis of N-sulfonyl-sub-
thetically and biologically useful molecules such as stituted 2-iminodihydrocoumarins and 2-iminocou-
the substituted piperidine 12 (Scheme 5).[8] In this marins via a copper-catalyzed three-component reac-
procedure, 4a was firstly reduced by NaBH4 to afford tion of sulfonyl azides with terminal alkynes and b-
10. Oxidation of secondary alcohol 10 to the ketone, (ortho-hydroxyphenyl)-a,b-unsaturated ketones or
followed by protection of the phenolic OH and then ortho-hydroxyphenylpropiolates. The trans-iminodihy-
reduction by NaBH4 furnished 11 smoothly. Finally, drocoumarins could be applied for the stereoselective
via an intramolecular Mitsunobu reaction, 12 was ob- synthesis of chiral piperidine scaffolds. Investigations
tained. Selective protection of the phenolic OH of 10 on more synthetic applications of the present ap-
failed. As a net result, starting from chalcone (3a), pi- proach are underway in our laboratory.
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Copper-Catalyzed Three-Component Synthesis of 2-Iminodihydrocoumarins and 2-Iminocoumarins
133.7, 129.3, 129.0, 128.8, 128.7, 128.0, 127.61, 127.57, 126.9,
126.0, 123.7, 116.6, 48.5, 43.4, 37.1, 21.6; IR (KBr): n=2950,
1686, 1639, 1598, 1332, 1157, 769 cmÀ1; MS (ESI): m/z=
494.3 ([MÀH]À); HR-MS (ESI): m/z=518.1385, calcd for
C30H25NO4S+Na+ ([M+Na]+): 518.1397.
Data for compound 8a: white solid; mp 205–2068C;
1H NMR (CDCl3, 400 MHz): d=7.81 (d, J=8.4 Hz, 2H),
7.60–7.55 (m, 2H), 7.50–7.48 (m, 2H), 7.44–7.39 (m, 2H),
7.39–7.35 (t, J=8.0 Hz, 1H), 7.28–7.26
ACHTUNGTREN(NUGN m, 2H), 7.23 (d, J=
8.4 Hz, 2 H), 3.68 (s, 5H), 2.38
AHCTUNGTRENNUNG
100 MHz): d=169.4, 158.1, 151.7, 142.8, 142.7, 139.2, 133.2,
131.9, 130.8, 129.5, 129.0, 128.6, 128.5, 126.9, 125.7, 124.8,
119.7, 117.0, 52.7, 35.8, 21.4; IR (KBr): v=1742, 1620, 1544,
1450, 1318, 1088, 1157, 777 cmÀ1; MS (ESI): m/z=470.0
([M+Na]+); HR-MS (ESI): m/z=470.1022, calcd for
C25H21NO5S+Na+ ([M+Na]+): 470.1033.
Acknowledgements
The authors gratefully acknowledge the financial support of
the National Natural Science Foundation of China (No.
20872128; J0830413).
Scheme 5. Synthesis of piperidine 12 from 4a.
Experimental Section
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