One-pot synthesis of cis-isoquinolonic acid derivatives via three-component reaction of homophthalic anhydride with aldehydes and amines using ytterbium(III) triflate as catalyst

Article abstract of DOI:10.1002/adsc.200404211

Ytterbium(III) triflate efficiently catalyzes the one-pot reaction of homophthalic anhydride with aldehydes and amines at ambient temperature to afford the corresponding cis-isoquinolonic acid derivatives in good to excellent yields with high diastereoselectivity. This method provides a novel and much improved modification of the three-component reaction in terms of mild reaction conditions, short reaction times, clean reaction profiles, small quantity of catalyst, and simple work-up procedure. Another important feature of this method is that the catalyst can be easily recovered from the aqueous layer after the reaction and can be reused with no loss of activity.

Full text of DOI:10.1002/adsc.200404211

FULL PAPERS
One-Pot Synthesis of cis-Isoquinolonic Acid Derivatives via
Three-Component Reaction of Homophthalic Anhydride with
Aldehydes and Amines using Ytterbium(III) Triflate as Catalyst
Limin Wang,a,* Jijun Liu,a He Tian,a Changtao Qian,b Jie Sunb
a
Institute of Fine Chemicals, Lab for Advanced Materials, East China University of Science and Technology, 130 Meilong
Lu, Shanghai 200237, Peopleꢀs Republic of China
Fax: (þ86)-21-6425-2288, e-mail: wanglimin@ecust.edu.cn, wcathy@china.com
b
Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354
Fenglin Lu, Shanghai 200032, Peopleꢀs Republic of China
Received: July 5, 2004; Revised: January 1, 2005; Accepted: February 7, 2005
Supporting Information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
Abstract: Ytterbium(III) triflate efficiently catalyzes catalyst, and simple work-up procedure. Another im-
the one-pot reaction of homophthalic anhydride portant feature of this method is that the catalyst can
with aldehydes and amines at ambient temperature be easily recovered from the aqueous layer after the
to afford the corresponding cis-isoquinolonic acid de- reaction and can be reused with no loss of activity.
rivatives in good to excellent yields with high diaster-
eoselectivity. This method provides a novel and much
improved modification of the three-component reac- Keywords: cis-isoquinolonic acids, homophthalic an-
tion in terms of mild reaction conditions, short reac- hydride, lanthanide triflates, Lewis acids, one-pot syn-
tion times, clean reaction profiles, small quantity of thesis
Introduction
employed for the synthesis of cis-isoquinolonic acids.[7]
Gesquiere and his group reported that the efficient pro-
Tetrahydroisoquinolonic acid derivatives have attracted cedure using the boron trifluoride diethyl ether complex
the attention of synthetic organic chemists due to their (BF3 ·Et2O) as a Lewis acid catalyst led to trans-isoqui-
potential activity in the field of pharmaceuticals, and ex- nolonic acid derivatives in moderate yields.[9] However,
hibit a wide spectrum of biological activities including most of these procedures involve stoichiometric
psychotropic, anti-allergenic, anti-inflammatory and es- amounts of a metal promoter, longer reaction time
trogenic behavior.[1] In particular, isoquinolonic acids and give low yields of the products. All of the methods
are useful precursors for the total synthesis of naturally mentioned above require lengthy procedures to prepare
occurring phenanthridine alkaloids[2] such as coryno- the starting materials. In addition, most of the imines are
line, oxocorynoline and epicorynoline as well as indeno- hygroscopic, unstable at high temperatures, and are dif-
isoquinolines[3] possessing significant anti-tumor activi- ficult to purify by distillation or column chromatogra-
ty. It is therefore not surprising that many synthetic phy, thus generating a lack of efficiency. Therefore, it
methods have been developed for these compounds. is of increasing importance to develop simple and effi-
Cushman and his group first reported that these com- cient synthetic methods towards this type of compounds
pounds could be synthesized by a simple cycloaddition involving reactions that need not only effectivecatalysts,
reaction of homophthalic anhydrides with imines under but also simple and convenient procedures. Most of the
mild conditions.[4] The reaction products resulting from conventional Lewis acids such as TiCl4, AlCl3, SnCl4 and
the cycloaddition of homophthalic anhydride with BF3 ·OEt2 are decomposed or deactivated by water that
imines using a base catalysis or no catalyst under ther- exists during imine formation. Thus we focused on the
mal conditions[5] possess two asymmetric centers and use of Lewis acid catalysts to increase the reactivities
are capable of existing as cis- and trans-diastereoisom- of imine groups in the imino reactions. For this purpose,
ers, favoring the cis-isomer. As a result, a variety of syn- we selected rare earth metal triflates as catalyst since
thetic approaches have been developed for the synthesis they have been reported to have excellent catalytic ac-
of isoquinolonic acids.[6–8] Recently, room temperature tivities as Lewis acids for a variety of reactions. Rare
ionic liquids[6] and trimethyl orthoformate have been earth metal triflates such as ytterbium triflate
Adv. Synth. Catal. 2005, 347, 689–694
DOI: 10.1002/adsc.200404211
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[Yb(OTf)3] and scandium triflate [Sc(OTf)3] are stable were tested: in most cases the reactions gave extremely
and serve as Lewis acids in water solution. Many nitro- lower yields and mixture of cis- and trans-products or
gen-containing compounds such as imines and hydra- very complicated mixtures.[9] Most of these Lewis acids
zones are also activated by rare earth metal triflates in react rapidly with water rather than the substrates and
both organic and aqueous solvents.[10] Moreover, they are decomposed or deactivated, thus, the reactions
can be recovered after the reactions are completed must be carried out under strictly anhydrous conditions.
and reused without loss of activity.[11] In continuation Furthermore, most of the imines are hygroscopic, unsta-
of our long-standing interest in lanthanide triflate-cata- ble at high temperatures, and are difficult to purify by
lyzed synthetic reactions,[12] we disclose a simple and ef- distillation or column chromatography. However, lan-
ficient procedure using lanthanide triflates as a novel thanide triflates can be used as efficient Lewis acids in
and recyclable catalyst for the synthesis of cis-isoquino- aqueous media, as their hydrolysis by water is generally
lonic acids through the one-pot coupling reaction of ho- slow.
mophthalic anhydride, aldehydes and amines under
mild reaction conditions.
These one-pot procedures have been developed for
this transformation using lanthanide triflates as cata-
lysts, and do not require the isolation of unstable imines
prior to reaction. It is desirable from a synthetic point of
view that the imines, generated in situ from aldehydes
and amines, be immediately reacted with homophthalic
Results and Discussions
We investigated the reaction of homophthalic anhydride anhydride to afford isoquinolonic acids in one-pot. It
(1a) with benzaldehyde (2a) and aniline (3a) under var- was found that the reaction of benzaldehyde, aniline
ious conditions (Scheme 1). The results are summarized and homophthalic anhydride was efficiently catalyzed
in Table 1. The reaction proceeded smoothly in the pres- by Yb(OTf)3 in the presence of anhydrous MgSO4 or
ence of 2 mol % of lanthanide triflates at ambient tem- 4 ꢂ molecular sieves, which are added to trap the water
perature to afford the corresponding cis-1-oxo-2,3-di- generated during the reaction (Scheme 1). The reaction
phenyl-1,2,3,4-tetrahydro-4-isoquinolinecarboxylic
was instantaneous and produced the isoquinolonic acid
acid (4a) in high yield. Interestingly, there was no evi- as expected. On the other hand, the reaction proceeded
dence for the formation of any trans-diastereoisomer. sluggishly in the presence of anhydrous MgSO4 without
This showed that the lanthanide triflates did effectively any catalyst, and only a trace amount of product was de-
catalyze the cycloaddition reaction. Among the lantha- tected after 24 h.
nide triflates screened, Yb(OTf)3 exhibited superior cat-
Various solvents were used in the model reaction with
alytic activity and afforded the corresponding cis-com- 2 mol % Yb(OTf)3 as a catalyst; the results are summar-
pound (4a) in 86% yield, which was higher than that ized in Table 1. In this reaction, dichloromethane played
with any other lanthanide triflate.
an important role for the high yield (86%). When the re-
Lanthanide triflates are more soluble in water than in action was carried out in acetonitrile, toluene, ether,
common organic solvents. These catalysts could be re- methanol, DMF and THF, lower yields were observed
covered almost quantitatively from the aqueous layer (46% in acetonitrile, 19% in toluene, 27% in ether,
after the reactions were completed and they can be 33% in methanol, 35% in DMF and 36% in THF). Fur-
reused without attenuated activity. For example, only a thermore, the reaction proceeded smoothly at room
catalytic amount of Yb(OTf)3 was enough to complete temperature in dichloromethane. If proceeding at high
the reaction, the catalyst could be reused three times temperature (in refluxing dichloromethane), the reac-
without showing any loss of activity (with the yields of tion gave mixtures of cis- and trans-products along
the product 4a being 85%, 84%, 83%, respectively). Fur- with homophthalic amide. The lower reaction tempera-
ther studies showed that increasing the amount of cata- ture resulted in an improvement of diasteroselective and
lyst did not improve the yield of the product. When using yields. The use of Yb(OTf)3 as a reaction catalyst for this
0.5 mol % of Yb(OTf)3, the reaction of benzaldehyde transformation avoids the use of a moisture-sensitive
and aniline with homophthalic anhydride gave only a catalyst and high temperature reaction conditions.
45% yield even after 12 h. It is obvious that the yield Yb(OTf)3 proved to be a efficient catalyst for promoting
of product was affected by the amount of Yb(OTf)3 cat- this reaction under mild conditions.
alyst.
Since then, not only Ln(OTf)3 but also other lantha-
nide compounds such as YbCl3, DyCl3 and TbCl3 were
evaluated in this reaction. However, the catalytic activ-
ities of YbCl3, DyCl3 and TbCl3 were lower than that of
lanthanide triflates in this reaction, and gave lower
yields (65%, 55% and 63%) at the first use. Various typ-
ical Lewis acid catalysts including AlCl3, SnCl4 and
ZnCl2 as well as protic acids (HCl and CH3COOH), Scheme 1.
690
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Table 1. Reaction of homophthalic anhydride, benzaldehyde
and aniline under different reaction conditions.
Table 2. One-pot synthesis of cis -isoquinolonic acid deriva-
tives catalyzed by Yb(OTf)3.[a]
Entry
Solvent[a]
Catalyst[b]
Additive
Yield [%][c]
Entry R1(-CHO)
R2(-NH2)
Product Yield [%][b]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH3CN
toluene
Et2O
None
YbCl3
TbCl3
DyCl3
MgSO4
MgSO4
MgSO4
MgSO4
MgSO4
MgSO4
MgSO4
4 ꢂ
MgSO4
MgSO4
MgSO4
MgSO4
MgSO4
MgSO4
MgSO4
trace
65
63
55
73
74
86
84
46
19
27
33
35
1
2
3
4
5
6
7
Ph
Ph
Ph
Ph
4-MeC6H4
3,4-Me2C6H3 4c
4a
4b
86
80
84
83
85
92
78
4-MeOC6H4 4-Me-C6H4
4-MeOC6H4 i-C3H7
4-Me2NC6H4 i-C3H7
C3H7
4d
4e
4f
Nd(OTf)3
Sm(OTf)3
Yb(OTf)3
Yb(OTf)3
Yb(OTf)3
Yb(OTf)3
Yb(OTf)3
Yb(OTf)3
Yb(OTf)3
Yb(OTf)3[d]
Yb(OTf)3
4 g
8
Ph
4 h
79
9
10
11
12
13
14
15
i-C3H7
2-Me-C6H4
Ph
i-C3H7
4i
4j
4k
4 l
82
88
85
88
80
89
93
CH3OH
DMF
THF
4-ClC6H4
4-ClC6H4
4-BrC6H4
Ph
36
Ph
CH2Cl2
85, 84, 83
2-NO2C6H4
4-MeOC6H4 C6H5CH2
4-NO2C6H4 Ph
4 m
4n
[a]
All reactions were carried out at room temperature for 2 h.
2 mol % of catalyst was used.
Yield of isolated product.
4’o[c]
[b]
[c]
[d]
[a]
All reactions were carried out at room temperature in
CH2Cl2 at for 2 h.
Yield of isolated product.
Catalyst was reused three times.
[b]
[c]
2-[E-1,2-benzamide-(4-nitrobenzo)ethenyl]benzoic acid.
To examine the scope of this process, several examples coupling constant J(H-3,H-4) is significantly smaller than
for the synthesis of cis-isoquinolonic acids were studied for the cis configuration (typical value 0–2 Hz).[9]
in the presence of catalytic amounts (2 mol %) of Remarkably, the reaction of p-nitrobenzaldehyde
Yb(OTf)3 and anhydrous MgSO4 in dichloromethane (2o), aniline (3o) and homophthalic anhydride did not
and the results are summarized in Table 2. The three- give the corresponding isoquinolonic acid, but rather af-
component one-pot reaction of various aldehydes, forded 2-[E-1,2-benzamide-(4-nitrobenzo)ethenyl]ben-
amines and homophthalic anhydride was clean and zoic acid (4’o) as the corresponding product (Scheme 3).
highly diastereoselective, and proceeded smoothly to A possible mechanism to account for the formation of
give the corresponding cis-isoquinolonic acids 4 in 4’o is illustrated in Scheme 4. Presumably, p-nitroben-
good to excellent yields (Scheme 2). Avariety of substi- zaldehyde is first activated by Yb(OTf)3 because of the
tuted aromatic and aliphatic aldehydes carrying either strong electron-withdrawing substituent (NO2) showing
electron-donating or -withdrawing substituents afford- a higher reactivity. The reaction may proceed through
ed high yields of products. Most importantly, both aro- the Yb(OTf)3-catalyzed aldol condensation reaction of
matic and aliphatic amines reacted easily under these p-nitrobenzaldehyde and homophthalic anhydride to
conditions to afford the desired cis-products in satisfac- yield the 4-(p-nitrobenzylidene)homophthalic anhy-
tory yields. In all reactions, the products were obtained dride intermediate (5’o) which is stabilized by the lan-
as the cis-diastereomer, and their structures were con- thanide, with subsequent acetylization and ring-opening
firmed by detailed 1H NMR analysis.
reactions resulting in the formation of 2-[E-1,2-benza-
In theory the most diagnostic parameter for the cis- mide-(4-nitrobenzo)ethenyl]benzoic acid (4’o), an X-
and trans-configuration is the scalar coupling constant ray crystallographic analysis of which was performed
between protons H-3 and H-4. In the compounds 4a– to confirm the molecular structure (Figure 1). A similar
n the coupling constant J(H-3,H-4) ¼4.2–6.0 Hz is typical phenomenon has also been reported in the synthesis of
for the cis configuration. In the trans compounds the optically active aromatic a-hydroxy esters.[13] It appears
that the reaction can only proceed with an activated ar-
omatic system such as phenol, since no reaction was ob-
served under the same conditions with alkylbenzenes.
Especially, a strong electron-withdrawing group on the
phenol ring (e.g., p-nitrophenol) significantly deactivat-
ed the system and prevented the reaction from happen-
ing.
To explore the mechanism of the reaction, we carried
Scheme 2.
out several reactions catalyzed by lanthanide triflate un-
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Limin Wang et al.
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Scheme 3.
Scheme 5.
mophthalic amide, and the end product was not ob-
served. Besides p-nitrobenzaldehyde, the cycloaddition
reaction of homophthalic anhydride with benzaldehyde
did not occur to give 3,4-dihydroisocoumarin-4-carbox-
ylic acid underwent catalysis by the Lewis acid lantha-
nide triflate as reported by Gesquiere.[14] Moreover, to
prove that the imine was produced, benzaldehyde was
reacted with aniline to give the corresponding benzyli-
deneaniline, and the latter was used for the following re-
action without purification. Thus, treatment of benzyli-
deneaniline with homophthalic anhydride in the pres-
ence of lanthanide triflate resulted in formation of 1-
oxo-2,3-diphenyl-1,2,3,4-tetrahydro-4-isoquinolinecar-
boxylic acid as the expected product.
Scheme 4.
We have proposed a mechanism similar to that of
Cushman[2] and Gesquiere[9] for the lanthanide triflate-
catalyzed reaction as shown in Scheme 5. The reaction
of the aldehyde 2 with amine 3 first afforded the imine
as intermediate 5, which is stabilized by the lanthanide
triflate. Subsequently, the homophthalic anhydride 1 is
activated by the lanthanide triflate, leading to a more re-
active intermediate 6, a mobile equilibrium of 6 exists
between the ketone and enol tautomers. Nucleophilic
attack of the imine nitrogen of the intermediate 5 on
the carbonyl carbon of the intermediate 6, in which ster-
ic factors are increased by the lanthanide triflate, gives
the less sterically hindered intermediate 7 and finally
Figure 1. X-ray molecular structure of 4’o with the atom
numbering scheme.
der the optimized conditions. First of all, the reaction of product 4 as the cis-isomer.
homophthalic anhydride and aniline with benzalde-
hyde, contrary to our expectation, gave an N-phenylho-
692
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One-Pot Synthesis of cis-Isoquinolonic Acid Derivatives
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Conclusion
Acknowledgements
We thank the National Nature Science Foundation of China and
the Science Foundation of East China University of Science and
Technology for their financial support.
In conclusion, lanthanide triflate was found to be a high-
ly efficient and convenient catalyst in the one-pot reac-
tion of homophthalic anhydride, aldehydes and amines
to afford cis-isoquinolonicacid derivatives in good to ex-
cellent yields. This method offers several advantages in-
cluding mild reaction conditions, enhanced reaction
rates, clean reaction profiles, small quantity of catalyst,
high diastereoselectivity, no by-products such as homo-
phthalic amides or other side products, operational and
experimental simplicity, making it a useful and attrac-
tive strategy for the synthesis of cis-isoquinolonic acid
derivatives. In addition, the catalyst lanthanide triflate
can be easily recovered from the aqueous layer after
the reaction and can be reused with no loss of activity.
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The rare earth catalysts were prepared by the reported proce-
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2 h.
One-Pot Reaction of Aldehydes, Amines and
Homophthalic Anhydride; Typical Procedure
Aldehyde 2 (1.0 mmol), amine 3 (1.0 mmol) and homophthalic
anhydride 1 (1.2 mmol) in CH2Cl2 (1.0 mL) were added to a
suspension of Yb(OTf)3 (0.02 mmol, 2 mol %) and MgSO4
(125 mg) in 4.0 mL CH2Cl2 at room temperature. The mixture
was stirred for 2.0 h at room temperature, and then the CH2Cl2
was removed under reduced pressure. Water was added, and
the product was extracted with EtOAc. After the organic layer
had been dried (Na2SO4) and evaporated, the crude product
was chromatographed on silica gel to afford the compound 4.
Characterization data for cis-isoquinolonic acid derivatives
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