Lanthanide Chloride Catalyzed Imino Diels-Alder Reaction. One-Pot Synthesis of Pyrano[3,2-c]- And Furo[3,2-c]quinolines

Full text of DOI:10.1021/jo982220p

6462
J . Org. Chem. 1999, 64, 6462-6467
found to be effective. Recently, InCl3 and others begin to
La n th a n id e Ch lor id e Ca ta lyzed Im in o
Diels-Ald er Rea ction . On e-P ot Syn th esis of
P yr a n o[3,2-c]- a n d F u r o[3,2-c]qu in olin es
find their use in this reaction too.10,11 All of the methods
mentioned above require lengthy procedures to prepare
the starting materials. To our knowledge, many imines
are hygroscopic, unstable at high temperature, difficult
to purify by distillation or column chromatography, and
thus lack efficiency. Therefore, developing simple and
efficient synthetic methods for preparing this type of
compound becomes more and more important.
Yun Ma, Changtao Qian,* Meihua Xie,† and J ie Sun
Laboratory of Organometallic Chemistry, Shanghai Institute
of Organic Chemistry, Chinese Academy of Sciences,
354 Fenglin Lu, Shanghai 200032, China, and Institute of
Organic Chemistry, Anhui Normal University,
Wuhu 241000, Anhui, China
For such reactions, not only effective catalysts but also
simple and convenient procedures are needed. Lan-
thanide chlorides, which are simple, low-cost, and com-
mercially available reagents, have been used as effective
catalysts in organic synthesis such as the cycloaddition
of epoxides to isocyanates,12 thioacetalization13 and nu-
cleophilic substitution,14 as well as some other reactions.15
Here, we describe an efficient one-pot aza-Diels-Alder
type reaction between the imine (formed in situ from
benzaldehyde and amines) and dihydropyran or dihy-
drofuran catalyzed by lanthanide chloride to afford
pyrano[3,2-c]- or furo[3,2-c]quinolines in high yields.
Received November 6, 1998
In tr od u ction
Tetrahydroquinoline derivatives are an important class
of natural products and exhibit biological activities in
various field1, such as psychotropic,2 antiallergenic,3
antiinflammatory,4 and estronegic activity.5 In addition,
pyranoquinoline derivatives are used as potential phar-
maceuticals.6 It is therefore not surprising that many
synthetic methods have been developed for these com-
pounds.7 Among them, the aza-Diels-Alder reaction
between N-arylimines and nucleophilic olefins is probably
one of the most powerful synthetic tools for constructing
N-containing six-membered heterocyclic compounds. Since
the pioneering work of Povarov,8 BF3‚OEt2 has been the
most commonly used catalyst for this reaction. Transition
metal complexes such as Co2(CO)8 and Ni(CO)49 are also
Resu lts a n d Discu ssion
Benzylideneaniline was treated with 3,4-dihydro-2H-
pyran in the presence of a catalytic amount of GdCl3 (20
mol %) in acetonitrile at room temperature. The reaction
proceeded smoothly to afford the corresponding pyrano-
[3,2-c]quinoline in 88% yield. The product was obtained
as a mixture of cis and trans isomers in a ratio of 34:66,
but no other isomer could be detected. It shows that
GdCl3 did effectively catalyze the imino Diels-Alder
reaction.
† Anhui Normal University.
* Corresponding author. Phone: 86-21-64163300. FAX: 86-21-
64166128. E-mail: qianct@pub.sioc.ac.cn.
It is desirable from a synthetic point of view that
imines, generated in situ from aldehydes and amines,
immediately react with dihydropyran to afford pyrano-
[3,2-c]quinolines in an one-pot way without the need of
preformation of the imines. It was found that the reaction
of benzaldehyde, aniline, and 3,4-dihydro-2H-pyran was
efficiently catalyzed by GdCl3 in the presence of 4 Å
molecular sieves or MgSO4 under mild conditions (Scheme
1). The reaction is instantaneous and produces the
pyrano[3,2-c]quinolines (stereoisomers II and III) as
expected. Among the lanthanide chlorides screened,
gadolinium chloride exhibited superior catalytic activity,
while the yield of the adduct was lower for other lan-
thanide chlorides. The reaction did not occur in the
presence of MgSO4 without any lanthnide chlorides even
after 12 h. Various solvents were used in the model
reaction with GdCl3 (20 mol %) as a catalyst; the results
are summarized in Table 1. Acetonitrile was the best
solvent among those tested, such as dichloromethane,
tetrahydrofuran, ether, toluene, and hexane.
(1) J ohnson, J . V.; Rauckman, S.; Baccanari, P. D.; Roth, B. J . Med.
Chem. 1989, 32, 1942. Carling, R. W.; Leeson, P. D.; Moseley, A. M.;
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K. W.; Moseley, A. M.; Smith, J . D.; Stevenson, G.; Chan, T.; Baker,
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P. D.; Marshall, G. R.; Moseley, A. M.; Smith, J . D.; Saywell, K.;
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Uzh. SSR, 1982, 34-36 (Russ); Chem. Abstr. 1983, 98, 83727q.
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123, 9315x.
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Fleming, I., Eds., Pergamon: Oxford, 1991; Vol. 5, p 401. Boger, D.
L.; Weireb, S. M., Hetero Diels-Alder Methodology in Organic Syn-
thesis, Academic: San Diego, 1987; Chapters 2 and 9. Nomura, Y.;
Kimura, M.; Takeuchi, Y.; Tomoda, S. Chem. Lett. 1978, 267. Boger,
D. L. Tetrahedron 1983, 39, 2869. Kametani, T.; Takeda, H.; Suzuki,
Y.; Honda, T. Heterocycles 1984, 22, 275. Kametani, T.; Takeda, H.;
Suzuki, Y.; Kasai, H.; Honda, T. Heterocycles 1986, 24, 3385. Koichi,
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Prato, M.; Scrrano, G.; Stivanello, M.; Valle, G. J . Chem. Soc., Perkin
Trans. 2 1992, 259. Makioka, Y.; Shindo, T.; Taniguchi, Y.; Takaki,
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M.; Scorrano, G.; Stivanello, M. J . Heterocycl. Chem. 1988, 25, 1831.
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G. J . Chem. Soc., Perkin Trans. 1 1989, 2245. Gilchrist, T. L.; Stannard,
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10.1021/jo982220p CCC: $18.00 © 1999 American Chemical Society
Published on Web 08/03/1999

Notes
J . Org. Chem., Vol. 64, No. 17, 1999 6463
Sch em e 1
F igu r e 1. H-H cross-peaks observed in H-HCOSY spectra
(in CDCl3) of IIa and IIIa .
Sch em e 2
Ta ble 1. Effect of Meta l Sa lts a n d Solven ts on th e
Rea ction of Ben za ld eh yd e, An ilin e, a n d
3,4-Dih yd r o-2H-p yr a n
entry
solvent
catalysta
additive
yield (%)b
1
2
3
4
5
6
7
8
9
10
11
12
13
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
toluene
hexane
THF
None
MgSO4
MgSO4
MgSO4
MgSO4
MgSO4
MgSO4
MgSO4
4 Å MS
MgSO4
MgSO4
MgSO4
MgSO4
MgSO4
no reaction
35
20
25
38
69
86
84
trace
no reaction
22
40
37
LaCl3
SmCl3
CeCl3
NdCl3
YbCl3
GdCl3
GdCl3
GdCl3
GdCl3
GdCl3
GdCl3
GdCl3
CH2Cl2
Et2O
orientation is only possible when the pyran ring and
phenyl group are on opposite sides of the quinoline ring
of IIIa . The H-HCOSY analysis confirms this structural
assignment for IIIa : a strong reciprocal interaction is
found between H-4a and H-10b, a weak one between
protons H-4a and H-5, but none between protons H-10b
and H-5, all in accord with a trans configuration.
The reaction of aldehyde, m-chloroaniline, and dihy-
dropyran gave a mixture of four isomers, IIg, IIg′, IIIg,
and IIIg′, with a ratio of 17:15:61:7, which was deter-
mined by 1H NMR in 78% combined yield. Unfortunately,
the four isomers could not be separated as pure com-
pounds by column chromatography. In addition, the
reaction of 3,4-dichloroaniline with aldehyde and dihy-
dropyran also produced IIh , IIh ′, IIIh , and IIIh ′ in a
ratio of 1:18: 21:60 with an overall yield of 80% (Scheme
3).
a
b
20 mol % of LnCl3 was used. Isolated yield.
Ta ble 2. On e-P ot Syn th esis of P yr a n o[3,2-c]qu in olin es
a
fr om Ald eh yd es Ca ta lyzed by Gd Cl3
substrate
time
productb
overall
entry (amine) R1
R2
R3 (min) ratio of II:III yield (%)
1
2
3
4
5
6
7
8
Ia
Ib
Ic
Id
Ie
If
H
H
H
H
H
H
Cl
H
H
Cl
H
H
H
Cl
H
30
45
30
33:67
42:58
47:53
39:61
35:65
23:77
86
70
75
80
60
81
78
68
CH3 45
OH
H
H
90
30
45
45
OCH3
H
Ig
Ih
Cl Cl
H
a
b
20 mol % of GdCl3 was used. The ratio is based on isolation
by chromatography.
Several amines were examined, and the results are
listed in Table 2. In all cases, the three-component one-
pot reaction proceeded smoothly to give the corresponding
pyrano[3,2-c]quinolines which could be separated by
column chromatography in most cases (Scheme 2).
The structures of compounds II and III were charac-
Further, we examined the reactivity of dihydrofuran
with aldehyde and anilines catalyzed by GdCl3. Thus,
according to our method a catalytic amount of gadolinium
chloride (20 mol %) and anhydrous MgSO4 was treated
at room temperature with a benzaldehyde and aniline
in acetonitrile, followed by addition of 3,4-dihydrofuran
to afford furo[3,2-c]quinolines Va and VIa in a ratio of
35:65 in an overall yield of 88% (Scheme 4). Therefore,
dihydrofuran exhibited analogous behavior to that of
dihydropyran. Similar results were obtained with other
aldehyde and amines. The results are listed in Table 3.
The structures of compounds V and VI were character-
ized by IR, 1H NMR, 13C NMR, MS, and elemental
analyses.
The X-ray analysis of compound IIIh and VIb was
achieved in order to confirm their molecular structure
as shown in Figures 2 and 3. The results clearly dem-
onstrate that compound IIIh is cis16 and VIb is the trans
configuration,17 which are in agreement with 1H NMR
analysis.
1
terized by IR, H NMR, 13C NMR, MS, and elemental
analyses. There are strong NH stretching band at 3200-
3450 cm-1 in the IR spectra. The most diagnostic param-
eter for structural assignment is the scalar coupling
constant between protons H-4a and H-5. In the isomer
IIa the coupling constant J (4a, 5) ) 5.6 Hz is significantly
smaller and typical for a gauche conformation. This
orientation is present in both conformers of the config-
uration having cis orientation of the pyran ring and
phenyl group. As expected for this configuration, recipro-
cal H-HCOSY (Figure 1) interaction was observed
among protons H-4a, H-5, and H-10b. In the isomer IIIa ,
the J (4a, 5) ) 10.8 Hz is relevant and indicative of the
antireciprocal orientation of protons H-5 and H-4a. This

6464 J . Org. Chem., Vol. 64, No. 17, 1999
Notes
Sch em e 3
Ta ble 3. On e-P ot Syn th esis of F u r o[3,2-c]qu in olin es
Sch em e 4
a
fr om Ald eh yd e Ca ta lyzed by Gd Cl3
substrate time
entry (amine) (min) ratio of V:VI yield (%)
productb
overall
R2
R1
1
2
3
4
5
6
IVa
IVb
IVc
IVd
IVe
IVf
H
H
CH3
OH
H
H
OCH3
H
H
Cl
30
30
30
60
30
35:65
45:55
25:75
48:52
38:62
40:60c
88
80
74
67
68
61
H
NO2
120
a
b
20 mol % of GdCl3 was used. The ratio is based on isolation
by chromatography. c The ratio is determined by 1H NMR.
using TMS as internal standard. 13C NMR spectral measure-
ments were performed at 75.4 MHz using CDCl3 as an internal
standard. IR spectra were obtained on FTS-185 as neat films.
Mass spectra were determined on a Finigan 8230 mass spec-
trometer. Benzylideneaniline was prepared from aniline and
benzaldehyde.18
Rea ction of Ben zylid en ea n ilin e w ith 3,4-Dih yd r o-2H-
p yr a n . GdCl3 (0.2 mmol), benzylideneaniline (1.0 mmol), and
3,4-dihydro-2H-pyran (1.4 mmol) were mixed in 5 mL of aceto-
nitrile, the mixture was stirred for 30 min at room temperature,
water was added, and the product was extracted with EtOAc.
The organic layer was dried with anhydrous Na2SO4 and
evaporated to give the crude product. Analytically pure products
It can be concluded that gadolinium chloride is an
efficient catalyst both in the reaction of imines with
dihydropyran or dihydrofuran and in the one-pot reaction
of aldehydes, amines, and dihydropyran or dihydrofuran
to afford dihydropyrano[3,2-c]- or furo[3,2-c]quinolines in
high yields under mild conditions. Further synthetic
application of these reactions is now in progress.
Exp er im en ta l Section
Gen er a l. CH3CN was distilled from CaH2 under Ar. 1H NMR
(17) For compound VIb: C18H19NO2, M ) 281.35, triclinic, space
group P1 (No. 2), crystal dimensions 0.2 × 0.2 × 0.3 mm, colorless
prismatic crystal, a ) 9.387(1) Å, b ) 11.442(2) Å, R ) 91.73(2)°, â )
101.62(1)°, γ ) 79.83(1)°, µ ) 728.5(2)°A3, by least-squares refinement
using the setting angles of 16 carefully centered reflections in the range
of 18.87 < 2θ < 21.6°, Z ) 2, Dc ) 1.283 g cm-3, F(000) ) 300.00. Data
collection and processing: Rigaku AFC7R diffractometer, graphite
monochromatic Mo-KR radiation (λ ) 0.71069 Å), µ(Mo-KR) ) 0.83
cm-1, 2736 reflections measured, maximum 2θ value 50.0°, 2564 unique
reflections measured (Rint ) 0.018), 1891 of these with I > 2.00σ(I)
used in refinement. The data were corrected for horizon and polariza-
tion effects. A correction for secondary extinction was applied (coef-
and 13C NMR spectra were recorded at 300 or 400 MHz in CDCl3
(16) For compound IIIh : C18H17Cl2NO, M ) 334.24, triclinic, space
group P1 (No. 2), crystal dimensions 0.2 × 0.2 × 0.3 mm, colorless
prismatic crystal, a ) 9.534(1) Å, b ) 11.2904(8) Å, R ) 93.730(8)°, â
) 107.215(8)°, γ ) 71.441(7)°, µ ) 787.4(1)°A3 by least-squares
refinement using the setting angles of 16 carefully centered reflections
in the range of 18.29 < 2θ < 24.56°, Z ) 2, Dc ) 1.41 g cm-3, F(000)
) 3348.00. Data collection and processing: Rigaku AFC7R diffracto-
meter, graphite monochromatic Mo-KR radiation (λ ) 0.71069 Å),
µ(Mo-KR) ) 4.12 cm-1, 2257 reflections measured, maximum 2θ value
of 49.9°, 2097 unique reflections measured (Rint ) 0.023), 1645 of these
with I > 2.00σ(I) used in refinement. The data were corrected for
horizon and polarization effects. The intensities of three representative
reflections were measured after every 200 reflections. Over the course
of data collection, the standards increased by 1.1%. A linear correction
factor was applied to the data to account for this phenomenon.
Structure solution of refinement: The structure was solved by direct
methods using SHELXS-86 expanded using a Fourier technique. The
non-hydrogen atoms were refined anisotropically. Hydrogen atoms
were included but not refined. The final cycle of full-matrix least
squares refinement was based on 1464 observed reflections of 199
variable parameters. Refinement converged at a final R ) 0.034 and
Rw ) 0.043. Max/min peaks in final difference map, 0.36/-0.22. All
calculations were performed using the TEXSAN crystallographic
software package of Molecular Structure Corp.
ficient
)
3.23461×100.6). The intensities of three representative
reflections were measured after every 200 reflections. Over the course
of data collection, the standards increased by 1.1%. A linear correction
factor was applied to the data to account for this phenomenon.
Structure solution of refinement: The structure was solved by direct
methods using SHELXS-86 of expanded using a Fourier technique.
The non-hydrogen atoms were refined anisotropically. Hydrogen atoms
were included but not refined. The final cycle of full-matrix least
squares refinement was based on 1891 observed reflections of 267
variable parameters. Refinement converged at a final R ) 0.036 and
Rw ) 0.043. Max/min peaks in final difference map 0.2/-0.12. All
calculations were performed using the TEXSAN crystallographic
software package of Molecular Structure Corporation.
(18) Katagiri, N. Miura, Y.; Niwa, R.; Xato, T. Chem. Pharm. Bull.
1983, 31, 538.

Notes
J . Org. Chem., Vol. 64, No. 17, 1999 6465
4.68 (1H, d, J ) 2.6 Hz), 3.58-3.85 (3H, m), 2.15 (1H, m), 1.50-
1.25 (4H, m); 13C NMR δ 145.2, 141.2, 128.4, 128.1, 127.7, 127.6,
126.9, 120.0, 118.4, 114.5, 72.8, 60.7, 59.4, 39.0, 25.5, 18.1; IR
(KBr) 3313 cm-1; MS (m/e) 265 (M+, 41), 206 (100). Anal. Calcd
for C18H19NO: C, 81.52; H, 7.16; N, 5.28. Found: C, 81.28; H,
7.23; N, 5.32.
IIIa : viscous oil; 1H NMR δ 7.42-7.36 (5H, m), 7.25 (1H, dd,
J ) 7.1, 0.5 Hz), 7.07 (1H, td, J ) 7.0, 1.3 Hz), 6.70 (1H, td, J )
7.0, 1.1 Hz), 6.51 (1H, dd, J ) 7.1, 1.0 Hz), 4.72 (1H, d, J ) 10.8
Hz), 4.39 (1H, d, J ) 2.7 Hz), 4.08 (2H, m), 3.71 (1H, td, J )
11.6, 2.5 Hz), 2.11 (1H, m), 1.83 (1H, m), 1.66 (1H, m), 1.48 (1H,
m), 1.25 (1H, m); 13C NMR δ 144.7, 142.3, 130.9, 129.3, 128.6,
127.9, 127.8, 120.7, 117.4, 114.2, 74.5, 68.5, 54.9, 38.9, 24.1, 22.1;
IR (KBr) 3373 cm-1; MS (m/e) 265 (M+, 42), 206 (100). HRMS
calcd for C18H19NO: 265.1471. Found: 265.1431.
A Typ ica l P r oced u r e for On e-P ot Rea ction of Ben za l-
d eh yd e, An ilin e, a n d 3, 4-Dih yd r o-2H-p yr a n . To a suspen-
sion of GdCl3 (0.2 mmol) and 4 Å molecular sieves or MgSO4
(125 mg) were added an aldehyde (1.0 mmol) in CH3CN (0.5 mL)
and aniline (1.1 mmol) in CH3CN (0.5 mL) at room temperature.
The mixture was stirred for 10 min at room temperature. Then
3,4-dihydro-2H-pyran (1.4 mmol) was added. The mixture was
further stirred for 30 min and it was then filtered through a
short plug of silica gel. After evaporation of the filtrate, the
residue was chromatographied on silica gel to afford the pure
products (IIa and IIIa ) in 86% yield.
The following compounds were prepared similarly.
IIb: mp 154-156 °C; 1H NMR δ 7.39-7.29 (6H, m),7.12 (1H,
d, J ) 7.6 Hz), 6.65 (1H, t, J ) 7.6 Hz), 5.29 (1H, d, J ) 5.4 Hz),
4.68 (1H, d, J ) 2.3 Hz), 4.41 (1H, br, s), 3.55 (1H, m), 3.33 (1H,
m), 2.12 (1H, m), 1.50-1.41 (2H, m), 1.20 (2H, m); IR (KBr) 3306
cm-1; MS (m/e) 299 (M+, 46), 240 (100). Anal. Calcd for C18H18
-
ClNO: C, 72.15; H, 6.01; N, 4.67. Found: C, 71.35; H, 6.00; N,
4.85.
IIIb: mp 109-101 °C ; 1H NMR δ 7.39-7.27 (5H, m), 7.15
(2H, m), 6.64 (1H, t, J ) 7.7 Hz), 4.66 (1H, d, J ) 10.7 Hz), 4.58
(1H, br, s), 4.34 (1H, d, J ) 2.7 Hz), 4.04 (1H, dt, J ) 10.0, 2.1
Hz), 3.66 (1H, td, J ) 10.8, 2.6 Hz), 2.01 (1H, m), 1.85 (1H, m),
1.63 (1H, m), 1.48 (1H, m), 1.30 (1H, m); 13C NMR δ 141.9 141.0,
129.7, 129.3, 129.2, 128.8, 128.1, 127.8, 121.9, 118.1, 117.0, 74.4,
68.6, 54.9, 38.8, 24.0, 22.1; IR (KBr) 3384 cm-1; MS (m/e) 301
F igu r e 2. X-ray molecular structure of IIIh with the atom
numbering scheme.
(M + 2, 14), 299 (M+, 38), 240 (100). Anal. Calcd for C18H18
-
ClNO: C, 72.15; H, 6.01; N, 4.67. Found: C, 72.10; H, 5.99; N,
4.85.
IIc: mp 170-172 °C; 1H NMR δ 7.39-7.32 (6H, m), 7.01 (1H,
dd, J ) 8.2, 0.7 Hz), 6.50 (1H, d, J ) 8.0 Hz), 5.25 (1H, d, J )
5.5 Hz), 4.60 (1H, d, J ) 2.5 Hz), 3.85 (1H, br), 3.60 (1H, m),
3.41 (1H, m), 2.13 (1H, m), 1.51 (3H, m), 1.25 (1H, m); 13C NMR
δ 143.7, 140.7, 128.5, 128.1, 127.7, 127.3, 126.8, 123.1, 121.7,
115.6, 72.5, 60.8, 59.3, 38.6, 25.3, 18.1; IR (KBr) 3370 cm-1; MS
(m/e) 301 (M+2, 33), 299 (M+, 99), 240 (100). Anal. Calcd for
C
18H18ClNO: C, 72.15; H, 6.01, N; 4.67. Found: C, 72.02; H,
6.01; N, 4.78.
IIIc: mp 125-126 °C; 1H NMR δ 7.39-7.30 (5H, m), 7.19 (1H,
d, J ) 2.3 Hz), 7.01 (1H, dd, J ) 8.0, 1.9 Hz), 6.41 (1H, d, J )
8.1 Hz), 4.63 (1H, d, J ) 10.6 Hz), 4.30 (1H, d, J ) 2.8 Hz), 4.02
(2H, m), 3.66 (1H, td, J ) 15.0, 3.0 Hz), 2.01 (1H, m), 1.75 (1H,
m), 1.62 (1H, m), 1.45 (1H, m), 1.27(1H, m); 13C NMR δ 143.3,
142.0, 130.4, 129.2, 128.7, 128.0, 127.7, 121.9, 121.8, 115.3, 74.0,
68.5, 55.0, 38.7, 24.0, 22.1; IR (KBr) 3298 cm-1; MS (m/e) 301
(M+2, 19), 299 (M+, 58), 240 (100). Anal. Calcd for C18H18
-
ClNO: C, 72.15; H, 6.01; N, 4.67. Found: C, 72.12; H, 6.02; N,
4.81.
IId : mp 143-144 °C; 1H NMR δ 7.48-7.32 (6H, m), 7.03 (1H,
dd, J ) 7.5, 0.6 Hz), 6.75 (1H, t, J ) 7.5 Hz), 5.37 (1H, d, J )
5.5 Hz), 4.71 (1H, d, J ) 2.4 Hz), 3.85-3.34 (3H, m), 2.15 (4H,
s), 1.32-1.29 (4H, m); 13C NMR δ 143.3, 141.5, 129.2, 128.5,
127.6, 126.9, 125.5, 121.6, 119.5, 117.8, 73.0, 60.7, 59.3, 38.8,
25.5, 18.1, 17.5; IR (KBr) 3338 cm-1; MS (m/e) 279 (M+, 62), 220
(100). Anal. Calcd for C19H21NO: C, 81.73; H, 7.52; N, 5.01.
Found: C, 81.33; H, 7.63; N, 5.02.
F igu r e 3. X-ray molecular structure of VIb with the atom
numbering scheme.
IIId : mp 130-132 °C; 1H NMR δ 7.48-7.44 (2H, m), 7.42-
7.39 (2H, m), 7.33-7.31 (1H, m), 7.12 (1H, dd, J ) 7.5, 1.2 Hz),
7.03 (1H, dd, J ) 7.5, 0.6 Hz), 6.66 (1H, t, J ) 7.5 Hz), 4.77 (1H,
d, J ) 9.9 Hz), 4.40 (1H, d, J ) 2.7 Hz), 4.11 (1H, dt, J ) 12.3,
2.3 Hz), 3.90 (1H, br), 3.73 (1H, td, J ) 11.7, 2.5 Hz), 2.11 (1H,
m), 2.07 (3H, s), 1.87 (1H, m), 1.69 (1H, m), 1.49 (1H, m), 1.32
(IIa and IIIa ) were then obtained by column chromatography
in 86% yield.
IIa : mp 130-132 °C (lit.7 mp 128.8-131 °C ); 1H NMR δ 7.43-
7.25 (6H, m), 7.03 (1H, tt, J ) 7.6, 0.7 Hz), 6.77 (1H, td, J ) 7.6,
1.0 Hz), 6.58 (1H, dd, J ) 7.8, 0.9 Hz), 5.31 (1H, d, J ) 5.6 Hz),

6466 J . Org. Chem., Vol. 64, No. 17, 1999
Notes
(1H, m); 13C NMR δ 142.8, 142.7, 130.3, 128.9, 128.7, 128.0,
127.9, 121.2, 120.2, 117.0, 74.9, 68.7, 55.0, 38.9, 24.2, 22.1, 17.3;
IR (KBr) 3389 cm-1; MS (m/e) 279 (M+, 40), 220 (100). HRMS
calcd for C19H21NO: C, 81.73; H, 7.52; N, 5.01. Found: C, 81.70;
H, 7.65; N, 5.13.
11.0 Hz), 3.62 (1H, td, J ) 11.0, 2.6 Hz), 1.96 (1H, m), 1.75 (1H,
m), 1.55 (1H, m), 1.46-1.25 (2H, m); IR (KBr) 3380 cm-1; MS
(m/e) 335 (M+ + 2, 26), 333 (M+, 40), 274 (100). HRMS calcd for
C
18H17Cl2NO: 333.0680. Found: 333.0642.
A Typ ica l P r oced u r e for On e-P ot Rea ction of Ben za l-
IIe: mp 218-219 °C; 1H NMR δ 7.41-7.20 (6H, m), 7.01 (1H,
t, J ) 3.8 Hz), 6.60 (2H, t, J ) 3.0 Hz), 5.30 (1H, d, J ) 5.2 Hz),
4.75 (1H, br), 4.62 (1H, m), 3.54 (1H, dt, J ) 9.8, 2.1 Hz), 3.37
d eh yd e, Am in e, a n d 2, 3-Dih yd r ofu r a n . To a suspension of
GdCl3 (0.2 mmol) and 4 Å molecular sieves or MgSO4 (125 mg)
were added an aldehyde (1.0 mmol) in CH3CN (0.5 mL) and an
amine (1.1 mmol) in CH3CN (0.5 mL) at room temperature. The
mixture was stirred for 10 min at room temperature. Then 2,3-
dihydrofuran (1.4 mmol) was added. The mixture was further
stirred for 30-120 min and then filtered through a short plug
of silica gel. After evaporation of the filtrate, the residue was
chromatographed on silica gel to afford the pure products (V and
VI) in 61-88% yield.
(1H, td, J ) 11.2, 2.5 Hz), 2.11 (1H, m), 1.52-1.25 (4H, m); 13
C
NMR δ 142.0, 141.2, 134.3, 128.4, 127.5, 126.9, 121.2, 120.0,
117.3, 113.3, 77.2, 73.0, 60.9, 59.1, 38.9, 25.4, 18.1; IR (KBr)
3397, 3238 cm-1; MS (m/e) 281 (M+, 100). Anal. Calcd for C18H19
-
NO2: C, 76.87; H, 6.76; N, 4.98. Found: C, 76.93; H, 6.75; N
5.15.
IIIe: mp 190-191 °C; 1H NMR δ 7.47-7.36 (6H, m), 6.88 (1H,
dd, J ) 7.1, 0.8 Hz), 6.65 (2H, m), 4.73(1H, d, J ) 10.6 Hz), 4.44
(1H, d, J ) 2.5 Hz),4.30 (1H, br), 4.11 (1H, dt, J ) 8.8, 2.0 Hz),
3.73 (1H, td, J ) 8.9, 2.4 Hz), 2.14 (1H, m), 1.83 (1H, m), 1.67
(1H, m), 1.51 (1H, m), 1.33 (1H, m); 13C NMR δ 142.3, 141.8,
134.2, 129.2, 129.0, 128.8, 128.3, 127.9, 123.3, 121.8, 116.7, 114.4,
74.3, 68.7, 54.7, 39.0, 24.2, 22.1; IR (KBr) 3390, 3372 cm-1; MS
(m/e) 281 (M+, 94), 222 (100). Anal. Calcd for C18H19NO2: C,
76.87; H, 6.76; N, 4.98. Found: C, 77.10; H, 6.86; N, 5.11
IIf: mp 144-146 °C (lit.7 144-146 °C); 1H NMR δ 7.44-7.26
(5H, m),7.02 (1H, d, J ) 2.8 Hz), 6.75 (1H, dd, J ) 8.7, 2.8 Hz),
6.60 (1H, d, J ) 8.7 Hz), 5.30 (1H, d, J ) 5.3 Hz), 4.60 (1H, d,
J ) 1.9 Hz), 3.75 (3H, s), 3.55 (1H, m), 3.33(1H, m), 3.85-3.12
Va : mp 117-118 °C (lit.7 mp 95 °C ); 1H NMR δ 7.47-7.26
(6H, m), 7.08 (1H, td, J ) 7.8, 1.5 Hz), 6.80 (1H, td, J ) 7.8, 1.1
Hz) 6.59 (1H, dd, J ) 7.8, 1.0 Hz), 5.26 (1H, d, J ) 8.0 Hz), 4.69
(1H, d, J ) 3.0 Hz), 3.77 (3H, m), 2.75 (1H, m), 2.19 (1H, m),
1.50 (1H, m); 13C NMR δ 144.9, 142.2, 130.1, 128.6, 128.3, 127.6,
126.5, 122.7, 119.2, 114.9, 75.9, 66.8, 57.5, 45.8, 24.7; IR (KBr)
3348 cm-1; MS (m/e) 251 (M+, 85), 206 (100). Anal. Calcd for
C
17H17NO: C, 81.28; H, 6.77; N, 5.58. Found: C, 80.88; H, 6.65;
N, 5.29.
VIa : viscous oil; 1H NMR δ 7.46-7.24 (6H, m), 7.12 (1H, td,
J ) 7.7, 1.1 Hz), 6.79 (1H, td, J ) 7.8, 0.9 Hz), 6.62 (1H, d, J )
8.0 Hz), 4.59 (1H, d, J ) 5.1 Hz), 4.08 (1H, m), 3.85 (3H, m),
2.45 (1H, m), 2.01 (1H, m), 1.72 (1H, m); 13C NMR δ 145.3, 141.7,
131.1, 128.8, 128.6, 128.2, 128.0, 120.0, 118.2, 114.6, 76.1, 65.0,
57.6, 43.3, 28.7; IR (KBr) 3327 cm-1; MS (m/e) 251 (M+, 68), 206
(100). HRMS calcd for C17H17NO: 251.1299. Found: 251.1409.
Vb: mp 132-133 °C; 1H NMR δ 7.46-7.25 (5H, m), 6.96 (1H,
d, J ) 2.8 Hz), 6.73 (1H, dd, J ) 8.6, 2.8 Hz), 6.52 (1H, d, J )
8.7 Hz), 5.23 (1H, d, J ) 8.0 Hz), 4.64 (1H, d, J ) 2.9 Hz), 3.77
(3H, s), 3.52-3.80 (3H, m), 2.75 (1H, m), 2.20 (1H, m), 1.52 (1H,
m); 13C NMR δ 153.1, 142.4, 139.0, 128.6, 127.6, 126.5, 123.5,
116.2, 115.8, 113.8, 76.3, 66.9, 57.9, 55.7, 45.9, 24.5; IR (KBr)
3300 cm-1; MS (m/e) 282 (M+ + 1, 29), 281 (100). Anal. Calcd
for C18H19NO2: C, 76.87; H, 6.76; N, 4.98. Found: C, 76.80; H,
6.77; N, 5.06.
(1H, br), 2.08 (1H, m), 1.48-1.24 (4H, m); IR (KBr) 3401 cm-1
;
MS (m/e) 295 (M+, 100). Anal. Calcd for C19H21NO2: C, 77.30;
H, 7.11; N, 4.74. Found: C, 77.12; H, 7.25; N 4.95.
IIIf: mp 98-100 °C; 1H NMR δ 7.37-7.27 (5H, m), 6.79 (1H,
d, J ) 2.8 Hz), 6.65 (1H, dd, J ) 8.4, 2.8 Hz), 6.45 (1H, d, J )
8.4 Hz), 4.60 (1H, d, J ) 10.4 Hz), 4.31(1H, d, J ) 2.8 Hz), 4.04
(1H, m), 3.70 (3H, s), 3.64 (1H, m), 2.05 (1H, m), 1.75 (1H, m)
1.61 (1H, m), 1.43 (1H, m), 1.25 (1H, m); 13C NMR δ 152.0, 142.4,
139.0, 128.6, 127.8, 121.4, 116.9, 115.5, 114.9, 74.6, 68.5, 55.9,
55.3, 39.0, 24.2, 22.1. IR (KBr) 3373 cm-1; MS (m/e) 295 (M+,
100). Anal. Calcd for C19H21NO2: C, 77.30; H, 7.11; N 4.74.
Found: C, 77.48; H, 7.23; N, 4.92.
IIg a n d IIg′: 1H NMR δ 7.38-7.27 (11H, m), 7.00 (1H, t, J
) 7.9 Hz), 6.75 (2H, t, J ) 7.7 Hz), 6.58 (1H, d, J ) 1.8 Hz),
6.50 (1H, d, J ) 7.9 Hz), 5.26 (1H, d, J ) 5.6 Hz), 5.05 (1H, d,
J ) 4.7 Hz), 4.67 (1H, d, J ) 2.5 Hz), 4.52 (1H, d, J ) 4.4 Hz),
3.76-4.30 (1H, b r), 3.34-3.65 (5H, m), 2.35 (1H, m), 2.14 (1H,
1
VIb: mp 94-96 °C; H NMR δ 7.46-7.39 (5H, m), 6.99 (1H,
d, J ) 2.8 Hz), 6.80 (1H, dd, J ) 8.1, 2.8 Hz), 6.61 (1H, d, J )
8.1 Hz), 4.63 (1H, d, J ) 5.3 Hz), 4.06 (1H, m), 3.78 (3H, s),
3.87-3.73 (2H, m), 2.49 (1H, br), 2.01 (1H, m), 1.70 (1H, m),
1.20 (1H, m); IR (KBr) 3298 cm-1; MS (m/e) 282 (M+ + 1, 3),
220 (100). Anal. Calcd for C18H19NO2: C 76.87; H, 6.76; N, 4.98.
Found: C, 77.02; H, 6.85; N, 5.17.
m), 1.78 (2H, m), 1.49 (3H, m), 1.28 (3H, m); IR (KBr) 3356 cm-1
;
MS (m/e) 301 (M+ + 2, 13), 299 (M+, 38), 240 (100). Anal. Calcd
for C18H18ClNO: C, 72.15; H, 6.01; N, 4.67. Found: C, 71.94; H,
6.12; N, 4.69.
1
Vc: mp 102-103 °C; HNMR δ 7.51-7.33 (5H, m), 7.25 (1H,
IIIg a n d IIIg′: 1H NMR δ 7.44-7.32 (10H, m), 7.11 (1H, m),
6.94 (1H, t, J ) 8.0 Hz), 6.73 (1H, d, J ) 8.0 Hz), 6.67 (1H, d, J
) 8.0 Hz), 6.39 (1H, s), 6.46 (1H, t, J ) 8.1 Hz), 4.76 (3H, m),
4.39 (1H, d, J ) 2.5 Hz), 4.18 (2H, dd, J ) 12.0, 4.5 Hz), 4.60-
3.80 (2H, br), 3.75 (2H, td, J ) 12.1, 2.3 Hz), 2.02-1.87 (4H, m),
1.80 (2H, m), 1.67 (2H, m), 1.49 (2H, m), 1.28 (2H, m); 13C NMR
δ (IIIg) 146.2, 141.8, 136.1, 129.8, 128.7, 128.1, 127.9, 118.0,
117.9, 112.8, 72.0, 69.0, 54.2, 38.8, 23.9, 21.8; IR (KBr) 3388
cm-1; MS (m/e) 301 (M + 2, 13), 299 (M+, 38), 240 (100). Anal.
Calcd for C18H18ClNO: C, 72.15; H, 6.01; N, 4.67. Found: C,
71.73; H, 5.99; N, 4.78.
d, J ) 6.6 Hz), 6.99 (1H, d, J ) 6.6 Hz), 6.77 (1H, t, J ) 7.5 Hz),
5.32 (1H, d, J ) 8.0 Hz), 4.70 (1H, d, J ) 3.0 Hz), 3.80-3.66
(3H, m), 2.79 (1H, m), 2.20 (1H, m), 2.14 (3H, s), 1.46 (1H, m);
13C NMR δ 143.1, 142.5, 129.4, 128.7, 127.9, 127.7, 126.6, 122.2,
121.8, 118.4, 76.2, 66.7, 57.3, 45.6, 24.6, 17.2; IR (KBr) 3322
cm-1; MS (m/e) 265 (M+, 100). HRMS calcd forC18H19NO:
265.1457. Found: 265.1467.
1
VIc: mp 92-94 °C; H NMR δ 7.46-7.26 (6H, m), 6.99 (1H,
d, J ) 7.4 Hz), 6.72 (1H, t, J ) 7.5 Hz), 4.55 (1H, d, J ) 4.9 Hz),
4.02 (2H, m), 3.82 (2H, m), 2.43 (1H, m), 2.08 (3H, s), 1.92 (1H,
m), 1.65 (1H, m); 13C NMR δ 143.4, 142.0, 130.0, 129.1, 128.7,
128.4, 128.2, 121.7, 119.4, 117.8, 76.5, 65.1, 57.8, 43.2, 28.9, 17.2;
IR (KBr) 3401 cm-1; MS (m/e) 265 (M+, 73), 220 (100). Anal.
Calcd for C18H19NO: C, 81.48; H, 7.16; N, 5.28. Found: C, 81.63;
H, 7.28; N, 5.43.
IIh a n d IIh ′: 1H NMR δ 7.53-7.16 (10H, m), 7.08 (1H, d, J
) 8.9 Hz), 6.84 (1H, s), 6.61 (1H, s), 6.35 (1H, d, J ) 8.9 Hz),
5.15 (1H, d, J ) 5.1 Hz), 4.91 (1H, d, J ) 4.5 Hz), 4.59 (1H, d,
J ) 4.2 Hz), 4.40 (1H, d, J ) 4.8 Hz), 4.20 (2H, br), 3.45 (4H,
m), 2.30 (2H, m), 1.84-1.40 (4H, m), 1.27 (2H, m), 0.88 (2H, m);
IR (KBr) 3402 cm-1; MS (m/e) 335 (M+ + 2, 25), 333 (M+, 39),
274 (100). HRMS calcd for C18H17Cl2NO: 333.0680. Found:
333.0750.
Vd : mp 188-189 °C; 1H NMR δ 7.53-7.44 (2H, m), 7.38-
7.26 (4H, m), 7.01 (1H, d, J ) 8.4 Hz), 6.71 (2H, m), 5.31 (1H, d,
J ) 6.5 Hz), 4.80 (1H, br), 4.68 (1H, s), 3.79 (2H, m), 2.81 (1H,
m), 2.25 (1H, m), 1.58 (1H, m); 13C NMR δ (300 MHz in DMSO-
d6) 143.7, 143.6, 142.6, 134.2, 128.3, 127.1, 126.3, 122.8, 120.1,
117.4, 112.6, 112.5, 75.2, 65.7, 56.3, 45.0, 24.3; IR (KBr) 3385
cm-1; MS (m/e) 267 (M+, 100). HRMS calcd for C17H17NO2:
267.1282. Found: 267.1512.
VId : mp 155-156 °C; 1H NMR δ 7.61-7.25 (6H, m), 7.01 (1H,
d, J ) 8.0 Hz), 6.69 (2H, m), 4.65 (1H, d, J ) 5.0 Hz), 4.07 (1H,
m), 3.87 (2H, m), 4.10-3.50 (1H,br), 2.63 (1H, m), 2.04 (1H, m),
1.69 (1H, m); 13C NMR δ 142.5, 141.7, 134.8, 128.7, 128.4, 128.2,
123.4, 121.2, 117.8, 114.1, 76.2, 65.3, 57.7, 43.4, 28.9. IR (KBr)
IIIh : mp 198-200 °C; 1H NMR δ 7.36-7.21(5H, m), 7.08 (1H,
d, J ) 9.1 Hz,), 6.30 (1H, d, J ) 9.1 Hz, 8 Hz), 4.66 (2H, m),
4.10 (1H, dd, J ) 18, 4.5 Hz), 3.85 (1H, br), 3.65 (1H, td, J )
12.2, 2.5 Hz), 1.90 (1H, m), 1.82 (1H, m), 1.61 (1H, m), 1.41 (1H,
m), 1.26 (1H, m); 13C NMR δ 144.6, 141.3, 134.0, 130.3, 128.8,
128.3, 127.9, 120.0, 113.7, 72.5, 69.1, 54.0, 38.6, 23.8, 21.8; IR
(KBr) 3378 cm-1; MS (m/e) 335 (M + 2, 17), 333 (M+, 26), 274
(100). HRMS calcd for C18H17Cl2NO: 333.0680. Found: 333.0750
IIIh ′: 1H NMR δ 7.31 (5H, m), 7.18 (1H, s), 6.56 (1H, s), 4.55
(1H, d, J ) 10.0 Hz), 4.25 (1H, d, J ) 2.6 Hz), 4.00 (1H, d, J )

Notes
J . Org. Chem., Vol. 64, No. 17, 1999 6467
3397, 3193 cm-1; MS (m/e) 267 (M+, 83), 222 (100). HRMS calcd
for C17H17NO2: 267.1255. Found: 267.1295.
8.0, 1.5 Hz), 7.75 (10H, m), 6.58 (1H, d, J ) 9.0 Hz), 6.54 (1H, d,
J ) 9.0 Hz), 5.25 (1H, d, J ) 7.5 Hz), 4.84 (1H, d, J ) 3.2 Hz),
4.75 (1H, br), 4.60 (2H, d, J ) 4.6 Hz), 4.10 (1H, m), 3.80-2.80
(4H, m), 2.80 (1H,m), 2.48 (1H, m), 2.10 (2H, m), 1.82 (1H, m),
1.64 (1H, m), 1.25 (1H, m); 13C NMR δ 150.5, 149.8, 140.6, 140.2,
129.1, 129.0, 128.8, 128.5, 128.4, 128.2, 127.0, 126.4, 125.7, 124.9,
121.8, 118.7, 113.9, 113.8, 75.4, 74.8, 66.9, 65.2, 57.1, 56.5, 44.7,
42.5, 28.6, 24.7; IR (KBr) 3363 cm-1; MS (m/e) 296 (M+, 33), 251
(100). HRMS calcd for C17H16N2O3: 296.1165. Found: 296.1205.
Ve: mp 153-155 °C; 1H NMR δ 7 42-7.21 (6H, m), 6.98 (1H,
dd, J ) 8.50, 3.4 Hz), 6.48 (1H, d, J ) 8.5 Hz), 5.16 (1H, d, J )
7.8 Hz), 4.63 (1H, d, J ) 2.9 Hz), 3.80-3.64 (3H, m), 2.72 (1H,
m), 2.14 (1H, m), 1.50 (1H, m); 13C NMR δ 143.4, 141.9, 129.8,
128.8, 128.4, 127.9, 126.6, 124.2, 123.8, 116.2, 75.7, 67.0, 57.4,
45.5, 24.6; IR (KBr) 3342 cm-1; MS (m/e) 285 (M+, 100). Anal.
Calcd for C17H16ClNO: C, 71.48; H, 5.60; N, 4.90. Found: C,
71.34; H, 5.58; N, 5.13.
VIe: mp 99-101 °C; 1H NMR δ 7.39-7.28 (6H, m), 7.05 (1H,
dd, J ) 8.5, 2.4 Hz), 6.51 (1H, d, J ) 8.5 Hz), 4.50(1H, d, J )
5.1 Hz), 3.89-4.25 (2H, m), 3.78 (2H, m), 2.43 (1H, m), 1.98 (1H,
m), 1.68 (1H, m); 13C NMR δ 144.0, 141.3, 130.8, 128.9, 128.8,
128.3, 128.2, 122.9, 121.6, 115.9, 75.7, 65.3, 57.8, 43.3, 28.8; IR
Ack n ow led gm en t. We thank the National Nature
Science Foundation of China and the Postdoctoral
Foundation for their financial support.
(KBr) 3343 cm-1; MS (m/e) 285 (M+, 100). Anal. Calcd for C17H16
-
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra of
the compounds synthesized. This material is available free of
charge via the Internet at http://pubs.acs.org.
ClNO: C, 71.48; H, 5.60; N, 4.90. Found C, 71.39; H, 5.63; N,
5.07.
Vf a n d VIf: 1H NMR δ 8.31 (1H, d, J ) 2.0 Hz), 8.30 (1H, d,
J ) 2.0 Hz), 8.04 (1H, dd, J ) 8.0, 1.5 Hz), 8.00 (1H, dd, J )
J O982220P