Aryl radical cyclization: Regioselective synthesis of 6a,7,8,12b- tetrahydro-6H-chromeno[3,4-c]quinolin-6-one

Article abstract of DOI:10.1080/00397910801982191

Regioselective synthesis of 6a,7,8,12b-tetrahydro-6H-chromeno[3,4-c] quinolin-6-ones 4 in good to excellent yields from 3-(2-bromoanilinomethyl) coumarins 3 by aryl radical cyclization is described. The cyclization precursors 3 were prepared by the reacti

Full text of DOI:10.1080/00397910801982191

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Aryl Radical Cyclization:
Regioselective Synthesis of
6a,7,8,12b‐Tetrahydro‐6H‐chromeno[3,4‐c]quino
K. C. Majumdar a , P. Debnath a & S. K. Chottopadhyay a
a Department of Chemistry , University of Kalyani , Kalyani, West Bengal,
India
Published online: 09 May 2008.
To cite this article: K. C. Majumdar , P. Debnath & S. K. Chottopadhyay (2008) Aryl Radical Cyclization:
Regioselective Synthesis of 6a,7,8,12b‐Tetrahydro‐6H‐chromeno[3,4‐c]quinolin‐6‐one, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 38:11,
1768-1777, DOI: 10.1080/00397910801982191
To link to this article: http://dx.doi.org/10.1080/00397910801982191
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Synthetic Communicationsw, 38: 1768–1777, 2008
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910801982191
Aryl Radical Cyclization: Regioselective
Synthesis of 6a,7,8,12b-Tetrahydro-6H-
chromeno[3,4-c]quinolin-6-one
K. C. Majumdar, P. Debnath, and S. K. Chottopadhyay
Department of Chemistry, University of Kalyani, Kalyani, West Bengal,
India
Abstract: Regioselective synthesis of 6a,7,8,12b-tetrahydro-6H-chromeno[3,4-
c]quinolin-6-ones 4 in good to excellent yields from 3-(2-bromoanilinomethyl)coumar-
ins 3 by aryl radical cyclization is described. The cyclization precursors 3 were
prepared by the reaction of 3-chloromethyl coumarin with different 2-bromoaniline.
Keywords: Aryl radical cyclization, coumarin derivatives, 6-endo trig, organotin
reagent, tetrahydroquinolines
INTRODUCTION
Substituted coumarin rings are common structural motifs in natural
products,[1] and they constitute attractive synthetic targets because of their
interesting biological and physiological activities.[2] In particular, those
coumarins fused to pyridines have been reported to possess antialergic,[3a]
antidiabetic,[3b] and analgesic properties.[3c] Several efforts have been made
to synthesize them.[4] Galariniotou et al.[5] reported the synthesis of some
pyrido coumarins and benzo-fused azacoumarins. Recently, aryl radical cycli-
zation has been developed as a potential method for preparing various types of
cyclic compounds via intramolecular carbon–carbon bond-forming
processes.[6] The synthesis of nitrogen heterocycles[7] using radical intermedi-
ates has become an invaluable tool in modern chemistry. In the interest of
Address correspondence to K. C. Majumdar, Department of Chemistry, University
of Kalyani, Kalyani 741235, West Bengal, India. E-mail: kcm_ku@yahoo.co.in
1768

Aryl Radical Cyclization
1769
synthesizing new coumarin ring systems of biological interest, we have
prepared a variety of coumarins such as furocoumarin, pyranocoumarin,[8]
and spirocoumarin[9] by using a radical cyclization strategy. In continuation
of our work, we describe here the synthesis of quinoline fused coumarins
via aryl radical cyclization reaction of 3-(2-bromoanilinomethyl)coumarins.
RESULTS AND DISCUSSION
The requisite radical precursors 3-(2-bromoanilinomethyl)coumarins 3a–f
were prepared in 80–92% yields by treating 3-chloromethyl coumarin (1)
with different 2-bromoaniline (2a–f) in refluxing acetone in the presence of
anhydrous potassium carbonate for 5–6 h (Scheme 1). Compounds 3a–f
were characterized from their elemental analyses and spectroscopic data.
A preliminary attempt to effect the desired radical cyclization was carried
out with the substrate 3a. Compound 3a, when heated at 80 8C with nBu3SnH
in dry degassed toluene in the presence of a catalytic amount of azobisisobu-
tyronitrile (AIBN) for 2.5 h, afforded cyclized product tetrahydropyrido[3,4-
c]coumarin (4a) in 81% yield (Scheme 2). Other substrates 3b and 3c were
also similarly treated to give cyclic products 4b and 4c in 85% and 88%
yields, respectively. To extend the scope of this reaction, we also attempted
a similar radical reaction with 3-[2-bromo(N-methyl)anilinomethyl]coumar-
ins 3d, employing similar reaction conditions. Unfortunately, we were
unable to obtain any cyclized product because the starting material decom-
posed under the reaction condition. Changing the solvent (benzene) and
lowering the reaction temperature (50–60 8C) did not divert the reaction
away from the observed decomposition. However, changing the tin reagent
eliminated the decomposition of the starting material. The compound 3d
was heated at 60 8C in dry degassed toluene under a nitrogen atmosphere
n
with radical initiator AIBN, Bu3SnCl, and Na(CN)BH3 for 1 h. Isolation of
the product by flash chromatography furnished solid 4d in 74% yield.
Similarly, other substrates 3e and 3f gave 4e and 4f in 82% and 78% yields,
respectively (Scheme 2). The structure of the product 4 was readily elucidated
Scheme 1. Reagents and conditions: (i) dry acetone, anhyd, K2CO3, reflux, 5–6 h.

1770
K. C. Majumdar, P. Debnath, and S. K. Chottopadhyay
Scheme 2. Reagents and conditions: (i) 00Bu3SnH, AIBN, toluene, 80 8C, 2–2.5 h; (ii)
00Bu3SnCl, Na(CN)BH3, AIBN, toluene, 60 8C, 1 h
from 1H NMR spectroscopy. Compound 4a exhibited one proton multiplet at d
3.18–3.22 and another one proton doublet at d 4.32 (J ¼ 5.6 Hz) due to ring
juncture protons. The stereochemistry of the ring juncture protons can be
surmised from the molecular model (Dreiding model), which showed a
strain-free cis[10] arrangement, and also from the small coupling constant
value (J ¼ 5.6 Hz) of the ring juncture protons of 4. The 13C NMR spectra
of 4a also supported the proposed structure. The mass spectrum of
compound showed a molecular ion peak at m/z ¼ 251 (Mþ).
The formation of the products 4 from 3 may be explained by the gen-
eration of aryl radical 5, which may undergo either a 5-exo trig or a 6-endo-
trig cyclization at the double bond of the pyrone ring of the coumarin
moiety. A 6-endo trig cyclization of radical 5 may produce the intermediate
radical 8, whereas 5-exo trig cyclization may give the spirocycle radical 6
(not isolated), followed by neophyl rearrangement[11] to radical intermediate
n
7. Abstraction of hydrogen by 8 from Bu3SnH may afford 4 (Scheme 3).
However, 5-exo cyclization with subsequent neophyl rearrangement is
unlikely with the present system. The stability and nonnucleophilicity[12]
of the intermediate bezylic radical due to excellent overlapping[13] of
p-orbital of radical center with the adjacent aromatic p-system might
prevent further attack to produce the intermediate cyclohexadienyl radical
7. The stabilization of the intermediate tertiary radical 8 by the adjacent
carbonyl group may also be responsible for the formation of 6-endo
products.
n
In conclusion, we have successfully described the Bu3SnH-mediated
mild and efficient synthesis of coumarin-annulated [6,6] fused nitrogen hetero-
cycles. The use of 2-bromoaniline provides easy access to tetrahydroquinoline
derivatives, which are of synthetic utility in organic synthesis.

Aryl Radical Cyclization
1771
Scheme 3. Mechanism of the cyclization reaction.
EXPERIMENTAL
Melting points were determined in open capillaries and are uncorrected. IR
spectra were recorded on a Perkin-Elmer L 120-000A spectrometer (gmax in
cm21) using samples as neat liquids, and solid samples were recorded
in KBr disks 1H NMR (300 MHz, 400 MHz, 500 MHz) and 13C NMR
(100 MHz, 125 MHz) spectra were recorded on Bruker DPX-300, Varian-
400, and Bruker DPX-500 spectrometers in CDCl3 (chemical shift in d)
with TMS as internal standard. Silica gel (60–120 mesh, Spectrochem,
India) was used for chromatographic separation. Silica gel G (E-Merck,
India) was used for thin-layer chromatography (TLC). Petroleum ether
refers to the fraction boiling between 60 8C and 80 8C.
General Procedure for the Preparation of 3-(2-
Bromoanilinomethyl)coumarins 3a–f
2-Bromoaniline 2a–f (5.15 mmol) and anhydrous potassium carbonate (2 g)
were added to a solution of 3-chloromethylcoumarin (1) (1 g, 5.15 mmol) in
dry acetone (100 mL), and the reaction mixture was refluxed for 5–6 h. The
reaction mixture was then cooled and filtered, and the solvent was removed.
The residual mass was extracted with CH2Cl2 (3 ꢀ 20 mL). The organic
layer was washed with water (3 ꢀ 20 mL) and finally with brine (20 mL).
After removal of the solvent, the residue was subjected to column

1772
K. C. Majumdar, P. Debnath, and S. K. Chottopadhyay
chromatography over silica gel. Elution of the column with 5% ethyl acetate in
petroleum ether afforded 3-(2-bromoanilinomethyl)coumarins 3a–f. All the
compounds were recrystalized from chloroform–methanol.
Data
3-[(2-Bromoanilino)methyl)]-2H-chromen-2-one (3a)
Yield: 82%; colorless solid; mp 105–106; IR (KBr): nmax ¼ 3413, 1714,
1
1601 cm21; H NMR (400 MHz, CDCl3): dH ¼ 4.40 (s, 2H, -NCH2), 4.97
(brs, 1H, NH), 6.54 (d, J ¼ 8.3 Hz, 1H, ArH), 6.61 (t, J ¼ 7.8 Hz, 1H,
ArH), 7.12 (t, J ¼ 8.6 Hz, 1H, ArH), 7.27–7.29 (m, 1H, ArH), 7.35
(d, J ¼ 8.3 Hz, 1H, ArH), 7.43–7.54 (m, 3H, ArH), 7.63 (s, 1H, vinylic H);
13C NMR (100 MHz, CDCl3): dc ¼ 43.2, 109.9, 111.5, 116.5, 118.7, 119.1,
124.5, 125.7, 127.8, 128.6, 131.2, 132.6, 138.2, 144.0, 153.1, 161.1; MS:
m/z ¼ 329, 331 (Mþ). Anal. calcd. for C16H12BrNO2: C, 58.20; H, 3.66; N,
4.24%. Found: C, 58.35; H, 3.59; N, 4.28%.
3-[(2-Bromo-4-methylanilino)methyl)]-2H-chromen-2-one (3b)
Yield: 88%; colorless solid; mp 122–123 8C; IR (KBr): nmax ¼ 3410, 1715,
1
1605 cm21; H NMR (400 MHz, CDCl3): dH ¼ 2.24 (s, 3H, ArCH3), 4.38
(s, 2H, -NCH2), 4.82 (brs, 1H, NH), 6.45 (d, J ¼ 8.3 Hz, 1H, ArH), 6.94
(d, J ¼ 2.5 Hz, 1H, ArH), 7.25–7.38 (m, 3H, ArH), 7.44 (dd, J ¼ 1.5,
7.8 Hz, 1H, ArH), 7.49–7.54 (m, 1H, ArH), 7.63 (s, 1H, vinylic H); MS:
m/z ¼ 343, 345 (Mþ). Anal. calcd. for C17H14BrNO2: C, 59.32; H, 4.10; N,
4.07%. Found: C, 59.15; H, 4.18; N, 4.10%.
3-[(2-Bromo-4-ethylanilino)methyl)]-2H-chromen-2-one (3c)
Yield: 80%; colorless solid; mp 98–99 8C; IR (KBr): nmax ¼ 3408, 1713,
1608 cm21
;
1H NMR (400 MHz, CDCl3): dH ¼ 1.16 (t, J ¼ 7.5 Hz, 3H,
ArCH2CH3), 2.49 (q, J ¼ 7.5 Hz, 2H, ArCH2CH3), 4.36 (s, 2H, -NCH2),
4.80 (brs, 1H, NH), 6.46 (d, J ¼ 8.5 Hz, 1H, ArH), 6.94 (dd, J ¼ 2.0,
8.5 Hz, 1H, ArH), 7.23–7.35 (m, 3H, ArH), 7.42 (dd, J ¼ 1.5, 7.5 Hz, 1H,
ArH), 7.47–7.51 (m, 1H, ArH), 7.62 (s, 1H, vinylic H); MS: m/z ¼ 357,
359 (Mþ). Anal. calcd. for C18H16BrNO2: C, 60.35; H, 4.50; N, 3.91%.
Found: C, 60.42; H, 4.55; N, 4.02%.
3-[(2-Bromo-N-methylanilino)methyl)]-2H-chromen-2-one (3d)
1
Yield: 90%; viscous liquid; IR (KBr): nmax ¼ 1704, 1605 cm21; H NMR
(400 MHz, CDCl3): dH ¼ 2.79 (s, 3H, NCH3), 4.13 (s, 2H, -NCH2),
6.91 (t, J ¼ 7.2 Hz, 1H, ArH), 7.18 (d, J ¼ 7.4 Hz, 1H, ArH), 7.24

Aryl Radical Cyclization
1773
(t, J ¼ 7.4 Hz, 2H, ArH), 7.31 (d, J ¼ 8.1 Hz, 1H, ArH), 7.46–7.51 (m, 2H,
ArH), 7.56 (d, J ¼ 7.6 Hz, 1H, ArH), 8.03 (s, 1H, vinylic H); 13C NMR
(100 MHz, CDCl3): dc ¼ 41.5, 54.7, 116.5, 119.5, 120.0, 122.0, 124.4,
124.8, 125.7, 127.8, 128.4, 130.9, 132.7, 133.9, 139.6, 152.9, 161.5; MS:
m/z ¼ 343, 345 (Mþ). Anal. calcd. for C17H14BrNO2: C, 59.32; H, 4.10; N,
4.07%. Found: C, 59.46; H, 4.13; N, 4.02%.
3-[(2-Bromo-4-dimethylanilino)methyl)]-2H-chromen-2-one (3e)
1
Yield: 92%; viscous liquid; IR (KBr): nmax ¼ 1717, 1608 cm21; H NMR
(500 MHz, CDCl3): dH ¼ 2.31 (s, 3H, ArCH3), 2.77 (s, 3H, -NCH3), 4.11
(s, 2H, -NCH2), 7.07–7.10 (m, 2H, ArH), 7.25–7.28 (m, 1H, ArH), 7.32
(d, J ¼ 8.3 Hz, 1H, ArH), 7.41 (s, 1H, ArH), 7.46–7.52 (m, 2H, ArH), 8.03
(s, 1H, vinylic H); MS: m/z ¼ 357, 359 (Mþ). Anal. calcd. for
C18H16BrNO2: C, 60.35; H, 4.50; N, 3.91%. Found: C, 60.56; H, 4.34; N,
3.95%.
3-[(2-Bromo-4-ethyl-N-methylanilino)methyl)]-2H-chromen-2-one (3f)
1
Yield: 87%; viscous liquid; IR (KBr): nmax ¼ 1710, 1606 cm21; H NMR
(500 MHz, CDCl3): dH ¼ 1.18 (t, J ¼ 7.1 Hz, 3H, ArCH2CH3), 2.55
(q, J ¼ 7.6 Hz, 2H, ArCH2CH3), 2.78 (s, 3H, NCH3), 4.11 (s, 2H, -NCH2),
7.08 (dd, J ¼ 1.9, 8.1 Hz, 1H, ArH), 7.12 (d, J ¼ 8.1 Hz, 1H, ArH), 7.25–
7.28 (m, 1H, ArH), 7.32 (d, J ¼ 7.8 Hz, 1H, ArH), 7.42 (d, J ¼ 1.7 Hz, 1H,
ArH), 7.47–7.52 (m, 2H, ArH), 8.04 (s, 1H, vinylic H); MS: m/z ¼ 371,
373 (Mþ). Anal. calcd. for C19H18BrNO2: C, 61.30; H, 4.87; N, 3.76%.
Found: C, 61.58; H, 4.99; N, 3.86%.
General Procedure for the Radical Cyclization of Compound 3a–f
nBu3SnH Procedure
nBu3SnH (0.12 mL, 0.33 mmol) was added dropwise under a nitrogen atmos-
phere to a magnectically stirred solution of 3(a–c) (0.30 mmol) and AIBN
(25 mg, 0.15 mmol) in dry toluene (5 mL). The reaction mixture was heated
at 80 8C for 2–2.5 h. After completion of the reaction, the solvent was
removed under reduced pressure. The residue was dissolved in CH2Cl2
(20 mL) and stirred with 10% KF solution (20 mL) for 1 h. The organic
phase was washed with water (3 ꢀ 10 mL) and brine (1 ꢀ 20 mL) and dried
(Na2SO4). The solvent was distilled off, and the crude solid was purified by
column chromatography over silica gel (230–400 mesh). Elution of the
column with petroleum ether–ethyl acetate (9:1) gave pure solids 4a–c.

1774
K. C. Majumdar, P. Debnath, and S. K. Chottopadhyay
nBu3SnCl and Na(CN)BH3 Procedure
This procedure is the same as the procedure described previously except that
nBu3SnCl (1.5 equiv.) and Na(CN)BH3 (1.5 equiv.) were added in one portion
n
instead of Bu3SnH at the beginning to the reaction mixture of 3(d–f).
Data
6a,7,8,12a-tetrahydro-6H-chromeno[3,4-c]quinolin-6-one(4a). Yield:81%;
colorless solid; mp 132–133 8C; IR (KBr): nmax ¼ 3390, 1745, 1604 cm21
;
1H NMR (300 MHz, CDCl3): dH ¼ 3.18–3.22 (m, 1H, ring juncture H), 3.51
(dd, J ¼ 3.5, 11.9 Hz, 1H, -NCH2), 3.82 (dd, J ¼ 4.7, 11.9 Hz, 1H, -NCH2),
4.02 (brs, 1H, NH), 4.32 (d, J ¼ 5.6 Hz, 1H, ring juncture H), 6.52–6.61
(m, 2H, ArH), 6.81 (d, J ¼ 7.5 Hz, 1H, ArH), 7.00–7.08 (m, 2H, ArH), 7.16
(t, J ¼ 7.4 Hz, 1H, ArH), 7.29–7.34 (m, 2H, ArH); 13C NMR (125 MHz,
CDCl3): dc ¼ 37.4, 37.9, 40.5, 115.3, 117.6, 117.7, 117.8, 124.9, 125.9, 128.9,
129.2, 129.6, 130.0, 143.2, 150.9, 167.8; MS: m/z ¼ 251 (Mþ). Anal. calcd.
forC16H13NO2: C, 76.48;H, 5.21;N, 5.57%. Found:C, 76.77; H, 5.27; N, 5.48%.
11-Methyl-6a,7,8,12b-tetrahydro-6H-chromeno[3,4-c]quinolin-6-one (4b).
Yield: 85%; colorless solid; mp 117–119 8C; IR (KBr): nmax ¼ 3394, 1746,
1617 cm21
;
1H NMR (300 MHz, CDCl3): dH ¼ 2.13 (s, 3H, ArCH3),
3.15–3.20 (m, 1H, ring juncture H), 3.47 (dd, J ¼ 3.6, 12.0 Hz, 1H, -NCH2),
3.79 (dd, J ¼ 5.0, 12.0 Hz, 1H, -NCH2), 4.29 (d, J ¼ 5.6 Hz, 1H, ring
juncture H), 6.46 (d, J ¼ 8.1 Hz, 1H, ArH), 6.63 (s, 1H, ArH), 6.83
(d, J ¼ 7.0 Hz, 1H, ArH), 7.06 (d, J ¼ 7.9 Hz, 1H, ArH), 7.17–7.25 (m, 1H,
ArH), 7.30–7.34 (m, 2H, ArH); 13C NMR (125 MHz, CDCl3): dc ¼ 20.9,
37.5, 38.2, 40.6, 115.7, 117.7, 117.8, 124.9, 125.9, 127.2, 129.2, 129.7,
129.9, 130.0, 140.8, 150.9, 169.1; MS: m/z ¼ 265 (Mþ). Anal. calcd. for
C17H15NO2: C, 76.96; H, 5.70; N, 5.28%. Found: C, 76.88; H, 5.86; N, 5.31%.
11-Ethyl-6a,7,8,12b-tetrahydro-6H-chromeno[3,4-c]quinolin-6-one (4c).
Yield: 88%; colorless solid; mp 161–163 8C; IR (KBr): nmax ¼ 3392, 1748,
1618 cm21
;
1H NMR (400 MHz, CDCl3): dH ¼ 1.07 (t, J ¼ 7.6 Hz, 3H,
ArCH2CH3), 2.39 (q, J ¼ 7.5 Hz, 2H, ArCH2CH3), 3.16–3.20 (m, 1H, ring
juncture H), 3.48 (dd, J ¼ 3.0, 11.9 Hz, 1H, -NCH2), 3.76 (dd, J ¼ 4.6,
12.0 Hz, 1H, -NCH2), 3.89 (brs, 1H, NH), 4.30 (d, J ¼ 5.5 Hz, 1H, ring
juncture H), 6.48 (d, J ¼ 8.1 Hz, 1H, ArH), 6.65 (s, 1H, ArH), 6.87
(d, J ¼ 7.9 Hz, 1H, ArH), 7.05 (d, J ¼ 7.9 Hz, 1H, ArH), 7.17–7.25 (m, 1H,
ArH), 7.29–7.32 (m, 2H, ArH); MS: m/z ¼ 279 (Mþ). Anal. calcd. for
C18H17NO2: C, 77.40; H, 6.13; N, 5.01%. Found: C, 77.53; H, 6.18; N, 5.09%.
8-Methyl-6a,7,8,12b-tetrahydro-6H-chromeno[3,4-c]quinolin-6-one (4d).
Yield: 74%; colorless solid; mp 144–145 8C; IR (KBr): nmax ¼ 1750,
1602 cm21
;
1H NMR (400 MHz, CDCl3): dH ¼ 2.97 (s, 3H, -NCH3),

Aryl Radical Cyclization
1775
3.28–3.32 (m, 1H, ring juncture H), 3.54 (dd, J ¼ 4.5, 11.4 Hz, 1H, NCH2),
3.70 (dd, J ¼ 5.2, 11.5 Hz, 1H, -NCH2), 4.33 (d, J ¼ 5.2 Hz, 1H, ring
juncture H), 6.59–6.65 (m, 2H, ArH), 6.78 (d, J ¼ 7.3 Hz, 1H, ArH), 7.06
(d, J ¼ 8.0 Hz, 1H, ArH), 7.13–7.19 (m, 2H, ArH), 7.27–7.33 (m, 2H,
ArH); MS: m/z ¼ 265 (Mþ). Anal. calcd. for C17H15NO2: C, 76.96; H,
5.70; N, 5.28%. Found: C, 77.03; H, 5.66; N, 5.23%.
8,11-Dimethyl-6a,7,8,12b-tetrahydro-6H-chromeno[3,4-c]quinolin-6-one
(4e). Yield: 82%; colorless solid; mp 168–170 8C; IR (KBr): nmax ¼ 1765,
1
1613 cm21; H NMR (500 MHz, CDCl3): dH ¼ 2.30 (s, 3H, ArCH3), 2.95
(s, 3H, -NCH3), 3.26–3.30 (m, 1H, ring juncture H), 3.48 (dd, J ¼ 4.2,
11.7 Hz, 1H, -NCH2), 3.67 (dd, J ¼ 5.2, 11.9 Hz, 1H, -NCH2), 4.32
(d, J ¼ 5.3 Hz, 1H, ring juncture H), 6.55 (d, J ¼ 8.2 Hz, 1H, ArH), 6.61
(d, J ¼ 7.9 Hz, 1H, ArH), 7.01–7.12 (m, 2H, ArH), 7.17–7.22 (m, 1H, ArH),
7.27–7.31 (m, 2H, ArH); MS: m/z ¼ 279 (Mþ). Anal. calcd. for C18H17NO2:
C, 77.40; H, 6.13; N, 5.01%. Found: C, 77.62; H, 6.24; N, 5.04%.
11-Ethyl-8-methyl-6a,7,8,12b-tetrahydro-6H-chromeno[3,4-c]quinolin-6-
one (4f). Yield: 78%; colorless solid; mp 141–143 8C; IR (KBr): nmax ¼ 1746,
1615 cm21
;
1H NMR (500 MHz, CDCl3): dH ¼ 1.10 (t, J ¼ 7.5 Hz, 3H,
ArCH2CH3), 2.43 (q, J ¼ 7.5 Hz, 2H, ArCH2CH3), 2.93 (s, 3H, -NCH3),
3.30–3.34 (m, 1H, ring juncture H), 3.46 (dd, J ¼ 4.5, 11.4 Hz, 1H, -NCH2),
3.62 (dd, J ¼ 5.8, 11.4 Hz, 1H, -NCH2), 4.29 (d, J ¼ 5.6 Hz, 1H, ring
juncture H), 6.57 (d, J ¼ 8.3 Hz, 1H, ArH), 6.65 (d, J ¼ 8.6 Hz, 1H, ArH),
6.98 (dd, J ¼ 1.8, 8.3 Hz, 1H, ArH), 7.07 (d, J ¼ 8.0 Hz, 1H, ArH), 7.15–
7.19 (m, 1H, ArH), 7.24–7.33 (m, 2H, ArH); MS: m/z ¼ 293 (Mþ). Anal.
calcd. for C19H19NO2: C, 77.79; H, 6.53; N, 4.77%. Found: C, 77.89; H,
6.55; N, 4.86%.
ACKNOWEDGMENTS
We thank the CSIR (New Delhi) for financial assistance. Two of us (P. D. and
S. K. C.) are thankful to the Council of Scientific and Industrial Research
(CSIR) (New Delhi) for fellowships. We also thank the DST (New Delhi)
for providing an IR spectrometer under the DST-FIST program.
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