Effect of substitution in stannic chloride-mediated heterocyclization of 4-allyl-3-hydroxyquinolin-2(1H)-ones

Article abstract of DOI:10.1080/00397910600908892

Effect of substituents at the allylic position in a stannic chloride-iodine-mediated heterocyclization of 4-allyl-3-hydroxyquinolin-2(1H)- ones for the regioselective formation of five- and six-membered heterocyclic rings has been rationalized by the application of restricted Hatree-Fock calculation. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910600908892

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Effect of Substitution in Stannic
Chloride–Mediated Heterocyclization of
4
‐Allyl‐3‐hydroxyquinolin‐2(1H)‐ones
a a
K. C. Majumdar & N. Kundu
a
Department of Chemistry , University of Kalyani , Kalyani, West Bengal,
India
Published online: 24 Nov 2006.
To cite this article: K. C. Majumdar & N. Kundu (2006) Effect of Substitution in Stannic Chloride–Mediated
Heterocyclization of 4‐Allyl‐3‐hydroxyquinolin‐2(1H)‐ones, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 36:21, 3191-3201, DOI:
10.1080/00397910600908892
To link to this article: http://dx.doi.org/10.1080/00397910600908892
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Synthetic Communications , 36: 3191–3201, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910600908892
Effect of Substitution in Stannic Chloride–
Mediated Heterocyclization of 4-Allyl-3-
hydroxyquinolin-2(1H)-ones
K. C. Majumdar and N. Kundu
Department of Chemistry, University of Kalyani, Kalyani, West Bengal,
India
Abstract: Effect of substituents at the allylic position in a stannic chloride–iodine–
mediated heterocyclization of 4-allyl-3-hydroxyquinolin-2(1H)-ones for the regio-
selective formation of five- and six-membered heterocyclic rings has been rationalized
by the application of restricted Hatree–Fock calculation.
Keywords: Claisen rearrangement, 6-endo-trig, 5-exo-trig, Hatree–Fock method,
iodine, regioselective cyclization, stannic chloride, substituent effect
INTRODUCTION
Quinolone derivatives are biologically significant because of their antimicro-
bial activity, DNA-gyrase inhibition, and marked cytotoxicity against animal
[
1]
and plant tumors. Keeping these biological activities in mind, a number of
attempts have been made in the past few decades to synthesize various bio-
logically active quinolone derivatives, many of which are abundant in
[
2]
nature.
(6H)-one derivatives are profusely distributed in nature, and a number of
Furo[2,3-c]quinolin-4(5H)-one and 2H-pyrano[3,2-c]quinolin-
5
synthesis of these heterocycles, including those from our own work,
[
3]
[4]
have been reported. Continued interest in this area inspired us to undertake
a study on the synthesis of these heterocycles.
Received in India April 13, 2006
Address correspondence to K. C. Majumdar, Department of Chemistry, University
of Kalyani, Kalyani 741235, West Bengal, India. E-mail: kcm_ku@yahoo.co.in
3
191

3
192
K. C. Majumdar and N. Kundu
Recently, we reported N-iodosuccinimide (NIS)–mediated heterocycliza-
0
[5]
tion of ortho-cyclohex-2 -enylphenols, 3-cyclohex-2 -enyl-4-hydroxycou-
0
[
6]
[7]
marin, and 3-allyl-4-hydroxycoumarin
almost quantitative yield. We have also reported heterocyclization using
in acetonitrile at 0–58C in
[
8,9]
[10]
pyridine hydrotribromide,
[
mercuric acetate, and hexamethylenetetra-
However, no study of the substitution effect on
9,11]
mine hydrotribromide.
these reactions was conducted. NIS has been used for 6-endo heterocycliza-
tion of different substrates via iodonium intermediate. Recently, SnCl -I
4
2
has been found to be a convenient and practical reagent to provide positive
[
12]
iodine . This prompted us to undertake a study on the heterocyclization
of 4-allyl-3-hydroxyquinolin-2(1H)-ones with SnCl -I . Herein we report
4
2
the results.
RESULTS AND DISCUSSION
[
13]
The starting materials 4a–f
by the thermal rearrangement of the corresponding allyl ethers 3a–f in
for this study were obtained in 85–95% yield
[13]
refluxing chlorobenzene (1328C). The ethers 3a–f were in turn synthesized
by the reaction of substrate 1 with allylic halides 2 in refluxing acetone in the
presence of anhydrous K CO and a catalytic amount of sodium iodide
2
3
(
(
Finkelstein condition). The ethers were obtained in 85–95% yield
Scheme 1).
Substrates 4a–f were treated with SnCl -I in dichloromethane at 258C for
4
2
6
h and surprisingly, depending on the substituents R and R , either exclusively
1 2
5-exo or 6-endo products or a mixture of 5-exo and 6-endo cyclization products
were formed (Scheme 2). With substrate 4a, where R ¼ R ¼ H was treated
1
2
2 2 3
Scheme 1. Reagents and conditions: (i) Me CO, K CO , reflux, 6–8 h; (ii) chloro-
benzene, reflux, 8–10 h.

Substitution in SnCl–Mediated Heterocyclization
3193
4 2 2 2
Scheme 2. Reagents and conditions: (i) SnCl /I , CH Cl , r.t., stirring, 6 h.
with SnCl -I in dichloromethane at 258C for 6 h, exclusively 6-endoproduct 6a
4
2
1
13
was formed. Apart from H NMR, C NMR, and mass spectrometry, the final
confirmation that 4a cyclizes to a 6-endo product 6a and not to a 5-exo product
was made by an APT experiment. Multiplicity was also assigned by the APT
experiment. There are nine carbons carrying hydrogen atoms: one CH , three
3
CH , and five CH moieties. If 4a would have cyclized to 5-exo product, multi-
2
plicities would have been exactly the same. However, a carbon resonance at d
7
1.82 due to a CH moiety clearly indicated that a CH moiety must be directly
2 2
attached to the ring oxygen atom. This is only possible if a 6-endo cyclization
takes place. With substrate 4c, where R ¼ R ¼ Me was treated with SnCl -I
1
2
4 2
in dichloromethane at 258C for 6 h, exclusively 5-exo product 7c was formed.
In this case also, final confirmation of the 5-exo product was made by the
Attached Proton Test (APT) experiment. APT showed ten protonated
carbons: three CH , two CH , five CH groups. Carbon resonance at d 91.86
3
2
due to a CH group clearly indicated that a CH group must be directly
attached to the ring oxygen atom. This is only possible if a 5-exo cyclization
takes place. However, with substrate 4c, where R ¼ H and R ¼ Me was
1
2
treated similarly with SnCl -I , a mixture of 6-endo 6c and 5-exo 7c
4
2
products was obtained.
The important role substituents R and R play in the formation of five-
1
2
membered and six-membered products can be explained by the semiemperical
calculation of the heat of formation values of each of the 6-endo and 5-exo
products by restricted Hatree–Fock method (Table 1) as well as by the use
of a molecular model (Dreiding model). When R ¼ R ¼ H (4a, 4d), the
1
2
heat of formation values clearly support the formation of the 6-endo
product (6a, 6d) and certainly not the 5-exo product. With R ¼ H and
1
R ¼ Me (4b, 4e), heat of formation values are comparable in case of
2
6
-endo (6b, 6e) and 5-exo (7b, 7e) products, and thus both the compounds
were formed in comparable yields. However, when R ¼ R ¼ Me (4f, 4c),
1
2
although a restricted Hatree–Fock calculation showed that 5-exo product
formation is slightly favorable over 6-endo product energetically, this could
not explain the exclusive formation of the 5-exo product (7c, 7f). Thus, in
this case, construction of the Dreiding model of the substrate showed that in
the transition state 5 (Scheme 3), 6-endo attack becomes sterically hindered

3
194
K. C. Majumdar and N. Kundu
Table 1. Yields of 5-exo and 6-endo products with varying substituents and semi-
emperical calculation of heat of formation by the retricted Hatree–Fock method
6
-endo cyclization
5-exo cyclization
Heat of
formation
(Kcal/mol)
Heat of
formation
(Kcal/mol)
Yield
(%)
Yield
(%)
Substrate
Product
Product
4a
4b
4c
4d
4e
4f
6a
6b
—
6d
6e
—
90
45
—
90
46
—
214.79
212.43
211.79
29.60
27.38
26.56
—
7b
7c
—
7e
7f
—
43
91
—
44
92
27.76
210.03
212.22
22.42
24.57
26.84
because of the close proximity of the iodonium ion to the two methyls,
favoring the formation of the 5-exo product (7c, 7f) exclusively. In the
present instance, the five-membered product 7 is more stable than the six-
membered one because of the anomeric effect present in the six-membered
ring product. In the six-membered ring product 6, the anomeric effect is
Scheme 3.

Substitution in SnCl–Mediated Heterocyclization
3195
derived from the interaction of the p-orbital of oxygen with the antibonding
s-orbital of the C-I bond, but in the case of the five-membered ring
product, this anomeric effect is absent because the iodine atom is not
bonded with the ring carbon.
A literature search revealed that SnCl -I has been used for the cyclization of
4
2
[
12]
ortho-allyl phenols by Orito et al.
Formation of five-membered and six-
membered products has been explained in terms of substituent effects at the
vinylic position. In thepresent study, we havesuccessfully demonstrated how sub-
stituents at the allylic position play a key role in the regioselective formation of
five- and six-membered heterocyclic compounds at room temperature.
The key step of the synthesis that we report here is based on the intra-
molecular cyclization allowed by activation of an olefinic double bond by
means of an iodonium intermediate. The intramolecular ring closure may
occur via 5-exo-trig or by 6-endo-trig cyclization to give five-membered
and six-membered heterocyclic rings respectively (Scheme 3).
Thus, we demonstrate the selectivity in the formation of five- and six-
membered oxygen heterocyclic rings by the combined Claisen rearrangement
followed by substituent dependent ring-closure methodology. All new
compounds gave satisfactory spectroscopic and analytical data. The reagent
SnCl -I , used for this protocol, is quite cheap and easily accessible
4
2
[14]
compared to other reagents for similar cyclizations.
synthesis for potentially bioactive heterocycles.
This offers a facile
EXPERIMENTAL
Melting points are uncorrected. IR spectra were recorded on a Perkin-Elmer L
2
20-000A spectrometer (nmax in centimeters ) using samples as neat liquids,
1
1
and solid samples were recorded on KBr disks. H NMR (300 MHz, 400 MHz,
1
1
00 MHz) and C NMR (125 MHz) spectra were recorded on a Bruker DPX-
3
5
3
00, Bruker DPX-400, and Bruker DPX-500 spectrometer in CDCl (chemical
3
shift in d) with TMS as internal standard. UV absorption spectra were
recorded in EtOH on a Shimadzu UV-2401PC spectrophotometer (lmax in
nanometers). Elemental analyses and mass spectra were recorded on a Leco
9
32 CHNS anlyser and on a JEOL JMS-600 instrument respectively.
Restricted Hatree–Fock calculations (semiemperical) were done using
Hyper-Chem software. Silica gel [(60–120 mesh), Spectrochem, India] was
used for chromatographic separation. Silica gel G [E-Merck (India)]
was used for TLC. Petroleum ether refers to the fraction boiling between 60
and 808C.
General Procedure for the Preparation of Compounds 3a–f
A mixture of 3-hydroxy-1-methylquinolin-2(1H)-one or 3-hydroxy-1-ethyl-
quinolin-2(1H)-one (1, 1 mmol), appropriate halides (2, 1 mmol), sodium

3
196
K. C. Majumdar and N. Kundu
iodide (50 mg), and anhydrous K CO (5 g) was refluxed in dry acetone
2
3
(
50 mL) for 6–8 h. The reaction mixture was cooled, filtered, and concen-
trated. The residual mass was subjected to column chromatography on silica
gel. Compounds 3a–f were obtained when the column was eluted with 10%
ethyl acetate–petroleum ether.
[13]
Compounds 3d and f were previously reported.
Data
-Allyloxy-1-ethylquinolin-2(1H)-one (3a)
3
21 1
Yield: 85%; viscous liquid; IR (neat): 3125, 1777, 1560, 1520, 1420 cm ; H
NMR (CDCl , 300 MHz): d ¼ 1.35 (t, J ¼ 7.2 Hz, 3H, -CH ), 4.41
3
H
3
(
q, J ¼ 7.2 Hz, 2H, -NCH ), 4.65 (d, J ¼ 5 Hz, 2H, -OCH ), 5.25–5.65
2 2
2
2
(
m, 2H, -CH 55 CH ), 5.95–6.37 (m, 1H, CH 55 CH ), 6.93 (s, 1H, -CH 55 ),
¼ 225,
þ
7
.25–7.62 (m, 4H, ArH); MS: m/z ¼ 229 (M ); UV (EtOH): l
max
280, 320 nm; anal. calcd. for C H NO : C, 73.36; H, 6.55; N, 6.11.
Found: C, 73.61; H, 6.33; N, 6.23.
14 15 2
3-(But-2-en-1-yloxy)-1-ethylquinolin-2(1H)-one (3b)
Yield: 88%; viscous liquid; IR (neat): 1774, 1721, 1620, 1595, 1547,
2
1
1
1
436 cm ; H NMR (CDCl , 300 MHz): d ¼ 1.36 (t, J ¼ 7.2 Hz, 3H,
3
H
-
CH CH ), 1.72 (d, J ¼ 5 Hz, 3H, 55 CHCH ), 4.41 (q, J ¼ 7.2 Hz, 2H,
2 2
2 3 3
-
NCH ), 4.60 (d, J ¼ 5 Hz, 2H, -OCH ), 5.57–6.15 (m, 2H, -CH 55 CH-),
þ
6
.82 (s, 1H, -CH 55 ), 7.25–7.79 (m, 4H, ArH); MS: m/z ¼ 243 (M ); UV
(
EtOH): l
¼ 222, 275, 320 nm; anal. calcd. for C H NO : C, 74.07; H,
max 15 17 2
6
.99; N, 5.76. Found: C, 74.35; H, 7.18; N, 5.51.
1-Methyl-3-(3-ethylbut-2-en-1-yloxy)quinolin-2(1H)-one (3c)
21 1
Yield: 87%; viscous liquid; IR (neat): 3124, 1622, 1605, 1458 cm ; H NMR
CDCl , 300 MHz): d ¼ 1.35 (t, J ¼ 7.2 Hz, 3H, -NCH CH ), 1.76 [s, 6H,
(
3
H
2
3
C(CH ) ], 4.42 (q, J ¼ 7.2 Hz, 2H, -NCH ), 4.65 (d, J ¼ 6 Hz, 2H,
3
2
2
-
OCH ), 5.54–5.69 [m, 1H, -CH 55 C(CH ) ], 6.91 (s, 1H, -CH 55 ),
2
3 2
þ
7
.28–7.59 (m, 4H, ArH); MS: m/z ¼ 257 (M ); UV (EtOH): l
¼ 225,
max
278, 320 nm; anal. calcd. for C H NO : C, 74.70; H, 7.39; N, 5.44.
Found: C, 74.49; H, 7.58; N, 5.28.
16 19 2
3-(But-2-en-1-yloxy)-1-methylquinolin-2(1H)-one (3e)
Yield: 88%; viscous liquid; IR (neat): 1770, 1745, 1622, 1598, 1545,
2
1
1
1
435 cm
;
H NMR (CDCl , 300 MHz): d ¼ 1.76 (d, J ¼ 5 Hz, 3H,
3 2
3
H
5
5CHCH ), 3.76 (s, 3H, -NCH ), 4.58 (d, J ¼ 5 Hz, 2H, -OCH ),
3

Substitution in SnCl–Mediated Heterocyclization
3197
5
.59–6.12 (m, 2H, -CH 55 CH-), 6.80 (s, 1H, -CH 55 ), 7.20–7.76 (m, 4H,
þ
ArH); MS: m/z ¼ 229 (M ); UV (EtOH): l
¼ 223, 276, 319 nm;
max
anal. calcd. for C H NO : C, 73.36; H, 6.55; N, 6.11. Found: C, 73.61;
2
1
4
15
H, 5.35; N, 5.92.
General Procedure for the Claisen Rearrangement of Compounds
a–f
3
The ether (3a–f, 2 mmol) was refluxed in chlorobenzene (4 mL) for 8–10 h.
Chlorobenzene was removed in vacuo, and the residual mass was chromato-
graphed on silica gel. Elution of the column with petroleum ether (60–808C)
removed the residual chlorobenzene, and then compounds 4a–f were
obtained by eluting the column with 10% ethyl acetate–petroleum ether.
[13]
Compounds 4d and f were previously reported.
Data
4
-Allyl-3-hydroxy-1-ethylquinolin-2(1H)-one (4a)
Yield: 90%; viscous liquid; IR (neat): 3545, 1738, 1719, 1617, 1562,
2
1
1
1
492 cm ; H NMR (CDCl , 400 MHz): d ¼ 1.37 (t, J ¼ 7.2 Hz, 3H,
3
H
-
CH ), 3.67–3.68 (m, 2H, -CH -CH 55 ), 4.42 (q, J ¼ 7.2 Hz, 2H, -NCH ),
3
2
2
5
.06–5.13 (m, 2H, -CH 55 CH ), 5.93–6.01 (m, 1H, -CH 55 CH ), 7.14–7.72
2 2
þ
(
m, 5H, ArH and OH); MS: m/z ¼ 229 (M ); UV (EtOH): l
¼ 222,
max
2
Found: C, 73.65; H, 6.34; N, 5.99.
74, 286, 331 nm; anal. calcd. for C H NO : C, 73.36; H, 6.55; N, 6.11.
14 15 2
3
-Hydroxy-1-ethyl-4-(1-methylallyl)-quinolin-2(1H)-one (4b)
21 1
Yield: 90%; viscous liquid; IR (neat): 3514, 2925, 1648, 1604, 1455 cm ; H
NMR (CDCl , 300 MHz): d ¼ 1.36 (t, J ¼ 7.2 Hz, 3H, -NCH CH ), 1.60
3
H
2
3
(
(
-
(
d, J ¼ 2 Hz, 3H, CHCH ), 4.12–4.35 (m, 1H, CHCH ), 4.41
3
3
q, J ¼ 7.2 Hz, 2H, -NCH ), 5.10–5.38 (m, 2H, 55 CH ), 6.14–6.50 (m, 1H,
2 2
þ
CH 55 CH ), 7.17–7.81 (m, 5H, ArH and OH); MS: m/z ¼ 243 (M ); UV
2
EtOH): l
.99; N, 5.76. Found: C, 74.26; H, 7.11; N, 5.06.
¼ 222, 278, 321 nm; anal. calcd. for C H NO : C, 74.07; H,
max
15 17
2
6
4
-(1,1-Dimethylallyl)-3-hydroxy-1-ethylquinolin-2(1H)-one (4c)
Yield: 91%; viscous liquid; IR (neat): 3265, 1622, 1600, 1505, 1468,
1
2
1
1
418 cm ; H NMR (CDCl , 300 MHz): d ¼ 1.36 (t, J ¼ 7.2 Hz, 3H,
2 3 3 2 2
3
H
-
NCH CH ), 1.73 [s, 6H, C(CH ) ], 4.41 (q, J ¼ 7.10 Hz, 2H, -NCH ),
4
.92–5.20 (m, 2H, CH 55 CH ), 6.15–6.49 (dd, 1H, J ¼ 16. 8 Hz,
2

3
198
K. C. Majumdar and N. Kundu
þ
CH 55 CH ), 7.15–7.87 (m, 5H, ArH and OH); MS: m/z ¼ 257 (M ); UV
2
(
EtOH): l
¼ 223, 278, 317 nm; anal. calcd. for C H NO : C, 74.70; H,
max
16 19
2
7.39; N, 5.44. Found: C, 74.92; H, 7.48; N, 5.23.
3-Hydroxy-1-methyl-4-(1-methylallyl)-quinolin-2(1H)-one (4e)
Yield: 90%; viscous liquid; IR (neat): 3510, 2920, 1640, 1600, 1455,
2
1
1
1
400 cm
;
CHCH ), 3.78 (s, 3H, -NCH ), 4.02–4.33 (m, 1H, -CHCH ), 5.00–5.36
H NMR (CDCl , 300 MHz): d ¼ 1.58 (d, J ¼ 2 Hz, 3H,
3 3
3
H
-
(
3
m, 2H, 55 CH ), 6.04–6.49 (m, 1H, -CH 55 CH ), 7.16–7.79 (m, 5H, ArH
2
2
þ
and OH); MS: m/z ¼ 229 (M ); UV (EtOH): l
¼ 224, 276, 320 nm;
max
anal. calcd. for C H NO : C, 73.36; H, 6.55; N, 6.11. Found: C, 73.11; H,
2
1
4
15
6
.71; N, 6.32.
General Procedure for the Preparation of Compounds 6 and 7
SnCl (0.13 mL, 2 mmol) and I (512 mg, 2 mmol) were added to a CH Cl
2
4
2
2
(10 mL) solution of the compounds (4a–h, 2 mmol) at room temperature,
and the mixture was stirred for 1 h. The mixture was treated with ice-cold
water (40 mL), extracted with CH Cl (3 ꢀ 10 mL), washed with 5%
2
2
Na S O (2 ꢀ 20 mL), water (2 ꢀ 20 mL), and dried (Na SO ). The
2
2
3
2
4
residual mass after removal of the solvent was subjected to column chromato-
graphy on silica gel, and the cyclic products 6, 7 were collected using 20%
ethylacetate–petroleum ether as eluant.
Data
2,3-Dihydro-6-ethyl-2-iodo-2H-pyrano[2,3-c]quinolin-5-one (6a)
Yield: 90%; white solid; mp 166–1688C; IR (KBr): 1647, 1620, 1461, 1210,
2
1 1
7
3
51 cm ; H NMR (CDCl , 300 MHz): d ¼ 1.34 (t, J ¼ 7.2 Hz, 3H, CH ),
3
H
3
.32 (dd, J ¼ 17.5, 8.5 Hz, 1H, 55 CCH ), 3.52 (dd, J ¼ 17.5, 5.5 Hz, 1H,
2
5
5CCH ), 4.26 (t, J ¼ 10.5 Hz, 1H, OCH ), 4.42 (q, J ¼ 7.2 Hz, 2H,
2
2
1
3
NCH ), 4.51–4.61 (m, 2H, OCH and CHI), 7.24–7.50 (m, 4H, ArH);
2 2
C
NMR (CDCl , 125 MHz): d ¼ 12.63 (NCH CH ), 15.05 (CHI), 33.83
3
C
2
3
(
CH CHI), 37.78 (NCH ), 71.82 (OCH ), 114.13 (ArCH), 118.53 (ArC),
2 2 2
1
19.90 (ArC), 122.28 (ArCH), 122.45 (ArCH), 127.90 (ArCH), 134.21
þ
(
ArC), 142.01 (ArC), 156.66 (CO); MS: m/z ¼ 355 (M ); UV (EtOH):
l
max
H, 3.94; N, 3.94. Found: C, 47.06; H, 4.13; N, 4.10.
¼ 225, 279, 290, 320, 334 nm; anal. calcd. for C H NO I: C, 47.32;
14 14
2

Substitution in SnCl–Mediated Heterocyclization
3199
2
,3-Dihydro-6-ethyl-1-methyl-2-iodo-2H-pyrano[2,3-c]quinolin-5-one
6b)
(
Yield: 45%; white solid; mp 160–1628C; IR (KBr): 1643, 1597, 1445, 1210,
2
1
1
7
51 cm
;
H NMR (CDCl , 500 MHz): d ¼ 1.35 (t, J ¼ 7.1 Hz, 3H,
3
H
NCH CH ), 1.53 (d, J ¼ 7.0 Hz, 3H, CH CH), 3.46–3.51 (m, 1H,
2
3
3
CH CH), 4.42 (q, J ¼ 7.1 Hz, 2H, NCH ), 4.47 (t, J ¼ 11.8 Hz, 1H,
3
2
OCH ), 4.59 (dd, J ¼ 11.0 Hz, 4.1 Hz, 1H, OCH ), 4.68–4.72 (m, 1H,
2
2
þ
CHI), 7.27–7.57 (m, 4H, ArH); MS: m/z ¼ 369 (M ); UV (EtOH):
l
4
¼ 226, 268, 280, 290, 321, 334 nm; anal. calcd. for C H NO I: C,
max
15 16
2
8.78; H, 4.33; N, 3.79. Found: C, 49.01; H, 4.45; N, 3.50.
2
,3-Dihydro-2-iodo-6-methyl-2H-pyrano[2,3-c]quinolin-5-one (6d)
Yield: 90%; white solid; mp 163–1658C; IR (KBr): 1649, 1623, 1457, 1119,
2
1 1
7
53 cm ; H NMR (CDCl , 300 MHz): d ¼ 3.30 (dd, J ¼ 17.5, 8.5 Hz, 1H,
3
H
5
(
5CCH ), 3.54 (dd, J ¼ 17.5, 5.5 Hz, 1H, 55 CCH ), 3.77 (s, 3H, NCH ), 4.27
2 2 3
t, J ¼ 10.5 Hz, 1H, OCH ), 4.50–4.60 (m, 2H, OCH and CHI), 7.28–7.50
þ
max
2
2
(
m, 4H, ArH); MS: m/z ¼ 341 (M ); UV (EtOH): l
¼ 225, 279, 290, 321,
3
4
35 nm; anal. calcd. for C H NO I: C, 45.74; H, 3.51; N, 4.10. Found: C,
13 12 2
5.97; H, 3.32; N, 3.98.
2
,3-Dihydro-2-iodo-1,6-dimethyl-2H-pyrano[2,3-c]quinolin-5-one (6e)
Yield: 46%; white solid; mp 138–1408C; IR (KBr): 1651, 1615, 1459, 1120,
2
1
1
7
CH CH), 3.47–3.51 (m, 1H, CH CH), 3.76 (s, 3H, NCH ), 4.46
38 cm
;
H NMR (CDCl , 500 MHz): d ¼ 1.53 (d, J ¼ 7.0 Hz, 3H,
3
H
3
3
3
(
t, J ¼ 11.8 Hz, 1H, OCH ), 4.60 (dd, J ¼ 11.0, 4.1 Hz, 1H, OCH ),
2
2
þ
4
UV (EtOH): l
.68–4.72 (m, 1H, CHI), 7.26–7.56 (m, 4H, ArH); MS: m/z ¼ 355 (M );
¼ 215, 225, 256, 263, 321, 335 nm; anal. calcd.
max
for C H NO I: C, 47.32; H, 3.94; N, 3.94. Found: C, 47.09; H, 4.15;
1
4
14
2
N, 3.83.
2
,3-Dihydro-5-ethyl-2-iodomethyl-1-methylfuro[2,3-c]quinolin-4-one
7b)
(
Yield: 43%; white solid; mp 120–1228C; IR (KBr): 1663, 1628, 1457, 1206,
2
1
1
7
51 cm
;
H NMR (CDCl , 500 MHz): d ¼ 1.36 (t, J ¼ 7.1 Hz, 3H,
3
H
NCH CH ), 1.52 (d, J ¼ 7.0 Hz, 3H, CHCH ), 3.22 (t, J ¼ 9.9 Hz, 1H,
2
3
3
CH I), 3.49 (dd, J ¼ 9.9, 3.86 Hz, 1H, CH I), 3.66–3.71 (m, 1H, CH CH),
2
2
3
4
.42 (q, J ¼ 7.1 Hz, 2H, NCH ), 4.64–4.68 (m, 1H, CHCH I), 7.25–7.54
2
2
þ
(
m, 4H, ArH); MS: m/z ¼ 369 (M ). UV (EtOH): l
¼ 228, 287, 298,
max
3
Found: C, 49.04; H, 4.14; N, 3.68.
24, 339 nm; anal. calcd. for C H NO I: C, 48.78; H, 4.33; N, 3.79.
15 16 2

3
200
K. C. Majumdar and N. Kundu
2,3-Dihydro-5-ethyl-2-iodomethyl-1,1-dimethylfuro[2,3-c]quinolin-4-
one (7c)
Yield: 91%; white solid; mp 92–948C; IR (KBr): 2917, 1662, 1622, 1463,
2
1
1
1
3
1
215, 755 cm ; H NMR (CDCl , 400 MHz): d ¼ 1.33 (t, J ¼ 7.1 Hz,
3
H
H, NCH CH ), 1.46 (s, 3H, CH ), 1.76 (s, 3H, CH ), 3.39 (dd, J ¼ 7.1,
2 3 3 3
0.6 Hz, 1H, CH I), 3.52 (dd, J ¼ 7.1, 10.6 Hz, 1H, CH I), 4.38
2
2
(
q, J ¼ 7.1 Hz, 2H, NCH ), 4.71 (t, 6.9 Hz, 1H, CHCH I), 7.24–7.74
3 C 2
2
2
1
3
(
m, 4H, ArH); C NMR (CDCl , 125 MHz): d ¼ 2 1.42 (CH I), 12.78
(
NCH CH ), 20.18 (CH ), 27.90 (CH ), 37.45 (NCH ), 47.28 [C(CH ) ],
2 3 3 3 2 3 2
91.86 (OCH), 115.08 (ArCH), 118.37 (ArC), 112.19 (ArCH), 122.72
(
ArCH), 127.27 (ArCH), 131.70 (ArC), 136.19 (ArC), 144.48 (ArC),
þ
1
3
54.28 (CO); MS: m/z ¼ 383 (M ); UV (EtOH): l
¼ 227, 287, 298,
max
24, 339 nm; anal. calcd. for C H NO I: C, 50.13; H, 4.69; N, 3.65.
1
6
18
2
Found: C, 50.24; H, 4.54; N, 3.51.
,3-Dihydro-2-iodomethyl-1,5-dimethylfuro[2,3-c]quinolin-4-one (7e)
Yield: 44%; white solid; mp 118–1208C; IR (KBr): 1663, 1628, 1457, 1226,
2
2
1 1
7
3
3
52 cm ; H NMR (CDCl , 500 MHz): d ¼ 1.52 (d, J ¼ 7.0 Hz, 3H, CH ),
3
H
3
.22 (t, J ¼ 9.9 Hz, 1H, CH I), 3.48 (dd, J ¼ 9.9, 3.8 Hz, 1H, CH I),
2
2
.66–3.71 (m, 1H, CH CH), 3.78 (s, 3H, NCH ), 4.63–4.67 (m, 1H,
3
3
þ
CHCH I), 7.26–7.54 (m, 4H, ArH); MS: m/z ¼ 355 (M ); UV (EtOH):
2
l
max
H, 3.94; N, 3.94. Found: C, 47.53; H, 3.83; N, 4.06.
¼ 227, 288, 298, 325, 340 nm; anal. calcd. for C H NO I: C, 47.32;
14 14
2
2,3-Dihydro-2-iodomethyl-1,1,5-trimethylfuro[2,3-c]quinolin-4-one
(7f)
Yield: 92%; white solid; mp 90–928C; IR (KBr): 2927, 1662, 1622, 1458,
2
1
1
1
1
1
238, 752 cm ; H NMR (CDCl , 300 MHz): d ¼ 1.49 (s, 3H, CH ),
3
H
3
.77 (s, 3H, CH ), 3.40 (dd, J ¼ 7.1, 10.5 Hz, 1H, CH I), 3.53 (dd, J ¼ 7.1,
3
2
0.50 Hz, 1H, CH I), 3.75 (s, 3H, NCH ), 4.75 (t, J ¼ 6.9 Hz, 1H,
2
3
þ
CHCH I), 7.24–7.75 (m, 4H, ArH); MS: m/z ¼ 369 (M ); UV (EtOH):
2
l
max
H, 4.33; N, 3.79. Found: C, 49.01; H, 4.21; N, 4.01.
¼ 227, 287, 298, 352, 340 nm; anal. calcd. for C H NO I: C, 48.78;
15 16
2
ACKNOWLEDGMENT
We thank the Council of Scientific and Industrial Research (CSIR)
(
(
(
New Delhi) for the financial assistance. N. Kundu is grateful to CSIR
New Delhi) for a junior research fellowship. We also thank Sandip Kar
Bhairab Ganguly College, Belgharia) for his help with the theoretical
calculations.

Substitution in SnCl–Mediated Heterocyclization
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(
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(
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1
23.
1
1
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