Synthesis of novel heterocyclic fused 1,3-diazabuta-1,3-dienes and accompanying rearrangements in their cycloaddition reactions with ketenes: Synthesis of heterocyclic fused pyrimidinone derivatives

Article abstract of DOI:10.1016/j.tet.2004.02.023

The reactions of 1,3-diazabuta-1,3-dienes 1 with 2-aminothiophenol have been shown to result in excellent yields of N-benzothiazol-2-yl-N′-aryl benzamidines 2. Their regioselective [4+2] cycloadditions with various ketenes are shown to yield novel benzoth

Full text of DOI:10.1016/j.tet.2004.02.023

Tetrahedron 60 (2004) 4315–4324
Synthesis of novel heterocyclic fused 1,3-diazabuta-1,3-dienes
and accompanying rearrangements in their cycloaddition
reactions with ketenes: synthesis of heterocyclic fused
pyrimidinone derivatives
*
S. Jayakumar, Parvesh Singh and Mohinder P. Mahajan
Department of Applied Chemistry, Guru Nanak Dev University, Amritsar 143005, India
Received 17 April 2003; revised 19 January 2004; accepted 12 February 2004
Abstract—The reactions of 1,3-diazabuta-1,3-dienes 1 with 2-aminothiophenol have been shown to result in excellent yields of
N-benzothiazol-2-yl-N0-aryl benzamidines 2. Their regioselective [4þ2] cycloadditions with various ketenes are shown to yield novel
benzothiazolo pyrimidinones 4. A similar and convenient protocol for the synthesis of bisthiosubstituted 1,3-diazabuta-1,3-dienes 8 and 9
and interesting rearrangements accompanying their [4þ2] cycloadditions with a number of ketenes are described.
q 2004 Published by Elsevier Ltd.
1. Introduction
1,3-dienes add as 4p components across CvC bond of the
ketenes.6 Over the years, we have been actively involved in
the synthesis and cycloaddition reactions of various
functionalized 1,3-diazabuta-1,3-dienes and have developed
a simple protocol for the synthesis of stable acyclic 1,3-
diazadienes.7 It is noticed that rearrangements accompany
the [4þ2] cycloaddition reactions of 4-tertiaryamino-4-
methylthio-1,3-diazabuta-1,3-dienes, 4-(N-arylamino)-4-
methylthio-1,3-diazabuta-1,3-dienes and 4-(N-arylamino)-
4-tertiaryamino-1,3-diazabuta-1,3-dienes with various
ketenes.8 In view of these observations and our interest in
the synthesis of new diazadienes, it was considered
worthwhile to synthesise and examine the reactions of
heterocyclic fused 1,3-diazabuta-1,3-dienes with various
ketenes.
Nitrogen-containing compounds are widely distributed in
nature and include many biologically important molecules.
The synthesis of nitrogen-containing heterocycles has
attracted considerable attention due largely to their
importance as building blocks for many therapeutically
useful materials and the wide range of potential biological
activity of both synthetic and naturally occurring deriva-
tives. The hetero-Diels–Alder methodology employing
azadienes represents a straightforward and an efficient
approach to nitrogen-containing six membered hetero-
cycles. Extensive studies have been carried out on this
[4þ2] cycloaddition process and the rapid and rigorous
development in this area has led to several reviews
highlighting the utility of azadienes as readily available
templates in the synthesis of novel heterocycles and
complex natural products.1 Dienes containing two nitrogen
atoms have attracted attention of chemists in recent years
because of their importance in natural product synthesis.1 In
the last decade there have been numerous reports concern-
ing the participation of 1,3-diazabuta-1,3-dienes as 4p
components in cycloaddition reactions with isocyanides,2
oxazolines,3 enamines,4 alkynes5 etc. On the other hand the
reactions of ketenes with 1,3-diaza-1,3-butadienes are
reported to undergo [4þ2] as well [2þ2] cycloadditions.
A vast prevalence of such reported cycloadditions corre-
spond to [4þ2] cycloaddition type in which 1,3-diazabuta-
2. Results and discussion
Thus, the treatment of 4-tertiaryamino-4-methylthio-1,3-
diazabuta-1,3-dienes 1 with 2-aminothiophenol, in refluxing
toluene resulted in good yields of the desired benzothiazolo
fused 1,3-diazabuta-1,3-dienes 2. The structural assign-
ments to the diazadienes 2 were based on spectral and
analytical evidence. The detailed spectral features of the
1,3-dienes 2 are described in the experimental section,
however; only the salient features are mentioned here. The
1,3-diene 2b, for example, characterized as N-benzothiazol-
2-yl-N0-p-tolyl-benzamidine, was analysed for C21H17N3S
Keywords: 1,3-Diazabuta-1,3-dienes; Pyrimidinones; Ketenes.
*
1
and showed a molecular ion peak at m/z 343. Its H NMR
spectrum showed the absence of the protons corresponding
Corresponding author. Tel.: þ91-183-2258802-09x3320; fax: þ91-183-
2258819-20; e-mail address: mohinderpmahajan@angelfire.com
0040–4020/$ - see front matter q 2004 Published by Elsevier Ltd.
doi:10.1016/j.tet.2004.02.023

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S. Jayakumar et al. / Tetrahedron 60 (2004) 4315–4324
to the secondary amine and the methylthio functions and the
presence of a singlet at d 2.29 for a methyl group attached to
an aromatic ring and a broad singlet appeared at d 12.62 for
an exchangeable N–H proton. The signals in its 13C NMR
spectrum are also in agreement with the assigned structure.
The formation of N-aryl-N0-(2-benzothiazolyl)-benza-
midines 2 in these reactions may be explained by the initial
displacement of methylmercaptan, by attack of the sulphur
of aminothiophenol on C-4 of 1,3-diazabutadiene, followed
by the displacement of secondary amine by the nitrogen of
aromatic amine group via an addition–elimination
mechanism (Scheme 1).
triethylamine in methylene chloride, resulted in good yields
of the products which were characterized as novel
benzothiazolo fused pyrimidinones 4. The detailed spectral
features of these pyrimidinones are discussed in the
experimental section while the salient features are men-
tioned here. For example, pyrimidinone 4b, analyzed for
C18H12N2OS showed a molecular ion peak at m/z 304 in its
mass spectrum. 1H NMR spectrum attests to the presence of
vinylic protons and loss of the aryl amine attached to the
phenyl-bearing carbon. The aromatic proton HA in pyrimi-
dinones 4 appeared unexpectedly downfield, around d
9.12–9.15 as doublet of a doublet, probably due to the
deshielding effect of the carbonyl group. The signals in
the 13C NMR spectrum were also in agreement with the
assigned structure. The probable mechanisms for the
formation of pyrimidinones 4 are depicted in Scheme 2. It
is assumed that the stereoselective [4þ2] cycloaddition of
tautomer 2B with ketene forms an intermediate 3, which on
elimination of the aromatic amine leads to the desired
benzothiazolopyrimidinone 4 (Path I). The formation of 4
may also be explained by an initial nucleophilic attack of the
N-5 of 2A on ketene carbonyl to form an intermediate 5, its
1,3-Diazabutadienes 2 probably exist in a number of
tautomeric forms (A, B and C). In order to have an idea
about the predominant tautomeric form in this mixture and
to examine the regiochemical aspects of their cyclo-
additions, we have examined their reactions with ketenes.
Thus, the reactions of 1,3-diazabutadienes 2 with mono-
phenyl, vinyl-, and isopropenyl ketenes, generated in situ
from phenylacetyl chloride, crotonyl chloride, and 3,3-
dimethylacryloyl chloride, respectively, in the presence of
Scheme 1.

S. Jayakumar et al. / Tetrahedron 60 (2004) 4315–4324
4317
Scheme 2.
cyclisation to 3 and usual elimination of aromatic amine
(Path II). The tautomeric form 2B appears to be more stable
and hence preferred over the form 2A due to the higher
stabilization imparted by its aromatic benzothiazole com-
ponent. Thus, the regioselective and stereoselective [4þ2]
cycloaddition (Path I) similar to one reported earlier,8e
appears to be a preferred route for the formation of fused
pyrimidinones 4 (Scheme 2).
was characterized on the basis of analytical data and spectral
evidence. It appears that the more stable tautomeric form 2B
of 1,3-diazabuta-1,3-dienes 2, undergoes regio/stereo-
selective [4þ2] cycloaddition reaction with butadienyl-
ketene to form an intermediate 3 which on elimination of
aromatic amine results in the formation of pyrimidinone 4d.
The alternative mechanistic possibility (Path II) involving
initial nucleophilic attack, followed by cyclisation and
elimination of aromatic amine, is less likely as this would
have resulted in rearranged pyrimidinone derivatives as
observed in reactions of N-arylamino-1,3-diazabuta-1,3-
diene with butadienylketene.9b A simpler and more
acceptable explanation for the exclusive formation of
pyrimidinones 4d in these reactions assumes an additional
nucleophilic push from sulfur in intermediate 3, which
shortens its life time and favours the elimination of
arylamine over rearrangement involving [1,5]H sigmatropic
shift followed by a [1,5]NH-Ph shift.
Recent disclosure from our laboratory has shown remark-
able substituent dependent tandem [1,5]H, [1,3]NHPh and
[1,5]NHPh sigmatropic shifts accompanying [4þ2]
cycloaddition reactions of 4-N-arylamino substituted 1,3-
diazabuta-1,3-dienes with butadienylketene.9 In con-
tinuation of these studies, we have examined the reactions
of benzothiazole-incorporated 1,3-diazabuta-1,3-dienes 2
with butadienylketene. The treatment of benzothiazolyl
incorporated 1,3-diazabuta-1,3-dienes 2 with butadienyl-
ketene, generated in situ, was found to result in the
exclusive formation of 5-butadienyl pyrimidinone 4d,
while no product corresponding to the rearrangement
observed earlier could be isolated. The pyrimidinone 4d
Inspired by the highly stereo- and regioselective cyclo-
additions observed in these reactions, it was considered
worthwhile to extend these studies to other similar

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S. Jayakumar et al. / Tetrahedron 60 (2004) 4315–4324
heterocyclic fused 1,3-diazabuta-1,3-dienes. Thus, simple
and elegant protocols for the synthesis of 4,4-bisthioalkyl
substituted 1,3-diazabuta-1,3-dienes have been developed
(Scheme 3). The treatment of benzamidines 6 with carbon
disulfide in the presence of potassium-tert-butoxide/sodium
hydride and subsequent treatment of resulting intermediate
7 with methyl iodide, 1,3-dibromopropane and 1,2-di-
bromoethane resulted in good yields of 4,4-bismethylthio-
1,3-diazabuta-1,3-dienes 8a–c, 1-aryl-2-phenyl-4[2-(1,3-
dithiolanyl)]-1,3-diazabuta-1,3-diene 9a and 1-aryl-2-
phenyl-4[2-(1,3-dithianyl)]-1,3-diazabuta-1,3-diene 9b
derivatives, respectively. The structural assignments to the
product 8 and 9 were based on analytical data and spectral
evidences. The compound 9b, for example, exhibited a
molecular ion peak at m/z 326. Its 1H NMR spectrum
exhibited a multiplet at d 2.03 (2H) for –CH2– group, a
singlet at d 2.31 for –CH3 and a multiplet at d 2.91 for four
methylene protons attached to sulfur, in addition to the
aromatic protons. The assigned structure was further
corroborated by its 13C spectrum which showed a peak at
d 20.8 for –CH2–, a peak at d 21.6 for –CH3 and a peak at d
29.7 corresponding to two –SCH2 carbons.
intermediate. However, [1,2]-methylthio shift, similar to
the one reported earlier,8c have been shown to accompany
the [4þ2] cycloadditions in reactions of 8 with chloro-
ketene. These reactions resulted in the formation of
2-phenyl-3-aryl-5,6-bismethylthio-pyrimidin-4(3H)-one 14
and probably involve an initial formation of an intermediate
12, its subsequent transformation to episulfonium inter-
mediate 13 before rearrangement to 14 (Scheme 4). On the
other hand, the reactions of 1,3-diazabuta-1,3-dienes 9 with
chloroketene resulted in a mixture (<1:1) of pyrimidinones
19 and 20 (Scheme 5). The separation of this mixture of 19
and 20 with very close Rf values was accomplished by
careful silica gel column chromatography with natural loss
of yields. The pyrimidinones 19 and 20 were characterized
on the basis of their analytical and spectral data. Compound
19b (Scheme 5), for example, analyzed for C22H20N2S2O2-
Cl2 exhibited in its mass spectrum a molecular ion peak at
m/z 479 (Mþ). Its IR spectrum showed a sharp peak at
1678 cm21, assigned to the a,b-unsaturated carbonyl group.
1
Its H NMR spectrum exhibited a multiplet at d 2.07 (2H)
for the –CH2– group, singlet at d 2.31 (3H) for the aromatic
substituted methyl group, a triplet (J¼7.0 Hz) at d 3.06 for
the methylene protons attached to sulfur, a triplet
(J¼7.0 Hz) at d 3.26 for methylene attached to another
sulfur and a singlet at d 4.12 for the methylene attached to
chlorine, in addition to the aromatic protons. Its 13C NMR
spectrum was also in agreement with the assigned structure.
The pyrimidinone 20b on the other hand was analyzed for
C20H18N2OS2 and exhibited in its mass spectrum a
molecular ion peak at m/z 366 (Mþ). Its IR spectrum
The 1,3-diazabuta-1,3-dienes, 8, 9a and 9b (Schemes 4 and
5) obtained were treated with various ketenes, generated in
situ from the corresponding acid chlorides. The treatment of
8b with phenylacetyl chloride in presence of dry triethyl-
amine resulted in the isolation of 2,5-diphenyl-6-
methylthio-3-(p-tolyl)-pyrimidin-4(3H)-one 11 presumably
via the initial formation of pyrimidinone 10 as an
Scheme 3.

S. Jayakumar et al. / Tetrahedron 60 (2004) 4315–4324
4319
Scheme 4.
showed intense absorption at 1672 cm21 due to the a,b-
unsaturated carbonyl group. Its 1H NMR spectrum exhibited
a multiplet at d 2.14–2.22 (2H) corresponding to the
methylene, a singlet at d 2.28 (3H) corresponding to the
aromatic substituted –CH3 group, a triplet (J¼6.0 Hz) at d
3.59 for the methylene attached to sulfur, another triplet
(J¼6.0 Hz) at d 3.69 for the for the second –S–CH2–
group, in addition to the aromatic protons. The assigned
structure was further corroborated by signals present in its
13C NMR spectrum which showed a signal at d 159.7
indicating the presence of a carbonyl carbon and two signals
at d 27.6 and 30.1 corresponding to two methylene carbons.
may also be the result of proton assisted sulfur ring opening
of intermediate 18, which in turn is obtained by the reaction
of the second molecule of ketene at the sulfur of
intermediate 15. The formation of pyrimidinones 20 from
intermediate 15 probably proceeds through a rearrangement
involving an episulfonium intermediate 17, wherein
dehydrohalogenation is accompanied by a 1,2-alkylthio
shift. The formation of pyrimidinones 20 by dehydrohalo-
genation of intermediate 16 may be ruled out on the basis of
arguments eluded to, earlier reported similar reactions.8c
Similarly, the reactions of 1-(p-tolyl)-2-phenyl-4-[2-(1,3-
dithiolanyl)]-1,3-diazabuta-1,3-diene 9a and 1-(p-tolyl)-2-
phenyl-4-[2-(1,3-dithianyl)]-1,3-diazabuta-1,3-diene 9b
with vinyl ketene, generated in situ from crotonyl chloride
and triethylamine in dry methylene chloride, resulted in the
isolation of products which were characterized as pyrimi-
dinones 23 on the basis of analytical data and spectral
evidence. For example, 2-phenyl-3-(p-tolyl)-5-vinyl-6-{8-
[(E)-5,8-dithiaoct-2-ene-4-one]}-pyrimidin-4(3H)-one 23a
(Scheme 6) analyzed for C25H24N2O2S2 showed by EIMS a
The plausible mechanism for the formation of pyrimidi-
nones 19 and 20 is depicted in Scheme 5. In this scheme it is
believed that 1,3-diazabuta-1,3-diene 9 undergoes [4þ2]
cycloaddition reaction with chloroketene resulting in initial
formation of intermediate 15 which leads to intermediate
16. The nucleophilic reaction of the thiol of intermediate 16
with either chloroketene or chloroaceteyl chloride results in
the formation of pyrimidinones 19. The pyrimidinones 19

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S. Jayakumar et al. / Tetrahedron 60 (2004) 4315–4324
Scheme 5.
molecular ion peak at m/z 448. Its IR spectrum showed a
strong absorption at 1669 cm21 due to a,b-unsaturated
carbonyl group. Its 1H NMR spectrum showed a doublet of
doublet (J¼6.8, 1.6 Hz) at d 1.68 for the isopropenyl –CH3
group, a singlet at d 2.30 for the aromatic substituted –CH3
group, two multiplets at d 3.26–3.34 (2H) and d 3.40–3.47
(2H) for the protons of two methylene groups attached to
sulfur, a doublet of doublet (J¼11.4, 2.6 Hz) at d 5.56 (Ha),
a doublet of a doublet with fine splitting (J¼15.3, 1.6 Hz) at
d 6.12 (He), a doublet of a doublet (J¼17.6, 2.6 Hz) at d 6.54
(Hb), a doublet of doublet (J¼17.6, 11.4 Hz) at d 6.73 (Hc),
a doublet of a quartet (J¼15.4, 6.9 Hz) at d 6.90 (Hd) in
addition to the aromatic protons. The assigned structure was
further corroborated by its 13C NMR spectrum. The
plausible mechanism for the formation of pyrimidinones
23 is depicted in Scheme 6 and is similar to the one
proposed for the formation of pyrimidinones 19. It is
believed that 1,3-diazabuta-1,3-diene 9 undergoes an initial
[4þ2] cycloaddition reaction with vinyl ketene leading to
the formation of an intermediate 21, which isomerises to
pyrimidinones 22 and its reactions with crotonyl chloride
results in the formation of desired pyrimidinones 23. It is
also possible that the sulfur of intermediate 21 attacks the
carbonyl carbon of another molecule of ketene to form an
intermediate 24 which undergoes proton assisted ring
opening to form the pyrimidinones 23 (Scheme 6).
Thus, a conceptually attractive strategy has been developed
for the synthesis of novel heterocyclic fused 1,3-diazabuta-
1,3-dienes, which have been shown to undergo
interesting cycloaddition with various ketenes. Addition-
ally, bisthio substituted 1,3-diazabuta-1,3-dienes have
also been formed. Depending on the ketene used, this
class of dienes leads to a series of structurally distinct

S. Jayakumar et al. / Tetrahedron 60 (2004) 4315–4324
4321
Scheme 6.
pyrimidinones, some of which are the result of an interesting
rearrangement.
dried over sodium benzophenone ketyl and distilled under
nitrogen. Dichloromethane dried over di-phosphorous
pentoxide and stored over molecular sieves (4A).
3.2. Starting materials
3. Experimental
3.1. General
Benzamidines,10 1-aryl-2-phenyl-4-thiomethyl-4-tertiary-
amino-1,3-diazabuta-1,3-dienes 17 were prepared by
reported methods. Phenyl-, propenyl-, crotonoyl-, 3,3-
dimethylacryl-, chlorides and sorbyl chloride11 where
prepared from the corresponding acid and thionyl chloride.
Melting points were determined by open capillary using
Veego Precision Digital Melting Point apparatus (MP-D)
and are uncorrected. IR spectra were recorded on a
Shimadzu D-8001 spectrophotometer. 1H NMR spectra
were recorded in deuterochloroform with Bruker AC-E 200
(200 MHz) and AC-E 300 (300 MHz) spectrometers using
TMS as internal standard. Chemical shift values are
expressed as ppm downfield from TMS and J values are
in Hz. Splitting patterns are indicated as s: singlet, d:
doublet, t: triplet, m: multiplet, q: quartet and br: broad
peak. 13C NMR spectra were also recorded on a Bruker
AC-200E (50.4 MHz) or Bruker AC-300E (75.0 MHz)
spectrometers in deuterochloroform using TMS as internal
standard. Mass spectra were recorded on Shimadzu GCMS-
QP-2000 mass spectrometer. Elemental analyses were
performed on Heraus CHN-O-Rapid Elemental Analyzer.
Column chromatography was performed on a silica gel
(60–120) mesh or Harrison Research Chromatotron using
2 mm plates (Silica gel 60 PF254). THF/Diethyl ether were
3.3. General method for the preparation of N-aryl-N0-(2-
benzothiazol)-benzamidine 2
A solution of 1-aryl-2-phenyl-4-thiomethyl-4-tertiary
amino-1,3-diazabuta-1,3-diene 1 (10 mmol) and 2-amino-
thiophenol (12 mmol) in dry toluene (30 mL) was refluxed
for a period of 6–7 h. After the completion of reaction (tlc),
solvent was removed under reduced pressure and the crude
product was purified through silica gel column chromato-
graphy and recrystallized using hexane–chloroform
mixture (5:1).
3.3.1. N-Benzothiazol-2-yl-N0-phenyl-benzamidine 2a.
Yellow crystalline solid, yield: 82%; mp 134–135 8C.
Anal. Calcd for C20H15N3S: C, 79.92; H, 4.59; N, 12.76.

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S. Jayakumar et al. / Tetrahedron 60 (2004) 4315–4324
Found: C, 80.05; H, 4.57; N, 12.80%. IR (KBr) nmax: 1651,
1589 cm21. dH (200 MHz, CDCl3): 6.96 (d, J¼7.7 Hz, 2H,
ArH); 7.05–7.42 (m, 8H, ArH); 7.58 (d, J¼7.9 Hz, 2H,
ArH); 7.76 (dd, J¼7.9, 3.7 Hz, 2H, ArH); 12.87 (s, 1H, NH,
D2O exchangeable). dC (50.4 MHz, CDCl3): 121.0, 121.2,
123.8, 124.2, 125.2, 125.8, 128.2, 129.0, 129.7, 130.3,
132.7, 134.8, 139.2, 151.0, 159.8, 173.2. m/z: 329 (Mþ).
Anal. Calcd for C19H14N2OS: C, 71.67; H, 4.43; N, 8.80.
Found: C, 71.68; H, 4.45; N, 8.81%; IR (KBr) nmax: 1662,
1526, 1454, 1861 cm21. dH (300 MHz, CDCl3): 2.04 (s, 3H,
–CH3); 4.96 (s, 1H, Ha); 5.30 (s, 1H, Hb); 7.38–7.71 (m,
8H, ArH); 9.12–9.15 (dd, J¼9.2, 1.8 Hz, 1H, HA). dC
(50 MHz): 119.5, 120.2, 121.9, 124.7, 127.0, 127.1, 127.6,
127.9, 128.3, 129.0, 129.7, 131.3, 133.7, 136.4, 137.9,
156.3, 159.6, 161.6. m/z¼318 (Mþ).
3.3.2. N-Benzothiazol-2-yl-N0-p-tolyl-benzamidine 2b.
Pale yellow crystalline solid, yield: 79%; mp 97–98 8C.
Anal. Calcd for C21H17N3S: C, 73.44; H, 4.99; N, 12.23.
Found: C, 73.45; H, 4.97; N, 12.20%. IR (KBr) nmax: 1652,
1589, 1437, 1385 cm21. dH (200 MHz, CDCl3): 2.29 (s, 3H,
–CH3); 6.84 (d, J¼8.1 Hz, 2H, ArH); 7.00 (d, J¼8.1 Hz,
2H, ArH); 7.23–7.33 (m, 5H, ArH); 7.55 (dd, J¼7.5,
1.4 Hz, 2H, ArH); 7.71–7.76 (m, 2H, ArH); 12.62 (br, 1H,
NH, D2O exchangeable). dC (50.4 MHz, CDCl3): 20.9
(–CH3) 121.0, 121.1, 123.7, 124.1, 125.7, 128.1, 129.5,
129.6, 130.1, 132.8, 134.8, 137.0, 151.0, 159.8, 173.2. m/z:
343 (Mþ).
3.4.4. 3-Buta-1,3-dienyl-2-phenyl-9-thia-1,4a-diaza-
fluoren-4-one 4d. White crystalline solid, yield: 62%; mp
174–175 8C. Anal. Calcd for C20H14N2SO: C, 72.70; H,
4.27; N, 8.48. Found: C, 72.68; H, 4.27; N, 8.50%. IR (KBr)
n
max: 1682, 1662, 1552 cm21. dH (300 MHz, CDCl3): 5.15
(d, J¼10.2 Hz, 1H, Ha); 5.38 (d, J¼16.8 Hz, 1H, Hb); 6.35
(ddd, J¼10.2, 10.2, 16.9 Hz, 1H, Hc); 6.47 (d, J¼15.5 Hz,
1H, He); 7.46–7.77 (m, 8H, ArH and Hd); 9.18–9.20 (dd,
J¼9.1, 1.8 Hz, 1H, HA). dC (50 MHz, CDCl3): 114.4, 116.1,
120.2, 121.7, 124.7, 125.9, 127.0, 127.1, 128.4, 129.4,
129.6, 135.0, 136.2, 137.3, 138.7, 159.6 and 161.6. m/z: 330
(Mþ).
3.4. Reactions of 1,3-diazabutadienes 2 with phenyl-
/vinyl-/isopropenyl-/butadienyl-ketenes
3.5. General method for the preparation of 1-aryl-2-
phenyl-4,4-bismethylthio-1,3-diazabuta-1,3-dienes 8, 1-
(p-tolyl)-2-phenyl-4[2-(1,3-dithianyl)]-1,3-diazabuta-1,3-
diene 9a and 1-(p-tolyl)-2-phenyl-4[2-(1,3-dithiolanyl)]-
1,3-diazabuta-1,3-dienes 9
General procedure. To a well stirred solution of 1,3-
diazabuta-1,3-diene 2 (10 mmol) and triethylamine
(40 mmol) in dry methylene chloride (30 mL) was added
dropwise a solution of phenylacetyl chloride/crotonyl
chloride/3,3-dimethylacryloyl chloride/sorbyl chloride
(20 mmol) in dry methylene chloride (30 mL) over a period
of 1 h at 0 8C. After completion of the reaction (tlc), the
reaction mixture was first washed with saturated sodium
bicarbonate solution (2£25 mL) and water (5£50 mL) and
the organic layer dried over anhydrous sodium sulfate.
Removal of solvent under reduced pressure yielded the
crude product, which was purified by silica gel column
chromatography using a mixture of ethyl acetate and hexane
(1:10, V/V).
To a well stirred suspension of potassium t-butoxide/sodium
hydride (22 mmol) in dry THF (30 mL) was added a
solution of benzamidine (20 mmol) in dry THF at 220 8C
under an atmosphere of nitrogen and stirring continued for
about 5–10 min. To this a solution of carbon disulphide
(22 mmol) in dry THF (10 mL) was added and the reaction
mixture allowed to stir for further 10–15 min and added a
solution of 1,3-dibromopropane/1,2-dibromoethane
(22 mmol) or methyl iodide (45 mmol) in dry THF
(10 mL). The reaction mixture was further stirred for a
period of 2–3 h. After the completion of the reaction (tlc),
solvent was evaporated under reduced pressure, the crude
product was washed with water (2£50 mL) and the organic
layer dried over anhydrous sodium sulfate. Removal of
solvent under reduced pressure yielded the crude product,
which was purified by silica gel column chromatography
using a mixture of ethyl acetate and hexane (1:10,V/V).
3.4.1. 2,3-Diphenyl-9-thia-1,4a-diaza-fluoren-4-one 4a.
White crystalline solid, yield: 73%; mp 132–133 8C.
Anal. Calcd for C22H14N2OS: C, 74.51; H, 3.91; N, 7.91.
Found: C, 74.45; H, 3.91; N, 7.90%. IR (KBr) nmax: 1662,
1526, 1454, 1861 cm21. dH (300 MHz): 7.19–7.41 (m, 8H,
ArH); 7.48–7.56 (m, 2H, ArH); 7.70–7.73 (m, 3H, ArH);
9.12–9.15 (dd, J¼9.2, 1.8 Hz, 1H, HA). dC (50.4 MHz,
CDCl3): 119.5, 120.2, 121.9, 124.7, 127.0, 127.1, 127.6,
127.9, 128.3, 129.0, 129.7, 131.3, 133.7, 136.4, 137.9,
156.3, 159.6, 161.6. m/z: 354 (Mþ).
3.5.1. 1,2-Diphenyl-4,4-bis(thiomethyl)-1,3-diazabuta-
1,3-diene 8a. Pale yellow crystalline solid, yield: 72%;
mp 93–94 8C. Anal. Calcd for C16H16N2S2: C, 63.96; H,
5.37; N, 9.32; Found: C, 63.98; H, 5.36; N, 9.34%. IR (KBr)
3.4.2. 2-Phenyl-3-vinyl-9-thia-1,4a-diaza-fluoren-4-one
4b. Colourless solid, yield: 78%; mp 141–142 8C. Anal.
Calcd for C18H12N2OS: C, 71.12; H, 3.94; N, 9.21. Found:
C, 71.10; H, 3.95; N, 9.17%. IR (KBr) nmax: 1679, 1549,
1504 cm21. dH (300 MHz, CDCl3): 5.48 (dd, J¼11.0,
4.4 Hz, 1H, Hb); 6.52 (dd. J¼18.0, 4.4 Hz, 1H, Ha); 6.59
(dd, J¼18.0, 11.0 Hz, 1H, Hc); 7.45–7.70 (m, 8H, ArH);
9.12–9.15 (dd, J¼8.2, 1.2 Hz, 1H, HA). dC (50.4 MHz,
CDCl3): 114.2, 120.1, 121.7, 124.5, 126.8, 126.9, 127.0,
129.3,129.4, 129.5,136.1, 137.6,159.4, 160.4.m/z: 304 (Mþ).
n
max: 1609, 1579, 1503 cm21. dH (200 MHz, CDCl3): 2.40
(s, 6H, 2£–SCH3); 6.95–6.99 (m, 3H, ArH); 7.21–7.26 (m,
2H, ArH); 7.39–7.46 (m, 3H, ArH); 7.86–7.91 (m, 2H,
ArH). dC (50.4 MHz, CDCl3): 15.0 (2£–SCH3), 121.2,
123.2, 127.9, 128.2, 128.2, 128.8, 130.7, 134.3, 149.3,
159.0, 163.1. m/z: 300 (Mþ, 5%), 287 (15%), 286 (20%).
3.5.2. 1-(p-Tolyl)-2-phenyl-4,4-bis(thiomethyl)-1,3-
diazabuta-1,3-diene 8b. Yellow crystalline solid, yield:
78%; mp 98–100 8C. Anal. Calcd for C17H18N2S2: C,
64.93; H, 5.77; N, 8.9; Found: C, 64.94; H, 5.79; N, 9.0%.
IR (KBr) nmax: 1609, 1579, 1503 cm21, dH (200 MHz,
CDCl3): 2.33 (s, 3H, –CH3); 2.40 (s, 6H, 2£–SCH3); 6.90
3.4.3. 3-Isopropenyl-2-phenyl-9-thia-1,4a-diaza-fluoren-
4-one 4c. Colourless solid, yield: 72%; mp 132–133 8C.

S. Jayakumar et al. / Tetrahedron 60 (2004) 4315–4324
4323
(d, J¼8.2 Hz, 2H, ArH); 7.05 (d, J¼8.2 Hz, 2H, ArH);
7.40–7.43 (m, 3H, ArH); 7.85–7.89 (m, 2H, ArH). dC
(50.4 MHz, CDCl3): 15.0 (2£–SCH3), 21.1 (q, –CH3),
121.4 (d), 127.9 (d), 128.2 (d), 128.9 (d), 130.5 (d), 132.2
(s), 134.8 (s), 148.8 (s), 158.1 (s), 162.5 (s). m/z: 315
(Mþþ1, 5%), 314 (Mþ, 6%), 300 (16%), 299 (80%).
3.6.2. 2,3-Diphenyl-5,6-bis(methylthio)-pyrimidine-
4(3H)-one 14a. White crystalline solid, yield: 71%; mp
221–222 8C. Anal. Calcd for C18H16N2OS2. C, 63.50; H,
4.74; N, 8.23. Found: C, 63.52; H, 4.75; N, 8.25%. IR (KBr)
n
max: 1668, 1550 cm21. dH (200 MHz, CDCl3): 2.58 (s, 6H,
2£–SCH3); 7.06–7.32 (m, 10H, ArH). m/z: 340 (Mþ).
3.5.3. 1-(o-Tolyl)-2-phenyl-4,4-bis(thiomethyl)-1,3-
diazabuta-1,3-diene 8c. Yield: 69%; viscous oil. Anal.
Calcd for C17H18N2S2: C, 64.93; H, 5.77; N, 8.9; Found: C,
64.92; H, 5.76; N, 9.1%. IR (KBr) nmax: 1609, 1579,
1503 cm21. dH (200 MHz, CDCl3): 2.14 (s, 3H, –CH3);
2.37 (s, 6H, 2£–SCH3); 6.86 (d, J¼7.8 Hz, 1H, ArH); 6.90
(dd, J¼7.2, 7.4 Hz, 1H, ArH); 7.06 (dd, J¼7.2, 7.4 Hz, 1H,
ArH); 7.12 (d, J¼7.8 Hz, 1H, ArH); 7.38–7.47 (m, 3H,
ArH); 7.90–7.94 (m, 2H, ArH). m/z: 314 (Mþ).
3.6.3. 2-Phenyl-3-(p-tolyl)-5,6-bis(methylthio)-pyrimi-
dine-4(3H)-one 14b. Colourless solid, yield: 67%; mp
190–192 8C. Anal. Calcd for C19H18N2OS2. C, 64.40; H,
5.08; N, 7.91. Found: C, 64.53; H, 4.98; N, 8.08%. IR (KBr)
n
max: 1669, 1548 cm21. dH (300 MHz, CDCl3): 2.31 (s, 3H,
–CH3); 2.47 (s, 3H, –SCH3); 2.59 (s, 3H, –SCH3); 6.98 (d,
J¼8.2 Hz, 2H, ArH); 7.11 (d, J¼8.2 Hz, 2H, ArH); 7.18–
7.32 (m, 5H, ArH). m/z: 354 (Mþ).
3.7. General procedure for the reactions of 1,3-diaza-
butadienes 9 with vinyl-/chloro ketene
3.5.4. N-[1,3]Dithian-2-ylidene-N0-p-tolyl-benzamidine
9a. Yellow crystalline solid, yield: 61%; mp 130–132 8C.
Anal. Calcd for C17H16N2S2: C, 65.35; H, 5.16; N, 8.97.
Found: C, 65.37; H, 5.14; N, 8.99%. IR (KBr) nmax: 1609,
1579, 1503 cm21. dH (300 MHz, CDCl3): 2.32 (s, 3H,
–CH3); 3.44 (m, 4H, 2£–CH2–); 6.68 (d, J¼7.9 Hz, 2H,
ArH); 6.99 (d, J¼8.3 Hz, 2H, ArH); 7.38–7.46 (m, 3H,
ArH); 7.92–7.94 (m, 2H, ArH). m/z: 312 (Mþ).
To a well stirred solution of 1,3-diazabuta-1,3-diene 9
(10 mmol) and triethylamine (40 mmol) in dry methylene
chloride (30 mL) was added dropwise a solution of
crotonylchloride/chloroacetyl chloride (25 mmol) in dry
methylene chloride (30 mL) over a period of one hour at
0 8C After completion of the reaction (tlc), the reaction
mixture was first washed with saturated sodium bicarbonate
solution (2£25 mL) and water (5£50 mL) and the organic
layer dried over anhydrous sodium sulfate. Removal of
solvent under reduced pressure yielded the crude product,
which was purified by silica gel column chromatography
using a mixture of ethyl acetate and hexane (1:10,V/V).
3.5.5. N-[1,3]Dithiolan-2-ylidene-N0-p-tolyl-benzamidine
9b. Colourless crystalline solid, yield: 58%; mp 90–91 8C.
Anal. Calcd for C18H18N2S2: C, 66.22; H, 5.56; N, 8.58.
Found: C, 66.26; H, 5.58; N, 8.56%. IR (KBr) nmax: 1609,
1579, 1503 cm21. dH (300 MHz, CDCl3): 2.03 (m, 2H,
–CH2–); 2.31 (s, 3H, –CH3); 2.91 (m, 4H, 2£–SCH2–);
6.97 (d, J¼8.0 Hz, 2H, ArH); 7.09 (d, J¼7.9 Hz, 2H, ArH);
7.38–7.46 (m, 3H, ArH); 7.90 (m, 2H, ArH). dC (75 MHz,
CDCl3): 20.8 (–CH2–), 21.6 (–CH3), 29.7 (2£–SCH2),
121.4, 127.6, 128.8, 129.1, 130.5, 132.5, 134.4, 146.0,
150.9, 165.3. m/z: 328 (Mþþ2), 327 (Mþþ1), 326 (Mþ).
3.7.1. 2-Phenyl-3-(p-tolyl)-5-chloro-6-{6-[3,6-dithiahex-
1-chloro-2-one]}-pyrimidine-4(3H)-one 19a. Pale white
solid, yield: 37%; mp 140–142 8C. Anal. Calcd for
C21H18N2O2S2Cl2: C, 54.19; H, 3.87; N, 6.02. Found: C,
53.94; H, 4.02; N, 5.88%. IR (KBr) nmax: 1672 cm21. dH
(300 MHz, CDCl3): 2.31 (s, 3H, –CH3); 3.29–3.35 (m, 2H,
–CH2–); 3.39–3.45 (m, 2H, –CH2–); 4.14 (s, 2H, –CH2–
); 6.99 (d, J¼8.2 Hz, 2H, ArH); 7.11 (d, J¼8.2 Hz, 2H,
ArH); 7.19–7.31 (m, 5H, ArH). dC (75 MHz, CDCl3): 21.1
(–CH3), 29.6 (–CH2–), 29.9 (–CH2–), 47.8 (–CH2–),
114.7, 127.8, 128.1, 129.1, 129.6, 129.9, 133.8, 134.1,
138.8, 156.2, 156.9, 160.8, 193.3. m/z: 465 (Mþ).
3.6. General procedure for the reactions of 1,3-
diazabutadienes 8 with phenyl-/chloroketenes
To a well stirred solution of 1,3-diazabuta-1,3-diene 8
(10 mmol) and triethylamine (40 mmol) in dry methylene
chloride (30 mL) was added dropwise a solution of
phenylacetyl chloride/chloroacetyl chloride (20 mmol) in
dry methylene chloride (30 mL) over a period of 1 h at 0 8C.
After completion of the reaction (tlc), the reaction mixture
was first washed with saturated sodium bicarbonate solution
(2£25 mL) and water (5£50 mL) and the organic layer dried
over anhydrous sodium sulfate. Removal of solvent under
reduced pressure yielded the crude product, which was
purified by silica gel column chromatography using a
mixture of ethyl acetate and hexane mixture (1:10, V/V).
3.7.2. 2-Phenyl-3-(p-tolyl)-5-chloro-6-{7-[3,7-dithiahept-
1-chloro-2-one]}-pyrimidine-4(3H)-one 19b. Colourless
crystalline solid, yield: 33%; mp 94–95 8C. Anal. Calcd for
C22H20N2O2S2Cl2: C, 55.11; H, 4.17; N, 5.84 Found: C,
54.90; H, 3.86; N, 5.56%. IR (KBr) nmax: 1678 cm21. dH
(300 MHz, CDCl3): 2.07 (m, 2H, –CH2–); 2.31(s, 3H,
–CH3); 3.06 (t, J¼7.0 Hz, 2H, –S–CH2–); 3.26 (t,
J¼7.0 Hz, 2H, –S–CH2–); 4.12 (s, 2H, –CH2–); 6.99 (d,
J¼8.2 Hz, 2H, ArH); 7.11 (d, J¼8.2 Hz, 2H, ArH); 7.20–
7.33 (m, 5H, ArH). dC (50.4 MHz, CDCl3): 21.1 (–CH3),
28.2 (–CH2–), 29.0 (–CH2–), 29.6 (–CH2–), 47.8
(–CH2–), 114.7, 127.9, 128.1, 129.1, 129.6, 129.8, 134.1,
134.2, 138.9, 156.0, 157.1, 161.5 (C-4), 193.7 (CvO). m/z:
479 (Mþ).
3.6.1. 2,5-Diphenyl-3-(p-tolyl)-6-methylthio-pyrimidine-
4(3H)-one 11. White crystalline solid, yield: 82%; mp 185–
186 8C. Anal. Calcd for C24H20N2OS: C, 75.00; H, 5.21; N,
7.29. Found: C, 74.75; H, 5.34; N, 6.99%. IR (KBr) nmax
:
1671 cm21. dH (200 MHz, CDCl3): 2.32 (s, 3H, –CH3);
2.49 (s, 3H, –SCH3); 6.98–7.41 (m, 14H, ArH). dC
(50.4 MHz, CDCl3): 15.0 (–SCH3), 21.0 (–CH3), 121.3,
127.9, 128.1, 128.6, 130.5, 132.2, 134.6, 146.6, 158.1,
162.5. m/z: 384 (Mþ).
3.7.3. 2-Phenyl-(p-tolyl)-3,6,7-trihydro-pyrimidino-
[4,5,b]-dithiane-4-one 20a. White crystalline solid, yield:
36%; mp 158–160 8C. Anal. Calcd for C19H16N2OS2: C,

4324
S. Jayakumar et al. / Tetrahedron 60 (2004) 4315–4324
64.77; H, 4.54; N, 7.95. Found: C, 63.97; H, 4.32; N, 7.74%.
IR (KBr) nmax: 1682 cm21. dH (200 MHz, CDCl3): 2.23 (s,
3H, –CH3); 3.42–3.48 (m, 2H, –CH2–); 3.64–3.66 (m,
2H, –CH2–); 7.00 (d, J¼8.3 Hz, 2H, ArH); 7.26 ((d,
J¼8.3 Hz, 2H, ArH); 7.24–7.51 (m, 5H, ArH). dC
(50.4 MHz, CDCl3): 20.9 (–CH3), 34.1 (–CH2–), 40.4
(–CH2–), 118.1, 128.2, 129.0, 129.2, 129.4, 133.6, 134.5,
160.2. m/z: 352 (Mþ).
Fellowship and the financial assistance by CSIR, New
Delhi, is gratefully acknowledged.
References and notes
1. For recent reviews on azadienes see: (a) Boger, D. L.
Tetrahedron 1983, 39, 2869. (b) Boger, D. L. Chem. Tract-
Org. Chem. 1996, 9, 149. (c) Barluenga, J.; Tomas, M. Adv.
Heterocycl. Chem. 1993, 57, 1. (d) Boger, D. L. Comprehen-
sive organic synthesis; Trost, B. M., Fleming, I., Eds.;
Pergamon: Oxford, 1991; Vol. 5. Chapter 4.3. (e) Ghosez, L.
Stereocontrolled organic synthesis; Blackwell: London, 1994;
p 193. (f) Boger, D. L.; Weinreb, S. M. Hetero Diels–Alder
methodology in organic synthesis; Academic: San Diego,
1987.
3.7.4. 2-Phenyl-3-(p-tolyl)-3,6,7,8-tetrahydro-pyrimido-
[4,5,b]-1,4-dithiapene-4-one 20b. White crystalline solid,
yield: 36%; mp 273–274 8C. Anal. Calcd for C20H18N2OS2
C, 65.57; H, 4.91; N, 7.65. Found: C, 64.64; H, 5.53; N,
7.54%. IR (KBr) nmax: 1672 cm21. dH (300 MHz, CDCl3):
2.14–2.22 (m, 2H, –CH2–); 2.28 (s, 3H, –CH3); 3.59 (t,
J¼6 Hz, 2H, –S–CH2–); 3.69 (t, J¼6 Hz, 2H, –S–CH2–);
6.96 (d, J¼8.3 Hz, 2H, ArH); 7. 08 (d, J¼8.3 Hz, 2H, ArH);
7.13–7.26 (m, 5H, ArH). dC (50.4 MHz, CDCl3): 21.1
(–CH3), 27.6 (–CH2–), 30.1 (–CH2–), 30.6 (–CH2–),
119.7, 127.8, 128.2, 129.1, 129.5, 133.8, 134.1, 136.5,
153.6, 159.7. m/z: 366 (Mþ).
2. Gorel, G.; Marchand, E.; Toupet, L.; Foucaud, A. J. Org.
Chem. 1989, 54, 1185.
3. (a) Sain, B.; Singh, S. P.; Sandhu, J. S. Tetrahedron Lett. 1991,
32, 5151. (b) Sain, B.; Singh, S. P.; Sandhu, J. S. Tetrahedron
1992, 48, 4567.
3.7.5. 2-Phenyl-3-(p-tolyl)-5-vinyl-6-{8-[(E)-5,8-
4. (a) Barluenga, J.; Tomas, M.; Bellestros, A.; Lopez, L. A.
Heterocycles 1994, 37, 1109. (b) Gilchrist, T. L.; Gonsalves,
A. M. R.; Teresa, M. D. V. P. Tetrahedron Lett. 1993, 4097.
(c) Molina, P.; Aller, E.; Lopez-Lazaro, A.; Alajarin, M.;
Lorenzo, A. Tetrahedron Lett. 1994, 35, 3817.
dithiaoct-2-ene-4-one]}-pyrimidine-4(3H)-one 23a.
Colourless crystalline solid, yield: 69%; mp 157–158 8C.
Anal. Calcd for C25H24N2O2S2: C, 66.93; H, 5.39; N, 6.24.
Found: C, 66.95; H, 5.38; N, 6.26%. IR (KBr) nmax
:
1669 cm21. dH (200 MHz, CDCl3): 1.68 (dd, J¼6.8, 1.6 Hz,
3H, –CH3); 2.30 (s, 3H, –CH3); 3.26–3.34 (m, 2H, –S–
CH2–); 3.40–3.47 (m, 2H, –S–CH2–); 5.56 (dd, J¼11.4,
2.6 Hz, 1H, Ha); 6.12 (dd, J¼15.3, 1.6 Hz, 1H, He); 6.54
(dd, J¼17.6, 2.6 Hz, 1H, Hb); 6.73 (dd, J¼17.6, 11.4 Hz,
1H, Hc); 6.90 (dq, J¼15.4, 6.9 Hz, 1H, Hd); 6.99 (d,
J¼8.2 Hz, 2H, ArH); 7.12 (d, J¼8.2 Hz, 2H, ArH); 7.16–
7.32 (m, 5H, ArH). dC (50.4 MHz, CDCl3): 18.0 (–CH3),
21.1 (–CH3), 29.3 (–CH2–), 30.2 (–CH2–), 116.0, 121.0,
127.0, 127.4, 127.8, 128.4, 129.3, 129.6, 129.7, 129.9,
134.5. 134.6, 141.3, 142.1, 155.4, 159.5, 116.1 (C-4), 189.0
(CvO). m/z: 448 (Mþ).
5. Ibnusaud, I.; Malar, E. P. J.; Sundaram, N. Tetrahedron Lett.
1990, 47, 1473.
6. (a) Crooks, S.; Sykes, P. J. Chem. Soc., Perkin Trans. 1 1977,
1791. (b) Mazumdar, S. N.; Sharma, M.; Mahajan, M. P.
Tetrahedron Lett. 1987, 28, 2641. (c) Mazumdar, S. N.;
Ibnusaud, I.; Mahajan, M. P. Tetrahedron Lett. 1986, 27, 5875.
(d) Barluenga, J.; Tomas, M.; Bellestros, A.; Lopez, L. A.
Tetrahedron Lett. 1989, 30, 4573. (e) Rossi, E.; Celentano, G.;
Stradi, R.; Strada, R. Tetrahedron Lett. 1990, 31, 903.
(f) Wurthwein, E. U.; Luthadart, P. Tetrahedron Lett. 1988,
29, 921. (g) Mastuda, I.; Yamamoto, S.; Ishii, Y. J. Chem.
Soc., Perkin Trans. 1 1976, 1528. (h) Bhartam, P. V.; Kumar,
R. S.; Mahajan, M. P. Org. Lett. 2000, 2, 2725.
3.7.6. 2-Phenyl-3-(p-tolyl)-5-vinyl-6-{9-[(E)-5,9-dithia-
non-2-ene-4-one]}-pyrimidine-4(3H)-one 23b. White
crystalline solid, yield: 72%; mp 98–100 8C. Anal. Calcd
for C26H26N2O2S2: C, 67.53; H, 5.62; N, 6.06. Found: C,
67.28; H, 5.86; N, 5.93%. IR (KBr) nmax: 1672 cm21. dH
(300 MHz, CDCl3): 1.88 (dd, J¼7.1, 1.5 Hz, 3H, –CH3);
2.00–2.12 (m, 2H, –CH2–); 2.31 (s, 3H, –CH3); 3.05 (t,
J¼7.1 Hz, 2H, –S–CH2–); 3.29 (t, J¼7.1 Hz, 2H, –S–
CH2–); 5.56 (dd, J¼11.7, 2.2 Hz, 1H, Ha); 6.11 (dd,
J¼15.4, 1.8 Hz, 1H, He); 6.54 (dd, J¼17.1, 2.2 Hz, 1H, Hb);
6.75 (dd, J¼17.1, 11.7 Hz, 1H, Hc); 6.90 (dq, J¼15.4,
7.1 Hz, 1H, Hd); 7.00 (d, J¼8.3 Hz, 2H, ArH); 7.12 (d,
J¼8.3 Hz, 2H, ArH); 7.18–7.32 (m, 5H, ArH). dC (75 MHz,
CDCl3): 17.9 (–CH3), 21.1 (–CH3), 27.4 (–CH2–), 29.2
(–CH2–), 30.2 (–CH2–), 115.8, 120.8, 127.5, 127.8, 128.5,
129.3, 129.6, 130.1, 134.6. 138.5, 140.8, 155.2, 159.5, 161.7
(C-4), 189.4 (CvO). m/z: 462 (Mþ).
7. (a) Mazumdar, S. N.; Mahajan, M. P. Synthesis 1990, 417.
(b) Dey, P. D.; Sharma, A. K.; Rai, S. N.; Mahajan, M. P.
Tetrahedron 1995, 51, 7459. (c) Sharma, A. K.; Mahajan, M. P.
Tetrahedron 1997, 53, 13841.
8. (a) Mukherjee, S.; Mazumdar, S. N.; Sharma, A. K.; Mahajan,
M. P. Heterocycles 1998, 47, 933. (b) Mazumdar, S. N.;
Mahajan, M. P. Tetrahedron 1991, 47, 1473. (c) Mazumdar,
S. N.; Sharma, A. K.; Mukherjee, S.; Sengupta, D.; Mahajan,
M. P. Tetrahedron 1994, 50, 7579. (d) Sharma, A. K.;
Mahajan, M. P. Heterocycles 1995, 40, 787. (e) Dey, P. D.;
Sharma, A. K.; Mahajan, M. P. Tetrahedron 1995, 51, 7459.
(f) Dey, P. D.; Sharma, A. K.; Bhartam, P. V.; Mahajan, M. P.
Tetrahedron 1997, 53, 13829.
9. (a) Sharma, A. K.; Jayakumar, S.; Mahajan, M. P. Tetrahedron
Lett. 1998, 39, 7205. (b) Sharma, A. K.; Jayakumar, S.;
Hundal, M. S.; Mahajan, M. P. J. Chem. Soc., Perkin Trans. 1
2002, 774–778.
10. Chaudhary, S.; Debroy, A.; Mahajan, M. P. Can. J. Chem.
1982, 60, 1122.
Acknowledgements
11. Sharma, A. K.; Mazumdar, S. N.; Mahajan, M. P. J. Org.
Chem. 1996, 61, 5506.
S.J. is grateful to CSIR, New Delhi for a Senior Research