Synthesis of chiral 10, 11 and 12-membered nitrogen and oxygen heterocycles by intramolecular nitrile oxide cycloadditon of tethered N-and O-allyl carbohydrate derivatives

Article abstract of DOI:10.1016/S0040-4020(00)00844-9

Chiral 10 to 12-membered nitrogen and oxygen heterocycles fused to isoxazoline rings have been prepared in a highly regioselective and stereoselective manner by intramolecular nitrile oxide cycloaddition of tethered N- and O-allyl carbohydrate derivatives. The use of a -Y-Ar-CH₂ tether containing a 1,2-disubstituted aromatic ring between the heteroatom attached to the nitrile oxide-bearing carbohydrate scaffold, and the allyl group, facilitates the formation of the medium-sized rings. The cycloaddition afforded bridged isoxazolines in the cases of O-tethered allyl carbohydrate derivatives, whereas a fused isoxazoline resulted when a N(Ts)-tethered allyl derivative was used. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00844-9

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 8945±8951
Synthesis of Chiral 10, 11 and 12-Membered Nitrogen and Oxygen
Heterocycles by Intramolecular Nitrile Oxide Cycloaddition of
Tethered N- and O-Allyl Carbohydrate Derivatives
*
Swapan Majumdar, Ranjan Mukhopadhyay and Anup Bhattacharjya
Indian Institute of Chemical Biology, 4 Raja S. C. Mullick Road, Calcutta 700 032, India
Received 18 May 2000; revised 29 August 2000; accepted 14 September 2000
AbstractÐChiral 10 to 12-membered nitrogen and oxygen heterocycles fused to isoxazoline rings have been prepared in a highly
regioselective and stereoselective manner by intramolecular nitrile oxide cycloaddition of tethered N- and O-allyl carbohydrate derivatives.
The use of a ±Y±Ar-CH2 tether containing a 1,2-disubstituted aromatic ring between the heteroatom attached to the nitrile oxide-bearing
carbohydrate scaffold, and the allyl group, facilitates the formation of the medium-sized rings. The cycloaddition afforded bridged isoxazo-
lines in the cases of O-tethered allyl carbohydrate derivatives, whereas a fused isoxazoline resulted when a N(Ts)-tethered allyl derivative
was used. q 2000 Elsevier Science Ltd. All rights reserved.
Introduction
carbohydrate system is expected to lead to the formation
of chiral isoxazolines 2 or 3, or both depending on the
regioselectivity of the reaction. An important structural
feature of 2 and 3 is the presence of a core macrohetero-
cycle, which is fused to an aromatic ring, a carbohydrate
ring (such as furanoside), and an isoxazoline ring. The ring
size of the core heterocycle is dependent on the value of n,
i.e. the number of intervening carbon atoms between the
nitrile oxide and the carbohydrate ring, and a bridged
isoxazoline 3 has a core ring one carbon atom larger than the
fused isoxazoline 2. It is apparent from the structures of 2
and 3 that the formation of 10 to 12-membered heterocycles
is a distinct possibility when nˆ0 and 1. Although
8-membered and other macrocycles have been prepared
by intramolecular nitrile oxide cycloadditions,11±13 to our
knowledge, synthesis of the aforementioned ring systems
have not to date been reported by this cycloaddition. We
describe herein the synthesis of some chiral 10 to
12-membered heterocycles based on the above strategy.
Nitrone and nitrile oxide cycloadditions are two of the most
useful and operationally simple cycloaddition reactions.1,2
The intramolecular variety of these reactions have been
extensively used in the preparation of a variety of cyclic
skeletons fused to isoxazolidine and isoxazoline rings.
Recent applications of these reactions to N- and O-alkenyl
carbohydrate nitrones and nitrile oxides has led to the
development of a powerful method for the synthesis of
enantiopure cyclic ether derivatives,3±8 such as tetrahydro-
furans, pyrans and oxepanes as well as cyclic amines such as
piperidines and azepines.9,10 Among the alkenyl groups
investigated in these cases, allyl or substituted allyl groups
are most widely used. We envisaged that if a tether Y±Ar-
CH2 (Scheme 1) containing a 1,2-disubstituted aromatic
moiety is incorporated between an heteroatom X attached
to a carbohydrate scaffold and the allyl moiety, the cyclo-
addition of a nitrile oxide 1 generated from this tethered
Scheme 1.
Keywords: medium ring heterocycles; nitrile oxide cycloaddition; tethered N- and O-allyl carbohydrate derivatives.
* Corresponding author. 191-33-4733491; fax: 191-33-4735197/0284; e-mail: anupbhattacharjya@iicb.res.in
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00844-9

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S. Majumdar et al. / Tetrahedron 56 (2000) 8945±8951
Scheme 2. Reagents: a: for 4a!5a and 4b!5b, 2-allyloxy benzyl bromide, Bu4NBr, CH2Cl2-50% aq. NaOH (1:1), 258C, 4 h, 78% (5a), 96% (5b); for 4c!
5d, 2-allyloxy benzyl bromide, anhydrous K2CO3, acetone, 258C, 16 h, 95%; for 4a! 5c, 2-N-allyl(Ts)amino benzyl bromide, Bu4NBr, CH2Cl2-50% aq.
NaOH (1:1), 258C, 4 h, 56%; b: 75% aq. AcOH; 258C, 14 h, 83% (6a), 78% (6b), 72% (6c), 72% (6d); c: NaIO4, MeOH±H2O (4:1), 0±258C, 1.5 h; d:
NH2OH´.HCl, MeOH-py (4:1), re¯ux, 8 h; e: Chloramine-T hydrate, EtOH, re¯ux, 8 h, 50% (12), 62% (13), 35% (14), 70% (15); f: (i) CH3NO2, KF, i-PrOH,
258C, 24 h (ii) Ac2O, DMAP, ether±CH2Cl2, 258C, 12 h (1:1); (iii) NaBH4, EtOH±THF (3;5), 08C, 4 h, 77%; g, PhNCO, Et3N, C6H6, 258C, 50 h, 50%; h (i) 4%
H2SO4 in CH3CN±H2O (10:1), 258C, 24 h (ii) NaIO4, MeOH±H2O (2:1), 258C, 2 h (iii) NaBH4, MeOH, 08C, 2 h (iv) Ac2O, py, DMAP, 258C, 12 h, 52% from
15.
Results and Discussion
be mentioned that the intermediates involved in the above
sequence of reactions were not rigorously puri®ed although
their NMR spectral characteristics were consistent with the
expected structures.
The tethered carbohydrate scaffold was readily prepared by
alkylation of the carbohydrate derivatives 4a±4c with
2-allyloxy benzyl bromide and 2-(N-p-toluenesulphona-
mido-N-allyl)amino benzyl bromide according to Scheme
2. Alkylation of 4a and 4b was effected14 in a biphasic
medium consisting of CH2Cl2 and 50% aquous NaOH solu-
tion in the presence of tetrabutylammonium bromide, while
alkylation of 4c was achieved in acetone in the presence of
K2CO3. The tethered carbohydrate derivatives 5a±5d were
converted to the oximes 8a±8d through a sequence of reac-
tions4,6 involving selective removal of the 5,6-isopropyl-
idene moiety giving diols 6a±6d, NaIO4 induced
oxidative cleavage of the diols to the aldehydes 7a±7d,
followed by treatment with NH2OH in pyridine. It should
Treatment of the oxime 8a with chloramine-T15 in ethanol
afforded, via the cycloaddition of the nitrile oxide 9a, the
bridged isoxazoline 12 exclusively in 50% yield as evident
from the 1H NMR spectrum of the product. The appearance
of two sets of double doublets at d 3.11 (Jˆ17, 3 Hz) and d
1
3.26 (Jˆ17, 10 Hz) in the H NMR spectrum and appear-
ance of a ±CH2± peak at d 39.0 and a quaternary carbon
peak (CvN) at d 160.1 or 157.5 in the 13C NMR spectrum
of 12 indicated the presence of the bridged isoxazoline
moiety. The structure of 12 was further corroborated by
HSQC and DQFCOSY NMR experiments. However, the

S. Majumdar et al. / Tetrahedron 56 (2000) 8945±8951
8947
stereochemistry of the newly formed chiral centre could not
be established even by a NOESY experiment. It was not
possible to assign the orientation of the bridge methylene,
because of the absence of any cross peak, which could
correlate either the bridgehead proton or the bridge methyl-
ene protons with other existing carbohydrate chiral centres.
The isoxazoline 12 incorporates a 1,5-dioxacycloundecane
ring, which is fused to a furanoside ring besides benzo and
an isoxazolo rings.
tethered allyl instead of a O-tethered allyl in 9b. Unlike the
previous cases, cycloaddition of 9d led to the formation of a
fused isoxazoline 15 in 70% yield. This was evident from
the appearance of a one-proton multiplet at d 3.68 in the 1H
NMR spectrum of 15 due to 5-H of the isoxazoline ring,
which is coupled to four vicinal protons. In addition, the
appearance of a ±CH-peak at d 48.8 due to 5-C in the 13C
NMR spectrum was consistent with the presence of the
fused isoxazoline moiety in 15. A conspicuous feature of
the 1H NMR spectrum of 15 was the rather unusual chemical
shift (d 2.31) of one of the protons (6-HB) of 6-CH2 which is
attached to an oxygen atom. This was con®rmed by de-
coupling experiments, which indicated its coupling to
6-HA at d 4.12. The attachment of 6-C to an oxygen atom
was con®rmed by a C,H-COSY experiment, which indi-
cated the attachment of both 6-HA and 6-HB with 6-C, the
signal for which appeared at d 69.2. The stereochemistry of
the methine proton in 15 could not be established from the
NOESY spectrum. In order to explore the possibility of
bringing the methine proton in a closer proximity with
2-H or 3-H for a better chance of getting NOESY cross
peaks, an attempt was made to transform 15 to a more
¯exible system. To this end, the isoxazoline 15 was
subjected to a known degradation of the furanoside ring.4,8
A sequence of reactions consisting of acid removal of the
isopropylidenedioxy group, vicinal diol cleavage with
NaIO4, reduction of the resulting hydroxyaldehyde by
NaBH4, and a ®nal acetylation yielded the diacetate 16.
A change in the stereochemistry at 3-C did not alter the
regioselectivity of the cycloaddition. This was evident
from the cycloaddition of the nitrile oxide 9b, the 3-C
epimer of 9a, obtained by treatment of the oxime 8b with
chloramine-T. The bridged isoxazoline 13 was formed
exclusively in 62% yield. The pattern of the 1H NMR spec-
trum of 13 was closely similar to that of 12. The bridged
isoxazoline structure of 13 was consistent with the appear-
ance of two sets of double doublets at d 2.57 (Jˆ16.9,
2.2 Hz) and d 3.15 (Jˆ17.0, 10.8 Hz) in the 1H NMR spec-
trum as well as a ±CH2± carbon peak at d 34.7 and a
quaternary carbon peak at d 158.0 or 158.1 (CvN) in the
13C NMR spectrum. The NOESY spectrum of 13 revealed
distinct cross peaks between 2-H and the 5-HB, i.e. the more
shielded of the bridge methylene protons. This correlation
established the b-orientation of the bridge methylene; since
2-C in 13 has the same stereochemistry as that of 3-C in 4b,
the 1,5-dioxacycloundecane skeleton present in 13 is dia-
stereomeric with that present in 12.
1
Both the H and 13C NMR spectrum of 16 indicated the
survival of the isoxazoline-fused azaoxaheterocycle through
the degradation procedure. Like its precursor 15, 6-HB of
±O-6-CH2 in 16 appeared as a high ®eld doublet of doublets
at d 2.04. The assignment was con®rmed by decoupling as
well as C,H-COSY experiments as was done for 15. The
NOESY spectrum of 16 exhibited a distinct cross peak
between 5-H and 3-H. It is well known that the 3-C does
not undergo any epimerisation during the degradation
procedure leading to 16.4,8 Keeping this in mind, the obser-
vation in the NOESY experiment indicated clearly that 5-H
has an a orientation i.e. the same as that of 3-H. Therefore,
the orientation of 5-H in the precursor 15 is also a.
The aforementioned observations led to the conclusion that
a change in stereochemistry at 3-C of the nitrile oxide had
no effect on the regioselectivity of the cycloaddition. In
order to investigate whether a change in the heteroatom Y
could bring about any change in the regioselectivity, the
oxime 8c was subjected to treatment with chloramine-T.
However, the resulting nitrile oxide 9c, which has N(Ts)-
allyl group instead of O-allyl, again gave rise to a bridged
1
isoxazoline 14 exclusively in 53% yield. The H and 13C
NMR spectra of 14 exhibited all the characteristics of a
bridged isoxazoline observed for 12 and 13. The appearance
of two sets of double doublets at d 3.21 (Jˆ17.1, 11.4 Hz)
and 3.61 (Jˆ17.1, 4.3 Hz) in the 1H NMR spectrum as well
as a signal at d 38.1 (bridge ±CH2±) and a quaternary
carbon peak at d 152.7 (CvN) was a clear indication of
the bridged isoxazoline nature of 14. The stereochemistry of
14 could be established on the basis of the NOESY spec-
trum, the most useful feature of which was the appearance
of distinct cross peaks between the less shielded of the
5-CH2 protons i.e. 5-HA with 2-H and 3-H and between
the more shielded proton i.e. 5-HB with 3-H. This obser-
vation led to an a-orientation of the bridge methylene of
the isoxazoline ring, because both 2-H and 3-H are a as 3-H
and 4-H in 4a. The core macrocycle of 14 is a 1-oxa-5-
azacycloundecane system.
It was apparent, therefore, that cycloaddition of the nitrile
oxides 9a±9c, which have a 3-O-tethered allyl carbohydrate
backbone resulted in the formation of the bridged isoxazo-
lines 12, 13 and 14. However, the regioselectivity of the
cycloaddition was drastically altered in the cycloaddition
of 3-N(Ts)-tethered allyl carbohydrate nitrile oxide 9d
resulting in the exclusive formation of the fused isoxazoline
15. The reason for this change in regioselectivity is not
known, although similar change in regioselectivity or
chemical reactivity, when oxygen atom is replaced by
-N(Ts) has been reported earlier.9,10,16 The fused isoxazoline
15 incorporates a 1-oxa-5-azacyclodecane system. So a
change in the regioselectivity of the cycloaddition made
available a 10-membered heterocycle, in contrast to the
11-membered one obtained in the previous cases.
Thus, it is observed that a change in stereochemistry at 3-C
of the nitrile oxide, or substitution of oxygen atom by nitro-
gen did not affect the regioselectivity of the cycoaddition,
and a bridged isoxazoline was the exclusive product in each
case. Still another variation was possible through a change
in heteroatom X. Thus, oxidation of the oxime 8d resulted in
the formation of the nitrile oxide 9d, which has a N(Ts)-
In a separate route, the aldehyde 7a was converted to the
nitro compound 10a following a known protocol,11 invol-
ving condensation with nitromethane, acetylation of the
resulting nitroaldol with acetic anhydride, and DMAP and
reduction with NaBH4 (Scheme 2). Treatment of 10a with

8948
S. Majumdar et al. / Tetrahedron 56 (2000) 8945±8951
1
phenyl isocyanate led to the exclusive formation of the
bridged isoxazoline 17 via the nitrile oxide 11a. The
appearance of two double doublets in the 1H NMR spectrum
at d 2.77 and d 3.23 with large geminal coupling constants
(16 Hz), as well as the bridge ±CH2± carbon peak (6-C) at d
41.6 and a quaternary carbon peak (CvN) in the 13C NMR
spectrum, is consistent with the presence of the bridged
isoxazoline moiety. The isoxazoline 17 has an extra
±CH2± group over the isoxazoline 12, and the protons of
this methylene group viz 4-HA and 4-HB appeared as two
double doublets at d 2.75 and 2.56. As expected, many of
the 1H NMR spectral features of 17 were similar to those of
12. Analysis of H,H-COSY, C,H-COSY and NOESY spec-
tra of 17 led to the assignment of a-orientation of the bridge
methylene i.e. ±6-CH2±, which was in accordance with the
appearance of a cross peak between 6-HA and 2-H in the
NOESY spectrum of 17. The nitrile oxide 11a has an extra
methylene group between the nitrile oxide moiety and the
carbohydrate backbone, and consequently the isoxazoline
17 incorporates a 1,5-dioxacyclododecane ring.
CHCl3); IR (neat) nmax 2988, 1647, 1376 cm21; H NMR
d 7.38 (d, Jˆ8.1 Hz, 1H), 7.22 (t, Jˆ8.3 Hz, 1H), 6.94 (t,
Jˆ7.4 Hz, 1H), 6.85 (d, Jˆ8.1 Hz, 1H), 6.05 (m, 1H), 5.89
(d, Jˆ3.6 Hz, 1H), 5.41 (dd, Jˆ17.2, 1.3 Hz, 1H), 5.28 (dd,
Jˆ10.5, 1.1 Hz, 1H), 4.76 (d, Jˆ12.3 Hz, 1H), 4.65 (d,
Jˆ12.9 Hz, 1H), 4.64 (d, Jˆ3.4 Hz, 1H), 4.53 (bd, Jˆ
5.1 Hz, 2H), 4.38 (dd, Jˆ13.1, 6.2 Hz, 1H), 4.18 (dd, Jˆ
7.2, 3.0 Hz, 1H), 4.05 (m, 3H), 1.49 (s, 3H), 1.42 (s, 3H),
1.34 (s, 3H), 1.31 (s, 3H); 13C NMR d 155.8 133.1, 128.9,
128.6, 126.2, 120.4, 117.2, 111.4, 111.2, 108.6, 105.1, 82.3,
81.7, 81.172.5, 68.5, 67.1, 66.9, 26.7, 26.6, 26.1, 25.3; MS
(EI) m/z 406, 391, 147, 91; Calcd for C22H30O7: C, 64.99; H,
7.44; Found: C, 64.83; H, 7.63%.
3-O-(2-Allyloxy benzyl)-1,2:5,6-diisopropylidene-a-d-
allofuranose (5b). Yield 96%; [a]2D4ˆ169.4 (c 0.49,
CHCl3); IR (neat) nmax 1599, 1374 cm21; H NMR d 7.42
1
(d, Jˆ7.4 Hz, 1H), 7.27 (t, Jˆ7.6 Hz, 1H), 6.96 (t, Jˆ
7.3 Hz, 1H), 6.85 (d, Jˆ8.2 Hz, 1H), 6.05 (m, 1H), 5.77
(d, Jˆ3.7 Hz, 1H), 5.42 (dd, Jˆ17.3, 1.4 Hz, 1H), 5.27
(dd, Jˆ10.5, 1.1 Hz, 1H), 4.83 (d, Jˆ12.2 Hz, 1H), 4.69
(m, 2H), 4.55 (bd, Jˆ5.0 Hz, 2H), 4.37 (dt, Jˆ9.6, 7.2,
2.5 Hz, 1H), 4.15 (dd, Jˆ8.8, 2.6 Hz, 1H), 3.93 (m, 3H),
1.58 (s, 3H), 1.36 (s, 3H), 1.34 (s, 3H), 1.27 (s, 3H); 13C
NMR d 156.4, 133.3, 130.1, 129.1, 126.0, 120.7, 117.3,
112.8, 111.6, 109.5, 103.9, 77.8, 77.7, 77.0, 74.7, 68.8,
66.6, 64.7, 26.8, 26.5, 26.0, 25.3; MS (EI) m/z 406, 233,
147, 91; Calcd for C22H30O7: C, 64.99; H, 7.44; Found: C,
64.72; H, 7.23%.
In conclusion, the work described above demonstrates that
10- to 12-membered heterocycles can be prepared through
the application of the nitrile oxide strategy depicted in
Scheme 1. This strategy can be extended to the synthesis
of heterocycles containing one heteroatom and even carbo-
cycles by replacing X or Y in 1 (Scheme 1) by one carbon
atom, or both of X and Y by two carbon atoms. The use of a
different tether resulting in structural variations adds to the
scope of this strategy.
3-O-[2-N-(p-Toluenesulphonyl)-allylamino]benzyl-1,2:5,6-
di-O-isopropylidene-a-d-glucofuranose (5c). Yield 56%;
[a]2D4ˆ225.8 (c 0.38, CHCl3); IR (neat) nmax 1642, 1597,
Experimental
1
1378 cm21; H NMR d 7.62 (d, Jˆ7.1 Hz, 1H), 7.53 (d,
1
Melting points are uncorrected. H and 13C NMR spectra
Jˆ8.2 Hz, 2H), 7.30 (m, 3H), 7.11 (t, Jˆ8.2 Hz, 1H), 6.48
(d, Jˆ7.9 Hz, 1H), 5.91 (d, Jˆ6.9 Hz, 1H), 5.76 (m, 1H),
5.09±4.88 (m, 3H), 4.83±4.66 (m, 2H), 4.42 (bd, Jˆ4.7 Hz,
2H), 4.18±4.00 (m, 4H), 3.77 (m, 1H), 2.45 (s, 3H), 1.50 (s,
3H), 1.43 (s, 3H), 1.37 (s, 3H), 1.33 (s, 3H); 13C NMR d
143.7, 140.0, 136.7, 135.2, 132.1, 129.5 (2£C), 129.1,
128.7, 128.0 (2£C), 127.6, 127.4, 119.8, 111.7, 109.0,
105.3, 82.4, 81.4, 72.5, 68.3, 67.4, 54.8, 26.8, 26.7, 26.2,
25.4, 21.5; MS (EI) m/z 559 (M1), 544 (M1215); Calcd for
C29H37O8NS: C, 62.23; H, 6.67; N, 2.50; Found: C, 62.01;
H, 6.47; N, 2.41%.
were measured for CDCl3 solutions at 300 and 75 MHz,
respectively unless otherwise stated. Mass spectra were
recorded on a JEOL AX-500 and JEOL D-300 instrument
using electron impact (70 eV) ionisation. Reactions were
monitored by thin layer chromatography using Merck 60
F254 precoated silica gel plates (No. 5554). Chloramine-T
and phenyl isocyanate were purchased from E-Merck
(Germany). Silica gel of mesh size 60±120 (SRL, India)
was used for column chromatography. Organic extracts
were dried over anhydrous Na2SO4. Solvents were removed
on a rotary evaporator under reduced pressure.
3-Deoxy-3-[-N-p-toluenesulphonyl)(2-allyloxybenzyl)]
amino-1,2:5,6-diisopropylidene-a-d-allofuranose (5d). A
mixture of 3-deoxy-3-(p-toluenesulphonamido)-1,2:5,6-di-
O-isopropylidene allofuranose 4c (3.64 g, 8.81 mmol),
anhydrous K2CO3 (5 g), 2-allyloxy benzyl bromide (2.0 g,
8.82 mmol) and acetone (50 ml) was stirred vigorously for
16 h at 258C. The mixture was ®ltered and residue was
washed repeatedly with acetone (100 ml). The syrup
obtained after removal of solvent was chromatographed
over silica-gel (ethyl acetate±hexaneˆ1:9) to give 5d as
colourless needles (4.71 g, 95%); mp 111±1128C; [a]2D8ˆ
172.4 (c 0.50, CHCl3); IR (neat) nmax 1375, 1336 cm21; 1 H
NMR d 7.72 (d, Jˆ8.2 Hz, 2H), 7.64 (d, Jˆ6.8 Hz, 1H),
7.27 (d, Jˆ8.1 Hz, 2H), 7.18 (t, Jˆ8.5 Hz, 1H), 6.94 (t,
Jˆ7.4 Hz, 1H), 6.78 (d, Jˆ8.2 Hz, 1H), 6.03 (m, 1H),
5.54 (d, Jˆ3.6 Hz, 1H), 5.34 (dd, Jˆ17.2, 1.4 Hz, 1H),
5.24 (dd, Jˆ10.4, 1.1 Hz, 1H), 5.00 (d, Jˆ17.2 Hz, 1H),
General procedure for the preparation of 5a, 5b and 5c
A mixture of 1,2:5,6-di-O-isopropylidene glucose (for 5a
and 5c) or allose (for 5b) (5.76 mmol) in CH2Cl2 (40 ml),
50% NaOH solution (40 ml), tetrabutylammonium bromide
(0.576 mmol) and 2-allyloxy benzyl bromide (for 5a and 5b)
or 2-N-allyl(p-toluenesulphonyl)amino benzyl bromide (for
5c) (5.94 mmol) was vigorously stirred for 4 h at 258C. Water
(50 ml) was added and the mixture extracted with CH2Cl2.
The combined organic layer was washed with water, dried
and the solvent removed under reduced pressure to afford a
syrup, which was chromatographed (10% ethyl acetate in
hexane) over silica-gel to give 5 as a colourless syrup.
3-O-(2-Allyloxy benzyl)-1,2:5,6-diisopropylidene-a-d-
glucofuranose (5a). Yield 78%; [a]2D8ˆ221.5 (c 0.41,

S. Majumdar et al. / Tetrahedron 56 (2000) 8945±8951
8949
4.73 (d, Jˆ17.2 Hz, 1H), 4.59 (bd, Jˆ5.3 Hz, 2H), 4.36 (m,
2.05 (bs, 1H), 1.68 (bs, 1H), 1.45 (s, 3H), 1.14 (s, 3H); 13
C
NMR d 155.4, 143.6, 137.1, 133.3, 130.0, 129.4 (2£C),
128.3, 127.5 (2£C), 126.3, 120.6, 117.6, 113.0, 111.4,
103.7, 79.4, 77.8, 71.6, 68.9, 62.3, 59.3, 44.6, 26.5, 25.8,
21.4; MS (EI) m/z 519 (M1), 504 (M1215), 461, 155, 91.
2H), 3.85 (m, 2H), 3.73 (m, 2H), 2.42 (s, 3H), 1.36 (s, 3H),
1.14 (s, 3H), 1.13 (s, 3H); 13C NMR d 155.4, 143.4, 137.4,
133.4, 130.8, 129.4 (2£C), 128.1, 127.5 (2£C), 126.4,
120.5, 117.6, 112.9, 111.2, 109.2, 103.8, 79.8, 75.7, 75.2,
68.9, 64.6, 60.8, 44.8, 26.4, 26.1, 26.0, 25.0, 21.5; MS (EI)
m/z 559 (M1), 544 (M1215), 107, 91; Calcd for
C29H37O8NS: C, 62.23; H, 6.67; N, 2.50; Found: C, 62.25;
H, 6.43; N, 2.49%.
General procedure for cycloaddition of the nitrile oxide
9a±9d
To an ice cold stirred solution of the above mentioned diol
(1 mmol) in methanol (20 ml), NaIO4 (1.05 mmol) in water
(5 ml) was added. After 30 min of stirring at 08C, the ice
bath was removed and the mixture was stirred for a further
1 h. The residue obtained after removal of methanol was
extracted with CH2Cl2 (3£20 ml) and the combined organic
layer washed with water, dried and evaporated to give the
aldehyde as syrup, which was not puri®ed further. IR: 7a:
General procedure for the preparation of 6a±6d
A solution of 5 (2.5 mmol) in aqueous acetic acid (75% v/v,
10 ml) was stirred for 14 h at room temperature. The
mixture was evaporated under reduced pressure and the
residue was repeatedly co-evaporated with dry toluene
(3£10 ml) to give a residue, which was chromatographed
over silica gel using ethyl acetate as the eluent to afford the
diol 6 as a syrup.
1740 cm21; 7b: 1737 cm21; 7c:1730 cm21; 7d: 1728 cm21
.
A mixture of this syrup, methanol (20 ml), pyridine (5 ml)
and NH2OH.HCl (1.5 mmol) was heated at re¯ux for 8 h.
After removal of solvent, the residue was extracted with
CH2Cl2 (2£20 ml). The combined organic extract was
washed with water (3£20 ml), dried and evaporated to
give the oxime 8 as a syrup, which was used for the next
step without further puri®cation. A mixture of 8 (5.7 mmol)
and chloramine-T hydrate (10.5 mmol) and ethanol (30 ml)
was heated under re¯ux for 8 h. After completion of the
reaction as revealed by TLC, the resulting colourless pre-
cipitate was ®ltered and the ®ltrate evaporated under
reduced pressure. The residue obtained was extracted with
with CH2Cl2 (3£50 ml) and the combined organic layer was
washed with water (3£50 ml), dried, and evaporated to give
a thick brown liquid. This crude material was chromato-
graphed over silica-gel using the solvents speci®ed below
for individual products.
6a: Yield 83%; [a]2D8ˆ231.9 (c 0.99, CHCl3); IR (neat)
1
nmax 3500, 2932, 1646, 1377 cm21; H NMR d 7.30 (m,
2H), 6.95 (m, 2H), 6.04 (m, 1H), 5.94 (d, Jˆ3.7 Hz, 1H),
5.41 (dd, Jˆ17.2, 1.0 Hz, 1H), 5.30 (dd, Jˆ10.5, 1.0 Hz,
1H), 4.70 (m, 2H), 4.59 (m, 3H), 4.13 (m, 2H), 3.97 (m,
1H), 3.78 (dd, Jˆ11.5, 3.3 Hz, 1H), 3.62 (dd, Jˆ11.5,
6.0 Hz, 1H), 1.48 (s, 3H), 1.33 (S, 3H); 13C NMR d
156.5, 132.9, 130.2, 129.6, 125.4, 120.8, 117.9, 111.9,
111.6, 105.2, 82.2, 81.7, 79.8, 69.5, 69.1, 67.8, 64.2, 26.6,
26.1; MS (EI) m/z 366 (M1), 351 (M1215), 326, 267, 205,
164, 147, 107, 91, 85.
6b: Yield 78%; [a]2D4ˆ241.2 (c 0.66, CHCl3); IR (neat)
1
nmax 3438 (br), 2924, 1452, 1378 cm21; H NMR d 7.30
(m, 2H), 6.93 (m, 2H), 6.06 (m, 1H), 5.76 (d, Jˆ3.6 Hz,
1H), 5.37 (m, 2H), 4.81 (m, 2H), 4.71 (m, 1H), 4.63 (m, 2H),
4.07 (dd, Jˆ8.9, 3.6 Hz, 1H), 3.91 (m, 1H), 3.62 (m, 3H),
1.58 (s, 3H), 1.36 (s, 3H); 13C NMR d 156.4, 133.0, 130.1,
129.4, 125.1, 120.9, 118.0, 112.1, 111.6, 105.2, 82.2, 81.5,
79.7, 69.6, 69.0, 67.9, 64.2, 26.3, 25.8; MS (EI) m/z 366
(M1), 351 (M1215).
Isoxazoline 12: CHCl3±MeOH (49:1); Yield 50%; colour-
less needles, mp196±1988C (chloroform±hexane); [a]2D7ˆ
289.3 (c 0.82, CHCl3); IR (KBr) nmax 2988, 2938, 1605,
1
1449, 1378 cm21; H NMR (400 MHz, CDCl3) d 7.30 (t,
Jˆ8 Hz, 1H), 7.18 (d, Jˆ8 Hz, 1H), 6.90 (t, Jˆ8 Hz, 1H),
6.81 (d, Jˆ8 Hz, 1H), 5.97 (d, Jˆ4 Hz, 1H), 5.25 (d, Jˆ
4 Hz, 1H), 4.87 (m, 1H), 4.69 (d, Jˆ8 Hz, 1H), 4.65 (d,
Jˆ4 Hz, 1H), 4.52 (d, Jˆ10 Hz, 1H), 4.47 (d, Jˆ10 Hz,
1H), 4.18 (d, Jˆ4 Hz, 1H), 3.83 (d, Jˆ10 Hz, 1H), 3.26
(dd, Jˆ17, 10 Hz, 1H), 3.11 (dd, Jˆ17, 3 Hz, 1H), 1.52
(s, 3H), 1.36 (s, 3H); 13C NMR (25 MHz, acetone-d6) d
160.1, 157.5, 131.9, 131.1, 126.7, 121.0, 113.3, 112.5,
106.6, 86.5, 84.9, 78.9, 77.7, 72.7, 72.1, 39.0, 27.3, 26.5;
MS (EI) m/z 347, 332, 318, 260, 219, 147, 129, 107, 91, 85;
Calcd for C18H21O6N: C, 62.22; H, 6.10; N, 4.03; Found: C,
61.93; H, 5.99; N, 3.93%.
6c: Yield 72%; [a]2D4ˆ232.6 (c 0.57, CHCl3); IR (neat)
nmax 3504 (br), 2930, 1643, 1597, 1451, 1375, 1344 cm21
;
1H NMR d 7.53 (m, 3H), 7.32 (m, 3H), 7.15 (t, Jˆ8.4 Hz,
1H), 6.48 (t, Jˆ7.6 Hz, 1H), 5.95 (d, Jˆ3.7 Hz, 1H), 5.71
(m, 1H), 5.01 (d, Jˆ9.5 Hz, 1H), 4.84 (m, 4H), 4.44 (m,
1H), 4.15 (m, 3H), 3.84 (dd, Jˆ11.5, 3.3 Hz, 1H), 3.73 (m,
2H), 2.45 (s, 3H), 1.51 (s, 3H), 1.30 (s, 3H); 13C NMR d
155.6, 142.9, 137.0, 133.3, 130.0, 129.2, 128.3, 127.9
(2£C), 126.0, 120.6, 117.9, 113.0, 111.2, 103.9, 79.2,
77.6, 71.5, 69.0, 62.7, 59.9, 45.9, 26.8, 25.9, 21.4; MS
(EI) m/z519 (M1), 504 (M1215).
Isoxazoline 13: CHCl3±MeOH (49:1); Yield 62%; colour-
less needles, mp187±1888C (chloroform±hexane); [a]2D5ˆ
261.3 (c 0.6, CHCl3); IR (KBr) nmax 2980, 1598, 1453,
6d: Yield 75%; [a]2D8ˆ164.4 (c 0.50, CHCl3); IR (neat)
1
nmax 3458, 2932, 1378, 1333 cm21; H NMR d 7.74 (d,
1
Jˆ8.2 Hz, 2H), 7.62 (d, Jˆ7.2 Hz, 1H), 7.28 (d,
Jˆ8.1 Hz, 2H), 7.21 (t, Jˆ8.3 Hz, 1H), 6.95 (t, Jˆ7.6 Hz,
1H), 6.80 (d, Jˆ8.2 Hz, 1H), 6.05 (m, 1H), 5.61 (d,
Jˆ3.5 Hz, 1H), 5.36 (dd, Jˆ17.3, 1.3 Hz, 1H), 5.26 (dd,
Jˆ10.5, 1.0 Hz, 1H), 5.16 (d, Jˆ16.8 Hz, 1H), 4.75 (d,
Jˆ16.8 Hz, 1H), 4.55 (bd, Jˆ5.3 Hz, 2H), 4.26 (m, 2H),
4.05 (dd, Jˆ9.7, 4.3 Hz, 1H), 3.51 (m, 3H), 2.42 (s, 3H),
1375 cm21; H NMR d 7.45 (d, Jˆ7.1 Hz, 1H), 7.30 (t,
Jˆ8.2 Hz, 1H), 6.99 (t, Jˆ7.4 Hz, 1H), 6.88 (d, Jˆ8.3 Hz,
1H), 5.68 (d, Jˆ3.4 Hz, 1H), 5.22 (d, Jˆ12.8 Hz, 1H), 5.08
(d, Jˆ8.7 Hz, 1H), 4.86 (bd, 1H), 4.55 (m, 2H), 4.47 (d,
Jˆ11.4 Hz, 1H), 4.10 (d, Jˆ11.9 Hz, 1H), 3.69 (dd,
Jˆ8.7, 4.4 Hz, 1H), 3.15 (dd, Jˆ17.0, 10.8 Hz, 1H), 2.57
(dd, Jˆ16.9, 2.2 Hz, 1H), 1.64 (s, 3H), 1.36 (s, 3H); 13C

8950
S. Majumdar et al. / Tetrahedron 56 (2000) 8945±8951
NMR d 158.1, 158.0, 131.9, 130.0, 125.2, 121.4, 113.6,
111.7, 103.2, 79.8, 78.7, 77.1, 74.1, 71.6, 64.9, 34.7, 26.8,
26.3; MS (EI) m/z 348 (M111), 347 (M1), 332 (M1215),
318, 190, 149, 107, 91; Calcd for C18H21O6N: C, 62.22; H,
6.10; N, 4.03; Found: C, 62.18; H, 5.83; N, 3.88%.
(c 0.41, CHCl3); IR (KBr) nmax 2960, 1742, 1599, 1440,
;
1368, 1334 cm21
1H NMR d 7.47 (d, Jˆ7.2 Hz, 1H),
7.23 (dt, Jˆ9.2, 7.8, 1.6 Hz, 1H), 7.07 (t, Jˆ7.3 Hz, 1H),
6.89 (m, 4H), 6.55 (d, Jˆ8.1 Hz, 1H), 5.80 (d, Jˆ11.1 Hz,
1H), 5.40 (m, 1H), 4.63 (dd, Jˆ12.0, 3.6 Hz, 1H), 4.41 (m,
3H), 4.19 (t, Jˆ9 Hz, 1H), 4.04 (t, Jˆ6.6 Hz, 1H), 3.91 (m,
1H), 3.77 (dd, Jˆ8.6, 3.6 Hz, 1H), 2.26 (s, 3H), 2.18 (s, 3H),
2.04 (dd, Jˆ7.3, 3.5 Hz, 1H); 13C NMR d 170.5, 170.3,
160.8, 157.8, 142.1, 139.3, 133.2, 129.7, 128.6, 127,
125.5, 122.7, 115.5, 71.4, 67.0, 62.2, 59.7, 49.2, 45.8,
21.3, 21.0, 20.7; Calcd for C25H28O8N2S: C, 58.12; H,
5.47; N, 5.48; Found: C, 57.92; H, 5.41; N, 5.21%.
Isoxazoline 14: CHCl3±MeOH (49:1); Yield 35%; colour-
less needles, mp 230±2318C (chloroform±ether); [a]2D7ˆ
1112.7 (c 0.30, CHCl3); IR (KBr) nmax 2984, 1596, 1450,
1
1376, 1348 cm21; H NMR d 7.43 (m, 3H), 7.26 (m, 3H),
7.08 (t, Jˆ7.7 Hz, 1H), 6.42 (d, Jˆ8.0 Hz, 1H), 6.02 (d,
Jˆ3.5 Hz, 1H), 5.04 (m, 1H), 4.94 (d, Jˆ3 Hz, 1H), 4.83
(d, Jˆ11.8 Hz, 1H), 4.75 (m, 2H), 4.36 (d, Jˆ3.0 Hz, 1H),
3.92 (dd, Jˆ14.5, 3.7 Hz, 1H), 3.61 (dd, Jˆ17.1, 4.3 Hz,
1H), 3.46 (dd, Jˆ14.5, 2.7 Hz, 1H), 3.21 (dd, Jˆ17,
11.4 Hz, 1H), 2.45 (s, 3H), 1.52 (s, 3H), 1.35 (s, 3H); 13C
NMR d 152.7, 144.4, 138.6, 137.7, 130.4, 129.6, 128.7,
128.2, 128.0, 125.6, 112.0, 105.0, 84.6, 83.5, 78.9, 77.2,
70.5, 53.4, 38.1, 26.9, 26.2, 21.6; MS (EI) m/z 500 (M1),
485 (M1215), 155, 91; Calcd for C25H28O7N2S: C, 59.98;
H, 5.64; N, 5.60; Found: C, 60.21; H, 5.65; N, 5.48%.
Isoxazoline 17
A mixture of the aldehyde 7a (1.25 g, 3.74 mmol), nitro-
methane (4 ml), anhydrous KF (0.3 g) and isopropanol
(20 ml) was stirred at 258C for 24 h. The residue obtained
after removal of solvent under reduced pressure was diluted
with ether (70 ml) and the mixture ®ltered. The syrup
obtained after evaporation of the ®ltrate was dissolved in
1:1 dry ether±CH2Cl2 (30 ml) containing a catalytic amount
of DMAP. Ac2O (1.5 ml) was added and the mixture kept
overnight at 258C. Water (25 ml) was added to the mixture,
which was then extracted with CH2Cl2. The CH2Cl2 extract
was washed with 10% HCl (5 ml), water and dried. The
syrup obtained after removal of the solvent was dissolved
in THF (25 ml) and this solution was added to a suspension
of NaBH4 (0.5 g) in EtOH (15 ml) at 08C and the resulting
mixture was stirred for 4 h. Excess NaBH4 was destroyed by
the addition of aqueous AcOH (10%) and the residue
obtained after removal of solvent was extracted with
EtOAc (3£20 ml). The combined organic layer was washed
with water, dried and solvent was removed under reduced
pressure. The syrupy residue on chromatography over
silica-gel, using CHCl3 as the eluent gave 10a as a colorless
syrup (1.10 g, 77%); [a]2D7ˆ236.9 (c 1.15, CHCl3); IR
(neat) nmax 2986, 2932, 1648, 1559, 1493, 1455,
Isoxazoline 15: CHCl3±MeOH (49:1); Yield 70%; colour-
less needles, mp 224±2258C (chloroform±hexane); [a]2D8ˆ
226.0 (c 0.5, CHCl3); IR (KBr) nmax 2930, 1604, 1459,
1
1381, 1343, 1248 cm21; H NMR d 7.47 (d, Jˆ6.4 Hz,
1H), 7.21 (t, Jˆ7.6 Hz, 1H), 7.03 (t, Jˆ7.4 Hz, 1H), 6.88
(m, 4H), 6.47 (d, Jˆ8.0 Hz, 1H), 5.94 (d, Jˆ3.3 Hz, 1H),
5.31 (d, Jˆ9.2 Hz, 1H), 4.93 (m, 2H), 4.80 (d, Jˆ14.7 Hz,
1H), 4.55 (d, Jˆ14.7 Hz, 1H), 4.23 (t, Jˆ9.2 Hz, 1H), 4.12
(t, Jˆ7.2 Hz, 1H), 3.91 (dd, Jˆ8.9, 3.3 Hz, 1H), 3.67 (m,
1H), 2.31 (dd, Jˆ11.6, 7.6 Hz, 1H), 2.26 (s, 3H), 1.60 (s,
3H), 1.38 (s, 3H); 13C NMR d 159.6,156.8, 142.1, 139.0,
133.6, 129.3, 128.7, 126.4, 125.3, 122.0, 112.6, 112.5,
103.5, 81.5, 71.5, 70.1, 69.2, 65.5, 48.8, 47.6, 26.6, 26.0,
21.3; MS (EI) m/z 500 (M1), 485 (M1215), 470, 441, 413,
254, 229, 202, 155, 91; Anal. Calcd for C25H28O7N2S: C,
59.98; H, 5.64; N, 5.60; Found: C, 59.69; H, 5.45; N, 5.31%.
1
1378 cm21; H NMR d 7.28 (m, 2H), 6.95 (t, Jˆ7.3 Hz,
Transformation of 15 to 16
1H), 6.87 (d, Jˆ8.1 Hz, 1H), 6.07 (m, 1H), 5.88 (d, Jˆ
3.8 Hz, 1H), 5.41 (dd, Jˆ17.3, 1.5 Hz, 1H), 5.29 (dd, Jˆ
10, 1.2 Hz, 1H), 4.74 (d, Jˆ11.8 Hz, 1H), 4.69 (d, Jˆ
3.8 Hz, 1H), 4.53 (m, 5H), 4.25 (m, 1H), 3.9 (d, Jˆ
3.2 Hz, 1H), 2.41 (m, 1H), 2.30 (m, 1H), 1.47 (s, 3H),
1.32 (s, 3H); 13C NMR d 156.2, 133.0, 129.6 (2£C),
129.3 (2£C), 125.5, 120.6, 117.5, 111.4, 104.7, 82.1, 76.6,
72.4, 68.7, 67.0, 26.6, 26.1, 26.1; MS (EI) m/z 379, 364, 331,
272, 217, 201, 188, 162, 146, 106, 91; Calcd for C19H25O7N:
C, 60.13; H, 6.65; N, 3.69; Found: C, 60.30; H, 6.55; N,
3.66.
A solution of 15 (150 mg, 0.3 mmol) in 10:1 CH3CN±H2O
(10 ml) containing 4% H2SO4 was stirred for 24 h at 258C.
The solution was neutralised by the addition of aq. NaHCO3
and ®ltered. After removal of solvent the residue obtained
was dissolved in methanol (10 ml), to which a solution of
sodium metaperiodate (50 mg) in water (5 ml) was added
dropwise with stirring over 2 h. The mixture was ®ltered and
the residue was washed with methanol. After concentration
of the ®ltrate, the intermediate hydroxy aldehyde was
obtained as a syrup which was dissolved in methanol
(5 ml) and cooled to 08C. To this solution NaBH4 (25 mg)
was added and the mixture was stirred for 2 h. The mixture
was then acidi®ed with aqueous AcOH (1:1). After extrac-
tion with chloroform the syrup obtained was dissolved in
pyridine (5 ml). Ac2O (2 ml) and a catalytic amount of
DMAP were added. The reaction was kept overnight at
258C, and then extracted with CHCl3 (3£10 ml). The
combined organic extract was washed with 5% HCl, water
(3£20 ml) and dried. The residue obtained after removal of
solvent was crystallised from CHCl3±petroleum ether
affording 16 as a colourless microcrystalline solid (80 mg,
52% overall yield from 15), mp 180±1818C; [a]2D7ˆ2161.0
A mixture of 10a (0.8 g, 2.1 mmol), PhNCO (3.0 ml), Et3N
(3.5 ml) and benzene (100 ml) was stirred for 50 h at 258C.
Water (50 ml) was added and the mixture stirred for further
24 h. Benzene was removed under reduced pressure and the
residue extracted with CHCl3 (2£50 ml). The combined
organic layer was washed with water, dried and evaporated
to give a residue which was chromatographed over silica-gel
using hexane±ethyl acetate (4:1) as the eluent to afford 17 as
colourless needles (0.37 g, 50%); mp 193±1958C; [a]2D7ˆ
264.6 (c 1.2, CHCl3); IR (KBr) nmax 2988, 2934, 1652,
;
1604, 1455, 1376, 1218 cm21 1H NMR (400 MHz,
CDCl3) d 7.29 (t, Jˆ8 Hz, 1H), 7.22 (d, Jˆ8 Hz, 1H),

S. Majumdar et al. / Tetrahedron 56 (2000) 8945±8951
8951
3. Bhattacharjya, A.; Chattopadhyay, P.; McPhail, A. T.; McPhail,
D. R. J. Chem. Soc., Chem. Commun. 1990; 1508±1509; Corri-
gendum, J. Chem. Soc., Chem. Commun. 1991, 136.
4. Datta, S.; Chattopadhyay, P.; Mukhopadhyay, R.; Bhattacharjya,
A. Tetrahedron Lett. 1993, 34, 3585±3588.
6.90 (t, Jˆ8 Hz, 1H), 6.83 (d, Jˆ8 Hz, 1H), 5.94 (d, Jˆ
4 Hz, 1H), 4.80 (m, 2H), 4.72 (d, Jˆ4 Hz, 1H), 4.50 (m,
2H), 4.26 (d, Jˆ10 Hz, 1H), 4.26 (d, Jˆ10 Hz, 1H), 4.25
(bs, 1H0, 4.03 (d, Jˆ10 Hz, 1H), 3.24 (dd, Jˆ16, 10 Hz,
1H), 2.76 (m, 2H), 2.55 (dd, Jˆ16.0, 10 Hz, 1H), 1.50 (s,
3H), 1.35 (s, 3H); 13C NMR (25 MHz, CDCl3) d 158.0,
155.7, 131.7, 130.0, 124.7, 120, 113.3, 110.0, 105.0, 82.9,
82.0, 77.4, 76.8, 70.0, 69.1, 41.6, 27.6, 26.9, 26.3; MS (EI)
m/z 361 (M1), 360 (M121), 359 (M122); Calcd for
C19H23O6N: C, 63.13; H, 6.42; N, 3.88; Found: C, 62.85;
H, 6.58; N, 3.71%.
5. Mukhopadhyay, R.; Kundu, A. P.; Bhattacharjya, A.
Tetrahedron Lett 1995, 36, 7729±7730.
6. Mukhopadhyay, R.; Datta, S.; Chattopadhyay, P.; Bhattacharjya,
A.; Patra, A. Indian J. Chem. 1996, 35B, 1190±1193.
7. Shing, T. K. M.; Fung, W.-C.; Wong, C.-H. J. Chem. Soc.,
Chem. Commun. 1994, 449±450.
8. Bhattacharjee, A.; Bhattacharjya, A.; Patra, A. Tetrahedron
Lett. 1995, 36, 4677±4680.
Acknowledgements
9. Majumdar, S.; Bhattacharjya, A.; Patra, A. Tetrahedron Lett.
1997, 38, 8581±8584.
The ®nancial assistance of DST, India to A. B. and the
award of a Senior Research Fellowship to S. M. by U G
C, India are gratefully acknowledged. Thanks are due to Dr
V. S. Giri and Mr A. Banerjee for spectral analysis, and
CSS, Department of Inorganic Chemistry, IACS, Calcutta
for microanalysis.
10. Majumdar, S.; Bhattacharjya, A.; Patra, A. Tetrahedron 1999,
55, 12157±12174.
11. Kozikowski, A. P.; Murrage, B. M. J. Chem. Soc., Chem.
Commun. 1988, 198±199.
12. Rai, K. M. L.; Hassner, A. Heterocycles 1990, 30, 817±830.
13. Ko, S. S.; Confalone, P. N. Tetrahedron 1985, 41, 3511±3518.
14. Bhattacharjee, A.; Chattopadhyay, P.; Kundu, A. P.;
Mukhopadhyay, R.; Bhattacharjya, A. Indian J. Chem. 1996,
35B, 69±70.
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