Cycloaddition reactions of carbohydrate derivatives. Part 8: Intramolecular cycloaddition of nitrilimines derived from sugars

Article abstract of DOI:10.1016/S0957-4166(01)00050-7

Nitrilimines containing a carbon-carbon double bond were prepared in several steps from 2,3,4-tri-O-benzyl-D-xylose, D-ribose and L-arabinose derivatives and their intramolecular 1,3-dipolar cycloaddition reactions were studied. The results were examined

Full text of DOI:10.1016/S0957-4166(01)00050-7

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 12 (2001) 469–476
Cycloaddition reactions of carbohydrate derivatives. Part 8:†
Intramolecular cycloaddition of nitrilimines derived from sugars
´
Attila Ago´cs, Tama´s E. Gunda, Gyula Batta, Arpa´d Kova´cs-Kulyassa and Pa´l Herczegh*
Research Group for Antibiotics of the Hungarian Academy of Sciences, University of Debrecen, PO Box 70,
H-4010 Debrecen, Hungary
Received 8 January 2001; accepted 1 February 2001
Abstract—Nitrilimines containing a carbonꢀcarbon double bond were prepared in several steps from 2,3,4-tri-O-benzyl-
D-xylose,
D
-ribose and -arabinose derivatives and their intramolecular 1,3-dipolar cycloaddition reactions were studied. The results were
L
examined with molecular modelling and compared with the literature data for similar cycloadditions. © 2001 Elsevier Science Ltd.
All rights reserved.
sented a stereochemical study of the intermolecular
[3+2] cycloadditions with carbohydrate nitrilimines.1
Investigation of the intramolecular variant of this kind
of transformation also seemed to be reasonable.
1. Introduction
The intramolecular cycloadditions of carbohydrate
derivatives are excellent tools in the stereoselective syn-
theses of polyfunctional cyclopentane and cyclohexane
derivatives containing several chiral centres.2 The stereo-
chemical outcome of these cycloadditions is determined
by the mechanism of the reaction, and also by the
conformation of the sugar chain in the transition state,
which is strongly dependent on the configuration of the
stereogenic centres. In a previous paper we have pre-
For this reason, the
was prepared from 2,3,4-tri-O-benzyl-
D
-xylo-pentodialdose mercaptal 2
-xylose in two
D
steps. The mercaptal 2 was then reacted with methylene-
triphenylphosphorane (Scheme 13), and the resulting
hex-5-ene-1-al mercaptal derivative 3 was hydrolysed
smoothly with N-bromosuccinimide in the presence of
EtS
SEt
CHO
OBn
EtS
SEt
NBS
BnO
BnO
1. EtSH / HCl
2. PCC
Ph3P=CH2
O
BnO
BnO
BnO
BnO
CdCO3
BnO
BnO
OBn
OH
OBn
CHO
OBn
25 %
58 %, ref 3.
3
1
4
2
p-Br-C6H4-NH-NH2
N
C6H4Br
BnO
BnO
N
CH=N-NH-C6H4Br
OBn
1. NBS / Me2S
N
BnO
BnO
BnO
BnO
2. Et3N, 0 °C
OBn
BnO
N
C6H4Br
30 %
H
5
7
6
Scheme 1.
* Corresponding author. E-mail: herczeghp@tigris.klte.hu
†
For the preceding paper of this series, see Ref. 1.
0957-4166/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(01)00050-7

470
A. Ago´cs et al. / Tetrahedron: Asymmetry 12 (2001) 469–476
For further investigation of the stereoselectivity in these
reactions the same sequence was performed with nitril-
imines having -arabino and -ribo stereotriads in the
tether chain between the alkene and the nitrilimine
moieties (Scheme 3). The tri-O-benzyl- -ribose
mercaptal15 11 (produced from
-ribose in four steps)
BnO
BnO
N
L
D
N
C6H4Br
H
D
BnO
H
H
H
H
D
was oxidised with pyridinium chlorochromate (PCC).
Wittig reactions of the crude aldehyde with methylene-
triphenylphosphorane and methoxycarbonylmethylene-
triphenylphosphorane furnished the protected enals, 12
and 15, respectively. After cleaving the mercaptal func-
tion with mercury(II) chloride the corresponding hydra-
zones 13 and 16 were produced. From 13 and 16
nitrilimines were generated with the Corey–Kim
reagent/triethylamine methodology, and in situ
intramolecular cycloaddition of these nitrilimines
resulted in 14 and 17, respectively. In a similar reaction
Figure 1. Observed nOE effects of key protons in 7.
cadmium carbonate to give the hex-5-ene-1-al deriva-
tive 4.4 Treatment of this enal with 4-bromophenyl-
hydrazine in dichloromethane gave the corresponding
hydrazone 5. The nitrilimine intermediate 6 was pre-
pared from 5 by using the N-bromosuccinimide/
dimethylsulphide reagent5 and subsequent dehydro-
halogenation with triethylamine. The nitrilimine 6
underwent rapid cycloaddition leading to the exclusive
formation of the hexahydro-cyclopentapyrazole
diastereoisomer 7. The configuration of the newly gen-
erated chiral centre in 7 was proved to be (S) on the
basis of nOE experiments as depicted in Fig. 1.
sequence the
D
-galactose mercaptal 1816 was oxidised
with lead(IV) tetraacetate and from the crude aldehyde
the alkenes 19 and 22 were prepared in Wittig reac-
tions. Deprotection of 19 and 22, followed by reaction
with 4-bromophenylhydrazine, resulted in the hydra-
zones 20 and 23. The nitrilimines generated from 20
and 23 underwent intramolecular cycloaddition to give
the bicyclic compounds 21 and 24, respectively. The
configuration of all of the new chiral centres was deter-
mined by means of 2D NOESY spectroscopy.
In a similar fashion 8 was prepared from 26 (Scheme 2).
The 4-bromophenylhydrazone 9 derived from 8 was
brominated, and the product was dehydrohalogenated.
Subsequent intramolecular cycloaddition of the inter-
mediary nitrilimine led to the formation of the
diastereoisomers 10a,b in a 1:1 ratio.
The yields of these nitrilimine cycloaddition reactions
are between 30 and 40%. We have performed three
consecutive reactions in one pot: bromination, nitril-
imine formation and cycloaddition. Consequently, the
average yield for each reaction is about 70%. All prod-
ucts were isolated that could be seen on TLC and in all
cases the reactions gave one or two isomers. Relatively
low yields of cycloaddition reactions can be explained
by the instability of the intermediate nitrilimine.
There are several examples in the literature for [3+2]
and [4+2] intramolecular cycloadditions in which the
reactants are connected with a tri-O-benzyl-D-xylo-
tribenzyloxypropyl chain analogously to 5 and 9. Some
Diels–Alder and hetero-Diels–Alder reactions,7 as well
as [3+2] dipolar cycloadditions of nitrones,8,9 nitrile
oxides,10 azomethine imines11,12 and oximes,13 have
been investigated where the dienophile or the dipolar-
ophile had the same tethering chain as in 5. By studying
the stereochemical outcome of these reactions (includ-
ing our case) we can conclude that the new stereocen-
tre(s) always have the same relative configuration
independent of the nature of the cycloaddition. Appar-
ently, the determining factor in these cases must be the
conformation in the transition states. On the other
hand, when the alkene moiety carried an alkoxycar-
bonyl group (as in 10) Jarosz et al.14 observed the
formation of two diastereomers in an intramolecular
Diels–Alder reaction.
When the alkene moiety does not carry a car-
boxymethyl group the diastereoselection in the 1,3-
dipolar intramolecular cycloaddition is complete (7, 14,
21), and in all cases the (3aS)-configuration is preferred
at the newly generated stereogenic centre. This finding
is in good accordance with the literature data for
various intramolecular cycloadditions of reactants with
D
-ribo12,17,18 and -arabino13,14,17,19 stereotriads. In the
L
favoured adducts the stereogenic centre that corre-
sponds to C-(3a) in 7, 14 and 21 possesses the same
BnO
N
BnO
N
C6H4Br
CH=N-NH-Ph-Br
CHO
1. Ph3P=CH2COOMe
80 °C, 6-7 h
2. NBS / CdCO3
BnO
BnO
BnO
BnO
H
1. NBS / Me2S
BnO
BnO
OBn
COOMe
OBn
p-Br-Ph-NH-NH2
2. Et3N, 0 °C
10a
2
60 %, ref 6.
59 %
N
COOMe
COOMe
BnO
N
C6H4Br
9
8
H
BnO
COOMe
10b
Scheme 2.

A. Ago´cs et al. / Tetrahedron: Asymmetry 12 (2001) 469–476
471
PrS
SPr
PrS
SPr
BnO
BnO
1. PCC
1. HgCl2/CdCO3
2. 4-bromophenyl-
hydrazine
CH=N-NH-C6H4-Br
OBn
1. NBS / Me2S
2. Ph3P=CH2
BnO
BnO
N
BnO
BnO
BnO
BnO
2. Et3N, 0 °C
BnO
N C6H4Br
OBn
OBn
CH2OH
11
15 %.
30 %
81 %
H
13
12
14
1. PCC
28 %
2. Ph3P=CH-COOMe
PrS
SPr
1. HgCl2/CdCO3
CH=N-NH-C6H4-Br
OBn
BnO
BnO
BnO
BnO
1. NBS / Me2S
2. 4-bromophenyl-
hydrazine
BnO
BnO
N
BnO
BnO
N
2. Et3N, 0 °C
OBn
N C6H4Br
BnO
N C6H4Br
38 %
77 %
H
H
BnO
COOMe
COOMe
COOMe
COOMe
17b
17a
17a:17b = 3:7
16
15
PrS
SPr
PrS
SPr
BnO
BnO
1. Pb(OAc)4
2. Ph3P=CH2
1. HgCl2/CdCO3
2. 4-bromophenyl-
hydrazine
CH=N-NH-C6H4-Br
OBn
BnO
BnO
1. NBS / Me2S
BnO
BnO
N
BnO
BnO
OBn
OH
2. Et3N, 0 °C
BnO
N C6H4Br
OBn
13 %.
36 %
71 %
H
OH
18
20
19
21
1. Pb(OAc)4
2. Ph3P=CH-COOMe
24 %
PrS
SPr
CH=N-NH-C6H4-Br
OBn
BnO
BnO
BnO
1. HgCl2/CdCO3
2. 4-bromophenyl-
hydrazine
BnO
BnO
BnO
BnO
1. NBS / Me2S
N
N
OBn
2. Et3N, 0 °C
BnO
N C6H4Br
N C6H4Br
24 %
61 %
H
H
BnO
BnO
COOMe
COOMe
COOMe
COOMe
24a
24a:24b =2:1
24b
23
22
Scheme 3.
configuration in each case as in these three adducts.
However, from nitrilimines which carry car-
boxymethyl group at the alkene moiety two
diastereomers of 10, 17 and 24 are formed in different
proportions.
difference in the heat of formation of 25 with Na-phenyl
and Nb-phenyl groups was 0.51 kcal/mol. Although in
our experimental work the benzyl derivative 9 was
used, the benzyl groups were simply represented by
methyl groups throughout the calculations (a simplified
system should reflect the relative differences between
the transition states and save time in the calculations).
a
For a deeper insight into the stereochemical outcome of
the
intramolecular
nitrilimine
cycloadditions,
MOPAC20 calculations were performed to estimate the
transition states of the reaction. The starting point in
these calculations was to figure out the most probable
conformations of the two products of the examined
cycloaddition (Fig. 2). To begin with, a simplified struc-
ture containing only the N-phenyl group was subjected
to conformational analysis, using the AM1 method in
the MOPAC program. Whatever the starting confor-
mation of the cyclopentane ring, subsequent minimisa-
tion led to the two structures 25 and 26. The position of
the phenyl rings was not relevant: for example, the
The starting geometry of the final products 28a,b and
29a,b was constructed on the basis of 25 and 26 (Fig.
3). These approximate structures were then fully opti-
mised with MOPAC using the AM1 Hamiltonian. The
MOPAC-AM1 heats of formations of the starting
materials and products and the transition states are
shown in Fig. 4.
In the case of 27a the relative transition state energies
are Hf=24.64 and 31.33 kcal mol−1 for the two prod-
ucts. The difference DHf=6.69 kcal mol−1 suggests that

472
A. Ago´cs et al. / Tetrahedron: Asymmetry 12 (2001) 469–476
Figure 2.
Figure 3.
Figure 4. Transition states for 28a,b and 29a,b.
the formation of 28a predominates. Similar calculations
were carried out for 27b, and the difference between the
transition state energies was considerably smaller
(DHf=0.73 kcal mol−1). These model calculations are in
accordance with our experimental results and may give
a satisfactory explanation of the stereochemical out-
come of analogous reactions.8–13 Similar calculations
including benzyl to methyl substitution in model com-
pounds and starting geometries similar as for 28a and
29a were performed for the transition states leading to
14 and 21. The results showed the same preference (4.4
and 8.0 kcal mol−1, respectively) for the (3aS)-
products.
The molecular modelling and experimental results show
that for the intramolecular 1,3-dipolar cycloaddition of
nitrilimines having D-ribo, L-arabino and D-xylo stereo-
triads in the tethering chain the same (3aS)-products
are preferred. In all cases introduction of a prochiral
centre into the nitrilimine by methoxycarbonyl ‘substi-

A. Ago´cs et al. / Tetrahedron: Asymmetry 12 (2001) 469–476
473
1
tution’ on the alkene results in a mixture of two
diastereomers after cycloaddition. These findings corre-
spond with the stereochemical outcome of other
intramolecular cycloadditions of carbohydrate deriva-
tives having the same stereotriads in the tethering
chain.
1.23, CH2Cl2). H NMR: l (ppm) 1.2 (6H, m, -Me),
2.65 (4H, m, S-CH2-), 3.8 (1H, d, H-1), 4.0 (2H, s,
O-CH2-), 4.35 and 4.75 (7H, 2m, H-2, H-3, H-4, -O-
CH2-), 5.35 (2H, m, H-6a,b), 5.95 (1H, m, H-5), 7.35
(15H, m, aromatic). 13C NMR: l (ppm) 14.4; 14.5
(CH3-CH2); 53.6 (S-CH2-); 70.4; 75,1; 75.4 (-CH2-O,
benzyl); 80.0; 82.8; 82.9 (C-2-C-4); 118.7 (ꢁCH2); 127.2–
128.4 (15C); 135.5 (-CHꢁ); 138.0; 138.7; 138.9 (C-O,
aromatic). Anal. calcd for C31H38O3S2: C, 71.22; H,
7.33; S, 12.27. Found: C, 71.10; H, 7.38; S, 12.30%.
2. Experimental
The organic extracts were dried over magnesium sul-
phate and the solutions were concentrated at 35–40°C
(bath) at ca. 17 mmHg. For TLC precoated aluminium-
backed plates (Silica gel 60 F254, Merck, layer thickness:
0.2 mmol) were used. Compounds were visualised by
charring with 5% sulphuric acid in ethanol or spraying
with 7% ammonium molybdate in 5% sulphuric acid
and heating. Column chromatography: Merck silica gel
60 (0.062–0.200 mmol). Specific rotations were mea-
2.2. (2S,3S,4R)-2,3,4-Tribenzyloxy-hex-5-ene-1-al 4-bro-
mophenylhydrazone 5
A solution of 3 (2.3 g, 4.4 mmol) in a mixture of
acetone (30 mL) and water (3 mL) was treated with
cadmium carbonate (6 g) and N-bromosuccinimide (1.7
g, 9.7 mmol) and stirred for 30–40 min. The suspension
was filtered and evaporated. The crude product was
taken up in dichloromethane and washed with sat.
NaHCO3 solution, dried and evaporated, giving a yel-
lowish oil (1.4 g, 77%). A solution of the crude alde-
hyde (1.4 g, 3.4 mmol) in dichloromethane (30 mL) and
a solution of 4-bromophenylhydrazine hydrochloride
(0.8 g) and NaHCO3 (0.3 g) in water (20 mL) was
added and the mixture was vigorously stirred overnight.
The organic phase was washed with water, dried and
evaporated. Column chromatography (hexane–ethyl
acetate 95:5) afforded 5 as a red oil (1.5 g, 82%); m/z
585 (M+H+, PSP), [h]D23=−5.7 (c 0.98, CH2Cl2). 1H
NMR: l (ppm) 4.1–4.9 (9H, m, -OCH2-, H-2, H-3,
H-4), 5.35 (2H, m, H-6a,b), 5.85 (1H, m, H-5), 6.55
(1H, m, H-1) 6.85 and 7.45 (19H, 2m, aromatic). 13C
NMR: l (ppm) 65.7; 71.0; 74.5; 78.1; 80.2; 81.5; 117.3;
120.0; 122.5; 127.9–128.8 (15C); 129.9; 131.5; 133.5;
134.8; 137.9. Anal. calcd for C33H33BrN2O3: C, 67.69;
H, 5.68; N, 4.78. Found: C, 67.70; H, 5.65; N, 4.67%.
1
sured on a Perkin–Elmer 141 MC polarimeter. The H
and 13C NMR spectra were recorded on Bruker WP
200 SY and Bruker AM 500 instruments in CDCl3 with
TMS as the internal standard. Plasmaspray (PSP) mass
spectra were recorded on a VG TRIO-2 instrument
connected with a Waters 501 HPLC pump in an iso-
cratic mode; samples were dissolved in a 0.1 M ammo-
nium acetate buffer–methanol mixture (1:1) and
injected into the same solvent system at a flow rate of 1
mL/min; PSP tip interface temperature 210°C.
In MOPAC calculations the starting geometries for
27a,b were based on 25 or 26, and assigned so that the
distance between the atoms 2–3 and 3a–7 were set just
beyond their respective vdW radii, and the molecules
were optimised again. The transition states of the reac-
tions were located as follows. The SADDLE routine of
the MOPAC package was used to locate an approxi-
mate saddle point, which was then refined using the
NLLSQ or TS option. Each TS was checked by the
presence of a single negative eigenvalue in the matrix of
force constants. The saddle point corresponding to the
reaction 27a“28a was located at an C-(7)–C-(3a) dis-
2.3. (4R,5S,6S)-4,5,6-Tribenzyloxy-7-(4-bromophenyl-
hydrazono)-7-oxo-hept-2-enoic acid methyl ester 9
3.15 g (5.4 mmol) of the product from the Wittig reac-
tion of 2 and methoxycarbonylmethylenephosphorane6
(3.15 g, 5.4 mmol) was transformed to 8 (1.74 g, 67%)
and then to the phenylhydrazone 9 (1.9 g, 80%, red oil)
as described for 7; m/z 643 (M+H+, PSP), [h]D23=+3.2 (c
,
tance of 1.914 A and an N-(2)–C-(3) distance of 2.498
A, and the nitrilimine moiety is slightly bent.
,
2.1. (2R,3S,4R)-2,3,4-Tribenzyloxy-hex-5-ene-1-al
diethyl dithioacetal 3
1
0.9, CH2Cl2). H NMR: l (ppm) 3.75 and 4.45 (13H,
2m, -OMe, -OCH2-, H-2, H-4, H-5, H-6), 6.1 (1H, m,
H-3), 6.8 and 7.3 (20H, 2m, -CHꢁN and aromatic).
Anal. calcd for C35H35BrN2O5: C, 65.32; H, 5.48; N,
4.35. Found: C, 65.24; H, 5.40; N, 4.37%.
2,3,4-Tri-O-benzyl-D-xylose diethyl dithioacetal (6.55 g,
14 mmol) was oxidised with pyridinium chlorochromate
(7 g) in dry dichloromethane (200 mL). After filtration
the solution was washed with sat. NaHCO3 solution
(200 mL), dried and evaporated. Methyltriphenylphos-
phonium bromide (10 g, 28 mmol) was dissolved in dry
toluene (200 mL) and under nitrogen atmosphere at
0°C butyllithium (2.5 M, 11.2 mL, in hexane) was
added in one portion. After 1 hour, the solution of the
aldehyde in dry toluene (30 mL) was added dropwise to
the phosphorane and kept at 0°C for 2 hours. The
suspension was washed with sat. NaHCO3 solution (100
mL), dried and evaporated to give 3 (2.3 g, 30%) as a
yellow syrup after chromatography (hexane–ethyl acet-
ate 98:2, then 9:1); m/z 540 (M+NH+4), [h]D23=−6.5 (c
2.4. (2R,3R,4R)-2,3,4-Tribenzyloxy-hex-5-ene-1-al di-n-
propyl dithioacetal 12
2,3,4-Tri-O-benzyl-D-ribose di-n-propyl dithioacetal
(2.5 g, 4.3 mmol) was oxidised with pyridinium chloro-
chromate (3 g) in dry dichloromethane (100 mL) and
the obtained
D-ribo-pentodialdose was reacted with
methylenetriphenylphosphorane without purification as
described for 3 to give 12 as a yellow oil (280 mg, 12%);
m/z 568 (M+NH4+, PSP), [h]D23=−4.0 (c 0.55, CH2Cl2).
1H NMR: l (ppm) 0.9 (6H, m, -Me), 1.6 (4H, m,

474
A. Ago´cs et al. / Tetrahedron: Asymmetry 12 (2001) 469–476
-CH2-CH3), 2.6 (4H, m, -S-CH2-), 3.8 (8H, m, H-1–H-
4, -O-CH2-), 5.0 (2H, m, H-6a,b), 5.3 (2H, ABq, -O-
CH2-), 6.0 (1H, m, H-5), 7.3 (15H, m, benzyl). 13C
NMR: l (ppm) 13.6 (CH3-); 22.7 (-CH2-CH3); 33.0
(S-CH2-); 54.2 (C-1); 70.1; 74.9; 75.3 (-CH2, benzyl);
81.3; 82.0; 82.5 (C-2, C-3, C-4); 119.6 (C-6); 127.4–
128.3 (15C, benzyl); 136.1 (C-5); 139.0 (C-4°, benzyl).
Anal. calcd for C33H42O3S2: C, 71.96; H, 7.69; S, 11.64.
Found: C, 72.02; H, 7.64; S, 11.68%.
toluene (50 mL) and methoxycarbonyl triphenyl-
methylenephosphorane (1.3 g, 3.9 mmol) was added,
and the mixture was stirred at 60°C for 6 hours. After
evaporation the product was purified with chromatog-
raphy using hexane–ethyl acetate 95:5 mixture to give
570 mg (24%) compound 22 as a yellow syrup; m/z 609
1
(M+H+, PSP), [h]D23=−9.3 (c 1.55, CH2Cl2). H NMR:
l (ppm) 0.95 (6H, m, -CH3), 1.5 (4H, m, -CH2-CH3),
2.55 (4H, m, -S-CH2), 3.65 (3H, s, OMe), 3.9, 4.25 and
4.7 (10H, 3m, -CH2, benzyl and H-4–H-7), 6.1 (1H, d,
J
2,3=16.1 Hz, H-2), 7.05 (1H, m, H-3), 7.3 (15H, m,
2.5. (4R,5R,6R)-4,5,6-Tribenzyloxy-7,7%-bis-(Z)-n-
propylthio-7-oxo-hept-2-enoic acid methyl ester 15
benzyl). 13C NMR: l (ppm) 13.6 (CH3-); 22.7 (-CH2-
CH3); 33.0 and 33.7 (-S-CH2); 51.6 (OMe); 54.2 (C7);
70.1; 74.9; 75.3 (-CH2, benzyl); 81.3; 82.0; 82.5 (C-4,
C-5, C-6); 123.3 (C-2); 127.4–128.3 (15C, benzyl); 139.0
(C-4°, benzyl); 146.0 (C-3); 166.3 (CꢁO). Anal. calcd for
C35H44O5S2: C, 69.04; H, 7.28; S, 10.53. Found: C,
69.10; H, 7.35; S, 10.57%.
2,3,4-Tri-O-benzyl-D-ribose di-n-propyl dithioacetal
(2.5 g, 4.3 mmol) was oxidised with pyridinium
chlorochromate (3 g) in dry dichloromethane (100 mL).
From the crude aldehyde 15 was produced with
methoxycarbonylmethylenetriphenylphosphorane using
the methodology described for 22. After chromatogra-
phy 15 was obtained as a yellow syrup (770 mg 28%);
2.8. General methodology for the cycloadditions of
nitrilimines
1
m/z 609 (M+H+, PSP), [h]D23=+8.9 (c 1.45, CH2Cl2). H
NMR: l (ppm) 0.95 (6H, m, -CH3), 1.5 (4H, m, -CH2-
CH3), 2.55 (4H, m, -S-CH2), 3.7 (3H, s, OMe), 3.8,
4.15, 4.5 and 4.9 (10H, 4m, -O-CH2 and H-4–H-7), 5.95
(1H, d, J2,3=15.8 Hz, H-2), 6.95 (1H, m, H-3), 7.3
(15H, m, benzyl). 13C NMR: l (ppm) 13.5 (CH3-); 22.6
(-CH2-CH3); 33.0 and 34.5 (S-CH2-); 51.5 (OMe); 54.1
(C-7); 71.5; 73.9; 74.3 (-CH2-, benzyl); 79.2; 81.4; 82.1
(C-4, C-5, C-6); 123.0 (C-2); 127.5-128.3 (15C, benzyl);
138.2 (C-4, benzyl); 145.0 (C-3); 166.4 (CꢁO). Anal.
calcd for C35H44O5S2: C, 69.04; H, 7.28; S, 10.53.
Found: C, 69.02; H, 7.30; S, 10.49%.
N-Bromosuccinimide (1.06 g, 6 mmol) was dissolved in
dry dichloromethane (30 mL) and methyl sulphide (0.88
mL, 6 mmol) was added to the solution (Corey–Kim
reagent). After 10 min 4-bromophenylhydrazone (1.5
mmol) was added and the dark orange suspension was
stirred at 0°C for 1.5 hours. After the addition of
triethylamine (1.5 mL, 10.7 mmol) in portions, the
solution was left to warm to room temperature and was
then washed with sat. NaHCO3 (50 mL), dried and
evaporated. The products were purified with column
chromatography (hexane–ethyl acetate 95:5).
2.6. (2R,3S,4S)-2,3,4-Tribenzyloxy-hex-5-ene-1-al di-n-
propyl dithioacetal 19
2.9. (3aS,4R,5S,6S)-2-(4-Bromophenyl)-4,5,6-tribenzyl-
oxy-2,3,3a,4,5,6-hexahydro-cyclopentapyrazole 7
2,3,4-Tri-O-benzyl-D-galactose di-n-propyl dithioacetal
From 5 (0.92 g, 1.7 mmol), according to the general
procedure, a red syrup (0.50 g) was obtained after
chromatography. Crystallisation from ether/hexane
mixture afforded 7 as a white powder (0.36 g, 39%). Mp
81–83°C, m/z 583 (M+H+, PSP), [h]2D3=−73.9 (c 1.0,
CHCl3); wmax (KBr) 3040, 2920, 1590, 1492, 1454, 1072
(2.53 g, 4.3 mmol) was oxidised with lead(IV) tetra-
acetate (2 g) in dry toluene (60 mL). After filtration the
organic phase was washed with sat. NaHCO3 solution,
dried and evaporated, and the obtained L-arabino-pen-
tadialdose was reacted with methylenetriphenylphos-
phorane as described for 3 to give compound 19 as a
yellow syrup (250 mg, 11%); m/z 568 (M+NH+4, PSP),
1
cm−1. H NMR (500 MHz): l (ppm) 3.5 (1H, t, J3,3%
=
10.2 Hz, J3,3a=10.2 Hz, H-3), 3.76 (1H, m, J3a,4=1.5
Hz, J3%,3a=15 Hz, H-3a), 3.83 (1H, dd, J5,6=6 Hz, H-6)
4.3 (2H, m, J4,5=3.2 Hz, H-5 and H-3%), 4.41 (1H, dd,
H-4), 4.7 (6H, m, -OCH2-), 6.8–7.4 (17H, m, aromatic).
13C NMR: l (ppm) 52.2 (C-3a); 55.2 (C-3); 71.0; 72.5
(-CH2-O); 86.0; 92.5 (C-4, C-5, C-6); 111.7 (C-Br, aro-
matic); 114.7; 131.8 (4C, 4-Br-phenyl); 127.8–128.5
(15C, benzyl); 137.5–137.8 (3C, C-O, benzyl); 145.3
(C-N, 4-Br-phenyl); 154.1 (CꢁN). Anal. calcd for
C33H31BrN2O3: C, 67.93; H, 5.35; N, 4.80. Found: C,
67.84; H, 5.31; N, 4.77%.
[h]2D3=+6.3 (c 0.85, CH2Cl2). H NMR: l (ppm) 0.95
1
(6H, m, -Me), 1.55 (4H, m, -CH2-CH3), 2.55 (4H, m,
-S-CH2-), 4.1 and 4.7 (10H, 2m, H-1–H-4, O-CH2-), 5.4
(2H, m, H-6a,b), 5.95 (1H, m, H-5), 7.4 (15H, m,
benzyl). 13C NMR: l (ppm) 13.6 (CH3-); 22.7 (-CH2-
CH3); 33.1 (S-CH2); 54.1 (C-1); 70.1; 74.7; 75.2 (-CH2-,
benzyl); 81.1; 82.2; 82.6 (C-2, C-3, C-4); 119.5 (C-6);
127.3–128.3 (15C, benzyl); 136.0 (C-5); 138.9 (C-4°,
benzyl). Anal. calcd for C33H42O3S2: C, 71.96; H, 7.69;
S, 11.64. Found: C, 71.90; H, 7.75; S, 11.60%.
2.7. (4S,5S,6R)-4,5,6-Tribenzyloxy-7,7%-bis-(Z)-n-
2.10. (3S,3aS,4R,5S,6S)-2-(4-Bromophenyl)-3-carboxy-
methyl-4,5,6-tribenzyloxy-2,3,3a,4,5,6-hexahydro-
cyclopentapyrazole 10a and (3R,3aR,4R,5S,6S)-2-(4-
bromophenyl)-3-carboxymethyl-4,5,6-tribenzyloxy-
2,3,3a,4,5,6-hexahydro-cyclopentapyrazole 10b
propylthio-7-oxo-hept-2-enoic acid methyl ester 22
2,3,4-Tri-O-benzyl-D-galactose di-n-propyl dithioacetal
(2.25 g, 3.85 mmol) was oxidised with lead(IV) acetate
(2 g) in dry toluene (60 mL). The suspension was
filtered and washed with NaHCO3 solution, dried and
evaporated. The crude aldehyde was dissolved in dry
From 9 (3 g, 4.67 mmol), according to the general
method, two diastereomers were obtained: 10a was

A. Ago´cs et al. / Tetrahedron: Asymmetry 12 (2001) 469–476
475
2.12. (3S,3aS,4R,5R,6S)-2-(4-Bromophenyl)-3-car-
obtained as white crystals from hexane/ether (845 mg,
28%), and 10b was a yellow syrup (830 mg, 28%,); m/z
641 (M+H+, PSP). 10a: mp 141–142°C, [h]2D3=+13.6 (c
1.75, CH2Cl2); wmax (KBr) 3060, 2922, 1738, 1590, 1492,
boxymethyl-4,5,6-tribenzyloxy-2,3,3a,4,5,6-hexahydro-
cyclopentapyrazole 17a and (3R,3aR,4R,5R,6S)-2-
(4-bromophenyl)-3-carboxymethyl-4,5,6-tribenzyloxy-
2,3,3a,4,5,6-hexahydro-cyclopentapyrazole 17b
1
1068 cm−1. H NMR (500 MHz): l (ppm) 3.4 (3H, s,
OMe), 3.75 (1H, dd, J3a,4=8.4 Hz, J4,5=5.85 Hz, H-4),
3.8 (1H, dt, J3a,3=8.4 Hz, J3a,6=1.1 Hz, H-3a), 3.88
(1H, s, J5,6=2.85 Hz, H-5), 4.4 (1H, dd, H-6), 4.5 (1H,
d, H-3), 4.6–4.9 (6H, m, -OCH2-), 6.9 and 7.6 (4H, 2d,
aromatic), 7.37 (15H, m, benzyl). 13C NMR: l (ppm)
53.1 (C-3a); 59.1 (OMe); 69.2 (C-3); 71.0; 72.0; 72.4
(-CH2-O); 76.4; 91.7 (C-4, C-5, C-6); 112.9 (C-Br, aro-
matic); 115.0; 131.8 (4C, 4-Br-phenyl); 127.6–128.4
(15C, benzyl); 137.3; 137.5 (3C, C-O, benzyl); 144.3
(C-N, 4-Br-phenyl); 151.8 (CꢁN); 171.2 (CꢁO). Anal.
calcd for C35H33BrN2O5: C, 65.52; H, 5.18; N, 4.37.
Found: C, 65.59; H, 5.11; N, 4.34. 10b [h]2D3=+1.5 (c
1.15, CH2Cl2); wmax (KBr) 3062, 2922, 1738, 1590, 1494,
From 15 (520 mg, 0.84 mmol) the corresponding hydra-
zone was synthesised using the methodology for 21 to
give compound 16 as a red syrup (417 mg, 77%); m/z
643 (M+H+, PSP), [h]D23=+9.2 (c 0.85, CH2Cl2). 1H
NMR: l (ppm) 3.7 (3H, s, -OMe) 3.9–5.1 (10H, m,
-OCH2-, H-4, H-5, H-6), 6.1 (1H, d, J2,3=15.2, H-2),
6.9–7.3 (21H, m, H-3, -CHꢁN and aromatic). Cycload-
dition (general method) starting from 16 (417 mg, 0.65
mmol) furnished two yellow syrups: 17a (45 mg, 11%)
and 17b (110 mg, 26%); m/z 641 (M+H+, PSP). 17a:
[h]2D3=+21.6 (c 0.94, CH2Cl2); wmax (KBr) 3064, 2922,
1
1738, 1590, 1454, 1102 cm−1. H NMR (500 MHz): l
(ppm) 3.8 (1H, m, J3a,4=6.7 Hz, J4,5=5.8 Hz, H-4), 3.9
(3H, s, OMe), 4.05 (1H, dd, J5,6=4.6 Hz, H-5), 4.2 (1H,
dd, J3a,3=10.0 Hz, H-3a), 4.35 (1H, d, H-3), 4.4 (1H, d,
H-6), 4.6–4.9 (6H, m, -OCH2-), 7.35 (19H, m, aro-
matic). 13C NMR: l (ppm) 53.0 (C-3a); 60.0 (OMe);
69.4 (C-3); 71.3; 71.6; 72.9 (-CH2-O); 71.8; 78.8; 79.9
(C-4, C-5, C-6); 112.6 (C-Br); 115.0; 131.8 (4C, 4-Br-
phenyl); 127.4-128.5 (15C, benzyl); 137.5 (3C, C-O,
benzyl); 144.5 (C-N, 4-Br-phenyl); 154.5 (CꢁN); 171.3
(CꢁO). Anal. calcd for C35H33BrN2O5: C 65.52; H, 5.18;
N, 4.37. Found: C, 65.39; H, 5.23; N, 4.31%. 17b:
[h]2D3=+53.5 (c 0.95, CH2Cl2); wmax (KBr) 3030, 2922,
1
1076 cm−1; H NMR (500 MHz): l (ppm) 3.75 (3H, s,
-OMe), 3.82 (1H, d, J4,5=6.6 Hz, J4,3a:0 Hz, H-4), 3.9
(1H, dd, J5,6=9.2 Hz, H-5), 4.2 (1H, dd, J3a,3=2.9 Hz,
H-3a), 4.3–4.5 (4H, m, -OCH2-), 4.6 (1H, d, H-3), 4.8
and 5.2 (2H, q, -OCH2-), 5.0 (1H, d, H-6), 6.95 and 7.4
(19H, 2m, aromatic). 13C NMR: l (ppm) 53.0 (C-3a);
58.0 (OMe); 64.2 (C-3); 71.0; 71.9; 72.3 (-CH2-O);
78.0; 89.7 (C-4, C-5, C-6); 112.6 (C-Br); 15.5; 131.7
(4C, 4-Br-phenyl); 127.6–128.5 (15C, benzyl); 137.2
(3C, C-O, benzyl); 145.6 (C-N, 4-Br-phenyl); 158.3
(CꢁN); 172.3 (CꢁO). Anal. calcd for C35H33BrN2O5: C,
65.52; H, 5.18; N, 4.37. Found: C, 65.62; H, 5.21; N,
4.29%.
1
1748, 1574, 1488, 1112 cm−1. H NMR (500 MHz): l
(ppm) 3.45 (1H, dd, J5,6=10.5 Hz, H-5), 3.8 (3H, s,
-OMe), 4.05 (1H, dd, J3a,3=3.2 Hz, H-3a), 4.13 (1H, d,
J
4,5=4.6 Hz, J3a,4=7.5 Hz, H-4), 4.5–5.1 (6H, m,
-OCH2-), 4.65 (1H, d, H-3), 4.70 (1H, d, H-6), 7.3
(19H, m, aromatic). 13C NMR: l (ppm) 52.8 (C-3a);
56.9 (OMe); 64.7 (C-3); 70.9; 71.9; 73.0 (-CH2-O); 68.7;
73.9; 83.7 (C-4, C-5, C-6); 112.6 (C-Br); 115.9; 131.7
(4C, 4-Br-phenyl); 127.3–128.7 (15C, benzyl); 137.7
(3C, C-O, benzyl); 145.9 (C-N, 4-Br-phenyl); 159.1
(CꢁN); 172.0 (CꢁO). Anal. calcd for C35H33BrN2O5: C,
65.52; H, 5.18; N, 4.37. Found: C, 65.64; H, 5.17; N,
4.42%.
2.11. (3aS,4R,5R,6S)-2-(4-Bromophenyl)-4,5,6-tribenzyl-
oxy-2,3,3a,4,5,6-hexahydro-cyclopentapyrazole 14
From 12 (80 mg, 0.55 mmol) the corresponding alde-
hyde and hydrazone were formed using the methodol-
ogy described for 21, to give 13 as a red syrup (69 mg
(81%); m/z 585 (M+H+, PSP), [h]2D3=−10.3 (c 0.9,
1
CH2Cl2). H NMR: l (ppm) 4.2–5.0 (9H, m, -OCH2-,
H-2, H-3, H-4), 5.65 (3H, m, H-5, H-6a,b), 6.55 (1H,
m, H-1) 6.85 and 7.45 (19H, 2m, aromatic). Cycloaddi-
tion starting from hydrazone 13 (69 mg, 0.12 mmol)
according to the general method furnished one
diastereomer, 14, as a yellow syrup (21 mg, 30%); m/z
583 (M+H+, PSP), [h]D23=−12.5 (c 0.6, CH2Cl2); wmax
(KBr) 3030, 2852, 1590, 1492, 1102 cm−1. 1H NMR
2.13. (3aS,4S,5S,6S)-2-(4-Bromophenyl)-4,5,6-tribenzyl-
oxy-2,3,3a,4,5,6-hexahydro-cyclopentapyrazole 21
To a solution of 17 (300 mg, 0.55 mmol) in acetone (20
mL) and water (2 mL) was added cadmium carbonate
(1 g) and mercury(II) chloride (360 mg, 1.33 mmol); the
suspension was then stirred for 24 hours. The suspen-
sion was filtered, evaporated and taken up in
dichloromethane. The organic phase was washed with
sat. NaHCO3 (50 mL) and 10% potassium iodide solu-
tion (50 mL), then dried and evaporated. From this
crude product 225 mg (71%) of the corresponding
4-bromophenylhydrazone 20 was obtained (as
described for 5) as a red syrup. Compound 20: m/z 585
(500 MHz): l (ppm) 3.15 (1H, dd, J3,3%=9.3 Hz, J3,3a
=
11.7 Hz, H-3), 3.7 (1H, t, H-4), 3.95 (1H, m, J3a,4=6.2
Hz, J3%,3a=11.1 Hz, H-3a), 4.05 (1H, t, H-3%), 4.15 (1H,
t, J4,5=5.2 Hz, H-5), 4.4 (1H, d, J5,6=4.8 Hz, H-6), 4.7
(6H, m, -OCH2-), 6.8–7.4 (19H, m, aromatic). 13C
NMR: l (ppm) 53.0 (C-3a); 54.9 (C-3); 71.8; 72.0
(-CH2-O); 77.7; 81.2; 84.9 (C-4, C-5, C-6); 111.5 (C-Br,
aromatic); 114.7 and 131.7 (4C, p-Br-phenyl); 127.7–
128.5 (15C, benzyl); 137.3–137.6 (3C, C-O, benzyl),
146.0 (C-N, p-Br-phenyl); 159.3 (CꢁN). Anal. calcd for
C29H33BrN2O3: C, 67.93; H, 5.35; N, 4.80. Found: C,
67.80; H, 5.29; N, 4.73%.
1
(M+H+, PSP), [h]D23=+7.5 (c 0.8, CH2Cl2). H NMR: l
(ppm) 4.0–5.0 (9H, m, -OCH2-, H-2, H-3, H-4), 5.6
(3H, m, H-5, H-6a,b), 6.7 (1H, m, H-1), 6.8 and 7.5
(19H, m, aromatic). Cycloaddition starting from 20

476
A. Ago´cs et al. / Tetrahedron: Asymmetry 12 (2001) 469–476
(225 mg, 0.39 mmol) according to the general method
resulted in 80 mg (36%) of 21 as yellow syrup; m/z 583
(M+H+, PSP), [h]D23=+43.5 (c 1.1, CH2Cl2); wmax (KBr)
3062, 2866, 1590, 1494, 1074 cm−1. 1H NMR (500
MHz): l (ppm) 3.2 (1H, t, J3,3%=9.3 Hz, J3,3a=9.3 Hz,
H-3), 3.95 (m, 1H, H-3a), 4.1 (1H, t, J3%,3a=9.5 Hz,
H-3%) 4.25 (1H, d, J3a,4=4.5 Hz, J4,5=0 Hz, H-4), 4.6
(8H, m, -OCH2-, H-5, H-6), 6.8–7.4 (17H, m, aro-
matic). 13C NMR: l (ppm) 53.0 (C-3a); 54.9 (C-3); 71.8;
72.0 (-CH2-O); 77.7; 81.2; 84.9 (C-4, C-5, C-6); 111.5
(C-Br, aromatic); 114.7 and 131.7 (4C, 4-Br-phenyl);
127.7–128.5 (15C, benzyl); 137.3–137.6 (3C, -C-O, ben-
zyl), 146.0 (C-N, 4-Br-phenyl); 159.3 (CꢁN). Anal.
calcd for C29H31BrN2O3: C, 67.93; H, 5.35; N, 4.80.
Found: C, 67.94; H, 5.39; N, 4.87%.
Anal. calcd for C35H33BrN2O5: C, 65.52; H, 5.18; N,
4.37. Found: C, 65.61; H, 5.09; N, 4.40%.
Acknowledgements
The authors are gateful for the financial support
received from the Hungarian Scientific Research Fund
(Grants No. T 019338, 029089, 30138 and 023592) and
thank the Ministry of Education for FKFP 500/1997
and 325/1997 support.
References
2.14. (3S,3aS,4S,5S,6S)-2-(4-Bromophenyl)-3-car-
boxymethyl-4,5,6-tribenzyloxy-2,3,3a,4,5,6-hexahydro-
cyclopentapyrazole 24a and (3R,3aS,4S,5S,6S)-2-
(4-bromophenyl)-3-carboxymethyl-4,5,6-tribenzyloxy-
2,3,3a,4,5,6-hexahydro-cyclopentapyrazole 24b
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ing hydrazone was synthesised with the methodology
described for 21 to give compound 23 as a red oil (206
mg, 61%). Compound 23: m/z 643 (M+H+, PSP),
[h]2D3=−11.4 (c 1.0, CH2Cl2). 1H NMR: l (ppm) 3.5
(3H, s, -OMe) 3.95–5.0 (10H, m, -OCH2-, H-4, H-5,
H-6), 6.3 (1H, d, J2,3=15.2, H-2), 6.9–7.5 (21H, m, H-3,
-CHꢁN and aromatic). Cycloaddition (general method)
starting from 23 (206 mg, 0.32 mmol) resulted in two
products: 24a (31 mg, 15%) and 24b (16 mg, 8%), both
yellow oils; m/z 641 (M+H+, PSP). 24a: [h]D23=−7.0 (c
0.8, CH2Cl2); wmax (KBr) 3030, 2922, 1738, 1590, 1494,
9. Ferrier, R. J. J. Chem. Soc., Perkin Trans. 1 1983,
1621–1625.
10. Nakata, M.; Akazawa, S.; Kitamura, S.; Tatsuta, K.
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1
1454, 1074 cm−1. H NMR (500 MHz): l (ppm) 3.85
(3H, s, OMe), 3.95 (1H, dd, J5,6=5.2 Hz, H-5), 4.2 (1H,
dd, J3a,6=1.2 Hz, H-6), 4.2 (1H, t, J3a,4=9.6 Hz, J4,5
=
11. Gallos, J. K.; Koumbis, A. E.; Xiraphaki, V. P.; Dellios,
C. C.; Coutouli-Argyropoulou, E. Tetrahedron 1999, 55,
15167–15180.
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9.7 Hz, H-4), 4.4 (1H, dd, J3a,3=5.0 Hz, H-3a), 4.60
(1H, d, H-3), 4.6–4.9 (6H, m, -OCH2-), 6.95 and 7.25
(4H, 2d, aromatic), 7.30 (15H, m, benzyl). 13C NMR: l
(ppm) 53.1 (C-3a); 60.1 (OMe); 68.9 (C-3); 71.6; 72.1;
72.4 (-CH2-O); 76.9; 77.6; 84.0 (C-4, C-5, C-6); 112.8
(C-Br); 115.0; 131.9 (4C, 4-Br-phenyl); 127.6–128.5
(15C, benzyl); 137.3 (3C, C-O, benzyl); 145.0 (C-N,
4-Br-phenyl); 156.5 (CꢁN); 171.5 (CꢁO). Anal. calcd for
C35H33BrN2O5: C, 65.52; H, 5.18; N, 4.37. Found: C,
65.50; H, 5.12; N, 4.42. 24b: [h]2D3=−3.7 (c 0.47,
CH2Cl2); wmax (KBr) 3030, 2922, 1736, 1590, 1492, 1122
cm−1. 1H NMR (500 MHz): l (ppm) 3.78 (1H, m,
15. Tadano, K.; Maeda, H.; Hoshino, M.; Iimura, Y.; Suami,
T. J. Org. Chem. 1987, 52, 1946–1956.
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J
J
3a,3=4.1 Hz, H-3a), 3.8 (3H, s, OMe), 4.15 (1H, t,
3a,4=4.0 Hz, J4,5=4.6 Hz, H-4), 4.3 (1H, t, J5,6=4.6
17. Herczegh, P.; Zse´ly, M.; Szila´gyi, L.; Bajza, I.; Kova´cs,
´
A.; Batta, G.; Bogna´r, R. Cycloaddition Reactions in
Hz, H-5), 4.57 (1H, dd, J3a,6=0.5 Hz, H-6), 4.65 (1H,
d, H-3), 4.6–5.0 (6H, m, -OCH2-), 7.2 (15H, m, benzyl).
13C NMR: l (ppm) 52.9 (C-3a); 57.7 (OMe); 64.7 (C-3);
71.6; 72.6; 73.6 (-CH2-O); 74.7; 76.1; 90.4 (C-4, C-5,
C-6); 112.3 (C-Br); 115.8; 131.8 (4C, 4-Br-phenyl);
127.6–128.4 (15C, benzyl); 137.7 (3C, C-O, benzyl);
144.3 (C-N, 4-Br-phenyl); 154.0 (CꢁN); 172.4 (CꢁO).
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