Stereoselective synthesis of homochiral annulated sultams via intramolecular cycloaddition reactions

Article abstract of DOI:10.1016/S0040-4020(01)00186-7

Different homochiral dipoles containing a sulfonamido group have been synthesized, starting from L-amino acids, and used for the construction of functionalized and enantiomerically pure annulated sultams.

Full text of DOI:10.1016/S0040-4020(01)00186-7

TETRAHEDRON
Pergamon
Tetrahedron 57 <2001) 3425±3433
Stereoselective synthesis of homochiral annulated sultams via
intramolecular cycloaddition reactions
Ugo Chiacchio,a,p Antonino Corsaro,a Antonio Resci®na,a Majdi Bkaithan,b Giovanni Grassi,b
Anna Piperno,b Tindara Priviterab and Giovanni Romeob
a
Á
Dipartimento di Scienze Chimiche, Universita di Catania, 95125 Catania, Italy
b
Á
Dipartimento Farmaco-Chimico, Universita di Messina, Messina, Italy
Received 3 November 2000; revised 25 January 2001; accepted 8 February 2001
AbstractÐDifferent homochiral dipoles containing a sulfonamido group have been synthesized, starting from l-amino acids, and used for
the construction of functionalized and enantiomerically pure annulated sultams. q 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
In this paper we have investigated the intramolecular
cycloaddition process of different dipoles, where the sulfon-
amido group is located in a-position with respect to the
reactive center, i.e. the aldehydic moiety on which different
dipoles have been built.
The synthetic versatility of the intramolecular cycloaddition
of nitrones, containing additional oxygen, nitrogen or sulfur
atoms in a tether connecting the dipole to the dipolarophile
moiety, has been widely exploited.1 Applications of this
methodology are seen in the synthetic routes towards func-
tionalized furan, pyrrole and thiophene nuclei, some of
which occur in natural and biologically active compounds.
In some cases these syntheses start from homochiral
educts.2
The presence of a stereocenter at C2 furnishes a valid tool
for the diastereoselective synthesis of isoxazole-, pyrazole-,
pyrrolo-fused isothiazole-1,1-dioxides, some of which have
also been accessible in enantiopure forms <Scheme 1).
The synthetic potential of this kind of sulfonamido-based
dipoles has not been fully exploited; moreover, sultams
have acquired good interest for the biological activity of
some members of this class of compounds6 and as chiral
auxiliaries in asymmetric syntheses.7
Factors controlling the stereochemical outcome of the reac-
tion have been elucidated on the basis of a kinetic control of
the process and the stability of the different transition states
leading to different diastereoisomers.3 A chiral center in the
starting nitrone could cause asymmetric induction giving
rise to the formation of new chiral centers with de®nite
con®guration in the obtained cycloadducts, so extending
the synthetic potential of the reaction.
2. Results and discussion
The different synthetic approaches which lead to the target
molecules are based on the sulfonamido aldehydes 4, which
have been obtained as reported in Scheme 2.
In this context, we have previously reported the intramo-
lecular 1,3-dipolar cycloaddition of suitably substituted a-
and b-sulfonamides, which leads to isoxazole and pyrazole
annulated g- and d-sultams: the obtained isothiazole 1,1-
dioxide derivatives belong to a class of heterocycles
which exhibit interesting pharmacological properties;4
in particular, the 2-methyl-5,6-diphenylperhydro-1l6-
pyrazolo[3,4-d]isothiazole-1,1-dioxide shows antimicotic
activity.5
Starting from l-amino acids 1, aminoalcohols 2 have been
obtained according to standard procedures.8 Compounds 2
have been treated with trans 2-phenylethenesulfonyl
chloride to give the corresponding sulfonamido alcohols
3, which have been converted into the a-sulfonamido alde-
hydes 4a±d by oxidation with Dess±Martin periodinane
<DMP).9 Subsequent treatment with N-substituted hydroxyl-
amines 5 <RˆMe or PhCH2) furnished nitrones 6a, b, d, e,
which immediately underwent intramolecular cycloaddition
to bicyclo compounds 7a, b, d, e in good yields <Scheme 3).
Keywords: sultams; Dess±Martin periodinane; intramolecular cyclo-
addition.
p
Corresponding author. Tel.: 139-095-738-5014; fax: 139-095-580138;
e-mail: uchiacchio@dipchi.unict.it
Similar treatment of 4a, c with hydroxylamine produces the
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020<01)00186-7

3426
U. Chiacchio et al. / Tetrahedron 57 '2001) 3425±3433
Scheme 1.
Scheme 2.
bicyclo compounds 10a, c which result from the thermally
induced oxime-nitrone 8!9 isomerization, followed by
subsequent intramolecular cyloaddition <Scheme 4). More-
over, the oxime 8a is converted by NaOCl oxidation to
nitrile oxide 11a, which gives rise to intramolecular
cycloaddition at the styryl group to afford intermediate
12a, which spontaneously aromatizes into isoxazole deriva-
tive 13a. On the contrary, compound 8c is converted into
Scheme 3.

U. Chiacchio et al. / Tetrahedron 57 '2001) 3425±3433
3427
Scheme 4.
compound 12c, which does not aromatize in our reaction
conditions.
retained in the cycloadducts and the relative stereochemistry
at C3 and C3a in the formed isoxazolidine and isoxazoline
ring is predetermined by the alkene geometry. Furthermore,
the ring junction between the two fused rings in compounds
7 and 10 is always cis, as con®rmed by coupling constants
and NOE measurements. For instance, in compound 7a, the
coupling constant for the cis ring junction protons <J3a,6a) is
8.4 Hz, indicative of a nearly eclipsed dihedral angle
between H3a and H6a. Irradiation of H3a gives rise to a
positive NOE effect for H6a <9.43%), for aromatic protons
at C3 <3.54%) and for benzylic protons at C6, so indicating a
cis relationship between these protons. By considering that
the C6 con®guration is S, the obtained data are only com-
patible with a <3S,3aR,6S,6aS) stereochemistry.
Structures of obtained cycloadducts were assigned on the
basis of analytical and spectroscopic data. High-resolution
mass spectra gave the correct molecular ions for all the
examined compounds. The 1H NMR spectra of compounds
7a, b, d, e, 10a, c and 12c showed the diagnostic resonances
of H3 protons in the range 5.34±5.95 ppm, while H3a protons
appear at 3.98±4.76 ppm; H6a protons, for compounds 7a, b,
e and 10a, c, resonate in the range 3.39±4.14 ppm; for
compound 7d the H8b proton results at 3.56 ppm. For
compound 13a the diagnostic resonance of H6 proton is at
4.64 ppm.
The investigated 1,3-dipolar cycloadditions showed high
regioselectivity; according to similar intramolecular
processes, no bridged adducts have been detected in the
crude reaction mixture.
The stereocenter at the a-position effectively controls the
formation of the three new contiguous stereocenters and one
of the eight possible stereoisomers is produced in a highly
stereoselective process.
The cycloaddition process has also been found to proceed
with complete diasteroselectivity: the NMR spectra or tlc of
crude products do not show evidence of any diastereo-
isomers. The chiral center at C2 induces a complete asym-
metric induction furnishing homochiral compounds 7, 10,
12 and 13 from homochiral starting material. In fact, the 1H
NMR spectra of the above reported compounds, recorded in
the presence of increasing amounts of the chiral shift
reagent [Eu<tfc)3], do not show any change of the single
resonances, apart from the expected shifts induced by the
paramagnetic reagent.
The syntheses of pyrazolo-fused g-sultams have also been
investigated, starting from sulfonamido aldehyde 1 <Scheme
5). Thus, reaction of 4a with phenylhydrazine afforded the
racemic phenylhydrazone 14 <see Section 3); thermal hydra-
zone±azomethine imine isomerization, performed in ethanol
at re¯ux temperature, generates the 1,3-dipole 15, which spon-
taneously underwent intramolecular cycloaddition to cyclo-
1
adduct 16, as evidenced in the H NMR spectrum of the
crude reaction mixture. The attempts to isolate this compound
by ¯ash chromatography led to the isolation of compound
17, which originates from a rapid air oxidation of 16.
The absolute stereochemistry of the cycloadducts 7, 10 and
12 was elucidated by H NMR. The stereochemical infor-
mation present in the dipolarophile moiety is completely
Compound 17 was obtained as a racemic mixture: this result
is the consequence of the racemization process, occurring in
the hydrazone formation.
1

3428
U. Chiacchio et al. / Tetrahedron 57 '2001) 3425±3433
Scheme 5.
In the attempt to establish the scope and limitations of the
investigated approach towards bicyclic sultams, we have
also examined the synthesis of pyrrolidino-isothiazole
dioxide fused systems, starting from the sulfonamido alde-
hyde 4c <Scheme 6).
a thermal imine±azomethine ylide 19 isomerization by 1,2
prototropic shift.10
The stereochemical assignments have been performed on
the basis of NOE measurements; thus, irradiation of H3a in
20 resulted in NOE enhancements for H5, H6a and the
methyl group at C3, so indicating a cis spatial relationship
between these protons.
Reaction with glycine methyl ester hydrochloride in the
presence of 6 equiv. of triethylamine afforded compounds
20 and 21 as racemic mixtures, in a 3:1 relative ratio.
Conversely, in compound 21, no NOE effect has been
detected between H3a and H5: irradiation of H3a gives rise
only to enhancement of H6a and the methyl group at C3.
The reaction pathway is rationalized on the basis of the
initial formation of imino derivative 18, which undergoes
Scheme 6.
Figure 1.

U. Chiacchio et al. / Tetrahedron 57 '2001) 3425±3433
3429
The absence of any diastereomeric control in the examined
process could be ascribed to the existence of two stereo-
isomeric azomethine ylides 19a and 19b, which inde-
pendently undergo the cycloaddition reaction <Fig. 1).
ethyl]-N-methyl-<E)-2-phenyleth-1-ene-1-sulfonamide 3a
25
<15.56 g, 94%) as a yellow solid, mp 89±918C; [a]D
ˆ
238.6 <c 1.20, CHCl3); nmax <KBr) 3380, 3030, 2995,
1600, 1330, 1060, 920, 750, 700 cm21; dH <500 MHz,
CDCl3) 2.40 <bs, 1H), 2.70 <dd, 1H, Jˆ9.6 and 14.1 Hz),
2.80 <s, 3H), 2.83 <dd, 1H, Jˆ6.0 and 14.1 Hz), 3.69 <d, 2H,
Jˆ5.7 Hz), 4.35 <m, 1H), 5.74 <d, 1H, Jˆ15.6 Hz), 7.19±
7.37 <m, 11H); dC <125 MHz, CDCl3) 27.74, 35.16, 60.81,
62.25, 123.88, 126.85, 128.27, 128.41, 128.66, 129.17,
130.46, 132.58, 137.62, 141.24. Exact mass calculated for
C18H21NO3S: 331.1242. Found: 331.1240.
The possible alternative, i.e. that compound 21 originates
from 20 by epimerization, can be ruled out: in fact,
when 20 was treated with triethylamine for several hours
at re¯ux temperature, starting material was recovered
unaltered.
Moreover, formation of 20 and 21 as racemic mixtures is
explainable on the basis of a racemization process occurring
in the initial step leading to the imino derivative, promoted
by the basic reaction medium.
3.1.2. Reaction of 2b with trans 2-phenylethenesulfonyl
chloride. First elution gave N-benzyl-N-[<1S)-1-benzyl-2-
hydroxyethyl]-<E)-2-phenyleth-1-ene-1-sulfonamide
3b
<18.32g, 90%) as a yellow solid, mp 110±113 8C; nmax
<KBr) 3380, 3035, 2995, 1650,1620, 1600, 1330, 1060,
920, 750, 700 cm21; dH <500 MHz, CDCl3) 2.75 <bs, 1H),
2.65 <dd, 1H, Jˆ7.2and 14.1 Hz), 2.85 <dd, 1H, Jˆ7.2
and 14.1 Hz), 3.47 <m, 1H), 4.17 <q, 2H, Jˆ6.0 and
7.2Hz), 4.31 <d, 1H, Jˆ15.4 Hz), 4.45 <d, 1H,
Jˆ15.4 Hz) 6.17 <d, 1H, Jˆ15.5 Hz), 7.19±7.55 <m,
16H); dC <125 MHz, CDCl3) 36.39, 48.32, 62.52,
62.98, 125.05, 126.79, 126.82, 127.96, 128.20, 128.26,
128.37, 128.56, 128.59, 128.65, 128.68, 128.73, 128.84,
128.95, 129.11, 129.25, 132.64, 137.68, 137.81, 141.19.
Exact mass calculated for C24H25NO3S: 407.1555.
Found: 407.1550.
In conclusion, the homochiral aldehyde 4 has been used as a
valid source of different homochiral dipoles for the
construction of functionalized isothiazoloisoxazole-4,4-
dioxides, pyrazoloisothiazole-1,1-dioxides and pyrrolo-
isothiazole-1,1-dioxides by exploiting the intramolecular
1,3-dipolar cycloaddition. In particular, enantiomerically
pure annulated sultams 7, 10, 12 and 13 with speci®c
absolute stereochemistry have been obtained. These ring
closures offer the possibility of usefully synthetic manipu-
lations directed towards the synthesis of biologically active
compounds.
3.1.3. Reaction of 2c with trans 2-phenylethenesulfonyl
chloride. First elution gave N-benzyl-N-[<1S)-2-hydroxy-
3. Experimental
1-methylethyl]-<E)-2-phenyleth-1-ene-1-sulfonamide
<13.08 g, 79%) as a white solid, mp 90±928C; [a]D
3c
ˆ
Melting points were measured on a Ko¯er apparatus and are
uncorrected. Elemental analyses were performed with a
Perkin±Elmer elemental analyzer. Infrared spectra were
recorded on a Perkin±Elmer 377 instrument. 1H NMR
spectra were measured on a 500 MHz Varian Unity Inova
instrument in CDCl3 as solvent. Chemical shifts are in ppm
<d) from TMS as internal standard. NOE difference spectra
were obtained by subtracting alternatively right-off-reso-
nance free induction decays <FIDS) from right-on-reso-
nance-induced FIDS. Merck silica gel 60H was used for
preparative short-column chromatography. Optical rota-
tions were measured on a PF 241 MC Polarimeter
<Perkin±Elmer). Compounds 2a±d have already been
reported.2a,11
25
122.1 <c 1.99, CHCl3); nmax <KBr) 3524, 3062, 3029,
2978, 2940, 1615, 1496, 1450, 1324, 1140, 1063, 1021,
863, 817, 747 cm21; dH <500 MHz, CDCl3) 1.13 <d, 3H,
Jˆ6.9 Hz), 2.23 <bs, 1H, OH), 3.41 <dd, 1H, Jˆ5.6 and
11.6 Hz), 3.47 <dd, 1H, Jˆ8.2and 11.6 Hz), 4.03 <ddd,
1H, Jˆ5.6, 6.9 and 8.2Hz), 4.30 <d, 1H, Jˆ15.8 Hz), 4.45
<d, 1H, Jˆ15.8 Hz), 6.79 <d, 1H, Jˆ15.4 Hz), 6.75±7.48 <m,
11H); dC <125 MHz, CDCl3) 15.66, 47.41, 56.10, 64.25,
124.99, 127.63, 127.78, 128.08, 128.57, 128.94, 130.59,
132.62, 137.94, 140.97. Exact mass calculated for
C18H21NO3S: 331.1242. Found: 331.1245.
3.1.4. Reaction of 2d with trans 2-phenylethenesulfonyl
chloride. First elution gave <<2S)-1-{[<E)-2-phenyleth-1-
3.1. Preparation of trans sulfonamido alcohols 3a±dÐ
general procedure
enyl]sulfonyl}tetrahydro-1H-pyrrol-2-yl)methanol
3d,
<9.35 g, 70%) as a yellow oil; nmax <neat) 3375, 3058,
3030, 2960, 1600, 1490, 1320, 1060, 980, 760 cm21; dH
<500 MHz, CDCl3) 1.81 <m, 2H), 1.96 <m, 2H), 2.71 <t,
1H, Jˆ6.0 Hz, OH), 3.46 <m, 1H), 3.48 <m, 1H), 3.71 <m,
3H), 6.75 <d, 1H, Jˆ15.3 Hz), 7.42±7.57 <m, 6H); dC
<125 MHz, CDCl3) 29.80, 29.09, 49.82, 61.80, 65.77,
128.15, 128.27, 129.00, 130.99, 137.61, 143.95. Exact
mass calculated for C13H17NO3S: 267.0929. Found:
267.0932.
A solution <11.14 g, 55 mmol) of trans 2-phenylethene-
sulfonyl chloride in anhydrous dichloromethane <50 mL)
was added dropwise, at 08C, to a stirred solution containing
compounds 2 <50 mmol) and triethylamine <5.44 g, 7.5 mL,
53.8 mmol). The reaction mixture was stirred at 08C for
30 min and then at 258C for 6 h. At the end of this time
the mixture was extracted with dichloromethane, washed
with 10% aqueous NaHCO3 and dried <Na2SO4). The
solvent was removed and the crude residue was puri®ed
by silica gel ¯ash chromatography <2% methanol/chloro-
form).
3.2. Preparation of trans sulfonamido aldehydes 4a±dÐ
general procedure
3.1.1. Reaction of 2a with trans 2-phenylethenesulfonyl
chloride. First elution gave N-[<1S)-1-benzyl-2-hydroxy-
Wet CH2Cl2 <20 mL; 20 mL H2O in 2 0 mL CHCl2)
2
was added slowly to a vigorously stirring solution of

3430
U. Chiacchio et al. / Tetrahedron 57 '2001) 3425±3433
sulfonamido alcohol 4 <1 mmol) and DMP9 <640 mg,
1 mmol) in dry CH2Cl2 <6 mL) and allowed to stir for
30 min. The mixture was then diluted with ether, and
concentrated into a few milliliters of solvent by rotary
evaporator. The residue was taken up in ether <50 mL)
and then washed with a 1:1 solution of 10% aqueous
Na2S2O3 in saturated aqueous NaHCO3 <30 mL), followed
by H2O <10 mL) and brine <10 mL). The aqueous washings
were back-extracted with ether <20 mL), and this organic
layer was washed with H2O and brine. The combined
organic layers were dried <Na2SO4) and the solvent
removed under reduced pressure. The residue was then
subjected to silica gel ¯ash chromatography <2% methanol/
chloroform).
27.61, 48.84, 66.45, 120.80, 128.53, 129.10, 131.11, 132.34,
143.83, 199.85. Exact mass calculated for C13H15NO3S:
265.0773. Found: 265.0777.
3.3. Preparation of isothiazolo[4,5-c]isoxazole-4,4-
dioxides 7a, b, d, eÐgeneral procedure
A mixture containing compound 4 <a, b or d) <50 mmol),
triethylamine <5.56 g, 7.66 mL, 55 mmol) and N-substituted
hydroxylamine hydrochloride <55 mmol) in absolute etha-
nol <50 mL) was re¯uxed for 24 h. At the end of this time
the solvent was removed and the residue extracted with
dichloromethane, washed with water and dried <Na2SO4).
The residue was then subjected to silica gel ¯ash chroma-
tography <2% methanol/chloroform).
3.2.1. Oxidation of 3a with DMP. First elution gave
N-[<1S)-1-benzyl-2-oxoethyl]-N-methyl-<E)-2-phenyleth-1-
ene-1-sulfonamide 4a <280 mg, 85%) as a white sticky oil;
3.3.1. Reaction of 4a with N-methyl hydroxylamine. First
elution gave <3S,3aR,6S,6aS)-6-benzyl-1,5-dimethyl-3-
phenylperhydro-4l6-isothiazolo[4,5-c]isoxazole-4,4-dioxide
7a <13.43 g, 75%) as a white solid, mp 152±1538C;
n
max <neat) 3060, 3020, 2980, 2850, 2730, 1740, 1600, 1500,
1315, 1030, 980, 920, 760 cm21; dH <500 MHz, CDCl3)
2.69 <s, 3H), 2.74 <dd, 1H, Jˆ9.9 and 15.1 Hz), 3.28 <dd,
1H, Jˆ7.3 and 15.1 Hz), 4.73 <dd, 1H, Jˆ7.3 and 9.9 Hz),
5.54 <d, 1H, Jˆ15.3 Hz), 7.08±7.27 <m, 11H), 9.60 <s, 1H);
dC <125 MHz, CDCl3) 29.95, 31.99, 67.23, 126.61, 126.99,
128.38, 128.50, 128.98, 130.19, 130.54, 132.32, 136.39,
141.84, 198.95. Exact mass calculated for C18H19NO3S:
329.1086. Found: 329.1085.
25
[a]D ˆ129.5 <c 1.15, CHCl3); nmax <KBr) 3075, 3025,
2980, 1490, 1315, 1050, 980, 760 cm21; dH <500 MHz,
CDCl3) 2.38 <s, 3H), 2.81 <dd, 1H, H7a, Jˆ10.5 and
12.6 Hz), 2.88 <s, 3H), 3.23 <dd, 1H, H7b, Jˆ5.4 and
12.6 Hz), 3.37 <dd, 1H, H6, Jˆ5.4 and 10.5 Hz), 3.42<d,
1H, H6a, Jˆ8.4 Hz), 3.98 <dd, 1H, H3a, Jˆ7.2and 8.4 Hz),
5.34 <d, 1H, H3, Jˆ7.2Hz), 7.23±7.44 <m, 10H); dC
<125 MHz, CDCl3) 29.44, 36.18, 42.69, 63.45, 70.10,
70.67, 81.36, 126.43, 127.31, 128.76, 128.93, 129.36,
130.51, 132.05, 136,28. Exact mass calculated for
C19H22N2O3S: 358.1351. Found: 358.1350.
3.2.2. Oxidation of 3b with DMP. First elution gave N-ben-
zyl-N-[<1S)-1-benzyl-2-oxoethyl]-<E)-2-phenyleth-1-ene-1-
sulfonamide 4b <324 mg, 80%) as a yellow sticky oil; nmax
<neat) 3035, 2995, 2850, 2750, 1740, 1650,1620, 1600,
1330, 1060, 920, 750, 700 cm21; dH <500 MHz, CDCl3)
2.87 <dd, 1H, Jˆ10.0 and 15.0 Hz), 3.35 <dd, 1H, Jˆ5.0
and 15.0 Hz), 4.18 <m, 2H), 4.42 <dd, 1H, Jˆ5.0 and
10.0 Hz), 5.95 <d, 1H, Jˆ15.3 Hz), 7.19±7.55 <m, 16H),
9.28 <s, 1H); dC <125 MHz, CDCl3) 32.92, 49.56, 67.66,
124.67, 127.10, 128.40, 128.63, 128.88, 129.08, 129.16,
129.19, 130.88, 132.33, 135.29, 137.13, 142.11, 142.14,
198.17. Exact mass calculated for C24H23NO3S: 405.1399.
Found: 405.1396.
3.3.2. Reaction of 4b with N-methyl hydroxylamine. First
elution gave <3S,3aR,6S,6aS)-5,6-dibenzyl-1-methyl-3-
phenylperhydro-4l6-isothiazolo[4,5-c]isoxazole-4,4-dioxide
25
7b <18.45 g, 85%); [a]D ˆ18.8 <c 0.75, CHCl3); nmax
<KBr) 3070, 3050, 3020, 2980, 1490, 1350, 1320, 1050,
980, 760 cm21; dH <500 MHz, CDCl3) 2.24 <s, 3H), 2.78
<dd, 1H, H7a, Jˆ10.8 and 13.3 Hz), 3.10 <dd, 1H, H7b, Jˆ
4.9 and 13.3 Hz), 3.25 <dd, 1H, H6, Jˆ4.9 and 10.8 Hz),
3.39 <d, 1H, H6a, Jˆ8.5 Hz), 4.06 <dd, 1H, H3a, Jˆ7.4 and
8.5 Hz), 4.24 <d, 1H, H8a, Jˆ14.6 Hz), 4.63 <d, 1H, H8b,
Jˆ14.6 Hz), 5.41 <d, 1H, H3, Jˆ7.4 Hz), 6.97±7.47 <m,
15H); dC <125 MHz, CDCl3) 36.70, 46.92, 52.03, 59.88,
70.96, 73.20, 81.50, 126.03, 126.49, 127.06, 127.54,
128.07, 128.55, 128.76, 128.81, 129.23, 129.35, 134.99,
136.55. Exact mass calculated for C25H26N2O3S:
434.1664. Found: 434.1663.
3.2.3. Oxidation of 3c with DMP. First elution gave N-
benzyl-N-[<1S)-1-methyl-2-oxoethyl]-<E)-2-phenyleth-1-
ene-1-sulfonamide 4c <263 mg, 80%) as a white solid, mp
25
78±808C; [a]D ˆ27.1 <c 5.62, CHCl3); nmax <KBr) 3058,
2982, 2833, 2755, 1735, 1615, 1449, 1239, 1143, 977, 934,
830, 750, 700 cm21; dH <500 MHz, CDCl3) 1.39 <d, 1H,
Jˆ7.2Hz), 4.09 <q, 1H, Jˆ7.2Hz), 4.33 <d, 1H, Jˆ
15.2Hz), 4.44 <d, 1H, Jˆ15.2Hz), 6.75 <d, 1H, Jˆ
15.4 Hz), 7.25±7.58 <m, 11H), 9.43 <s, 1H); dC <125 MHz,
CDCl3) 12.33, 49.74, 61.75, 124.62, 128.26, 128.36, 128.51,
128.82, 129.10, 131.04, 132.34, 135.74, 142.42, 198.83.
Exact mass calculated for C18H19NO3S: 329.1086. Found:
329.1090.
3.3.3. Reaction of 4d with N-methyl hydroxylamine. First
elution gave <3S,3aR,8aS,8bS)-1-methyl-3-phenylperhydro-
4l6-pyrrolo[10,20:2,3]isothiazolo[4,5-c]isoxazole-4,4-dioxide
7d <10.29 g, 70%) as a yellow solid, mp 142±1448C;
25
[a]D ˆ27.3 <c 0.83, CHCl3); nmax <KBr) 3050, 3020,
2970, 1500, 1350, 1320, 1050, 980, 760 cm21; dH
<500 MHz, CDCl3) 1.79 <m, 1H), 1.97 <m, 2H), 2.17 <m,
1H), 2.80 <s, 3H), 3.23 <dt, 1H, H6a, Jˆ7.5 and 11.7 Hz),
3.56 <dd, 1H, H8b, Jˆ2.5 and 9.0 Hz), 3.74 <m, 2H,
H6b and H8a), 4.05 <dd, 1H, H3a, Jˆ6.3 and 9.0 Hz),
5.68 <d, 1H, H3, Jˆ6.3 Hz), 7.33±7.45 <m, 5H); dC
<125 MHz, CDCl3) 25.26, 31.51, 44.14, 47.40, 59.35,
63.97, 72.62, 80.90, 126.18, 128.57, 128.80, 134.15.
3.2.4. Oxidation of 3d with DMP. First elution gave
<2S)-1-{[<E)-2-phenyleth-1-enyl]sulfonyl}tetrahydro-1H-
pyrrole-2-carbaldehyde 4d <172mg, 65%) as a yellow oil;
n
max <neat) 3050, 3030, 2960, 2750, 1760, 1600, 1490,1350,
1060, 980, 760 cm21; dH <500 MHz, CDCl3) 2.05 <m, 4H),
3.47 <m, 2H), 4.05 <m, 1H), 6.79 <d, 1H, Jˆ17.1 Hz), 7.42±
7.56 <m, 6H), 9.65 <s, 1H); dC <125 MHz, CDCl3) 24.94,

U. Chiacchio et al. / Tetrahedron 57 '2001) 3425±3433
3431
Exact mass calculated for C14H18N2O3S: 294.1038.
Found: 294.1039.
3.5. Preparation of 1-N-unsubstituted isothiazolo[4,5-c]-
isoxazole-4,4-dioxides 10a,cÐgeneral procedure
3.3.4. Reaction of 4a with N-benzyl hydroxylamine. First
elution gave <3S,3aR,6S,6aS)-1,6-dibenzyl-5-methyl-3-
phenylperhydro-4l6-isothiazolo[4,5-c]isoxazole-4,4-dioxide
7e <18.88 g, 87%) as a white solid, mp 157±1588C;
A solution containing sulfonamido oxime 8a, c <2.24 mmol)
in absolute ethanol <100 mL) was re¯uxed for 60 h. The
reaction mixture was evaporated under reduced pressure
and the residue puri®ed by silica gel ¯ash chromatography
<3% MeOH/CHCl3).
25
[a]D ˆ118.2< c 1.65, CHCl3); nmax <KBr) 3080, 3040,
3025, 2980, 1490, 1320, 1050, 980, 760 cm21; dH
<500 MHz, CDCl3) 2.70 <dd, 1H, H7a, Jˆ4.5 and 13.5 Hz),
2.78 <s, 3H), 3.13 <dd, 1H, H7b, Jˆ6.9 and 13.5 Hz), 3.31
<ddd, 1H, H6, Jˆ4.5, 6.9 and 8.4 Hz), 3.66 <d, 1H, H8a,
Jˆ13.8 Hz), 3.72<dd, 1H, H 6a, Jˆ8.4 and 8.7 Hz), 3.89
<d, 1H, H8b, Jˆ13.8 Hz), 3.98 <dd, 1H, H3a, Jˆ7.2and
8.7 Hz), 5.34 <d, 1H, H3, Jˆ7.2Hz), 7.12±7.48 <m, 15H);
dC <125 MHz, CDCl3) 30.62, 36.57, 59.98, 64.09, 69.97,
70.03, 81.04, 125.99, 126.34, 126.92, 127.67, 128.27,
128.53, 128.72, 129.23, 129.27, 135.04, 136.39, 136.49.
Exact mass calculated for C25H26N2O3S: 434.1664. Found:
434.1665.
3.5.1. Reaction of oxime 8a. <3S,3aR,6S,6aS)-6-Benzyl-5-
methyl-3-phenylperhydro-4l6-isothiazolo[4,5-c]isoxazole-
25
4,4-dioxide 10a <539 mg. 70%); sticky oil; [a]D ˆ222.4
<c 0.62, CHCl3); dH <500 MHz, CDCl3) 2.77 <s, 3H), 2.99
<dd, 1H, H7a, Jˆ9.3 and 13.8 Hz), 3.20 <dd, 1H, H7b, Jˆ6.3
and 13.8 Hz), 3.49 <dd, 1H, H6, Jˆ6.3, and 9.3 Hz), 4.14
<dd, 1H, H6a, Jˆ7.2and 7.3 Hz), 4.19 <dd, 1H, H 3a, Jˆ6.0
and 7.3 Hz), 5.31 <d, 1H, NH, Jˆ7.2Hz), 5.57 <d, 1H, H 3,
Jˆ6.0 Hz), 7.23±7.42 <m, 10H); dC <125 MHz, CDCl3)
33.15, 37.81, 65.92, 69.46, 70.83, 82.97, 125.97, 127.14,
128.36, 128.86, 129.09, 129.33, 135.92, 136.33. Exact
mass calculated for C18H20N2O3S: 344.1194. Found:
344.1195.
3.4. Preparation of sulfonamido oximes 8a,cÐgeneral
procedure
3.5.2. Reaction of oxime 8c. <3S,3aR,6S,6aS)-5-Benzyl-6-
methyl-3-phenylperhydro-4l6-isothiazolo[4,5-c]isoxazole-
25
4,4-dioxide 10c <539 mg, 70%); sticky oil; [a]D ˆ215.6 <c
A mixture containing compound 4a, c <3.3 mmol), 95%
aqueous ethanol <30 mL), hydroxylamine hydrochloride
<330 mg, 4.8 mmol) and sodium acetate <390 mg,
4.8 mmol) was stirred at 08C for 6 h. At the end of this
time the solvent was evaporated at reduced pressure and
the residue was extracted with dichloromethane, washed
with 10% aqueous NaHCO3 and dried <Na2SO4). The
solvent was removed and the crude residue was
puri®ed by silica gel ¯ash chromatography <70% CCl4/
ethyl acetate).
0.52, CHCl3); dH <500 MHz, CDCl3) 1.11 <bs, 1H, NH),
1.26 <d, 1H, Jˆ6.7 Hz), 3.20 <dq, 1H, H6, Jˆ1.7 and
6.7 Hz), 4.01 <dd, 1H, H6a, Jˆ1.7, and 8.3 Hz), 4.03 <dd,
0
1H, H3a, Jˆ1.2and 8.3 Hz), 4.06 <d, 1H, H 5 a, Jˆ14.6 Hz),
0
4.41 <d, 1H, H5 b, Jˆ14.6 Hz), 5.53 <d, 1H, H3, Jˆ1.2Hz),
7.23±7.35 <m, 10H); dC <125 MHz, CDCl3) 16.38, 44.61,
68.65, 68.66, 70.21, 86.75, 126.14, 128.20, 128.36, 128.91,
129.09, 135.00, 136.32. Exact mass calculated for
C18H20N2O3S: 344.1194. Found: 344.1189.
3.4.1. Reaction of 4a with hydroxylamine hydrochloride.
First eluted product was a syn±anti mixture <1:3) of N-[<1S)-
1-benzyl-2-hydroxyiminoethyl]-N-methyl-<E)-2-phenyleth-
3.6. Preparation of sultams 12c and 13aÐgeneral
procedure
1-ene-1-sulfonamide 8a <1.02g, 90%) as a sticky oil;
c 0.41, CHCl3). Major isomer: dH
To
a solution containing sulfonamido oxime 8a,c
25
[a]D ˆ24.82<
<2.24 mmol) in dichloromethane <250 mL) was added
dropwise sodium hypochlorite <6 mL, 7% solution) at 08C
with vigorous stirring. After 3 h the reaction mixture was
evaporated and the residue subjected to silica gel ¯ash
chromatography <40% CCl4/ethyl ether).
<500 MHz, CDCl3) 2.78 <s, 3H), 2.94 <dd, 1H, Jˆ10.2and
14.6 Hz), 3.15 <dd, 1H, Jˆ5.7 and 14.6 Hz), 4.99 <ddd, 1H,
Jˆ4.3, 5.7 and 10.2Hz), 5.65 <d, 1H, Jˆ15.3 Hz), 7.24±
7.39 <m, 11H), 7.52<d, 1H, Jˆ4.3 Hz), 8.15 <bs, 1H, OH);
dC <125 MHz, CDCl3) 29.74, 35.54, 57.71, 123.75, 127.06,
128.33, 128.78, 128.91, 129.354, 130.61, 132.55, 137.12,
141.64, 149.63. Exact mass calculated for C18H20N2O3S:
344.1194. Found: 344.1190.
3.6.1. Reaction of oxime 8c. <3S,3aR,6S)-5-Benzyl-6-
methyl-3-phenyl-3a,4,5,6-tetrahydro-3H-4l6-isothiazolo-
25
[4,5-c]isoxazole-4,4-dioxide 12c <590 mg, 77%); [a]D
27.14 <c 1.08, CHCl3); dH <500 MHz, CDCl3) 1.37 <d,
3H, Jˆ6.4 Hz), 4.07 <d, 1H, Jˆ15.2Hz), 4.09 <q, 1H, H 6,
ˆ
3.4.2. Reaction of 4c with hydroxylamine hydrochloride.
First eluted product gave a syn±anti mixture <1:3) of N-ben-
zyl-N-[<1S)-2-hydroxyimino-1-methylethyl]-<E)-2-phenyl-
eth-1-ene-1-sulfonamide 8c <1.05 g, 93%) as a white solid,
Jˆ6.4 Hz), 4.56 <d, 1H, Jˆ15.2Hz), 4.76 <dd, 1H, H 3a
,
Jˆ2.2 and 10.8 Hz), 5.95 <d, 1H, H3, Jˆ10.8 Hz), 7.05±
7.49 <m, 10H); dC <125 MHz, CDCl3) 16.94, 46.16, 52.38,
74.28, 85.34, 126.36, 128.16, 128.26, 128.31, 128.37,
128.95, 134.40, 135.17, 158.53. Exact mass calculated for
C18H18N2O3S: 342.1038. Found: 342.1041.
25
mp 132±1358C; [a]D ˆ21.20 <c 8.36, CHCl3). Major
isomer: dH <500 MHz, CDCl3) 1.27 <d, 3H, Jˆ7.0 Hz),
4.27 <d, 1H, Jˆ16.0 Hz), 4.30 <d, 1H, Jˆ16.0 Hz), 4.55
<dq, 1H, Jˆ4.5 and 7.0 Hz), 6.57 <d, 1H, Jˆ15.0 Hz),
7.16±7.39 <m, 12H), 7.52 <bs, 1H, OH); dC <125 MHz,
CDCl3) 16.97, 48.39, 53.08, 125.13, 127.71, 128.12,
128.16, 128.29, 128.62, 129.03, 129.05, 130.81, 132.60,
132.61, 141.53, 151.06. Exact mass calculated for
C18H20N2O3S: 344.1194. Found: 344.1192.
3.6.2. Reaction of oxime 8a. <6S)-6-Benzyl-5-methyl-3-
phenyl-5,6-dihydro-4H-4l6-isothiazolo[4,5-c]isoxazole-
4,4-dioxide 13a <609 mg, 80%); white solid, mp 109±
25
1128C; [a]D ˆ22.41 <c 2.49, CHCl3); dH <500 MHz,
CDCl3) 2.83 <s, 3H), 3.30 <d, 2H, H7, Jˆ6.3 Hz), 4.64 <t,

3432
U. Chiacchio et al. / Tetrahedron 57 '2001) 3425±3433
1H, H6, Jˆ6.3 Hz), 7.25±7.93 <m, 10H); dC <125 MHz,
CDCl3) 29.67, 38.59, 61.01, 113.59, 124.33, 127.50,
127.70, 128.70, 129.57, 129.66, 132.68, 134.84, 156.39,
165.41. Exact mass calculated for C18H16N2O3S:
340.0881. Found: 340.0877.
<dd, 1H, H6, Jˆ6.0 and 8.5 Hz), 4.08 <d, 1H, Jˆ14.5 Hz),
4.50 <d, 1H, Jˆ14.5 Hz), 7.28±7.42 <m, 10H); dC
<125 MHz, CDCl3) 16.19, 44.54, 52.46, 53.83, 55.34,
66.57, 68.74, 69.05, 127.53, 127.68, 128.04, 128.39,
128.83, 129.04, 135.24, 138.94, 171.56. Exact mass calcu-
lated for C21H24N2O4S: 400.1457. Found: 400.1459. Further
eluted product was methyl <3SR,3aSR,5RS,6RS,6aSR)-2-
benzyl-3-methyl-1,1-dioxo-6-phenylperhydro-1l6-pyrrolo-
[2,3-d]isothiazole-5-carboxylate 21 <3.00 g, 15%); white
solid, mp 120±1228C; nmax <KBr): 3350, 3020, 3015,
2960, 1730, 1600, 1450, 1350, 1310, 1140, 860, 800,
750 cm21; dH <500 MHz, CDCl3) 1.27 <d, 3H, Jˆ6.5 Hz),
3.7. Preparation of sultam 17
A mixture containing compound 4a <2.04 g, 6.20 mmol),
95% aqueous ethanol <30 mL), phenylhydrazine <670 mg,
6.20 mmol) and p-toluenesulfonic acid <10 mg) was stirred
at 08C for 6 h, under nitrogen. At the end of this time
the solvent was evaporated at reduced pressure and the
residue was extracted with dichloromethane, washed
with 10% aqueous NaHCO3 and dried <Na2SO4).
Evaporation of the solvent and silica gel ¯ash chromato-
graphy <70% CCl4/ethyl acetate) gave N-<1SR)-1-benzyl-
2-<2-phenylhydrazono)ethyl-N-methyl-<E)-2-phenyleth-1-
ene-1-sulfonamide 14 <2.21 g, 85%) as a white solid,
mp 118±1218C; dH <500 MHz, CDCl3) 1.47 <bs, 1H, NH),
2.73 <s, 3H), 2.98 <dd, 1H, Jˆ9.6 and 14.2Hz), 3.26 <dd,
1H, Jˆ6.0 and 14.2Hz), 4.98 <ddd, 1H, Jˆ3.6, 6.0 and
9.6 Hz), 5.67 <d, 1H, Jˆ 15.3 Hz), 7.29±7.46 <m, 12H);
dC <125 MHz, CDCl3) 31.21, 36.98, 62.43, 112.57,
116.69, 125.13, 125.93, 126.51, 127.83, 128.59, 130.01,
135.99, 144.18, 144.81, 151.46, 163.12. Exact mass calcu-
lated for C24H25N3O2S: 419.1667. Found: 419.1669.
2 .42 <bs, 1H, NH), 3.16 <dq, 1H, H, Jˆ4.3 and 6.5 Hz),
3
3.69 <s, 3H), 4.02<dd, 1H, H 6a, Jˆ2.6 and 8.6 Hz), 4.21
<dd, 1H, H3a, Jˆ4.3 and 8.6 Hz), 4.2
6 <d, 1H,
Jˆ15.2Hz), 4.28 <dd, 1H, H , Jˆ2.6 and 6.8 Hz),
6
4.29 <d, 1H, Jˆ15.2Hz), 4.33 <d, 1H, H 5, Jˆ6.8 Hz),
7.05±7.39 <m, 10H); dC <125 MHz, CDCl3) 17.34,
44.99, 51.47, 51.74, 56.77, 65.74, 66.20, 66.42, 127.51,
127.77, 128.26, 128.32, 128.61, 128.71, 135.86, 137.13,
170.50. Exact mass calculated for C21H24N2O4S:
400.1457. Found: 400.1456.
Acknowledgements
We thank the M.U.R.S.T. for its partial ®nancial support.
A solution of 14 <914 mg, 2.18 mmol) in ethanol <100 mL)
was heated under nitrogen at re¯ux temperature for 72h.
The solution was cooled off, evaporated and the residue
subjected to ¯ash chromatography <40% CCl4/ethyl ether),
giving <3SR,6SR,6aSR)-3-benzyl-2-methyl-5,6-diphenyl-1,2,3,
5,6,6a-hexahydro-1l6-pyrazolo[3,4-d]isothiazole-1,1-dioxide
17 <636 mg, 70%) as a white solid, mp 180±1828C; dH
<500 MHz, CDCl3) 2.89 <s, 3H), 3.14 <d, 2H, Jˆ4.2Hz),
3.50 <dd, 1H, H6a, Jˆ1.8 and 7.6 Hz), 4.30 <dt, 1H, H3,
Jˆ1.8 and 4.2Hz), 5.41 <d, 1H, H 6, Jˆ7.6 Hz), 6.84±7.40
<m, 15H); dC <125 MHz, CDCl3) 37.06, 56.25, 61.74, 67.92,
73.02, 114.76, 121.29, 125.21, 126.37, 127.40, 128.56,
128.83, 129.37, 129.84, 134.79, 138.74, 143.81, 145.06.
Exact mass calculated for C24H23N3O2S: 417.1511. Found:
417.1507.
References
1. <a) Chiacchio, U.; Romeo, G.; Resci®na, A. In Targets in
Heterocyclic Systems: Chemistry and Properties; Attanasi,
O. A., Spinelli, D., Eds.; Stereoselective synthesis of
functionalized heterocyclic systems via intramolecular cyclo-
Á
addition of C-alkenyl nitrones and nitrile oxides; Societa
Chimica Italiana: Italia, 1997; Vol. 1, pp. 225±276.
<b) Zecchi, G.; Bruggini, G. Synthesis 1999, 905±917.
2. <a) Chiacchio, U.; Casuscelli, F.; Corsaro, A.; Librando, V.;
Resci®na, A.; Romeo, R.; Romeo, G. Tetrahedron 1995, 51,
5689±5700. <b) AuÈrich, H. G.; Biesemeier, F. Synthesis 1995,
1171±1178. <c) Frederikson, H. Tetrahedron 1997, 53, 403±
425.
3.8. Preparation of sultams 20 and 21
3. Cinquini, N.; Cozzi, F. In Methods in Organic Chemistry:
Stereoselective Synthesis; Hellmchen, G., Hoffman, R. W.,
Mulzer, J., Schaumann, E., Eds.; Thieme <Georg): Stuttgart,
NY, 1995; Vol. E21c <Chapter 1.6.1.2).
Á
4. Chiacchio, U.; Corsaro, A.; Gumina, G.; Pistara, V.; Resci®na,
A.; Alessi, M.; Piperno, A.; Romeo, G.; Romeo, R.
Tetrahedron 1997, 53, 13855±13866.
A mixture containing 4c <16.45 g, 50 mmol), triethylamine
<33.39 g, 46 mL, 330 mmol) and glycine methyl ester
hydrochloride <6.90 g, 55 mmol) in absolute ethanol
<50 mL) was stirred at rt for 16 h. At the end of this time
the solvent was removed and the residue extracted with
dichloromethane, washed with water and dried <Na2SO4).
The residue, subjected to silica gel ¯ash chromatography
<2% methanol/chloroform), gave, as ®rst eluted product,
methyl <3SR,3aSR,5SR,6RS,6aSR)-2-benzyl-3-methyl-1,1-
dioxo-6-phenylperhydro-1l6-pyrrolo[2,3-d]isothiazole-5-
carboxylate 20 <8.60 g, 43%) as a white solid, mp 110±
1118C; nmax <KBr): 3337, 3026, 2990, 2900, 1741, 1600,
5. Chiacchio, U.; Piperno, A.; Pizzimenti, F.; Resci®na, A.;
Romeo, G. Unpublished results.
6. Ries, U. J.; Mihm, G.; Narr, B.; Hasselbach, K. M.; Wittneben,
H.; Entzeroth, M.; van Meel, J. C.; Wienen, W.; Hauel, N. H.
J. Med. Chem. 1993, 36, 4040±4051.
7. <a) Oppolzer, W.; Bochet, C. G.; Meri®eld, E. Tetrahedron
Lett. 1994, 35, 7015±7018. <b) Larsson, E.; Luning, B. Acta
Chem. Scand. 1996, 50, 54±57. <c) Curran, D. P.; Shen, W.;
Zhang, J.; Gieb, S. J.; Lin, C. H. Heterocycles 1994, 37, 1773±
1788.
1495, 1450, 1280, 1218, 1130, 910, 855, 748, 697 cm21
;
dH <500 MHz, CDCl3) 1.31 <d, 3H, Jˆ7.0 Hz), 2.28 <bs,
1H, NH), 3.28 <dq, 1H, H3, Jˆ1.5 and 7.0 Hz), 3.70 <s,
3H), 3.83 <dd, 1H, H6a, Jˆ6.0 and 7.5 Hz), 3.86 <d, 1H,
H5, Jˆ8.5 Hz), 3.96 <dd, 1H, H3a, Jˆ1.5 and 7.5 Hz), 4.01
8. Chiacchio, U.; Buemi, G.; Procopio, A.; Resci®na, A.;
Romeo, R. Tetrahedron 1994, 50, 5503±5514.

U. Chiacchio et al. / Tetrahedron 57 '2001) 3425±3433
3433
9. <a) Dess, D. B.; Martin, J. C. J. Org. Chem. 1983, 48, 4155±
4156. <b) Dess, D. B.; Martin, J. C. J. Am. Chem. Soc. 1991,
113, 7277±7287. <c) Ireland, R. E.; Liu, L. J. Org. Chem.
1993, 58, 2899. <d) Meyer, S. D.; Schreiber, S. J. Org.
Chem. 1994, 59, 7549±7552.
10. Grigg, R. Chem. Soc. Rev. 1987, 16, 89±121.
11. <a) Janin, Y. L.; Aubertin, A.-M.; Chiaroni, A.; Riche, C.;
Monneret, C. Tetrahedron 1996, 52, 15157±15170.
<b) Regainia, Z.; Abdaoui, M.; Aouf, N.-E.; Dewynter, G.;
Montero, J.-L. Tetrahedron 2000, 56, 381±387.