Synthesis and mass spectral study of new phenylsulfonyl substituted isoxazolidines

Article abstract of DOI:10.1002/jhet.5570430519

Ten 2,3-disubstituted 4-phenylsulfonyl isoxazolidines (3a-j) were prepared by 1,3-dipolar cycloaddition reaction of substituted nitrones (1a-j) with phenyl vinyl sulfone (2). The reaction products were identified by means of IR, NMR, and MS data. In addition, the factors influencing on the electron ionization induced mass spectral fragmentation of the title products are discussed in detail.

Full text of DOI:10.1002/jhet.5570430519

Sep-Oct 2006
1267
Synthesis and Mass Spectral Study of
New Phenylsulfonyl Substituted Isoxazolidines
Yaꢀar Dürüst and Cevher Altuꢁ
Department of Chemistry, Abant ꢂzzet Baysal University, TR-14280, Bolu, Turkey
Jari Sinkkonen, Olli Martiskainen and Kalevi Pihlaja*
Laboratory of Organic Chemistry and Chemical Biology, Department of Chemistry, University of Turku, Vatse-
lankatu 2, FI-20014 Turku, Finland; Email: kpihlaja@utu.fi
Received December 8, 2005
R2
R1
N
Ph
O
O
R1
H
R2
O
toluene
reflux
O
S
N
O
S
Ph
O
1
2
3
Ten 2,3-disubstituted 4-phenylsulfonyl isoxazolidines (3a-j) were prepared by 1,3-dipolar cycloaddition
reaction of substituted nitrones (1a-j) with phenyl vinyl sulfone (2). The reaction products were identified
by means of IR, NMR, and MS data. In addition, the factors influencing on the electron ionization induced
mass spectral fragmentation of the title products are discussed in detail.
J. Heterocyclic Chem., 43, 1267 (2006).
Introduction.
Scheme 1
1,3-Dipolar cycloaddition (1,3-DC) reactions belong to
the most important processes from both synthetic and
mechanistic points of view. The usefulness of these cy-
cloaddition reactions arises from their versatility and their
remarkable stereochemistry. By varying the nature of the
reagents many different types of carbocyclic and hetero-
cyclic structures can be built up. The interaction between
unsymmetrical reagents in a 1,3-DC reaction can give two
isomeric adducts depending on the relative position of the
substituent (S) in the cycloadduct, head-to-head, 5-
regioisomer, or head-to-tail, 4-regioisomer (Scheme 1).
High stereospecificity/stereoselectivity associated with
these reactions makes them synthetically important. It has
been found that 1,3-DC reactions proceed with a con-
certed mechanism. Among the large variety of strategies
available for the synthesis of five-membered heterocycles,
1,3-DC reaction of nitrones with olefins is an extremely
powerful one, which usually occurs under mild condi-
tions. It can lead to as many as three new contiguous
stereogenic centers in a single step and to yield efficiently
the respective isoxazolidines with good regio- and stereo-
selectivity. Both inter- and intramolecular nitrone–alkene
cycloaddition reactions have received much attention as
useful methods for the formation of biologically interest-
ing heterocycles [1].
S
head-to-head
head-to-tail
X
Y
Z
S
X
Z
5-regioisomer
Y
X
S
1,3-dipole
dipolarophile
Y
Z
4-regioisomer
readily available from simple starting materials such as
alkenes and nitrones, are useful intermediates in organic
synthesis [2].
Literature survey reveals that isoxazolidine compounds
have been synthesized to investigate their activities
against various bacteria, fungi species and also viruses
including HIV virus and tumor cells. In addition, they
were assayed for transcriptional activation property and
anxiolytic activity [3]. Multistep synthetic routes that in-
volve isoxazolidine construction to the natural products,
alkaloids like histrionicotoxin, have also been reported
[4].
In this study, a set of new isoxazolidines (3a-j) were
obtained by 1,3-DC reaction of N-substituted 4-(substi-
tuted)benzylidineamine N-oxides (1a-j) with phenyl vinyl
sulfone (2) (Scheme 2). The reaction products were iden-
tified by means of IR, NMR, and MS data. Due to the
limited amount of mass spectrometric information avail-
1,3-Dipolar cycloaddition reactions of nitrones with a
variety of unsaturated systems, including the multisubsti-
tuted ones, have been extensively exploited to synthesize
isoxazolidine and isoxazoline heterocycles. Isoxazolidi-
nes, the saturated five-membered 1,2-O,N-heterocycles

1268
Y. Dürüst, C. Altuꢀ, J. Sinkkonen, O. Martiskainen and K. Pihlaja
Vol 43
able [5-7] the mass spectral fragmentations of the synthe-
sized products (3aꢀj) under electron ionization were dis-
cussed in detail to clarify the effect of the phenylsulfonyl
substitution.
NOE measurements were used in order to assign
the orientations of the substituents of isoxazolidine
ring, since the values of the coupling constants did
not allow conclusions with certainty about the con-
figuration of substituents [2n,9]. The phenylsulfonyl
group and the substituent R1 can be deduced to be in
the trans position from the NOESY spectra. If they
were cis, there should be an intensive NOE correlation
between H-3 and H-4, but this NOE signal is not ob-
served. H-5 protons can be assigned from their cou-
pling constants and NOE results. H-5a (Table 1 and 2)
was found to be close to H-4 by NOESY, and therefore
to have a cis relationship to H-4. The large coupling
constant (approximately 8 Hz) is in agreement with cis
orientation, because the torsion angle between H-4 and
H-5a is relatively close to 0° and thus coupling con-
stant fairly large (Karplus equation). H-5b has not NOE
correlation with H-4 and the coupling constant is me-
dium size, which fits well for the envelope type con-
formation of isoxazolidine ring in which oxygen atom
is out of plane.
Scheme 2
R2
N 2
R1
O
Ph
O
R1
H
R2
O
toluene
reflux
3
4
O 1
5
S
N
O
S
Ph
O
1
2
3
R1
R2
3a
4-NMe2-C6H4
4-NMe2-C6H4
4-OMe-C6H4
4-OMe-C6H4
(3-OMe-4-OCH2Ph)-C6H3
2-OH-C6H4
2-pyridyl
2-furyl
2-thienyl
2-(3-methyl)-thienyl
Me
Ph
Me
Ph
Me
Ph
Me
Me
Me
Me
3b
3c
3d
3e
3f
3g
3h
3i
3j
It was noted that, in the case of N-Me substituted com-
pounds, the signals H-3, H-4 and N-Me, as well as the
corresponding carbon signals, were considerably broad-
ened, whereas N-Ph substituted compounds gave very
sharp signals. This is most likely due to the nitrogen in-
version, which can happen with the methyl group being
slow in NMR timescale, and which is inhibited by the
sterically large phenyl group. Systematic differences were
Results and Discussion.
NMR Spectroscopy.
Structures of all substances were determined by NMR
spectra measured in CDCl3. Chemical shifts were as-
signed, in addition to the information from basic proton
and carbon spectra, using gradient-selected DQF-COSY,
NOESY, HSQC and HMBC (see Experimental). Proton
and carbon NMR results are presented in Tables 1, 2 and
3, respectively.
The assignment of the signals from the isoxazolidine
ring was easy. The methylene C-5 was first identified
being only CH2 type carbon. All the proton and carbon
signals in isoxazolidine ring were assigned with the
aid of HSQC and COSY. The ortho protons from the
benzene sulfonyl group were identified by the NOESY
correlation with protons H-4 and H-5b. The remaining
signals from the SO2-phenyl moiety were revealed by
the COSY, HSQC and HMBC correlations. The sig-
nals from the substituent R1 were assigned first based
on the long-range correlations with H-3 or C-3. There-
after the whole assignment of R1 was done by, again,
by the combination of COSY, HSQC and HMBC. In a
similar way, the signals of the R2 substituent were
identified resulting into the unambiguous assignment
1
observed in the H-1H coupling constants between N-Me
and N-Ph structures (Table 1 and 2). For example, the
J(H-3, H-4) was approximately 7 and 5 Hz with N-Me
and N-Ph compounds, respectively. This refers to the
slightly different torsion angles, i.e. conformations of the
isoxazolidine ring.
To understand better the dynamic behavior of N-Me
compounds, low temperature measurements were also
utilized. For this purpose, compound 3g was selected
since it gave the most broadened signals at room tem-
perature. As the temperature was decreased, the sig-
nals began first to sharpen. The sharpest signals were
observed approximately at –20 °C. So, in this tempera-
ture, the nitrogen inversion seems to be inhibited.
However, the value of J(H-3, H-4) was 7.0 Hz; the
same as for the N-Me compounds at room temperature,
and only one set of signals was observed. Thus, there
is only one isomeric form all the time; only the dy-
namical process at room temperature broadens the sig-
nals. As the temperature was further decreased, the
signals began to broaden again. At –60 °C, the proton
signals for isoxazolidine and pyridyl (3g) protons were
very broad. This indicates the restricted rotation of the
pyridyl substituent.
1
of the whole structure. The H NMR results, i.e. proton
chemical shifts and proton-proton coupling constants,
are in accordance with the ones for 4-phenylsulfonyl-
2-methyl-3-phenyl-isoxazolidine reported by Caddick
and Bush [8].

Sep-Oct 2006
Synthesis and Mass Spectral Study of New Phenylsulfonyl Substituted Isoxazolidines
1269
Table 1
The proton chemical shifts in ppm (and coupling constants for stereochemically essential oxazolidine ring protons in Hz) for compounds 3a-e
in CDCl3 at 298 K referenced internally to TMS (0.00 ppm).
3a
3.75 br. d
6.0
3b
4.79 d
4.9
3c
3.81 br. d
7.0
3d
4.85 d
5.0
3e[a]
3.80 br. d
7.1
H-3
J
H-4
J
H-5ª
J
H-5b
J
H-2’/H-6’
H-3’/H-5’
H-4’
4.04 ddd
3.2; 6.0; 8.2
4.26 dd
8.2; 10.0
4.48 dd
3.2; 10.0
7.83
4.11 ddd
4.5; 4.9; 7.5
4.38 dd
7.5; 10.0
4.54 dd
4.5; 10.0
7.83
4.03 ddd
3.5; 7.0; 8.2
4.26 dd
8.2; 10.0
4.48 dd
3.5; 10.0
7.81
4.12 ddd
4.8; 5.0; 7.5
4.37 dd
7.5; 10.0
4.53 dd
4.8; 10.0
7.83
4.03 ddd
3.4; 7.1; 8.3
4.25 dd
8.3; 10.0
4.48 dd
3.4; 10.0
7.80
7.45
7.55
7.48
7.61
7.48
7.60
7.49
7.62
7.44
7.54
R1: H-2
R1: H-3
R1: H-4
R1: H-5
R1: H-6
R1: CH3
R2: H-2/H-6
R2: H-3/H-5
R2: H-4
R2: NCH3
7.00
6.55
-
7.16
6.62
-
7.09
6.75
-
7.26
6.82
-
6.75
-
-
6.68
6.59
3.83
-
=R1: H-3
=R1: H-2
2.91
=R1: H-3
=R1: H-2
2.94
=R1: H-3
=R1: H-2
3.77
=R1: H-3
=R1: H-2
3.79
-
-
-
6.85
7.16
6.95
-
-
-
-
6.84
7.17
6.97
-
-
-
2.58
2.58
2.60
[a] For R1: 5.10 and 5.13 (CH2), 7.42 (H-2’/H-6’), 7.38 (H-3’/H-5’), 7.32 (H-4’).
R2NOH where the hydrogen transfer occurs from
Mass Spectrometry.
C-4 (cf.
Scheme 3). In the other report [6], it has been shown that
a typical primary fragmentation is also the formation of an
enamine (B+ in Scheme 3). The most recent report [7]
deals with the fast atom bombardment mass spectra of
isoxalidinyl nucleosides. It is interesting that even here
the [M+H]+ ion lost NH2OH (protonation occurred on
The electron ionization mass spectra of 3aꢀj were also
studied in detail since very limited and mostly very old
information has been available on the mass spectra of
isoxazolidines [5-7]. An early report [5] proved that a
typical primary fragmentation for substituted isoxazolidi-
nes (not having the PhS(O)2 substituent) is the loss of
Table 2
The proton chemical shifts in ppm (and coupling constants for stereochemically essential oxazolidine ring protons in Hz) for compounds 3f-j in
CDCl3 at 298 K referenced internally to TMS (0.00 ppm).
3f
3g
3h
3i
3j
H-3
J
H-4
4.82 d
6.1
4.06
very br.
4.79
very br.
4.33 dd
8.2; 9.8
4.55 dd
4.0; 9.8
7.83
7.45
7.55
-
8.50
7.16
7.56
7.16
-
3.91
very br.
4.37 ddd
3.3; 7.5; 8.6
4.29 dd
8.6; 9.9
4.54 dd
3.3; 9.9
4.21
very br.
4.03 ddd
3.3; 7.0; 8.2
4.26 dd
8.2; 10.0
4.50 dd
3.3; 10.0
4.28
very br.
4.11 ddd
3.3; 7.0; 8.3
4.26 dd
8.3; 10.0
4.43 dd
3.3; 10.0
4.25 ddd
3.2; 6.1; 7.6
4.47 dd
7.6; 10.1
4.68 dd
3.2; 10.1
7.86
7.53
7.66
-
6.90
7.19
6.70
6.75
8.98 (OH)
7.06
7.24
7.12
-
J
H-5a
J
H-5b
J
H-2’/H-6’
H-3’/H-5’
H-4’
7.83
7.49
7.60
-
7.25
6.17
6.06
-
-
-
-
-
7.86
7.52
7.64
-
7.20
6.81
6.66
-
-
-
-
-
7.84
7.49
7.61
-
7.14
6.68
-
R1: H-2
R1: H-3
R1: H-4
R1: H-5
R1: H-6
R1: CH3
R2: H-2/H-6
R2: H-3/H-5
R2: H-4
R2: NCH3
-
2.19
-
-
-
-
-
-
2.69
2.66
2.68
2.62

1270
Y. Dürüst, C. Altuꢀ, J. Sinkkonen, O. Martiskainen and K. Pihlaja
Vol 43
Table 3
The carbon chemical shifts in ppm for compounds 3a-j in CDCl3 at 298 K referenced internally to TMS (0.00 ppm).
3a
73.47
75.15
66.09
138.13
128.60
129.26
133.89
123.48
128.58
112.38
150.51
=R1: C-3
=R1: C-2
40.44
-
3b
70.26
76.96
66.51
3c
73.15
75.38
66.11
138.06
128.55
129.34
134.01
128.50
128.97
114.09
159.60
=R1: C-3
=R1: C-2
55.28
-
3d
70.02
77.01
66.66
3e[a]
73.27
75.32
66.06
138.05
128.51
129.30
134.02
129.52
110.62
149.69
148.10
113.65
120.31
56.02
-
3f
3g
74.44
73.18
66.23
138.21
128.48
129.22
133.90
154.92
-
149.96
123.30
136.73
123.88
-
3h
67.41
71.33
65.80
137.86
128.42
129.31
134.07
147.68
-
143.23
110.51
110.00
-
-
-
3i
69.14
75.61
65.93
137.89
128.63
129.44
134.20
139.59
-
126.12
126.88
126.67
-
-
-
3j
C-3
C-4
C-5
C-1'
71.87
74.49
67.34
137.39
128.78
129.61
134.46
121.61
155.41
117.94
130.20
120.56
129.08
-
67.01
75.35
66.25
137.96
128.32
129.31
134.05
132.37
-
125.06
130.05
137.13
-
137.80
128.82
129.37
134.10
126.57
127.73
112.61
150.30
=R1: C-3
=R1: C-2
40.47
149.20
116.26
128.65
122.93
-
137.70
128.75
129.44
134.23
131.36
128.12
114.32
159.43
=R1: C-3
=R1: C-2
55.31
149.00
116.21
128.78
123.13
-
C-2'/C-6'
C-3'/C-5'
C-4'
R1: C-1
R1: C-2
R1: C-3
R1: C-4
R1: C-5
R1: C-6
R1: CH3
R2: C-1
14.14
-
-
-
-
147.09
118.78
129.05
125.79
-
-
-
-
-
R2: C-2/C-6
R2: C-3/C-5
R2: C-4
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
R2: NCH3
42.58
42.60
42.74
43.00
42.46
42.83
42.46
[a] For R1: 70.85 (CH2), 136.96 (C-1'), 127.23 (C-2'), 128.58 (C-3'), 127.93 (C-4'). Assignments italisized may be vice versa.
Table 4
Main electron impact induced fragmentations m/z(%) in compounds 3a-j.
Compound [a-j]
A+ [a]
-
-
-
-
-
[A-H]+• [b]
204(10)
-
191(90)
253(10)
297(9)
239(55)
161(12)
[A-2H]+ [c]
203(7)
-
190(100)
252(7)
296(3)
238(19)
161(13)
[A-3H]+• [d]
B+ [e]
178(100)
240(6)
165(29)
-
3a
3b
3c
3d
3e
3f
-
189(10)
-
-
-
-
271(3)
-
240(9)
163(27)
3g
136(41)[f]
134(69)[g]
125(21) [h]
141(26) [i]
155(20)
3h
3i
3j
-
151(95)
167(86)
181(100)
150(100)
166(100)
180(66)
149(6)
165(9)
-
168(83)
-
[a] A+ = [MꢀPhSO2]+. [b] [AꢀH]+• = [MꢀPhSO2H]+•. [c] [Aꢀ2H]+ = [MꢀPhSO2H2]+. [d] [Aꢀ3H]+• = [MꢀPhSO2H3]+. [e] B+
=
[MꢀPhSO2C2H3]+. [f] C8H10NO+ = [MꢀPhSO2ꢀHCN]+. [g] C8H8NO+ = [MꢀPhSO2H2ꢀHCN]+. [h] One fourth corresponds to C6H5SO+.
+
[i] C6H5SO2 .
+
+
+
•
the nitrogen) and also CH3N parallel to what was ob-
served for some of our compounds as well even though
the effect of the PhS(O)2 substituent in 3aꢀj substantially
dominates the fragmentation routes found.
for the formation of the ions D , [DꢀH] , and [Dꢀ2H] ,
(Table 5) except 3e, via loss of [R2NOꢀH], R2NO, and
R2NOH, respectively. It also lost C2H2O (compounds
3c,d,f,i,j) and C2H3O (compounds 3a,c,d,fꢀj) leading to
fragments [C+H]+• and C+, respectively. In the case of
compounds 3c,e,f,g,i, and j [AꢀH]+• also lost OH giving
the ions m/z 174, 280, 222, 145, 150 and 164, respectively
(shown in italics in Table 6) in variable amounts (RA 2-
31%).
Most of the compounds 3aꢀj gave relatively abundant
molecular ions (RA 12-100%) except 3g (2%) ,which
showed also other peculiarities as discussed later. All of
the compounds except 3b exhibited the primary loss of
PhSO2Hx ([AꢀH]+•, x = 1 and [Aꢀ2H]+, x = 2, Scheme 3
and Table 4). For 3c,h,i this ion with x = 2 forms the base
peak and for 3j the ion with x = 1 although in each com-
pound these ions are of comparable abundance. Further-
more 3f,g,i gave also the fragment corresponding to x = 0
(A+) and 3c,h,i some amount of the fragment correspond-
ing to x = 3 ([Aꢀ3H]+•). [AꢀH]+• was mainly responsible
Compounds 3a,b,d showed also some loss of CH2O
(Scheme 3 and Table 6, m/z values given in italics) and
compounds 3a,b,d,j a primary loss of R2NOH (Scheme 3)
which ion in these cases led also to ions D+, [DꢀH]+•, and
[Dꢀ2H]+ via loss of C6HySO2 (y = 4ꢀ6), respectively. For
3b D+ was the base peak of the spectrum. It should be

Sep-Oct 2006
Synthesis and Mass Spectral Study of New Phenylsulfonyl Substituted Isoxazolidines
1271
Table 5
More main electron impact induced fragmentations m/z(%) in compounds 3a-j.
•
Compound [a-e]
[C+H]+
162(11)
224(9)
149(9)
211(72)
255(14)
197(21)
-
C+
D+
[DꢀH]+•
159(17)
159(21.5)
146(10)
146(10)
-
132(8)
117(45)
106(3)
122(7)
136(17)
[D-2H]+
158(8)
158(10)
145(5.5)
145(10)
-
3a
3b
3c
3d
3e
3f
3g
3h
3i
161(16.5)
223(10)
148(16)
210(65)
254(2)
196(55)
119(60)
108(8)
160(59)
160(100)
147(27)
147(31)
-
133(38)
118(91)
107(24)
123(46)
137(54)
131(18)
-
-
-
-
125(49.5) [f]
139(7.5)
124(33.5)
138(35)
3j
135(21)
[a] [C+H]+• = [MꢀPhSO2C2H3O]+•. [b] C+ = [MꢀPhSO2C2H4O]+. [c] D+ = [MꢀPhSO2ꢀR2NO]+. [d] [DꢀH]+• = [MꢀPhSO2HꢀR2NO]+.
[e] [Dꢀ2H]+ = [MꢀPhSO2H2ꢀR2NO]+. [f] One third corresponds to C6H5SO+.
Table 6
Other fragments (Rel. abundance mostly > 5%) in the mass spectra of compounds 3a-j.
Compound
m/z(%)
3a
3b
3c
3d
3e
3f
346(21), 316(0.7), 300(2.5), 149(9), 148(5.5), 146(7), 145(11), 144(8.5), 134(5), 131(5), 125(5), 118(5), 116(5), 115(4.5),
91(5), 78(8), 77(22), 51(10), 42(7)
408(19), 378(9), 300(20), 237(5.5), 222(6), 193(6), 149(5), 146(7), 145(13), 144(11), 134(5), 118(10), 117(5), 116(6), 115(5),
104(6), 91(9), 78(11), 77(57), 65(5.5), 51(21), 50(5), 42(6), 39(6)
333(38), 174(8), 164(21), 133(8), 132(8), 131(6), 125(4), 121(9), 118(3), 117(4), 116(4), 115(8), 104(6), 103(7), 91(15), 84(5),
78(16), 77(37), 65(7), 51(17), 50(5), 43(7), 42(11), 41(5), 40(6), 39(6.5)
395(31), 365(1), 287(2), 224(8), 212(16), 209(6.5), 167(9), 160(13), 156(7), 142(5), 141(10), 132(8), 125(5), 115(5), 104(7),
93(11), 92(5), 91(22), 78(20), 77(100), 76(5), 65(12), 64(5), 63(6), 51(38), 50(10), 43(11), 40(8), 39(10)
439(12), 280(2), 206(5), 164(10), 149(5), 125(6), 91(100), 78(8), 77(27), 65(10), 51(13), 44(5), 43(9), 42(7), 41(5), 40(20),
39(6)
381(100), 222(14), 210(19), 209(5), 180(5), 147(5), 125(3.5), 118(5), 105(9), 104(6), 93(7.5), 92(5), 91(23), 78(10), 77(51),
65(8), 51(13)
3g
304(2), 274(2), 246(100), 226(3), 180(3), 147(10), 145(28), 134(69), 133(61), 132(5), 125(6), 106(28), 105(14), 103(32),94(5),
93(6), 92(22), 91(12), 90(5.5), 85(51), 84(48), 79(18), 78(54), 77(54), 68(14), 65(17), 64(7), 63(5), 56(5), 53(79, 52(16),
51(47), 50(11), 43(59, 42(24), 41(7), 40(12), 39(15)
3h
3i
293(17), 94(5), 93(3), 81(7), 79(20), 78(12), 77(44), 65(7), 53(10), 52(6), 51(19), 50(5), 41(16), 41(5), 39(16)
309(25), 150(6), 140(36), 139(25), 138(8), 111(18), 110(15.5), 109(26), 108(5), 99(14), 98(13), 97(43), 96(6), 94(6), 85(10),
84(20), 82(4.5), 79(16), 78(22), 77(95.5), 71(6), 70(5), 69(9), 67(5), 66(7), 65(15), 63(6), 58(8), 56(15), 55(5), 54(5), 53(10),
52(7), 51(54), 50(14), 45(44), 42(73), 41(10), 39(33.5)
3j
323(49), 277(3), 179(4), 166(5), 164(31), 152(7), 151(11), 150(7), 149(4), 125(8), 124(8), 123(14), 122(17), 121(8), 111(11),
110(4), 109(5), 104(6), 103(7), 97(25), 94(5), 91(11), 85(8), 84(9), 79(5), 78(16.5), 77(50), 71(5), 69(5), 65(8.5), 59(15),
53(13), 51(28), 50(7), 45(26), 42(19), 41(6), 39(13)
mentioned that for 3g both C+ and [D+H]+• has the same
nominal mass but accurate mass measurements showed
that the former dominated in a ratio of 6:1. Most of the
compounds, namely 3aꢀc,e,h,j, gave also an enamine type
primary fragment, namely B+ (Scheme 3, Table 4) corre-
sponding to the loss of PhSO2C2H3, i.e. a retro-1,3-dipolar
cycloaddition reaction [6]. This ion formed also an alter-
native route to ions [C+H]+• (3aꢀc,e,j) and C+ (3aꢀc,e,h,j)
via loss of O and OH, respectively.
It has been reported [10] that sulfones often rearrange
to sulfinic acids under electron ionization. All except 3b
of the studied compounds exhibit an ion m/z 125,
C6H5SO+ which in fact can result from such a rearrange-
ment: PhS(=O)2ꢀ ꢁ PhS(=O)Oꢀ. However, this ion did
not result directly from the molecular ion but after the loss
of R2NOH which makes it evident that some amount of
the primary loss of R2NOH occurs also in these isoxa-
zolidines although in most cases in a concerted manner
leading to the above ion and the D-type ions.
Compound 3g deserves a special notion. It is the only
compound which shows some loss of CH4N giving the
ion m/z 274. In this case the base peak of the spectrum
is a specially stabilized ion, m/z 246 corresponding to
the loss of C2H4NO from the molecular ion (Scheme
4). This ion is also obtained via m/z 274 after loss of
CO. Two other exceptional though not abundant ions

1272
Y. Dürüst, C. Altuꢀ, J. Sinkkonen, O. Martiskainen and K. Pihlaja
Vol 43
Scheme 3
-[C2H2O]
[M–CH2O]
[C+H]
C
c,d,f,i,j
a,b,d
-[C2H3O]
-[PhSO2]
-[O]
A
[C+H]
f,g,i
a,c,d,f-j
-[R2NO-H]
a-c,e,j
-[PhSO2H]
R2
R1
S
[A-H]
[A-2H]
[A-3H]
D
N
-[PhSO2C2H3]
a-d,f-j
a,c-j
B
O
-[R2NO]
O
a-c,e,h,j
-[PhSO2H2]
[D-H]
a-d,f-j
a,c-j
Ph
O
-[OH]
C
-[R2NOH]
-[PhSO2H3]
M
a-c,e,h,j
[D-2H]
c,h,i
a-d,f,g,j
a,b,d,j
[M–R2NOH]
-[C6H6SO2]
[D-2H]
-[C6H4SO2]
-[C6H5SO2]
[D-H]
a,b,d,j
a,b,d,j
a,b,d,j
D
are also observed, namely m/z 226 (3%), corresponding
to the loss of pyridyl, C5H4N and m/z 180 corresponding
to the consecutive loss of of CH2O and SO2 or vice versa.
Instead of ion B+ 3g gave ions m/z 136 and 134 corre-
sponding to [MꢀPhSO2ꢀHCN]+ and [MꢀPhSO2H2ꢀHCN]+,
respectively.
In the case of compounds 3d and 3e the base peaks of
the spectra were m/z 77 and 91. The former was fairly
abundant in all of the spectra but only for 3d (R2 = Ph) it
was the base peak. In case of 3e the 4-PhCH2O substituent
on R1 is responsible for the formation of tropylium ion
giving the base peak of the spectrum. In the latter case
this explains also why D-type ions are not formed since
the ion [AꢀH]+• decomposes preferably to the ions m/z 91
Compounds 3hꢀj also exhibit a unique secondary frag-
+
•
mentation via the [AꢀH] ions (an alternative route for 3i
and 3j is from the ion [AꢀHꢀOH]+) due to their furyl or
thiophenyl substitutions (Scheme 4). For 3h this ion, m/z 93
is weak but corresponds structurally those from 3i and 3j.
The latter compounds also give the ions m/z (109 or 123) ±
H, respectively but 3h only a small amount of the ion m/z
94(2%), C6H6O+• since major part (3%) of this nominal
mass corresponded to the structure C6H8N+.
+
and 206 (C11H12NO3 ) of which the former predominates.
EXPERIMENTAL
General Experimental Procedures.
Melting points were determined on a Meltemp apparatus and
are uncorrected. IR spectra were recorded on a Jasco 430 FT/IR
instrument (KBr pellet for solids, neat for oil or liquids using
NaCl disks). Preparative flash column chromatography was
performed on Merck silica gel 60 (230-400 mesh). Rf-values
were determined by thin layer chromatography (TLC) on Merck
silica gel 60 F254 and spots were visualized with UV light, iodine
or potassium permanganate stain solutions.
Scheme 4
Me
N
N
H
N
N
NMR-spectra were acquired using a Bruker Avance 500 spec-
trometer (equipped with BBO-5mm-Zgrad probe) operating at
CH
O
O
CH
CH
CH
S
1
500.13 MHz for H and 125.77 MHz for 13C. Spectra were re-
S
Ph
O
O
OH
corded using CDCl3 as a solvent with a non-spinning sample in
5 mm NMR-tubes. Spectra were processed by a PC with Win-
dows XP operating system and XWin-NMR software. Proton
and carbon spectra were referenced internally to TMS signal
using value 0.00 ppm.
Ph
3g
m/z (%) 104 (32)
m/z (%) 246 (100)
1H-NMR spectra were acquired with single-pulse excitation,
30° flip angle and with spectral width of 8 kHz consisting of 64
k data points (digital resolution 0.12 Hz/pt). No apodisation was
applied prior to Fourier transformation. 13C-NMR proton-
decoupled spectra were acquired with single-pulse excitation,
30° flip angle and with spectral width of 30 kHz consisting of 64
k data points (digital resolution 0.46 Hz/pt). 1 Hz exponential
weighting was applied prior to Fourier transformation. Gradient
selected DQF-COSY spectra were acquired with cosygpmfqf
R
Me
O
X
N
X
O
R
CH
CH
S
Ph
O
3h X=O, R=H, m/z (%) 93 (3)
3i X=S, R=H, m/z (%) 109 (26)
3j X=S, R=Me, m/z (%) 123 (14)
3h-j

Sep-Oct 2006
Synthesis and Mass Spectral Study of New Phenylsulfonyl Substituted Isoxazolidines
1273
pulse program (pulse programs refer to original ones installed by
Bruker), with spectral widths of 6.7 kHz, 1024ꢀ128 data points
and processed with zero-filling (ꢀ1, ꢀ8) and non-shifted sine
weighting applied in both dimensions prior to Fourier transfor-
mation. Gradient selected NOESY spectra were acquired with
noesygpph pulse program, with spectral widths of 5 kHz,
1024ꢀ128 data points and processed with zero-filling (ꢀ1, ꢀ8)
and shifted (SSB 2) qsine weighting applied in both dimensions
the flash chromatography (nH:EA 3:1) and recrystallization
from benzene-light petroleum as yellow needles (208 mg, 51%).
Mp 172-175 °C. Rf: 0.46 (EA:nH 1:1). IR (KBr): ꢂ (cmꢁ1) 2922,
1614, 1447, 1309 (SO2, symmetric), 1147 (SO2, asymmetric).
HRMS: M+• C23H24N2O3S, Calcd. 408.1508, Obsd. 408.1501.
Anal. Calcd. for C23H24N2O3S (MW 408.52). C 67.62; H 5.92;
N 6.86; S 7.85. Found: C 67.40; H 5.76; N 6.90; S 7.72.
1
(3R*,4R*)-3-(4-Methoxyphenyl)-2-methyl-4-(phenylsulfonyl)-
isoxazolidine (3c).
prior to Fourier transformation. Gradient selected H-13C HSQC
spectra were acquired with hsqcetgpsisp.2 pulse program (using
shaped pulses), with spectral widths of 6.7ꢀ27.5 kHz, 1024ꢀ256
data points, 145 Hz one-bond coupling constant and processed
with zero-filling (ꢀ1, ꢀ4) and shifted (SSB 2) qsine weighting
applied in both dimensions prior to Fourier transformation. Gra-
dient selected 1H-13C HMBC spectra were acquired with
hmbcgplpndqf pulse program, with spectral widths of 6.5ꢀ28
kHz, 1024ꢀ128 data points, 10 Hz long-range coupling constant
and processed with zero-filling (ꢀ2, ꢀ8) and shifted (SSB 2)
qsine weighting applied in both dimensions prior to Fourier
transformation.
Mass spectra were measured on a VG ZabSpec mass spec-
trometer (Micromass, Manchester, UK) equipped with Opus
V3.3X program package. For low-resolution EI spectra (70
eV) and metastable ion analyses (B/E and B2/E linked scans
in the first field-free region), the resolution was approxi-
mately 3,000 (at 10% peak height), the acceleration voltage
was 8 kV, and the ionization current was 200 μA. For accu-
rate mass measurements, the resolution was in the range of
8,000ꢁ12,000 (measured at 10% peak height) and voltage
scanning or peak-matching techniques were applied using
PFK as a source of reference signals. For all experiments,
samples were introduced via a solids inlet system; the tem-
perature of the ion source was 433 K.
N-Methyl-4-(methoxy)-benzylidene amine N-oxide (1c, 0,25
mmols of starting materials were used) gave 3c after the flash
chromatography (nH:EA 2:1) as a yellow solid (62 mg, 55%).
Mp 146-147 °C. Rf : 0.62 (EA:nH 1:1), IR (KBr): ꢂ (cm-1):
3050, 2845, 1615 , 1445 , 1295 (SO2, symmetric), 1142 (SO2,
asymmetric). HRMS: M+• C17H19NO4S, Calcd. 333.1035, Obsd.
333.1037.
Anal. Calcd. for C17H19NO4S (MW 333.402). C 61.24; H 5.74;
N 4.20; S 9.62. Found: C 61.40; H 5.82; N 4.12; S 9.76.
(3R*,4R*)-3-(4-Methoxyphenyl)-2-phenyl-4-(phenylsulfonyl)-
isoxazolidine (3d).
N-Phenyl-4-(methoxy)-benzylidene amine N-oxide (1d) gave
3d after the flash chromatography (nH:EA 3:1) and recrystalli-
zation from benzene-light petroleum as yellow needles (200 mg,
50%). Mp 145-146 °C. Rf : 0.61 (EA:nH 1:1). IR (KBr): ꢂ (cm-1)
3415, 3056 , 1611 ,1486, 1309 (SO2, symmetric), 1147 (SO2,
asymmetric). HRMS: M+• C22H21NO4S, Calcd. 395.1191, Obsd.
395.1191.
Anal. Calcd. for C22H21NO4S (MW 395.47). C 66.82; H 5.35;
N 3.54; S 8.11. Found: C 66.62; H 5.16; N 3.70; S 8.30.
(3R*,4R*)-3-(3-Methoxy-4-phenoxyphenyl)-2-methyl-4-(phenyl-
sulfonyl)isoxazolidine (3e).
General Procedure for Preparation of 3aꢁj.
N-Methyl-(3-methoxy-4-phenoxy)-benzylidene amine N-
oxide (1e) gave 3e after the flash chromatography (petroleum
ether 40-60 °C: EA 2:1) as a yellow solid (276 mg, 63%). Mp
115-117 °C. Rf: 0.77 (EA:nH 2:1). IR (KBr): ꢂ (cm-1) 3050,
2959, 1604, 1454, 1305 (SO2, symmetric), 1153 (SO2, asymmet-
ric). HRMS: M+• C24H25NO5S, Calcd. 439.1453, Obsd.
439.1452.
A 1-substituted N-methyl (or phenyl) methanimine N-oxide
(1, 1 mmol if not otherwise stated) was added to a solution of
phenyl vinyl sulfone (2, 168 mg, 1 mmol if not otherwise stated)
in dry toluene (10 mL) and the mixture was heated to reflux for
overnight. The progress of the reaction was monitored by TLC.
Then the reaction mixture was concentrated in vacuo and the
crude product purified by flash column chromatography using a
mixture of n-hexane (nH) and ethyl acetate (EA) to give the
products.
Anal. Calcd. for C24H25N2O5S (MW 437.53). C 65.58; H 5.73;
N 3.19; S 7.29. Found: C 65.42; H 5.73; N 3.30; S 7.42.
(3R*,4R*)-3-(2-Hydroxyphenyl)-2-phenyl-4-(phenylsulfonyl)-
isoxazolidine (3f).
(3R*,4R*)-3-(4-N,N-Dimethylphenyl)-2-methyl-4-(phenylsulfonyl)-
isoxazolidine (3a).
N-(2-hydroxyphenyl)-benzylidene amine N-oxide (1f) gave 3f
after the flash chromatography (nH:EA 2:1) as a dark coloured
oil (48 mg, 13%). Rf : 0.46 (EA:nH 1:1). IR (KBr): ꢂ (cm-1) 3411
(OH), 1596, 1447, 1307 (SO2, symmetric), 1149 (SO2, asymmet-
ric). HRMS: M+• C21H19NO4S, Calcd. 381.1035, Obsd.
381.1037.
N-Methyl-4-(N,N-dimethylamino)-benzylidene amine N-
oxide (1a) gave 3a after the flash chromatography (nH:EA 2:1)
as a yellowish solid (190 mg, 55%). Mp 116-117 °C. Rf : 0.55
(nH:EA 2:1). IR (KBr): ꢂ(cmꢁ1) 2922, 1614, 1447, 1309 (SO2,
symmetric), 1147 (SO2, asymmetric). HRMS: M+• C18H22N2O3S,
Calcd. 346.1351, Obsd. 346.1351.
Anal. Calcd. for C21H19NO4S (MW 381.45). C 66.12; H 5.02;
N 3.67; S 8.40. Found: C 66.30; H 5.15; N 3.48; S 8.60.
Anal. Calcd. for C18H22N2O3S (MW 346.44). C 62.40; H 6.40;
N 8.09; S 9.25. Found: 62.25; H 6.30; N 8.24; S 9.40.
(3R*,4R*)-2-Methyl-4-(phenylsulfonyl)-3-(pyridin-2-yl)isoxa-
zolidine (3g).
(3R*,4R*)-3-(4-N,N-Dimethylphenyl)-2-phenyl-4-(phenylsulfonyl)-
isoxazolidine (3b).
N-methyl-1-(pyridin-2-yl)-methanimine N-oxide (1g) gave 3g
after the flash chromatography (nH:EA 2:1) as a black solid
(126 mg, 41%). Mp 119-122 °C. Rf: 0.62 (EA:nH 1:1). IR
(KBr): ꢂ (cm-1) 2853, 1591, 1443, 1302 (SO2, symmetric), 1154
N-Phenyl-4-(N,N-dimethylamino)-benzylidene amine N-oxide
(1b, two mmols of starting materials were used) gave 3b after

1274
Y. Dürüst, C. Altuꢀ, J. Sinkkonen, O. Martiskainen and K. Pihlaja
Vol 43
(SO2, asymmetric). HRMS: M+• C15H16N2O3S, Calcd. 304.0882,
Obsd. 304.0883.
Anal. Calcd. for C15H16N2O3S (MW 304.36). C 59.19; H 5.30;
N 9.20; S 10.53. Found: C 59.40; H 5.22; N 9.38; S 10.25.
[j] H. M. I. Osborn, N. Gemmell, L. M. Harwood, J. Chem. Soc., Perkin
Trans. 1, 2419–2438 (2002); [k] S. Kanemasa, Synlett., 1371–1387
(2002); [l] R. W. Bates, K. Sa-Ei, Tetrahedron, 58, 5957–5978 (2002);
[m] J. K. Gallos, A. E. Koumbis, Curr. Org. Chem., 7, 397–425 (2003);
[n] K. V. Gothelf, S. Kobayashi, K. A. Jørgensen, Cycloaddition Reac-
tions in Organic Synthesis, Wiley-VCH, Weinheim, 2002, pp. 211–247;
[o] H. M. I. Osborn, N. Gemmell, L. M. Harwood, J. Chem. Soc., Perkin
Trans. 1, 2419–2438 (2002); [p] W. R. Carruthers, Cycloadditions in
Organic Synthesis; Pergamon Press: London, 1990, Chapter 6, p 269.
[2] For isoxazolidine synthesis see [a] A. Brandi, Y. Dürüst, F.
M. Cordero, F. De Sarlo, J. Org. Chem., 57, 5666–5670 (1992); [b] A.
Brandi, A. Guarna, A. Goti, F. Pericciuoli, F. De Sarlo, Tetrahedron
Lett., 27, 1727–1730 (1986); [c] A. Brandi, S. Garro, A. Goti, A. Corde-
ro, F. De Sarlo, J. Org. Chem., 53, 2430–2434 (1988); [d] A. Brandi, F.
M. Cordero, F. De Sarlo, A. Goti, A. Guarna, Synlett., 128 (1993), and
references therein; [e] A. Goti, B. Anichini, A. Brandi, S. Koshushkov,
C. Gratkowski, A. de Meijere, J. Org. Chem., 61, 1665–1672 (1996); [f]
A. Guarna, A. Brandi, A. Goti, F. De Sarlo, J. Chem. Soc.,Chem. Com-
mun., 1518–1519 (1985); [g] A. Guarna, A. Brandi, F. De Sarlo, A. Goti,
F. Pericciuoli, J. Org. Chem., 53, 2426–2429 (1988); [h] F. M. Cordero,
I. Barile, F. De Sarlo, A. Brandi, Tetrahedron Lett., 40, 6657–6660
(1999); [i] A. Brandi, S. Carli, A. Goti, Heterocycles, 27, 17–20 (1988);
[j] F. M. Cordero, B. Anichini, A. Goti, A. Brandi, Tetrahedron, 43,
9867–9876 (1993); [k] A. Goti, A. Brandi, F. De Sarlo, A. Guarna,
Tetrahedron, 48, 5283–5300 (1992); [l] A. Goti, A. Brandi, F. De Sarlo,
A. Guarna, Tetrahedron Lett., 27, 5271–5274 (1986); [m] Y. Dürüst, H.
A. Döndaꢂ, N. Özkoru, Heterocyclic Commun., 5, 173–178 (1999); [n]
P. Merino, V. Mannucci, T. Tejero, Tetrahedron, 61, 3335–3347 (2005);
[o] V. Sridharan, S. P. Saravanakumar, S. Muthusubramanian, J. Hete-
rocycl. Chem., 42, 515–518 (2005); [p] V. Sridharan, S. Muthusubrama-
nian, S. Sivasubramanian, K. Polborn, Tetrahedron, 60, 8881–8892
(2004); [q] M. Shirahase, S. Kanemasa, Y. Oderaotoshi, Org. Lett., 6,
675–678 (2004); [r] P. Merino, T. Tejero, M. Laguna, E. Cerrada, A.
Moreno, J. A. Lopez, Org. Biomol. Chem. 1, 2336–2342 (2003); [s] B.
Janza, A. Studer, Synthesis, 2117–2123 (2002); [t] M-O. J. Charmier, N.
Moussalli, J. Chanet-Ray, S. Chou, J. Chem. Res., Synopses, 9, 566–567
(1999); [u] P. Bayon, P. De March, M. Figueredo, J. Font, Tetrahedron,
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71 (1997).
(3R*,4R*)-3-(Furan-2-yl)-2-methyl-4-(phenylsulfonyl)isoxazol-
idine (3h).
N-methyl-1-(furan-2-yl)methanimine N-oxide (1h) gave 3h
after the flash chromatography (nH:EA 2:1) and recrystallization
from benzene-light petroleum as white needles (125 mg, 40%).
Mp 122-124 °C. Rf: 0.50 (EA:nH 1:1). IR (KBr): ꢀ (cm-1) 3137,
2967, 1448, 1315 (SO2, symmetric), 1149 (SO2, asymmetric).
HRMS: M+• C14H15NO4S, Calcd. 293.0722, Obsd. 293.0718.
Anal. Calcd. for C14H15NO4S (MW 293.34). C 64.34; H 5.78;
N 5.36; S 12.27. Found: C 64.50; H 5.65; N 5.50; S 12.40.
(3R*,4S*)-2-Methyl-4-(phenylsulfonyl)-3-(thiophen-2-yl)isoxa-
zolidine (3i).
N-methyl-1-(thiophen-2-yl)methanimine N-oxide (1i) gave 3i
after the flash chromatography (nH:EA 2:1) and recrystallization
from benzene-light petroleum as white needles (126 mg, 41%).
Mp 99-101 °C. Rf: 0.49 (EA:nH 3:2). IR (KBr): ꢀ (cm-1) 1581,
1446, 1307 (SO2, symmetric), 1147 (SO2, asymmetric). HRMS:
M+• C14H15NO3S2, Calcd. 309.0493, Obsd. 309.0500.
Anal. Calcd for C14H15NO3S2 (MW 309.40). C 54.35; H 4.89;
N 4.53; S 20.72. Found: C 54.20; H 5.02; N 4.70; S 20.54.
(3R*,4S*)-2-Methyl-3-(3-methylthiophen-2-yl)-4-(phenylsulfonyl)-
isoxazolidine (3j).
N-methyl-1-(3-meth-ylthiophen-2-yl))methanimine N-oxide
(1j) gave 3j after the flash chromatography (nH:EA 2:1) and
recrystallization from hexane as white needles (126 mg, 41%).
Mp 87-89 °C. Rf: 0.46 (EA:nH 1:1). IR (KBr): ꢀ (cm-1) 3058,
2877, 1447, 1307 (SO2, symmetric), 1153 (SO2, asymmetric).
HRMS: M+• C15H17NO3S2, Calcd. 323.0650, Obsd. 323.0648.
Anal. Calcd. for C15H17NO3S2 (MW 323.42). C 55.70; H 5.30;
N 4.33; S 19.82. Found: C 55.65; H 5.50; N 4.18; S 19.65.
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Acknowledgements.
Abant ꢁzzet Baysal University (Bolu, Turkey) Research Fund
(BAP,grant no:2002.02.02.121) and TÜBꢁTAK are gratefully
acknowledged for financial support. The authors also thank Ms
Kirsti Wiinamäki for helping in recording the mass spectra. We
also wish to thank the Magnus Ehrnrooth Foundation for a grant
to Olli Martiskainen.
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