Supporting Information
Page
2
Spectrum 11
2
Spectrum 21
NMR of  0.05 M (Z)-1 in CDCl3
(immediately upon dissolution;
1H NMR of (Z)-1 and (E)-1 (major)
CDCl3 after equilibration
1H
Manuscript
Table 2; entry 2;
footnote a
in Table 2; entry 3;
footnote a
Z/E ISOMERIZATION DATA
3
4
Spectrum 31
Spectrum 32
1H
1H
NMR of (Z)-4 (CDCl3); Z/E ratio: 96/4
NMR of (Z)-4 (CDCl3); Z/E ratio: 43/57
5
Spectrum 33
1H
NMR of (Z)-4 (CDCl3); Z/E ratio: 10/90
VT 1H NMR DATA
6
7
8
9
Spectrum
Spectrum
Spectrum
Spectrum
(Z)-1  (E)-1 at 35 C
(Z)-1  (E)-1 at 45 C
(Z)-1  (E)-1 at 55 C
(Z)-1  (E)-1 at 60 C
41
42
43
44
ADDITIONAL
CHARACTERIZATION DATA
10
11
12
14
Spectrum 5
Spectrum 6
1H
NMR of (Z)-2 (DMSO-d6)
NMR of (Z)-3 (DMSO-d6)
Crystal structure of (Z)-4
IR (KBr) of (Z)-1
1H
Table 2; entry 10
Table 2; entry
11; footnote a
Table 2; entry
12; footnote b
Spectral data and comments related to the regioselective synthesis of ethyl (Z)-(5ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)ethanoate (4)
Spectrum
31
1
H NMR spectrum (200 MHz) of the (Z)-4 isomer containing traces of the
(E)-4 isomer, recorded in CDCl3 almost immediately after dissolution of the
isolated product (or recrystallized from alcohol).
H NMR (200 MHz, CDCl3):  1.28 (t, 6H, 2CH3, J = 7.2 Hz), 2.93 (dd, HA, JAB = 17.3 Hz, JAX = 8.5
Hz), 3.13 (dd, HB, JAB = 17.3 Hz, JBX = 4.1 Hz), 4.19 (q, 4H, 2CH2O, J =7.2 Hz), C(5)-H signal buried
below the quartet centered at  4.19, 5.59 (s, 1H, =CH(2')), 9.35 (s, 1H, NH); IR (KBr):  3188, 3122,
3079, 2985, 1739, 1722, 1691, 1605, 1474, 1380, 1298, 1196, 1144, 1093, 1029, 817, 725, 676 cm-1
(the band at 3122 cm-1 is attributed to NH vibration of (E)-4 that is present in very small amount).
1
Attention should be drawn to the presence of the very small signal at  5.12 which is assigned to the (E)-isomer. It implies
that the spectrum of the freshly isolated (Z)-4 isomer was not recorded immediately after the solution was prepared, but few
minutes later, time enough for Z/E isomerization to begin. This is why the Z/E ratio is above 96.0, but not equal to 100
(Manuscript, please, see Table 2, entry 10).
Spectrum 32
1
H NMR spectrum of Z/E mixture of 4-oxothiazolidine push-pull derivative
4, recorded in CDCl3 after two days; the mixture is enriched in the (E)-4
isomer (Z/E ratio 43/57).
The chemical shift of the lactam proton of the E-isomer, which forms an intramolecular hydrogen bond with the C=O group
in weakly polar chloroform, is larger (  10.63 ppm) than that of the corresponding lactam proton of the Z-isomer ( 8.70
ppm). A large chemical shift difference ( 1.93 ppm) serves in this case, and in many similar push-pull compounds that we
synthesized, as reliable means for the stereochemical characterization of C-C double bond.
Spectrum 33
1
H NMR spectrum of Z/E mixture of 4-oxothiazolidine push-pull derivative
4, recorded in CDCl3 after six days; (Z/E ratio 10/90).
Spectrum 5
(Z)-(5-Ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-N-phenylethanamide (2)
H NMR (DMSO-d6):  1.19 (t, 3H, CH3, J = 7.1 Hz), 2.92 (dd, 1H, CHAHBCOO, JAB = 17.5 Hz, JAX =
8.0 Hz), 3.02 (dd, 1H, CHAHBCOO, JAB = 17.5 Hz, JBX = 4.6 Hz) 4.10 (q, 2H, CH2O, J = 7,1 Hz), 4.19
(dd, 1H, CHXS, JAX = 8.0 Hz, JBX = 4.6 Hz), 5.79 (s, 1H, =CH), 6.98 (t, 1H, p-phenyl), 7.26 (t, 2H, mphenyl), 7.59 (d, 2H, o-phenyl), 9.85 (s, 1H, NHexo), 11.58 (s, 1H, NHring);
13
C NMR (DMSO-d6):  14.6 (CH3), 37.2 (CH2COO), 42.4 (CHS), 61.2 (CH2O), 93.3 (=CH), 119.2 (ophenyl), 123.1 (p-phenyl), 129.3 (m-phenyl), 140.4 (C-1 phenyl), 153.5 (C=), 165.9 (COexo), 170.9
(COring), 175.9 (COester);
Anal. Calcd for C15H16N2O4S: C, 56.24; H, 5.03; N, 8.74; S, 10.00. Found: C, 56.16; H, 4.94; N, 8.87;
S, 10.15.
1
Spectrum 6
(Z)-(5-Ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-N-phenylethylethanamide (3)
H NMR (DMSO-d6):  1.18 (t, 3H, CH3, J = 7.2 Hz), 2.69 (t, 2H, CH2Ph, J = 7.4 Hz), 2.85 (dd, 1H,
CHAHBCOO, JAB = 17.2 Hz, JAX = 8.4 Hz), 2.97 (dd, 1H, CHAHBCOO, JAB = 17.2 Hz, JBX = 4.3 Hz)
J
J
3.22-3.32 (m, 2H, NCH2, CH 2CH 2 = 7.4 Hz, NHCH 2 = 5.4 Hz), 4.09 (q, 2H, CH2O, J = 7.2 Hz), CHXS
not seen, 5.55 (s, 1H, =CH), 7.16-7.33 (m, 5H, Ph), 7.85 (t, 1H, NHexo, J = 5.4 Hz), 11.30 (s, 1H,
NHring);
13
C NMR (DMSO-d6):  14.6 (CH3), 36.0 (CH2Ph), 37.4 (CH2COO), 40.6 (NCH2), 42.3 (CHS), 61.1
(CH2O), 93.2 (=CH), 126.7 (p-phenyl), 128.9 (o-phenyl), 129.2 (m-phenyl), 140.2 (C-1 phenyl), 150.8
(C=), 167.1 (COexo), 170.9 (COring), 175.5 (COester);
Anal. Calcd for C17H20N2O4S: C, 58.60; H, 5.79; N, 8.04; S, 9.20; Found: C,
58.76; H, 5.81; N,
8.08; S, 9.20
1
Crystal structure of (Z)-4
Figure 1 shows a perspective view of the X-ray crystal structure of the thiazolidinone derivative (Z)-4.
Selected bond lengths, bond angles and torsional angles are listed in Table 1. The tautomeric enamine
form was definitively determined by location and refinement of the NH hydrogen. The central
thiazolidinone ring is planar (mean deviation from planarity = 0.014 Å, maximum deviation 0.023 Å).
The X-ray analysis of derivative 4 proved the Z-configuration of the double bond. The C2 side chain is
also essentially coplanar with the ring which brings O21 into close proximity with the sulfur atom
(O21…S1 = 2.873(2) Å). This distance is less than the sum of the van der Waals radii (3.22 Å) but
greater than that previously observed in similar thiadiazolones.1 The molecular packing is controlled by
intermolecular hydrogen bonds between the NH group and the C4 carbonyl of an adjacent molecule
related by a crystallographic two-fold screw axis [H3…O41’ = 2.00(3) Å; N3…O41’ = 2.765(2) Å; N3H…O41’ = 165(2) °].
Figure 1. ORTEP view of ethyl (Z)-(5-ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)ethanoate (4) (arbitrary
numbering of the atoms)
1. J.A.M. Guard and P.J. Steel. Aust. J. Chem., 1995, 48, 1609.
Table 1. Selected bond lengths [Å], bond angles [°] and torsional angles [°] for 3d
_____________________________________________________________________________________
Bond lengths
S(1)-C(2)
S(1)-C(5)
C(2)-C(21)
C(2)-N(3)
N(3)-C(4)
C(4)-C(5)
C(5)-C(51)
C(22)-O(21)
C(51)-C(52)
C(52)-O(51)
1.758(2)
1.831(2)
1.347(3)
1.384(3)
1.349(3)
1.524(3)
1.530(3)
1.219(3)
1.506(3)
1.205(3)
Torsion angles
C(5)-S(1)-C(2)-C(21)
C(5)-S(1)-C(2)-N(3)
S(1)-C(2)-N(3)-C(4)
O(41)-C(4)-C(5)-C(51)
N(3)-C(4)-C(5)-C(51)
S(1)-C(2)-C(21)-C(22)
C(2)-C(21)-C(22)-O(21)
C(2)-C(21)-C(22)-O(22)
C(4)-C(5)-C(51)-C(52)
C(5)-C(51)-C(52)-O(51)
C(5)-C(51)-C(52)-O(52) 158.63(19)
Bond angles
C(2)-S(1)-C(5)
C(21)-C(2)-N(3)
C(21)-C(2)-S(1)
N(3)-C(2)-S(1)
C(4)-N(3)-C(2)
O(21)-C(22)-O(22)
O(21)-C(22)-C(21)
C(52)-C(51)-C(5)
O(51)-C(52)-C(51)
C(52)-O(52)-C(53)
179.9(2)
1.92(16)
-4.2(2)
54.8(3)
-127.9(2)
0.5(3)
0.1(3)
-178.73(19)
56.0(2)
-22.5(3)
92.44(10)
121.78(19)
127.65(16)
110.54(15)
118.68(18)
123.5(2)
125.6(2)
112.27(18)
124.0(2)
114.3(2)
IR (KBr) of (Z)-1
IR (KBr):  3277, 3091, 2993, 2979, 1737, 1714, 1636, 1599, 1523, 1453, 1373, 1248, 1243, 1187,
1161, 1046, 1025, 883, 810, 777, 683 cm-1