MAGNETIC RESONANCE IN CHEMISTRY
Magn. Reson. Chem. 2004; 42: 1053–1055
Published online 24 September 2004 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/mrc.1488
Spectral Assignments and Reference Data
Complete 1H and 13C NMR spectral
corresponding proton and could be assigned without help of 2D
techniques.
We conclude that the sydnone ring influences the chemical shifts
on the stilbene ring mainly owing to sterric effects. It is known that
ortho-substitution decreases the ꢂ-delocalization by changing the
planarity of the system.
assignment of cis- and trans- 3-f2-[2-(4-
methylphenyl)ethenyl]phenyl]gsydnones
1
ˇ
2
Kristina Butkovi c´ , Zeljko Marini c´ and
ˇ
1∗
Marija Sindler-Kulyk
EXPERIMENTAL
1
Department of Organic Chemistry, Faculty of Chemical Engineering
and Technology, University of Zagreb, Marulicev trg 19, 10000 Zagreb,
Croatia
All reagents were obtained from commercial sources and used
without purification. Melting-points were recorded on an Original
Kofler Mikroheiztisch apparatus (Reichert, Vienna, Austria) and
are uncorrected. Silica gel (Merck, 0.05–0.2 mm) was used for
chromatographic purifications.
2
NMR Center, Institute Rudjer Boskovic, Bijenicka cesta 54, 10000
Zagreb, Croatia
Received 24 May 2004; accepted 20 July 2004
General synthetic procedure
0
The starting compounds (Fig. 3), cis- and trans-2-nitro-4 -methylstil-
1H and 13C NMR spectra of cis- and trans-3-f2-
bene (2), were prepared by Wittig reaction from 2-nitrobenzaldehyde
[
2-(4-methylphenyl)ethenyl]phenyl]gsydnones, the first
(
(
(
(
0.020 mol) and the triphenylphosphonium salt of p-xylyl bromide
0.022 mol) in ethanol (60 ml) and addition of sodium ethoxide
0.022 mol). The isomers were separated by column chromatography
stilbene-substituted mezoionic oxadiazolium rings, were
fully assigned combining the information in various
solvents, such as deuterated benzene, acetone and chlo-
roform, using 2D NMR techniques. Copyright 2004
John Wiley & Sons, Ltd.
CH2Cl2 –light petroleum, 7 : 3) and treated separately to the sydnone
4
derivative 1. Reduction of 2 (0.021 mol) with zinc (0.131 mol) in
acetone (40 ml) and NH4Cl (0.053 mol) disolved in water (13 ml)
0
under reflux gave 2-amino-4 -methylstilbene (3). Using a known
KEYWORDS: NMR; H NMR; 13C NMR; 2D NMR; sydnones;
1
5,6
method, amino derivative 3 (0.017 mol) was converted to amino
stilbenes; inner oxadiazolium salt; isomers
acid 4 by substitution with ethyl bromoacetate (0.017 mol) in
refluxing ethanol (12.5 ml) in the presence of sodium acetate
(
0.026 mol) and subsequent base-promoted hydrolysis in water. The
isolated amino acid 4 (0.0041 mol) was nitrosated with NaNO2
(0.0062 mol) in water (30 ml) and addition of HCl (1 : 1, 1.5 ml) in an
ice-cold bath, filtered, dried and, without purification, the obtained
nitroso derivative 5 was refluxed in acetic anhydride (4 ml) to give
sydnone derivative 1. Pure products were obtained by crystallization
from ethanol. The yields and melting-points are reported in Table 4.
INTRODUCTION
Sydnones,1 five-membered heterocycles with a sextet of electrons,
belong to a class of dipolar compounds known as a ‘mesoionic’ and
can be represented as hybrids of a number of mesomeric/ionic forms
(
Fig. 1). They are studied not only because of their structure, physical
properties and reactivity, but also because a series of derivatives have
2
NMR spectroscopy
shown various biological activities.
Here we report the full assignment of the 1H and 13C
All NMR spectra were recorded with a Bruker Avance 600
1
spectrometer, operating at 600.13 MHz for H and 150.92 MHz for
NMR spectra of stilbenyl derivatives, cis- and trans-3-f2-[2-
1
3
C. The compounds were dissolved in CDCl3, C6D6 and ꢀCD3ꢁ2CO,
(
4-methylphenyl)ethenyl]phenyl]gsydnones (1) (Fig. 2), the aro-
matic stilbene molecule substituted in the ortho-position with
the mesomeric oxadiazolium ring. Although stilbene and their
derivatives are the most extensively studied conjugated systems,
3
this is the first example of sydnonylstilbene. They are obtained by a
sequence of reactions (see Experimental).
Figure 1. Resonance structures of sydnones.
RESULTS AND DISCUSSION
All assignments of the 1H and 13C chemical shifts and coupling
constants for cis- and trans-1 (Fig. 2) are given in Tables 1 and 2. To
be able to make complete assignments of all carbons and hydrogens,
it was necessary to use not only a single solvent such as CDCl3
but also C6D6 and ꢀCD3ꢁ2CO. In the case of cis-1, the protons H-
2
7
to H-5 appear in CDCl3 as a four-proton multiplet (Table 1) at
.53–7.44 ppm. In ꢀCD3ꢁ2CO only H-2 and H-5 are well resolved,
but in C6D6 all four protons were assigned. H-2 and H-3 of trans-1
(Table 2) are not separable in CDCl3 whereas in C6D6 and ꢀCD3ꢁ2CO
they are well resolved and appear as dd or dt, respectively.
The resonances of the stilbene moiety were obtained from the
combined information observed in 1D and 2D (COSY, HMQC,
HMBC) experiments. The carbon type (C, CH, CH3) was determined
using APT experiments. In Table 3 are given H– H and C– H
correlations, based on which the unambiguous assignment of all
carbons and hydrogens was made. The typical small signal for the
sydnone carbon was upfield of other aromatic carbons and the
Figure 2. cis- and trans- 3-f2-[2-(4-methylphenyl)ethenyl]
phenyl]gsydnones (1).
1
1
13
1
Ł
ˇ
Correspondence to: Marija Sindler-Kulyk, Department of Organic
Chemistry, Faculty of Chemical Engineering and Technology, University of
Zagreb, Marulicev trg 19, 10000 Zagreb, Croatia. E-mail: msindler@fkit.hr
Contract/grant sponsor: Ministry of Science and Technology of the Republic
of Croatia; Contract/grant numbers: 0125004; 0098059.
Figure 3. Structures of compounds 2–5.
Copyright 2004 John Wiley & Sons, Ltd.