The (E) and (Z) isomers of 1-(4-methylthiophenyl)-2-nitrobutene were formed in the reaction mixture of 4-methylthiobenzaldehyde and 1-nitropropane in refluxing toluene, using N,N-dimethylethylenediamine as catalyst, in an approximately 92:8 molar ratio, judging from the 1H NMR spectrum of the crude product. Both products [(E)-1a and (Z)-1a, respectively] were separated chromatographically and fully characterized by 1H- and 13C-NMR spectroscopy, using HMBC, HMQC and NOESY experiments for complete assignment of the signals. Tables 1 and 2 allow direct comparison of the 1H and 13C chemical shifts of stereoisomers (E)-1a and (Z)-1a.
Fig. 2a. NOESY spectrum of (E)-1-(4-methylthiophenyl)-2-nitrobutene [(E)-1a] (CDCl3).
Fig. 2b. NOESY spectrum of (Z)-1-(4-methylthiophenyl)-2-nitrobutene [(Z)] (CDCl3).
(E)-1-(4-Methylthiophenyl)-2-nitrobutene [(E)-1a] and (Z)-1-(4-Methylthiophenyl)-2-nitrobutene [(Z)-1a].
A mixture of 4-methylthiobenzaldehyde (1.3 ml, 0.010 mol), N,N-dimethylethylenediamine (1.3 ml, 0.010 mol), 1-nitropropane (4.5 ml, 0.041 mol) and toluene (10 ml) was refluxed for 24 h with continuous water removal under a Dean-Stark trap. All volatiles were removed under reduced pressure and the residue was fractionated chromatographically over silica gel, eluting with CHCl3, to afford the E [(E)-1a] (1.08 g, 92% in the mixture) and Z isomers [(Z)-1a] (0.096 g, 8% in the mixture) as viscous orange colored liquids.
(E)-1a: 1H-NMR (CDCl3) δ 1.28 (t, 3H, J = 7.4 Hz, CH2CH3), 2.52 (s, 3H, S-CH3), 2.88 (q, 2H, J = 7.4 Hz, CH3CH2C=CH), 7.29 (d, 2H, J = 8.5 Hz, H3' and H5'), 7.36 (d, 2H, J = 8.5 Hz, H2' and H6'), 7.98 (s, 1H, Ar-CH=C). HREIMS m/z (M+) = 223.06621; calc. for C11H13NO2S = 223.06670.
(Z)-1a: 1H-NMR (CDCl3) δ 1.20 (t, 3H, J = 7.4 Hz, CH2CH3), 2.46 (s, 3H, S-CH3), 2.67 (q, 2H, J = 7.4 Hz, CH3CH2C=CH), 6.29 (s, 1H, Ar-CH=C), 7.16 (apparent s, 4H, J = 9.2 Hz, Ar-H). HREIMS m/z (M+) = 223.06622; calc. for C11H13NO2S = 223.06670.
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