- 2-(N,N-Disubstituted Amino)thiazoles with Electron-withdrawing Groups at Position 5: Prepaeation and Investigation on Structural Features
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A convenient procedure for preparing N-mono- and NN-di-substituted cyanamides from cyanogen bromide has been developed.N,N-Disubstituted thioureas, obtained from the cyanamides, were condensed with α-bromo-α-cyanoketones to give 5-cyano-2-(N,N-disubstituted amino)thiazoles and with α-bromo-ketones to give 2-(N,N-disubstituted amino)thiazoles.Substitution in the latter products afforded 5-trifluoroacetyl- and 5-nitro-2-(N,N-disubstituted amino)thiazoles; nitration is greatly facilitated by the presence of a 4-aryl group.The average values of the barriers of rotation of the barriers to rotation of the 2-NR2 groups (ΔG298) in the 5-substituted thiazoles were established by variable temperature 1H n.m.r. spectrometry to be 57.4 kJ mol -1 (5-NO2), 56.2 (5-COCF3), and 51.5 (5-CN).I.r. examination showed that the 5-trifluoroacetyl compounds adopt one rotational form preferentially; this is probably the carbonyl O,S-syn-conformation.
- Birkinshaw, Timothy N.,Gillon, David W.,Harkin, Shaun A.,Meakins, G. Denis,Tirel, Malkom D.
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p. 147 - 153
(2007/10/02)
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- N,N-Disubstituted 2-Aminothiazole-5-carbaldehydes: Preparation and Investigation of Structural Features
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Methods of preparing N,N-disubstituted 2-aminothiazoles have been investigated. 4-Substituted N,N-dimethyl-, N-benzyl-N-methyl-, and N-methyl-N-phenyl-amines were prepared and converted by Vilsmeier formylation into 2-amino-5-carbaldehydes which were examined by i.r. and 1H n.m.r. spectrometry.The aldehyde group adopts the carbonyl O,S-syn-conformation.With the N,N-dimethyl and N-benzyl-N-methyl compounds the barrier to rotation of the amine group (ΔG(excit.)) is 50-55 kJ mol-1 and is insensitive to the nature of the 4-substituent.The amine group of the N-methyl-N-phenyl compounds has a marked preference for one orientation.This was shown by a crystallographic study of 4-t-butyl-2-(N-methyl-N-phenylamino)thiazole-5-carbaldehyde to have the phenyl group directed towards the sulphur atom of the thiazole ring.
- Gillon, David W.,Forrest, Ian J.,Meakins, G. Denis,Tirel, Malcolm D.,Wallis, John D.
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p. 341 - 348
(2007/10/02)
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