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Thiazole
Thiazole numbering.png
Thiazole3d.png
Identifiers
CAS number 288-47-1 Yes check.svgY
SMILES
Properties
Molecular formula C3H3NS
Molar mass 85.13 g mol−1
Boiling point

116-118 °C

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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Thiazole, or 1,3-thiazole, is a clear to pale yellow flammable liquid with a pyridine-like odor and the molecular formula C3H3NS. It is a 5-membered ring, in which two of the vertices of the ring are nitrogen and sulfur, and the other three are carbons.[1]

Thiazole is used for manufacturing biocides, fungicides, pharmaceuticals, and dyes.

Contents

Thiazoles and thiazolium salts

Thiazoles are a class of organic compounds related to azoles with a common thiazole functional group. Thiazoles are aromatic.

The thiazole moiety is a crucial part of vitamin B1 (thiamine) and epothilone. Other important thiazoles are benzothiazoles, for example, the firefly chemical luciferin.

Thiazoles are structurally similar to imidazoles. Like imidazoles, thiazoles have been used to give N-S free carbenes[2] and transition metal carbene complexes.

Structure of thiazoles (left) and thiazolium salts (right)


The amino atom can be alkylated to create a thiazolium cation; thiazolium salts are catalysts in the Stetter reaction and the Benzoin condensation. Thiazole dyes are used for dying cotton.

Oxazoles are related compounds, with sulfur replaced by oxygen. Thiazoles are well represented in biomolecules; oxazoles are not.

Organic synthesis

Various laboratory methods exist for the organic synthesis of thiazoles.

Hantsch Thiazole Synthesis

Reactions

Thiazoles are characterized by larger pi-electron delocalization than the corresponding oxazoles and have therefore greater aromaticity. This is evidenced by the position of the ring protons in proton NMR (between 7.27 and 8.77 ppm), clearly indicating a strong diamagnetic ring current.

The calculated pi-electron density marks C5 as the primary electrophilic site, and C2 as the nucleophilic site.

Thiazole electron densities and numbering scheme

The reactivity of a thiazole can be summarized as follows:

Thiazole deprotonation
2-(trimethylsiliyl)thiazole [5] (with a trimethylsilyl group in the 2-position) is a stable substitute and reacts with a range of electrophiles such as aldehydes, acyl halides, and ketenes
Thiazole bromination
Thiazole Nucleophilic Aromatic Substitution
Thiazole oxidation
  • Thiazoles can react in cycloadditions, but in general at high temperatures due to favorable aromatic stabilization of the reactant; Diels-Alder reactions with alkynes are followed by extrusion of sulfur, and the endproduct is a pyridine; in one study [4], a very mild reaction of a 2-(dimethylamino)thiazole with dimethyl acetylenedicarboxylate (DMAD) to a pyridine was found to proceed through a zwitterionic intermediate in a formal [2+2]cycloaddition to a cyclobutene, then to a 1,3-thiazepine in an 4-electron electrocyclic ring openening and then to a 7-thia-2-azanorcaradiene in an 6-electron electrocyclic ring, closing before extruding the sulfur atom.
Thiazole cycloaddition

References

  1. ^ The Chemistry of Heterocycles : Structure, Reactions, Syntheses, and Applications Theophil Eicher, Siegfried Hauptmann ISBN 3-527-30720-6
  2. ^ A. J. Arduengo, J. R. Goerlich and W. J. Marshall (1997). "A Stable Thiazol-2-ylidene and Its Dimer". Liebigs Annalen 1997 (2): 365–374. doi:10.1002/jlac.199719970213.  
  3. ^ George Schwarz (1955), "2,4-Dimethylthiazole", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv3p0332  ; Coll. Vol. 3: 332  
  4. ^ a b Mateo Alajarín, José Cabrera, Aurelia Pastor, Pilar Sánchez-Andrada, and Delia Bautista (2006). "On the [2+2] Cycloaddition of 2-Aminothiazoles and Dimethyl Acetylenedicarboxylate. Experimental and Computational Evidence of a Thermal Disrotatory Ring Opening of Fused Cyclobutenes". J. Org. Chem. 71 (14): 5328–5339. doi:10.1021/jo060664c.  
  5. ^ a b Alessandro Dondoni and Pedro Merino (1998), "Diastereoselective Homologation of D-(R)-Glyceraldehyde Acetonide using 2-(Trimethylsilyl)thiazole", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv9p0052  ; Coll. Vol. 9: 952  
  6. ^ Elizabeta Amir and Shlomo Rozen (2006). "Easy access to the family of thiazole N-oxides using HOF·CH3CN". Chemical Communications 2006: 2262–2264. doi:10.1039/b602594c.  
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