Thiazole and thiadiazole .S -oxides

Heteroaromatic sulfur compounds do form sulfoxides and sulfones, but these derivatives have their own special reactivity. Francesca Clerici (Milan, Italy) has now provided an up-to-date survey of the preparation and properties of the S-oxides of thiazoles and thiadiazoles, collecting literature scattered in many publications. 

Elimination of the ring s x-orbital delocalization in five-membered heterocycles is a most efficient chemical manipulation used to synthesize highly reactive dienes for Diels-Alder reactions from heterocycles that would otherwise not readily participate in the Diels-Alder reaction. One way to accomplish this goal using heterocycles that contain sulfur atoms is through their oxidation to sulfone derivatives. We will demonstrate the usefulness of this approach by studying the reactivity of 1,3-thiazole 1,1-dioxide and 1,3,4-thiadiazole 1,1,-dioxide as dienes for Diels-Alder reactions with acetylene, ethylene, and cyclopropene. 

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