Thiazole intramolecular Diels-Alder reaction

Thiazoles have a low reactivity in cycloaddition reactions. However, it has been possible to achieve intramolecular Diels-Alder reactions in some cases (e.g. 362 — 363). 

Thiazoles have a low reactivity in cycloaddition reactions due to their high aromatic character. However, it has been possible to achieve intramolecular Diels-Alder reactions in some cases. The reaction of the acetylenic thiazole (66) in decalin at 350 °C affords, after loss of acetonitrile, the thiophene derivative (67) in 75% yield (Equation (16)). The reaction is also applicable to other thiazoles although with some limitations <88T3327>. 

A selected intramolecular Diels-Alder reaction of an acetylenic thiazole provided the expected thiophene product [Eq. (10)].59g... 

Unlike the case of oxazoles, the attempted intramolecular Diels-Alder reactions of thiazoles bearing electron-deficient alkynes have proved unsuccessful.59 ... 

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