Applications of Cheletropic Reactions

The cheletropic elimination reactions are widely used for generation of relatively unstable dienes in situ for Diels-Alder reactions. For example, extrusion of nitrogen from diazene 146, and sulfur dioxide from 2,5-dihydrothiophene-l,1-dioxide 147 

Extrusion of carbon monoxide from Diels-Alder adducts 149 and 150 gives benzene and cyclopentanone derivatives [157, 158]. 

Cheletropic eliminations of SO2 from cycloadducts 151-155 generate dienes and triene, which are usedin Diels-Alder and electrocyclic reactions. 

Cheletxopic addition of SO2 to a polyene depends on the geometry of the intrusion adduct. For example, cheletropic addition of SO2 to 1,3,5-cyclooctatriene 156 gives cycloadduct 157 using 4jt e system in a disrotatory motion process [163]. 

Similarly, the reverse process of extrusion is more facile for 6e process. For example, the adducts 158 and 159, on heating above 300 °C undergo extrusion process the rate of 158 is about 60,000 times faster than 159 [163]. 

---