The Diels-Alder reactions of 4

4-dimethoxythiobenzophenone（2）with sorbic acid oc-curred at room temperature to afford 83%cycloadduct and 17%isomer

while the reaction withsorbic acid methyl ester occurred at room temperature and the main cycloadduct was formed. The kinetic study showed that the Diels-Alder reactions of 2 with sorbic acid and its methylester are much slower than those with trans-1-substituted -1

3-butadienes.The reactions becomethe reversible due to the fact that the dienes have two substituted groups at C

1

4