Influence of the Sulfinyl Group on the Chemoselectivity and π-Facial Selectivity of Diels−Alder Reactions of <i>(S)</i>-2-(<i>p</i>-Tolylsulfinyl)-1,4-benzoquinone

Diels−Alder reactions of <i>(S)</i>-2-(<i>p</i>-tolylsulfinyl)-1,4-benzoquinone <b>(1a)</b> with cyclic (cyclopentadiene and cyclohexadiene) and acyclic dienes (1-[(trimethylsilyl)oxy]-1,3-butadiene and <i>trans</i>-piperylene) under different thermal and Lewis acid conditions are reported. Chemoselectivity (reactions on C<sub>2</sub>−C<sub>3</sub> versus C<sub>5</sub>−C<sub>6</sub> double bonds) is mainly related to the cyclic (on C<sub>5</sub>−C<sub>6</sub>) or acyclic (on C<sub>2</sub>−C<sub>3</sub>) structure of the diene. The high π-facial selectivity observed could be controlled by choosing adequate experimental conditions.