Diels-Alder reactions with 2-(arylsulfinyl)-1,4-benzoquinones:: Effect of aryl substitution on reactivity, chemoselectivity, and π-facial diastereoselectivity

Diels-Alder reactions of (SS)-2-(2'-methoxynaphthylsulfinyl)-1,4-benzoquinone (1b), 2-(p-methoxy-phenylsulfinyl)-1,4-benzoquinone (1c), and 2-(p-nitrophenylsulfinyl)-1,4-benzoquinon (1d) with cyclopentadiene are reported. These cycloadditions allowed the highly chemo- and stereoselective formation of both diastereoisomeric endo-adducts resulting from reaction on the unsubstituted double bond C-5-C-6 of quinones working under thermal and Eu(fod)(3)- or BF3 . OEt2-catalyzed conditions. The synthesis of endo-adduct [4aS*,5S*,8R*,8aR*,SS*]-9d resulting from cycloaddition On the substituted C-2-C-3 double bond was achieved in a chemo- and diastereoselective way from quinone Id in the presence of ZnBr2. The reactivity and selectivity of the process proved to be dependent on the electron density of the arylsulfinyl group.