The Diels–Alder reactions of 2-phenylthio-, 2-phenylsulfinyl-, and 2-phenylsulfonyl-1, 4- naphthoquinones, which were unsymmetrically substituted by methoxyl group on the benzenoid ring, with some vinylketene acetals were studied. The regioselectivity of the reactions was cleanly controlled by each of these sulfur substituents. In addition, the reactivity of the naphthoquinones were greatly enhanced by introduction of the sulfone or ...
