Utilization of Sulfide, Sulfoxide, and Sulfone Groups as Regiochemical Control Elements in the Diels–Alder Reaction of Naphthoquinones

Abstract

Abstract 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 sulfoxide group. As a result of this study, several anthraquinones including natural products, such as pachybasin and phomarin 6-methyl ether, and 11-deoxyanthracyclinones were efficiently synthesized.