Stereocontrolled desymmetrization of 2,5-cyclohexadienones via organocatalytic domino sulfa-1,6-/1,4-addition or sulfa-1,6-/1,4-/sulfa-1,4-addition reactions

Abstract

We have developed a desymmetrization of 2,5-cyclohexadienone-tethered 3-cyano-4-styrylcoumarins via the amino-squaramide-catalyzed initial regio-/enantio-selective sulfa-1,6-addition to the 3-cyano-4-styrylcoumarin moiety of the substrate, followed by an intramolecular vinylogous 1,4-addition to the dienone portion. An additional sulfa-Michael addition was observed when the thiols were taken in excess to create an additional stereogenic center. With our divergent approach, two unique classes of hydrophenanthrene skeletons have been synthesized as single diastereoisomers with good to excellent yields and enantioselectivities (up to >99.5 : 0.5 er).