Asymmetric Synthesis of Dihydrocoumarins through Chiral Phosphoric Acid-Catalyzed Cycloannulation of para-Quinone Methides and Azlactones.

A chiral phosphoric acid-catalyzed approach constructing dihydrocoumarin motifs by the addition of azlactones to para-quinone methides (p-QMs) was developed. The reaction proceeded smoothly with a wide range of p-QMs and azlactones to generate corresponding products in high yields with excellent diastereoselectivities (>19:1 dr) and enantioselectivities (up to 99% ee). Two possible pathways were proposed to explain the stereoselectivity.

Bismuth Triflate-Catalyzed Vinylogous Nucleophilic 1,6-Conjugate Addition of para-Quinone Methides with 3-Propenyl-2-silyloxyindoles.

A highly diastereoselective vinylogous nucleophilic 1,6-conjugate addition reaction of para-quinone methides with 3-propenyl-2-silyloxyindoles by a bismuth triflate catalyst has been developed. A number of diphenylmethane type compounds functionalized with oxindole motifs was obtained with excellent yields (up to 99%) and very good diastereoselectivities (up to Z/E > 99:1).