Pseudo-Diastereodivergent Synthesis of Chiral Fluorenes Bearing Bis-1,3-Nonadjacent Stereogenic Centers via Organocatalytic Desymmetrization of meso-Epoxides

Organocatalytic Enantioselective Synthesis of [5.7]-Fused ε-Sultam N,O-Heterocycles via (3 + 2)-Annulation of Seven-Membered Cyclic N-Sulfonylimines with γ-Hydroxy-α,β-Unsaturated Ketones

A highly stereoselective protocol for the (3 + 2)-annulation of biphenyl-bridged seven-membered cyclic N-sulfonylimines with γ-hydroxy-α,β-unsaturated ketones was developed. The reactions afforded a wide range of chiral [5.7]-fused ε-sultams bearing N-adjacent 1,3-stereocenters in excellent yields (93-98% yields) and high enantio/diastereoselectivities (up to >99% ee, >20:1 d.r.) and two other examples with alkoxyl groups were obtained in 52-61% yields, 95% ee, and >20:1 d.r. by utilizing organocatalysis with quinine-derived squaramides.

Chromium(III)-Catalyzed Desymmetrization of meso-Epoxides via Remote Stereocontrol: Synthesis of Chiral Fluorenes Bearing All-Carbon Quaternary Stereocenters

An asymmetric desymmetrization of fluorene-derived meso-epoxides is disclosed for the construction of chiral fluorenes bearing an all-carbon quaternary stereocenter at C9. This desymmetrization is catalyzed by a chiral (salen)CrIII complex via remote stereocontrol, producing diverse chiral fluorenes with excellent yields and stereoselectivity. The practicality of this protocol was demonstrated through the transformation of the obtained products to some intriguing enantioenriched polymerizable monomers.