Catalytic Asymmetric Synthesis of Chiral Dihydrobenzofurans through a Formal [4+1] Annulation Reaction of Sulfur Ylides and In Situ Generated orthoortho ‐Quinone Methides

摘要

> The first example of a catalytic asymmetric formal [4+1] annulation reaction between sulfur ylides and in situ generated ortho ‐quinone methides ( o ‐QMs) is reported in this work. A C 2‐symmetric chiral urea was identified to be the best H‐bonding catalyst, affording a wide range of chiral 2,3‐dihydrobenzofurans in high yields and moderate enantioselectivities [70–98?% yields, up to 89:11 e.r. (enantiomeric ratio)].