Chemoselective Borane‐Catalyzed Hydroarylation of 1,3‐Dienes with Phenols

Just diene to be arylated: A strategy was developed for the chemoselective hydroarylation of 1,3‐dienes with phenols through a borane‐promoted protonation/Friedel–Crafts‐type mechanism (see scheme). The transformation showed good functional‐group compatibility for the efficient synthesis of diverse ortho‐allyl phenols.

Abstract

A B(C₆F₅)₃‐catalyzed hydroarylation of a series of 1,3‐dienes with various phenols has been established through a combination of theoretical and experimental investigations, affording structurally diverse ortho‐allyl phenols. DFT calculations show that the reaction proceeds through a borane‐promoted protonation/Friedel–Crafts pathway involving a π‐complex of a carbocation–anion contact ion pair. This protocol features simple and mild reaction conditions, broad functional‐group tolerance, and low catalyst loading. The obtained ortho‐allyl phenols could be further converted into flavan derivatives using B(C₆F₅)₃ with good cis diastereoselectivity. Furthermore, this transformation was applied in the late‐stage modification of pharmaceutical compounds.

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