Lewis Acid Catalyzed Cyclization of Propargylic Alcohols with 2‑Vinylphenol

An unprecedented
Lewis acid catalyzed, protection-free, and high-efficiency
synthesis of valuable 3,4-dihydro-2H-2,4-methanochromans
via cycloaddition of propargylic alkynols with 2-vinylphenol is described.
This cycloaddition protocol, which tolerates a wide variety of functional
groups, provides practical, versatile, and atom-economical access
to a new class of appealing bridged-ring products in satisfactory
yields. Compared with the reported reaction conditions for bridged-ring
skeletons synthesis, the present reaction conditions are neutral,
mild, and without any additives.