Photoredox Generated Carbonyl Ylides Enable a Modular Approach to Aryltetralin, Dihydronaphthalene, and Arylnaphthalene Lignans

A one-pot synthesis
of dihydronaphthalenes and arylnaphthalenes
from epoxides and common dipolarophiles is described. The reaction
proceeds through photoredox activation of epoxides to carbonyl ylides,
which undergo concerted [3 + 2] dipolar cycloaddition with dipolarophiles
to provide tetrahydrofurans or 2,5-dihydrofurans. In the same flask,
acid promoted rearrangement affords densely functionalized dihydronaphthalenes
and arylnaphthalenes, respectively, in an overall redox-neutral sequence
of transformations. Succinct total synthesis (4–6 steps) of
pycnanthulignene B and C and justicidin E are reported.