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.