Scheme 6. (A) Radical Cascade Annulation and (B) Proposed Catalytic Cycle.

Conditions: 1a (0.2 mmol), 2b (0.4 mmol), 3b (0.8 mmol), FeCl₃(10 mol %), dcpe (20 mol %), THF (c 1.0 M), 0 °C, slow addition of 3b in 1 h, argon atmosphere. 0.4 mmol of 3b was used.

Diastereomeric ratio (dr) was determined by crude ¹H NMR.