Scheme 4. Synthetic and NMR support for the structural reassignment of spiroviolene (4): (a) BH₃·THF (1.0 equiv.), THF, 0 °C, 5 h, then NaOH/H₂O₂ (1 : 1), 23 °C, 1 h, 58%; (b) TCDI (3.0 equiv.), 4-DMAP (0.5 equiv.), CH₂Cl₂/pyridine (1 : 1), 23 °C, 12 h; (c) n-Bu₃SnH (2.0 equiv.), AIBN (0.15 equiv.), toluene, 110 °C, 10 min, 47%; (d) 6 M HCl/THF (1 : 2), 50 °C, 4 h, >99%; (e) TCDI (4.0 equiv.), 4-DMAP (0.5 equiv.), CH₂Cl₂/pyridine (1 : 1), 23 °C, 12 h; (f) (TMS)₃SiH (4.0 equiv.), AIBN (0.2 equiv.), toluene, 110 °C, 30 min.