New Protocols for the Assembly of the Tetracyclic Framework Associated with the Aromatic Erythrina Alkaloids

Treatment of the anion derived from the ring-fused gem-dichlorocyclopropane 4c with silver tetrafluoroborate afforded the spirocyclic compound
17 in 74% yield. Product 17 was readily converted, over three steps, into the β-iodoethyl derivative 20 and treatment of this latter compound
with n-Bu3SnH then afforded, in 93% yield and via a radical addition/elimination sequence, compound 2 incorporating the ABCD framework
of the aromatic erythrina alkaloids.