catalyzed condensation/cycloisomerization/cycloaddition cascade afforded
spiroacetals 299 in good to excellent yield as single diastereomers.
Two groups have since taken advantage of this cascade-type approach for the
synthesis of berkelic acid. Fan ˜ana ´s et al. [161] modified their method to incorporate
the final ring of the tetracyclic scaffold and adapted the sequence to the large-scale
synthesis of 96 (Scheme 75).
Scheme 72 Recently disclosed mild methods for the formation of o-quinone methides
240
M.A. Brimble and L.A. Stubbing
spiroacetals 299 in good to excellent yield as single diastereomers.
Two groups have since taken advantage of this cascade-type approach for the
synthesis of berkelic acid. Fan ˜ana ´s et al. [161] modified their method to incorporate
the final ring of the tetracyclic scaffold and adapted the sequence to the large-scale
synthesis of 96 (Scheme 75).
Scheme 72 Recently disclosed mild methods for the formation of o-quinone methides
240
M.A. Brimble and L.A. Stubbing