Transformation of the B Ring to the C Ring of Bryostatins by Csp3-H Amination and Z to E Isomerization.

An interesting approach to transform the B ring of bryostatins to the C ring has been developed. The key tactics of the approach feature an intramolecular Csp3-H bond amination to form spirocyclic hemiaminal, which undergoes ring opening to afford the C ring found in bryostatin 17. The subsequent epoxidation/oxidation sequence results in Z to E isomerization of the exo-cyclic enoate, delivering the common precursor, which could be transformed into the C ring found in bryostatins 1, 2, 4-9, 12, 14, and 15.