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Synthesis of the diversifiable pentacycline precursors 43 and 44 by Michael–Claisen cyclization using the benzylic bromide 42 and enone 1 as substrates, with an in situ protocol for selective lithium-halogen exchange. Further transformation of 44 by a reductive amination reaction provides a route to alkylaminomethylpentacyclines, as illustrated by the synthesis of the tert-butylaminomethylpentacycline 45.
