Alkylation of lactam 10, first with iodide 15 and then with MeI, gave mainly (18:1) lactam 18. This was converted by treatment with t-BuLi and then with aqueous base into enone 4, which was elaborated into (-)-hamigeran B. A key feature of the last part of the synthesis is the use of t-BuMe2Si-groups (as in intermediate 24) both to direct hydrogenation from the appropriate face and to protect the benzylic C-O bond from hydrogenolysis. (C) 2003 Elsevier Ltd. All rights reserved.
Stereospecific Total Synthesis of the Antiviral Agent Hamigeran B—Use of Large Silyl Groups to Enforce Facial Selectivity and to Suppress Hydrogenolysis