Synthesis of natural (−)-hamigeran B

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.