Stereoselective assembly of a 1,3-diene via coupling between an allenic acetate and a (B)-alkylborane: synthetic studies on amphidinolide B1.

The preparation of three fragments for the total synthesis of amphidinolide B1 has been described. The C16 stereochemistry was set by asymmetric allylic alkylation. C21 and C25 stereogenic centers were set by an enantioselective/diastereoselective double allylation reaction. The C9 configuration was set by an asymmetric heteroene reaction. A differentially substituted stereodefined 1,3-diene iodide was synthesized by iodide-mediated S(N)2' reaction. A novel stereoselective method to assemble a 1,3-diene by coupling an allenic acetate and (B)-alkylborane is also reported. [structure: see text]