Total synthesis of brevetoxin B; part 2: Second generation strategies and construction of the dioxepane region [DEFG]

An alternative method for the synthesis of brevetoxin B uses the heptacyclic phosphonium iodide and the tricyclic aldehyde as the basic materials for the brevetoxin B framework. The production of the tricyclic lactone and the dioxepane region of the molecule are carried out by Yamaguchi lactonization. Murai coupling which involves the addition of a higher order organocuprate to the lactone-derived enol triflate attaches the essential appendage on ring E. Fetizon cyclization produces the pentacyclic lactone while Cr/Ni coupling reaction produces allylic alcohol as a precursor to the pentacyclic lactol.