Total Synthesis of Brevitaxin.

Brevitaxin was prepared in nine steps from commercially available carnosic acid. The construction of the 1,4-benzodioxin moiety involved an unique stepwise ortho -quinone-engaged [4+2] cycloaddition. Two strategic stages were employed to prepare the highly unsaturated cycloaddition precursor 3 : (1) synthesizing the diene moiety (C1-C2 and C10-C20 double bonds) by regioselective ortho -quinone tautomerization, and (2) installing four sp 2-hybridized carbon atoms (C3, C5, C6 and C7) in one step using a SeO 2 -promoted chemo- and regioselective oxidation reaction.