An enantioselective total synthesis of (+)-picrasin B

An enantioselective total synthesis of (+)-picrasin B (1) from the R-(-)-enantiomer of the Wieland-Miescher ketone (4) employed an A-AB-ABC-ABCD sequence to assemble the tetracyclic skeleton and relied upon a free radical cyclization of an α-bromoacetal to an enone in order to introduce the D ring and a manganese(III) acetate oxidation of a tricyclic enone intermediate in order to introduce the C-11 oxygen substituent.