Chiral [η6-Arene-Cr(CO)3] Complexes as Synthetic Building Blocks: A Short Enantioselective Total Synthesis of (+)-Ptilocaulin

The usefulness of the chiral transition metal π complex 1 as synthetic building block was demonstrated by its conversion into the functionalized enone 2, which in turn could be efficiently transformed into the marine natural product (+)-ptilocaulin (3). The crystal structures of 3 and rac-3 exhibit highly interesting patterns of hydrogen bonding resulting in helical or ribbonlike arrangements of the guanidinium nitrate monomers.