THE SYNTHESIS AND ELECTROPHILIC REACTIVITY OF MANGANESE TRICARBONYL COMPLEXES OF THE C-RING AROMATIC DITERPENOID METHYL O-METHYLPODOCARPATE

The aromatic ring in the diterpenoid methyl O-methylpodocarpate (podo) coordinates readily to the Mn(CO)(3)(+) moiety to afford in high yiel d a nearly 1:1 isomeric distribution of [(eta(6)-podo)Mn(CO)(3)]BF4 ([ 2]BF4), in which the metal is situated on the alpha or beta face. The nucleophiles PhLi, PhMgBr, MeLi, MeMgCl, LiCH2C(O)CMe(3) and NaBH4 wer e found to add cleanly to the activated aromatic ring in 2(+) to give neutral cyclohexadienyl complexes. Nucleophilic addition occurs predom inantly meta to the OMe substituent in the case of the alpha-isomer of 2(+), and at both ortho and meta sites in the case of the beta-isomer . The X-ray structure is reported for a typical alpha-meta and a typic al beta-ortho cyclohexadienyl product, namely beta-(eta(5)-podo.Ph)Mn( CO)(3) and alpha-(eta(5)-podo.CH2C(O)CMe(3))Mn(CO)(3) The high yield a nd regioselectivity of the nucleophilic additions suggests that the ma nganese-mediated functionalization of aromatic diterpenes and steroids will prove to provide a useful synthetic methodology.