Single and double nucleophilic addition to methylated podocarpic acid coordinated to manganese tricarbonyl

Abstract

Coordination of the Mn(CO)(3)(+) moiety to the arene ring in dimethylated podocarpic acid (1) occurs with similar probability to both alpha and beta faces (2.). The nucleophile MeMgCl adds predominantly to the ortho C-13 site when the metal is situated beta and to the meta C-14 site when the metal is alpha, to afford cyclohexadienyl complexes 3(beta) and 4(alpha). The minor isomers 3(alpha) and 4(beta) (Nu = Me) were isolated and characterized by X-ray diffraction, from which it is concluded that the diterpenoid Me-17 group interacts sterically with a carbonyl ligand when the metal is beta and the nucleophile is at the meta C-14 position. Complexes 3(beta) and 4(alpha) are readily converted into cationic Mn(CO)(2)NO+ salts 5(beta) and 6(alpha), which add hydride ion to afford cyclohexadiene complexes. (C) 2001 Elsevier Science B.V. All rights reserved.