Stereoselective synthesis of axially chiral natural products, (-)-steganone and O,O′-dimethylkorupensamine A, utilizing planar chiral (arene)chromium complexes

Palladium(0)-mediated Suzuki-Miyaura cross-coupling of planar chiral (2,6-disubstituted bromobenzene)chromium complexes with o-substituted arylboronic acids in the presence of sodium carbonate under refluxing in aqueous methanol gave stereoselectively axially chiral mono Cr(CO)(3)-complexed biaryls. The axial stereochemistry of the cross-coupling products was found to be largely dependent on the steric bulkiness of ortho substituent of arylboronic acids and reaction conditions. The cross-coupling with o-alkyl or hydroxymethyl substituted arylboronic acids gave kinetically controlled products in which the ortho substituents were oriented in syn-configuration to the tricarbonylchromium fragment. On the other hand, o-formyl phenylboronic acid produced thermodynamically stable anti-coupling products under the same conditions. By utilizing these methodologies, biologically active axially chiral natural products, (-)-steganone and O,O-1-dimethyl derivative of the natural product of korupensamine A, were stereoselectively synthesized. (C) 2000 Elsevier Science Ltd. All rights reserved.