The ‘lactone method’: enantioselective preparation of novel P,N-biaryl ligands and their use in the synthesis of the biarylic alkaloids, ancistrotanzanine B and ancistroealaine A
The ‘lactone method’ is a versatile tool for the atroposelective synthesis of axially chiral biaryls. The potential and scope of the concept are highlighted, in particular with respect to its use in the preparation of natural products and chiral auxiliaries. As a new application, the synthesis of novel axially chiral phosphineamines in enantiopure form is described; these ligands were used in the asymmetric
The "lactone concept" has been efficiently employed for the first atropo-enantioselective synthesis of knipholone and related natural phenylanthraquinones. Besides the regio- and stereoselective construction of the biaryl axis, another important step was the "synthetically late" introduction of the C-acetyl group, either by a Friedel-Crafts type acetylation or by an ortho-selective Fries rearrangement