A Stereoselective Switch: Enantiodivergent Approach to the Synthesis of Isoflavanones

A modular six-step asymmetric synthesis of two naturally occurring and three non-natural isoflavanones containing tertiary alpha-aryl carbonyls is reported. This synthetic route, utilising a Pd-catalyzed decarboxylative asymmetric protonation, produces isoflavanones in excellent enantioselectivities from 76-97 %. A switch in the sense of stereoinduction was observed when different H+ sources were employed, showing the first example of dual stereocontrol in an asymmetric protonation reaction. The first enantioselective synthesis of the naturally occurring isoflavanones sativanone and 3-o-methylviolanone has been accomplished.