Unusual Enantiodivergence in Chiral Brønsted Acid-Catalyzed Asymmetric Allylation with β-Alkenyl Allylic Boronates

Abstract

We report herein a rare example of enantiodivergent aldehyde addition with β-alkenyl allylic boronates via chiral Brønsted acid catalysis. 2,6-Di-9-anthracenyl-substituted chiral phosphoric acid-catalyzed asymmetric allylation using β-vinyl substituted allylic boronate gave alcohols with R absolute configuration. The sense of asymmetric induction of the catalyst in these reactions is opposite to those in prior reports. Moreover, in the presence of the same acid catalyst, the reactions with β-2-propenyl substituted allylic boronate generated homoallylic alcohol products with S absolute configuration. Unusual substrate-catalyst C-H⋅⋅⋅π interactions in the favoured reaction transition state were identified as the origins of observed enantiodivergence through DFT computational studies.

Keywords: Boronates; Chiral Phosphoric Acids; C−H⋅⋅⋅π Interactions; Enantiodivergence; Organocatalysis.