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

We report herein a rare example of enantiodivergent aldehyde addition with beta-alkenyl allylic boronates via chiral Bronsted acid catalysis. 2,6-Di-9-anthracenyl-substituted chiral phosphoric acid-catalyzed asymmetric allylation using beta-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 beta-2-propenyl substituted allylic boronate generated homoallylic alcohol products with S absolute configuration. Unusual substrate-catalyst C-H center dot center dot center dot pi inter- actions in the favoured reaction transition state were identified as the origins of observed enantiodivergence through DFT computational studies.

Automated summary

We report a rare example of enantiodivergent aldehyde addition with beta-alkenyl allylic boronates via chiral Bronsted acid catalysis. The use of 2,6-di-9-anthracenyl-substituted chiral phosphoric acid catalyst enabled the asymmetric allylation using beta-vinyl substituted allylic boronate, leading to alcohols with R absolute configuration. Surprisingly, the sense of asymmetric induction of the catalyst in these reactions was opposite to previous reports. Moreover, the reactions with beta-2-propenyl substituted allylic boronate under the same acid catalyst resulted in the formation of homoallylic alcohol products with S absolute configuration. Computational studies suggested that unusual substrate-catalyst C-H...pi interactions in the favored reaction transition state were responsible for the observed enantiodivergence.