Chiral Phosphoric Acid Catalyzed Cascade Asymmetric Allylboration/Oxa-Cyclization of Aldehydes for Access to Multisubstituted Tetrahydrofurans

Abstract Optically pure homoallylic alcohols, important synthons for natural products and bioactive compounds, can be assembled by a chiral phosphoric acid catalyzed asymmetric allylboration of aldehydes. Based on this reaction, two unprecedented cascade reactions of functionalized aldehydes (allylation/oxa-Michael or oxa-Pictet–Spengler reactions) for the synthesis of chiral 2,5-disubstituted and 2,2,5-trisubstituted tetrahydrofurans using a single chiral phosphoric acid catalyst have been developed. The reaction mechanism proposed here of the oxa-Pictet–Spengler reaction was investigated through control experiments.