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.
Key words
substituted tetrahydrofurans - chiral phosphoric acid - cascade reaction - allylboration
- oxa-cyclization