Neighboring Hydroxyl Group-Assisted Allylboration and Lewis Acid-Mediated Carbonyl-Ene Reaction for Access to a Hapalindole Cyclohexane Core with Multiple Contiguous Stereogenic Centers

A neighboring hydroxyl group-assisted
allylboration of 3-indolyl
ketones with γ,γ-disubstituted allylboronic acids is reported,
affording various 3-indolyl-substituted homoallylic alcohols in good
yields with excellent diastereoselectivies (up to >20:1 dr). The
hydroxyl
group not only played a vital role in the challenging allylboration
but was elaborated for the subsequent construction of a hapalindole
cyclohexane core by a highly diastereoselective Lewis acid-catalyzed
carbonyl-ene reaction. In the overall process, four contiguous stereogenic
centers including two quaternary stereogenic centers were installed.