Bi(cyclopentyl)diol-Derived Boronates in Highly Enantioselective Chiral Phosphoric Acid-Catalyzed Allylation, Propargylation, and Crotylation of Aldehydes

In this study, we disclose the catalytic
addition of bi­(cyclopentyl)­diol-derived
boronates to aldehydes promoted by chiral phosphoric acids, allowing
for the formation of enantioenriched homoallylic, propargylic, and
crotylic alcohols (up to >99% enantiomeric excess (ee), diastereomeric
ratio (dr) >20:1). These boronate substrates provided superior
enantioselectivities,
allowing for the reactions to proceed with low catalyst loading (0.5–5
mol %) and reduced reaction time (15 min at room temperature for aldehyde
allylboration). A wide substrate scope was exhibited, and the novel
boronates provided high enantiocontrol. Reactions with substituted
allylboronates and aldehydes yielded vicinal stereogenic alcohols
bearing β-tertiary or quaternary carbon centers. High enantio-
and diastereoselectivities were found due to the closed six-membered
chair-like transition state, with backbone modifications of the boronate
and its interactions with the chiral phosphoric acid being the most
likely contributing factor.