Abstract
Allyl- and crotylboration of aldehydes is a useful and interesting transformation, due to predictable stereochemical outcomes which can be understood through cyclohexane chair-like transition state models. We have recently found that cyclopropanated allyl- and crotylboronate reagents react through transition states analogous to allylation; in an equally predictable manner, they stereoselectively deliver structural motifs which were difficult to access through previous methods. Although this reaction was originally promoted by stoichiometric amounts of PhBCl2, we have recently found that boron carboxylates can catalyze homoallylation by a ligand exchange mechanism. Herein, we report further explorations in this mode of catalysis, using chiral and achiral ligands including carboxylates and phosphates.