The Effect of β-Substituents in Aldol Reactions of Boron Enolates

Significance Traditional aldol reactions of boron enolates yield 1,5- anti diastereomers; forming the 1,5- syn diastereomer has proven to be challenging. This report describes that both PMB and TBS protecting groups of β- tert -butyl methyl ketones will result in 1,5- syn stereocontrol when reacting with an achiral aldehyde. These outcomes can be explained by theoretical calculations of transition states.