Enantioselective addition of β-functionalized allylboronates to aldehydes and aldimines. Stereocontrolled synthesis of α-methylene-γ-lactones and lactams

We report results regarding the development of condensations of chiral β-alkoxycarbonylallylboronates on aldehydes and imines. These allylboronates add in a highly enantioselective and diastereospecific manner to afford biologically and synthetically useful chiral α-methylene-γ-butyrolactones and lactams. The nature of the electrophile (aldehyde vs imine) is shown to have a dramatic influence on the mechanism of the reaction, probably directing the stereoselectivity of the process through different transition states.