BINAPHANE-Catalyzed Asymmetric Formal [2+2] Cycloaddition

Significance

Kerrigan and co-workers report a [2+2] cycloaddition of aldehydes and ketenes ­catalyzed by BINAPHANE providing access to highly substituted β-lactones. A variety of arylketo-ketenes and a range of electron-poor as well as electron-rich aldehydes could be applied in the developed method forming the corresponding products in high enantio- and diastereoselectivity. Noteworthy is the activation of unactivated aliphatic aldehydes with a high level of asymmetric induction (er > 95:5). Two competing mechanistic pathways are suggested to proceed via a phosphonium alkoxide (mechanism A) or via a phosphonium enolate intermediate (mechanism B).