Direct Asymmetric Synthesis of α-Aminoimines from 1,2-Bis-N-Sulfinylimines by Using Allyl Boronic Acids

A unique direct asymmetric synthesis of α-aminoimines is realized, through rapid and exclusive mono-allylation of chiral bis-N-sulfinylimines using allylboronic acids. The highly selective allylation was possible as electrophilic imine functional group in the product α-aminoimines remained unreactive towards allyl boronic acid nucleophiles. Notably, by varying the geometry and chiral auxiliary, all four isomers of the α-aminoimines were accessed from readily available precursors. A range of allyl nucleophiles, which are tricky to generate by other means possessing highly reactive functional groups also took part in this reaction, expanding the scope further. The applicability of the products α-aminoimines were further demonstrated by accessing a range of structurally diverse chiral cyclic and acyclic 1,2-diamines bearing adjacent stereocenters through addition of a second nucleophile or Prins-type cyclization by exploiting the nucleophilicity of the tethered alkene moiety. Moreover, the leaving group aptitude of sulfinyl auxiliary attached to imine, was exploited to access valuable chiral α-aminonitriles under thermal conditions without employing any reagents. Detailed DFT calculation revealed a chair-like transition state, arising from corresponding allylboroxine species, likely operating for the allylboration reaction across imine.