Diastereoselective Synthesis of β‑Heteroaryl <i>syn</i>-α-Methyl-β-Amino Acid Derivatives via a Double Chiral Auxiliary Approach

The addition of the SuperQuat enolate to five- and six-membered heterocyclic tert-butyl sulfinimines led to a high syn-selectivity of up to 99:1 in good to excellent yields. The reaction is tentatively proposed to proceed through an open-chain transition state with the presence of an α-heteroatom on the sulfinimine leading to high diastereoselectivities. The adducts were derivatized to β-amino esters and amides in a facile manner.