The asymmetric synthesis of all stereoisomers of α-methylthreonine using a stereodivergent synthetic route starting from (S)- and (R)-N-Boc-N,O-isopropylidene-α-methylserinals is reported. The key step involves the asymmetric addition of methylmagnesium bromide to these aldehydes with a high level of asymmetric induction being observed. This methodology represents a powerful tool for the synthesis of different β-substituted α-methylserines.