Synthesis of optically active α,β‐disubstituted β‐amino nitriles and β‐amino acids starting from asparagine

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Abstract
Starting from the enantiomerically pure building block 2 which is readily available from D‐asparagine α,β‐disubstituted β‐amino nitriles and β‐amino acids could be synthesized. After deprotonation of the nitrile α‐position the introduction of substituents was performed by alkylation of either 2 or the TBDMS‐protected derivative 3. Starting from the β homoserine equivalent 2 the reaction proceeds via a dianionic intermediate resulting in a preferred formation of the threo‐configured products 6a,b (ratio of isomers: 7:1). Modification of the side chain was demonstrated by displacement reactions with LiBH4 or potassium thioacetate.