Asymmetric inverse electron-demand 1,3-dipolar cycloaddition of ynolates with a chiral nitrone derived from L-serine leading to β-amino acid derivatives

Asymmetric 1,3-dipolar cycloaddition of lithium ynolates with a nitrone derived from Garner's aldehyde is described. The cycloadducts, 5-isoxazolidinones, were obtained in good yields with high diastereoselectivity. Alkylation of the intermediates, the 5-isoxazolidinone enolates, was also achieved with high selectivity, the products of which were converted into the enantiomerically pure β-amino acids, β-lactams, and γ-lactams. In our cycloaddition, lithium ynolates proved to be much better as nucleophiles than lithium enolates.