Asymmetric Access to α-Substituted Functional Aspartic Acid Derivatives by a [3+2] Strategy Employing a Chiral Dienophile
Résumé
Enantiopure vinyl ethers of Stericol® underwent diastereoselective thermal 1,3 dipolar cycloadditions with N-benzyl, N-benzhydryl, and N-PMB aspartate ester nitrones. Chemoselective N-debenzylation of the resulting cycloadducts afforded diastereomerically and enantiomerically pure crystalline NH-isoxazolidine, the absolute configuration of which was established by X-ray crystallography. N-Protection and N–O cleavage of this isoxazolidine gave enantioenriched quaternary aspartate derivatives bearing functionalized side chains.