Stereoselective 1,3-dipolar cycloadditions of nitrones derived from amino acids. Asymmetric synthesis of N-(alkoxycarbonylmethyl)-3-hydroxypyrrolidin-2-ones

3. Diastereoselective asym. 1,3-dipolar cycloaddns. of N-(alkoxycarbonylmethyl) nitrones derived from glycine, alanine and phenylalanine have been studied both exptl. and theor. Asym. induction is evaluated by either introducing a chiral group at the nitrone nitrogen atom or by using Oppolzer's sultam acrylamide. In both cases the sense of the asym. induction is the same, the (3R,5R)-isomer being preferentially obtained. The best results were obsd. with the chiral dipolarophile, which afforded an only isomer in all cases. The obtained isoxazolidines are easily transformed into the corresponding 5-substituted-3-hydroxypyrrolidin-2-ones. DFT studies are in a qual. agreement with the obsd. exptl. results.