Asymmetric cycloadditions, diels-alder and cyclopropanation transformations, with (S)-Benzyl N-2-trifluoroacetamidoacrylyl oxazolidinone

Abstract

Asymmetric transformations to access derivatives of amino acids offer useful approaches to intermediates for target directed synthesis and for medicinal agents. Two new selective transformations are reported using S-benzyl acetamidoacrylate oxazolidinone 1 include Diels-Alder [4 + 2]-cycloaddition with cyclopentadiene and cyclopropanation via aryl tosyl hydrazones. Use of titanium (IV) chloride at room temperature (3 h) with 1 and cyclopentadiene generated the norbornene amino acyloxazolidinone product 6 (82 %) with high dienophile facial preference and 2:1 exo over endo selectivity. Cyclopropanation of 1 with phenyl tosyl hydrazone under phase transfer conditions at 60 °C gave product 8 (71 %) with 3:1 E to Z selectivity. Observed selectivity is consistent with proposed transition states of metal chelates of 1 in low energy conformation.