SmI₂-Mediated Coupling of Nitrones and <i>tert</i>-Butanesulfinyl Imines with Allenoates: Synthesis of β-Methylenyl-γ-lactams and Tetramic Acids

Nitrones and <i>tert</i>-butanesulfinyl imines undergo conjugate addition to alkyl allenoates under SmI₂-mediated reductive coupling conditions to produce novel β-methylenyl-substituted γ-amino esters. The latter were readily transformed into the corresponding β-methylenyl-γ-lactams by simple zinc reduction (<i>N</i>-hydroxy amines) or by acid hydrolysis (sulfinamides). The diastereoselective preparation of various β-methylenyl-γ-lactams offers a route to tetramic acids, the key structural features of an important class of bioactive natural products