SmI2-mediated coupling of nitrones and tert-butanesulfinyl imines with allenoates: synthesis of β-methylenyl-γ-lactams and tetramic acids.

Nitrones and tert-butanesulfinyl imines undergo conjugate addition to alkyl allenoates under SmI(2)-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 (N-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.