γ-methylidene-δ-valerolactones as a coupling partner for cycloaddition:: Palladium-catalyzed [4+3] cycloaddition with nitrones

A new type of reagent, gamma-methylidene-delta-valerolactones, has been devised, which acts as a four-carbon unit in a palladium-catalyzed cycloaddition reaction through the formation of a 1,4-zwitterionic species. The utility has been demonstrated in the context of stereoselective [4 + 3] cycloaddition with nitrones to provide highly functionalized 1,2-oxazepines, including the asymmetric variant with high enantioselectivity.