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

Paper based on a presentation at the 14th International Symposium on Organometallic Chemistry Directed Towards Organic Synthesis (OMCOS-14), 2-6 August 2007, Nara, Japan. Other presentations are published in this issue, pp. 807-1194A new type of reagent, γ-methylidene-δ-valerolactones, has been devised, which acts as a four-carbon unit in a Pd-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. [ABSTRACT FROM AUTHOR]