We have investigated the 1,3-dipolar cycloaddition of several nitrile yields to unsaturated five, six, and seven membered lactones. The cycloaddition proceeds effectively only with very electron-poor olefins. The αmethylene-γ-butyrolactone with an exocyclic double bond is the most reactive lactone. In all cases, exo adducts are obtained as major or exclusive products.
- Nitrile ylids