DDQ-Mediated Oxidative [5+2] Cycloaddition Reactions of Isochroman-4-ones with Alkynes

A DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone)-mediated oxidative [5+2] cycloaddition of isochroman-4-ones with alkynes has been described. This strategy provides an alternative method for the generation of the key benzopyrylium ylides as dipoles and affords structurally diverse benzo-fused 8-oxabicyclo[3.2.1]octanes in moderate to good yields. Mechanistic studies disclosed that the generation of benzopyrylium ylides is a radical-based process.