Palladium-Catalyzed Cascade Endo - dig Cycloisomerization and Olefination with Alkenes to Access Fused Oxatricyclic Compounds

A novel cascade Pd(II)-catalyzed endo-dig cycloisomerization and olefination reaction of 2-benzyl-3-alkynyl chromones with activated/unactivated alkenes has been developed for the synthesis of fused oxatricyclic compounds. This concise one-pot synthetic approach was applied to the difunctionalization of unbiased alkynes based on 2-benzyl-3-(alkynyl)-4H-chromen-4-one via O-attack endo-dig cycloisomerization, followed by olefination with both activated and unactivated alkenes.