Tandem aldehyde–alkyne–amine coupling/cycloisomerization: A new synthesis of coumarins

Abstract

Cu-catalyzed A3 coupling of ethoxyacetylene, pyrrolidine and salicylaldehydes led to a concomitant cycloisomerization followed by hydrolysis of the resultant vinyl ether to afford coumarins in a cascade process. The reaction proceeded through exclusive 6-endo-dig cyclization and is compatible with halo and keto groups giving coumarins in good to moderate yields.

Keywords

• A3 coupling
• cooperative catalysis
• coumarin synthesis
• cycloisomerization
• transition-metal catalysts