An efficient and environmentally benign synthesis of 3-substituted or 3,4-disubstituted coumarins was accomplished via iron(III) chloride-catalyzed cascade reactions of salicylaldehydes and activated methylene compounds. The reaction preceded cleanly under mild reaction conditions to provide the desired coumarin derivatives in good to excellent yields.
Titanium Tetraisopropoxide Promoted Reactions for the Synthesis of Substituted Coumarins
Substituted coumarins are synthesized by the reaction of salicylaldehyde derivatives with malonitrile, isopropyl cyanoacetate or diisopropyl malonate promoted by Ti(O-i-Pr)(4). When i-PrOH is used as a solvent, these reactions proceeded by the catalytic amount of Ti(O-i-Pr)(4) (similar to 0.1 equivalent)
One-Pot Synthesis of 3-Carboxycoumarins via Consecutive Knoevenagel and Pinner Reactions in Water
Chloro-, hydroxy-, methoxy-, and tert-butyl-substituted 3-carboxycoumarins have been prepared by one-pot procedure by reaction of suitably substituted salicylaldehydes with malononitrile in water. The over-all yields are high and the protocol does not require organic solvents.