DABCO-Promoted three-component regioselective synthesis of functionalized chromen-5-ones and pyrano[3,2-c]chromen-5-ones via direct annulation of α-oxoketene-N,S-arylaminoacetals under solvent-free conditions

摘要

An efficient and convergent route to 3-aroyl-4-aryl-2-arylamino-4,6,7,8-tetrahydrochromen-5-ones and hitherto unreported 3-aroyl-4-aryl-2-arylamino-4H-pyrano[3,2-c]chromen-5-ones has been developed by an one-pot three-component domino coupling of α-oxoketene-N,,S-arylammo-acetals, aromatic aldehydes, and dimedone/4-hydroxycoumarin in the presence of DABCO under solvent-free conditions in high yields. Further, suitably substituted pyrano[3,2-c]chromen-5-ones undergo intramolecular aromatic nucleophilic substitution (S_NAr) to give pentacyclic pyrano[3,2-c]chromenoquinolines in excellent yields. The merit of this cascade Knoevenagel condensation/Michael addition/cyclization sequence is highlighted by its high atom-economy, good yields, efficiency of producing three new bonds (two C-C and one C-O), and one stereocenter in a single operation. The protocol avoids the use of expensive catalysts, toxic organic reagents/solvents, and anhydrous condition. In particular the attractive feature of this approach is the synthesis of three important bioactive heterocyclic frameworks from the same α-oxoketene-N,S-arylaminoacetal under the similar reaction conditions making this new strategy highly useful in diversity oriented synthesis (DOS).