Silver-Catalyzed Radical Cascade Cyclization toward 1,5-/1,3-Dicarbonyl Heterocycles: An Atom-/Step-Economical Strategy Leading to Chromenopyridines and Isoxazole-/Pyrazole-Containing Chroman-4-Ones

A novel and convenient silver-catalyzed radical cascade cyclization toward a large variety of 1,5-/1,3-dicarbonyl heterocycles containing a chroman-4-one, indanone, or 2,3-dihydroquinolin-4(1H)-one moiety was developed, by reacting various 2-functionalized benzaldehydes, including 2-allyloxy benzaldehydes, 2-allyl benzaldehyde, and 2-N(Ts)CH2–CH═CH2 substituted benzaldehyde, with 1,3-dicarbonyl compounds in the presence of AgNO3/K2S2O8 in one pot under mild reaction conditions. The newly obtained 1,5-/1,3-dicarbonyl-containing heterocycles were further used directly to synthesize more structurally diverse polyheterocycles, mainly including chromenopyridines as well as isoxazole- or pyrazole-containing chroman-4-ones.