One-pot construction of highly functionalized 4H-chromenes using K-10 montmorillonite in aqueous medium

Herein, we report the first one-pot K-10 montmorillonite-promoted construction of densely functionalized 4H-chromene skeletons, which are broadly existing structural motifs in natural products and pharmaceutically active molecules, from salicylaldehydes, dimedones and carbon, nitrogen, or sulfur-based bioactive nucleophiles in aqueous medium. Easy recovery and reusability of K-10 montmorillonite without significant reaction erosion, in a short reaction time, with broad substrate scope, and excellent yields, without requiring a toxic organic solvent during the entire process makes this protocol very useful for both industry and academia. Montmorillonite was proven to be the key to furnishing the reactions because the use of other catalysts other than montmorillonite predominantly afforded many side products.