Aerobic Lewis Acid-Catalyzed Construction of 4-Azafluorenones from 2-Arylidene-1,3-Indandiones and β-Enamino Carbonyl Compounds.

A Lewis acid-catalyzed method for the synthesis of functionalized 4-azafluorenones is reported. The reaction proceeds through a one-pot Michael addition-[3+3] annulation cascade reaction between 2-arylidene-1,3-indandiones and β-enamino ketones or esters under aerobic conditions, enabling the simultaneous formation of C-C and C-N bonds in a single operation. The protocol is transition-metal-free, operates under mild conditions, and exhibits broad substrate scope and functional group tolerance. Gram-scale synthesis and late-stage functionalization highlight the practicality of the method. Mechanistic studies support a pathway involving Lewis acid activation followed by aerobic aromatization.