The synthetically useful N-acylated oxazolidinones were also applied in the synthesis of a 2-chromanone-scaffold found in the natural products of the calomelanol family (Scheme 5). Compound 3 was reacted with phloroglucinol in toluene at 100 °C using montmorillonite K10 as catalyst giving compound 30 in 87% yield through a tandem Friedel-Craft alkylation lactonization. In summary, the first oxidative NHC-catalyzed N-acylation of oxazolidinones and pyrrolidinone has been reported. In combination with an ETM system the reaction uses molecular oxygen as a terminal oxidant in an atom efficient manner. The reaction has a high functional group compatibility, providing a broad scope of N-acylated oxazolidinones. The method was also used for the synthesis of two natural products, Piperlotine F and Piperlotine G. The acylated oxazolidinones were further modified in the synthesis of a 2-chromanone using montmorillonite K10 as catalyst. The developed methodology offers a sustainable way of using readily available aldehydes as acylation reagents circumventing the need for highly reactive prefunctionalized substrates.