A simple, environmentally friendly, tandem C-benzylation and intramolecular O-arylation for the sequential one-pot synthesis of functionalised 4H-chromenes is reported. The reactions between 2-halobenzylbromides and cyclic-1,3-diketones were catalysed by CuO/oxalohydrazide/hexane-2,5-dione in water to produce 2,3,4,9-tetrahydro-1H-xanthen-1-ones in moderate to high yields. A simple, environmental friendly, tandem C-benzylation and intramolecular O-arylation for the sequential one-pot synthesis of 2,3,4,9-tetrahydro-1H-xanthen-1-ones in water is described.