Na2EDTA: an efficient, green and reusable catalyst for the synthesis of biologically important spirooxindoles, spiroacenaphthylenes and spiro-2-amino-4H-pyrans under solvent-free conditions

For the first time, the organic salt Na(2)EDTA was used as a catalyst for an effective and facile preparation of spiro-4H-pyrans via single-pot three-component condensation of isatin/acenaphthoquinone/ninhydrin, malononitrile, and CH-acids through Knoevenagel-Michael-annulation sequence. This new protocol employing Na(2)EDTA, which is a green, recyclable, and inexpensive catalyst, offers advantages such as solvent-free and highly efficient reaction conditions, short reaction times (10-15 min), easy work-up and high yields which make it more economic than other environmentally synthetic methods.