A green, synthesis of spiro-indene-2,6′-thiazines from tetramethylguanidine-heterocumulene and ninhydrin-malononitrile adducts

<p></p> <p>A useful and simple strategy for the synthesis of spiro(indene-2,6′-thiazine) <i>via</i> a four-component reaction between ninhydrin, malononitrile, tetramethylguanidine and heterocumulene in water at room temperature is described. The use of simple and readily available starting materials, no column chromatography, good to high yields, and short reaction times are important features of this protocol.