Convenient synthesis of linear 2<i>H</i>,6<i>H</i>-pyrano[3,2-<i>g</i>] chromenes from natural occurring compound; visnagin
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A simple and convenient rout for the synthesis of linear 2-imino-2<i>H</i>,6<i>H</i>-pyrano[3,2-<i>g</i>] chromen-6-ones and 2<i>H</i>,6<i>H</i>-pyrano[3,2-<i>g</i>]chromene-2,6-diones has been described starting from natural occurring furochromone; visnagin (<b>1</b>). Ring opening of <b>1</b> yielded 6-formyl-7-hydroxy-5-methoxy-2-methylchromone (<b>2</b>), which underwent reaction with different acetonitrile derivatives furnished 2-imino-2<i>H</i>,6<i>H</i>-pyrano[3,2-<i>g</i>] chromen-6-ones (<b>5a–h</b>). Acid hydrolysis of <b>5a–h</b> led to the formation of 2<i>H</i>,6<i>H</i>-pyrano[3,2-<i>g</i>]chromene-2,6-diones (<b>6a–h</b>). Structures of the synthesized compounds were clarified based on their elemental analyses and spectral data. The entire target compounds were selected for <i>in vitro</i> anticancer activity against 60 human cancer cell lines at a single dose (10<sup>−5</sup> M) by the National Cancer Institute (NCI, Bethesda, USA).
