Substituted 3-E-styryl-2H-chromenes and 3-E-styryl-2H-thiochromenes: synthesis, photophysical studies, anticancer activity, and exploration to tricyclic benzopyran skeleton.

A series of densely substituted 2H-chromenes and 2H-thiochromenes were synthesized in good yield through cyanuric chloride-dimethylformamide mediated cleavage of different spiro-4-hydroxychroman-3,1'-cyclopropanes and similar thiochroman analogues. This protocol involves operationally very simple, facile and cost-effective reactions using easily accessible reagents under mild reaction condition with tolerance of a variety of sensitive moieties. Results of steady state and time-resolved absorption and emission spectroscopy highlighted the potential of these compounds as fluorescence probes and designated the suitability for subcellular bioimaging. The prepared 2H-chromenes demonstrated profound cytotoxic activity against MCF-7 cell line. DFT calculations were done on a representative compound where the results indicated promising reactivity of the title compounds as electron-donating dienes. As a continuation, some of these compounds underwent [4 + 2] Diels-Alder cycloaddition with electron-deficient dienophiles in the absence of any activator or catalyst, which provided an easy access to an array of hitherto unreported molecular frameworks related to bioactive cannabinoid skeletons. These newly constructed Diels-Alder adducts also bear substantial antiproliferative properties.