Regioselective photochemical [2+2]-cycloadditions of chromenones to substituted alkynes

With respect to the synthesis of biologically active natual products such as Blennolide A and their artificial congeners, functionalization of the chromenone scaffold remains a significant challenge.Photochemical [2+2]cycloaddition reactions between chromenone-2-carboxylate 2 and alkyl substituted alkynes were investigated.The Investigation showed that the photocycloadditions proceed in high yields and with remarkable regioselectivities when conducted in 2,2,2-trifluoroethanol (TFE) as the solvent.The cycloadducts were further functionalized by oxidative cleavage of the formed cyclobutene moiety.