Quantitative and regiocontrolled cross-photocycloaddition of the anticancer drug 5-fluorouracil achieved in a cocrystal

We describe a [2+2] cross-photocycloaddition of the anticancer drug 5-fluorouracil in the solid state that proceeds regioselectively and in quantitative yield. The photocycloaddition occurs in a cocrystal with trans-2,2′-bis(pyridyl)ethylene.