Porphyrins in Diels–Alder reactions. Improvements on the synthesis of barrelene-fused chlorins using microwave irradiation

The microwave irradiation technique was applied to the Diels–Alder reaction of tetrakis(pentafluorophenyl)porphyrin with pentacene and naphthacene. Both reactions proceed within minutes to afford the corresponding monoadducts in 83% and 23% yield, respectively. When compared with the yields obtained under classical heating (22% and no reaction, respectively), this represents an impressive improvement of these reactions. Bisadducts (bacteriochlorins and isobacteriochlorins) are also obtained in the reaction with pentacene; these compounds are not formed under classical heating.