Iodine-catalyzed oxidative annulation: facile synthesis of pyrazolooxepinopyrazolones via methyl azaarene sp 3 C-H functionalization.

An iodine-catalyzed methyl azaarene sp 3 C-H functionalization has been developed for the synthesis of a seven-membered O -heterocyclic architecture containing three different heterocyclic aromatic hydrocarbons. This method can be applied to a wide range of substituted methyl azaarenes and diverse 2,4-dihydro-3 H -pyrazol-3-ones, and brings about the efficient preparation of 2,9-dihydrooxepino[2,3- c :6,5- c ']dipyrazol-3(7 H )-ones in high yields with the merits of low catalyst loading, good functional group tolerance and metal-free conditions.