Synthesis of Indole-Fused Oxepane through (4 + 3) Cycloadditions of Indolyldimethanols with Pyrazolones

An efficient phosphoric acid-catalyzed cycloaddition reaction between pyrazolones and 2-indolyldimethanols for the construction of indole-fused seven-membered oxepane skeletons was developed. This protocol featured excellent functional group tolerance, broad substrate generality, and high reaction yields. Moreover, the scalable gram-scale synthesis and facile product derivatization further demonstrated its synthetic practicability. This work provided a reliable strategy for the assembly of complex oxepane heterocyclic frameworks.