Annulative π-Extension (APEX) of Indoles to Pyrido[1,2-a]indoles Using 4-Oxo Peroxides as C4 Units.

Annulative π-extension (APEX) of 3-substituted indoles to pyrido[1,2-a]indoles is developed by using 4-oxo peroxides as π-extending reagents, which are employed as versatile C4 building blocks. This transformation is initiated by Brønsted acid-mediated Hock rearrangement of the peroxyl group. Notably, the pyrido[1,2-a]indole products are obtained by elimination of the indole moiety from the corresponding dihydropyrido[1,2-a]indoles, which could be selectively formed at room temperature.