Synthesis of Indoles via Sigmatropic Rearrangements and Olefin Isomerization

Abstract

Indoles are important heterocycles in pharmaceuticals and agrochemicals, and their atom‐economical synthesis is needed. Herein, we describe the synthesis of indoles using sigmatropic rearrangements. The N‐allylaniline was oxidized by environmentally benign hydrogen peroxide, and spontaneous [2,3]‐Meisenheimer rearrangement gave N‐allyloxyaniline. Subsequent treatment with a ruthenium catalyst afforded N‐vinyloxyaniline, which underwent [3,3]‐sigmatropic rearrangement to give indoles, expelling water as the only byproduct. The whole sequence is free of quantitative salt byproducts, thereby avoiding aqueous work up and cutting off the inorganic waste.