Brønsted Acid-Catalyzed Cascade Reactions Involving 1,2-Indole Migration

A cascade reaction of indoles with propargylic diols involving an unprecedented metal‐free 1,2‐indole migration onto an alkyne was carried out. DFT calculations support a mechanism consisting of a concerted nucleophilic attack of the indole nucleus with loss of water, followed by the 1,2‐migration and subsequent Nazarov cyclization. This Brønsted acid‐catalyzed protocol affords indole‐functionalized benzofulvene derivatives in high yields. A Brønsted acid‐catalyzed cascade reaction involving an unprecedented metal‐free‐promoted 1,2‐indole migration onto an alkyne has been developed. The reaction of simple indoles with propargylic diols furnishes 2‐indol‐3‐ylbenzofulvenes in high yields and wide scope producing only water as a side product. The proposed mechanism was supported by DFT calculations.