Synthesis of indoles via 6π-electrocyclic ring closures of trienecarbamates

A new method for the preparation of indoles from readily available α-haloenones and α-(trialkylstannyl)enecarbamates is described. Following a Stille coupling, trienecarbamate 2 is electronically activated to undergo a facile 6π-electrocyclic ring closure and subsequent oxidation to afford protected aniline 4. Upon deprotection and reductive amination, acid 5 underwent clean cyclization to N-acetylindole 6 (Ac₂O, NEt₃, 130 °C). This method has been used to construct a variety of substituted indoles that are not easily prepared by conventional indole annelation methods.