Tandem Nitration-Cyclization-Rearrangement of Indole-Tethered 1,6-Enynes To Access NO₂-Featured Heterocycles.

An efficient cascade nitration-annulation-rearrangement of indole-tethered 1,6-enynes, tert-butyl nitrite (TBN) with O₂ was developed for the synthesis of various NO₂-dicarbonyl substituted pyrrolo[1,2-a]indole derivatives. This radical cascade process selected O₂ as the carbonyl oxygen source and low-cost TBN as the nitro reagent. Meanwhile, the stable indole skeleton could smoothly undergo rearrangement to access dicarbonyl fused cycles. In addition, complex molecular transformation and scaled-up experiments examined the application of this tandem system. Finally, diverse mechanistic studies (including isotopic labeling, radical inhibition/capturation experiments) explored the reaction pathway.