Reaction of Indole‐2‐Carboxylates/Carboxylic Acids with Propargylic Alcohols: Dearomative Ring Expansion/Spirocyclization vs Fused Pentacyclics

Abstract Dearomative ring expansion/spirocyclization of indole‐2‐carboxylates with propargylic alcohols bearing electron‐withdrawing aromatic groups in the presence of PTSA leading to spiro[benzo[b]oxazine‐furans] via oxygen insertion along with dihydrocyclopenta[e]indole‐2‐carboxylates is developed; the same reactants under moderately high temperatures, afford fused pyrano‐indolones. In contrast, copper(II) catalyzed annulation of indole‐2‐carboxylic acids with propargylic alcohols at room temperature provides rapid access to a different class of pentacyclic indene fused pyrano‐indolones. magnified image