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

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.

Automated summary

Dearomative ring expansion/spirocyclization and annulation of indole-2-carboxylates with propargylic alcohols under different conditions lead to the synthesis of spiro[benzo[b]oxazine-furans] and fused pyrano-indolones, respectively, showcasing the versatility of these reactions in accessing diverse pentacyclic indene fused compounds.