An Acid Catalyzed Alkynyl‐Prins Cyclization–Rearrangement Cascade of 2‐(Alkynol)benzoates: An Approach to 3‐Alkyl‐[n,5]‐oxaspirophthalides

Abstract The oxaspiro‐phthalides ([n,5]‐oxaspirobenzalactones) bearing a phthalide spirofused to a cyclic‐ether of various sizes are frameworks found in bioactive natural products. The discovery and development of an alkynyl‐Prins cyclization based, strategy for the construction of structurally interesting, medicinally useful [5,5]‐[6,5]‐, and [7,5]‐oxaspirophthalides is reported in this manuscript. Our strategy represents a report on the construction of oxaspiro‐phthalides using the alkynyl‐Prins cyclization. This approach exhibits broad substrate scope with respect to carbonyl compounds and 2‐(alkynol)benzoates, with yields ranging between 43–98%. Isolation of intermediate, and further conversion of it to the end‐product supported the proposed mechanistic pathway.