Beyond a solvent: HFIP as a game-changing medium in heterocyclic ring construction

1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) has emerged as one of the most powerful and versatile solvents in modern organic synthesis owing to its exceptional hydrogen-bond-donating ability, low nucleophilicity, high ionizing power, and remarkable capacity to stabilize ionic and radical intermediates. These unique physicochemical properties enable HFIP to facilitate proton transfer, activate otherwise unreactive bonds, and promote a wide range of intermolecular interactions, making it highly valuable in heterocycle synthesis. Over the past decade, the application of HFIP has expanded significantly, particularly in C-H functionalization and heterocyclic ring construction, where it frequently acts not only as a solvent but also as a promoter, cocatalyst, and reaction-directing medium. In this review, we comprehensively and critically summarize the latest representative advances in HFIP-enabled heterocyclic ring formation reported from 2022 to 2025. Particular emphasis is placed on mechanistic understanding, synthetic efficiency, substrate scope, and the multifunctional role of HFIP in controlling chemo-, regio-, and stereoselectivity. HFIP-mediated transformations often proceed under mild, metal-free, oxidant-free, or redox-neutral conditions and enable challenging cyclizations, annulations, dearomatizations, rearrangements, and cross-dehydrogenative coupling reactions that are difficult to achieve using conventional solvents. Mechanistic discussions throughout the review highlight the ability of HFIP to stabilize cationic, radical, and transition-state intermediates through extensive hydrogen-bonding networks and cooperative interactions with catalysts or reagents. For clarity, the review is organized according to the structural classes of the target heterocycles and the nature of the synthetic strategies employed. The review focuses on the construction of simple five-membered heterocycles; fused heterocyclic systems, including five-six- and six-six-fused frameworks and polycyclic fused architectures; spiro heterocycles, including five-five- and five-six-spiro systems generated through radical, ionic, electrochemical, and dearomative cascade processes; and saturated and non-aromatic heterocycles, encompassing three-, five-, six-, seven-, and nine-membered rings, mixed five-/six-membered frameworks, and polyfused saturated systems. Overall, this review demonstrates that HFIP has evolved far beyond a conventional fluorinated solvent and now serves as a powerful reaction-enabling platform in modern heterocyclic chemistry. By critically comparing recent methodologies and mechanistic paradigms, this review aims to provide a unified perspective on the expanding role of HFIP and inspire future developments in sustainable heterocycle synthesis.