Synthesis of Fluoromethyl‐Substituted Cyclopentanones via Radical Fluorination and 1,2‐Alkyl Migration Cascade of Alkenyl Cyclobutanols

Hypervalent Fluoro-iodane-Triggered Semipinacol Rearrangements: Synthesis of α-Fluoro Ketones

Hypervalent fluoro-λ3-iodanes have emerged as versatile reagents that provide unusual fluorination selectivities under mild reaction conditions. Here, we report on adding a semipinacol rearrangement, fluorination, and aryl migration cascade reaction of styrene derivatives. Thus, various cyclopentanones became accessible in up to 96% yield, all bearing tertiary C,F-carbon centers adjacent to the ketone group. Such fluorinated structural motifs are difficult to build with previously established methods. Preliminary experiments on enantioselective processes validated that asymmetric transformations are likewise feasible.

Small rings in the bigger picture: ring expansion of three- and four-membered rings to access larger all-carbon cyclic systems

The release of the inherent ring strain of cyclobutane and cyclopropane derivatives allows a rapid build-up of molecular complexity. This review highlights the state-of-the-art of the ring expansions of three- and four-membered cycles and is organised by types of reactions with emphasis on the reaction mechanisms. Selected examples are discussed to illustrate the synthetic potential of this elegant synthetic tool.

Iodine(III)-Mediated Fluorination/Semipinacol Rearrangement Cascade of 2-Alkylidenecyclobutanol Derivatives: Access to β-Monofluorinated Cyclopropanecarbaldehydes

A hypervalent iodine(III)-mediated ring-contractive fluorination reaction of 2-alkylidenecyclobutanol derivatives is presented. The protocol allows the facile synthesis of β-monofluorinated cyclopropanecarbaldehydes via a fluorination/semipinacol rearrangement cascade using nucleophilic Py·HF as the fluorine source. For challenging electron-rich arene substrates, the installation of a protecting group on the free alcohol is pivotal for maintaining the reaction efficiency. The synthetic utility was demonstrated by the scalability of this reaction and further transformations of the products.

Photoredox-mediated N-centered radical addition/semipinacol rearrangement for the convenient synthesis of β-amino (spiro)cyclic ketones

A photoredox-mediated N-centered radical addition/semipinacol rearrangement cascade of cycloalkanol-substituted 1H-indenes or styrenes with N-arylsulfonyl protected 1-aminopyridinium salts for the efficient synthesis of β-amino (spiro)cyclic ketones is presented.