Alkynyl Triazenes as Fluoroalkyne Surrogates: Regioselective Access to 4-Fluoro-2-pyridones by a Rh(III)-Catalyzed C–H Activation–Lossen Rearrangement–Wallach Reaction
Jin-Fay Tan, Carl Thomas Bormann, Kay Severin, Nicolai Cramer
Abstract
Fluorinated pyridones are an important scaffold displaying relevant biological activities. Efficient assembly strategies of pyridones are transition metal-catalyzed C–H annulations with alkynes. The inaccessibility and extreme lability of fluoro alkynes render any direct utilization in catalysis futile. We report a highly regioselective synthesis of 4-fluoro-2-pyridones using 1-alkynyl triazenes as a convenient fluoroalkyne surrogates. The protocol comprises an alkenyl C–H annulation with 1-alkynyl triazenes followed by a treatment with HF·pyridine smoothly delivering a broad range of 4-fluoro-2-pyridones in a one-pot fashion in 90 min at 23–60 °C. Notably, a rare Lossen rearrangement occurs during the C–H functionalization part of the transformation, allowing selective access to the less-available 4-fluoro-2-pyridone framework. Furthermore, the triazenyl intermediate was elaborated into additional fluorine-containing substituents like fluorinated alkoxy and trifluoromethyl groups.