The development of catalytic enantioselective transformations, enabling the construction of complex molecular scaffolds from simple precursors, has been a long-standing challenge in organic synthesis. Recent achievements in transition-metal catalyzed enantioselective functionalizations of carbon–hydrogen (C–H) bonds represent a promising pathway toward this goal. Over the last two decades, iridium catalysis has evolved as a valuable tool enabling the stereocontrolled synthesis of chiral molecules via C–H activation. The development of iridium-based systems with various chiral ligand classes, as well as studies of their reaction mechanisms, has resulted in dynamic progress in this area. This review aims to present a comprehensive picture of the enantioselective functionalizations of C–H bonds by chiral iridium complexes with emphasis on the mechanisms of the C–H activation step.

Densely functionalized fused aromatic triazenes can be prepared by [2 + 2 + 2] cyclotrimerization reactions of 1alkynyl triazenes. The Cp*Ru-catalyzed cyclization proceeds well both with simple alkynyl triazenes and tethered 1-diynyl triazenes. Attractively, the methodology can be extended to pyridine synthesis by replacing an alkyne with a nitrile. The reaction is regioselective and yields the sterically more hindered product. The triazene group precisely installed on the synthesized aryl and pyridyl ring is a highly versatile moiety, which is effortlessly converted into the most important and frequently used functional aryl substituents, including fluorides. It is also suited for intramolecular transformations to afford a variety of valuable heterocycles. The coordination chemistry of alkynyl triazenes and Cp*RuCl was studied, and led to the structural characterization of a Cp*RuCl(η 2-alkyne) complex, a Cp*RuCl(η 4-cyclobutadiene) complex, and an unusual dinuclear Ru complex with a bridging tetramethylfulvene ligand. Complexes of this type are potentially involved in catalyst deactivation pathways. 9 tional complexes. These species may be linked to catalyst deactivation and can provide some guidance to design even better performing catalysts. ASSOCIATED CONTENT Supporting Information Synthetic procedures, characterization data for all new compounds. This material is available free of charge via the Internet at http://pubs.acs.org.

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.

The 2-pyrone motif occurs frequently in bioactive natural products and is appreciated as synthetic intermediates. However, only few methods allow for diversifying functional group modifications on this relevant heterocycle. The...