Iron/Photosensitizer Hybrid System Enables the Synthesis of Polyaryl-Substituted Azafluoranthenes

A Versatile, Functional Group-Tolerant, and Bench-Stable Iron Precatalyst for Building Arene and Triazine Rings by [2+2+2] Cycloadditions

We report an efficient iron-catalyzed cycloaddition procedure leading to the construction of (hetero)aromatic rings by alkyne [2+2+2] cycloisomerization. This method relies on the use of an air-stable (N,N)Fe(II) precursor easily prepared from a commercially available ligand derived from 1,10-phenanthroline, reduced in situ into a catalytically active non-innocent (N,N ⋅-)2Fe(II) species. This system displays a large scope application, operates under mild conditions and at low catalytic charges (25 cycloadducts formed, up to 1.5 mol% catalyst). Moreover, this method also enables access to 29 cycloadducts by cross-cycloisomerization between 1,6- or 1,7-diynes and alkynes in near-equimolar conditions. 1,3,5-Triazines can also be prepared with this procedure starting from the corresponding cyanamides. Scale-up reactions and post-functionalization of several cycloadducts also show that this [2+2+2] cycloaddition can be used in multistep sequences.

Energy transfer photocatalysis: exciting modes of reactivity

Excited (triplet) states offer a myriad of attractive synthetic pathways, including cycloadditions, selective homolytic bond cleavages and strain-release chemistry, isomerizations, deracemizations, or the fusion with metal catalysis. Recent years have seen enormous advantages in enabling these reactivity modes through visible-light-mediated triplet-triplet energy transfer catalysis (TTEnT). This tutorial review provides an overview of this emerging strategy for synthesizing sought-after organic motifs in a mild, selective, and sustainable manner. Building on the photophysical foundations of energy transfer, this review also discusses catalyst design, as well as the challenges and opportunities of energy transfer catalysis.

Modern Organometallic C-H Functionalizations with Earth-Abundant Iron Catalysts: An Update

Iron-catalyzed C-H activation has recently emerged as an increasingly powerful synthetic method for the step- and atom- economical direct C-H functionalizations of otherwise inert C-H bonds. Iron's low-cost and toxicity along with its catalytic versatility have encouraged the scientific community to elect this metal for the development of new C-H activation methodologies. Within this review, we aim to present a collection of the most recent examples of iron-catalyzed C-H functionalizations with a particular emphasis on modern synthetic strategies and mechanistic aspects.

One-Pot Synthesis of Benzo[c]phenanthridine Alkaloids from 7-Azabenzonorbornadienes and Aryl Nitrones

An efficient synthesis of benzo[c]phenanthridine alkaloids via a synergistic combination of C-C bond formation and a cycloaromatization reaction is described. Aryl nitrones react with 7-azabenzonorbornadienes in the presence of a Rh(III) catalyst, providing pharmaceutically useful benzo[c]phenanthridine derivatives in good to moderate yields. Using this methodology, highly useful alkaloids such as norfagaronine, norchelerythrine, decarine, norsanguinarine, and nornitidine were prepared in a single step.