Recent advances in Fe-catalyzed C–H aminations using azides as nitrene precursors

Abstract

The intramolecular Fe-catalyzed amination of C–H bonds using azides as nitrene precursors represents an elegant approach toward N-heterocycles. This review summarizes the most recent achievements while focussing on fundamental mechanistic aspects.

Iron‐Catalyzed Intramolecular C—H Amidation of N‐Benzoyloxyureas

“…[ 2 ] Iron‐catalyzed nitrene insertion is among the most attractive approaches of C—H amination due to the abundant and environmentally benign nature of iron. [ 3 ] In the last few decades, tremendously remarkable results have been disclosed with a variety of C(sp 3 )—H bonds, both activated and inert, successfully aminated in high selectivities and reactivities. Sulfamates were commonly used as the nitrene precursors in iron‐catalyzed amination reaction, but necessitated exogenous oxidants ( e.g ., bis(trifluoroacetoxy)iodo]benzene (PIFA), Scheme 1A).…”

A Bu4N[Fe(CO)3(NO)]‐Catalyzed Hemetsberger–Knittel Indole Synthesis

“…Most recently, iron complexes were shown to be potent catalysts for intramolecular C–H‐aminations using aryl or alkyl azides , . Depending on the nature of the catalyst open‐shell‐ or closed‐shell‐type C–H‐insertions are realized, which might open up new ventures in the field of C–H‐aminations . Despite these efforts, it is somewhat surprising that a third class of azides, the vinyl azides, have rarely been used in catalytic C–H‐aminations .…”

“…Azides are useful synthetic building blocks that, after either photochemical or thermal denitrogenation to the corresponding nitrene, undergo a plethora of interesting transformations such as the Curtius rearrangement of carboxylic acid azides to the corresponding isocyanates/amines, Although the formation of a stable nitrene as an intermediate is under debate, the addition of transition metal complexes leads to the formation of stable metal nitrene complexes that were shown to be reactive in a variety of amination reactions . Aryl or alkyl azides can undergo C–H‐ and C–C‐bond aminations under thermal or photochemical conditions, however, the field of transition metal‐catalyzed activation of aryl or alkyl azides as compared to the activation of acyl azides is comparably less developed , , . Most recently, iron complexes were shown to be potent catalysts for intramolecular C–H‐aminations using aryl or alkyl azides , .…”

“…Aryl or alkyl azides can undergo C–H‐ and C–C‐bond aminations under thermal or photochemical conditions, however, the field of transition metal‐catalyzed activation of aryl or alkyl azides as compared to the activation of acyl azides is comparably less developed , , . Most recently, iron complexes were shown to be potent catalysts for intramolecular C–H‐aminations using aryl or alkyl azides , . Depending on the nature of the catalyst open‐shell‐ or closed‐shell‐type C–H‐insertions are realized, which might open up new ventures in the field of C–H‐aminations .…”

Efficient Amination of Activated and Non‐Activated C(sp3)−H Bonds with a Simple Iron–Phenanthroline Catalyst

“…Our new method is clearly distinguished from reported iron catalyzed C À H aminations which most frequently employ organic azides as substrates or reagents, require hypervalent iodine oxidants, or need elaborate ligands for iron coordination, or a combination thereof. [13,14] For example, with respect to azide substrates, Betley [14f] and Che [14o] recently reported ring-closing C(sp 3 )-H aminations of organic azides to pyrrolidines using an iron-dipyrrinato complex and iron porphyrin complex with axially coordinated N-heterocyclic carbene ligands, respectively. De Bruin and van der Vlugt used an iron catalyst with a redox-active pyridineaminophenol ligand for the same conversion.…”