Electrophilic Amination with Nitroarenes

Abstract

An exceptionally general electrophilic amination, which directly transforms commercially available nitroarenes into alkylated aromatic aminoboranes with zinc organyl compounds was developed. The reaction starts with a two-step partial reduction of the nitro group to a nitrenoid, which is used in situ as the electrophilic amination reagent. To facilitate isolation, the resulting air- and moisture-sensitive aminoboranes were reacted with a range of electrophiles. The method not only represents a direct transformation of nitro compounds into electrophilic amination reagents but also provides an elegant alternative to dehydrocoupling methods for the generation of aminoboranes.

Reductive Molybdenum‐Catalyzed Direct Amination of Boronic Acids with Nitro Compounds

“…This example clearly shows that the reaction does not proceed through the amino group, which would allow unconventional disconnections in retrosynthetic analysis.Notable performance is accomplished with nitroarenes bearing strong electron-withdrawing groups (EWG) such as cyano (7,21), ester (10, 22)o ra mide (11). Despite being areductive process,ketones (8,9,23)and even aldehydes (15)a re not reduced, as opposed to the classic reductive amination that would again require protection of these functional groups.Moreover, a,b-unsaturated carbonyls and alkenes emerged unaltered affording the corresponding diarylamines in good yields (12,16). Thep rocess has also revealed to be compatible with nitroarenes bearing several functional groups in the same ring (24-27)a nd with highly sterically demanding ortho-disubstituted nitroarenes (30), although with more moderate yields.A tt he same time, polycyclic nitroarenes are well tolerated (28, 29).…”

“…[15] More recently,N iggemann has described an elegant reductive coupling of zinc organyls with both aromatic and aliphatic nitro compounds.This is based in the partial reduction of the nitro group with B 2 Pin 2 that yields an itrenoid as the electrophilic amination reagent (Scheme 1c). [16] Despite the potential of this transformation, it is currently underexploited since af ine tuning of the nitrenoid could allow the amination of less nucleophilic reagents such as boronic acids.…”

Catalyst‐Free Reductive Coupling of Aromatic and Aliphatic Nitro Compounds with Organohalides

“…Among these, THF proved best (entry 11). Unexpectedly, the omission of the NEt 3 additive, which was crucial for the suppression of aniline formation in our previous work, further improved the result, allowing the isolation of 3 a in 93 % yield (entry 12). The amount of zinc was reduced to 4 equivalents with no loss in efficiency (entry 13), while less proved insufficient (entry 14).…”

Photoinitiated carbonyl-metathesis: deoxygenative reductive olefination of aromatic aldehydes via photoredox catalysis

“…With these mechanistic challenges in mind, we envisioned the possibility of combining the photocatalytic carbonyl reduction system with a diboron reagent allowing an efficient McMurry-type process based on the following considerations: (1) the Lewis acidity of the boron atom of the diboronate compounds could potentially activate the carbonyl groups thus facilitating the single electron reduction process 16. (2) The formation of a strong B–O bond would provide a significant thermodynamic driving force for the deoxygenation process 16b,17…”