O₂‐Mediated Oxidation of Aminoboranes through 1,2‐N Migration

Abstract

In analogy to the classical reaction of C-B bonds with peroxides, the first oxidative functionalization of aminoboranes through a 1,2-N migration was realized. Readily available aliphatic nitro compounds are thereby transformed into N- and O-functionalized hydroxylamines in a single synthetic operation. Addition of hazardous peroxides is avoided. Instead, the insertion of O , as the terminal oxidant, into Zn-C bonds provides the necessary peroxides. The required zinc organyls, in turn, are formed through a boron-to-zinc exchange, from an organoboronic ester byproduct of the nitro-to-aminoborane transformation.

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

“…This observation is not surprising, as the residual concentration of the zinc organyl is expected to be rather low in this reaction with the concentration of zinc salts continuously rising. Hence, a rapid boron to zinc transmetalation is promoted, and feeds the boronic ester R 1 Bpin back into the reaction sequence . Confirming the participation of B and nitrenoid II in the partial reduction of the nitro group, a stepwise reaction of 1 a with a preformed borate, [B 2 pin 2 ⋅ R 1 ] − , was also analyzed by time‐resolved 11 B{ 1 H} NMR analysis (see the Supporting Information).…”

Recent progress in the synthesis of N-substituted arylamines by reductive cross-coupling of nitroarenes

“…Based on their own previous research, the Niggemann group realized oxygenmediated oxidation of aminoboranes via 1,2-N migration; thus, N-and O-functionalized hydroxylamines were obtained from readily available aliphatic nitro compounds and organozinc reagents. 69 Subsequently, the Li group established a method for the synthesis of N,N-dialkylanilines via reductive dialkylation of nitroarenes with alkyl halides in the presence of NiI 2 and manganese powder (Scheme 43). 70 The method employs classical alkyl iodides as the alkyl source to achieve the construction of two C-N bonds in one step via a radical-mediated strategy.…”

“…Based on their own previous research, the Niggemann group realized oxygen-mediated oxidation of aminoboranes via 1,2- N migration; thus, N - and O -functionalized hydroxylamines were obtained from readily available aliphatic nitro compounds and organozinc reagents. 69…”

Recent Advances to Mediate Reductive Processes of Nitroarenes Using Single-Electron Transfer, Organomagnesium, or Organozinc Reagents

“…This nitrenoid then reacts with ZnR 2 X to produce anion 39 , which triggers a 1,2-migration to afford aminoborane 34 . 31 Hydrolysis then furnishes the secondary amine product. Analysis of the reaction using time-resolved 11 B-{ 1 H} NMR spectroscopy revealed the formation of boron anions 36 and 39 , which provided evidence for the proposed mechanism.…”