Mechanistic Insights for Nitromethane Activation into Reactive Nitrogenating Reagents
Zheng‐Wang Qu, Hui Zhu, Stefan Grimme
Abstract
Abstract Recently, it was found that nitromethane (CH 3 NO 2 ) can be activated into a useful nitrogenating reagent for the synthesis of amide and nitrile compounds. In this work, the mechanisms of CH 3 NO 2 activation are explored in detail by extensive DFT calculations. In aqueous triflic acid (HOTf) solution, the formal 1,3‐H‐shift of CH 3 NO 2 into transient CH 2 =NO 2 H is identified as the rate‐limiting step over a barrier of 29.6 kcal/mol, followed by multistep acid hydrolysis to cleave the C=N bond to form NH 3 OH + (and HCOOH) as final product. In contrast, in non‐aqueous acetic acid (AcOH) solution with electrophilic Tf 2 O and nucleophilic HCOOH additives, the C=N bond is cleaved by sequential steps of H 2 O elimination, electrophilic Tf 2 O activation, nucleophilic HCOOH addition and acetate/TfO − exchange, affording AcONH 3 + as more reactive nitrogenating reagent for Beckmann‐type reactions.