Regiospecific Synthesis of Nitroarenes by Palladium‐Catalyzed Nitrogen‐Donor‐Directed Aromatic CH Nitration

Abstract

Nitration of N‐heteroaromatics: The first example of palladium‐catalyzed direct ortho‐nitration of aryl CH bonds is described. A range of azaarenes, such as 2‐arylquinoxalines, pyridines, pyrazoles, and O‐methyl oximes, were nitrated with excellent chemo‐ and regioselectivity (see scheme; DCE=1,2‐dichloroethane). Preliminary mechanistic investigations support a silver‐mediated radical mechanism involving palladium(II/III) and/or palladium(II/IV) catalytic cycles under oxidizing conditions.

Rhodium(III)‐Catalyzed Azidation and Nitration of Arenes by CH Activation

“…In particular, pendent formyl, ester, and halogen groups should enable further functionalization. The CH nitration of arenes under palladium and copper catalysis with chelation assistance has been described previously;24 however, these systems required harsh conditions (130 °C) and a more expensive stoichiometric AgNO 3 or AgNO 2 reagent 24a,b…”

Regiospecific Synthesis of Substituted 2‐Nitrobenzaldehydes from Benzaldehydes through Palladium‐Catalyzed Chelation‐Assisted C–H Nitration

“…Surprisingly, a variety of meta ‐substituted benzaldehyde O ‐methyl oximes having two possible positions for nitration, exclusively gave one regioisomer in which the nitro group was introduced to the para ‐position relative to the already present substituent ( 2j – x , Scheme ). We speculated that such regioselectivity could be ascribed to a steric effect upon the formation of the corresponding palladacycle intermediate, thus leading to cleavage of the less sterically hindered ortho ‐C–H bond 10a,15. Apart from high regioselectivity, the present method exhibited excellent chemoselectivity; in all cases, only mononitrated products were obtained, and overnitrated products were not detected.…”

A convenient room temperature ipso‐nitration of arylboronic acid catalysed by molecular iodine using zirconium oxynitrate as nitrating species: An experimental and theoretical investigation

“…Although some reports claim successful ipso ‐nitration of arylboronic acids, yet, in most cases, use of strong acids, prolonged reaction time (30–72 h), high temperature, etc., were necessary to maximize catalytic performances. Moreover, many of them suffer limitations regarding poor substrate scope and intolerance to heterocyclic moieties.…”