Metal-free hypervalent iodine/TEMPO mediated oxidation of amines and mechanistic insight into the reaction pathways

Abstract

A highly efficient, metal free rapid protocol studied mechanistically the oxidation of primary and secondary amines to their corresponding carbonyl compounds using PhI(OAc)2 and catalytic TEMPO to provide diverse products in excellent yields.

5-Endo Trig Oxidative Radical Cyclizations of Ugi-3CR Products toward 1,4-Imidazolidinones

“…Thus, consistent with the reported literature and experimental data, a plausible mechanism for this oxidative cyclization is represented in Scheme . ,− PIDA is activated by the Br – anion to afford 14 , which, with 1b , forms N–I complex 15 . The weak I–Br bond, which is prone to homolytic cleavage in 16 , may be responsible for the formation of the various radical species throughout this proposed mechanism .…”

“…The weak I−Br bond, which is prone to homolytic cleavage in 16, may be responsible for the formation of the various radical species throughout this proposed mechanism. 18 The formation of 13 (Table 2) and observation of 7v suggest formation of the α-amino radical 16, which is then oxidized to imine (17). 19 Kita has previously reported the formation of carbonyloxy radicals with PIDA, and, since the aryl amide is a bioisostere of carboxylic acids, we propose 17 undergoes N−H abstraction to form radical 18, although a nonradical process cannot be definitively ruled out.…”

Electrochemical Oxidation Dearomatization of Anisol Derivatives toward Spiropyrrolidines and Spirolactones

“…In fact, there are several challenges associated with such a transformation under electrochemical conditions: (1) Without hypervalent iodines which can selectively oxidize arenols through aryl-λ 3 -iodane species, 35 the aromatic ring will be difficult to be preferentially oxidized in the presence of amine group (XH = NHR), 36,37 which may lead to many unfavourable side reactions. [38][39][40][41][42] (2) Direct oxidation of substrates can yield active radical or radical cation intermediates, which may go through self-coupling or react with polar solvent to produce unfavoured byproduct. [43][44][45][46][47] To solve the prior challenge, methoxyamides were chosen as substrates by Nishiyama and co-workers to be employed for direct anodic oxidation with limited substrate scope and yields up to 67%.…”

2,2,6,6‐Tetramethylpiperidinyloxyl (TEMPO) Radical Mediated Electro‐Oxidation Reactions: A Review

“…Generally, in all those reactions, the oxoammonium species was regenerated by a stoichiometric secondary oxidant such as bleach, bromine, [9] or hypervalent iodine species. [10] Chemical industries for a long period were making use of the Anelli and Montanari method, which was reported in 1989, for the oxidation reactions using aqueous sodium hypochlorite as a primary oxidant under alkaline conditions. The major drawback of this method was revealed to be the generation of the undesirable hypochlorite as a byproduct.…”