Oxidation of Alcohols and Activated Alkanes with Lewis Acid-Activated TEMPO

Abstract

The reactivity of MCl 3 (η 1 -TEMPO) (M = Fe, 1; Al, 2; TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) with a variety of alcohols, including 3,4-dimethoxybenzyl alcohol, 1phenyl-2-phenoxyethanol, and 1,2-diphenyl-2-methoxyethanol, was investigated using NMR spectroscopy and mass spectrometry. Complex 1 was effective in cleanly converting these substrates to the corresponding aldehyde or ketone. Complex 2 was also able to oxidize these substrates; however, in a few instances the products of overoxidation were also observed. Oxidation of activated alkanes, such as xanthene, by 1 or 2 suggests that the reactions proceed via an initial 1-electron concerted proton−electron transfer (CPET) event. Finally, reaction of TEMPO with FeBr 3 in Et 2 O results in the formation of a mixture of FeBr 3 (η 1 -TEMPOH) ( 23) and [FeBr 2 (η 1 -TEMPOH)] 2 (μ-O) (24), via oxidation of the solvent, Et 2 O.

Aerobic Oxidation of 2-Phenoxyethanol Lignin Model Compounds Using Vanadium and Copper Catalysts

“…Similar products have been observed for the CAN-catalyzed α-aminoxylation of ketones , and copper-catalyzed aminoxylation of ketones and hydrocarbons . Additionally, Hayton and co-workers proposed formation of an α-keto radical in a ketone (similar to compound 12 ), which is rapidly quenched by TEMPO following a one-electron concerted proton–electron transfer to produce the TEMPO-adduct …”

Recent Advances in Boron‐Substituted 1,3‐Dienes Chemistry: Synthesis and Application

“…The first step of the reaction is the addition of TEMPO molecule to the electrophilic boron atom of B(C 6 F 5 ) 2 group, which leads to intermediate zwitterionic borate anion/amine radical cation 464 . Later, instead of the well‐known H‐atom abstraction reactions, which are common for TEMPO–[M] adducts, the 4‐ exo cyclization was observed. The 4‐exocyclization process occurs by nitrogen‐radical moiety addition to the adjacent internal dienyl p ‐system and it leads to four‐membered heterocycle 465 .…”

“…This N,O-addition process occursb etween two molar equivalents of nitroxide radicals such as tetramethylpiperidine-1-oxyl (TEMPO) with, as trongly Lewis acidic, boryldienes containing B(C 6 F 5 ) 2 moiety.T he proposed mechanism for this transformation is shown in Scheme 121. The first step of the reactioni st he addition of TEMPO molecule to the electrophilicb oron atom of B(C 6 F 5 ) 2 group, which leads to intermediate zwitterionic boratea nion/amine radical cation 464.L ater,i nsteado ft he well-known H-atom abstraction reactions, whicha re common for TEMPO-[M]a dducts, [203][204][205][206][207] the 4-exocyclization was observed. The 4-exocyclization process occurs by nitrogen-radical moiety addition to the adjacent internal dienyl p-system and it leads to four-membered heterocycle 465.T his allyl radicals ite is then connected with an additional TEMPO equivalent after which the product 466 is generated (Scheme 121).…”

Iron(iv) complexes with tetraazaadamantane-based ligands: synthesis, structure, applications in dioxygen activation and labeling of biomolecules

“…23 The observed bond lengths are close to those observed in coordinated anionic hydroxylamine ligands (1.40–1.41 Å). 30–32 The N–O bond lengths in coordinated (1.30–1.32 Å (ref. 30 and 32)) and free (1.27–1.31 Å (ref.…”

“…These values are close to previously reported iron complexes with anionic hydroxylamine ligands (1.86-1.88 Å). 22,[30][31][32] In the known iron complexes with nitroxide radicals (such as TEMPO and 4,4-dimethyl-2,2-di(2-pyridyl)oxazolidine-N-oxide radical), the Fe-O distances are somewhat longer (1.88-1.90 Å). 30,32 The 36 and metal hydroxamates, 22,37 ca.…”