Oxoiminium ions for N-demethylation: 1-oxo-2,2,6,6-tetramethylpiperidinium chloride

Abstract

In an attempt to assess the synthetic utility of oxoiminium ions as oxidizing agents and to delineate their reaction mechanisms, we reacted l-oxo-2,2,6,6-tetramethylpiperidinium chloride (1) with several MlV-dialkylanilines. With jVJV-dimethylaniline the only basic product was AT-methylaniline while JV-methylformanilide was the only neutral product. The relative amounts of base and neutral product proved to be sensitive to the amount of water present in the reaction medium. With jV-alkyl-jV-methylanilines, the basic products were N-alkylanilines from exclusive loss of the IV-methyl group. The neutral products were the IV-alkylformanilides. The alkyl groups studied were ethyl, n-butyl, isopropyl, and benzyl. With IV-tert-butyl-lV-methylaniline, there was no observed reaction, and jV^V-diethylaniline was found to be significantly less reactive than JVJV-dimethylaniline. This study has shown that 1 is selective in N-demethylation of anilines in the presence of other alkyl groups either on the same nitrogen or on separate nitrogens. These results have been interpreted in terms of important steric interactions resulting from formation of an adduct en route to an intermediate iminium ion.Oxoiminium salts are an interesting but relatively unexplored class of oxidizing agents in which only a few examples1-3 have been isolated and characterized. Of these, the l-oxo-2,2,6,6-tetramethylpiperidinium ion (1) is the first to be reported1 23 4and is the most studied. The chloride

A Radical Approach to Hydroxylaminotrichlorosilanes: Synthesis, Reactivity, and Crystal Structure of TEMPO‐SiCl3 (TEMPO = 2,2,6,6‐Tetramethylpiperidine‐N‐oxyl)

“…It can be prepared directly from TEMPO and Cl 2 and has been employed as an oxidation reagent in organic synthesis. [23][24][25][26] …”

Oxoammonium‐ and Nitroxide‐Catalyzed Oxidations of Alcohols

“…12 Generally, oxoammonium salts have a reputation for being hygroscopic and unstable upon storage for long periods of time. 11,124,128,129 These traits are probably more true for the halide salts of simple TEMPO derivatives. The tetrafluoroborates appear to be more stable and non-hygroscopic.…”

Polyurethane‐ and Polystyrene‐Supported 2,2,6,6‐Tetramethyl‐ piperidine‐1‐oxyl (TEMPO); Facile Preparation, Catalytic Oxidation and Application in a Membrane Reactor

“…[1] Several functional groups are readily oxidized using nitroxides, the most prominent being amines, [2] phenols, [3] phosphines, [4] aniline [5] and alcohols. [6] Oxidation of alcohols to aldehydes, ketones and carboxylic acid is an important transformation in synthetic organic chemistry.…”

“…The new obtained polymer-supported catalysts (3,5) were applied in the partial oxidation of alcohols to the corresponding carbonyl derivatives under mild conditions in a biphasic system (H 2 O/dichloromethane, NaOCl used as co-oxidant) and/or monophasic…”