Amines aminium salts

No other adducts are formed, and the endo/exo diastereomeric ratio is essentially the same for all of these methods. Further, the existence of an acid catalyzed mechanism for cycloaddition can be explicitly excluded by using an excess of a hindered amine base (2,6-di-tert-butylpyridine, DTBP) in the aminium salt induced reaction and by examining the results of an authentic acid catalyzed reaction (using, for example, triflic acid). In the former case, the same endo and exo adducts are formed in virtually the same relative amounts, but in the latter case neither of these adducts is formed. It is worth noting that acid catalyzed reactions have indeed sometimes been observed under typical aminium salt conditions [70], but these have never been observed, nor would they be expected, under PET conditions. Finally, in the instance where cation radicals are generated by the aminium salt method, the intervention of substrate cation radicals can usually be verified by the addition of the reduced form of the catalyst, i.e., the neutral triarylamine, to the reaction mixture. 

For workup the solution was quenched by the addition of a solution of NaOMe in MeOH. More CHjClj was added to dissolve all of the products and the mixture was extracted in a separating funnel successively with H2O, sat. aq brine and HjO. The organic solution was then dried and filtered by passing it through a plug of cotton. The solution was concentrated on a rotary evaporator and the product mixture analyzed by GC (30-cm column, 5% OV-101). Preparative separations were effected either by GC or by TLC. In the latter case, some of the free amine could be removed by decanting the product mixture from the precipitated free amine. The insolubility of the free amine became evident as the solution was concentrated and subsequently cooled. In large-scale syntheses the recovered free amine could be recycled to the aminium salt. The product usually ran at Rj- values between that of the free amine and the diazo ester. 

When primary, secondary, and tertiary amines act as bases and react with acids, they form compounds called aminium salts. In an aminium salt the positively charged nitrogen atom is attached to at least one hydrogen atom ... 

Alkylation of Ammonia Salts of primary amines can be prepared from ammonia and alkyl halides by nucleophilic substitution reactions. Subsequent treatment of the resulting aminium salts with a base gives primary amines ... 

Couplings between arenediazonium cations and amines take place most rapidly in slightly acidic solutions (pH 5—7). Under these conditions the concentration of the arenediazonium cation is at a maximum at the same time an excessive amount of the amine has not been converted to an unreactive aminium salt ... 

Amines form relatively stable radical cations, and back electron transfer often overrides chemical reactions, except in the presence of good electrofugal groups in the a—position. Nevertheless, a-deprotonation (or alternatively a proton or hydrogen transfer process within an exciplex) may be fast enough to cause addition to unsaturated esters and ketones, " aromatics, and arylalkenes." " Deprotonation and further oxidation of some tertiary amines appear to produce aminium salts that are then aUylated by aUyl radicals simultaneously produced by fragmentation of allylsilane. Both processes are brought about by photosensitized electron transfer." ... 

Asymmetric Michael Reactions. Asymmetric induction has been observed in Michael-type addition reactions that are catalyzed by chiral amines. The Ai-benzyl fluoride salt of quinine has been particularly successful since the fluoride ion serves as a base and the aminium ion as a source of chirality. Drastic improvements in optical purity (1-23%) have resulted by changing from quinine to the N-benzyl fluoride salt (eq 11). ... 

The amine radical cation formed in the initial one-electron-transfer process de-protonates at the oc-carbon and the amino alkyl radical formed is oxidized to the iminium salt which hydrolyzes to the dealkylated amine and a carbonyl compound. With the use of benzoyl peroxide as oxidant the aminium radical is also believed to... 

Various aminoalkyl and alkylaminoalkyl halides react with starch in alkaline media and are readily available by the reaction of epichlorohydrin with primary, secondary, and tertiary amines and even aqueous ammonia. Prior to the reaction with starch, the quaternary ammonium compounds were either decomposed to free amines, or they reacted as amminium compounds to give cationic aminium starches. Cationic starches were produced by the reaction of starch with arylalky-laminoalkyl epoxides. In the presence of formaldehyde, inorganic ammonium salts provided the source of amino groups.1316... 

Wieland, 1907 Wieland and Wecker, 1910). Oxidation was carried out in an inert solvent such as benzene, from which the salt precipitated. The easier and more reliable preparation of perchlorate salts by the iodine-silver perchlorate method (Weitz and Schwechten, 1926, 1927), to which we have referred earlier (p. 168), allowed a much clearer understanding of the nature of triarylaminium ions to be obtained. Isolation of perchlorates permitted chemical studies, and easy reduction to the triarylamine by iodide ion, ferrous ion, etc., was consistent with the cation-radical view that was developed. The name aminium ion was coined by Weitz. Other salts were prepared such as tritolylaminium picrate (by oxidation of the amine with lead dioxide in the presence of picric acid), and it was also recognized that conjugate anions in salts obtained by oxidation with antimony pentachloride, phosphorus pentachloride and ferric chloride had to be complex anions rather than simple anionic radicals. This is a particularly pertinent point in antimony pentachloride oxidations (p. 165). 

The mechanism in Scheme 8 was proposed for the oxidation reaction. In the first step, the Cu(II) salt, which is formed in the autooxidation of cuprous chloride, forms a complex with the amine. This is followed by a rate-determining electron transfer from the amine to the Cu(II) species giving Cu(I) and an aminium radical. The subsequent steps were considered to be fast. The authors accounted for the secondary hydrogen-deuterium kinetic isotope effect by suggesting that there was hyperconjugative electron release to the aminium ion nitrogen that forms in the slow step of the reaction. 

Asymmetric Michael addition. Michael addition of nitromethane to chalcone (equation I) in the presence of a chiral amine (quinine, N-methylephedrine) proceeds in methanol (but not in aprotic solvents) in 60-807) yield, but the optical yield at best is 17>. However, if these amines are converted into aminium fluorides, the addition takes place in aprotic solvents (CaHsCHg, CH3CN) in 50-100% yield of more interest, asymmetric inductions of 207, can be obtained. (- )-BenzyIquininium fluoride (1) is particularly effective. The hydroxyl group in these salts is believed to play an important role in the stereochemical outcome of the reaction. Moreover, the fluoride ion is important as a strong base. 

It has recently become appreciated that cysteine derivatives can undergo substantial levels of racemization specifically at the step where they are incorporated (58-60). For example, standard protocols for coupling mediated by the recently popularized phosphonium and aminium (uroniuni) salts (BOP, PyAOP, HBTU, HATU) (61) typically involve 5-min pre-activation times and are conducted in the presence of suitable additives, such as FIOBt or HOAt, plus a tertiary amine base, such as DIPEA or NMM. Under such conditions, the levels of racemization in a model peptide were in the range 5-33% (60). However, these levels were in general reduced by a factor of six-or sevenfold by avoiding the pre-activation step (60). Additional strategics to... 

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