Reactions with immonium ions

Reactions with immonium ions the Mannich reaction" ... 

As shown in Table 11 and Scheme 112, a C-H bond of terminal alkynes is activated by an Au(i) species producing gold acetylenide intermediates, which react with immonium ions generated in situ from aldehydes and secondary amines to provide propargylamines in high yields. This reaction proceeds in water with 1 mol.% of Au(i) or Au(m)... 

Direct Reaction of Immonium Ions with Nitrite... 

Protonation with HCIO4 of 2-(/ -tolyl)-2,3-didehydrosparteine 76 resulted in the formation of an immonium bond gave 77 which, upon reaction with cyanide ion, led to the introduction of the cyano group in position 2 of the sparteine system affording 78 (Scheme 12) <2004JST(688)111>. 

Branching of the polymer occurs in two ways, namely (i) reaction of secondary amine groups in the polymer chain with active end-groups and (ii) formation and reaction of immonium ions within the chain ... 

An important extension of these reactions is the Mannich reaction, in which aminomethyl-ation is achieved by the combination of formaldehyde, a secondary amine and acetic acid (Scheme 24). The intermediate immonium ion generated from formaldehyde, dimethyl-amine and acetic acid is not sufficiently reactive to aminomethylate furan, but it will form substitution products with alkylfurans. The Mannich reaction appears to be still more limited in its application to thiophene chemistry, although 2-aminomethylthiophene has been prepared by reaction of thiophene with formaldehyde and ammonium chloride. The use of A,iV-dimethyf (methylene) ammonium chloride (Me2N=CH2 CF) has been recommended for the iV,iV-dimethylaminomethylation of thiophenes (83S73). 

Example The observed KER values and also peak shapes may change dramatically as Eor decreases. Here, the chain length of a leaving alkene increases with an increase of the reacting alkyl substituent. Nevertheless, the mechanism of the reaction - McLafferty rearrangement of immonium ions (Chap. 6.7) - remains unaffected. [58]... 

The formation of oxygen-containing heterocyclic compounds is also a consequence of the Maillard reaction. Amines and amino acids have a catalytic effect upon the formation of 2-furaldehyde (5), 5-(hydroxy-methyl)-2-furaldehyde (11),2-(2-hydroxyacetyl)furan (44),2 and 4-hy-droxy-5-methyl-3(2//)-furanone (111) (see Ref. 214). This catalytic effect can be observed with several other non-nitrogenous products, including maltol. The amino acid or amine catalysis has been attributed to the transient formation of enamines or immonium ions, or the 1,2-2,3 eno-lization of carbohydrates. Of interest is the detection of A -(2-furoyl-... 

When treated with formaldehyde, esters of AAs form immonium ions which undergo reaction with cyclopentadiene to give 2-azanorbornenes 58. Decomposition of 58 afforded esters of N-methylamino acids without racemization (87JOC5746). 

The immonium ion derived from oxidation of N,N-dimethylaniline can be trapped by reaction with methanol to give the relatively stable a-methoxymethyl... 

N,N-Dialkylamides undergo a related series of reaction steps on anodic oxidation. The immonium ion from dimethylformamide can be generated in solution by oxidation in acetonitrile with no added nucleophile [100]. Solutions of the ion are used in further reactions such as with 1,1-diphenylethene forming 22. When acetic... 

The Diels-Alder reaction of a-phellandrene with acrylic acid derivatives has been examined, apparently superficially in contrast to the re-investigation of the reaction with benzalbisurethane, catalysed by BF3,Et20-CuBr. The 1,4-adducts (161 endo exo/31 63) may result effertively from the concerted [4 -I-2 ] addition involving the immonium ion (PhCH=NHC02Et) however, with the corresponding unsubstituted immonium ion, formal 1,3-addition to a-phellandrene occurs essentially via the isomerized a-terpinene and isoterpinolene to yield [(162) (163)/84 16]. ... 

The first clues that compounds of structure I might be involved in nitrosamine-forming reactions came during the study of tertiary amine nitrosations. Smith and Loeppky had proposed ( ) in their detailed, classical investigation of the mechanism of this reaction that the first steps involve nitrosammonium ion formation followed by elimination of nitroxyl (HNO). The resulting immonium ion was postulated to hydrolyze to the secondary amine, which reacted with nitrosating agent to form the observed product. These mechanistic proposals are summarized in Fig. 2a. 

A similar mechanism was invoked by Ohshima and Kawabata (2) to account for their results in the nitrosation of tertiary amines and amine oxides. In applying these concepts to the nitrosative dealkylation of tetraalkyltetrazenes, Michejda al. 5) introduced an interesting variant by suggesting that immonium ions could be formed in two successive one-electron oxidation steps (for example by ferric ion oxidation of tertiary amine to the radical cation followed by radical abstraction of a hydrogen atom from the alpha position), rather than exclusively through the one-step removal of a hydride ion as nitroxyl. The resulting immonium ion was again considered to react directly with nitrite to produce the N-nitroso derivative. These reactions are summarized in Fig. 2b. 

Assuming that the above rationale for tertiary amine nitrosation was valid, we predicted 3) that the reaction of secondary amines with nitrite at milder pH s should be catalyzed by electrophilic carbonyl compounds, since secondary amines are known to form immonium ions on admixture with appropriate aldehydes and ketones. The prediction turned out to be true. Formaldehyde was shown to promote nitrosamine formation from a... 

Another possible mechanism for this reaction was suggested by Dr. G.R. Krow (private communication), this one involving a a bona fide a-amino nitrite ester as an intermediate. If the qumone monoxime tautomer of the nitrosophenol were reacting as an electrophilic carbonyl compound with the amine according to Fig. 3, the resulting immonium ion, VII, could attack nitrite to yield the nitrosamine via intermediate Ih with regeneration of the nitrosophenol. This proposal is summarized in Fig. 9. 

An alternative to the mechanism of Isbell and Frush was proposed by Deulofeu and coworkers.22 The initial stage of the reaction would be similar in the formation of the aminol precursor 94. This intermediate would be in resonance with an immonium ion 95 that, after acetyl migration, would afford 97. Nucleophilic attack by ammonia on C-l of this intermediate would give 98, and, finally, the 1,1-bis-(acylamido)-l-deoxyalditol (100), after migration of another acyl group as depicted in 99,... 

Azomethine ylides are organic 1,3-dipoles possessing a carbanion next to an im-monium ion [ 12]. Cycloadditions to dipolarophiles provide access to pyrrolidine derivatives, useful intermediates in organic synthesis with stereo- and regiochem-ical control. Azomethine ylides can be readily produced upon decarboxylation of immonium salts derived from the condensation of a-amino acids with aldehydes or ketones. When they are added to C60, a fulleropyrrolidine monoadduct is formed in which a pyrrolidine ring is fused to the junction between two six-memberedrings of afullerene [13-15].Very importantly,functionalized aldehydes lead to the formation of 2-substituted fulleropyrrolidines, whereas reaction with AT-substituted glycines leads to AT-substituted fulleropyrrolidines (Scheme 1). 

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