Pyridinium alkylation

The effect of variation of the length of the pyridinium alkylating agent was also investigated by Zhu et at. (1992d). It was found that both the counterion and the hydrophobic ty of the quaternization agent (alkyl iodide or bromide) determined whether the surface micelles were surface-adsorbed (starfish conformation) or were submerged (jellyfish conformation). In one extreme, the C]0 and C 8 alkyl chain derivatives formed starfish micelles at low surface pressures. In... 

Deoxygenation of aUyBc and benzyUc alcohols. Allylic and benzylic alcohols are conveniently reduced to the corresponding hydrocarbons in two steps. The alcohol is first converted into a pyridinium alkyl sulfate by reaction with sulfur trioxide-pyridine in THF at 0-3° (3-20 hours). Then lithium aluminum hydride (or LiAIH -AlClj, 3 1) in THF is added and the mixture stirred for I hour at 0° and then at 25° for 3-5 hours. Yields are high. In the case of allylic alcohols... 

A wide class of aiyl-based quaternary surfactants derives from heterocycles such as pyridine and quinoline. The Aralkyl pyridinium halides are easily synthesized from alkyl halides, and the paraquat family, based upon the 4, 4 -bipyridine species, provides many interesting surface active species widely studied in electron donor-acceptor processes. Cationic surfactants are not particularly useful as cleansing agents, but they play a widespread role as charge control (antistatic) agents in detergency and in many coating and thin film related products. 

Two synthetic bridged nitrogen heterocycles are also prepared on a commercial scale. The pentazocine synthesis consists of a reductive alkylation of a pyridinium ring, a remarkable and puzzling addition to the most hindered position, hydrogenation of an enamine, and acid-catalyzed substitution of a phenol derivative. The synthesis is an application of the reactivity rules discussed in the alkaloid section. The same applies for clidinium bromide. 

Usually, organoboranes are sensitive to oxygen. Simple trialkylboranes are spontaneously flammable in contact with air. Nevertheless, under carefully controlled conditions the reaction of organoboranes with oxygen can be used for the preparation of alcohols or alkyl hydroperoxides (228,229). Aldehydes are produced by oxidation of primary alkylboranes with pyridinium chi orochrom ate (188). Chromic acid at pH < 3 transforms secondary alkyl and cycloalkylboranes into ketones pyridinium chi orochrom ate can also be used (230,231). A convenient procedure for the direct conversion of terminal alkenes into carboxyUc acids employs hydroboration with dibromoborane—dimethyl sulfide and oxidation of the intermediate alkyldibromoborane with chromium trioxide in 90% aqueous acetic acid (232,233). 

Reactive halogen compounds, alkyl haUdes, and activated alkenes give quaternary pyridinium salts, such as (12). Oxidation with peracids gives pyridine Akoxides, such as pyridine AJ-oxide itself [694-59-7] (13), which are useful for further synthetic transformations (11). 

Alkyl and aryl isocyanates react with anhydrous hydrogen fluonde to give carbamyl fluorides [J, 55], the more conveniently handled pyridinium poly(hydro-gen fluoride) reagent can also be used, although the yields tend to be poorer [9] (equation 10). 

Organometallic reagents react with iminium salts to give C-alkylated products. The reactions can be divided into two categories the reactions of pyridinium, quinolinium, and isoquinolinium salts and the reactions of... 

The Zincke reaction is an overall amine exchange process that converts N- 2,A-dinitrophenyl)pyridinium salts (e.g, 1), known as Zincke salts, to iV-aryl or iV-alkyl pyridiniums 2 upon treatment with the appropriate aniline or alkyl amine. The Zincke salts are produced by reaction of pyridine or its derivatives with 2,4-dinitrochlorobenzene. This venerable reaction, first reported in 1904 and independently explored by Konig, proceeds via nucleophilic addition, ring opening, amine exchange, and electrocyclic reclosure, a sequence that also requires a series of proton transfers. By... 

Likewise, a cis-2,6-disubstituted piperidine natural product, (-)-lobeline (98, Scheme 8.4.30) was synthesized from the chiral Af-alkyl pyridinium salt ent-80 via a sequence that included addition of a Reformatsky reagent to an intermediate oxazolidine. °... 

Chiral dihydropyridines such as 103 were also accessible from Zincke-derived N-alkyl pyridinium salt 102 (Scheme 8.4.34). The dihydropyridine underwent cycloaddition with methylacrylate, providing chiral isoquinuclidine derivative 104 as the major diastereomeric product. ... 

Tire and NMR parameters of some 1-alkyl-4-benzimidazolyl-2-idene- (type 72) and l-alkyl-4-(5-methylpyrazolyl-3-idene)-l,4-dihydro pyridines (type 73) were discussed in 89CC1086 and 91JOC4223. Comparison of the shifts for DMSO-dg and CDCI3 solutions with data reported for quaternary pyridinium compounds as well as anionic species in the azole series and data obtained for mesoionic betaines of the azinium azolate class left no doubt that these heterofulvalenes have a betaine character and, therefore, the NMR signals correspond to their dipolar resonance form. 

Several N-(chloromethyl)pyridinium platinum complexes have been described in the literature [89JOM255 92JCR(S)296 92JOM155]. Interestingly, 2-pyridyl platinum(II) complexes 11 and 12, having been dissolved in dichloromethane, are slowly N-alkylated by the solvent, yielding the N-(chloromethyl)pyridinium compounds 13 (76%) and 14 (77%) (Scheme 3). 

An interesting intermediate 30 was proposed to result from the sequential addition of pyridine to tetrachlorocyclopropene (31). Compound 30 represents an alkyl nitrogen ylide with two 1-chloroalkyl pyridinium moieties in the same molecule. Pyridines with electron-withdrawing groups and heterocycles with an electron-deficient nitrogen, for example, pyridine-3-carbaldehyde or quinoline, react with 31 to yield the corresponding mono-substituted products 32a and 32b (83JOC2629) (Scheme 8). 

A -(l-Haloalkyl)pyridinium halides have been advantageously employed in the Hantzsch multicomponent synthesis, yielding alkyl 1,4-dihydropyri-dine-3,5-dicarboxylates, which are a well-known class of calcium channel modulators (81AGE762). Tire halides readily interact with an excess of an ethyl 3-aminobut-2-enoate 82 (R = H) in dichloromethane at room temperature to afford the heterocycles 83 (R = H) in good to excellent yields (65-95%) (92T1263). Tliis observation has been exploited to perform a quantitative study of the reactivity of the salts (93CB1251).Tlie results have... 

An interesting result has been observed when 4-formylantipyrine 89 was converted into the corresponding pyridinium salt 90 and reacted with alkyl 3-aminobut-2-enoates. Tire expected 1,4-dihydropyridines 91 are transient species in these syntheses and readily lose the 4-substituent (antipyrine, 93) so that dialkyl 2,6-dimethylpyridine-3,5-dicarboxylates 92 are obtained (85-95%) (94H815). Protonation of the pyrazole ring by the evolved hydrochloric acid accounts for this particular behavior (Scheme 29). 

Reaction of pyridinium-A -(2-pyridyl)amidine (402) and alkyl haloace-tates in the presence of K2CO3 afforded a mixture of 4-oxo-4/f-pyrido[l, 2-u]pyrimidine-2-carboxylates 407 and 2-aminopyridine derivatives 406 through intermediers 403- 05, as depicted in Scheme 15 (00TL5837). Compound 406 could be cyclized on the action of heat or silica gel into 407. The best yield was achieved in the case of ethyl bromoacetate. 

Similar lamellar structures are formed for l-alkyl-3-methylimida2olium cations with [PdCl4] when n > 12. As with the pyridinium systems, mesomorphic liquid crystal structures based on the smectic A structure are formed [24]. 

Other liquid-crystalline materials that have been investigated by X-ray scattering include single- and double-chained pyridinium [33] and N-substituted 4-(5-alkyl-l,3-dioxan-2-yl)pyridinium salts [34]. In the former case, diffraction analysis allowed an explanation for the differences in mono- and di-substituted salts to be proposed. 

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