Dimethyl-pyridinium

Die Reduktion von 1,4-Dimethyl-pyridinium-jodid mit Aluminium-hydrid (in situ aus Lithium-alanat und Aluminium-chlorid in Ether) ergibt 1,4-Dimethyl-l,2,3,6-telrahydro-pyridin in hoher Ausbeute ( 90%)3 ... 

Alkyl-2,6-dimethyl-pyridinium-broinide werden beim Erhitzen mit Methylamin-Dihy-drogensulfit in Wasser zu N-Alkyl-anilinen (z.B. N-Hexyl-3-methyl-anilin 96%) um-gelagert1 ... 

Both 4-arylimino-2,6-dimethylpyran salts (167) and l-aryl-4-methoxy-2,6-dimethyl-pyridinium salts (168) result from the reaction of 4-methoxy-2,6-dimethylpyrylium salts with primary aromatic amines (78JCS(P1)1373). The ratio of the products varies with the basicity of the amine, the less basic amines giving mainly the pyran salt. The free iminopyrans (169), which have limited stability at room temperature, are readily obtained from the salts. 

Also, the primary amine moities of polar lipids catalyze the aldol condensation of Cm-Cig aldehydes resulting from plasmalogen hydrolysis, thus forming a,3-unsaturated aldehydes (l2t). Phosphatidyl ethanolamine reacted with propanal and n-hexanal forming phosphatidyl l-(2-hydroxyethyl)-2-ethyl-3,5-dimethyl pyridinium, and phosphatidyl-1-(2-hydroxy ethyl)-2-hexyl-3,5-dipentyl pyridinium, respectively (125). The peridinium ring is formed by the reaction between one mole of amino-N of phosphatidyl ethanolamine and three moles of n-alkanals. The same reaction took place in the synthesis of substituted pyridines by condensation of carbonyl compounds with ammonia (126, 127). 

Similarly, 13,14-bis(2-pyridyl)pentaphene (29) (Fig. 8) was synthesized from condensation of 26 with benzyne, generated in situ from anthranilic acid and isoamyl nitrite [36]. Variable-temperature NMR studies of the mono- (30) and dimethylated pyridinium salts (31) indicated rapid rates of racemization on the NMR time scales below 79°C with the monomethylated 30 having an activation barrier of 16.6 kcal/ mol at 30°C. A S5uichronous rotation with the pyridyl rings remaining parallel to each other was proposed as the molecular movement for racemization. 

The nature of the cation grafted and the counteranion used, have unsurprisingly a direct effect on the efficiency of the catalysis. Whereas changing the anion from chloride or bromide to iodide led to a loss of activity only for the iodide (after 2 h Cl 65% Br 66% 1 44%), decreasing the acidity by changing the cation from dimethyl pyridinium to the unsubstituted pyridinium led in comparison to a decrease in conversion from 74% to 51% (5 h). 

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). 

Pyridinium perchlorate, 1,2-dimethyl-kinetic data, 2, 198 <74JOC3481)... 

Thiazolo[3,2-a]pyridinium, 6-amino-2,3-dihydro- H NMR, 6, 675 (78ACS(B)70) Thiazolo[3,2-a]pyridinium, anhydro-7-bromo-3a-carboxy-2,3-dihydro-8-hydroxy-2ft5-dimethyl-1 or-0X0-... 

Pyridinium salts, l-aryl-4-methoxy-2,6-dimethyl-synthesis, 3, 762 Pyridinium salts, N-aryloxy-rearrangements, 2, 354 Pyridinium salts, 1-benzyl-covalent amination, 2, 239 Pyridinium salts, N-benzyl-reactions... 

Pyrrolo[2,3-6]pyridinium iodide, 1,7-dimethyl-reduction, 4, 508 Pyrrolo[3,2- 6]pyridin-2-ones spectra, 4, 502... 

Thiadiazolo[4,5-d]pyridinium hydroxide, anhydro-3,6-dimethyl-5-hydroxy-7(6)-oxo-... 

The most intensively studied oxidizing system is that developed by Pfitzner and Moflatt in which the oxidation is carried out at room temperature in the presence of dicyclohexylcarbodiimide (DCC) and a weak acid such as pyridinium trifluoroacetate or phosphoric acid. The DCC activates the DMSO which in turn reacts with the carbinol to give an oxysulfonium intermediate. This breaks down under mild base catalysis to give the desired ketone and dimethyl sulfide. 

Fulvene-type enamines, which possess some nonbenzenoid aromatic character, have been synthesized by treating cyclopentadienylsodium with an amide-dimethyl sulfate eomplex (117aJ17b) or quaternary pyridinium salts (117c). One of the simplest ones produced is 6-(dimethylamino)fulvene (117a,117d). 

Tliere is only one report concerning the reaction of A -(l-chloroalkyl)-pyridinium chlorides with secondary diamines (92BSB233). 2-Substituted 1,3-dimethyl- and 1,3-diphenyl-imidazolidines 79 have been prepared (75-95% yields) starting from either -dimethyl- or A, A -diphenylethane-1,2-diamines, respectively (Scheme 25). Reactions are particularly fast for the preparation of the 1,3-dimethylimidazolidines. Reaction times as short as 5 min have been claimed. 

B) Preparation of 2-(Hydroxyiminomethyl)-1-Methyl Pyridinium Chloride An aqueous solution of 15 ml of 1-methyl-2-picolinium chloride having a concentration of 477 mg/ml Is covered with 50 ml of benzene in an atmosphere of nitrogen and cooled to below 10°C. An aqueous solution of sodium hydroxide is added dropwise and the mixture is stirred for 5 minutes and allowed to stratify. The aqueous phase Is then drawn off and the benzene solution is added slowly to a solution of 3 ml of nitrosyl chloride in 175 ml of benzene containing 0.5 ml of dimethyl formamide at about 10°C in an atmosphere of nitrogen with good agitation. The mixture is then stirred for 1.5 hours and then extracted with four... 

In pyridinium chloride ionic liquids and in l,2-dimethyl-3-hexylimida2olium chloride ([HMMIMjCl), where the C(2) position is protected by a methyl group, only [PdClJ was observed, whereas in [HMIMjCl, the EXAFS showed the formation of a bis-carbene complex. In the presence of triphenylphosphine, Pd-P coordination was observed in all ionic liquids except where the carbene complex was formed. During the Heck reaction, the formation of palladium was found to be quicker than in the absence of reagents. Overall, the EXAFS showed the presence of small palladium clusters of approximately 1 nm diameter formed in solution. 

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