Lutidines, amination

Because of these difficulties, special mechanisms were proposed for the 4-nitrations of 2,6-lutidine i-oxide and quinoline i-oxide, and for the nitration of the weakly basic anilines.However, recent remeasurements of the temperature coefficient of Hq, and use of the new values in the above calculations reconciles experimental and calculated activation parameters and so removes difficulties in the way of accepting the mechanisms of nitration as involving the very small equilibrium concentrations of the free bases. Despite this resolution of the difficulty some problems about these reactions do remain, especially when the very short life times of the molecules of unprotonated amines in nitration solutions are considered... 

The carbonyiation of o-diiodobenzene with a primary amine affords the phthalimide 501 [355,356]. Carbonyiation of iodobenzene in the presence of (9-diaminobenzene (502) and DBU or 2,6-lutidine affords 2-phenylbenzimida-zole (503)[357, The carbonyiation of aryl iodides in the presence of pentaflnor-oaniline affords 2-arylbenzoxazoles directly, 2-Arylbenzoxazole is prepared indirectly by the carbonyiation of (9-aminophenol[358j. The optically active aryl or alkenyl oxazolinc 505 is prepared by the carbonyiation of the aryl or enol triflates in the presence of the opticaly active amino alcohol 504, followed by treatment with thionyl chloride[359]. 

Further organic storing materials Phenyl bromide [14], pyridine, 1 -picoline, 2,6-lutidine [15-17] Arsonium salts [18, 19] Phosphonium salts [20] Pyridinium bromides [21] Aromatic amines [22] Urotropin-bromine adduct [23] Pyridinium and sulfonium salts [24] Propionitril [25]... 

Note The following solvent systems were tried but gave no separation dioxane/water (7 3, v/v) n-butanol saturated with water amyl alcohol/ace-tone/water/benzyl amine (40 35 20 5, v/v) 2,6-lutidine/water/ethnol/diethylamine (55 25 20 1, v/v). 

It has to be assumed that these processes are occurring on the boundary between SN1(P) and SN2(P) mechanisms in whose transition states considerable P—0(—Ar) bond cleavage takes place. The lifetime of the resulting, more or less free metaphosphate anion 102 then depends upon the nucleophilicity of the surrounding solvent. With pyridine, for example, a very fast reaction occurs so that the overall process approaches an SN2 reaction. Acceleration of the reaction by amines such as 2,6-lutidine, which are disqualified from acting as nucleophiles by steric hindrance, or by solvents such as dioxane, whiche are presumably too... 

Finally, Persson et al. (1995) measured the UC/14C KIEs for the SN2 reactions between several amine nucleophiles and labelled methyl iodide in dimethoxyethane or acetonitrile at 15°C and 30°C, respectively, to determine how sterically hindered nucleophiles affects the transition state of a Menshut-kin reaction. The results in Table 25 show that all the fc11// 14-values for these reactions are large. In fact, they are all near the theoretical maximum value for these KIEs. Secondly, the KIE for the reaction with the more sterically hindered amine, 2,6-lutidine, is larger than that for the less sterically hindered... 

Parker and Eberson [17] demonstrated that the oxidation of 9,10-dibromoanthracene in the presence of a nucleophile (e.g. 3,5-lutidine) results in the replacement of a bromine by the nucleophile. In a series of papers [18], various polyfluoroaromatic amines were oxidized at platinum in an acetone-water mixture for example, octafluoroacridone was synthesized from 2-aminononafluorobenzophenone (Scheme 2). 

Typical procedure A solution of (dodecane thiol, = Me(CH2) , 1 mL, 4.17 nunol), trimethyl phosphite (591 pL, 5.01 mmol) and terf-amine (lutidine 681 pL, 5.84 nunol) or calcium carbonate (1.4 mol equiv based on the thiol) in CH2CI2 (20 mL) was cooled to -42°C in an MeCN-solid CO2 bath, and TeCl4 (0.8 equiv) was added. The mixture was stirred at the same temperature for 5-10 min and then, after removal of the bath, stirring was continued at room temperature (1.5-3 h). Precipitates were filtered off and the filtrate was washed with water and dried (MgS04). The solvent was removed under reduced pressure and the phos-phorothioate (1.24 g, 96% yield) were isolated by column chromatography on silica gel. 

Nitroxyl mediated electro-oxidation of primary amines also leads to formation of the imine and the further oxidation to the nitrile. In anhydrous acetonitrile containing 2,6-lutidine as a base, the nitrile is formed. In aqueous acetonitrile, hydrolysis of the imine intermediate is fast and good yields of the aldehyde result... 

Aromatic Ketones The DIOP-Rh [116] and DBPP-Rh [117] complexes, in conjunction with a tertiary amine, have been employed in the asymmetric hydrogenation of acetophenone, albeit with moderate enantioselectivity (80 and 82% respectively Tab. 1.10). The asymmetric hydrogenation of aromatic ketones was significantly improved by using the Me-PennPhos-Rh complex, with which enantioselectivities of up to 96% ee were achieved [36]. Interestingly, the additives 2,6-lutidine and potassium bromide were again found to be crucial for optimum selectivity, although their specific role has not been determined. 

Other organic mediators act as hydride atom-abstracting agents. This is true, for example, with 2,2-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and the oxoammonium ion which is anodically accessible from 2,2,6,6-tetramethylpiperidyl oxide (TEMPO). DDQ has been electrochemically regenerated either externally or internally The in situ electrochemical oxidation, of TEMPO to the active oxoammonium ion is performed in lutidine-containing acetonitrile. Thus, primary alcohols can be oxidized to the aldehydes, while secondary ones are stable Primary amines are transformed to nitriles. If water is present, the amines are cleaved via the Schiff bases to the corresponding carbonyl compounds... 

The clean conversion of support-bound, primary amines into sulfonamides by treatment with sulfonyl chlorides is more difficult to perform than the acylation of amines with carboxylic acid derivatives, probably because of the oxidizing properties of sulfonyl chlorides and because primary amines can be doubly sulfonylated. Weak bases (pyridine, 2,6-lutidine, NMM, collidine), short reaction times, and only a slight excess of sulfonyl chloride should therefore be used to convert primary amines into sulfonamides (Table 8.7). 

Protection of alcohols.1 Dimethylthexylsilyl ethers are prepared from primary or secondary alcohols by reaction with 1 and either imidazole or N(C2H5)3 in DMF. The ethers of tertiary alcohols are prepared by reaction with dimethylthexylsilyl trifluoromethanesulfonate in the presence of lutidine or N(C2H5)3. Silylation of amines, amides, mercaptans, and acids is conducted under similar conditions. 

Special care has to be taken, however, that the quinoline titer truly represents the minimum amount of catalyst poison. In most cases this type of base is adsorbed by inactive as well as active sites. Demonstration of indiscriminate adsorption is furnished by the titration results of Roman-ovskii et al. (52). These authors (Fig. 13) showed that introduction of a given dose of quinoline at 430°C in a stream of carrier gas caused the activity of Y-zeolite catalyst (as measured by cumene conversion) to drop with time, reach a minimum value, then slowly rise as quinoline was desorbed. The decrease in catalytic activity with time is direct evidence for the redistribution of initially adsorbed quinoline from inactive to active centers. We have observed similar behavior in carrying out catalytic titrations of amorphous and crystalline aluminosilicates with pyridine, quinoline, and lutidine isomers. In most cases, we found that the poisoning effectiveness of a given amine can be increased either by lengthening the time interval between pulse additions or by raising the sample temperature for a few minutes after each pulse addition. 

Poisoning effectiveness of the basic reagent should be optimized by choosing an appropriate amine (e.g., 2,6-lutidine) and by using a titration technique that will enable distribution of amine among active centers within a convenient time interval. 

Extensive use of Pd-catalyzed reactions was included in the synthesis of 2,6,8-trisubstituted purines (Fig. II).33 The synthesis started by anchoring dichloropurine to Rink resin via N9 linkage. Polymer-bound 2,6-dichloropurine (63) was selectively substituted at C6 via acid-catalyzed SNAr substitutions. In the absence of Pd catalysis, the substitution on C2 could be performed only with strongly nucleophilic amines. To expand the scope of C2 substitution, catalytic amounts of Pd were used. Under these reaction conditions arylboronic acids and amines successfully substituted the chloro atom on C2 to afford C2-C and C2-N bonds. Subsequently, the C8 position was brominated with a bromine-lutidine complex33 (66) to give resin 67. 

Careful analysis of the reaction products in the HDN of the 2,6-lutidine (2,6-dimethylpyridine) and the 2,6-lupetidine (2,6-dimethylpiperidine) allowed Ledoux et al.37 to conclude that under these low pressure conditions (1 atm H2, 5-10 Torr amine, in a steady state flow system, at 300°C on Mo03/A1203 in a fixed-bed reactor) the hydrogenated product is not the intermediate for the HDN of the aromatic compound because the distributions of the products obtained by the reaction of the two amines are fundamentally different. 2,6-Lutidine gives at initial conversion 60% toluene, 21% C3 + C4 and 8% olefinic n-C7, while 2,6-lupetidine gives only 18% toluene, 4% C3 + C4 but 69% of olefinic n-C7. Under the same experimental conditions (but at 380°C), analysis of the pyridine and piperidine HDN products38 shows that... 

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