2,6-Di-/-butylpyridine

A series of graft polymers on polychloroprene were made with isobutjiene, /-butyl vinyl ether, and a-methylstyrene by cationic polymerization in solution. The efficiency of the grafting reaction was improved by use of a proton trap, eg, 2,6-di-/-butylpyridine (68). 

Steric effects are usually unimportant however, in extreme cases as in 2,6-di-/-butylpyridine (p Ta = 3.6) the pKu does fall significantly below that of pyridine. This is attributed to entropy rather than enthalpy effects as it is the entropy change for the transfer of the protonated 2,6-di-/-butylpyridine from the gas phase to the aqueous phase that is abnormal. Aqueous protonated 2,6-di-/-butylpyridine is hydrogen bonded to a water molecule via the NH bond and the observed loss of entropy is due to the substantial restrictions in the internal rotations in the solution complex of protonated 2,6-di-/-butylpyridine <1984JA4341>. 

Activation of a side-chain primary alcohol function with trifluoromethanesulfonic acid anhydride led to exclusive C-alkylation resulting in a cationic ring closure to afford the tetrahydroindoles (A)-584 (Equation 140) <2004T1197>. When R = H the N-Tf-substituted compound (5)-584 was formed as a side product in 18% yield. It was important to conduct the reaction in the presence of 4-methyl-2,6-di-/-butylpyridine as a sterically demanding and effective proton scavenger. 

Steric factors and especially hindered rotations may change the pK of an acid by up to two p/fa units as has been found for 2,6-disubstituted pyridines 2,6-di-/-butylpyridine [70k] is an unusual (Kanner, 1982) non-nucleophilic base which has a surprisingly low pKa value. When [70k] is compared to other 2,6-dialkylsubstituted pyridines [70] it is found to be the only disubstituted pyridine with a smaller pKa than pyridine itself (see Table 29). The exceptional behaviour of [70k] has been investigated intensively... 

The reaction of the mesoionic miinchnones with alkynes affords pyrroles. The azlactones afford A(-unsubstituted pyrroles. If the azlactones are treated with a strong alkylating agent such as methyl trifluoromethylsulfonate or triethyloxonium tetrafluoroborate in the presence of 2,6-di-/-butylpyridine and the alkyne, TV-substituted pyrroles are obtained <88S999>. Pyrroles with an N-alkyl substituent that contains a reactive group, such as a bromine atom, may be prepared by this method (Equation (6)). An intramolecular 1,3-dipolar cycloaddition of an alkyne with a mflnchnone affords a fused pyrrole (Scheme 31) <89JCS(Pi)36i>. 

Bases Alumina, see p-Toluenesulfonylhydrazine. Dehydroabietylamine. 1,5-Diazabicyclo [4.3.0]nonene-5. 1,4-Diazabicyclo[2.2.2]octane. l,S-Diazabicyclot5.4.0]undecene-5. 2,6-Di-/-butylpyridine. N,N,-Diethylglycine ethyl ester, see /-Amyl chloroformate. 2,6-Dimethyl-piperidine. Ethanolamine. Lithium diisopropylamide, see Diphenylsulfonium isopropylide. Lithium nitride. Magnesium methoxide. N-Methylmorpholine. Piperidine. Potassium amide. Potassium hydroxide. Potassium triethylmethoxide. Pyridine. Pyrrolidine. Sodium methoxide. Sodium 2-methyl-2-butoxide. Sodium thiophenoxide. Thallous ethoxide. Triethyla-mine. Triphenylphosphine, see l-Methyl-2-pyrrolidone. 

When pyridine-4-siilfonic acid is heated with ammonium hydroxide or with an alkylamine in the presence of a maii amount of zinc chloride it gives 4 minopyridine and 4-alkylaminopyiidine, respectively. 4-Amino-2,6-di- -butylpyridine is obtained on heating 2,6-di-r-butylpyiidine-4-sulfonic acid with aqueous ammonia in a small sealed tube. The cyano group in the 4-position is also labile thus 4-cyanopyridinium methiodide reacts with ammonium hydroxide to give 4-aminopyridine methiodide (IX-28). °... 

AgOTf, Mel, 2,6-di-f-butylpyridine, 39-96% yield. This method can be used to prepare alkyl, benzyl, and allyl ethers. ... 

From a silylated hydroxy acid RCHO, TMSOTf, 2,6-di-t-butylpyridine, 77% yield."- ... 

The reaction of 2,6-di-tert-butylpyridine with SO3 at elevated temperatures gives (43) in addition to the 3-sulfonic acid. ... 

Although trityl perchlorate is used to accomplish the glycosidation of the C-8 hydroxyl in 44 with acetoxy glycoside 49, control experiments have demonstrated that no reaction takes place in the presence of 4 A molecular sieves or 2,6-di-terf-butylpyridine. This observation suggests that the actual catalyst is not trityl perchlorate, but perchloric acid. Consistent with this conclusion is the observation that catalytic amounts of a strong Brpnsted acid such as triflic or perchloric acid can catalyze the glycosidation of 44 with 49 in the absence of trityl perchlorate. 

The synthesis and purification of cumyl alcohol (CumOH), p-dicumyl methyl ether (DCE)) and 2-chloro-2,4,4-trimethylpentane (TMPC1), and the sources and purification of methyl chloride (MeCl), methylcyclohexane (MCHx), isobutylene have been described [9, 10]. P-Pinene (P-PIN), (Aldrich), was chromatographed over alumina (activity I, Fisher), and freshly distilled over CaH2 under nitrogen according to 1H-NMR spectroscopy and GC analysis the purity was >99%. 2,6-Di-/er/-butylpyridine (DtBP), (Aldrich), anhydrous A,A-dimethylacetamid (DMA), (Aldrich), ethylaluminum dichloride (EtAlCl2), 1.0 M solution in hexanes (Aldrich), and methanol (Fisher) were used as received. 

When the iron-based catalyst 66 was used, a high level of enantiomeric excess in the cycloadditions between cyclopentadiene (18) and a,/i-unsaturated aldehydes [65] was observed. The cycloadditions were carried out in the presence of 2,6-di-t-butylpyridine (Scheme 3.15) which was added to scavenge residual acid impurities. 

Another type of steric effect is the result of an entropy effect. The compound 2,6-di-fert-butylpyridine is a weaker base than either pyridine or 2,6-dimethylpyridine. The reason is that the conjugate acid (8) is less stable than the conjugate acids of nonsterically hindered pyridines. In all cases, the conjugate acids are hydrogen bonded to a water molecule, but in the case of 8 the bulky tert-butyl groups restrict rotations in the water molecule, lowering the entropy. 

Similar ring openings have been achieved using trimethylsilyl triflate and 2,6-di-r-butylpyridine.155... 

General Considerations. The following chemicals were commercially available and used as received 3,3,3-Triphenylpropionic acid (Acros), 1.0 M LiAlH4 in tetrahydrofuran (THF) (Aldrich), pyridinium dichromate (Acros), 2,6 di-tert-butylpyridine (Acros), dichlorodimethylsilane (Acros), tetraethyl orthosilicate (Aldrich), 3-aminopropyltrimethoxy silane (Aldrich), hexamethyldisilazane (Aldrich), tetrakis (diethylamino) titanium (Aldrich), trimethyl silyl chloride (Aldrich), terephthaloyl chloride (Acros), anhydrous toluene (Acros), and n-butyllithium in hexanes (Aldrich). Anhydrous ether, anhydrous THF, anhydrous dichloromethane, and anhydrous hexanes were obtained from a packed bed solvent purification system utilizing columns of copper oxide catalyst and alumina (ether, hexanes) or dual alumina columns (tetrahydrofuran, dichloromethane) (9). Tetramethylcyclopentadiene (Aldrich) was distilled over sodium metal prior to use. p-Aminophenyltrimethoxysilane (Gelest) was purified by recrystallization from methanol. Anhydrous methanol (Acros) was... 

Reaction of Chlorodimethyl(2,3,4,5-tetramethyl-2,4-cyclopentadien-l-yl)silane with Silica Materials. Chlorodimethyl-(2,3,4,5-tetramethyl-2,4-cyclopentadien-l-yl)silane (excess) was added to a mixture of amine-functionalized silica with hexanes in a drybox. 2,6-Di-tert-butylpyridine (excess) was added as a proton sponge. The mixture was allowed to react while stirring for 24 h. The solid was filtered and washed with hexanes and THF in the drybox. The solid was then contacted with another aliquot of chlorodimethyl-(2,3,4,5-tetramethyl-2,4-cyclopentadien-l-yl)silane and the procedure was repeated. 

As evidenced by experiments carried out on partially poisoned catalysts with 2,6-di-tert-butylpyridine, a significant decrease in the catalytic activity (of about 65-70 %) occurs because of a partial neutralization of the external acid sites. This means that the alkylation takes place predominantly on the external surface. 

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