Acyl pyridines, hydrogenation

Other diprotonated acyl-pyridines have likewise been studied.61 In studies of 5-, 6-, 7-, and 8-hydroxyquinolines and 5-hydroxyisoquinoline, dicationic intermediates like 185 (Table 4) were found to be involved in superacid catalyzed reactions with benzene and cyclohexane.59 For example, 8-hydroxyquinoline (187) reacts in CF SOsH-SbFs to generate dications (188 and 189) and undergoes ionic hydrogenation in the presence of cyclohexane (eq 64). Compound 187 also reacts with benzene in suspensions of aluminum halides (eq 65). 

While the hydrogenation of unactivated aliphatic aldehydes and ketones does not generally take place over palladium, this catalyst readily promotes the hydrogenolysis of aryl aldehydes and ketones to the methylene at room temperature and 1-4 atmospheres pressure. The use of an acidic solvent facilitates this reaction2 -29 but is not essential for obtaining good to excellent yields of the desoxy product (Eqn. 18.8). 0 With a basic substrate such as a 2- or 4-acyl-pyridine, however, the alcohol product was obtained (Eqn. 18.9).31... 

Acyl chlorides react with carboxylic acids to yield acid anhydrides When this reaction is used for preparative purposes a weak organic base such as pyridine is normally added Pyridine is a catalyst for the reaction and also acts as a base to neutralize the hydrogen chloride that is formed... 

Pyridine, 3-(dimethylamino)-amination, 2, 236 methylation, 2, 342 nitration, 2, 192 iV-oxide synthesis, 2, 342 Pyridine, 4-(dimethylamino)-in acylation, 2, 180 alkyl derivatives pK, 2, 171 amination, 2, 234 Arrhenius parameters, 2, 172 as base catalysts, 1, 475 hydrogen-deuterium exchange, 2, 286 ionization constants, 2, 172 methylation, 2, 342 nitration, 2, 192 iV-oxide synthesis, 2, 342... 

Pyridin-4-one, 1 -hydroxy-2,6-dimethyl-hydrogen-deuterium exchange reactions, 2, 196 Pyridin-4-one, 1-methyl-hydrogen-deuterium exchange, 2, 287 pK 2, 150 Pyridin-2-one imine tautomerism, 2, 158 Pyridin-2-one imine, 1-methyl-quaternization, 4, 503 Pyridin-4-one imine tautomerism, 2, 158 Pyridinone methides, 2, 331 tautomerism, 2, 158 Pyridinones acylation, 2, 352 alkylation, 2, 349 aromaticity, 2, 148 association... 

In the course of this study, the authors determined /Lvalues for dibenzyl, methyl phenyl, methyl p-nitrophenyl, di-p-tolyl, di-isopropyl and tetramethylene sulphoxides and for diethyl, dipropyl and dibutyl sulphites. The /Lscales are applied to the various reactions or the spectral measurements. The /Lscales have been divided into either family-dependent (FD) types, which means two or more compounds can share the same /Lscale, family-independent (FI) types. Consequently, a variety of /Lscales are now available for various families of the bases, including 29 aldehydes and ketones, 17 carboxylic amides and ureas, 14 carboxylic acids esters, 4 acyl halides, 5 nitriles, 10 ethers, 16 phosphine oxides, 12 sulphinyl compounds, 15 pyridines and pyrimidines, 16 sp3 hybridized amines and 10 alcohols. The enthalpies of formation of the hydrogen bond of 4-fluorophenol with both sulphoxides and phosphine oxides and related derivatives fit the empirical equation 18, where the standard deviation is y = 0.983. Several averaged scales are shown in Table 1588. 

Sulfonic esters are most frequently prepared by treatment of the corresponding halides with alcohols in the presence of a base. The method is much used for the conversion of alcohols to tosylates, brosylates, and similar sulfonic esters. Both R and R may be alkyl or aryl. The base is often pyridine, which functions as a nucleophilic catalyst, as in the similar alcoholysis of carboxylic acyl halides (10-21). Primary alcohols react the most rapidly, and it is often possible to sulfonate selectively a primary OH group in a molecule that also contains secondary or tertiary OH groups. The reaction with sulfonamides has been much less frequently used and is limited to N,N-disubstituted sulfonamides that is, R" may not be hydrogen. However, within these limits it is a useful reaction. The nucleophile in this case is actually R 0 . However, R" may be hydrogen (as well as alkyl) if the nucleophile is a phenol, so that the product is RS020Ar. Acidic catalysts are used in this case. Sulfonic acids have been converted directly to sulfonates by treatment with triethyl or trimethyl orthoformate HC(OR)3, without catalyst or solvent and with a trialkyl phosphite P(OR)3. ... 

Bis(oxazolinyl)pyridine-Ce(IV) triflate complex 78 catalyzed the enantioselective 1,3-DC of acyclic nitrones with a, 3-unsaturated 2-acyl imidazoles. For example, C-phenyl 7V-benzyl nitrone reacted with 77 in the presence of 78 to give the adduct 79 with excellent diastereo-and enantioselectivity. Isoxazolidine 79 was then converted into P -hydroxy-P-amino acid derivatives by hydrogenation of the N-0 bond in the presence of Pd(OH)2/C and cleavage of the 2-acyl imidazole with MeOTf in MeCN <06OL3351>. 

It must further be mentioned that the acylation of alcohols, phenols, and amines with acid chlorides (and also anhydrides) is now frequently carried out in pyridine solution instead of according to the older Schotten-Baumann method (action of acid chloride in aqueous-alkaline suspension). The hydrogen chloride is fixed by the pyridine. 

This reaction is also used to characterise organic bases and to identify through a melting-point determination small amounts, particularly of the liquid bases, by converting them into their usually crystalline acyl derivatives. In order to cause the whole of the base to react—one mole is fixed by the hydrochloric acid liberated—alkali or carbonate is added when aqueous solutions or suspensions are used and dry potassium carbonate or pyridine when anhydrous solvents are employed. Since tertiary bases do not react with acid (acyl) chlorides, no further replaceable hydrogen atom being present, it is possible by the use of an acid chloride to determine also whether a base is, on the one hand, primary or secondary, or, on the other hand, tertiary. 

Ethyl 3-oxoalkanoates when not commercially available can be prepared by the acylation of tert-butyl ethyl malonate with an appropriate acid chloride by way of the magnesium enolate derivative. Hydrolysis and decarboxylation in acid solution yields the desired 3-oxo esters [59]. 3-Keto esters can also be prepared in excellent yields either from 2-alkanone by condensation with ethyl chloroformate by means of lithium diisopropylamide (LDA) [60] or from ethyl hydrogen malonate and alkanoyl chloride usingbutyllithium [61]. Alternatively P-keto esters have also been prepared by the alcoholysis of 5-acylated Mel-drum s acid (2,2-dimethyl-l,3-dioxane-4,6-dione). The latter are prepared in almost quantitative yield by the condensation of Meldrum s acid either with an appropriate fatty acid in the presence of DCCI and DMAP [62] or with an acid chloride in the presence of pyridine [62] (Scheme 7). 

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