Acylation indirect

Other carbon electrophiles which are frequently employed include aldehydes, ketones, esters, nitriles and amides of the type RCONMei. An indirect method of acylation involves the initial reaction of a lithio compound with an aldehyde followed by oxidation of the resulting secondary alcohol to the corresponding acyl derivative. 

While enamines can usually be obtained directly from ketones and secondary amines their formation by an indirect route may bo advantageous. The previously mentioned condensation of rnethyl ketones during azeotropic enamine formation has prompted the alklyation (J) or acylation and reduction (59) of Schiff s bases. A parallel method uses the formation and desulfurization of N-acylthiazolines followed by hydride reduetion (60,61). 

Acylation of the vinylogous pyrrolidine amide of dimedone with acetic anhydride or acetyl chloride led (possibly indirectly) to the carbon acylation product, whereas trichloroacetyl chloride gave rise to products derived from attack of chloride at the oxygenated double bond position in an initial 0-acylation product (401-404). 

Quinoxaline gave l,4-diethyl-l,2,3,4-tetrahydroquinoxaline by indirect reductive alkylation (AcOH, KBHai, <15°C, 1 h, then reflux, 6h 87% presumably by nuclear reduction, A-acylation, and further reduction of the acetyl groups ). ... 

Note The conversion of a quinoxahnecarboxyhc acid into a quinoxalinecarbox-amide is usually done indirectly via the corresponding acyl halide or ester. However, the direct conversion of an acid or anhydride into an amide is possible. 

In an indirect amination process, acyl halides are converted to amino acids. Reaction of the acyl halide with a chiral oxazolidinone leads to a chiral amide, which reacts with the N=N unit of a dialkyl azodicarboxylate [R"02C—N=N—CO2R ]. Hydrolysis and catalytic hydrogenation leads to an amino acid with good enantioselectivity. ... 

Acyl complexes of a range of transition metals (Pd, Pt, Ir, Co, and Mo) undergo this reduction, although in some cases only indirect evidence could be obtained for the ethyl complex. 

On the other hand, the action of acid chlorides on ethyl acetoacetate in pyridine leads to the formation of O-acyl-derivatives, whilst the O-alkyl-derivatives can only be obtained indirectly from the acetals (p. 140) by elimination of alcohol (Claisen). 

Mardones, C., Vizioli, N., Carducci, C., Rios, A., and Valcarcel, M. (1999). Separation and determination of carnitine and acyl-carnitines by capillary electrophoresis with indirect UV detection. Anal. Chim. Acta 382, 23—31. 

So far, the work dealing with the PFR mechanism has paid more attention to the detection and fate of aryloxy radicals than to acyl radicals. It is generally accepted that aryloxy radicals afford phenols (or naphthols) through H abstraction from the solvent, but little has been said about the other partners of the radical pair, namely the acyl radicals. Their detection has been accomplished both directly and indirectly. 

Indirect detection of the acyl radicals in the PFR has been achieved by means of spin trapping with 2-methyl-2-nitrosopropane and subsequent ESR detection of the resulting stable radicals [53]. The ESR technique has also been used for the study of the PFR of diphenyl carbonate but only a line g = 2.005) corresponding to the phenoxy radical could be detected [54], The recorded signal in the spin-trapping experiment consists of a typical sharp triplet with small... 

The above correlation provides indirect proof that the rate-limiting step in the acyl-group migration 84 86 is the formation of the intermediate... 

The instability of primary nitramines in acidic solution means that the nitration of the parent amine with nitric acid or its mixtures is not a feasible route to these compounds. The hydrolysis of secondary nitramides is probably the single most important route to primary nitramines. Accordingly, primary nitramines are often prepared by an indirect four step route (1) acylation of a primary amine to an amide, (2) A-nitration to a secondary nitramide, (3) hydrolysis or ammonolysis with aqueous base and (4) subsequent acidification to release the free nitramine (Equation 5.17). Substrates used in these reactions include sulfonamides, carbamates (urethanes), ureas and carboxylic acid amides like acetamides and formamides etc. The nitration of amides and related compounds has been discussed in Section 5.5. 

Attack at nitrogen is inhibited because no delocalization of charge is possible in the intermediate (Scheme 6.3). A-Alkylation and -acylation of pyrrole are best carried out indirectly using the anion of pyrrole (see Section 6.1.3). 

Important other examples include electrophiles involved in aromatic alkylation, acylation and nitration. While in some instances quantitative gas-phase heats of formation are available, primarily indirectly from measurements of gas-phase proton afRnities, there are insufficient... 

Further indirect evidence for the incursion of tetrahedral intermediates in acyl-transfer reactions has been obtained from experiments which indicate a change in rate-determining step and hence the incursion of an intermediate (Jencks and Gilchrist, 1964, 1968 Jencks, 1969 Johnson, 1967 Schowen et al., 1966 Fedor and Bruice, 1965 Hibbert and Satchell, 1967 Chaturvedi et... 

In the earlier kinetic study26 the rate constant for hydrolysis of lauryl-caproylimidazole PEI to caproate ion and laurylimidazole PEI was estimated to be 0.06 min-1 at pH 7.3. In the present study we have found the rate constant for hydrolysis of laurylacetylimidazole PEI to acetate ion and laurylimidazole PEI under similar conditions to be 0.1 to 0.2 min-1. In the earlier study the hydrolysis rate was inferred by an indirect method from the turnover rate in a steady-state situation. In view of the uncertainties in the indirect method and the difference in size of the acyl group in the two cases, the approximate equality of the deacylation rate constants is gratifying. 

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