Electrophilicity acylating agents

The amino group at tetrazole C-5 behaves as a normal nucleophile towards electrophilic acylating agents but acylation may also occur at the tetrazole N-1 or N-2 positions often giving ring degra-... 

Irreversible inhibitors act by covalently modifying the enzyme, generally at the active site. The active site is then blocked, and the enzyme is permanently rendered inactive. Because functional groups in the active site tend to be electron rich and nucleophilic, irreversible inhibitors tend to be electrophiles. Acylation agents are especially common. 

Another method is to use a much less electrophilic acylating agent than an ester. This sounds crazy but DMF 20 reacts directly with organo-lithium compounds to give good yields of aldehydes... 

The first step is the Claisen ester condensation of two molecules of acetyl CoA, one acting as an enol and the other as an electrophilic acylating agent to give acetoacetyl CoA. We saw the same reaction in the biosynthesis of the pyrrolidine alkaloids earlier in this chapter. 

Antimony.— Acetic anhydride usually acts as an electrophilic acylating agent, but in the reaction with Sb(OR)a the variation of rate with the nature of the alkyl group leads to the conclusion that antimony is the electrophilic centre, and that it attacks the ether oxygen of acetic anhydride ... 

Orientation of the incoming acyl group with an electron-releasing monosubstituted benzene, however, is predominantly para over ortho but selectivity can depend also on reaction conditions. For acylation or benzoylation of simple benzene monoalkylbenzene derivatives, the para-selectivity can approach 20 1 or greater. The reason for this was initially attributed to steric factors but a systematic analysis has shown that the relative reactivity of the electrophilic acylating agents can also affect the selectivity. For example, acylation of more reactive less stable acylium ion derivatives such as formyl and dinitrobenzoyl ion, the ortho para selectivity can diminish greatly ( 1 1). ... 

Another well-established process to generate fluoro ketones proceeds via acylation ofenolates [68, 69] or activated methylene compounds [70 71] as well as by Claisen type condensation reactions [72] Because of the electrophilic power of the acylating agents, there is usually no need tor a catalyst [68]... 

Acceptor-monosubstituted diazomethanes can be further converted into other types of diazo compound. C-Acylation of diazoacetic esters generally requires very reactive acylating agents, such as acid chlorides [969,970] or bromides [971]. C-Alkylations of acyldiazomethanes are best accomplished by metallation followed by treatment with a carbon electrophile [972-977], C-alkylation can also occur without any base if sufficiently electrophilic aldehydes or ketones are used [973,978 -982] or if the alkylation proceeds intramolecularly [983]. 

Although 334 is very air sensitive, products of substitution by electrophiles are stable. Compounds 334 react with acylating agents to yield 335, and with cyanogen chloride, 359 is produced. The observed direction of electrophilic substitution in 334 is consistent with charge distribution and... 

With this purpose, several different types of solid acid catalysts have been investigated for the acylation of aromatics, but the best performances have been obtained with medium-pore and large-pore zeolites (3-9). In general, however, the use of acylating agents other then halides, e.g., anhydrides or acids, is limited to the transformation of aromatic substrates highly activated towards electrophilic substitution. In a previous work (10), we investigated the benzoylation of resorcinol (1,3-dihydroxybenzene), catalyzed by acid clays. It was found that the reaction mechanism consists of the direct 0-benzoylation with formation of resorcinol monobenzoate, while no primary formation of the product of C-benzoylation (2,4-dihydroxybenzophenone) occurred. The latter product formed exclusively by... 

Electrophiles may be alkylating and acylating agents and C02. Tertiary alkyl halides couple more efficiently than primary. The following examples illustrate the scope.39 55... 

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