199 Hoesch reaction

The Hoesch Reaction is employed for the introduction of the - COR group into the aromatic ring of phenol or a phenolic ether, and usually proceeds particularly readily with polyhydric phenols. If an ethereal solution of resorcinol (I)... 

By the condensation of a nitrile with a phenol or phenol ether in the presence of zinc chloride and hydrogen chloride a hydroxyaryl- or alkoxyaryl-ketone is produced. The procedure is termed the Hoesch reaction and is clearly an extension of the Gattermann aldehyde reaction (Section IV,121). The reaction gives the best results with polyhydric phenols and their ethers with simple monohydric phenols the imino ester hydrochloride is frequently the sole product for example ... 

Haworth reaction Hell-Volhard-Zelinsky reaction Hoesch reaction Hofmaim reaction. ... 

To explain the experimentally observed high reactivity of HCN and alkyl nitriles under snperacidic condition, Shndo found that in the Gat-terman and Houben-Hoesch reactions, diprotonated HCN (or nitriles) are involved as the de facto reagents (HC N H2, RC N H2). 

Friedel-Crafts acylation using nittiles (other than HCN) and HCI is an extension of the Gattermann reaction, and is called the Houben-Hoesch reaction (120—122). These reactions give ketones and are usually appHcable to only activated aromatics, such as phenols and phenoHc ethers. The protonated nittile, ie, the nitrilium ion, acts as the electrophilic species in these reactions. Nonactivated ben2ene can also be acylated with the nittiles under superacidic conditions 95% trifluoromethanesulfonic acid containing 5% SbF (Hg > —18) (119). A dicationic diprotonated nittile intermediate was suggested for these reactions, based on the fact that the reactions do not proceed under less acidic conditions. The significance of dicationic superelectrophiles in Friedel-Crafts reactions has been discussed (123,124). 

An analogous reaction is the Houben-Hoesch reaction,(sometimes called the Hoesch reaction) using nitriles 7 to give aryl ketones 8. This reaction also is catalyzed by Lewis acids often zinc chloride or aluminum chloride is used. The Houben-Hoesch reaction is limited to phenols—e.g. resorcinol 6—phenolic ethers and certain electron-rich aromatic heterocycles ... 

The synthetic importance of the Houben-Hoesch reaction is even more limited by the fact that aryl ketones are also available by application of the Friedel-Crafts acylation reaction. 

Hoesch reaction. In most cases, a Lewis acid is necessary zinc chloride is the most common. The reaction is generally useful only with phenols, phenolic ethers, and some reactive heterocyclic compounds (e.g., pyrrole), but it can be extended to aromatic amines by the use of BCls. Acylation in the case of amines is regioselectively ortho. Monohydric phenols, however, generally do not give ketones " but are attacked at the oxygen to produce imino esters. Many nitriles... 

Houben-Hoesch reaction, 12 179 Household appliances, virtual two-way SMA devices in, 22 348 Household laundering, 4 45-46 detersive systems for, <5 413t Household products emulsion use in, 10 129 organic esters in, 10 518-519 Household uses, sodium sulfates in,... 

Heterocyclic bases, amination of, 1, 4 in nucleosides, 55, 1 Heterodienophiles, 53, 2 Hilbert-Johnson method, 55, 1 Hoesch reaction, 5, 9... 

For further work in the field of benzofurans see <99TA1521> (synthesis of TAK-218 using (i )-2-methylglycidyl tosylate as a chiral building block), <99SL495> (heterocyclic rubicene analogues) and <99S751> (synthesis of benzofuro[2,3-b]benzofuran derivatives under Hoesch reaction conditions). 

Acylation with Nitriles. The Hoesch Reaction Acylation or Acyl-de-hydrogenation... 

A method for the preparation of 1-hydroxypyrrolizidine was published by Adams et al.7i Cyclization of 1 -(/ -cyanoethyl)pyrrole under the conditions of the Houben-Hoesch reaction gave rise to l-oxo-3/f-l,2-dihydropyrrolo(l,2-a)pyrrole (123) (cf. refe. 48 and 73), which can be converted into 1-hydroxypyrrolizidine by either direct hydrogenation over rhodium on alumina or hydrogenation of the corresponding hydroxy derivative 124. This route has some interest as a potential... 

The Houben-Hoesch Reaction refers specifically to phenols as substrates, where the reaction is generally most useful. 

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