Acylation of heterocycles

Acylation of heterocyclic enamines is to a great extent similar to alkylation, and usually occurs on the /3-carbon atom of the enainine grouping. 

Acylation of heterocyclic compounds carrying an imine grouping has been studied630-632. Although E Z isomerism is possible, the Z-isomer is usually formed exclusively633,634. A variety of other methods has been used to synthesize enamides. 

Cyclic enamides 79 are formed by treatment of the 2-arylaminonicotinonitriles 75 with either anhydrous hydrogen chloride in benzene, ethanol or dioxane, or perchloric acid in glacial acetic acid, followed by the acylation of heterocycles 76 by acetic, succinic, trifluoroacetic anhydrides as well as benzoyl chloride67 (equation 28). 

Acylation of heterocyclics, such as thiophene, seems to require a lower acid strength of the catalyst which is best met by B-ZSM-5. The reaction of thiophene with acetic anhydride to 2-acetylthiophene proceeds with 99% selectivity at 24% conversion and the conversion of pyrrole with acetic anhydride to 2-acetylpyrrole with 98% selectivity at 41% conversion [115]. 

N-Acyloxazolidin-2-ones. A convenient A-acylation of heterocycles is performed by heating a carboxylic acid with PivCl and triethylamine in toluene. 

Y zeolites also show promising activity in the acylation of heterocyclic compounds. Acylation of benzofurans by AAN was extensively studied, and some good S mthetic results have been achieved. Benzofuran and 2-methylbenzofuran undergo acylation with AAN under mild conditions, giving 2-acetylbenzofuran 13 and 2-methyl-3-acetylbenzofuran 14 respectively, as the main products over Y(32) zeolite (Scheme 4.8). 

Richard, F, Drouillard, J., Carreyre, FI., Lemberton, J. L., and Perot, G. 1993. Zeolite catalyzed acylation of heterocyclic aromatic compounds. 1. Acylation of benzofuran. Stud. Surf. Sci. Catal. 78 601-606. 

Richard, F, Carreyre, H., and Perot, G. 1995. Zeolite catalyzed acylation of heterocyclic compounds. Part It. Acylation of benzofuran over Y zeolites. Effect of reaction conditions on the activity and stability. /. Mol. Catal. A Chem. 103 51-61. 

Acylation of heterocyclics on R-exchanged zeolites has been also reported. This is the case for the acylation of furan with acetic anhydride to form 2-acetylfuran Ce,B- and La,B-ZSM-5 catalysts (Lermer et al. 1987) or the acylation of substituted benzofuran (Amouzegh et al. 1995). 

Zeolite catalyzed acylation of heterocyclic aromatic compounds. I -Acylation of benzofuran. 

Use of solid catalysts in Friedel-Crafts acylation reactions, particularly, in acylation of heterocycles 06CRV1077. 

This reaction has been modified by using a catalytic amount of ZnCl2 for the acylation of heterocycles. ... 

The acylation of heterocycles has been reported. Diketones are prepared by the Friedel-Crafts method using adipyl chloride, benzene, and aluminum chloride. 

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