1 -Acyl-3,5-dimethylpyrazole

Acylimidazoles and 1-acyl-3,5-dimethylpyrazoles reacted with phenols and phenol ethers in the presence of AICI3 and at higher temperatures (110-120 °C) to give ketones in moderate yield.1"1... 

The templates used in these reactions have a significant impact on the reaction outcome and in determining product enantioselectivity. Sibi et al. also showed that changing the oxazolidinone template as in 119 to a 3,5-dimethylpyrazole in 131 resulted in a reversal of stereochemistry using the same chiral Lewis acid (Scheme 34) [91]. Additions in the presence of stoichiometric amounts of zinc triflate and ligand 19 gave good yields and moderate selectivities of 132. These acylated pyrazoles 131 form 5-membered... 

Active carboxylic acid compounds are useful acylating agents for ring-closure reactions. For example, dibenzomacrocycles were obtained in yields of about 20% using the dimethylpyrazol activated amides (Biernat and Lu-boch, 1984) (method Z-27). Acid chlorides have been used instead of active carboxylic acid compounds to obtain the same type of product as in the method... 

Ried et ah551 recently found a generally applicable aldehyde synthesis in the hydrogenolytic fission of l-acyl-3,5-dimethylpyrazole by lithium aluminum hydride, a reaction that takes place with very good yields in ether at 0-20°. An appreciably better method still is to use the same hydride in ether or tetrahydrofuran to reduce the corresponding 1-acylimidazoles, which are readily obtained from the free acids and l,l -carbonyldiimidazole with 0.25 mole of hydride per mole of acylimidazole the reduction is complete in 30-60 min at —20°,552 and it is an advantage of the method that it can be carried out entirely in one vessel without isolation of the acylimidazole intermediate. 

Ishihara and Fushimi designed an interesting Cu(I I) catalyst prepared in situ from Cu(OTf)2 and an L-DOPA-derived monopeptide (270) as a small-molecule artificial metalloenzyme (Scheme 17.61) [87]. The catalyst provides Diels-Alder cycloadducts (271) with excellent diastereo- and enantioselectivities for cycloadditions between a variety of dienes and a,P-unsaturated l-acyl-3,5-dimethylpyrazoles (269). Results for cycloaddition of cyclopentadiene with a, P-unsaturated l-acyl-3,5-dimethylpyrazoles bearing a variety of P-substituents are illustrated in Scheme 17.61. The authors... 

A soln. of phenol in ligroin heated 20 min. at 115-120° with N-acetyl-3,5-di-methylpyrazole and AIGI3 4-hydroxyacetophenone. Y 69%.—N-Acyl-3,5-dimethylpyrazoles and N-acylimidazoles are much weaker acylating agents than the corresponding acid chlorides. F. e. and limitations s. W. Ried and H.-J. Schubert, A. 653, 181 (1962). 

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