1.3- Diketones, Knorr pyrazole synthesis

Application of the Knorr pyrazole synthesis has also been demonstrated on solid support. ° To prepare trisubstituted pyrazoles, the diketone was linked to the solid support to make 57 using a linker with an amide bond. Alkylation of the diketone followed by condensation of the hydrazine with the resulting diketone gave the desired pyrazoles as mixtures of isomers. Subsequent cleavage of the amide bond linker then provided the pyrazole amides 59. ... 

Reaction between 1,4-diketones and primary amines (or ammonia) to give pyrroles. A variation of the Knorr pyrazole synthesis (page 317). 

Condensation of 1,3-diketones with hydrazines or hydroxyamines was conducted in a microflow system to give pyrazoles and isoxazoles in good yields [22]. High-throughput synthesis of pyrrole by the Paal-Knorr condensation of ethanolamine and acetonylacetone was achieved using the CPC CYTOS Lab System [23], The running of the system for 165 min resulted in 714 g of the pyrrole (Scheme 4.14). 

One of the most popular reactions of (l-diketones in heterocyclic chemistry is the Knorr reaction, that is, the synthesis of pyrazoles by interaction of P-diketones with hydrazines. It was described that the interaction of 3-(arylacylidene)-3,4-dihydroquinoxalin-2(l//)-ones 50 (the schematical presentation of the 3-arylacylidene-3,4-dihydroquinoxalin-2(l//)-ones as analogues of P-diketones has... 

The ferrite-anchored glutathione-catalyzed Paal-Knorr method, described earlier for the synthesis of pyrroles, [40] has also been used for the synthesis of pyrazoles 105 by taking various hydrazines and hydrazides 104 and the 3-keto esters/1,3-diketones 103 as substrates (Scheme 34). All these reactions proceeded well in aqueous medium and got completed in 20 min under microwave irradiation. 

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