Regioselective synthesis of N1-substituted-4-nitropyrazole-5-carboxylates via the cyclocondensation of ethyl 4-(dimethylamino)-3-nitro-2-oxobut-3-enoate with substituted hydrazines

A simple and expeditious method for the regioselective synthesis of N1-substituted-4-nitropyrazole-5-carboxylates was developed. The method involves cyclocondensation of ethyl 4-(dimethylamino)-3-nitro-2-oxobut-3-enoate with a series of monosubstituted hydrazines to give N1-substituted-4-nitropyrazole-5-carboxylates with excellent regioselectivity and good yields. Solvent effects on regioselectivity of the cyclocondensation were examined.

Theoretical and experimental investigation of the polyeletrophilic β-enamino diketone: straightforward and highly regioselective synthesis of 1,4,5-trisubstituted pyrazoles and pyrazolo[3,4-d]pyridazinones

A highly efficient regioselective synthesis of 1,4,5-trisubstituted pyrazoles and pyrazolo[3,4-d]pyridazinones from enamino diketone along with a theoretical and experimental study of the chemical reactivity enamino diketone.

Synthesis of 3,5-disubstituted pyrazoles via Cope-type hydroamination of 1,3-dialkynes

An efficient method for the synthesis of 3,5-disubstituted pyrazoles is described. The reactions of 1,3-dialkynes with hydrazine proceeded smoothly in dimethyl sulfoxide under mild reaction conditions to produce 3,5-disubstituted pyrazoles in satisfactory to excellent yields. A one-pot procedure of the transformation has been developed.

Three-component synthesis of cyclic enaminones via ketene cyclization

Cyclic six-membered enaminones were synthesized from three components (bromodiazoacetone, primary amine, and alkyne) in high yields via aza-Michael addition, Wolff rearrangement, and nucleophilic ketene cyclization.

Synthesis of amino acid derived enaminones via Wolff rearrangement using vinylogous amides as carbon nucleophiles

Cyclic enaminones were synthesized in high yields from amino acids in two steps via Wolff rearrangement. The cyclization represents a rare 6-exo-dig cyclization involving a ketene as an electrophile. No racemization was observed during this reaction.