943987-30-2Relevant academic research and scientific papers
The use of enaminones and enamines as effective synthons for MSA-catalyzed regioselective synthesis of 1,3,4-tri- And 1,3,4,5-tetrasubstituted pyrazoles
Duan, Liancheng,Zhou, Hui,Gu, Yucheng,Gong, Ping,Qin, Mingze
, p. 16131 - 16137 (2019)
In the present work, an efficient regioselective synthesis of 1,3,4-tri- and 1,3,4,5-tetrasubstituted pyrazoles via a methanesulfonic acid (MSA)-catalyzed reaction of hydrazones with enaminones or enamines is reported. Mechanistically, the formation of the title compounds involves the [2+3] cycloaddition of hydrazones with enaminones or enamines followed by aromatization with acid and oxygen. This convenient method under mild conditions with various hydrazones, enaminones, and enamines was well-tolerated to afford products in good to excellent yields. Compared with the literature methods, this strategy has advantages such as materials that are available economically, metal-free catalysis, excellent regioselectivity, and high efficiency.
Studies with enamines: Reactivity of N,N-dimethyl-N-[(E)-2-(4-nitrophenyl)- 1-ethenyl]amine towards nitrilimine and aromatic diazonium salts
Al-Matar, Hamad M.,Riyadh, Sayed M.,Elnagdi, Mohamed H.
, p. 603 - 607 (2008/09/18)
(Chemical Equation Presented) In the presence of triethylamine, cycloaddition reaction of enamine 1 with hydrazonoyl halides 2 followed by dimethylamine elimination was achieved, yielding the corresponding 1,3,4-trisubstituted pyrazoles 4. Coupling of enamine 1 with aromatic diazonium salts afforded 2-(arylhydrazono)-2-(4-nitrophenyl)acetaldehyde 9 in good yield. Refluxing the phenyl hydrazone 9a with chloroacetone in ethanol in the presence of triethylamine afforded 1,3,5-trisubstituted pyrazole 12a, formed via intermediate 11a. Reaction of 9a with hydroxylamine hydrochloride in ethanol in the presence of anhydrous sodium acetate yielded oxime 13a which was irradiated in a microwave oven in the presence of acetic acid to afford a mixture of 15a and 16a.
