K2CO3-Promoted Pyrazoles Synthesis from 1,3-Dipolar Cycloaddition of N-Tosylhydrazones with Acetylene Gas was written by Li, Dongying;Qiu, Shanguang;Chen, Yuxue;Wu, Luyong. And the article was included in ChemistrySelect in 2020.Formula: C9H7BrN2 This article mentions the following:
A series of pyrazoles I (R1 = Me, Ph, 4-(trifluoromethyl)phenyl, etc.; R2 = H, Me, Ph, 4-chlorophenyl, etc.) was provided in mediate to good yields. The 1,3-dipolar cycloaddition of N-tosylhydrazones 2-R3-3-R4-4-R5-C6H2C(R6)=NNHS(O)2(4-CH3C6H4) [R3 = H, Me, OMe; R4 = H, Me, Br, Cl; R5 = H, Me, N(CH3)2, OMe, Br, CF3, Cl; R6 = H, Me] (II) with acetylene gas on balloon was investigated. Bases and solvents were screened and K2CO3 was verified to be an efficient base to promote this process. DMSO gave the better result in the reaction of N-tosylhydrazones derived from aldehyde II (R6 = H), and NMP was a better suitable solvent in the reaction of ketone N-tosylhydrazones II (R6 = Me). This process was easy to handle and suitable to the industrial application. In the experiment, the researchers used many compounds, for example, 3-(4-Bromophenyl)-1H-pyrazole (cas: 73387-46-9Formula: C9H7BrN2).
3-(4-Bromophenyl)-1H-pyrazole (cas: 73387-46-9) belongs to pyrazole derivatives. Pyrazole has two ring nitrogen atoms in which N1 is pyrrolic and N2 is pyridine-like. The N1 nitrogen is not reactive but is deprotonated in the presence of a base-forming anion. Protonation of pyrazole in strong acid leads to pyrazolium cations, which undergo electrophilic substitution preferentially at C3 rather than C4. The pyrazole anion is not reactive toward nucleophiles but is mostly reactive to electrophiles.Formula: C9H7BrN2
Referemce:
Pyrazole – Wikipedia,
Pyrazoles – an overview | ScienceDirect Topics