Synthesis of Important New Pyrrolo[3,4‐c]Pyrazoles and Pyrazolyl‐Pyrrolines from Heterocyclic β‐Ketonitriles

Abstract

Treatment of heterocyclic β‐ketonitriles 1a,b with hydrazine hydrate and phenylhydrazine afforded the hydrazine derivatives 2a‐d which cyclized in PPA into pyrrolo[3,4‐c]pyrazoles 3a‐d. Reaction of 1a,b with cyanoacetohydrazide furnished the cyanoacetyl pyrrolo[3,4‐c]pyrazoles 4a,b. The hydrazine 2c reacted with β‐diketone and β‐ketoesters to afford pyrazolyl‐pyrrolines 5‐7. Also the later hydrazine reacted with some D‐aldoses and aceteophenone to give the corresponding hydrazones 10‐12 and hydrazine carboxamide derivatives 15a,b respectively.

Reactivity of 1-methylisoquinoline synthesis of pyrazolyl triazoloisoquinoline and thia-diazolyl isoquinoline derivatives

“…For example, in the pyrazole ring system C (4) is the most electron rich carbon, thus, H (4) in is expected to appear at higher field at δ 6.31 ppm. On the other hand, H (5) is linked to the carbon attached to nitrogen atom and thus it's deshielded to appear in the region δ 7.5 -8.5 ppm [26][27][28]. The 1 H NMR spectra of isolated reaction products revealed, in each case, a singlet signal at δ 8.5 ppm which indicates the presence of the pyrazole H (5) rather than H (4) in the structure of the isolated products.…”

Enaminones as Building Blocks in Heterocyclic Preparations: Synthesis of Novel Pyrazoles, Pyrazolo[3,4-d]pyridazines, Pyrazolo[1,5-a]pyrimidines, Pyrido[2,3-d]pyrimidines Linked to Imidazo[2,1-b]thiazole System

“…The latter reaction products were assumed to be formed via initial 1,3-dipolar cycloaddition of the nitrilimines 5a-m to the activated double bond in compound 3 to afford the non-isolable cycloadducts 6a-m which undergoes loss of dimethylamine yielding the final pyrazole derivatives 7a-m. [44][45][46] The 1 H NMR spectra of the isolated products 7a-m revealed, in each case a singlet signal in the region of 8.40-8.72 ppm which indicates the presence of the pyrazole H-5 rather than H-4. This conclusion was further confirmed chemically by the reaction compounds 7a,d,g with hydrazine hydrate, to afford pyrazolo[3,4-d]pyridazines 8a-c, respectively (Scheme 2).…”

Synthesis and Characterization of Some New Heterocycles Incorporating the 1-Phenyl-5-(2-thienyl)pyrazole Moiety

“…17 Moreover various sulfur compounds have been found to have other biological properties. [22][23][24][25] In view of these reports and in continuation with our previous work in the synthesis of biologically active heterocycles, [26][27][28][29][30] in this article we detail our synthesis of some new heterocycles with 1-phenyl-5-(thiophen-2-yl)-pyrazole moiety.…”