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Chemistry of Bipyrazoles
Synthesis and Applications
Kamal M. Dawood, Ashraf A. Abbas
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eBook - ePub
Chemistry of Bipyrazoles
Synthesis and Applications
Kamal M. Dawood, Ashraf A. Abbas
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About This Book
Chemistry of Bipyrazoles: Synthesis and Applications covers the synthetic pathways for all types of bipyrazoles. 5 chapters cover bipyrazole systems, N, N- and N, C-bipyrazoles, namely 1, 1`-bipyrazole, 1, 3`-bipyrazole, 1, 4`-bipyrazole, 3, 3`-bipyrazoles, 3, 4`-bipyrazoles and 4, 4`-bipyrazoles The contents explain several types of reactions: 1) condensation reactions of hydrazines with tetracarbonyls, dihydroxydicarbonyl compounds or pyrazole-based difunctional compounds; 2) 1, 3-dipolar cycloaddition of pyrazole-based hydrazonoyl halides with activated methylene compounds; 3) metal catalyzed cross-coupling reactions. The book concludes with a chapter that details the applications of bipyrazole derivatives in different industries. Information about advanced concepts used in chemical engineering such as metal-organic frameworks (MOFs) and corrosion inhibition are highlighted. The book contents are presented in an easy-to-understand manner suitable for readers in organic chemistry at senior levels of education and industry expertise. Each chapter is supplemented with detailed references.
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Organic ChemistryChemistry of 3,4`-Bipyrazoles
Kamal M. Dawood, Ashraf A. Abbas
Abstract
All the possible synthetic routes to the 3,4`-bipyrazole systems were thoroughly reported. Such synthetic platforms include: cyclocondensation and 1,3-dipolar cycloaddition reactions. Many of the reported 3,4`-bipyrazoles have potent applications in the field of pharmaceutical and material science.
Keywords: 1,3-dipolar cycloaddition, 3,4`-bipyrazoles, 3,4`-bipyrazolines, Cross-coupling, Cyclocondensation, Pyrazolylhydrazones.
1. Introduction
Various 3,4`-bipyrazoles ring skeletons were reported in the literature. They are composed of either two aromatic pyrazole units or 4-pyrazolyl attached with pyrazoline at C-3 or 4-pyrazolinyl attached to pyrazole at C-3. As a result, there will be the aromatic 3,4`-bipyrazole skeleton or partially aromatic pyrazolylpyrazoline skeleton. The two pyrazole unites are connected directly with a sigma bond between the two units. A number of tautomeric forms can be constructed, as shown in Scheme (1). Synthesis of such 3,4`-bipyrazole skeletons was achieved via several synthetic routes as outlined in Scheme (2). Such synthetic routes include: 1) cyclocondensation of an activated 4-pyrazole ring having chalcones or 1,3-dicarbonyl functions with hydrazines; 2) 1,3-dipolar cycloaddition of pyrazolylhydrazones with activated olefins or acetylenes; 3) 1,3-dipolar cycloaddition of nitrilimines with bis-olefines with nitrilimines or diazo-alkanes; and 4) C-C cross coupling reactions of pyrazolylboronic acids with halopyrazoles or pyrazoles themselves via C-H activation using palladium catalysts.
The fully aromatic 3,4`-bipyrazoles and their partially aromatic ones (pyrazolylpyrazolines) are potent inhibitory active heterocycles with significant biological potentialities. The 3,4`-bipyrazole derivatives were also considered to have anticancer [1-5], antimicrobial [6-12], anti-inflammatory [13-19], antioxidant [20], antitubercular [21-23] and antimalarial activities [24]. They
were found to be effective enzyme inhibitors against carbonic anhydrase inhibitory activity [25], human Tropomyosin-related kinase A (TrkA) [26-30], and Janus kinase (JAK1/JAK2) [31]. 3,4`-Bipyrazole-based metal coordination complexes were reported to display remarkable pharmaceuticals applications. For example, gold(III) and iridium(II) complexes of 3,4`-bipyrazoles were useful as anticancer agents [4, 5]. In addition, the palladium(II) and platinum(II) complexes of 3,4`-bipyrazoles were found to have excellent antibacterial and antifungal activities [6, 32].
The possible direct connected 3,4`-bipyrazole derivatives
The possible synthetic routes to 3,4`-bipyrazoles systems
2. Synthesis of 3,4`-bipyrazole derivatives
2.1. From 1,3-dipolar Cycloaddition Reactions
1,3-Dipolar cycloaddition of 4-pyrazolylformylhydrazone 1 with some activated dipolarophiles such as dimethyl fumarate 3 and ethyl 3-phenylpropiolate 5 under solvent-free conditions using microwave irradiation technique resulted in the construction of the corresponding 3,4`-bipyrazoles 4 and 6, respectively. Similar reaction of the hydrazone 1 with ethyl propiolate 7 under microwave heating at 170 °C afforded a mixture of the 3,4`-bipyrazole derivatives 8 and 9 (Scheme 3). The 1H NMR analysis of structure 9 presented the following data: Ύ 5 1.37 (t, J = 7.1 Hz, 3H, CH3), 4.33 (q, J = 7.1 Hz, 2H, CH2), 7.35 (s, 1H, H-5'), 7.28-7.48 (m, 8H, ArH`s) 7.64 (d, J = 8.6 Hz, 2H, o-H 1-Ph), 8.17 (s, 1H, H-3), 8.40 (s, 1H, H-5). Mechanistically, the regioselective cycloaddition process proceeded via the addition of the dipolarophiles 3 and 5 to the dipolar intermediate 2 followed by aromatization ...