Estudo de reações de flúor-inserção em 1H-pirazóis utilizando os reagentes fluorantes selectfluor, DAST e MFSDA

Abstract

This thesis describes the studies carried out using fluorinating reagents with different approaches: Selectfluor as an electrophilic fluorine source; DAST for nucleophilic fluorinations and MFSDA as a nucleophilic trifluoromethylating reagent. Fluorinations reactions were carried out in 1H-pyrazoles possessing different substituents in the C3 and C5 positions with the goal of explore the insertion of fluorine atoms and/or fluoroalkyl groups in the C4 position of these substrates. Initially, we design suitable starting materials for the fluorination reactions with Selectfluor and DAST. Thus, 3-aryl-4-formyl-1H-1-pyrazoles compounds were synthetized in two steps reactions from ketones and hydrazines followed by a subsequent Vilsmeier-Haack reaction and reacting the respective hydrazones with POCl3/DMF. Next, a new series of 3-aryl-4-hydroxymethyl-1H-1-pyrazoles was synthetized from 3-aryl-4-formyl-1H-1-pyrazoles compounds utilizing NaBH4 as carbonyl reducing agent. Subsequently, we carried out metal-free electrophilic fluorination, promoted by Selectfluor, of pyrazoles with methylene groups (-CH2-X) in which X = OH, Ome, F, N3, and NHMe at the C-4 position furnishing the 4-fluoro-pyrazole products from unexpected C-C bond cleavage, at moderate to good yields. Otherwise, under the same reaction conditions, when X = NEt2 or SPr the oxidation product 4-formyl-pyrazole was obtained. In continuation, a synthetic study of two new series of 4-fluorinated 1,3,5-substituted 1H-pyrazoles are described. Thus, an efficient synthesis of new series of 3-aryl-4-(di)fluoromethyl-1H-1-phenylpyrazoles, where [aryl = Ph, 4-NO2C6H4, 4-OCH3C6H4] is described, from deoxofluorination reactions of 4-(formyl)- and 4-(hydroxymethyl)-1H-1-phenylpyrazoles in dichloromethane as solvent at room temperature, employing diethylaminosulfur trifluoride (DAST) as fluorinating agent in 41 to 73 % yield. Finally, from 5-trifluoromethyl-1H-1-phenylpyrazoles previously obtained from the cyclocondesation reaction of 4-alkoxy-4-alkyl(aryl)-1,1,1-trifluoroalk-3-en-2-ones [in which alkyl/aryl = CH3, C6H5], we performed the iodination using NIS and CF3OOH at the C4 position of these azoles. In a subsequent step, we applied the trifluormetilating reagent MFSDA to promote the trifluormethyl insertion to obtain examples of 4,5-(bis)-trifluoromethyl-1H-1phenylpyrazoles.