title: Efficient and highly regioselective synthesis of ethyl 1-(2,4-dichlorophenyl)-1H-pyrazole-3-carboxylates under ultrasound irradiation.
abstract: A series of 14 ethyl 1-(2,4-dichlorophenyl)-1H-pyrazole-3-carboxylates has been synthesized from the cyclocondensation reaction of ethyl 4-methoxy-2-oxoalk[cycloalk]-3-enoates [EtO(2)CC(O)C(R(2))=C(R(1))OR, where R=H, Me; R(1)=Pr, Ph, 4-MeOC(6)H(4), 4-MeC(6)H(4), 4-FC(6)H(4), 4-ClC(6)H(4), 4-BrC(6)H(4), 4-NO(2)C(6)H(4), fur-2-yl; R(2)=H; R(1), R(2)=-(CH(2))(3)-, -(CH(2))(4)-, -(CH(2))(5)-, -(CH(2))(6)-, 3,4-dihydronaphth-2-yl] with 2,4-dichlorophenyl hydrazine hydrochloride under ultrasound irradiation with high regioselectivity and in 71-92% yields. The main goal of this methodology was the significant reduction of reaction times. The compounds were obtained after irradiation for 10-12 min. In addition, the structure of the ethyl 1H-pyrazole-3-carboxylates was supported by crystallographic data.
authors.affiliation: Núcleo de Química de Heterociclos (NUQUIMHE), Departamento de Química, Centro de Ciências Naturais e Exatas, Universidade Federal de Santa Maria, 97.105-900, Santa Maria, RS, Brazil.
authors.forename: Pablo
authors.initials: P
authors.lastname: Machado
authors.forename: Glauber R
authors.initials: GR
authors.lastname: Lima
authors.forename: Mariane
authors.initials: M
authors.lastname: Rotta
authors.forename: Helio G
authors.initials: HG
authors.lastname: Bonacorso
authors.forename: Nilo
authors.initials: N
authors.lastname: Zanatta
authors.forename: Marcos A P
authors.initials: MA
authors.lastname: Martins
mesh_terms: D003500:Cyclization; D015394:Molecular Structure; D011720:Pyrazoles / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism; D014465:Ultrasonics
chemical_list: D011720:Pyrazoles