Reações de abertura de oxiranas promovidas por organocalcogenolatos de zinco

• Autor(a) principal: Silva, Francielle Rodrigues da
• Data de Publicação: 2017
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da UFG
• Texto Completo: http://repositorio.bc.ufg.br/tede/handle/tede/8739
• topic: Oxirana; Organocalcogenolato de zinco; Oxirane; Zinc organochalcogenolates; QUIMICA::QUIMICA ORGANICA

Several methodologies has been reported to generate zinc organocalcogenolate reagents (NOGUEIRA; ZENI; ROCHA, 2004; NOGUEIRA et al., 2003; MUGESH; DU MONT; SIES, 2001). In this work, these reagents are generated by reductive cleavage of the calcogen-calcogen binding of the respective diorganoyl dicalcogenets using the Zn / NH4OH system. This work describes the opening reactions of oxiraneses promoted by organocalcogenolatos of zinc leading to a production of -hydroxyselenetos. The scope of the hydroselenation reaction was exploited with a variety of epoxides. Alkyloxiranes with low degree of substitution, produced hydroxyselenetos in good yields. The reactions, forming, were regioselective, with the nucleophile phenylselenolate attacking the least impeded medium of the oxirane, suggesting an opening mechanism type SN2. For aryl epoxides, the hydroxyselenic products are the phenylcalcogenolate group, and have also been subjected to a faster replacement, but regioselectivity is not complete, with signs of product mixing. Epoxides with two aryl groups bound to the same carbon, in turn, led to the major formation of the corresponding aldehyde, a result of the mechanism with migration of hydride. Finally, for alkyl epoxides, but with a greater degree of substitution, the regiochemical control, led to the formation of -hydroxyselene by the most substituted side. The methodology was efficient and the generation of the phenylcalcogenolate anion occurred easily within the system compared to other methods. Because the results are possible, finally, the reaction of opening epoxides using organocalcogenolate reagents is useful in this work because of the good regiochemical control, easy reproducibility and mild conditions employed.