Reações de abertura de oxiranas promovidas por organocalcogenolatos de zinco
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2017-03-20
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Universidade Federal de Goiás
Resumo
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.
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SILVA, F. R. Reações de abertura de oxiranas promovidas por organocalcogenolatos de zinco. 2017. 66 f. Dissertação (Mestrado em Química) - Universidade Federal de Goiás, Goiânia, 2017.