Krzysztof Durka, A. Górska, Tomasz Kliś
Apr 1, 2015
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Journal
Tetrahedron Letters
Abstract
Abstract A series of 1-alkyl-1 H -5-M-pyrazol-4-ylboronic acids (alkyl = Me or Et, M = SiMe 3 , SiMe 2 CH 2 CH CH 2 , SiMe 2 OH, SiPh 2 OH, or GeMe 3 ) has been obtained by the sequential lithiation/silylation (or germylation) and lithiation/boronation of the respective 1-alkyl-1 H -4-bromopyrazoles. The boronic acids containing –SiMe 2 OH or –SiPh 2 OH groups were formed as a result of the Si–H bond activation initiated by the boron Lewis acid centre in the respective intermediates containing –SiMe 2 H or –SiPh 2 H groups. The activation process is facilitated by the presence of water, however, depending on the structure of the starting material, it can lead to the formation of products containing –Si–OH or –Si–O–Si– groups. The boronic acids obtained have been characterized by 1 H and 13 C NMR spectroscopy and by X-ray crystallography.