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Les pyridylsilanes : Des précurseurs réactifs pour les couplages organométalliques et la synthèse en phase solide

Abstract : The aim of this work was to study the reactivity of pyridylsilanes in organometallic cross-couplings and their use as scaffolds for heterocyclic synthesis on solid phase. Pyridylsilanes syntheses have been achieved by regioselective metallation reactions of the pyridine ring. An unprecedented t-BuLi reactivity toward bromopyridines has been discovered since a stoichiometric amount of this base led to the clean ortholithiation on the C-4 position. In order to examine the mechanism of this new selectivity, we have performed low- temperature NMR measurements on mixtures of n-BuLi or t-BuLi with 2-chloro-5-bromopyridine. We have demonstrated for the first time the formation of a pyridinic carbanion during a bromine-lithium exchange. The incorporation of chloro-, fluoro- or methoxy substituents on the pyridine ring of pyridyl-trimethylsilanes allowed to perform efficient Hiyama cross-couplings with various (het)aryl halides. The reactions proceeded smoothly at room-temperature leading to the corresponding functional bis(het)aryl in fair to excellent yields. 2-Chloro-5-bromo-pyridine has been immobilized on a Merrifield resin via the selective introduction of a traceless silicon linker at the C-4 position using our new t-BuLi induced ortholithiation reaction. A useful heterocyclic scaffold was thus obtained and submitted successfully to selective reactions with polar and transition organometallic reagents opening a new access to pyridine-based libraries of synthons and chromophores.
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Philippe Pierrat. Les pyridylsilanes : Des précurseurs réactifs pour les couplages organométalliques et la synthèse en phase solide. Autre. Université Henri Poincaré - Nancy 1, 2006. Français. ⟨NNT : 2006NAN10107⟩. ⟨tel-01754314⟩

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