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Calcium-mediated C(sp3)-H Activation and Alkylation of Alkylpyridines
Xizhou Zheng1, Iker Del Rosal2, Xian Xu1
1Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, P. R. China.
Abstract:
Main-group metal calcium-mediated alkylpyridine benzylic C(sp3)-H activation and functionalization have been achieved. The reaction of a calcium hydride complex [{(DIPPnacnac)CaH(thf)}2] (DIPPnacnac = CH{(CMe)(2,6-Pr2-C6H3N)}2) with two equivalents of 2,6-lutidine rapidly yields a monomeric calcium alkyl complex with the release of dihydrogen. A hydride/carbon-bridged binuclear calcium complex [{(DIPPnacnac)Ca}2(μ-H){2-Me-6-(μ-CH2)-Py}(thf)] is obtained from an equimolar treatment of calcium hydride and 2,6-lutidine that is readily converted into mono- or binuclear calcium alkyl complexes upon subsequent addition of 2,6-lutidine. DFT calculations and kinetic studies are conducted to determine their reaction profiles. More significantly, this calcium hydride complex catalyzes regioselective benzylic C-H bond addition of alkylpyridines to a variety of alkenes, affording linear or branched alkylated pyridine derivatives.
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