Removal of the Pyridine Directing Group from α-Substituted<i>N</i>-(Pyridin-2-yl)piperidines Obtained via Directed Ru-Catalyzed sp<sup>3</sup>C–H Functionalization
作者:Veerle Smout、Aldo Peschiulli、Stefan Verbeeck、Emily A. Mitchell、Wouter Herrebout、Patrick Bultinck、Christophe M. L. Vande Velde、Didier Berthelot、Lieven Meerpoel、Bert U. W. Maes
DOI:10.1021/jo401521y
日期:2013.10.4
Two strategies, "hydrogenation-hydride reduction" and. "quaternization-hydride reduction", are reported, that make use of mild reaction conditions (room temperature) to efficiently remove the N-pyridin-2-yl directing group from a diverse set of C-2-substituted piperidines that were synthesized through directed Ru-catalyzed Sp(3) C-H functionalization. The deprotected products are obtained in moderate to good overall yields irrespective of the strategy followed, indicating that both methods are generally. equally effective. Only in the case of 2,6-disubstituted piperidines, could the "quaternization-hydride reduction" strategy not be used. The "hydrogenation-hydride reduction" protocol was successfully applied to trans- and cis-2-methyl-N-(pyridin-2-yl)-6-undecylpiperidine in a short synthetic route toward (+/-)-solenopsin A (trans diastereoisomer) and (+/-)-isosolenopsin A (cis diastereoisomer). The absolute configuration of the enantiomers of these fire: ant alkaloids could be determined via VCD spectroscopy.