First selective direct mono-arylation of piperidines using ruthenium-catalyzed C–H activation
摘要:
A Ru-catalyzed mono-arylation in alpha-position of saturated cyclic amines is reported employing a C-H activation protocol. Substitution of the pyridine directing group with a bulky group, e.g., trifluoromethyl in the 3-position, proved to be crucial to avoid bis-arylation. This highly selective transformation can be performed with different amines and arylboronate esters. Additionally, the directing group can be cleaved, taking advantage of an unprecedented detrifluoromethylation reaction.
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.