- Borane-Catalyzed Reduction of Pyridines via a Hydroboration/Hydrogenation Cascade
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We have developed a method for a B(C6F5)3-catalyzed hydroboration/hydrogenation cascade reduction of pyridines. The method was particularly effective for 2,3-disubstituted pyridines, which generated piperidines in high yields with high cis selectivity. Mechanistic studies indicated that the pyridine substrates and the piperidine products sequentially acted as bases in cooperation with B(C6F5)3to split H2. The broad functional group tolerance of the method allowed its use for the synthesis of some biologically active molecules.
- Yang, Zhao-Ying,Luo, Heng,Zhang, Ming,Wang, Xiao-Chen
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p. 10824 - 10829
(2021/09/08)
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- Direct α-C-H bond functionalization of unprotected cyclic amines
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Cyclic amines are ubiquitous core structures of bioactive natural products and pharmaceutical drugs. Although the site-selective abstraction of C-H bonds is an attractive strategy for preparing valuable functionalized amines from their readily available parent heterocycles, this approach has largely been limited to substrates that require protection of the amine nitrogen atom. In addition, most methods rely on transition metals and are incompatible with the presence of amine N-H bonds. Here we introduce a protecting-group-free approach for the α-functionalization of cyclic secondary amines. An operationally simple one-pot procedure generates products via a process that involves intermolecular hydride transfer to generate an imine intermediate that is subsequently captured by a nucleophile, such as an alkyl or aryl lithium compound. Reactions are regioselective and stereospecific and enable the rapid preparation of bioactive amines, as exemplified by the facile synthesis of anabasine and (-)-solenopsin A.
- Chen, Weijie,Ma, Longle,Paul, Anirudra,Seidel, Daniel
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p. 165 - 169
(2018/02/06)
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- B(C6F5)3-Catalyzed Cascade Reduction of Pyridines
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B(C6F5)3 has been found to be an effective catalyst for reduction of pyridines and other electron-deficient N-heteroarenes with hydrosilanes (or hydroboranes) and amines as the reducing reagents. The success of this development hinges upon the realization of a cascade process of dearomative hydrosilylation (or hydroboration) and transfer hydrogenation. The broad functional-group tolerance (e.g. ketone, ester, unactivated olefins, nitro, nitrile, heterocycles, etc.) implies high practical utility.
- Liu, Zhi-Yun,Wen, Zhi-Hui,Wang, Xiao-Chen
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supporting information
p. 5817 - 5820
(2017/05/12)
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- Borane-Catalyzed Transfer Hydrogenations of Pyridines with Ammonia Borane
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With the use of ammonia borane as a hydrogen source, a borane catalyzed metal-free transfer hydrogenation of pyridines was successfully realized for the first time to furnish a variety of piperidines in 44-88% yields with moderate to excellent cis-selecti
- Zhou, Qiwen,Zhang, Lanqiong,Meng, Wei,Feng, Xiangqing,Yang, Jing,Du, Haifeng
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supporting information
p. 5189 - 5191
(2016/11/02)
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- Facile denitrosation of Cyclic N-nitrosamines with hydrazoic acid
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A simple and facile method for the denitrosation of cyclic N-nitrosamines using HN3 (concentrated H2SO4+NaN3) is reported. In this method, limited usage of this reagent does not affect the carbonyl group.
- Ponnuswamy,Akila,Kiruthiga Devi
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supporting information
p. 2030 - 2034
(2015/08/18)
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- Addition of organometallic reagents to chiral N-methoxylactams: Enantioselective syntheses of pyrrolidines and piperidines
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Enantioselective iridium-catalyzed allylic substitutions were used to prepare N-allyl hydroxamic acid derivatives that were suitable for ring-closing metathesis, giving N-methoxylactams. Reactions of these derivatives with Grignard or organolithium compou
- Jaekel, Mascha,Qu, Jianping,Schnitzer, Tobias,Helmchen, Guenter
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p. 16746 - 16755
(2014/01/06)
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- Metal-free borane-catalyzed highly stereoselective hydrogenation of pyridines
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A metal-free direct hydrogenation of pyridines was successfully realized by using homogeneous borane catalysts generated from alkenes and HB(C 6F5)2 via in situ hydroboration. The reaction affords a broad range of piperidines in high yields with excellent cis stereoselectivities.
- Liu, Yongbing,Du, Haifeng
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supporting information
p. 12968 - 12971
(2013/09/24)
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- Diastereoselective access to nonracemic 2-cis-substituted and 2,6-cis-disubstituted piperidines
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Access to nonracemic amino ketones via a hydrozirconation/transmetalation/ acylation sequence applied to Boc-protected 1-aminobut-3-enes is presented. This method was applied to the stereoselective synthesis of cyclic imines (or iminiums) which were diastereoselectively converted into 2-cis-substituted and 2,6-cis-disubstituted piperidines. The potential of this approach in the field of alkaloid synthesis was illustrated by the synthesis of (-)-coniine and (-)-indolizidine 209D. Furthermore, access to indolizidines bearing a quaternary center could also be envisioned through this strategy.
- Coia, Nicolas,Mokhtari, Naima,Vasse, Jean-Luc,Szymoniak, Jan
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p. 6292 - 6295
(2012/01/06)
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- Facile diastereoselective reactions of chiral 1,3-oxazolidines with grignard reagents; asymmetric syntheses of 2-substituted and 2,6-disubstituted piperidines
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(S)- and (R)-2-Phenylpiperidines, (S)- and (R)-2-methylpiperidines, meso- and (2R, 6R)-2,6-diphenylpiperidines, and meso- and (25, 65)-2,6-dimethylpiperidines were synthesized asymmetrically starting from the diastereoselective addition of Grignard reagents to chiral 1,3-oxazolidines, converting of 1-aza-4-oxabicyclo[4.3.0]nonane derivatives as pivotal intermediates.
- Poerwono, Hadi,Higashiyama, Kimio,Yamauchi, Takayasu,Takahashi, Hiroshi
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p. 385 - 400
(2007/10/03)
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- Conformational analysis of r-2,c-6-diphenylpiperidines by NMR and molecular mechanics methods
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The title compounds 6-10 have been prepared by the Wolf-Kishner reduction of the piperidin-4-ones (1-5) and their stereochemistry investigated by 1H and 13C NMR specteroscopy.Wolf-Kishner reduction of t-3,t-5-dimethyl-r-2,c-6-diphenylpiperidin-4-one (5) l
- Ravindran, T,Jeyaraman, R
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p. 677 - 682
(2007/10/02)
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- FORMATION OF NITROGEN HETEROCYCLES IN THE HYDROAMINATION OF 1,5-DIKETONES
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It was established that the principal pathway in the catalytic hydro(alkyl,aryl)amination of 1,5-diketones is, depending on the structure of the diketone and the amine component, the stereospecific formation of substituted piperidines, octa- and decahydroquinolines, and perhydroacridines or pyridine and tetrahydro- and benzodihydroquinoline structures.
- Kharchenko, V. G.,Kriven'ko, A. P.,Fedotova, O. V.,Nikolaeva, T. G.
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p. 720 - 723
(2007/10/02)
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