Pyrrolidines bearing a quaternary α-stereogenic center. Part 2: Access to proline chimeras, stereoselective approach and mechanistic aspects
摘要:
The present work describes the access to various proline chimeras bearing a quaternary cx-stereogenic center, via the Duhamel ring contraction of heterocyclic enamines. Attempts to induce diastereoselectivity are reported. The 'chiral enamine' strategy afforded the required aminoaldehydes with diastereomeric ratios as high as 85:15. (C) 2000 Elsevier Science Ltd. All rights reserved.
A directive Ni catalyst overrides conventional site selectivity in pyridine C–H alkenylation
作者:Tao Zhang、Yu-Xin Luan、Nelson Y. S. Lam、Jiang-Fei Li、Yue Li、Mengchun Ye、Jin-Quan Yu
DOI:10.1038/s41557-021-00792-1
日期:2021.12
Achieving the transition metal-catalysed pyridine C3âH alkenylation, with pyridine as the limiting reagent, has remained a long-standing challenge. Previously, we disclosed that the use of strong coordinating bidentate ligands can overcome catalyst deactivation and provide Pd-catalysed C3 alkenylation of pyridines. However, this strategy proved ineffective when using pyridine as the limiting reagent, as it required large excesses and high concentrations to achieve reasonable yields, which rendered it inapplicable to complex pyridines prevalent in bioactive molecules. Here we report that a bifunctional N-heterocyclic carbene-ligated NiâAl catalyst can smoothly furnish C3âH alkenylation of pyridines. This method overrides the intrinsic C2 and/or C4 selectivity, and provides a series of C3-alkenylated pyridines in 43â99% yields and up to 98:2 C3 selectivity. This method not only allows a variety of pyridine and heteroarene substrates to be used as the limiting reagent, but is also effective for the late-stage C3 alkenylation of diverse complex pyridine motifs in bioactive molecules. Selective CâH alkenylation of pyridines at the C3 position, with the pyridine as the limiting reagent, is a long-standing synthetic challenge. Now, it has been shown that this can be achieved using a bifunctional N-heterocyclic carbene-ligated NiâAl catalyst that overrides the intrinsic C2/4 selectivity of pyridines and enables the selective late-stage functionalization of a range of complex pyridyl-containing motifs.
Enantioselective C2–H Alkylation of Pyridines with 1,3-Dienes via Ni–Al Bimetallic Catalysis
作者:Jiang-Fei Li、Deng Pan、Hao-Rui Wang、Tao Zhang、Yi Li、Genping Huang、Mengchun Ye
DOI:10.1021/jacs.2c09306
日期:2022.10.19
A chiral phosphine oxide-ligated Ni–Al bimetallic catalyst was used to realize an enantioselective C2–H alkylation of pyridines without the need of a C2-block. A wide range of pyridines, including unsubstituted pyridine, C3, C4, and C2-substituted pyridines, and even complex pyridine-containing bioactive molecules are well compatible with the reaction, providing up to 81% yield and up to 97% ee.
Photochemical Organocatalytic Functionalization of Pyridines via Pyridinyl Radicals
作者:Emilien Le Saux、Eleni Georgiou、Igor A. Dmitriev、Will C. Hartley、Paolo Melchiorre
DOI:10.1021/jacs.2c12466
日期:2023.1.11
We report a photochemical method for the functionalization of pyridines with radicals derived from allylic C–H bonds. Overall, two substrates undergo C–H functionalization to form a new C(sp2)–C(sp3) bond. The chemistry harnesses the unique reactivity of pyridinyl radicals, generated upon single-electron reduction of pyridinium ions, which undergo effective coupling with allylic radicals. This novel
Nickel-Catalyzed Transesterification of Methyl Esters
作者:Stephen G. Newman、Yan-Long Zheng、Omid Daneshfar、Jia-Yi Li、Jeanne Masson-Makdissi、Émile Pinault-Masson
DOI:10.1055/s-0042-1751485
日期:2024.5
transesterification of methyl esters with aliphatic alcohols was developed using Ni/dcype catalysis. This reaction features the cleavage of the strong C(acyl)–OMe bond in the absence of acidic or basic additives, providing volatile methanol as the only stoichiometric waste product. A wide range of (hetero)aromatic and aliphatic methyl esters can be converted into the corresponding functionalized esters in good to excellent