Synthesis of 2- and 2,3-Substituted Pyrazolo[1,5-a]pyridines: Scope and Mechanistic Considerations of a Domino Direct Alkynylation and Cyclization of N-Iminopyridinium Ylides Using Alkenyl Bromides, Alkenyl Iodides, and Alkynes
摘要:
Direct functionalization and tandem processes have both received considerable recent interest due to their cost and time efficiency. Herein we report the synthesis of difficult to obtain 2-substituted pyrazolo[1,5-a]pyridines through a tandem palladium-catalyzed/silver-mediated elimination/direct functionalization/cyclization reaction involving N-benzoyliminopyridinium ylides. As such, these biologically important molecules are prepared in an efficient, high-yielding manner, only requiring a two-step sequence from pyridine. Aryl-substituted alkenyl bromides and iodides are effective ylide coupling partners. Mechanistic studies led to the use of terminal alkynes, which extended the scope of the reaction to include alkyl substitution on the unsaturated reactive site. The optimization, scope, and mechanistic considerations of the process are discussed.
Visible-Light-Enabled <i>Ortho</i>-Selective Aminopyridylation of Alkenes with <i>N</i>-Aminopyridinium Ylides
作者:Yonghoon Moon、Wooseok Lee、Sungwoo Hong
DOI:10.1021/jacs.0c05025
日期:2020.7.15
By utilizing an underexplored reactivity mode of N-aminopyridinium ylides, we developed the visible-light-induced ortho-selective aminopyridylation of alkenes via radical-mediated 1,3-dipolar cycloaddition. The photocatalyzed single-electron oxidation of N-aminopyridinium ylides generates the corresponding radical cations that enable previously inaccessible 1,3-cycloaddition with a broader range of
通过利用 N-氨基吡啶鎓叶立德的未充分探索的反应模式,我们通过自由基介导的 1,3-偶极环加成开发了可见光诱导的烯烃邻位选择性氨基吡啶化。N-氨基吡啶鎓叶立德的光催化单电子氧化产生相应的自由基阳离子,使以前无法实现的1,3-环加成与更广泛的烯烃底物成为可能。所得的环加成加合物迅速进行随后的 NN 键均裂,赋予显着的热力学驱动力以产生各种 β-氨基乙基吡啶。值得注意的是,在无金属和温和条件下,氨基和吡啶基可以通过模块化控制邻位选择性和 1,2- 顺式非对映选择性安装到活化和未活化的烯烃中。
Photocatalytic Vicinal Aminopyridylation of Methyl Ketones by a Double Umpolung Strategy
作者:Honggu Im、Wonjun Choi、Sungwoo Hong
DOI:10.1002/anie.202008435
日期:2020.9.28
umpolung strategy for the vicinal aminopyridylation of ketones was developed using pyridinium N−N ylides. The inversion of the polarity of the pyridinium N−N ylides by single‐electron oxidation successfully enables radical‐mediated 1,3‐dipolar cycloadditions with enolsilanes formed in situ from ketones, followed by homolytic cleavage of the N−N bond. Intriguingly, the nucleophilic amino and electrophilic
Highly regioselective synthesis of 2,4,5-(hetero)aryl substituted oxazoles by intermolecular [3+2]-cycloaddition of unsymmetrical internal alkynes
作者:Elli Chatzopoulou、Paul W. Davies
DOI:10.1039/c3cc45410j
日期:——
A robust N-nucleophilic 1,3-N,O-dipole equivalent reacts with unsymmetrical internal alkynes under gold catalysis. Conjugation from a remote nitrogen lone pair enables and controls this convergent and highly regioselective process.
Reaction of Diphenylcyclopropenethione with Pyridinium Imines
作者:J. W. Lown、K. Matsumoto
DOI:10.1139/v72-090
日期:1972.2.15
Reaction of diphenylcyclopropenethione with a variety of N-substituted pyridinium imines in refluxing benzene gives 2,4,5-trisubstituted-6H-1,3-oxazin-6-thiones in good to excellent yields. The structure of 2,4,5-triphenyl-6H-1,3-oxazin-6-thione prepared in this manner was proven by oxidation and by hydrolysis to the known 2,4,5-triphenyl-6H-1,3-oxazin-6-one. In the preparation of 4,5-diphenyl-2-ethoxy-6H-1
Rh(III)-Catalyzed C–H Diamidation and Diamidation/Intramolecular Cyclization of <i>N</i>-Iminopyridinium Ylides with Dioxazolones
作者:Xiang Li、Qing Zhao、Yang Shen、Ran Ma
DOI:10.1021/acs.joc.1c03042
日期:2022.3.4
A highly efficient Rh(III)-catalyzed C–H diamidation and diamidation/intramolecular cyclization of N-iminopyridinium ylides with dioxazolones has been developed, providing diamidated products and benzoxazinone products in good to excellent yields. Notably, the tunable selectivity of this reaction can be controlled by simply switching the solvent and the temperature. This reaction features operational