Nitration of N‐heteroaromatics: The first example of palladium‐catalyzed direct ortho‐nitration of aryl CH bonds is described. A range of azaarenes, such as 2‐arylquinoxalines, pyridines, pyrazoles, and O‐methyl oximes, were nitrated with excellent chemo‐ and regioselectivity (see scheme; DCE=1,2‐dichloroethane). Preliminary mechanistic investigations support a silver‐mediated radical mechanism involving
Palladium-Catalyzed Chelation-Assisted Aromatic C–H Nitration: Regiospecific Synthesis of Nitroarenes Free from the Effect of the Orientation Rules
作者:Wei Zhang、Shaojie Lou、Yunkui Liu、Zhenyuan Xu
DOI:10.1021/jo400594j
日期:2013.6.21
ortho-nitration of aryl C–H bond is described. A range of azaarenes such as 2-arylquinoxalines, pyridines, quinoline, and pyrazoles were nitrated with excellent chemo- and regioselectivity. Using the O-methyl oximyl group as a removable directing group, the regiospecific synthesis of a variety of o-nitro aryl ketones was achieved starting from aryl ketones via a three-step process involving the Pd-catalyzed
The mechanism of two reactions leading to isomeric 2-(N,N-disubstituted amino)thiazol-5-yl ketones
作者:Katherine Challacombe、Susan E. Leach、Simon J. Plackett、G. Denis Meakins
DOI:10.1039/p19880002213
日期:——
A study has been made of the condensations between N-acyl-N′,N′-disubstituted thioureas and α-halogeno ketones [reaction (I)], and between N,N-disubstituted thioureas and 2-bromo-1,3-diketones [reaction (II)]. The mechanistic details were elucidated by using substrates with pairs of (almost) equally reactive but spectrometrically distinguishable acyl groups, e.g., CH3CO and CD3CO. In the presence of
Base catalysed rearrangements involving ylide intermediates. Part 15. The mechanism of the Stevens [1,2] rearrangement
作者:W. David Ollis、Max Rey、Ian O. Sutherland
DOI:10.1039/p19830001009
日期:——
The Stevens [1,2] rearrangement of acyl-stabilised ammoniumylides has been investigated with regard to stereoselectivity, intramolecularity and the formation of products in addition to the [1,2] rearrangementproduct. A detailed study of the effects of reaction conditions upon the rearrangement of the ylidederivedfrom the salt (13) has shown that the stereoselectivity (retention of the configuration
A selective oxidative [4+2] annulation of alkenes with imidazo-fused heterocycles has been developed by using the synergistic combination of photoredox and cobaloxime catalysts. It allows facile access to various imidazole-fused polyaromatic scaffolds accompanied by H2 evolution. This protocol features high regioselectivity as well as a broad substrate scope. Detailed mechanistic studies indicate that
通过使用光氧化还原和钴肟催化剂的协同组合,开发了烯烃与咪唑稠合杂环的选择性氧化[4+2]环化。它允许轻松获得各种咪唑稠合的聚芳族支架,并伴随 H 2 的演化。该方案具有高区域选择性和广泛的底物范围。详细的机理研究表明,该催化系统促进的电子/氢转移过程的两倍实现了咪唑稠合杂环与烯烃的环π延伸。