A thorough investigation of the challenging Pd-catalyzed fluorination of five-membered heteroaryl bromides is presented. Crystallographic studies and density functional theory (DFT) calculations suggest that the challenging step of this transformation is C-F reductive elimination of five-membered heteroaryl fluorides from Pd(II) complexes. On the basis of these studies, we have found that various heteroaryl bromides bearing phenyl groups in the ortho position can be effectively fluorinated under catalytic conditions. Highly activated 2-bromoazoles, such as 8-bromocaffeine, are also viable substrates for this reaction.
Hexafluoroisopropanol as solvent and promotor in the Paal-Knorr synthesis of N-substituted diaryl pyrroles
作者:Robert H.E. Schirmacher、Daniel Rösch、Franziska Thomas
DOI:10.1016/j.tet.2021.131985
日期:2021.3
An additive-free synthesis of challenging N-substituted aryl pyrrolesfrom the often poorly soluble corresponding 1,4-diketones by means of the Paal-Knorr pyrrole synthesis is reported, which makes use of the unique properties of 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) as a solvent and reaction promotor. Our procedure offers simple execution and purification as well as easy scale-up and can be applied
step, which can be further exploited for the synthesis of 2,5-diaryl-3-bromothiophenes and 2,3,5-triarylthiophenes. The decarbonylative dibromination of 2-thiophenecarboxaldehyde derivatives with bromine under mild conditions is developed. The mechanism for the decarbonylation is investigated by experimental and instrumental techniques and is extended by a computational study. Alongside removal of the
Cu-catalyzed [2 + 2 + 1] cascade annulation of vinyl iodonium salts with elemental sulfur/selenium for the modular synthesis of thiophenes and selenophenes
作者:Yaxing Wu、Chao Wu、Fei Wang、Chao Chen
DOI:10.1039/d1nj05433c
日期:——
A [2 + 2 + 1] annulation protocol has been established for the modular synthesis of 2,4-disubstituted thiophenes/selenophenes, with excellent regioselectivity. The reactions have been catalyzed by copper salt with elemental sulfur and selenium serving as the chalcogen source. The mechanistic study has revealed that this process was initiated by a trisulfur radical anion using EPR.
4-diaryl- and 2,3-diarylthiophenes were synthesized from 2,5-dichlorothiophene via 4-aryl-2-chlorothiophenes in two and four steps including Ni-mediated cross-coupling, respectively. Aluminumchloride-catalyzedreaction of 3-aryl-2-chlorothiophenes with some aromatic ethers unexpectedly led to the formation of the corresponding 2,4-isomers.
不对称取代的 2,4-二芳基-和 2,3-二芳基噻吩分别由 2,5-二氯噻吩通过 4-芳基-2-氯噻吩在两步和四步(包括 Ni 介导的交叉偶联)中合成。氯化铝催化的 3-芳基-2-氯噻吩与一些芳香醚的反应出人意料地导致了相应的 2,4-异构体的形成。
Transition-Metal-Free Sulfuration/Annulation of Alkenes: Economical Access to Thiophenes Enabled by the Cleavage of Multiple C–H Bonds
作者:Liang Chen、Hao Min、Weilan Zeng、Xiaoming Zhu、Yun Liang、Guobo Deng、Yuan Yang
DOI:10.1021/acs.orglett.8b03078
日期:2018.12.7
and transition-metal-free strategy for the synthesis of thiophenes from substituted buta-1-enes with potassium sulfide has been presented. The reaction achieves double C–Sbondformations via cleavage of multiple C–H bonds and provides an efficientapproach to access various functionalized thiophenes. Moreover, the strategy can also be used for the synthesis of thiophenes from 1,4-diaryl-1,3-dienes.