5661-06-3Relevant articles and documents
Bioinspired Radical-Mediated Transition-Metal-Free Synthesis of N-Heterocycles under Visible Light
K. Bains, Amreen,Ankit, Yadav,Adhikari, Debashis
, p. 324 - 329 (2020/11/30)
A redox-active iminoquinone motif connected with π-delocalized pyrene core has been reported that can perform efficient two-electron oxidation of a class of substrates. The design of the molecule was inspired by the organic redox cofactor topaquinone (TPQ), which executes amine oxidation in the enzyme, copper amine oxidase. Easy oxidation of both primary and secondary alcohols happened in the presence of catalytic KOtBu, which could reduce the ligand backbone to its iminosemiquinonate form under photoinduced conditions. Moreover, this easy oxidation of alcohols under aerobic condition could be elegantly extended to multi-component, one-pot coupling for the synthesis of quinoline and pyrimidine. This organocatalytic approach is very mild (70 °C, 8 h) compared to a multitude of transition-metal catalysts that have been used to prepare these heterocycles. A detailed mechanistic study proves the intermediacy of the iminosemiquinonate-type radical and a critical hydrogen atom transfer step to be involved in the dehydrogenation reaction.
Direct synthesis of ring-fused quinolines and pyridines catalyzed byNNHY-ligated manganese complexes (Y = NR2or SR)
Han, Mingyang,Lin, Qing,Liu, Qingbin,Liu, Song,Ma, Ning,Solan, Gregory A.,Sun, Wen-Hua,Wang, Zheng,Yan, Xiuli
, p. 8026 - 8036 (2021/12/27)
Four cationic manganese(i) complexes, [(fac-NNHN)Mn(CO)3]Br (Mn-1-Mn-3) and [(fac-NNHS)Mn(CO)3]Br (Mn-4) (whereNNHis a 5,6,7,8-tetrahydro-8-quinolinamine moiety), have been synthesized and evaluated as catalysts for the direct synthesis of quinolines and pyridines by the reaction of a γ-amino alcohol with a ketone or secondary alcohol;NNHS-ligatedMn-4proved the most effective of the four catalysts. The reactions proceeded well in the presence of catalyst loadings in the range 0.5-5.0 mol% and tolerated diverse functional groups such as alkyl, cycloalkyl, alkoxy, chloride and hetero-aryl. A mechanism involving acceptorless dehydrogenation coupling (ADC) has been proposed on the basis of DFT calculations and experimental evidence. Significantly, this manganese-based catalytic protocol provides a promising green and environmentally friendly route to a wide range of synthetically important substituted monocyclic, bicyclic as well as tricyclicN-heterocycles (including 50 quinoline and 26 pyridine examples) with isolated yields of up to 93%.
Homogeneous Nickel-Catalyzed Sustainable Synthesis of Quinoline and Quinoxaline under Aerobic Conditions
Bains, Amreen K.,Singh, Vikramjeet,Adhikari, Debashis
, p. 14971 - 14979 (2020/11/30)
Dehydrogenative coupling-based reactions have emerged as an efficient route toward the synthesis of a plethora of heterocyclic rings. Herein, we report an efficacious, nickel-catalyzed synthesis of two important heterocycles such as quinoline and quinoxaline. The catalyst is molecularly defined, is phosphine-free, and can operate at a mild reaction temperature of 80 °C. Both the heterocycles can be easily assembled via double dehydrogenative coupling, starting from 2-aminobenzyl alcohol/1-phenylethanol and diamine/diol, respectively, in a shorter span of reaction time. This environmentally benign synthetic protocol employing an inexpensive catalyst can rival many other transition-metal systems that have been developed for the fabrication of two putative heterocycles. Mechanistically, the dehydrogenation of secondary alcohol follows clean pseudo-first-order kinetics and exhibits a sizable kinetic isotope effect. Intriguingly, this catalyst provides an example of storing the trapped hydrogen in the ligand backbone, avoiding metal-hydride formation. Easy regeneration of the oxidized form of the catalyst under aerobic/O2 oxidation makes this protocol eco-friendly and easy to handle.
