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101.
In base, a 2-aminopyrrole reacted with a 1,3,5-triazine to give a zwitterion (Meisenheimer complex). Acid promoted its conversion to the pyrrolo[2,3-d]pyrimidine. A cascade mechanism with reversible steps is proposed to explain why both a base and an acid are needed for the cycloaddition to occur. 相似文献
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105.
The optimal weighting scheme and the role of coupling strength against load failures on symmetrically and asymmetrically coupled interdependent networks were investigated. The degree-based weighting scheme was extended to interdependent networks, with the flow dynamics dominated by global redistribution based on weighted betweenness centrality. Through contingency analysis of one-node removal, we demonstrated that there still exists an optimal weighting parameter on interdependent networks, but it might shift as compared to the case in isolated networks because of the break of symmetry. And it will be easier for the symmetrically and asymmetrically coupled interdependent networks to achieve robustness and better cost configuration against the one-node-removal-induced cascade of load failures when coupling strength was weaker. Our findings might have great generality for characterizing load-failure-induced cascading dynamics in real-world degree-based weighted interdependent networks. 相似文献
106.
Alexander V. Aksenov Igor Yu. Grishin Nicolai A. Aksenov Vladimir V. Malyuga Dmitrii A. Aksenov Mezvah A. Nobi Michael Rubin 《Molecules (Basel, Switzerland)》2021,26(14)
Nitroalkanes activated with polyphosphoric acid serve as efficient electrophiles in reactions with various nucleophilic amines. Strategically placed second functionality allows for the design of annulation reactions enabling preparation of various heterocycles. This strategy was employed to develop an innovative synthetic approach towards 3,4-dihydroquinazolines from readily available 2-(aminomethyl)anilines. 相似文献
107.
A novel [4 + 1] annulation protocol for the synthesis of polysubstituted pyrrole derivatives from β-keto acids and α,β-unsaturated imines via a tandem Michael addition, decarboxylation and TBAI-catalyzed oxidative annulation has been developed. This method provides a new and facile application of β-keto acids as 1,1-nucleophilic/electrophilic type C1 synthons. 相似文献
108.
[1,3]-Rearrangement reactions of an oxygen atom from a nitrogen atom to a carbon atom is an ideal way to synthesize highly elaborate molecules in which nitrogen and oxygen functionalities are vicinally arranged. Recently, it has been disclosed that this intriguing transformation takes place in the presence of Lewis acidic metal catalysts. In this digest, we summarize recent findings on the catalytic [1,3]-oxygen rearrangement reactions, such as direct [1,3]-rearrangement of N-oxygenated enamines and anilines, as well as π-acidic metal-catalyzed cascade reaction involving the [1,3]-rearrangement process. 相似文献
109.
《Tetrahedron letters》2019,60(35):150992
An efficient and concise approach for rapid assembly of the ABC tricyclic carbon skeleton of mexicanolide-type limonoids is described. The acetal/ketal diketoester precursors were prepared from simple starting materials by LiOH-mediated Michael reactions. The ABC tricyclic skeleton bearing multiple stereogenic centers was efficiently constructed by a powerful one-pot cascade reaction, which includes acetal/ketal hydrolysis, double intramolecular aldol condensation, and alkene migration. 相似文献
110.
Hao Dong Dawen Xu Wangsheng Liu Yaopeng Zhang Hao Guo 《Journal of Saudi Chemical Society》2019,23(8):1041-1048
An intramolecular-intermolecular cascade cyclization reaction via multi metal-carbene intermediates has been developed. This reaction uses catalytic amount of Nd(OTf)3, which actives both alkyne and aldehyde moieties. This protocol provides a novel strategy for the synthesis of phenanthro[9,10-b]furans. 相似文献