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31.
A direct, concise, synthetic method for the generation of [1,2,3]triazolo[5,1-a]isoquinoline derivatives, using a selective cascade cyclization of unsymmetrical substituted 1,2-bis(phenylethynyl)benzene derivatives with NaN3, has been developed. The reaction gave different substituted [1,2,3]triazolo[5,1-a]isoquinolines in moderate to good yields. It was found that the substituents on the alkynes were important for the selectivities of the cascade cyclization sequences. 相似文献
32.
A convenient and sustainable synthesis of pyrazolo[1,5-a]quinazolin-5(4H)-ones and [1,2,4]triazolo[1,5-a]quinazolin-5(4H)-one through copper-catalyzed cascade reactions of 2-bromobenzoates with 1H-pyrazol-5-amines or 1H-1,2,4-triazol-5-amine under ligand-free conditions in water is presented. It is notable that aqueous medium turned out to be crucial for the chemoselective formation of the title compounds. Compared with literature protocols, this new method showed advantages such as simple and sustainable procedure, commercially available starting materials, and convenient reuse of the reaction medium together with the copper catalyst. 相似文献
33.
《Tetrahedron》2013,69(36):7592-7607
A formal synthesis of didehydrostemofoline and isodidehydrostemofoline has been accomplished by preparing an intermediate in the Overman synthesis of these alkaloids from commercially available 2-deoxy-d-ribose. The work presented in this account chronicles the evolution of our explorations to identify the optimal steric and electronic control elements necessary to generate the tricyclic core structure of these alkaloids in a single operation from an acyclic precursor. The key step in the synthesis is a novel dipolar cycloaddition cascade sequence that is initiated by cyclization of a rhodium-derived carbene onto the nitrogen atom of a proximal imine group to generate an azomethine ylide that then undergoes spontaneous cyclization via dipolar cycloaddition. The synthesis features several other interesting reactions, including a Boord elimination to prepare a chiral allylic alcohol, a highly diastereoselective Hirama–Itô cyclization, and a useful modification of the Barton decarboxylation protocol. 相似文献
34.
A concise total synthesis of PDE-I and -II featuring copper-mediated double aryl amination with the combination of CuI, CsOAc, and Cs2CO3 is described. The highly substituted pyrroloindole skeleton was constructed by a one-pot five-step sequence including double aryl amination, β-elimination, deprotection of a Cbz group, and unexpected formation of an indole via removal of an Ns group followed by rearomatization. The undesired elimination of the protecting group (Ns group) was hampered by using the Boc group as a protecting group in the second-generation synthesis, which excluded the reduction of the indole required in the first-generation synthesis. 相似文献
35.
Cascade reactions of nitroallylic acetates with methanesulfonyl 2-aminoethanones affords either the 3-pyrrolines or the pyrroles in one pot depending on reaction solvents and temperature. A possible mechanism for the entire sequence is proposed. 相似文献
36.
Tao Wang Shuai Shi Dr. Mie Højer Vilhelmsen Tuo Zhang Dr. Matthias Rudolph Prof. Dr. A. Stephen K. Hashmi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(37):12512-12516
New and chemoselective gold(I)‐catalyzed transformations of 1‐(arylethynyl)‐7‐oxabicyclo[4.1.0]‐ heptan‐2‐ones were developed. Two completely different products—6,7‐dihydrobenzofuran‐4(5H)‐ones and benzofurans—could be obtained from the same starting material. The selectivity is determined by the ligand of the gold catalyst: triphenylphosphine delivers 6,7‐dihydrobenzofuran‐4(5H)‐ones, and 1,3‐bis(diisopropylphenyl)imidazol‐2‐ylidene leads to benzofurans. Eleven examples of each case are provided. The mechanistic suggestions for the pathways to both product types are supported by isotope labeling experiments. 相似文献
37.
Nuancheng Wang Prof. Dr. Bin Li Prof. Dr. Haibin Song Prof. Shansheng Xu Prof. Dr. Baiquan Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(1):358-364
The mechanism of the [(Cp*MCl2)2] (M=Rh, Ir)‐catalyzed oxidative annulation reaction of isoquinolones with alkynes was investigated in detail. In the first acetate‐assisted C? H‐activation process (cyclometalated step) and the subsequent mono‐alkyne insertion into the M? C bonds of the cyclometalated compounds, both Rh and Ir complexes participated well. However, the desired final products, dibenzo[a,g]quinolizin‐8‐one derivatives, were only formed in high yield when the Rh species participated in the final oxidative coupling of the C? N bond. Moreover, a RhI sandwich intermediate was isolated during this transformation. The iridium complexes were found to be inactive in the oxidative coupling processes. All of the relevant intermediates were fully characterized and determined by single‐crystal X‐ray diffraction analysis. Based on this mechanistic study, a RhIII→RhI→RhIII catalytic cycle was proposed for this reaction. 相似文献
38.
39.
A novel class of thiourea–phosphine was prepared from l-proline as a chiral renewable resource. The original structure of the chiral framework offers an interesting potential to the construction of bifunctional organocatalysts for asymmetric transformations. 相似文献
40.
Yuta Suzuki Tetsuhiro NemotoShun-ichi Nakano Zengduo ZhaoYuta Yoshimatsu Yasumasa Hamada 《Tetrahedron letters》2014
A novel method for synthesizing 4,5-fused tricyclic quinoline derivatives based on an acid-promoted intramolecular Friedel–Crafts allenylation of anilines. Using aryl group-substituted propargyl alcohol derivatives with a meta-substituted N-Boc aniline unit as substrates, a four-step reaction sequence involving an acid-promoted intramolecular Friedel–Crafts allenylation of anilines, an acid-promoted intramolecular C–N bond formation, deprotection of the Boc group, and air oxidation proceeded in a single pot, producing the corresponding 4,5-fused tricyclic quinoline derivatives in 31–84% yield. 相似文献