Browsing by Subject "Heterocycles"

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Open Access
Catalytic aza-Nazarov cyclization reactions to access α-methylene-γ-lactam heterocycles
(Beilstein-Institut Zur Forderung der Chemischen Wissenschaften, 2023-07-17) Yağcı, Bilge Banu; Dönmez, Selin Özge; Şahin, O.; Türkmen, Yunus Emre
We have developed a catalytic aza-Nazarov reaction of N-acyliminium salts generated in situ from the reaction of a variety of cyclic and acyclic imines with α,β-unsaturated acyl chlorides to afford substituted α-methylene-γ-lactam heterocycles. The reactions proceed effectively in the presence of catalytic (20 mol %) amounts of AgOTf as an anion exchange agent or hydrogen-bond donors such as squaramides and thioureas as anion-binding organocatalysts. The aza-Nazarov cyclization of 3,4-dihydroisoquinolines with α,β-unsaturated acyl chlorides gives tricyclic lactam products 7 in up to 79% yield with full diastereocontrol (dr = >99:1). The use of acyclic imines in a similar catalytic aza-Nazarov reaction with 20 mol % of AgOTf results in the formation of α-methylene-γ-lactam heterocycles 19 in up to 76% yield and with good to high diastereoselectivities (4.3:1 to 16:1). We have demonstrated the scalability of the reaction with a gram-scale example. The relative stereochemistry of the α-methylene-γ-lactam products 19 has been determined via the single-crystal X-ray analysis of lactam 19l. In order to shed light on the details of the reaction mechanism, we have performed carefully designed mechanistic studies which consist of experiments on the effect of β-silicon stabilization, the alkene geometry of the α,β-unsaturated acyl chloride reactants, and adventitious water on the success of the catalytic aza-Nazarov reaction.
Open Access
Synthesis of some substituted 6-phenyl purine analogues and their biological evaluation as cytotoxic agents
(Slovensko Kemijsko Drustvo, 2017) Kucukdumlu, A.; Tuncbilek, M.; Guven, E. B.; Atalay, R. C.
A series of 6-(4-substituted phenyl)-9-(tetrahydropyran-2-yl)purines 3–9, 6-(4-substituted phenyl)purines 10–16, 9-((4-substituted phenyl)sulfonyl)-6-(4-substituted phenyl)purines 17–32 were prepared and screened initially for their in vitro anticancer activity against selected human cancer cells (liver Huh7, colon HCT116, breast MCF7). 6-(4-Phenoxy-phenyl)purine analogues 9, 16, 30–32, had potent cytotoxic activities. The most active purine derivatives 5–9, 14, 16, 18, 28–32 were further screened for their cytotoxic activity in hepatocellular cancer cells. 6-(4-Phenoxyphenyl)-9-(tetrahydropyran-2-yl)-9H-purine (9) had better cytotoxic activity (IC50 5.4 μM) than the well-known nucleobase analogue 5-FU and known nucleoside drug fludarabine on Huh7 cells. The structure–activity relationship studies reported that the substitution at C-6 positions in purine nucleus with the 4-phenoxyphenyl group is responsible for the anti-cancer activity.