Browsing by Author "Şahin, O."
Now showing 1 - 5 of 5
Results Per Page
Sort Options
Item 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 EmreWe 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.Item Open Access Determining F2 layer parameters via optimization using IRI model and IONOLAB TEC estimations(IEEE, 2011) Şahin, O.; Sezen, U.; Arıkan, F.; Arıkan, OrhanWe know that F2 layer of the ionosphere is most important layer in the progaration of high frequency (HF) waves. In this study, The relation of the height (HmF2) and the critical frequency (FoF2) of F2 layer-among the parameters of the Internation Reference Ionesphere (IRI) model-to the Total Electron Content (TEC) structure of ionosphere is investigated within their defined parametric range. These two parameters are then optimized using IONOLAB TEC estimations. Performance of the optimization algorithm is examined seperately for the cases of processing daily (24-hour) and hourly TEC data. It is observed that using hourly data produce results with much smaller errors. By using this optimization method, the height and the critical frequency of F2 layer are obtained for countries located on low and high latitudes including Turkey for the same quite day. Results are compared with ionosonde data and it is observed that error norms were in an acceptable range. By this way it is attained the more realistic electrical structure of ionosphere.Item Open Access Harmonic cantilevers for nanomechanical sensing of elastic properties(IEEE, 2003-06) Şahin, O.; Yaralıoğlu, G.; Grow, R.; Zappe, S. F.; Atalar, Abdullah; Quate, C.; Solgaard, O.We present a micromachined scanning probe cantilever, in which a specific higher order flexural mode is designed to be resonant at an exact integer multiple of the fundamental resonance frequency. We have demonstrated that such cantilevers enable sensing of nonlinear mechanical interactions between the atomically sharp tip at the free end of the cantilever and a surface with unknown mechanical properties in tapping-mode atomic force microscopy.Item Embargo Intramolecular through-space charge transfer between benzofuran and ynone groups on a naphthalene spacer(Royal Society of Chemistry, 2023-12-07) Çalıkyılmaz, Eylül; Karaoğlu, Gözde; Demir, M.; Şahin, O.; Ulgut, Burak; Akdağ, A.; Türkmen, Yunus EmreItem Open Access Polarization‐enhanced hydrogen bonding in 1,8‐dihydroxynaphthalene: conformational analysis, binding studies and hydrogen bonding catalysis(Wiley, 2020-11-16) Mammadova, Flora; Hamarat, B.; Ahmadli, Dilgam; Şahin, O.; Bozkaya, U.; Türkmen, Yunus EmreIn this article, the presence and effects of polarization‐enhanced hydrogen bonding in 1,8‐dihydroxynaphthalene (1,8‐DHN) were investigated in detail through a series of experimental and computational studies. First, the conformation of 1,8‐DHN, and its ability to make intra‐ and intermolecular hydrogen bonds were investigated in solid state by X‐ray crystallography, in solution by NMR spectroscopy, and computationally by density functional theory. Second, equilibrium binding constants, which were determined by 31P‐NMR titration studies, demonstrated stronger complexation of Ph3PO with 1,8‐DHN compared to mono‐naphthol derivatives 8‐methoxy‐1‐naphthol and 1‐naphthol. In the final section, 1,8‐DHN was observed to be an effective catalyst for the Friedel‐Crafts‐type addition reaction of indoles to β‐nitrostyrenes, and a rationale for this catalytic activity was provided via computational studies. All the findings described in this work support the enhanced hydrogen bond donating ability of 1,8‐DHN due to polarization caused by the six‐membered intramolecular hydrogen bond present in its structure.