Browsing by Author "Omur, Cenk"

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Enantio-Pure Synthesis of Enyne Epoxides and Their Iron-Catalyzed Sn2" Reactions With Grignard Reagents
(01. Izmir Institute of Technology, 2020-12) Omur, Cenk; Artok, Levent; 04.01. Department of Chemistry; 04. Faculty of Science; 01. Izmir Institute of Technology
The use of transition-metal catalysts in synthetic chemistry has gained a lot of significance in the last decade, by virtue of their selectivity wheather regio-isomerically, or enantiomerically, or both. Besides their superior selectivity, these reactions have also been considered as atom economic and environmental-friendly. Iron-catalyzed reactions gained undeniable attention in regard to their low toxicity and presence in enzymatic reactions. Thus, use of the iron catalyst in the synthesis of biologically important and intermediary chemicals bear great significance. Allene motifs, which exist in vast number of naturally occuring compounds are important intermediates in synthesis of bio-active materials due to their versatile reactivity and instrict chirality. The first transition metal-mediated sythesis of allenes was accomplished by 1,3-substitution reaction of propargylic acetates with stoichiometric amounts of organocuprates (Rona et al.,1968). Later on, Fürstner and co-workers have established a technique that, allows the use of catalytic amounts of iron complexes for the reaction of Grignard reagents with propargylic oxiranes which yields -allenol compounds with different modes of addition (Fürstner et al., 2003). In addition to significant developments in this field, our group has established iron-promoted reactions of enyne acetates and oxiranes with Grignard reagents, producing functionalized vinyl allene structures. (Taç et al., 2017). In that study, reactions proceeded regioselectively in 1,5-substitution (SN2'') manner yielded vinylallenes in good to high yields. However, stereoselectivity of the method was not sufficiently satisfactory. Nevertheless, we disclose herein that the corresponding iron-catalyzed reactions of enyne oxiranes with an endocyclic alkenyl moiety are highly stereoselective; vinyl allene products could be obtained in high diastereomeric ratios by this method. Moreover, the ability to synthesize oxirane substrates in high enantiomeric purity allowed the production of the desired enantiopure vinyl allenes.
Iron-Promoted 1,5-Substitution Reaction of Endocyclic Enyne Oxiranes With Memgbr: a Stereoselective Method for the Synthesis of Exocyclic 2,4,5-Trienol Derivatives
(MDPI, 2023) Kuş, Melih; Omur, Cenk; Karaca, Sila; Artok, Levent; 04.01. Department of Chemistry; 04. Faculty of Science; 01. Izmir Institute of Technology
The iron-promoted 1,5-substitution reaction of endocyclic oxiranes with MeMgBr yields exocyclic 2,4,5-trienols with high diastereomeric ratios of up to 100:0. However, for the method's success, the oxirane ring must have a trans-configuration. The reactions exhibit strong stereoselectivity concerning the methylation mode and the configuration of the resulting exocyclic double bond. Enantiomerically pure enyne oxiranes can be synthesized through Sharpless asymmetric dihydroxylation and subsequent manipulations. With these reagents, it has been possible to produce exocyclic 2,4,5-trienols in enantiopure forms. Importantly, this process maintains chirality without degradation during the center-to-axis transfer of chirality.