Intramolecular Kinugasa reactions on in situ generated carbohydrate-derived alkynylnitrones are described. The effects of the length of chains, their mutual configuration, influence of experimental conditions on product distribution and feasibility of the β-lactam ring construction were studied. Intramolecular reactions proceed with high stereoselectivity to provide in each case one product only. The cycloadducts from tartaric acid were converted into the corresponding non-racemic 4-acetoxy azetidinones in good yields.
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Mechanism of the Kinugasa Reaction Revisited.
J Org Chem
August 2021
Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden.
The mechanism of the Kinugasa reaction, that is, the copper-catalyzed formation of β-lactams from nitrones and terminal alkynes, is re-evaluated by means of density functional theory calculations and in light of recent experimental findings. Different possible mechanistic scenarios are investigated using phenanthroline as a ligand and triethylamine as a base. The calculations confirm that after an initial two-step cycloaddition promoted by two copper ions, the resulting five-membered ring intermediate can undergo a fast and irreversible cycloreversion to generate an imine and a dicopper-ketenyl intermediate.
View Article and Find Full Text PDFMolecular Basis for Two Stereoselective Diels-Alderases that Produce Decalin Skeletons*.
Angew Chem Int Ed Engl
October 2021
Department of Chemistry and Biotechnology, Graduate School of Engineering, Tottori University, 4-101 Koyama-cho, Minami, Tottori, 680-8552, Japan.
Enzymes catalyzing [4+2] cycloaddition have attracted increasing attention because of their key roles in natural product biosynthesis. Here, we solved the X-ray crystal structures of a pair of decalin synthases, Fsa2 and Phm7, that catalyze intramolecular [4+2] cycloadditions to form enantiomeric decalin scaffolds during biosynthesis of the HIV-1 integrase inhibitor equisetin and its stereochemical opposite, phomasetin. Computational modeling, using molecular dynamics simulations as well as quantum chemical calculations, demonstrates that the reactions proceed through synergetic conformational constraints assuring transition state-like substrates folds and their stabilization by specific protein-substrate interactions.
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Org Biomol Chem
April 2020
Institute of Organic Chemistry of the Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland.
Intramolecular Kinugasa reactions on in situ generated carbohydrate-derived alkynylnitrones are described. The effects of the length of chains, their mutual configuration, influence of experimental conditions on product distribution and feasibility of the β-lactam ring construction were studied. Intramolecular reactions proceed with high stereoselectivity to provide in each case one product only.
View Article and Find Full Text PDFTheoretical study of mechanism and stereoselectivity of catalytic Kinugasa reaction.
J Org Chem
March 2015
Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden.
The mechanism of the catalytic Kinugasa reaction is investigated by means of density functional theory calculations. Different possible mechanistic scenarios are presented using phenanthroline as a ligand, and it is shown that the most reasonable one in terms of energy barriers involves two copper ions. The reaction starts with the formation of a dicopper-acetylide that undergoes a stepwise cycloaddition with the nitrone, generating a five-membered ring intermediate.
View Article and Find Full Text PDFA novel synthesis of beta-lactam fused cyclic enediynes by intramolecular Kinugasa reaction.
Chem Commun (Camb)
July 2006
Bioorganic Laboratory, Department of Chemistry, Indian Institute of Technology, Kharagpur, India.
A general synthetic route to beta-lactam-fused enediynes by intramolecular Kinugasa reaction has been successfully developed. The method has widened the scope of Kinugasa reaction in the synthesis of sensitive systems like the one described in this communication.
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