- Visible-Light-Induced Radical Cascade Cyclization: Synthesis of the ABCD Ring Cores of Camptothecins
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A new strategy for constructing indolizino[1,2-b]quinolin-9(11H)-ones (ring cores of camptothecins) from readily available isocyanoarenes and N-(alkyl-2-yn-1-yl)pyridin-2(1H)-ones has been developed through a visible-light-induced radical cascade cyclization process. The reaction proceeds under mild conditions with fair to excellent yields. The easy introduction of substituents for both reactants and the broad functional group tolerance of the reaction make it a straightforward route to the cores of the marketed camptothecins and their derivatives.
- Yuan, Yao,Dong, Wuheng,Gao, Xiaoshuang,Gao, Huang,Xie, Xiaomin,Zhang, Zhaoguo
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supporting information
p. 2840 - 2846
(2018/03/09)
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- Noncryogenic synthesis of functionalized 2-methoxypyridines by halogen-magnesium exchange using lithium dibutyl(isopropyl)magnesate(1-) and lithium chloride
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2-Methoxypyridines functionalized in the 3-, 5-, or 6-position and 2,6-dimethoxypyridines functionalized in the 3-position were prepared from the corresponding bromo or iodo analogues by using lithium dibutyl(isopropyl) magnesate(1-) and lithium chloride
- Struk, Lukasz,Sosnicki, Jacek G.
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experimental part
p. 735 - 746
(2012/04/04)
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- Highly selective metalations of pyridines and related heterocycles using new frustrated lewis pairs or tmp-zinc and tmp-magnesium bases with bf 3·oet2
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(Figure Presented) Efficient and selective: Frustrated Lewis pairs based on BF3·OEt2 and LiCl-com-plexed tmpMg or tmpZn amides (tmp = 2,2,6,6-tetramethylpiperidyl) allow the efficient and regioselective metalation of various functionalized N heterocycles (see scheme for examples). Moreover, such metalations carried out in the presence or absence of BF 3·OEt2 enable a complete switch of regioselectivity, thus allowing complementary fuctionalization.
- Jaric, Milica,Haag, Benjamin A.,Unsinn, Andreas,Karaghiosoff, Konstantin,Knochel, Paul
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supporting information; experimental part
p. 5451 - 5455
(2010/09/16)
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- Homoleptic zincate-promoted room-temperature halogen-metal exchange of bromopyridines
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Homoleptic lithium tri- and tetraalkyl zincates were reacted with a set of bromopyridines. Efficient and chemoselective bromine-metal exchanges were realized at room temperature with a substoichiometric amount of nBu 4ZnLi2·TMEDA reagent (1/3 equiv; TMEDA=N,N,N′,N′-tetramethylethylenediamine). This reactivity contrasted with that of tBu4ZnLi2·TMEDA, which was inefficient below one equivalent. DFT calculations allowed us to rationalize the formation of N...Li stabilized polypyridyl zincates in the reaction. The one-pot difunctionalization of dibromopyridines was also realized using the reagent stoichiometrically. The direct creation of C-Zn bonds in bromopyridines enabled us to perform efficient Negishi-type cross-couplings. Mild zincation! nBu4ZnLi2·TMEDA (in substoichiometric amounts) promoted efficient and chemoselective room-temperature bromine-metal exchange of a range of bromopyridines (see scheme). DFT calculations strongly supported the formation of a stabilized tripyridylzincate, which could be reacted with electrophiles or be directly involved in palladium-catalyzed cross-coupling reactions.
- Chau, Nguyet Trang Thanh,Meyer, Maxime,Komagawa, Shinsuke,Chevallier, Floris,Fort, Yves,Uchiyama, Masanobu,Mongin, Florence,Gros, Philippe C.
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experimental part
p. 12425 - 12433
(2011/01/05)
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- A general synthetic approach to the (20s)-camptothecin family of antitumor agents by a regiocontrolled cascade radical cyclization of aryl isonitriles
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A general and efficient synthesis of (20S)-camptothecin (1a) is reported. A key common intermediate containing the pyridone and lactone (DE) rings of camptothecin and most derivatives was constructed from 2-trimethylsilyl-6-methoxypyridine by a series of metalation reactions and a Heck cyclization to provide an achiral bicyclic enol ether. Sharpless asymmetric dihydroxylation followed by lactol oxidation and iododesilylation produced the key intermediate in 94% enantiomeric excess. Alkylation with prop-argyl bromide and a cascade radical reaction with phenyl isonitrile then produced 1a. About 20 other penta-and hexacyclic analogues of camptothecin with differing single or multiple substituents at C7, C9, C10, C11, and/or C12 were made by changing the propargylating agent and the isonitrile. Included among these are several drug candidates and the approved drugs topotecan and irinotecan. The synthesis of the prodrug irinotecan is a direct one that does not pass through the active metabolite. The use of ortho-trimethylsilyl-substituted isonitriles allows the regioselective synthesis of camptothecin analogues in cases where isomeric mixtures are formed from the parent isonitriles. The synthesis of the derivatives relies on the broad scope and functional group tolerance of the key cascade radical reaction.
- Josien, Hubert,Ko, Sung-Bo,Bom, David,Curran, Dennis P.
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- Tandem radical reactions of isonitriles with 2-pyridonyl and other aryl radicals: Scope and limitations, and a first generation synthesis of (±)-camptothecin
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Photolysis of N-propargyl-6-halo-2-pyridones and related aromatic halides in the presence of aryl isonitriles provides tetra- and penta-cyclic products in a single step by a sequence of radical addition to the isonitrile followed by two cyclizations. The scope and limitations of the process are described along with a first generation synthesis of racemic camptothecin.
- Curran, Dennis P.,Liu, Hui,Josien, Hubert,Ko, Sung-Bo
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p. 11385 - 11404
(2007/10/03)
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