共查询到20条相似文献,搜索用时 15 毫秒
1.
A range of 5-azaoxindoles have been synthesised employing homolytic aromatic substitution onto pyridine as the pivotal step. 相似文献
2.
Matthew D. Helm 《Tetrahedron》2009,65(52):10816-346
Dialdehydes undergo ‘radical then aldol’ cyclization cascades upon treatment with SmI2, generating four contiguous stereocenters with high diastereocontrol. The scope of the process has been explored and the cascade has been extended to also include lactone reduction. 相似文献
3.
Hee-Yoon Lee 《Tetrahedron letters》2004,45(39):7225-7229
A facile route to tricyclo[4.3.n.01,5]alkane skeletons from conjugated cyclic enones was developed through tandem free radical cyclization reaction sequence involving the cyclopropylmethyl radical mediated rearrangement. The scope and limitation of the reaction was investigated. 相似文献
4.
The effect of positional change of the carbonyl group of enamides on Bu3SnH-mediated alkyl radical cyclization leading to five-, six-, seven-, and eight-membered nitrogen-containing heterocycles was examined. A 5-exo cyclization is generally preferred over a 6-endo ring closure in systems having an alkyl radical center on the enamide-acyl side chain, whereas enamides having an alkyl radical center opposite to the acyl side chain predominantly gave 6-endo cyclization products. These results suggest that the exo or endo selectivity of radical cyclization onto the alkenic bond of enamides can be controlled by positional change of the carbonyl group. For an understanding of these selectivities, heat of formation for each transition state was calculated. 6-endo-Selective radical cyclization was applied to the radical cascade, enabling a concise synthesis of a cylindricine skeleton. A 7- or 8-endo alkyl radical cyclization, however, predominated over a corresponding 6- or 7-exo ring closure regardless of the positional change of the carbonyl group of enamides. 相似文献
5.
Alejandro F. Barrero José F. Quílez del Moral Ingrid Loayza Jesús F. Arteaga 《Tetrahedron》2006,62(22):5215-5222
Ring size on Ti(III)-mediated radical cyclization of monoepoxypolyprenoids can be controlled by varying the substitution pattern and/or the electronic distribution of the double bond involved in the ring closure. The feasibility of applying this idea to tandem cyclizations has also been proven. Besides, when a silyloxy function is located in α position to the oxirane ring of the acyclic polyprene, the cyclization leads to carbocyclic terpenoids doubly functionalized in the A ring with acceptable yields. These results widen significantly the scope of this methodology. 相似文献
6.
Tsunehisa Hirashita 《Tetrahedron letters》2005,46(2):289-292
Intramolecular cyclization of allylic radicals generated from allylindium compounds both by photolysis or by the reaction of radical initiators was examined. The photolysis of allylic indium compounds, prepared from 8-bromo- or 8-iodooct-1,6-dienes and powdered indium metal, led to the formation of the 5-exo-trig products. Benzoyl peroxide as a radical initiator was also effective for the cyclization. In contrast, the radical initiators with oxidizing nature, such as tert-butyl hypochlorite, induced iodocyclization producing iodomethylcyclopentane via an oxidation of the iodide on the indium atom. 相似文献
7.
Zeng-Zeng Li Jian Yu Liang-Neng Wang Shi-Lu Chen Rui-Long Sheng Shi Tang 《Tetrahedron》2018,74(45):6558-6568
A Cu/Fe-cocatalyzed cyclization of halobenzamides with azo reagents involving regioselective radical/radical cross-coupling toward functionalized isoquinolinediones was developed. Applying azo reagents as the coupling partner, in the presence of cheap, facile and ligand-free catalytic combination of CuI/Fe(NH4)2(SO4)2·6H2O/air, the halobenzamide radicals generated by a prior radical addition/cyclization process underwent radical/radical cross-coupling via the cleavage of C-X (X?=?F, Cl, Br, I, OMe, OBn) bond with excellent site selectivity, leading to a series of isoquinolinediones furnished dual distal α-functional quaternary moieties. In addition, the theoretical calculation on the C-X bond cleavage and the positional selectivity using unrestricted density functional theory (DFT) was also conducted. 相似文献
8.
Atom transfer cyclization reactions (ATRC) provide rapid access to functionalized γ-butyrolactones. 相似文献
9.
Hideki Sugimoto 《Tetrahedron letters》2004,45(22):4213-4216
Enantioselective intramolecular radical cyclization of benzimidazolyl iodoalkenyl and iodoalkadienyl sulfones using chiral Lewis acids gave products with good enantioselectivity. Newly formed chiral centers could be induced effectively by enantioselective coordination to one of the sulfonyl oxygens. 相似文献
10.
Krishna C. Majumdar Uday K. Kundu Swapan K. Samanta Nirmal K. Jana 《Monatshefte für Chemie / Chemical Monthly》2003,134(8):1137-1143
Summary. Two hitherto unreported pyrimidine annelated heterocycles were synthesized from 6-cyclopent-2-enyl-5-hydroxy-1,3-dimethylpyrimidine-2,4(1H,3H)-dione and 5-cyclopent-2-enyl-6-hydroxy-1,3-dimethylpyrimidine-2,4(1H,3H)-dione by reaction with pyridine hydrotribromide or hexamethylenetetramine hydrotribromide. The first one was also obtained by reaction with concentrated sulfuric acid.Received October 28, 2002; accepted October 30, 2002
Published online June 2, 2003 相似文献
11.
Okiko Miyata 《Tetrahedron》2008,64(7):1270-1284
We have developed a novel synthetic route to nitrogen-containing heterocycles via radical addition-ionic cyclization reaction. Treatment of oxime ethers carrying the tosyloxy group with Et3B and alkyl iodide in the presence of Lewis acid gave the substituted pyrrolidines and piperidines. The reaction of oxime ethers carrying the methoxycarbonyl group proceeded under the same conditions to give the amino esters, which were easily converted into the corresponding lactams by the treatment with concd HCl. On the other hand, the oxime ether bearing the phenoxycarbonyl group afforded directly alkylated lactams under the radical reaction conditions. The utility of this domino reaction was demonstrated by the synthesis of (±)-bgugaine and the formal synthesis of 5,8-disubstituted indolizidine alkaloids. 相似文献
12.
13.
Stefan van Rootselaar Evert Peterse Dr. Daniel Blanco-Ania Prof. Dr. Floris P. J. T. Rutjes 《European journal of organic chemistry》2023,26(22):e202300053
Piperidine alkaloids are members of the alkaloid family that is characterized by the presence of a six-membered nitrogen-containing heterocycle. Piperidine alkaloids are found mainly in plants and often exhibit interesting biological and pharmacological activities. Despite the accumulation of these natural products in plants, relatively low quantities of alkaloids are produced in absolute terms and thus synthesis of alkaloids and derivatives thereof remains relevant to identify targets for drug discovery. Throughout the years, researchers have come up with a myriad of methods to synthesize piperidine derivatives. This review describes methods that employ stereoselective Mannich reactions to create the core of piperidine alkaloids. Asymmetric induction in the Mannich reaction has been achieved by a range of methods that have been divided into three conceptual approaches: (1) chiral pool-based (internal asymmetric induction), (2) chiral auxiliary-based (relayed asymmetric induction) and (3) asymmetric catalysis-based (external asymmetric induction). Of each approach, we describe the reaction mechanism and rationalize the stereochemical outcome of the Mannich products. 相似文献
14.
Krishna C. Majumdar Swapan K. Samanta 《Monatshefte für Chemie / Chemical Monthly》2002,133(9):1187-1192
Summary. 5-(Cyclohex-2-enyl)-1,3-dimethyl-6-hydroxyuracil undergoes regioselective heterocyclization to afford fused tricyclic heterocycles
upon treatment with bromine and m-CPBA. However, the same substrate furnished bridged tricyclic heterocycles when treated with N-iodosuccinimide and conc. H2SO4 and a mixture of bridged tricyclic heterocycles and fused tricyclic heterocycles when treated with hexamine hydrotribromide
or pyridine hydrotribromide.
Corresponding author. E-mail: kcm@klyuniv.ernet.in
Received September 27, 2001. Accepted (revised) December 3, 2001 相似文献
15.
Amino acids are firstly employed in transition-metal free heterocyclization reaction of 1,3-diynes in the presence of K3PO4 and DMSO at 120 °C. This method produces 2,3,6-trisubstituted pyridines with up to 86% yield. The –CO2H group on the amino acids is crucial for this heterocyclization reaction. The mechanism of such a heterocyclization reaction is discussed, as well. 相似文献
16.
《Tetrahedron》2019,75(50):130716
A visible-light-induced photocatalytic cyanomethyl radical addition/intramolecular cyclization cascade reaction of olefinic amides has been developed under mild conditions. This reaction provides a novel method for the synthesis of various cyanomethyl-containing benzoxazines, which are useful pharmaceutical framework. The method exhibits good functional group tolerance and a wide range of substrate scope. 相似文献
17.
Manjula Singh Arvind K. Yadav Lal Dhar S. Yadav Rana Krishna Pal Singh 《Tetrahedron letters》2018,59(33):3198-3201
A convenient and straightforward synthesis of 6-sulfonylated phenanthridines via silver-catalyzed sequential radical insertion, cyclization and aromatization of 2-isocyanobiphenyls is reported. The protocol does not require a phenanthridine scaffold as a substrate and presents a highly regioselective synthesis of 6-alkyl/arylsulfonyl phenanthridines. The protocol utilizes readily available and easy to handle sodium sulfinates as sulfonating agents and potassium persulfate as an oxidant to afford good to excellent yields of the desired products in a one-pot operation at room temperature. 相似文献
18.
The synthesis of several A and AE ring analogues of the alkaloid methyllycaconitine is reported. The key 2-(2″-methylsuccinimido)benzoate ester pharmacophore is introduced using an efficient two step procedure. Esterification of the alcohol precursors with N-(trifluoroacetyl)anthranilic acid under Steglich conditions followed by sodium borohydride mediated cleavage of the trifluoroacetyl group affords the anthranilate esters. Subsequent fusion with methylsuccinic anhydride affords the N-substituted anthranilate derivatives containing the key pharmacophore present in a range of commonly occurring Delphinium and Aconitum alkaloids. 相似文献
19.
Substrates were designed to undergo tandem radical cyclizations to afford the cis, cis-fused hexahydrobenzofurobenzopyran ring system of the bisabosquals. Studies with these revealed that different initiating systems gave different yields and somewhat different diastereomeric ratios. A photocatalytic cyclization was also successful with the bisabosqual substrate. 相似文献
20.
Using radical chemistry novel highly condensed heterocycles have been synthesized. The mechanism for their formation is discussed. 相似文献